Last summer I was able to attend only two of the summer metalworking classes offered by the art school at UWM. With the classes running again this summer, I signed up for two more sessions. The object of this class was to make a prison shiv letter opener via the techniques of riveting, small fasteners, […]
Last summer I was able to attend only two of the summer metalworking classes offered by the art school at UWM. With the classes running again this summer, I signed up for two more sessions. The object of this class was to make a prison shiv letter opener via the techniques of riveting, small fasteners, and slots and tabs. In reality, we stuck with various styles of riveting – I’m quite familiar with fasteners, and slots/tabs are kind of a pain.
First up was just making a sample piece. I liked the simplicity and look of flush rivets vs. raised rivets (especially since if done well, you can carefully sand and polish the surface flat to hide the fact that rivets exist, assuming they are the same material as the base), so I did two flush rivets – one hollow and one solid. With that complete, I could turn my attention to the design of the letter opener. I knew I better keep it simple to have a prayer of completing it in 3 classes, but as usual, I vastly underestimated the time required to complete such a project.
I had come across a picture of a Strider MK1A Tanto knife a few years ago, and really liked the lines of it. Rather than pay $450 for one, I thought it might be fun to try making my own (being a simple tanto grind with paracord grip). I took the photo, dropped it into SolidWorks, and traced around the edge to create a 2D profile. I then ordered some flat ground O-1 oil hardening metal stock in the requisite size, and… …that’s as far as I got. So for this letter opener project, I thought it might be a nice profile to try, though I had to shrink the size a little in order to fit it on the supplied piece of nickel sheet. I then needed scales – while hydraulic pressed scales would have been really neat, I’d have to cut my own die from acrylic block, and I wasn’t sure I’d be able to get it right on the first try. So I went the simple (ha!) route and sketched out rounded scales over the blade profile that while ergonomically unsound, at least looked interesting.
Then I tossed in some locations for rivets into the drawing, and determined coordinates for them. With all the math out of the way, I went to the shop, slapped two pieces of brass sheet onto the nickel sheet secured via strips of carpet tape, and started drilling out locations. The next night I drew the profiles onto the pieces using the holes for location, and bolted the two brass pieces together so I could shape them identically. After sawing the nickel and brass to a rough outline, I went at them with the belt sander. This got me to this point:
No envelopes will mess with me once this bad boy is assembled.
I wound up going with more margin on the scales (in order to help cover up some mistakes made along the way), which makes it even less ergonomic than before. Oh well. As for the riveting, I thought I’d give the grip even more depth by raising the brass slabs up on standoffs. This required cutting 20 tiny little pieces of brass tubing, and I was cursing myself for making so many blasted holes in the first place. Hopefully I can have all the pieces ready for assembly in time for the open workshop, and maybe I’ll even be able to complete it.
I’ve been attending the CNC Workshop since the very first one (circa 2004 or so). The event’s host and organizer, Roland Freistadt, passed the reins over to Village Press after the 2008 event, and we finally had another workshop this year. As always, Rick Chownyk had presentations on getting started in CNC. Although I’m past […]
I’ve been attending the CNC Workshop since the very first one (circa 2004 or so). The event’s host and organizer, Roland Freistadt, passed the reins over to Village Press after the 2008 event, and we finally had another workshop this year.
"Cheap and Free" Rick Chownyk with the world famous Rick-O-Matic, a tabletop CNC machine he built out of various scavenged parts.
As always, Rick Chownyk had presentations on getting started in CNC. Although I’m past the point of ‘getting started’, Rick is such an entertaining person that I just had to sit in on a session.
Rick's Thursday aluminum casting - the block on the right is just a Mickey Mouse logo, while the block on the left is a woman's head (fresh off of a Tormach machine) that became much more recognizable once bead blasted. These were created from foam cores.
Rick also does a demonstration of backyard aluminum casting. While I’ve never tried it myself (and don’t currently have a need for it), I’d be quite confident in the procedure after seeing Rick explain and illustrate the process.
The two neatest new things at the workshop were Carmen Gianforte’s miniature firearms and Helmut’s (whose last name I didn’t catch) homebuilt wire EDM machine.
An actual Remington Derringer, and one of Carmen's 50% replicas
Despite having an interest in firearms, I know almost nothing about the field of miniature firearms. Carmen explained that they are not models, but are sub-scale replicas, and as such are fully functional.
