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Heh, that mirrors what the guy at Gear Center said yesterday. "40mm... hmm... *calculator*... that's pretty close to 1 5/8"..."

The tool you showed looks like the male spline, not the female, but, $18 is a great price. If couplers are going to be roughly in that range, I'd be happy.
More critical than the tool is the list of potential donor tractors - although half of those are likely to be the smaller 21 tooth configuration that the front of the tool covers.
 

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Discussion Starter #83
More critical than the tool is the list of potential donor tractors
Oh, gotcha. I thought you were posting the tool itself. That's clever.

I don't have a farm equipment junkyard near me. I'm not sure what type of business to call to find out about that either. Bit out of my wheelhouse.
 

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Discussion Starter #84
I called a half-dozen more places today.

Most transmission shops noped out. They have nothing that big.

Called a few tractor places, no match.

Did find some things on Ebay under $100 (a few more above $300):

https://www.ebay.com/itm/1865836-Massey-Ferguson-PTO-Disc-10-Fine-Splined-1-5-8-25-Spline-PACK-OF-1/140998794695?hash=item20d42eddc7:g:RCwAAOSwjMBc0xPA

https://www.ebay.com/itm/Tisco-E3NN7550EA-Clutch-Disc-12-25-Spline-1-5-8-Hub/271113737980?hash=item3f1fa356fc:g:2WAAAMXQzopRGD1S&shqty=1&isGTR=1#shId

So, theonetruerat was spot on. Tractor clutches.

I wish there was a place where I could go through the junk bins for someone who bought a new one, since, almost certainly what wears is the clutch plate itself, not the splines.

After shipping they'll be at least $100 each. I don't think I want to pay that much. I think I'm more likely to turn the shaft down with a grinder and make a taper-lock.

Waiting/hoping to hear back from a few other tractor part sellers.
 

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Discussion Starter #85
Trickier than I thought.

There aren't any tractor boneyards around for me to pick through.

PTOs from Massey-Ferguson and Fords, or clutches (same thing? pictures look the same, are all PTO's clutches?)... and seems to be around $65 US is the cheapest.

Called the forklift place. They said the transmission shaft would probably work if I could give them a matching model. I asked for a ballpark price and the guy said "Oh... thousands?" Lol. Nope.

Tried McMasterCarr. Nope.

It's weird, I would've thought that this would be a thing that already exists, somewhere, even if rare.
 

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Matt

PTO is a clutch, just not sprung so it stays disengaged if 'off'.

Not sure who you contacted but who services these tractors?you could try a service agent or a friendly farmer, they never throw stuff out so might have something lying around.

Cheers
Tyler
 

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Discussion Starter #87
Not sure who you contacted but who services these tractors?you could try a service agent or a friendly farmer, they never throw stuff out so might have something lying around.
No one nearby apparently.

And, I can't just run around and ask any farmer if they have particular models of Massey-Ferguson or Ford tractors with blown clutches.

That's like asking random car enthusiests if they have winter tires they want to sell you.

Dealers want like $120 for the clutches, locally.

I'm tempted to go with Plan B: Grind it down, Taper Lock.

But maybe I'll try Plan A2: Get out the hacksaw and fabricate my own 25-spline female coupler.

Or, JB-weld was on sale the other day. Maybe I'll chop up a dollarstore strainer for its stainless mesh, pick up some grinder sweepings with a magnet, and use the three of those together an epoxy spline coupler :p. I don't expect it to hold, but I am half-tempted to try.

There are many wrong ways to do this before I go spend $100+ on some teeth.

It's been a few years since I fired up the Tormach or the milling machine I have access to. Not really keen to do that though, definitely cheating to use a pair of $12,000 machines on a $2000 project.
 

