Joystick Repair

I intended to post this a few months ago, but the old server had simply gotten too rickety to cope with new posts, much less OS or WordPress updates.  So I opted to roll an entirely new VM with an OS version published this decade.  Hopefully previous posts imported properly, but the site may be a work-in-progress for a while.

A friend’s all-in-one Namco joystick had broken, and they wondered if I might be able to fix it.

The issue was that the bushing that the joystick shaft is pressed into had split.  Since it looked to be Nylon, my guess was that just trying to glue it back into place (even with epoxy) would not last long as a fix.

While the manufacturer is still in business (though on a different URL), their site doesn’t appear to have any mention of this particular unit.  I wasn’t really expecting to find an exploded diagram and parts ordering form anyhow, but once in a while pleasant surprises pop up.  Not so in this case, so time to wield Phillips screwdrivers with careless abandon.

The joystick mechanism looks to be secured under that square base plate.

This turned out to be a far more complex mechanism than I had anticipated.  It wasn’t until I gave the unit back that I learned that this is due to the Pole Position game using joystick twist for steering instead of normal left/right movement.

My plan was to find some thinwall stainless or brass tubing to sleeve the outside of the bushing and thus collapse down the split section.  I didn’t have much luck in finding an appropriate size tube in the McMaster-Carr catalog, however.

No big deal when you have machine tools, though!  I found a piece of scrap stainless rod, faced the end, and drilled a shallow hole with a W size drill bit (0.386″, which is just the size of the bushing’s outside diameter).  I then thinned down the outside until I reached a point of ‘that looks about right’.  This turned out to be a wall thickness of around 0.017″ which I hoped would be thin enough to retain full movement of the stick.

After parting off the ring, I did a little light deburring.

The ring pressed snugly into place on the bushing, and the crack is practically invisible now.

I carefully hammered the joystick shaft back into the bushing when done.  Interestingly, the end of the shaft has both splines and ridges to keep it from pulling out and from twisting – that should have been a clue to me regarding the twist operation.

A few games of Galaga verified that operation is back to normal!

4-jaw chuck for the Keiyo Seiki

I recently had another Keiyo Seiki/Homach lathe owner contact me, and I mentioned that I had been meaning to get around to posting a copy of the manual that came with my machine.  It turns out that other owners have been looking for one, so hopefully this helps a few people: Keiyo Seiki Homach KM-1800C lathe manual

When I purchased my lathe, it came with both a 3-jaw and a 4-jaw chuck – the 3-jaw was mounted to the headstock and the 4-jaw was in a box.  However, the first time I wanted to try using the 4-jaw, I discovered that the chuck uses a D-6 camlock mount, not the A-6 mount that the lathe spindle actually has.  Apparently I had been given the incorrect chuck, but it had been long enough that I didn’t have the seller’s information anymore.

My first thought was to see if I could somehow mount the 4-jaw with an adapter plate of some sort – the jaw body itself mounts to a ‘spider’ that has the camlock lugs on it, so all I would need to do is to replace the spider with a backplate.  Well, in an ideal world, that would be the case.  The screws that attach the spider to the chuck body are attached from the spider side, not from the front face of the chuck.  Thus, using an adapter plate would be a mechanical impossibility with no way to reach the attaching screws.  So now I have a D-6 4-jaw that needs a new home, and I needed to start from scratch.  Off to Enco!

Enco did in fact have the sort of 4-jaw chuck I was looking for (I selected it based on the size of object it could pass – anything smaller than the headstock ID would be wasteful), so I purchased it during one of their free shipping promotions.  All I needed then was a backplate, which I procured from “Industry Recycles” on Ebay.  I think it was actually an Enco offering but I managed to snag it for about half price.  Score!

Unlike the backplate for the 5C collet chuck, this backplate mounted up just fine.  The trick, then, was mounting the chuck to the backplate rather than mounting the backplate to the lathe.  Mounting hardware was easily purchased from McMaster-Carr, and then it was time to start making holes in things.

Given my experience with the 5C collet chuck mounting, I decided to be a little more precision oriented this time around.  I started by measuring the hole locations on the chuck itself.  Using calipers and screws inserted into the mounting holes, I measured the distance across each pair of screws (both ‘inside’ and ‘outside’ measurements).

I found that the locations of the four mounting bolt centerpoints differed by about 5 thousandths of an inch.  Instead of just basing my cuts on a single measurement, I opted to use the average instead, which came out to be a bolt circle of 5.10425″, or a radius of 2.552″.  Easy work – put the backplate in the vise in an orientation that will clear the existing holes, indicate the center bore, and drill 4 holes at +X, -X, +Y, and -Y locations of 2.552″.

