FCG pocketing with CNC

A long-running project I’ve been tinkering with occasionally over the years has been machining an AR-15 lower receiver from scratch (or more precisely, a raw 0% forging).  I’ve made a fair amount of progress thanks to the excellent video done by Frank Roderus (which is a great machining tutorial even if you have no interest in firearms) as well as the Ray-Vin machining tutorial.  However, it’s really slow going, and I’ve made a few small mistakes.  Completing an 80% lower seemed like a good way to feel like I’ve accomplished something and would be a nice CNC project.

Drilling the holes for the takedown pins, selector, hammer and trigger pins, etc. is pretty straightforward after planing the top surface of the forging.  For an 80% lower, the takedown pin holes are already drilled and you can just use a drilling jig to drill out the holes on a drill press.  Call me a purist, but I still prefer just putting the lower in the mill vise as above, indicating from the front takedown pin hole, and drilling the rest of the holes with positions called out with the DRO.  The jig is invaluable for the various milling operations, though.

While the jig works great on the big manual mill, I can’t exactly clamp it into the diminutive vise on the CNC Taig, so I needed to determine a way to secure the fixture to the Taig table.

The 10-32 tapped holes on the A2Z tooling plate I use are spaced at 1.16″ intervals, and it turns out this spacing could be accommodated by the CNC Gunsmithing jig I use.  I drilled a line of holes for 10-32 clearance on the right jig half, and three 1/4″ holes on the left jig half (I used larger holes on one side to allow for slight differences in receiver thicknesses).  The magwell and trigger guard still stick out from the bottom of the jig, so I use a par of 1″ square bars on either side to raise everything up.

Generating G-code was pretty straightforward – I used HSMExpress to generate a path for the upper ‘shelf’ and a second path for the rest of the pocket.  Yes, I tend to make Z-steps very shallow, but hogging out material with a 3/8″ endmill with a fairly long length of cut is quite a bit for the Taig to handle, so I try to keep all the cutting lightweight, even if it means really long cycle times.  This was my first attempt to use HSMExpress, and I had no idea how well the toolpaths would work, or if the mill would suddenly take off on its own and carve a giant trough through the piece, turning a $70 part into 62 cents of scrap metal.  If only I had some sort of cheap plastic version for proving out the setup…  Quick, to the 3D printer!

I took a standard AR lower CAD model and filled in the FCG area to simulate an 80% lower.  I made sure to print the part with sparse infill to save plastic and time, but I still needed a way to have a ‘solid’ FCG area to provide material for the mill to actually cut.  I cut an opening over the FCG area and mixed up a batch of West System epoxy (I wish every hardware stored carried bulk epoxy supplies – luckily I live near one) loaded with a whole bunch of talcum powder.  I could have used some other filler, but I went with talc specifically to give minimal wear on the cutting tool – many common epoxy fillers can be quite abrasive (to say nothing of the fiberglass, carbon fiber, etc. that generally constitutes the matrix of a composite material layup).  I poured the epoxy/talc mix into the FCG area and let it sit overnight to cure.  In retrospect, I should have tried doing a vapor treatment on the part first, as the epoxy seeped out the sides a bit, but it wasn’t enough to affect the part’s purpose.

After reaming out the takedown pins, I was able to mount the printed 80% lower in the jig bolted to the Taig’s table.  I ran my generated program, and it worked great!  Right up until the very end, when the mill plunged right through the rear of the bolt catch area.  Precisely the sort of thing I wanted to test for, so it was all worthwhile.  I made a few adjustments to the G-code and ran the program through again to make sure that nothing else looked awry.

After that, I switched out the printed plastic lower for my partially completed 0% lower.  This showed me some other issues I hadn’t anticipated, specifically that the endmill liked to bog down in the aluminum.  I hit STOP right away, turned off the spindle power and took a step back to ponder.  The 4-flute endmill was probably not the optimal tool for this pocketing operation, but I had gone with it to increase rigidity due to the long tool length required.  The default toolpaths were also using climb cutting rather than conventional paths – this should result in less power required, but I’ve had bad luck before with climb cutting on the Taig and wanted this pocketing program to ‘just work’ even if sub-optimal.