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Hi Matt

They are not working just now because of the shut down but we normally have LOCAL Facebook buy and sell pages - may be worth advertising on those sites

Wanted old tractor clutch plate from a XXX
 

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It's been a few years since I fired up the Tormach or the milling machine I have access to. Not really keen to do that though, definitely cheating to use a pair of $12,000 machines on a $2000 project.[/QUOTE]

If you have access to a cnc or a manual mill you can use them to turn down the shaft. Mount the motor and apply a low voltage - the motor becomes the "4th axis" in the mill and you can cut down the teeth and add a key slot. Pick up a coupler with a slightly smaller internal diameter to the shaft and turn the shaft to fit. A straight keyed shaft will be a lot easier to cut than a taper lock.
 

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Discussion Starter #90
Been thinking about spline coupler options...

I'm getting closer to being tempted by the JB weld option, at least temporarily.

Another option is to just fabricate a coupler manually with a bandsaw or scroll saw cutting the tooth profile (maybe using a JB welded ring as a template).

Another option that I'm actually pretty close to attempting is to use the motor shaft as a form to sand-cast a copper equivalent. Then use the sand cast splines as the tooling electrode on a crude sinker EDM machine I'd build (capacitor, lightbulbs, bolt, fishtank pump and tupperware).

I could use the motor directly, but the electrode does wear a little bit, and as it's a thermal process, the shaft will wear about as fast as the workpiece. Plus I'd have to suspend the 255lb motor above the bath.

I've never sand cast before (or EDM), but I think it's worth attempting.

Not the easiest way to save $100 but, that's two other things I'm interested in learning how to do anyways and I'm always looking for an excuse to build new tools.
 

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Been thinking about spline coupler options...
using hand tools or epoxy to build a transmission coupler to carry a couple hundred ft-# of torque at significant RPM is really just asking for disaster.

If couplers are not well-aligned and of appropriate materials, they won't last long, and failure will be spectacular and potential dangerous if the driveshaft starts whipping round under the car when the coupler fails.

Matt, you have astounding electrical skills, and have made great progress mechanically on your frame and bodywork.... but DO NOT SKIMP on transmission/driveshaft couplers or driveshaft.

I'd suggest you call around local machine shops, hot rod or 4x4 shops that modify driveshafts, and they can probably make you a custom driveshaft with U-joints matching the splines you need.
 

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Discussion Starter #92
using hand tools or epoxy to build a transmission coupler to carry a couple hundred ft-# of torque at significant RPM is really just asking for disaster.
I mostly concur. But, lots of times people say "can't" when they really mean sub-optimal. People said I couldn't built an EV with recycled 18650s, people said I couldn't weld thin sheetmetal with a flux core welder. People said you can't cast copper in plaster of paris. If it's not much cost or effort, I at least like to see why something is a bad idea sometimes, because half the time there's no issue.

The diameter of this coupler is going to be like 2", compared to the 3/4" of stock. If I cut some steel ribs to slide into the splines before I epoxy, I think it would probably be fine for stock performance.

Since it's not much to try it out, and at least get the motor spinning and all that stuff figured out, I might still try it.

If couplers are not well-aligned and of appropriate materials, they won't last long, and failure will be spectacular and potential dangerous if the driveshaft starts whipping round under the car when the coupler fails.
That will not be possible with my build.

I should be more clear. The original driveshaft is going to slide into the original transmission tailshaft housing, onto the transmission output shaft. Like so:



Then, I am going to try to mate that transmission shaft to the motor shaft.

The transmission tail housing is going to mount to the back of the motor somehow (drill bolts, it's a 1.5" thick plate of steel).

Here's the motor next to a full transmission, imagine getting rid of the bell housing and the gear housing, and just putting the grey tail housing with a bit of a spacer ring, to the motor:



So, if my coupler shatters, it will mean that the motor is no longer spinning the transmission output shaft, but the driveshaft is still contained by 2" inside the tail housing and the tail housing still bolted to the motor. The only part that fails will be the coupling itself.

I'd consider that a "soft" fail with the consequences similar to a flat tire or running out of gas.

I'd suggest you call around local machine shops, hot rod or 4x4 shops that modify driveshafts, and they can probably make you a custom driveshaft with U-joints matching the splines you need.
This is definitely the right way to do it.