A glass display box showing some of the component partsA more complete selection of some of the minature parts for one of the Derringers - all the screws are single pointed on a lathe!A variety of objects on Carmen's display table. In the far upper left, a cutaway of one of the brass cartridges that was used to check for correct drilling depth in the prototype stage. To the right of that is the smallest bullet mold I've ever seen. Below that is another epoxied cutaway, this time of Carmen's latest miniature project, a knuckleduster revolver. In the upper right are the molds used to form the Alumilite grips. And the Winchester primers are what he uses as the source of the mercury fulminate for his own miniature primers.The frame and barrel are investment cast, but Carmen needs to supply wax masters to the casting company. He makes these masters in a multi-part process with custom injection molds. The bottom left shows the first part - water soluble wax is formed into a 'core'. This core is then placed into another mold and standard blue casting wax is injected into the cavity, yielding the piece seen in the lower right. Carmen then drops these pieces into a tin of water and lets the water soluble wax dissolve away overnight, leaving the hollow wax part in the upper left (such a part would require terribly complex molds to create in one pass without a disposable core). The resulting stainless steel frame in the upper right is what comes back from the casting company.
When I say ‘fully functional’, yes, that means they actually shoot (they even have rifling in the barrel bores). Carmen actually manufactures his own ammunition – I forgot to ask what caliber, but they looked to be around .125″, perhaps less. Making the cartridges is fairly standard (if eye-crossingly tiny) lathe work. But they also need primers, and Carmen makes his own – anvils and all. It took him an immense amount of trial-and-error work to draw the tiny copper discs into cups with a set of progressive dies and punches. For the mercury fulminate, he takes shotshell primers and adds a few drops of water to desensitize the compound, and is then able to smear a bit of the resulting paste into his own primer cups. After pressing these primers into the cartridges with anvil in place, and allowing them to dry, the cartridges are live and can be fired. I have no idea how he adds powder and seats the bullet – I had so many questions for him that I could have quizzed him for a week, yet he very graciously answered all my questions and happily explained his techniques.
Helmut’s wire EDM was a fantastic little machine:
A wire EDM machine uses a copper wire as an electrode to cut a 2D shape in a plate of metal, just like if you took a hot wire to cut a shape in a stick of butter (just much more slowly). Generally wire EDM machines are very large, expensive machines – this is the only homebuilt one I’ve even seen in person, and it’s a clever little contraption. Helmut is able to pull the whole machine up out of the tank (which is filled with distilled water) to inspect progress and make adjustments. The pencil on the back side traces out the pattern being cut (stars in this case).
A nice long holiday weekend is a great occasion to tinker around with a rapid prototyper. Well, all right, any weekend. Or weekday for that matter. There’s something enthralling about watching your creation emerge slowly, slice-by-slice from the build platform. POV-Ray enthusiasts will know the feeling well – watching your file slowly transformed into an […]
A nice long holiday weekend is a great occasion to tinker around with a rapid prototyper. Well, all right, any weekend. Or weekday for that matter. There’s something enthralling about watching your creation emerge slowly, slice-by-slice from the build platform. POV-Ray enthusiasts will know the feeling well – watching your file slowly transformed into an image, one line of pixels at a time. Although in the case of a rapid prototyper, the transformation is subtly different – you know exactly what the output object will be (unlike in POV-Ray, where you have to alternate between adjusting your scene description file and rendering that file until you achieve the effect you want – enjoyable, yes, but lacking a direct translation of vision into result). A rapid prototyper on the other hand, allows a leap between the digital domain and the physical one. Perhaps not as exciting in terms of watching the process, but more profound in concept (as evidenced by the abundance of ‘replicators’ in science fiction).
I’ve done a lot of research into the Stratasys machines and RepRap lately, especially as I now have to feed this beast which I posses. While I have a decent amount of filament, the cost of getting more has kept my use of the Stratasys to a bare minimum. Bolson Materials charges $250 for a 4 pound reel of filament, which is probably a great price, considering that the HP-branded Stratasys units recently released for sale in Europe have filament cartridges that are (as of this writing) $987.94 each after currency conversion. And you thought buying inkjet consumables was bad. Given that this is only $12.06 less than what I paid for the machine (yes, I practically stole the Stratasys for a cool grand, and everyone I speak to agrees that I basically won the Craigslist lottery), I began looking into the filament itself.
The first step was to determine exactly what material I was dealing with. I knew that it was ABS plastic, but I didn’t know if there was anything special about it (I know almost nothing of plastics engineering, but I know that numerous formulations are possible – Lego bricks, for example, are not pure ABS, but a custom formulation). I knew Stratasys wouldn’t be keen on divulging this information (imagine the response at a KFC counter when you ask precisely which 11 herbs and spices are used – okay, not the best analogy, but bear with me). I had discovered many years ago that MSDS sheets are an excellent window into proprietary information, divulging industrial secrets by virtue of safety legislation. So I did some searching and found that the MSDS sheet for the modeling material indicated that the filament was essentially pure ABS, with perhaps a tiny amount of mineral oil, tallow, and/or wax thrown in for a lubricant. Similarly, I discovered that the breakaway support material appears to be nothing more than HIPS (High-Impact Polystyrene).