With those changes made to the program and the purchase of a 2-flute endmill, I felt confident enough to subject a purchased 80% lower to the gauntlet.  One thing that proved very helpful were a pair of 1/4″ ground drill rods from McMaster-Carr that I could slide through the takedown pin holes in the left jig plate all the way through the holes in the lower.  This helped keep everything perfectly aligned while tightening down all the screws, and then I also used the rod to indicate in my X-axis position with an edge finder.  Make sure to remove the rear rod before starting the machining operation, though, as it sits right in the area to be machined.

Gripping a WD-40 sprayer in one hand, and Shop-Vac hose in the other, I exhaled deeply, turned on the spindle, and hit the green Start button in Mach3.  This operation makes a lot of noise, and I worried that something would seize up eventually, but my revised toolpath (I used a slightly different step-down path between Z-levels as well) seemed to do the trick.  When the program finished and the spindle fully retracted, I had no unintended cuts on the part and a nice, bright, shiny FCG pocket.

After washing it off, I installed the FCG components and did a safety check (make sure it will not fire if the safety is engaged, make sure the disconnector is working properly, etc).  Everything functions perfectly!  I’ll do a bit of identification engraving on the lower, and then it’s time to start picking out anodizing colors…

Reverse engineering for molds

On the Diamond 2500 powered sailplane, there are small ‘pods’ on the underside of the wings in front of the servos for the flaps and ailerons.  I’m guessing that these pods are intended to serve as some form of protection for the servo arm and linkage on landing, but the problem is that the pods will then be torn to smithereens (being foam, just like the rest of the wing).  While my quest to protect these 4 measly foam bumps seems to be ever-increasing overkill, it’s turning out to be a fun project and I’m learning a number of new skills from it.

While there were several ways to approach this, I decided to try making conformal covers for these pods out of fiberglass.  I could have just applied fiberglass directly over the pods, but I wanted to try something a little more precise (and replaceable, though I don’t know why I’m clinging to that notion when the plane is likely to be damaged in far more horrific ways).  I’ve been watching Tom Siler’s work on building his own fully molded F3K competition planes, and his videos are fascinating. He uses Corian for his molds, as it machines really nicely and is easily sanded and polished to provide an excellent finish on the composite parts pulled from the molds. I don’t yet have a vacuum system to bag parts, but I figured if I made a 2-piece mold, I could perfectly form pod covers without needing any sort of vacuum.

First things first – I needed to model the pod in SolidWorks.  Normally I just grab my calipers, radius gauges and other measuring tools, but the pod had me stymied – it’s a more complex feature than I initially thought and isn’t as simple as a truncated swept profile.  What’s worse is that it’s located on an airfoil, so I don’t even have a flat plane to reference.  I started to consider making a rubber mold of the pod, then casting an epoxy plug from the mold, then digitizing the plug with the touchprobe I have for the Taig (but have yet to finish wiring up), but that was turning into quite a production.  I remembered that one of Frankie’s toys is a NextEngine scanner, which would be perfect for this application, so I took the wing along during one of our Zcorp hacking sessions.

First step was to position the wing in front of the scanner itself.  The base will automatically rotate in increments if needed, but I just needed a 1-pass scan.

Once in place, let the scanner rip – a few of the laser beams are visible sweeping over the scan area, and the monitor screen shows a rough pass of the scanned pod.

I brought the generated STL into MeshLab and did some minor cleanup before bringing it into SolidWorks.  SolidWorks actually has some impressive mesh-to-surface capabilities, but since I was working with a mesh with a few holes in it, it would have taken a bit of work to get usable output (and I didn’t see a way to define a symmetry plane, but maybe I didn’t look hard enough).

Instead, I did my own surfacing, which took me quite a while.  I’m not good at it, and I know some of my techniques are wrong, but the final output should serve its intended function.

After finishing the male side of the mold, I thickened the surface by 0.010″  (I figure that should be plenty of fiberglass) to create a solid and extracted the far surface as the female side of the mold.  I set the two halves side-by-side in an assembly and exported it to GibbsCAM.