I will almost certainly not be doing that. At least not at first, because, the weak point in my driveline is the rear end and I may want to replace it all later anyway. My goal has been "Get it rolling, make it nicer later", since feature creep kills my projects.

Not a lot of custom driveshaft shops open right now anyway.
 

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Matt,
I looked at your motor spec sheet again and I'm wondering if you have considered using the "non-drive" end shaft. It looks like a 1-1/8" 17 tooth spline. I was able to find a hub with that configuration out of Australia, https://www.hydairdrives.com.au/ part number 94/50027. No idea on price.

I also found a tractor clutch but that was ~$170, so not useful.

Just a thought.
Bill
 

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Discussion Starter #94
I looked at your motor spec sheet again and I'm wondering if you have considered using the "non-drive" end shaft.
Briefly entertained it, yes.

Few reasons not to:

1 - It puts all the cables and sensors farther away from the engine bay if I do that. And into the tighter (narrower) area of the trans tunnel where there's no room for them, or room to service them. I am limited by how far I can shove the motor, by the size of the trans tunnel so, this would mean moving the motor further back.

2 - Currently, not even sure it has that under there, there is a metal cover over it and I'm not sure how to take it off.

3 - The face doesn't have anything to grab onto. The big shaft side has a massive plate. The smaller shaft side is mostly fins.

4 - Cooling would work best if the open face of the fins shovelled air through and out to the opposite side.

5 - It's not future proof. I may some day upgrade the rest of the driveline and want the beefier splines in use.

You are correct that it would be a lot easier to find a matching spline though. I probably have dozens of cheaper options.
 

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Discussion Starter #95
New milestone: I have now spent as much avoiding buying a coupler, to avoid buying a coupler, without having spent enough to actually make a coupler yet.

Well, time for an update on a series of failures that may someday lead to a success. Half of this is just so I have this written somewhere, it might not be that interesting.

There are 3 sub-projects to this, in increasing complexity:

1 - Make a mold of the driveshaft splines
2 - Make a furnace to melt the copper into a copper clone of the driveshaft.
3 - Make an EDM machine to use the copper clone to cut a female coupler out of steel.

Mold-making:

Almost complete failure. I have now attempted to make 10 or so molds.



Plaster of Paris works okay, but it's fragile and you're supposed to have 2 degrees of draft angle. I have zero degrees of draft and a bajillion grippy sections (cylindrical shaft with splines). This almost always results in the mold gripping the shaft too well and shattering the plaster when I try to take it off. I've let it sit 2 hours, overnight, and 4 days. None held up.

I've tried mixing Plaster of Paris with sand and bentonite clay (kitty litter ground up using an immersion blender), for extra rigidity and temperature handling at the expense of surface finish. It also shattered taking it off.

I tried using green casting sand (sand with bentonite clay). The "right way" to cast copper. This is impossible, because you have to pack the sand around the object, you can't pack it first. The motor shaft is in a recessed hole, there's no way to pack sand around it. I tried anyways, not even partial success, there is no way. Loose sand won't hold, pre-packed sand won't crush. Neither sand will release even when I have an otherwise unuseable mold, even if I liberally cornstarch the splines and the sand surface. This is a dead end without having access to pack sand.



Furnace:

As earlier, a stove burner won't work. This is the garage equivalent of those Pinterest-mom drain cleaning or home remedy ideas, everyone keeps repeating it, no one knows what they're talking about.

I dug out both of my carbon arc torches that I've never used and bought some 3/16" and 5/16" carbon gouging rods (on clearance, 60% off). I'm not gouging, but no one has used carbon arc torches since oxy/ace has been around. Copper-coated carbon should just be copper-coated carbon, gouging is just when you direct air parallel to it to blow the molten metal away. I don't have a gouging head anyway, so should be fine.