Wait, the Y handwheel stopped….

Noooooooooo!  I ran out of travel little more than an eighth of an inch from the lowest hole location.  I started to resign myself to moving the vise to a new location on the table (I hate having to re-indicate in a vise almost as much as tramming the head), when I realized “duh, just rotate the hole pattern by 45 degrees”.  So each hole would be at X/Y +/- 1.8045″.

After drilling, I ran a M14x2.0 tap through the holes.

The backplate mounts just fine to the lathe spindle….

And the 4-jaw mounts just fine to the backplate!  I started right in on drilling some Delrin for a new product offering.

A pair of quick machining projects

It’s been a busy summer/fall/early winter, but I’ve managed to make a few chips in the shop over the past few months.  First up, dad had a front tractor axle that needed a little work.  The hole drilled through it wasn’t quite at the needed 5 degree angle to allow for proper assembly, so he ground out the sleeve that had been welded in and I gave the boring operation a try.

Clamping the part was a little easier than I thought it would be.  It’s a heavy beast, and is as long as the entire mill table.  There’s a pair of blocks near either end that worked great for aligning it on a a horizontal plane, then I just had to clamp the center section in the vise.  I tipped the head forward by 5 degrees to complete the setup.

I seem to have lost the feeler clamp screw for my trusty Blake Co-Ax indicator, so I used an edge finder to pick up the hole center instead.

I didn’t have a boring bar long enough to plunge all the way through, so I bought one just for this project.  I selected a bar tipped with C2 carbide since the cut would be interrupted due to being a slightly different angle than the original hole.  I started by setting the boring head to a small enough diameter that it would just start cutting at the bottom of the hole (where the offset between the existing hole and my new cutting axis is greatest).  I then adjusted the boring head to make the hole a little larger, set the powerfeed, and bored again.  It was long, slow work, but I finally got to the point where I had better than 50% circumference all the way through.  Finally, I turned a matching sleeve on the lathe that dad could weld into the axle hole for the whole assembly to ride on an axis pin.

A friend is assembling a new upper for his AR, and one of the components is a Sentry 7 adjustable gas block.  Unfortunately, the freefloat handguard he’s using makes adjustment of the metering setscrew almost impossible.  Dremeling out a simple slot would fix things just fine, but would look pretty ugly – milling the slot would look much cleaner.

The problem is, how do you clamp a round object while also properly indicating it so the cut is right over the central axis?  After a bit of pondering, I came up with the above solution.  I first drilled and tapped holes in a 1″ square aluminum bar and clamped that into the mill vise.  I used strips of tape on the vise jaws to protect the anodizing on the handguard, and then used a pair of 1/2″ bolts to secure the handguard – tightening the bolts works to wedge the handguard against the top edges of the jaw faces, perfectly centering and aligning the handguard.

At that point, milling the slot (really just removing the web from between two holes) was a piece of cake.

Carbs

A few weeks ago I finally got the GS500 running for the season.  I rode with friends out to Madison and around the Kettle Moraine area as shakeout runs for a trip from Milwaukee to Minneapolis in a few weeks (should be interesting on little 500-650 cc bikes).  My bike, while it worked, needed some attention.

That’s the contents of my gas tank after draining it.  I’m surprised it ran at all – I needed to drain an entire Starbucks cup (thank you, parking lot litterbugs) worth of crud out of the float bowls in order to get home from Madison.  The second issue was the choke – it’s been getting progressively stickier until our 4-person ride to Kettle Moraine, where it seized entirely in the open position.  At stoplights I got to look like a tremendous jerk with my bike idling at 4000 RPM (and a Vance & Hines exhaust to boost the noise even further).  So after the ride I knew it was time to really dive into the bike guts.

After pulling the tank (and discovering the red-brown horror within), I removed the airbox and had a look at the carb itself.  The core issue was plainly obvious – a bent plate and choke plunger end on the left side.  So, just bend the end of the choke plunger back into pla… *snap*

Well, dang.  Fortunately, there’s a Suzuki dealer just down the road, and 2 weeks later I had a replacement plunger in hand.  Once I went to install it, though, something wasn’t right.

Yeah, the new plunger (top) was a bit different.  I don’t have another 2 weeks to get the correct part (if the shop can figure out the right part number), so I chucked the old plunger in the lathe.

A #43 drill and a 4-40 tap provided the threads I was after.  I installed the plunger back into the carb, and attached the plate.  A loctited 4-40 socket head cap screw finished off the assembly.

The carb, airbox, and most hoses are now reattached.  Once I put the gas tank back on and put fresh fuel in I’ll see if everything works.

Rotary Phase Converter – Part 3, aka 'What temperature do electrons burn at?'