Once in Gibbs, I created my toolpaths (this shows the paths for the second operation, which uses a 0.250″ ball end mill).  After posting the file, I was finally ready to start cutting material.

Not having yet found any 1″ thick scrap Corian (everything I’ve gotten is 1/2″), I glued two pieces together.  The cold temperatures meant that the epoxy hadn’t fully cured after 24 hours, so I stuck it in front of a space heater for a day, and that firmed everything right up.

I drilled and counterbored mounting holes and then bolted the block to the tooling plate on the Taig.  This shows the results of the first pass, which was roughed with a 0.250″ flat end mill.  Note the curvature in the parting plane to match the airfoil surface.

This is the third and final pass, which used a 0.125″ ball end mill (and a generous amount of WD-40 as cutting fluid).

Once washed off, this is the result.  The pattern of the Corian makes it impossible to see any fine detail in the photo, but the surface finish is phenomenal – I used a 0.010″ stepover for the final pass (overkill, but it’s my CNC, so I’m not paying any extra for machine time) and it looks superb when you hold the machined surfaces up to the light.  All that remains now is to chop the two halves apart, then sand and polish the mold surfaces.

I made a Thingi

I’ve made several upgrades to my trusty Taig CNC mill over the years, but one of the best was replacing the original headstock with an ER16 headstock. This upgrade has thankfully become standard on the Taig machines, as the original proprietary collets were pretty lousy (and only allowed tool shanks of 5/16″ diameter, versus the far more versatile 3/8″ offered by ER16 collets). I quickly became enamored with the ER16 collets and now have a pair of 3/4″ shank collet holders for the Tree mill, one of which permanently holds an edge finder (this serves as a much more affordable alternative to an actual 3/4″ shank edge finder).

As my collection of ER16 collets grows (and I haven’t even started acquiring any metric sizes), I found that my storage method (consisting of keeping them on whatever relatively horizontal surface is available – oddly enough, also my storage method for everything else) was rather lacking.  Dropping a precision ground object on a concrete floor is seldom beneficial, so I looked for a better system.  While storage caddies for R8 and 5C collets are readily available (and I have a 5C collet organizer that is immensely helpful – when I remember to return the collets to it, that is), I’ve found no comparable options for the diminutive ER16 collet.  [edit – Naturally, after completing this project and post, I managed to find just such a thing.]

Of course, the obvious solution is to make something myself. A simple tray with appropriately sized holes would be functional enough, but I wanted something with just a little more elegance. While some of my most treasured tools have wooden cases, I have no problems with a good plastic case (and have on at least one occasion purchased a really crummy tool for no other purpose than for the halfway decent plastic case that it comes in).  So I whipped up a box in SolidWorks that could contain 15 ER16 collets with a matching lid.  I added some bumps around the outside edge between the halves to key them together so the lid would stay in place, and then sent it off to the printer.  The result was the box mentioned in this post from a few months ago. It wasn’t a great quality print as mentioned in the post, and I had incorrectly estimated the sizing of the cutouts for the collets which left them sticking up too far to let the lid close fully.

I gave it another try with a fixed model in Insight with the black Bolson ABS material, and things fared much better.  The interface between the support and model material wasn’t great, but I quickly discovered part of the problem:

The lid (upper right) has a darker triangular patch on the bottom left corner.  This is because no material was deposited there on the first model layer – there was so much ooze from the model material that a good deal of it flowed out during the lengthy build of the support layers.  As the machine was trying to print the perimeters of the first layer and the start of the infill on the lid, no material was coming out since the liquifier wasn’t full. Thankfully, this can actually be accounted for in Insight, as you can instruct the printer to purge material for longer than normal in order to top off the liquifier – I’ll need to remember to do this on builds with lots of base layer surface area.

No matter – collets fit this version just fine, and I’m not terribly concerned about aesthetics on something that’s going to get knocked around in the garage.

My original plan was to build hinges into the model – I wanted to have lugs coming off the back of the base and lid with circular recesses into which small disc magnets would be glued.  The magnets would attract each other and act as a hinge axis while hopefully providing enough friction to keep the lid open even when at an angle.  I’d still like to explore that concept in the future, but to finish this project in a hurry I simply used a pair of small hinges from Lowe’s.  I now have all my collets in one place next to the Taig in easy reach, and was pleased enough with how it turned out that I uploaded the design to Thingiverse. Much to my delight, it was chosen as a featured item!