Obviously, buying Stratasys branded filament would quickly become prohibitively expensive (the classic razor and blades business model in evidence). It’s generally a bad sign when you go looking for a product, but can’t find a price for said product. Yet diligent web searches led me to stumble onto this post. Given that New Image Plastics could apparently supply smaller diameters than the 3mm RepRap standard (I needed .070″ for the FDM 1600), I figured I’d give them a shot. I called them up and inquired about getting a few pounds of ABS and HIPS in a .070 filament size. Unexpectedly, I was speaking with James Waring, owner of the company. He told me that a number of customers were using .070 ABS filament from them in Stratasys machines with no problems, and that for newer Stratasys machines that had chipped cartridges, he is aware of someone who is successfully reloading cartridges and will hopefully be revealing the technique once perfected. Anyhow, I ordered 5 lbs. each of ABS and HIPS, and James said that he’d have it scheduled for production this weekend! I can’t imagine a more phenomenal response time from a vendor. If the spools feed through the Stratasys without issue (shouldn’t be hard – the current ‘lobster red’ spool appears to be about a decade old from the tag information, so they’re not exactly prime material), I’m sure I’ll be ordering lots more.
Meanwhile, I also tried my luck with contacting Stratasys to see if any spare parts or other service was still available for the unit (not that it appears to need any, but I wanted to be prepared). Their tech support department told me that no parts or service were available for the FDM 1600, and they couldn’t direct me to any third parties that did service on the unit. I also asked about the availability of a document called the “Stratasys Modeler Language Programming Reference Manual” that I found referenced in a thesis I came across. The thesis covers the building of an automated build platform loading/unloading system, and the document appears to detail the format of the .SML file that gets uploaded to the printer. Unsurprisingly, the person I spoke to knew absolutely nothing about the document. Getting updated software required speaking to the software licensing department, which I called next. I found that the last version of software to support the FDM 1600 was Insight 6.3, and that yes, I could certainly get a copy. However, that would mean paying $2000 for an annual software support contract. Oh, and the FDM 1600 is being dropped from support at the end of the year, so it would essentially be $2000 for 6 months of software support. I declined to sign up.
Friday I decided to try and tackle the offset between the ABS and support material. The manual explains the procedure, but references a calibration filename that doesn’t exist in my software version. After opening a few different similar files, I finally found the one I needed – one that would print out a square of ABS and then deposit a single circuit of support material on top.
Progressive improvement from left to right - the leftmost one was simply the wrong file.
I’d run one, estimate the offset, then launch the tip calibration program to upload the offset to the FDM 1600. After a few iterations, I finally was pleased with the path matching and decided to try a larger print to run overnight. I grabbed the Mendel SolidWorks file and created an assembly with some of the larger parts that don’t lend themselves well to machining easily. This step is needed because Quickslice can only work with a single .STL file (whereas Insight can work with multiple objects). In order to print multiple parts, I have to create a SolidWorks assembly of how those parts are to be printed, and then export the entire assembly as a single .STL file. Quickslice churned through the slice and road generation slowly – I’m guessing this old software was far from optimized. Once done, I uploaded the file to the FDM, hung around for a little while to make sure the base layers were being laid down correctly, and left the machine to its business for the night.
I wasn’t sure what to expect the next day – RepRap machines seem to still be at the stage of needing a lot of monitoring during a build, and I worried that I’d come back to find a giant birdsnest of filament occupying the build chamber. But no such disasters had happened – I had a beautiful print waiting for me:
It took a bit of coaxing to remove from the foam, but I could then admire the work.
I’m not sure why Quickslice decided to run supports up on the left – the teardrop holes on the Mendel parts are less than the overhang support threshold in Quickslice, but perhaps a rounding error tipped the scales. This print took 14 hours, so the FDM is no speed demon. I think a Mendel could probably run the job in half that time, although RepRap currently bypasses bases and supports, and has a coarser output due to the 0.5mm nozzle orifice.
I’m pondering whether or not to actually build the Mendel right now, but I’ll probably pass the parts over to Chuck so that he can have a crack at the project. I’m still interested in the RepRap project, but if I were to build one, I’d probably redesign the system into something that looks more like the FDM, but has a larger working envelope.