When machining the scope mount spacer rings in a previous post, I had been planning to finish them when Max had stopped by one evening.  Simple enough – fire up the RPC and turn on the lathe.  Only thing was, the red ‘start’ button on the RPC was stuck and I couldn’t press it in.  What the heck?  Being in an impatient, Neanderthal-esque mood (I was hoping Max could take home all the parts for the project that night), I powered down the system and removed the button so that I could hammer it into a variable on/off mechanism rather than being restricted to the single, not-terribly-useful state of ‘off’.  With my ‘fix’ complete, I re-installed the switch in the semi-dangling sheet metal front panel (I plan to fully enclose the whole thing nicely one of these days, honest).

After throwing the mighty disconnect to ‘on’ once more, I pressed the just-tweaked red start button again, and the system fired up.  However, things were not sounding right, so I pressed the black stop button right away.  I surmised that the growling must be due to loose items sitting atop the plywood sheet that adorns the RPC cart (and acts as more horizontal storage space than I care to admit).  So I pressed the red start button again, and let the system growl angrily while I prepared to turn some perfectly good aluminum tubing into swarf.  After perhaps 10 seconds, there were loud popping sounds coming from the RPC, followed by me hopping around trying to turn off every electron flow nearby.  After I finally hit the main disconnect, I had a look at the carnage underneath the plywood sheet, where we both saw some rather impressive green flames emanating from what had been the bank of starter capacitors.

“Um, what temperature do electrons burn at?” he quizzed, a highly amused grin on his face.  After I had finished blowing out the flames (note to self – buy fire extinguisher for garage) and giggling over the absurdity of the situation, I determined that finishing the scope rings would simply have to wait for another night.  We pulled out the smoking remains of the capacitor bank and had a look.

So, that’s what’s inside an electrolytic capacitor – foil, paper, and magic smoke.  As everyone knows, once you let out the magic smoke, nothing works correctly, and you can’t get the smoke back into the component it escaped from.  After I checked my notes (that is, my previous blog posts on actually building the RPC), I re-familiarized myself with the circuit.  I had connected the starter capacitors directly through another pushbutton module, as I didn’t have a suitable relay at the time.  I recalled consulting with our EE at work about the use of just the pushbutton for the starter capacitor array, and he said that while it wasn’t ideal given the amperages in play, it would probably hold up just fine for several dozen to a hundred startups, which sounded just fine to me at the time (and then I promptly forgot about that limited lifespan).  I don’t know exactly how many RPC startups I’ve had since building it, but it’s certainly within that range – he gets major bonus points for accurate estimation of the failure mode and timeframe.

Really, I should have noted the signs of excessive current when I first pulled the pushbutton out of the panel.

The melted plastic housing right next to the screw terminal at the very rear of the module is a dead giveaway for “something ain’t right over here”.  So I replaced that module with a spare that I had, and decided to actually do things correctly this time.  Well, more correct at any rate – if it blows up again, I may have to reconsider my approach.

I used an Allen-Bradley contactor (the gray device on the left) with the 120v coil wired in to the start switch by way of the step-down auto-transformer (black box in the upper right).  The previous bank of ten 64mfd start capacitors (bits of their innards still sprinkle various components) has been replaced with three 208mfd caps (which I would have used initially if Surplus Center had them in stock at the time).  The big rectangular run capacitors remain unused, the poor things (well, it’s a better life than erupting into a cloud of electrolyte and flame).

Starting the newly repaired RPC was not quite as nail-biting an experience as the very first time, but still caused me to grit my teeth when pressing the red button.  Fortunately, all my work had been properly done, and the RPC started up in a flash without issue.  In fact, it seems to be even more reliable at this point – I’ve started it up perhaps 5 times or so, and each time was perfect.  I didn’t have to release the start button after 1.2 seconds because it didn’t sound quite right – every start has been confidently powered, with no hesitation.  The scope rings were turned with ease, and the system is better than ever!

Nerdy Derby

In August, Pete posted an innocuous message to the Milwaukee Makerspace mailing list:

Now that Power Wheels is (mostly) over, we should turn our attention to this:
http://www.nerdyderby.com/
I mean, we'd need space to do such a thing, but I think it would be awesomely cool.
Who's in??

Hmmm…  A ‘no rules’ pinewood derby?  I was never in Boy Scouts, but racing cars certainly was appealing to any boy (and I raced many many Hot Wheels cars in my youth, with extravagantly banked and looped tracks, often borrowing construction elements from Lincoln Logs, Legos, Tinkertoys, and whatever else was at hand).  What better way to relive my childhood than to downhill race blocks of wood in the same fashion as I did with Hot Wheel cars with friends and cousins: without any rules.