Quick CNC work

I’m always impressed by Frankie’s ability to machine one-off parts on his Taig with minimal time spent on generating the toolpaths, which is something that I want to become better at. I’ll frequently over-think and puzzle over the CAM side so much that I wind up just bashing out parts manually on the Tree. However, for a recent project I needed to do a lot of cutting in odd shapes that would be crazy to do manually for a single part, so I gritted my teeth and dove in.

As part of my growing RC aircraft addiction, I had purchased an Ikarus SU27-XXL kit as a fun ‘zoomy’ plane to advance beyond my trusty Slow Stick. My original plan was to use the brushed motor included with the kit – why discard a perfectly good motor, even though it may not be as powerful and efficient as a brushless one?  Well, a good reason is that brushed ESCs (electronic speed controller) are much more difficult to find these days than their brushless counterparts.  So I went brushless anyhow and purchased a motor and ESC.

Since the new 400 brushless was mounted at the base rather than the face, I couldn’t use the included light plywood motor mount.  I needed to build my own custom motor mount, and I happened to have some 3″x3″ squares of 1/16″ G-10 fiberglass sheet left over from a project that would make for very sturdy construction.  I drew up the needed parts in Cadkey and then tinkered with GibbsCAM at work to hopefully output usable toolpaths.  Fortunately, I’ve gotten much better in this regard, and the G-code worked out just fine.

I used a hunk of scrap polycarbonate bolted to the tooling plate on my Taig as a sacrificial base.  Frankie recommended using carpet tape to hold sheet stock flat for machining, and it worked like a charm.  I’m using a 1/32″ carbide cutter to do the milling – I think it cut through the sheet in 3 or 4 passes.  When done, the parts were easily pulled off of the base.

After removing the tape and adhesive with a ‘Goo Gone’ type of solvent, here’s the parts I had.  As it turned out, I could have skeletonized them far more than I did, and using 1/32″ G-10 may have been an even better material.  I did have to do a bit of filing by hand to make things fit – the original plywood parts were laser cut and so had perfect square cornered slots, which obviously can’t be done with a round endmill.

Glued together, it looks pretty good!

Fits beautifully on the plane and certainly looks like the beefiest part of the entire airframe.

Unfortunately, she would never look this good again…  On the final flight (just after I had moved up to a larger prop that finally provided the performance I wanted), I pulled out of a fast low level loop right into a tree, and the brittle Depron foam snapped all over.  The motor and mount tore free from the plane and was unscathed, however, so I’ll be dropping the unit into a scratchbuilt MiG-29 made out of pink sheet foam from the home improvement store.  I have a feeling that the motor mount will easily outlast that airframe as well…

CNC router build – now with wheels

As of the previous post on the project, I had loosely test assembled the router base. Since then, I got more fasteners and did the final assembly of the base frame. I initially was fine with the idea of having the router live on the floor in the basement, but after considering the size and weight of the unit, it seemed that some measure of mobility was in order. Plus, having the router up a bit higher would be nice for accessibility. So with another order of 80/20 extrusion, and the scrap left over from my initial cutting, I had just enough material to make a very nice mobile cart. I’m becoming addicted to 80/20 – it’s expensive, but makes building such assemblies a breeze.

I grabbed some cheap locking casters at Harbor Freight, and they were perfect for the project, as the mounting holes were just right for the 5/16″ carriage bolts used to assemble the rest of the frame.  A piece of MDF makes for a nice lower shelf where the controlling computer may live once I get that far.  I can even add in another shelf easily thanks to the T-slots.

One thing that I wanted to address with adding the cart base was to increase the (already substantial) rigidity of the table and allow any twist to be adjusted out.  I tapped the bottoms of the original stubby 8″ legs for 5/16″ screws, and then turned points onto some hex head screws to center them into the holes of the adjoining extrusion.  A piece of angle extrusion on the inside corner of each leg then clamps the two pieces together once the screws have been adjusted to level out the table.  I haven’t gotten the leveling to be perfect, but it is most definitely ‘good enough’, especially for the expected accuracy of such a machine.