I previously wrote about my start on building a Mendel RepRap. I recently purchased the bearings and stepper motors, and have had the shafts and threaded rod at the ready for several months. But on Monday, while scanning the local tools section on Craigslist, one of the titles jumped out at me: “Stratasys FDM 1600 […]
I previously wrote about my start on building a MendelRepRap. I recently purchased the bearings and stepper motors, and have had the shafts and threaded rod at the ready for several months. But on Monday, while scanning the local tools section on Craigslist, one of the titles jumped out at me: “Stratasys FDM 1600 Machine”. Stratasys… I could scarcely believe that someone was selling an actual rapid prototyping machine on Craigslist. Not just a rapid prototyper, but a fused deposition modeler (FDM) – the very same type as a RepRap. For anyone wondering just what in the world I’m talking about, imagine a CNC controlled hot glue gun – a FDM rapid prototyper builds up an object out of many thin layers of plastic extruded out of a tiny nozzle. This particular machine has two nozzles – one for the plastic (ABS to be specific) and one for a support material (a very brittle plastic that supports overhangs and is broken off once the part is complete).
The asking price was simply too good to be true, and I called the seller immediately, who confirmed that it was still available, and that it was in fine working condition. I told him I’d stop by around 6pm to have a look at it. Well, perhaps my eagerness was far more apparent, as I told the fellow to consider it sold (I was actually shaking from excitement). The size of the unit was probably going to be too big for my truck, so I called my dad to see if I could possibly borrow his. As generally happens, I wound up borrowing dad as well (which is always a comfort when buying and moving machinery – something about decades of prior experience to keep me from doing something boneheaded).
Sure enough, the machine was just like the ad indicated. The seller gave me a crash course in using the machine and the software, though I knew I’d have to do a lot of reading as well – running a rapid prototyper isn’t something you can really do with only 10 minutes of fragmented instruction. The three of us managed to wrestle the unit and accompanying stand into dad’s truck and we were off. Dad helped me unload the unit at work, where I hoped to be able to keep it indefinitely (as we’d probably find it useful to have for the engineering department – I couldn’t imagine having enough to run on it personally to keep the machine very busy).
The mighty Stratasys FDM 1600
It took a few days to get the unit situated in the office area (an office environment is needed as the machine needs reasonably controlled temperature and humidity), but I was finally ready to attempt actual use of the machine. I had read enough of the manual to understand how to load the plastic filament (about 0.070″ in diameter, fed from a reel) into the extrusion head, so I started with this simple procedure. I managed to get the gray support material extruding out of the nozzle, and then the red ABS, but when I switched back to the support material, there must have been a jam and no more came out. I powered down the machine, let the head cool, and cleared the backflow from the head. I tried it again, but once more I could get the support material to extrude only at first, but not after having switched to the ABS. Close inspection of the head indicated that the gripper wheels weren’t getting proper traction on the filament (perhaps it was getting a touch too soft from the heat).
A few days later I felt ready to try actually making a part, even if the support material extrusion gave me issues. I also powered on the air conditioner on the back of the unit for the first time, hoping that the cool air blown onto the backside of the head unit would improve my luck with the support material (this cold air flow seems to be critical in keeping the filament from melting before it actually enters the heating chamber). Again, I was unable to get the support material to extrude after switching to ABS, so I decided to try just running without support material at all. I was going to just try making one of the .stl files for Mendel, and then I remembered that the traditional first part made on a RepRap is the shot glass (or ‘minimug‘) to allow you to make a toast to your own creation. While the FDM had likely made hundreds of parts already, I figured the minimug was the perfect inaugural part for me to try. I drew up my own version with zero overhang and generous draft angles, not knowing how well things would actually work – best to start simple.
Looking into the heated build chamber, the dual nozzles of the extrusion head can be seen. On the left is the ABS head with a good amount of extruded filament that should probably be wiped off. On the right is the support material nozzle, currently refusing to extrude anything. The base is a cellular glass foam.
The file I sent to the FDM included about 1/16″ worth of support material as a base – since the support extruder wasn’t cooperating, I was hoping the ABS would ‘fluff’ itself up to form a reasonable support for the build (much like a basket of clothes dumped on the floor would have a height greater than if the items were folded and stacked).
The first few layers of the minimug
This actually worked quite well, but about halfway up, disaster struck when the part lifted from the foam base. After making a presentation in my experimentation class many years ago (detailing a blower and heatsink and subsequent failure of the test heating element when we applied too much power for the airflow to effectively remove the thermal energy), my professor implored me and my lab partner that there was no such thing as a failed experiment. He was so emphatic about this point that it has stuck with me ever since, and I recall it whenever I am disheartened by a setback. I suppose the old maxim “every cloud has a silver lining” is an approximation, though I feel the Dilbert-esque phrase of ‘learning experience’ is closer to capturing the sentiment of retrieving useful knowledge from mishaps.