Discussion on the mailing list quickly dove into the underlying physics, and how heavier cars will lose less of their overall potential energy to friction, which led many people to work on designs maximizing mass (and then resulted in questions on how to do lead casting – the competition was serious for the event).  My own thoughts were originally along this line as well, thinking of building a car out of steel plate with rails to keep it on the track.  But then I figured that just adding power to the car was really the best solution – the heaviest derby car still has only gravity to propel it, and a lightweight (though powered car) should certainly be able to best it.

Powering the wheels was the obvious method, but I had never messed with RC cars, slot cars, or any other powered car toys enough to know what sort of motor/transmission system they used.  The closest I had come was years ago when helping someone with concepts for a mousetrap racer.  My idea was to have a foam cone on the drive axle around which the string from the driving arm would be wrapped.  The string would first pull from the large end of the cone to maximize the torque and get off the starting line faster, and as the string unwound, it would be on successively smaller diameters to decrease torque and increase speed.  But how to determine the best shape for the cone, and what would be the best power source?  Rubber bands?  Torsion springs?  And how to make sure that power isn’t engaged before the starting gate drops?

I quickly discarded that line of thinking in favor of just brute force – stick a model rocket motor on the back of the car.  Of course, that would probably run afoul of the one rule imposed in an otherwise ‘no rules’ race – don’t damage the track.  While I could argue that scorch marks are merely cosmetic, it probably wouldn’t fly with race officials, and the open flame indoors may not be a great idea.  Plus, how to trigger it only after the start gate?  Someone else on the mailing list linked to information on CO2 powered derby cars, which are most certainly fast, but any bit of off-center thrust gives them a bad tendency to leave the track.  Given that there is a hump right in the middle of the official Nerdy Derby track, it was very likely that such a car would become airborne.

I then recalled a novel race car I had read about as a kid – the Chaparral 2J.  What made it so interesting was that it was built as the opposite of a hovercraft, so that a blower unit would actually evacuate air from underneath the car, keeping it glued to the road surface even when at low speed (compare to a modern F1 car that can generate tremendous downforce via aerodynamics, but only as a function of its speed).  Of course, the Chaparral 2J was banned from competition very quickly – sounds like just the thing for a ‘no rules’ race.  What to use for a fan suction system, then?  Well, a ducted fan seemed a logical choice – I hadn’t yet used one in any of my RC planes, but this seemed like an excellent opportunity to experiment.  If I angled the ducted fan back on the car, I could use it for thrust as well as forcing it down on the track.  With a propulsion method in mind, I briefly turned my attention to the wheels.  It sounded like plain old off-the-shelf pinewood derby wheels were being used by most other builders, but I figured disc style wheels with ball bearings could only help.

With the basics in mind, it was time to start designing.  Charles and Frankie were also building cars, so we met up at Frankie’s studio a few weeks ago for a day of design, construction, and the bull session that invariably occurs whenever the 3 of us get together.  Frankie was already well underway constructing his belly tanker design, and Charles had some solid design concepts sketched out for his own car.  I had only the vaguest notion of what I wanted to achieve and a copy of SolidWorks – okay, time to get designing.  I started out with the track itself, and drew up a section about a foot long.  Wheels around 1.25″ diameter felt about right, and I roughed out a model of the EDF unit that I had in mind for the car.  Throwing them all together netted me a skeleton of the main components.

Given that the car’s stance was pretty narrow, I figured adding a set of outrigger wheels would be a good idea – just in case the car lost its footing due to the EDF’s torque.

Most of the day was spent on hashing out the body itself.  What I originally envisioned was something sculpted, smoothly flowing and elegant yet powerful, like a Lola T70.  I may have fallen a bit short in that department.  I designed the parts to be laser cut out of 1/16″ plywood on one of the makerspace’s laser cutters, and figured that I’d somehow use 1/4″ aluminum tubing with 5mm fasteners for the axles (with appropriate flanged bearings pressed into the wheels).

I converted the models of the plywood pieces to be cut into DXF files and then arranged them together into a single panel that would span a 12″ wide piece of plywood.  The DXF for the sheet is here.  I stopped by the space on a Thursday night, but only the 25W laser was operational, and it was only able to be run at half power.  As it turned out, 12.5W was simply not enough – even after multiple passes, the poor little photons had managed to fling themselves no further than 1/3 of the way through the plywood.  I took the piece home, expecting that maybe I could cut the rest of the way through with a hobby knife and jeweler’s saw.

Fortunately, I didn’t have to resort to that, as a week later both lasers were fully functional, and Shane was just finishing up one of his nifty laser cut/engraved card boxes.  He helpfully assisted me with the finer points of the big 60W laser, and I was off and running.  Wow, what a difference!