Finally, I completed the two carriages for the main axis. Fine Line Automation and CNC Router Parts carry these for $33.50 each, which I thought to be a bit high. After machining a pair of them myself, I’ve rethought that assessment, and now they seem like a pretty good deal. I used bearings from VXB for the rollers, and everything went together quite nicely (though I did have to machine down the heads on the machine screws for clearance). I’ll have to readjust the torque on the fasteners, though – the nylon washers I used between the bearings and the blocks crush and deform enough to let the washer wear against the red seal on the bearings, causing drag. With a bit of red Loc-Tite to keep things in place, I should be able to back off the pressure to allow the carriages to slide more freely.

As much of a pain as they were, I’ll still machine the remaining 4 carriages myself, seeing as how I have the bar stock already rough sawed (and all the bearings purchased).  But before that, I’ll start work on the main leadscrew and associated hardware so that I can have an axis of motion to be proud of.

PS – James Jones directed me to an intriguing project he’s heading called CubeSpawn. It’s a flexible manufacturing system based on T-slot extrusion – once I realized that it’s not just another T-slot machine, but a modular system, I began to ponder the sorts of automated assembly line things it could make possible on a small scale.

Categories: CNC

Another CNC machine?

My Taig CNC mill has served me well for many years, and continues to perform admirably. Perhaps too well, as I always have it fixtured up for one thing or other, and as such I no longer have a CNC machine that I can just hack/play/tinker on.  The foundry class got me thinking about CNC milling foam cores, or perhaps patterns and matchplates out of wood or plastic.  This led me to think that perhaps I should build a CNC router for such work.  I say build rather than buy – gantry type routers are quite simple in construction and building a machine is half the fun anyhow.  There’s many free designs available for CNC routers, so I went looking for one that I liked.  I knew I wanted something based on T-slot extrusion for ease of assembly and straightness (some warping would be almost inevitable if I were to try welding a frame out of square tubing).  After a brief search, I found a promising looking design done by cncrouterparts.com and Fine Line Automation. A 24″ x 36″ working area sounded big and roomy, and I was most impressed by the use of cold rolled steel and skate bearings for linear motion (in a similar fashion to a RepRap) rather than much more expensive linear bearings. The last time I looked at building my own CNC, I realized that the least expensive route would be to buy surplus linear bearings and rails from Ebay in whatever sizes I could manage, and then design the machine around those components. But in this case, I could follow the plans more-or-less as published – a good thing, as once I start redesigning something, I never really stop the design process, and whatever I was working on winds up with a severe case of kitchen sink syndrome.

While Fine Line Automation has kits available, I knew it would be much less expensive for me to simply get the raw materials myself and do the requisite cutting on my own. I did look around for cheaper alternatives to the 80/20 T-slot extrusion that the plans called for (many companies offer ‘aluminum structural framing’), but eventually found that 80/20’s garage sale Ebay store had the best prices, and they actually had all the components that the bill of material called out.

Rough bandsawed extrusion awaiting cleanup on the mill

I chopped the pieces to rough length on the big horizontal bandsaw at work, and then took them home to machine the ends to the final precise lengths.  After tapping the holes in the ends to 5/16″-18 and drilling access holes in strategic locations (all detailed in the prints contained in the set of plans available on Fine Line’s site), the extrusion pieces were complete. A trip to Speedy Metals netted me the cold rolled steel, which I also drilled out on the mill. With stepper motors on the way from Keling, bearings from VXB, ballnuts and ballscrews from McMaster-Carr and couplers from Enco, it seemed like a good time to at least start assembling the base.

Definitely larger than I had envisioned - I'll need to build a special cart for it

Many of the builds that I’ve seen of this design include additional bracing in corners.  The framing itself is quite stout and I don’t intend to do any metal cutting with the machine, but more rigidity never hurts on a machine tool, so I used some aluminum angle on the inside corners.  I ran out of screws, so the base isn’t yet quite fully assembled, but at least I have a sign of progress.