Top and bottom of the first attempted part
While the top portion of the minimug looked pretty good, the underside showed a rather loose fill – the lines of ABS should be much straighter. There is also very little adhesion of the ABS to the glass foam base. I knew that I had to remove the dead space that should have been filled with support material, or increase the surface area of the part bottom. I wound up doing both. I figured out how to remove the support layer from the part (Stratasys Quickslice 6.4 is not exactly intuitive, dating to the previous millenium), and I added on a hefty plate to the bottom that would hopefully improve adhesion to the foam. These two changes worked beautifully.
The second attempt at a minimug - the various 'flecks' seen on the part are not fragments of the glass foam base, but are bits of the support material that the second nozzle had dragged across the part and deposited.
To make things interesting, I added some holes and flanges to the bottom flange of the part. The very first layer was close enough to the glass foam base that the plastic was injected into the pores. This worked almost too well to secure the part, and I needed a putty knife to pop it off of the substrate.
The underside of the second attempt - excellent adhesion
I then decided to give the support material one more try. The ABS had absorbed a good deal of moisture – the manual instructs to test for ‘droop’ by extruding some ABS, wiping the nozzle, and then seeing how much leaks out over the next 10 minutes. The more moisture the ABS contains, the more the material will ‘droop’ – an acceptable level of moisture is to have 0.5″ or less of ABS dripping out of the nozzle after 10 minutes. I was seeing several inches after 5 minutes. I guessed that maybe just running through a foot or so of support material through the head might finally get to a drier section of material (the spools of plastic filament are kept in a ‘dry box’ on the machine with desiccant bags). Wonder of wonders, this actually worked (or perhaps I was simply just lucky this time) – after feeding support material through the head, I was able to switch to ABS and back again and be able to extrude at will on both nozzles. I loaded up a small Mendel part and gave it a go.
Building the light gray support structure
This support (which appears to be called the ‘raft’ among RepRap users, though they currently have no separate support material) looked to be adhering to the substrate very well.
Holy X-axis mismatch, Batman!
Once the ABS started being extruded, however, I could see that all was not well – the support material should be perfectly centered between the two uprights. Still, things were progressing smoothly, so I let the part complete.
Despite the head mismatch, the part looks very clean!Underside - very clean rows with light adherence to the substrate
I’ll need to calibrate the head so that the support material gets extruded properly in line with the ABS, but I’m extremely pleased with the results thus far. In short, I’ve leapfrogged well beyond where I would be if I actually had a working Mendel. Rather than trying to figure out how to make the machine work, I can now decide what I actually want to make.
Blimey, 5 months without an update! While I haven’t done as much on various projects as I’d hoped, slight progress is underway on the rotary phase converter and other sundry topics. On Sunday I did a bit of milling for a customer on a Phantom trigger frame. While I generally point people in the direction […]
Blimey, 5 months without an update! While I haven’t done as much on various projects as I’d hoped, slight progress is underway on the rotary phase converter and other sundry topics. On Sunday I did a bit of milling for a customer on a Phantom trigger frame. While I generally point people in the direction of Ken at KPCS whenever I’m asked about doing custom paintball gun work, once in a while I’ll take on a simple project if it interests me.
Ball end milling on a CCI frame
This was nothing fancy, but it was the first time I had actually tried it. I wish I could say that I did everything on the fly by eye, but I drew it up in SolidWorks first. This actually was good, as it allowed me to determine the best depth of cut on the area right behind the trigger, and more importantly, I was able to give the customer a screenshot of what it would look like before actually making chips.
I wired up the motor controller to the vibratory deburrer today. Since I had already bench tested the motor and controller, I had no real concerns other than making sure I was using the right terminals on the controller. I put a tub of ceramic media with some aluminum parts into the unit, and gave […]
I wired up the motor controller to the vibratory deburrer today. Since I had already bench tested the motor and controller, I had no real concerns other than making sure I was using the right terminals on the controller. I put a tub of ceramic media with some aluminum parts into the unit, and gave it a shot. The media swirled around the tub much like it had in the suspended version, which was something I was hoping to eliminate. After realigning the weights to 90 degrees apart, I found that the swirling was eliminated if I ran the motor at about 60% of full speed. I covered the tub and left it run – thankfully the noise is a little less than the suspended version (but just a little). About 45 minutes later, I heard what sounded like a muffled crash, and ran downstairs to see what had happened. The bucket frame was leaning way over, and after powering off the motor controller, I had a look at the damage.
Snapped spring - given how tough these were to grind to length, I'm amazed that it broke.
One of the 4 springs that support the tub frame had snapped from the vibration. As the frame keeled over to one side, the hose that coupled the motor to the weight shaft was twisted and sheared off.
Torn hose - despite being fiber and wire reinforced, it still gave way. In retrospect, this wasn't a bad thing - easier to replace the hose than the motor, after all.