Even through the protective window of the 60W unit, its vigor was unmistakable.  There was a little more charring than I would have liked, but I’m not about to complain – having it cut all the way through beats the heck out of cutting it by hand.  At home, I broke the pieces free.

Next step, I needed wheels.  I found a length of 1.25″ diameter plastic (some sort of phenolic, I can only assume), chucked it in the lathe, and started cutting.

I drilled a hole in the stock before parting it off to provide (hopefully) a decent diameter to press-fit the flanged bearings into.  My parting tool has a bad tendency to drift to the left as I part off stock, so I needed a way to true up the wheels to be entirely flat on each side.  I figured I’d try machining an expanding arbor to hold the wheels, as it’s been rattling around in a tool drawer for years, awaiting a purpose.

While it machined really nicely, it didn’t work out well in practice.  The plastic wheels still flexed quite a bit while being cut, and wanted to walk off the arbor as a result.  It was now getting down to the wire, and race day was approaching.  Scratch that – race day was here.  As of Saturday morning, I wasn’t sure if I’d be racing at all, but I’d certainly make a go of it.  After soldering bullet connectors onto the EDF unit, I was ready to glue together the shell of the car.

I used CA to bond the plywood together (having used copious amounts to seal/strengthen the parts themselves) and hot glue to mount the EDF unit.  While waiting for the CA to cure, I headed to the garage to do more work on the wheels.

Good old carpet tape worked well enough to machine the wheels to thickness – just go slow, take light cuts.

7 wheels (always make more than you need, because you just know you’ll mangle one during subsequent operations).  However, Friday had brought a potentially devastating bit of news – the raised center section of track was 1.65″ wide, and not the 1.5″ wide that I had designed to.  Much wailing and gnashing of teeth ensued.  Fortunately, I had designed the body after the wheels, and as such the wheels could actually be moved outside of the body with no ill effects. Realistically, this this even better, since having the wheels external would remove the need for outrigger wheels, and internal wiring wouldn’t have a chance to get tangled up in them.  Also fortunate was the fact that I am a horrific procrastinator, and since I hadn’t yet gotten to the stage of machining axles, I was free to modify my design as needed.

I drilled out some pieces of 1/4″ thick wall aluminum tubing and tapped the ends for 5mm threads.  I also cut some spacers so that the bearings wouldn’t run against anything else.  I then started packing the inside with components – a 22A ESC, a 2.4 GHz receiver, and an 800mAh LiPo battery (all credit to Charles for suggesting that I stick the battery inside – I had planned on running it externally for ease of access until he convinced me otherwise).  Ideally the ESC and battery should have been rated higher, but for burst use (under 3 seconds from start to finish), these components should hold up fine.  Besides, there’s always the ‘epic fail’ prize category should something go wrong.  Internal accessibility was not considered at all in the design phase, so the right body panel is held on by the axle spacers and wheels.

So 30 minutes before heading out the door to Bucketworks to attend the Derby, this is what I had.  A radio that I was using when attempting to fly my latest RC plane on it’s first and last airborne adventure (maybe I shouldn’t have transferred the ‘Centrino Inside’ and ‘Windows Vista’ stickers from my laptop to it), and a car held together with hot glue, CA, a few pieces of fiberglass fabric, and medical tape.  Perhaps MacGyver would be proud.  Or appalled.  Eh, whatever.  The car was assigned #32 as a race sticker, and I had a glance at the competition, which looked tough.

Pete’s ‘Raster Mobile’ certainly had mass, and Brant’s ‘Safety Car’ had lots of lights.

Fortunately, Kevin B’s “car” was deemed by race judges as illegal.  However, I admired his extension of the rules.  “Roads? Where we’re going, we don’t need… roads.” Brew’s Dorito-laden vehicle was a crowd-pleaser when it invariably ejected salted snack chips at the end of a run.  Unfortunately, Jim’s ‘Sparky’ was having electrical issues and wasn’t running nearly as fast as it had been on test runs.

Brent’s ‘Pootystang’ really had me worried.  A full diameter propeller will easily best a ducted fan unit in thrust, and he looked to be using the same battery as I was.

Ed’s “Aghghhhh!” was the best (only?) 3D printed car in the race.  [edit – Pete’s ‘Great White’ was also printed – forgot about that one!]