Short vid:

https://www.youtube.com/watch?v=toGhu-bXvN4

My idea was to keep the steel crucible and waft the arc up and down around it like you would with a torch. I could not get my rods to light. They'd spark, but never light. I tried for an hour to feather it every possible way. I was moving the tips by a millimetre at a time, no luck. Even with an arc welder designed specifically for dual use as a carbon arc torch (you flip the ground clamp around, slide the stinger onto one side, and the clamp itself becomes the spring tension between the "V" to light the arc). I could get an arc, but only momentary. Not sure what I'm doing wrong.

Another short vid showing the torch, which I had to un-repair the previous owner's repair (drill out one side to fit carbons):
https://www.youtube.com/watch?v=apj_EL-rMQQ

I cut up and machined a cavity and access holes into some fire brick. Normally fire brick is how you insulate your furnace walls, inside of which you put a crucible. I just used the fire brick itself as the crucible, which will consume it but, I'm not doing this 20 times. I replaced the carbon arc torch with a pair of jumper cables and lit the arc inside. It was so hot it turned the ceiling of the furnace into glass in about 3 seconds, which then dripped into the copper below. It's plenty hot, just not focused. I tried 5 different things and none worked, and it blew the breaker every 3 seconds so I gave up and took the lid off.

Still kept blowing breakers. Without a lid, no way to add energy fast enough to keep the copper molten without blowing the breaker.

So I stepped my game up. I took 3 beyond-junk car batteries and hooked them up in series. Then put a 15A car charger on Battery #1, and hooked my flux core welder (27.6v output) to Battery #2 and Battery #3 in series (13.8v per battery, about right). Was about 45v open circuit, 36v loaded. The idea being, the batteries would help pick up some of the load. I could leave them to charge for a half hour, and then use that stored energy combined with the welder and charger, and buy enough time to liquefy the copper while having higher average power output than the 1800w I could get from the breaker.

Still couldn't get the arcs to light for more than a couple seconds.

I changed methods. I stuck the positive carbon directly against the copper and then hovered the negative over top. Instant success. And I mean instant. Anywhere that arc moved, the 10g scrap copper melted like it was made of butter. Took seconds to melt the copper wires into a pool. I was having so much fun messing around with it heating and cooling that I eventually started blowing breakers again because the batteries were too low.

For scale: An entire 100 amp service to a home is 240v * 100a = 24,000 watts. A 50A outlet for your welder can be at most half that. 12,000 watts. A 15a 120v breaker is only 1800 watts.

Starter batteries are 12v, ~700 CCA. So, more like 1000A at room temp. 12 * 1000 = 12,000 watts per battery. 3 of them makes 36,000 watts. 50% more than the entire power grid to a house. 20x the max power of my welder. Even if they were underperforming junk batteries... ludicrous amounts of power.

I eventually just ignored the breaker being blown and ran the batteries into the ground to keep the arc lit, until the copper was almost boiling.



I poured it into the only mold that survived, the awful one I described in my previous post that was super wet and didn't transfer detail well. I'd only baked it dry for a few hours.

.... surprisingly, it worked. I'll make some videos of it when they have better context.



I'll have to run it through a bandsaw to cut off the top half, and, it doesn't matter how ugly the inside looks, it'll be getting mounted to an arbor regardless. Just the outside profile matters. Voids and such in the finish don't matter either, as I'll be plunging the whole thing through the workpiece.

I've been told you cannot cast copper in plaster of paris, it breaks down. Mine held up fine. The only errors were errors in how crappy of a mold it originally was.

My copper might have glass dissolved in it. Hard to tell. I didn't use enough copper either.

I'm 100% satisfied with my ability to melt copper in the "furnace" (an open bowl shape cut into firebrick). If my furnace survived (debatable, it started to crack) I just need a better mold to pour it into.

The current copper clone might be usable with some cleanup to make sure there's no extra material (extra material will cause extra material to be removed, and thus be missing teeth). It's ugly, but the electrode wears perhaps 10% as fast as the workpiece, so, it might be enough.


... (Cont'd)...
 

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Discussion Starter #96
... (cont'd)...