Categories: CNC

2010 CNC Workshop

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 parts
A 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).

Simple CNC Engraving Head

My very first summer job was working at the local trophy shop, where we had several computerized engravers.  As it turns out, they were extremely similar to the Taig CNC mill that I would many years later acquire – driven by steppers in the X and Y axes and controlled via a desktop PC, it’s really not a stretch to consider them specialized CNC tools.  Our most commonly used engraver was a ‘diamond drag’ type, which essentially used a diamond tipped tool to scratch through the lacquer covering a sheet of brass or aluminum (our other engraver used a rotary cutter for engraving on plastics).

Once I had my Taig, I realized I could certainly do a little engraving myself, I just needed the right tool.  On the engraver at the trophy shop, the ‘head’ was actually pneumatic – rather than a Z axis, there was simply a 3-way solenoid valve that would apply air to a spring retracted engraver.  More air pressure meant deeper engraving.  There had been plans in Home Shop Machinist (might have been the sister publication, Machinist’s Workshop) for a spring-loaded engraver for use on CNC mills a while back, but I wasn’t thrilled with the design – not only did it reduce the working travel in Z, but had to go in the spindle.  I wanted an engraver that could be attached to the side of the headstock (Taig headstocks have T-slots for such purposes) which would not only be a bit more rigid, but would allow me to machine a shallow flat on a part and immediately engrave in that area without any tool changes.

Construction is simple – the only purchased parts were the diamond drag engraver (I used a DG-250 from Antares), a pair of clamp collars, and a spring. The body was a hunk of scrap extrusion from work – it had a 5/16″ hole already down the length of it. I machined a pair of bushings from some Oilite bronze rod stock and pressed them into each end of the body (I had bored each end out a little bit). Though I had reamed the bushings to have a 1/4″ hole through them, there was enough axial misalignment between the two to cause the engraver to bind when I tried to run it through. So I tried something a little crazy – I chucked a long piece of 1/4″ drill rod in the lathe, lightly scuffed the last two inches or so of the rod with a diamond hone, slathered it in oil, and ran it through the bushings. This trued things up just enough to allow the engraver to slide through the bushings freely, but with zero side play. A bit of strip steel, some threaded rod and wingnuts, and it’s ready to attach.

Assembled engraving head
Assembled engraving head
Engraving head parts
Engraving head parts

The mother of all CNC programs

I’ve been working on cocker threaded Phantom bodies for quite some time, and the latest incarnation is a ‘full round’ version.  I had a job shop do the internal machine work on them as I didn’t yet have the big lathe running (which I’m now having some regrets on – the cost was substantial, it took over 5 months, and despite what I was told at first, they want the invoice paid in full NOW).  I wanted to do the final machining in a single setup, as they’re round and alignment would be a concern were I to try multiple setups.  Furtheremore, a single setup would require 4th axis operation, as there are features on the top and bottom of the part.  In short, there were a lot of ‘firsts’ for me in this project, and it’s the most ambitious CNC program I’ve yet done (experienced CNC machinists would laugh at its simplicity, but hey, I’m learning).

Roundhead body on the mill
Detent slot milling operation in progress

I broke the program down into pieces, some of which I had already done.  There are 5 subroutines in use:

  • sear slot
  • threaded insert counterbore
  • feed port
  • threadmilling for insert counterbore
  • detent slotting

The sear slot is first, then the underside counterbore, rotate 180 degrees, then the topside counterbore and feed port.  Tool is changed to the threadmill, top counterbore is threaded, rotate 180 degrees and thread the bottom counterbore.  Finally switch to the ball end mill and run the detent slots.  Total run time is still over a half hour, which I hope to cut down a bit by removing some unneeded ‘air’ cuts, increasing feeds, etc.  Still, the satisfaction is immense – I’ve had a lot of tools (the 4th axis, tooling plate, tailstock, bullnose live center, etc.) sitting idle for a very long time (they were all purchased with this project in mind), and it’s a great feeling to finally have them put to use.

Mach3 while running the CNC program
The three tools used in the program, held in A2Z endmill holders
The three tools used in the program, held in A2Z endmill holders