Charles finally gave his (highly polished after 5 hours of work) car a name of ‘2 ways’.  I added ‘both of them wrong’ to it (not shown in photo).  In the photo, it appears to be heading the right way (right to left).  He claims that the front end is actually the right side of the photo, for which he deserves to be mocked endlessly.   I think Rose entered ‘5 Rings’ and Dillon had entered ‘Indus’ (which was based on a pull-back racer).  Since we were to name our own vehicles, I decided to call mine “Waste of a Perfectly Good Afternoon” (that’s all that it was until that point).

Fortunately, I was paired against Charles for the first 2 heats.  He gave me a sporting chance by running his car in reverse – he keeps claiming that’s the front end “like a Studebaker”, but I know better.  I applied the throttle just enough to keep my car in the lead (seriously, I was worried about something erupting into sparks and flame – this was a 22A ESC with an EDF unit that can draw 33A).  This got me into the finals (thanks, Charles!  Sucker…).  I raced Jim’s ‘I Win’ and Brent’s ‘Sneaky Weasle’, which was amazingly fast.  Every time, I throttled up just enough to ensure that I was in the lead, but no more – damage to the car upon contacting the deceleration zone (a chunk of open cell foam at the end of the track) had me worried, as one race broke the EDF unit free of the body, necessitating emergency hot glue gun surgery.  In the end, I was in the lead at the final race, and gave it full thrust from start to finish to see just how quick it could go – 1.595 seconds was the elapsed time.  Incredibly, it survived intact!  After that, it was requested to see if the car could run the track in reverse and actually make it up the hill.  Our intrepid race official quoted Doc Brown’s famous words, the crowd gave a countdown, and I floored the throttle, easily sending it off the far end (thankfully Jim was there to catch it).  After that, there were the awards.

Frankie is out in Denver at the moment speaking at a conference, so this award certainly went to his belly tanker.

My car not only won as the ‘fastest’, but also captured ‘the noisiest’ and ‘best name’ awards.  No trophies or cash prize – just bragging rights.  As such, I’ve been telling attractive females that I’m a 3-time auto racing champion, but when they learn the details, they tend to edge away nervously.  *shrug*

http://wiki.milwaukeemakerspace.org/projects/nerdyderby

Stupid broaching tricks

One of the little trinkets I sell in my online paintball store is nothing more than a modified stock part that adjusts the gun’s muzzle velocity.  The modification is straightforward – I simply drill a big hole through the middle to increase the airflow (just like porting the cylinder head of an engine, this improves efficiency) and then broach a hex through that hole so that the velocity can be adjusted with a hex wrench.  From the beginning, broaching the hex has been the fly in the ointment when modifying these parts.  The concept is simple enough – a hardened steel plug with a hexagonal cross section (and cutting edges shaped appropriately) is pressed with great force into a hole drilled the same diameter (or a teeny bit bigger) as the distance between flats on the hexagon.  The points of the hexagon carve into the circle, peeling six chips downwards along the walls of the hole.  In this case, I’m using an ‘F’ size drill bit (0.257″) and following up with a 1/4″ hex broach.

The problem with the broaching operation has been twofold – generating sufficient force to press the broach through the hole to the needed depth while at the same time keeping the broach as centered as possible with the hole it is cutting.  My initial method was to use a 5C collet fixture on the bed of the mill to hold the workpiece while gripping the broach in a drill chuck (with a short piece of metal rod as backing) in the spindle.  I’d crank down hard on the spindle feed lever (spindle not rotating – this is entirely linear) and plow the broach through the part with a fair bit of effort – while this worked just fine, I always felt like I was abusing the machine (though my buddy tells me he knows of a shop that punched metal parts in exactly this way on their Tree mill – they are certainly rugged).

As such, I’ve looked for alternative ways to broach the holes.  The most interesting method is rotary broaching, which is also more descriptively known as wobble broaching.  Some years ago in either The Home Shop Machinist or Machinist’s Workshop was a project for a nice rotary broach holder that could be fabricated out of mostly scrap with a bit of work.  Unfortunately, not only am I cheap, but I am also lazy.  The concept did give me an idea, though – the Taig headstock now comes standard with an ER16 spindle.  If I could simply bolt a headstock to the toolpost on my lathe, I’d be set.  I ran the idea past Nick Carter, who agreed that the idea seemed sound in theory, so I purchased a Taig ER16 headstock from him.

Taig ER16 headstock and mounting plate

Ideally I’d make my own dovetail block to bolt the headstock to (the dovetail then mates to the quick change toolpost), but laziness got the best of me here (and then bit me as will be seen shortly) and I bolted the headstock to an unused boring bar holder.