EDM Machine:

This is pretty simple. When you bring two electrical contacts together, they spark. A tiny dust fleck of material is vaporized from the positive side. But, only when the electricity first "lands" there. So you want to keep starting and stopping the spark as fast as possible. Around 5,000-20,000 times per second. The arc will happen whenever the two surfaces happen to be closest, which jumps around because you keep flicking a spec of dust off of what used to be the closest point.

You can do this with transistors and brains, telling it to start and stop. Or you can just control the rate that a capacitor charges, which eventually has enough voltage to ionize the fluid, jump the gap, get discharged, not have enough to sustain an arc, and charge up again. I went with the capacitor.

Old Popular Mechanics articles have shown this back in the 60s, when GTs were being made. It's just DC voltage to a light bulb (resistor) and a capacitor.



2 kinds of EDM: Wire EDM, and Sinker EDM.

Wire EDM is like a spark-erotion bandsaw that cuts through material and carves out a shape. That takes computer control. The electrode is very fine copper wire and, what survives out the other end isn't reusable. Wire EDM typically uses a trickle of distilled water as the bath.

Sinker EDM is just an electrode you slowly lower into the workpiece, and it copies the shape. The electrode is typically graphite. Sinker EDM typically uses kerosene as the bath. I'm building a sinker.

I tried using tap water on a test piece, lowing copper pipe into 1/8" steel. It sucked.

I've seen plans for EDM machines for over a decade, they usually have computerized stepper motors to control the sinking electrode, having it regularly back up to wash the swarf away and prevent it from sticking. I just used my drill press to lower it.

About every 3rd spark made the electrode stick to the workpiece. There's an instant visual indicator of this, because your light bulb stays lit rather than flickering. Then you have to back it off, then lower it again.

Also, because tap water is conductive, it electrolyzed the water, splitting it into H2 and O2. O2 goes to the positive side, forcibly rusting my steel workpiece. I had a frothy foam of rust that interfered with the sparking and soon rusted up the whole tank.



So I bought some Kerosene. 20,000 electrical arcs per second, in a tub of kerosene? Apparently, unlike the instant bomb this would be with gasoline, with kerosene this is safe. You can throw a lit match into a pool of kerosene (or diesel) and it won't light.

It worked... poorly, but it worked. I ran it for 1 hour before stopping to inspect.



My copper was cut crooked, so that's why it's a semi-circle, that half has always been closest to the workpiece.

The whole tank was black with iron oxide, I had no filter. I had a small pump, but my "small" marine pump pumps a gallon every 3 seconds. I don't want a kerosene fire hose, so I didn't use it.



I started off with perhaps 5 hz, and ended up feathering the gap better and achieving maybe 50-100hz. Not the optimal 10,000-ish, so it was very slow. Mostly due to setup I think. My capacitor timing is right, I just have no flushing of the worksurface so it regularly sticks and fails.


How much material did I remove?

Quick maths:

3/4" semicircle = 1.1775" length.
0.050" wide track.
0.050" deep, but in a V shape, so, average 0.025" deep.

Total material removed: 0.00147 cubic inches in an hour (24 cubic mm/hour).

In a proper setup, I should be doing 14-29mm^3/min that rate per minute, not per hour, but it's roughly in the same ballpark that my frequency is off by, and the first 30-40 minutes were much worse.

You can just add more power, 10x much even, to a point, as long as there's enough surface area that sparks are spread out.

How much do I need to remove?

After drilling out the coupler to the minor diameter of the splines (mechanical removal is thousands of times faster), I would sink the copper into the workpiece so only the splines themselves have to be spark eroded. On my splines, the major diameter is ~41mm (1320mm^2) and minor diameter is 37mm (1075mm^2). Sanity check, that's 4mm difference total, which is 2mm deep teeth on each side, seems about right. And call it a 50% that needs to be removed between those two diameters to create splines. (1320mm^2 - 1075mm^2) / 2 = 122.5 mm^2 of area needing to be cut. Or, 122.5 cubic mm per mm of depth.