At this point, spending the money for a proper industrial unit is looking more and more attractive.
I stopped at the hardware store hoping to find some suitable rod that would fit the undersized bearings of the previous post. Naturally, the rod sizes they stock jump from 1/2″ to 3/4″ with nothing in between. While pondering the unsavory prospect of shaving down the diameter of a stainless shaft on the lathe, I […]
I stopped at the hardware store hoping to find some suitable rod that would fit the undersized bearings of the previous post. Naturally, the rod sizes they stock jump from 1/2″ to 3/4″ with nothing in between. While pondering the unsavory prospect of shaving down the diameter of a stainless shaft on the lathe, I wandered around the store aisles aimlessly. This is something I tend to do more often than not when I enter any hardware or mechanically inclined store – seeing the blue building insulation makes me think that I should build a hot wire foam cutter for R/C airplane wings, while the plumbing section reminds me that I’d like to build a pneumatic launcher with a Rainbird sprinkler valve as the core. Thank heavens the Boeing Surplus Store is now closed – if I ever would have entered their doors, I never would have left.
In my meanderings, I found a nice large 5/8″ diameter bolt that slipped through the bearings nicely (there’s a little bit of play, but I don’t think it will be an issue). Unfortunately, I found that I had been a bit enthusiastic in welding the weight plates:
On the bottom unit, I seem to have run the weld bead up into the hole for the clamping screw, locking the screw into place.
Fortunately, I was able to use an endmill to break through the weld and free the screw. I did a test assembly of the bearing unit, and things looked pretty good:
I then shaved down the threads to about 1/2″ diameter so that I could use a piece of 1/2″ ID hose to couple the bolt to the motor shaft. I also had to round the outer corners of the top weight to keep it from hitting the frame members. After attaching the weight and bearing unit to the old motor mount plate, I reassembled the bucket frame and installed it on top of the springs. I did have to reduce the spring height by 2″, but once assembled, the whole unit ‘felt’ about right. I finished by adding the hose coupling and adjusting the motor height.
I managed to locate a suitable DC motor and controller for the vibratory deburrer, and then set about designing a proper lower ‘chassis’ for the system. I’ve been trying to make all equipment wheeled as much as possible for easy movement around the garage or basement, but I also needed leveling pads on the unit […]
I managed to locate a suitable DC motor and controller for the vibratory deburrer, and then set about designing a proper lower ‘chassis’ for the system. I’ve been trying to make all equipment wheeled as much as possible for easy movement around the garage or basement, but I also needed leveling pads on the unit (I want it to shake and rattle, but not roll). The bottom chassis looks rather small, and I hope that it won’t have a tendency to fall over as a result.
3/4HP DC motor mounted and ready for action.
I welded pipe nipples to the chassis and stuck what I hope will be appropriately sized springs onto them. The legs of the bucket frame now have pipe nipples and washers welded to their bottoms – they should slip into the springs from the top. The motor location is adjustable back and forth by a little bit so that it can be aligned with the weight shaft (which will be bolted to the previous motor mounting plate on the bucket frame). The weight shaft mounting has been a bit of an annoyance – I started with a hunk of aluminum bar stock and bored a pocket on each side to hold a 5/8″ ID bearing. A short shaft then passes through the bearings and will have a weight plate on either end of the shaft:
Not the prettiest welding , but as long as it holds together I'll be happy.
I’ll be able to adjust the vibration amplitude by simply aligning the plates – 180 degrees apart for ‘purr like a kitten’ all the way up to 0 degrees apart for ‘funny, I don’t recall there being any fault lines around here’.
Although the bearings are 5/8″ ID, I’ve had a heck of a time trying to coax any 5/8″ rod through them. I finally decided to see if thermal expansion could assist, so I threw the rod in the freezer and stuck the bearing bar in the oven on low. Half an hour later, I pulled out both parts, tried to slide the rod through and…
"Oh, bother," said Pooh.
The rod managed to get perhaps 1/16″ into the bearing before thermal conductivity stepped in and ruined the fun. It turns out that perhaps I should have been a little more careful when selecting bearings – these are +0″/-0.0003″ on the inside diameter. Either I’ll need to find some undersized rod (generally $$$) or I’ll have to make a stab at turning down this existing rod by just a couple thou.
I’ve been rather fascinated lately with the RepRap project. In a nutshell, this is a project to build a low-cost rapid prototyping machine. Specifically, RepRap aims to design and build rapid prototypers that can make as many of their own parts as possible, which is a noble goal, but not a design facet that particularly interests me right now. There are other rapid prototyping projects such as Fab@Home and Makerbot’sCupCake CNC (which is based on the earlier RepRap design known as ‘Darwin’), but the latest RepRap design known as ‘Mendel’ is really elegant. Mendel is a far simpler design than its predecessor, has a larger working envelope, and should prove far more scalable – stretching any of the axes for more travel should be pretty trivial if the design ever needs expansion for making larger parts.