Boring bar holder with mounting plate attached for the ER16 headstock
ER16 headstock mounted awkwardly on toolpost

Well, I overestimated the torsional rigidity of the toolpost mounting.  Really, I should have seen it coming – that’s a heck of a long moment arm between the centerline of the broach and the centerline of the shaft that bolts the toolpost to the compound.  When I ran the assembly into a part to be broached, the whole works just pivoted around the toolpost shaft, making a small (though roughly hex-shaped) indentation in the part.  The idea still has merit, I think, but even if I used a shorter block, I still worry that it wouldn’t be rigid enough.  I should probably think about mounting the headstock to the side of the toolpost so that there’s no moment arm to push it out of alignment.

I considered using the small arbor press I have to do the broaching, but it needs a more secure mounting to the benchtop, and I’d have no way to make sure that the broach is correctly centered with the part.  Unless, of course, I built some sort of system to always keep the part aligned with the broach…  Quick, to the scrap pile!

Alignment sleeve on top, with the broach and part holder underneath. Below that is the broach backup, the broach itself, and the part to be broached.

I dug up a piece of stout stainless tubing and some hardened shaft material that slid nicely through the tubing once I turned off a thou or so from one side (I love the big Keiyo Seiki – while the finish isn’t great on the cut areas of the hardened shaft, I wouldn’t have had a prayer of accomplishing such work on the 9×20 lathe).  The ‘from one side’ part is because I still haven’t addressed the 1.5 thou runout on the 5C collet chuck…  I made a short backup stop from a bolt to sit behind the broach – this let me adjust the depth of the broach without having to drill the hole in the broach holder to a precise depth.  Everything looked pretty good, so I stuck the broach in place with a bit of RTV silicone (I didn’t want anything too permanent).  I slipped a part into the part holder, then dropped the two holders into either end of the alignment sleeve.  Since the assembly looked a bit large for the arbor press, I threw the mess into the bench vise.

Broaching assembly pressed in bench vise

The part to be broached acts as a stop, so I merely needed to crank the vise down until I felt abrupt resistance.  After pulling the holders out of the sleeve, things looked like a success.

Broached to full depth

A little wiggling and the broach pulled out of the part easily.

The broaching on the part was superb – the chips were more symmetric than previous broaching done with the quill on the mill, and all that remained was to drill the chips out.  The batch of parts came back from plating on Friday, and they nearly sold out over the weekend.  Guess I better start making more.

From extrusion to injection molding

Charles is working on a tabletop plastic injection molder based on the Gingery design, but the machining needed for the heater chamber is a bit more than what his Sherline mill can handle, so I ran it on the big Keiyo Seiki (which also gave me an excellent excuse to finally get a big Rohm drill chuck for the tailstock). I figured he’d probably want to see the steps needed to do the machining, so I took some photos of the process (which simply reminded me of why I need a better camera, as the autofocus on mine in abysmal).

After taking off the 5C collet chuck and installing the standard 3-jaw chuck on the lathe, I chucked up the piece of 1.5″ steel rod, powered up the RPC and lathe, and got to making chips.

The bar was cut quite nicely as it was, so rather than face the end first (and have to fiddle with getting the tool bit exactly on center) I center drilled it.

Then I faced the end with a beater carbide tipped bit that had come with the lathe.

I started drilling with a screw machine length 1/4″ drill bit (I love the screw machine length bits as they’re short, strong, and don’t wander as much) and then switched to the much longer 1/4″ bit shown here.  One big advantage to drilling on the lathe rather than on a drill press or mill is that long holes are much straighter.  On a drill press, the workpiece is stationary, and the drill bit is allowed to wander off of its axis a bit.  However, on lathe, the workpiece spins, and the path of least resistance for the drill bit is to seek the rotational axis of the workpiece, ensuring that the hole stays straight.  From what I’ve read, the most accurate hole drilling is done by rotating both the workpiece and the drill bit simultaneously (in opposite directions, of course).

Once I had the 1/4″ hole drilled all the way through, I moved up to a 15/32″ bit to bring the hole nearly to size.

Then came the 0.501″ reamer.  I put the lathe into a very low gear, as high speed will kill a reamer quick.  Lots of Tap Magic and backing out frequently to clear chips made the procedure go without a hitch.

Finally, I flipped the part around, faced the other end and topped it off with a a slight chamfer where the piston will actually enter.

And then the moment of truth – the 0.500″ ground rod that will serve as the piston slid through cleanly with zero wobble.  I also machined the end of the piston where the linkage rod will connect.  Unfortunately, my camera refused to focus for any of those shots.  Fortunately, this means that no photographic record of my ‘oops’ exists (the endmill caught the workpiece and slapped it back through the 5C block I used for workholding).  It was a good reminder that steel is not as forgiving to machine as aluminum, so I removed the 4 flute endmill I had been using and switched to a flycutter and took nice small cuts to create the flats needed.