If I want at least an inch (25mm) of depth, that's 3000+ cubic mm to be cut (1/5th of a cubic inch). I probably have 2 inches of splines if I want to cover them completely, but, let's no go crazy.

At my current average (really, worst-case) rate of 24mm^3/hour, that's 125 hours, or 5-ish days of cutting. At a proper rate, that would be about 2 hours of cutting. At a fast rate with aggressive settings and poor finish, 20 minutes.

I'm fine standing at a drill press feathering a cut for 2 hours, but I'm not standing there for 5 days. So, the viability of this depends on how good I can get my setup compared to a small commercial tap-burning rig.

...

So, plan moving forward:

Mold: Be less ambitious in depth, try to get 1/4" deep mold instead of 1/2" or 3/4", and hope it survives. I can make multiples of these and just swap them out if they get consumed by the EDM. Stick with plaster of paris. If that doesn't work,switch to green sand, which means finding a way to pack around the splines. I think I can add 2 more steps and create a low-temp mold first. Make an epoxy copy of the shaft (or a heated PVC copy), then melt plastic or pour expoxy into that female mold (with some kind of oil or release so it doesn't stick to the sides), then use the plastic male clone to create a proper packed green sand casting that can handle copper temps.

Furnace: Add more copper next time, see if firebrick survived, consider switching back to the steel crucible buried in sand, power isn't really a limit anymore.

EDM: I really want to avoid building a proper jig, with sliders and stepper motors and current sensing with computer controlled reversing. It might be inescapable to have to do that. That's a whole project in itself, ordering parts, troubleshooting, programming, etc. I'll try adding a pump, increasing capacitor size, and seeing if I can burn fast enough without doing anything else. I'll need to filter the kerosene too, coffee filter maybe, not sure. I have to remove 125x as much material, and the kerosene was already ink black.

... I'm almost content having experimented with the 3 side projects and just want to go buy a proper coupler now. The appeal was "Maybe it'll work easily, and I don't mind wasting a little time to find out". But I'm there now. Mixed results, and patience for side projects is wearing thin. A hacksaw would have had my splines cut by now.


Here's the "expense report":

Kitty Litter: $7.98
50lbs Play Sand: $8.20
Strainer: $3.50
Plaster of Paris: $6.47
Cornstarch Baby Powder: $3.47
Containers: (free, had some)

Mold total: $29.62

Black pipe & plate: (free, had some)
Black pipe cap (didn't use): $2.12
Firebrick: $7.50
Flower pot (didn't use): $2.50
Stainless tongs: $1.25
3/16" Gouging Rods: $8.33
5/15" Gouging Rods: $9.13
Borax (sprinkle into molton metal to clean out oxides): $5.47
Car batteries, chargers, jumper cables: (free, had some)

Furnace total: $36.30

2 Gal Distill water (didn't use): $4.00
Tubs: $5.25
Lightbulbs: $4.25
1/4" tubing: $4.99
3/4" tubing: $5.45
Kerosene: $14.98
Pumps: (free, had some)

EDM Total: $38.92

Coupler experiments: $104.84 + tax
Cost of a coupler: $105+ shipping.
 

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Wow this is very impressive stuff Matt. I love your inginuity! Looking forward to seeing your progress.

Cheers
Tyler
 

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Discussion Starter #98
Well, it's now been a year since I first arrived in Arizona and saw my GTs and begun working on them (cash already changed hands but I didn't legally own them for a couple more days after that).

A year in review... (no car stuff, safe to skip)

A bit bittersweet. I started what I thought would be a fun summer project. I had a lot of naysayers that said "Ha, you won't even get it driving in a year!!" which, as of today, have their moment in the sun. They were right.