Ideally, building a Mendel for myself would start with getting a set of rapid prototyped Mendel parts from someone else, but there seems to be hardly anyone making Mendel parts yet. Besides, I really have no interest in having a ‘pure’ machine that was replicated as much as possible – in fact, I’d prefer to actually machine my own parts for it. I’ve been eagerly following Shane Wighton’s blog, as he also wanted to build a Mendel and has access to a machine shop. We both came across the same issue of trying to view the 3D assembly of Mendel in the downloadable solid model files – the files were created in an academic licensed version of Solid Edge, which the freely downloadable Solid Edge Viewer refuses to display. I thought perhaps it was a video driver issue until I tried running the program on another machine. A student friend who has access to an academic version at school was kind enough to create an eDrawings version of the assembly for me. I’ve used eDrawings created from SolidWorks many times, and they work beautifully. However, the .easm created from a trial copy of eDrawings for Solid Edge was abyssmal. Missing parts galore, including one of the steppers (why it singled out a single stepper is beyond me – they’re all from the same part file). Geometric Ltd. seems to think that the software is worth $395. I suggest they revise that figure downwards by a few orders of magnitude.
I finally realized I’d just have to re-create the parts in SolidWorks. Not a huge deal – SolidWorks barfed a bit on importing the entire assembly of Mendel (no issues with being from an academic version of Solid Edge – take note Siemens, as even competing products are doing better with your own files), but opens the individual .par files quite happily. Like Shane, I decided to start with the vertex pieces – while he opted to use a sine bar in the vise to provide the right angle on the vertex pieces, his use of a tooling ball (which I had never heard of before, and it took me a little while to figure out how they are used) gave me an idea of how I could do all the machining without worrying about angles. The trick is simply in relocating the hole that Shane was using for the tooling ball so that it runs in line with the two outside holes (and using the same diameter for all 3). Then, by using short 5/16″ rods through 2 holes at a time, I can accurately cut any of the faces.
I started with 3 pieces of scrap 3/4″ aluminum plate and drilled six 5/16″ holes though each at the coordinates that I had determined by a CAD sketch. I then bandsawed the pieces in a chevron shape:
Then I ran two pins through the holes of what would be a ‘leg’ on the part and clamped it in the mill vise:
In order to set the tool height, I placed a parallel across the pins and brought the endmill down onto it, then locked the quill, after which I lowered the knee by the appropriate amount:
This allowed me to machine the ‘convex’ side of each part. The other piece clamped in the left of the vise is just there to even out the force on the vise, not to have any machining done on it (I actually had something always clamped on the left, but removed it for most of these photos for clarity). To machine the concave side as well as the end of each ‘leg’, I needed to use an end stop:
Note that I started using 5/16″ drill bits rather than the 5/16″ pins of the previous photographs. The stainless steel pins were a very tight fit (I didn’t have a 5/16″ reamer on hand, so the holes are slightly undersized) and I had resorted to using a hammer and punch to drive them in and out of the holes. This got old really fast, so I just used a pair of drill bits instead – they had drilled the holes anyhow and were a loose enough fit that I could pull them out by hand, which really sped things up. After machining the ends, all milling was complete, and I just had to drill the two cross holes:
A touch with a countersink tool on all holes and a pass of a file on any rough edges completed the work. I’ll toss them into the vibratory deburrer later to give them a nice even finish.
One last thing – I’d like to give a shout out for Milwaukee Makerspace, which is a group of hackers/makers/tinkerers hoping to start a local ‘makerspace’ (think ‘a place for geeks to play with machine tools’). Come join us – the more people we can get, the cheaper it will be for everyone.
After a brief vibratory stint on some Roundhead bodies to test out the efficacy of my thread insert plugs during the ceramic deburring cycle, I tried turning on the motor once more only to be greeted with a loud angry hum from the motor but no movement (and an ominous dimming of the lights). A […]
After a brief vibratory stint on some Roundhead bodies to test out the efficacy of my thread insert plugs during the ceramic deburring cycle, I tried turning on the motor once more only to be greeted with a loud angry hum from the motor but no movement (and an ominous dimming of the lights). A bit of investigation showed that a wire nut had fallen off of a pair of wire ends, and they had probably contacted the steel tubing that served as the frame of the unit. I replaced the wire nut after checking for any other signs of damage, and tried plugging in the motor once more. Again, the lights dimmed and an angry hum flowed forth.