Rotary Phase Converter – Part 2

I’ve sadly used the big Keiyo Seiki lathe only a handful of times since getting it, as what passed for my rotary phase converter (pull cord, 10HP idler and a big disconnect switch) left a great deal to be desired.  Not just in terms of ease-of-use, but also in terms of voltage balancing, and exposed wires just waiting for errant chips to come into contact.  Getting the rotary phase converter past the pull cord stage has taken a good deal of time because it’s somewhat of a pain, and I’m not entirely certain of what I’m doing (which is probably why it’s somewhat of a pain).  Given that 240VAC will provide some impressive sparks and smoke (not to mention affecting one’s nervous system in a negative manner should the conductance of Homo sapiens come into play), I’ve approached further development of the unit with a good deal of caution.

My primary guide has been Jim Hanrahan’s tutorial, which I’ve referred to continually while adding indicator lamps and pushbuttons to the system.  At this point, I still only have the 10HP idler in use, with the 7.5HP idler still to be added.  With the two idler motors on the bottom shelf, I’ve been adding the various controls to the second shelf (the top shelf of the cart will be a good spot to keep the dividing head and tilting vises for the mill).  Here’s a breakdown of what the system looks like right now:

A) The unfinished control panel is a rather flimsy piece of sheet metal – I’ll need to stiffen it up before I mount it permanently.  On the left of the panel (top of the photo) are two indicator lamps – one for the incoming 240VAC and one for the 120VAC from the transformer (I know, I could have run a neutral line from the breaker panel and gotten my 120VAC that way, but this is how I decided to run things).  The center modules consist of a start button (which has two contact sets – one connects to the motor starter, the other connects to the starter capacitors.  Ideally, I’d use another contactor for the starter caps, but the pushbutton contacts are rated for 10 Amps, and they should last a good long while), a stop button, and an indicator lamp.  The empty holes will contain the start and stop buttons and indicator lamp for the 7.5HP idler once I get it wired in.  The pushbuttons and lamps are from Surplus Center.

B) Motor starter for the 10HP idler, purchased from Igor Chudov.

C) 200mF 370VAC run capacitors from Surplus Center.  Note that one lead on each is disconnected – more on this later.

D) Bank of ten 64mF 220VAC start capacitors, also from Surplus Center.

E) Step-up/Step-Down Autotransformer from Jameco.

F) Power distribution board, consisting of a few terminal bars from the hardware store mounted on a piece of polycarbonate.

G) Motor starter for the 7.5HP idler (currently unused, and it seems to smoke a bit when I power the coil).

I’ve needed to get the lathe going in order to kick out some custom paintball gun parts for my friend Blue Fish, so recently I fired up the RPC for some actual use.  Jim Hanrahan’s guide seemed to indicate that there’s simply no substitute for measuring volts/amps of an RPC setup to dial in the system with regards to capacitance (the 200uF run caps were simply a guess as to the needed value – that, and large run caps aren’t easy to come by, so I thought I’d start on the high end).  With the beefy run caps in place, I fired up the system to see what voltage and amperage I had on the 10HP idler without it powering any equipment:

Unloaded Amps:

Red 0.2 – Blk 22.3 – Wht 16.5

Unloaded Volts:

Red/Blk 280 – Red/Wht 315 – Blk/Wht 233

Wow, the voltage differences are pretty severe – how do the values change when I’m actually using the lathe?

Loaded (lathe running at 600 RPM) Amps

Red 7.6 – Blk 21.3 – Wht 12.8

Loaded (lathe running at 600 RPM) Volts

Red/Blk 261 – Red/Wht 297 – Blk/Wht 234

Things look a little better when the system is actually in use rather than standing by, idling.  Still, the noise from the idler is excessive – rather than the quiet purr I recall, it growls continuously and vibrates the whole cart.  Even more, the housing of the motor was HOT after use.  Something was certainly not right, so I disconnected the run capacitors and tried again.

Unloaded Amps

Red 0.2 – Blk 13.1 – Wht 12.1

Unloaded Volts

Red/Blk 212 – Red/Wht 209 – Blk/Wht 233

Loaded (lathe running at 600 RPM) Amps

Red 3.3 – Blk 12.4 – Wht 14

Loaded (lathe running at 600 RPM) Volts

Red/Blk 203 – Red/Wht 211 – Blk/Wht 211

Wow, what a difference!  Running with no run capacitors whatsoever seems to result in a much better voltage distribution.  What’s more, the idler is much quieter and stayed cool while running.  This is a pretty clear indication that I should just leave the run caps out of the circuit, and the voltage and current may even out even more once I add the 7.5HP idler in.

I'm not dead yet.

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.