Partially it's that things were more work than I thought, they always are, that's okay. Partly it's been that I chose to do other things for a few months, I'm okay with that too, that's why I did other things. But mostly it's been that I don't have a garage of my own, and I work long days 7 days a week. I'm still in the mindset of "I'll do that in the evening/I'll work on that on the weekend". Just, mentally that's how life normally has gone right from kindergarden through college then career. My brain subconsciously still books that "work on it on your next day off" time even though it's not there. It still gets me into trouble overcommitting because I still instinctively feel like I'm no more than 5 days away from a couple days off. That there's evenings and weekends to look forward to doing stuff. But for me now, by evening it's too late to make noise, and I've only taken 1 day off since I left Arizona with my cars last year.

So that's been a disappointment, not just because it didn't get done and I haven't been able to enjoy it, but because some of the choices I've made in my build were in line with "cheap, easy, summer project", where the goal was to have it done soon, not better. Shitty project done quick, that's the tradeoff I was okay with. But if I was stepping back and planning a 1-2 year build, I'd have upgraded some of those efforts and made different choices. I'm now going to end up with the same shitty end result, but that took me a medium amount of time to complete. Which is also my biggest source of frustration on the project, juggling all the options between slapped-together and done-right and never knowing how much more time to spend making something better. I get builder's block for days at a time.

On the flip side, part of the reason I was gunning for a summer project is that I've had a few years now of nose to the grindstone and I was burning out, and I wanted something creative to put effort into long term and look forward to. Conversation has been dead for me, "So what've you been up to lately?", "Nothing, I work." being the literal truth, have nothing to contribute because nothing changed. Not just socially, personally too. So in that respect it's been a success. Not as much of a success as driving the car and making little upgrades as I go, but, better than another year of doing nothing but work and get fatter.

We're more than half way through spring, and I'd really like it to be drivable by the end of summer this year. I've slacked most of the last couple months, wanted a break after I mostly-finished the nightly welding march.

Anyway, enough blah. I did have a bunch of car updates I might get to tomorrow, will save those for another post.
 

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Keep at it Matt, you'll have a nice build and a great project to keep improving over the years too. We all get things blocking our progress and it's part of the journey.

I look forward to your updates tomorrow.

Cheers
Tyler
 

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Discussion Starter #100
Not having immediate success with buying a coupler, nor casting, nor EDM, I've spent some time laying out my options. Organizing my thoughts, not much progress to show.

1 - Hire a machine shop to fabricate a coupler.
2 - Fabricate a coupler myself, using a machine shop.
3 - Buy a Massey-Ferguson tractor PTO clutch to match the motor side, weld it to something for the transmission shaft.
4 - Continue with EDM experiments.
5 - Grind off/fill in the splines, make a taper-lock coupler.
6 - Weld the motor shaft directly to the transmission shaft.
7 - Wait for the forklift yard to maybe have a matching coupler.
8 - Carve a coupler by hand with a saw and file.
9 - Cast a coupler from aluminum or zamak.

And in detail why/why not:

1 - Hire a machine shop to fabricate a coupler.

- It'll get done right.
- It'll be the most expensive.
- It'll probably take some time.


2 - Fabricate a coupler myself, using a machine shop.

- I have access to a machine shop with $50,000 of tools. A giant lathe, a manual milling machine, a Tormach CNC milling machine, etc. I'm trained on all the machinery, I can let myself in 24/7 and use whatever equipment I want, make as much noise as I want. No one else will be there at night I'll have the place to myself.
- It's cheating, on a simple project, to go use $50,000 of industrial machinery. Even more so to throw a piece in a machine and click a button and let the computer do it (which I could do, like, tomorrow). In as much as my project might be educational, this is the antithesis of what anyone else could get done at home. It's like commuting in a helicopter.
- I used to spend a lot of time there, don't have time to be there regularly anymore, and don't really want to remember how much I miss it.


3 - Buy a Massey-Ferguson tractor PTO clutch to match the motor side, weld it to something for the transmission shaft.

- Ruining something brand new just for the splines.
- Kind of expensive.
- Still only a partial solution, still have to kludge the transmission half.
- Probably won't be very deep, (might need 2 couplers).


4 - Continue with EDM experiments.