So I started disassembling the deburrer frame so I could pull the motor off of its mounting plate. Once I had the motor entirely free, I tried plugging it in again, and it spun up like a champ. I figured I must have knocked some bit of debris loose or something, and re-assembled the frame. Wouldn’t you know it, I tried plugging it in once more, and again got the ‘growling of extreme displeasure’ that unhappy motors are so very good at making. At this point I surmised that the eccentric weight that I had bolted to the motor shaft (which is what provides the vibration) was the culprit, and that the motor would spin up only when entirely unloaded.
I asked one of our EEs at work about the issue, and he indicated that single phase motors are generally an annoyance. I mentioned that the motor had a bulged cover on one side that probably housed a capacitor, and he said that this would be the start capacitor. Furthermore, toasting this cap as a result of the dangling wires was certainly a possibility, and that a slighty loaded shaft could be just enough to keep it from starting without the cap, giving the angry hum. “Pop off that cover, and you may find the gooey innards of the cap coating the inside”, he suggested. However, removing the cover revealed a fully intact, apparently functional capacitor (crude tests with a multimter indicated that yes, it was indeed holding a charge). I brought the motor in to work and disassembled it on a bench (with the help of the EE, who had once worked for Leeson Electric, and hence knows a thing or three about motors). Everything inside looked just fine – we couldn’t see any signs of trouble. I re-assembled the unit and tried powering it up. As before, it would spin up happily when unloaded, but when I held my foot against the shaft and tried turning it on, I got the angry hum. The EE surmised that the motor may very well have a bad winding – using a clamp-on ammeter seemed to indicate that the motor was drawing quite a bit of current at idle. To fix the winding (if even possible for one of these cheap overseas made motors) would almost certainly be more than simply buying a new motor. Off to Ebay I went, and found a beauty of a 1/2HP Marathon for much less than I paid for the 1/3HP Worldwide Electric.
Note the internal plate indicated by the red arrow – I’ll mention this in a bit. The Marathon motor (manufactured for Graymills for use in a pump) was pleasant to hook up, as the connections are all spade terminals inside a cover plate on the tail end. Despite being more powerful, the motor is actually smaller in diameter than the 1/3HP I had used. I assembled the vibratory deburrer with the Marathon, and set the whole thing going on a Saturday. A few hours later, the noise in the basement ceased, and I wondered what the heck had happened. The motor case was really really hot, so I let it cool off for the night. The next day, I tried spinning the counterweight by hand to see if perhaps it had seized or something, and I got a nasty shrieking squeal in return. Great, “another blown motor”, I thought.
I disassembled the deburrer and had a look at the motor. Thankfully the squeaking wasn’t a failed bearing as I had feared, but was the internal fan scraping against a sheetmetal plate of some sort (the thing pointed out by the red arrow in the above pic). I tried using a screwdriver to push the plate back down towards the windings (away from the fan), but this was near impossible to do correctly, as there were vents on only one side of the housing, and I managed to tip the plate even further. I disassembled the motor at work and carefully pressed the plate down into place (our EE said I could probably remove the plate altogether, as it was probably just for splash protection, but it’s captive due to a pressed bearing that I didn’t care to try removing). I’m wondering if perhaps the excessive temperature walked the plate out of place and up into the fan. Sticking a desk fan next to the motor seemed like a good idea, though I really needed to keep the motor from overheating in the first place. Excessive slip was probably the cause of the heat according to the EE, which meant I was simply trying to use too heavy a weight. Why I didn’t have this issue on the 1/3HP motor is a mystery to me, but at any rate I removed the hunk of steel from the weight. I immediately noticed that the unit was a good bit quieter, and the media hardly moved anymore. Well, at least the motor wouldn’t be turning itself into a puddle of slag while I come up with a better system.
I also noticed something slightly disturbing – some nasty chain wear. I guess this is the cause of the sprinkling of metal dust that appears on the tub cover, and indicates that a top suspended deburring system simply isn’t going to work very well.
This chain simply won't survive long-term
I then have two big changes that I intend to make to the deburrer – switching to a DC motor and going to a standard bottom supported tub rather than a suspended tub. Using a DC motor will allow me to vary the speed with a motor controller, and I also won’t have to worry about excessive slip causing increased current consumption and massive heat buildup. Even better, I can vary the motor speed in order to best match the load’s characteristics and find a sweet spot of maximum amplitude. In order to support the unit from beneath, I bought some beefy spring stock and will have to come up with a base of some sort. My plan is to also detach the motor from the tub plates, and have the motor attach to the new base instead. Then I’ll use a flexible coupling (a piece of hose, actually) between the motor shaft and the shaft of a weight system. Not only will this be kinder on the motor’s bearings, but the motor will no longer be useless dead weight in the vibrational system.