- My EDM machine has been on pause for 10 years, it would be nice to finish it and use it.
- I'm most interested in this.
- I've already sunk a bunch of time into it.
- Casting hasn't gone well but is becoming passible.
- Solution might not be sufficiently accurate. EDM has small, but existant air gap between electrode and workpiece by function of the process itself. EDM can be about 0.0005" accurate (half-thou), but that would be around a circumference so 0.001" total. Automotive fit is usually around 0.001" for sliding parts, so I would have to be at the limit of the technology on a home-built machine. This isn't a rigidity constraint like on a milling machine, it's a configurable attribute related to voltage, current and frequency, but the construction of my plunge die has to be within those tolerances for that to matter. Alternatively I could undersize my electrode to compensate, but that means I can't just cast an image of the shaft, I'd have to machine it smaller, making the whole process moot.
- I risk going off on a tangent project that will sink too much time (for example, as it already has).


5 - Grind off/fill in the splines, make a taper-lock coupler.

- A taper-lock is just a barrel of aluminum with a narrow slot in it and some bolts to squeeze that gap (nearly) shut.
- It's apparently as strong as a weld.
- It's proven strong enough for DIY EVs in the past, it's the common machined solution.
- I don't like damaging the motor splines because I can't undo that later.
- I could fill in the splines with JB Weld and leave it large, it's just surface to squeeze on.
- 2" aluminum bar in short lengths is probably as much as a PTO clutch would cost, and I doubt my machining ability with steel.
- I could also/instead cut a keyway and use a keyed shaft. But I presume there's a reason that keyed shafts are never used like this even though that's simpler and easier.


6 - Weld the motor shaft directly to the transmission shaft.

- Shaft is permanently damaged if I screw it up.
- Can I create a jig to weld it sufficiently square and centered?
- Solution in general is pretty permanent, most other solutions I can just abandon and try something else with no consequence.
- It limits serviceability or making other changes.
- This has always been my backup plan, and tempting.


7 - Wait for the forklift yard to maybe have a matching coupler.

- Forklift yard mentioned they have 2 more machines like the one I took the motor from, that they're combining into one. They'd pull the gearbox for me so I could recover the matching splined shaft. Though they're not sure when, or if they have a buyer for that. Or time to do it.
- This has been my backup plan for a while, knowing it might be "a month" or more, but, it's been 6 weeks not no call yet so, probably won't happen.
- I have no idea how long I might wait for that to happen.
- Is still only half a solution.


8 - Carve a coupler by hand with a hack saw and file.

- Seems like the worst choice, but it's so, so simple, and unlike welding, not a permanent commitment. It just takes time. And honestly not that much time compared to fancier solutions.
- I've done it before, and it worked then.
- I hate this.


9 - Cast a coupler from aluminum or zamak.

- Instead of casting the female image in a plaster mold, then pouring copper into this mold to create a male image, then using the male to EDM out a matching female, instead just cast the female directly.
- Make a silicone mold of the splines, use that only as a shape to pack a high-temp sand mold, pour metal into the sand mold.
- Aluminum has a lower melting point than copper, so if I could cast copper I can easily cast aluminum.
- Zamak (Zinc/Aluminum) is stronger than bare aluminum, melts at a lower temperature, and is considered "zero machining" surface finish quality.


...


As much as I hate throwing away my casting and EDM efforts of the last 6 weeks, and I'm confident it'll eventually work, I'm worried that I'll get it working but it still won't be good enough regardless of my effort because of physical limits. I guess it's time to put my EDM project back on the shelf.

I think I'm going to try casting a Zamak coupler. A car guy's suggestion of using silicone mold to cast tin (no good) gave me the idea that, the only reason I can't cast a female directly is because I don't have a female mold. A plaster mold wouldn't survive being used as an image, but silicone would be fine to pack sand around and then remove.

If that fails, Plan B is an aluminum taper-lock.

If that fails, Plan C is to just weld it up solid. Or braze it so there's less warpage.
 
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