Finding a machine shop for a simple milling job?

I bought one of the Grin Tech. GMAC motors for an old full suspension mountain bike frame with 51mm I.S. caliper tabs. The disc ends up being 1.5-2 mmm too far to the left (outboard). There isn't enough material to enlarge the holes on the caliper so I thinned the mount adapter by 2mm with a Dremel 115 bit. It works, but I'm sure the faces are far from parallel now, so long term I'd like to get another adapter & have it properly milled down.

There are welding and machine shops around me that do custom work, but I'm guessing this is too small a job for many of them. I'm willing to ship it to someone, too, but how to find 'em? It's not a CNC job-- I don't have the software or knowledge, really-- I just want an 11mm thick adapter milled down to 9mm.

Any ideas?

I'm in Sunnyvale, California, 94086.

I'd expect to pay about $50-$100. I'm tempted to bite the bullet & get a Sherline or Taig mill. I'd always thought I'd want a CNC one which made them kind of prohibitive, but most of my metalworking projects are simple & could be done manually, so they're under $1k with a few end mills and hold downs.

If you can’t measure and face a brake mounting bracket with the tools that you have, many bike shops have a brake mount facing tool set and will do the brake alignment job for you.

I make and fit them custom brake mounts with hand tools, so never considered machine shops or bike shops for this simple task.

morganw said:

I'd expect to pay about $50-$100. I'm tempted to bite the bullet & get a Sherline or Taig mill. I'd always thought I'd want a CNC one which made them kind of prohibitive, but most of my metalworking projects are simple & could be done manually, so they're under $1k with a few end mills and hold downs.

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Ahh, I have many projects that I've used to justify acquiring more tools. Not sure you really need much precision here though, but I support the tool purchase. :lol:

For aluminum, I've had success throwing an end mill bit in my cheap drill press. Not good for the press, but mine's a $50 Craigslist purchase, so not too worried about it for a small job. Just have a decent vise and go slow.

Type machinist into Google maps and start calling?

I think like you said you might struggle to find someone who will do small jobs but you might get lucky

I had someone machine my dropout, brake mount, and torque arm for 50 bucks which was a pretty sick deal now that I think about it

Noisebridge in San Francisco is a free anarchist run work place with machine tools. There’s other maker spaces around that are free. I think that’s the term and you could search for that

bike frame with 51mm I.S. caliper tabs. The disc ends up being 1.5-2 mmm too far to the left (outboard). There isn't enough material to enlarge the holes on the caliper so I thinned the mount adapter by 2mm with a Dremel 115 bit. It works, but I'm sure the faces are far from parallel now

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Use a file to get it as straight as you can.
Add washers if you need to.
Buy a measurement caliper to confirm how flat it is or how out of whack it is.

Other alternatives, buy a new cover plate for the motor and/or buy a new caliper adapter, also there are cover plate rotor spacers you can buy.

You might be able to put a washer on the axle between the motor and the frame and pull the dropouts apart to fit it in.

I have a milling machine here, but I'm not very good with it.

E-HP said:

For aluminum, I've had success throwing an end mill bit in my cheap drill press. Not good for the press, but mine's a $50 Craigslist purchase, so not too worried about it for a small job. Just have a decent vise and go slow.

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Once I started looking at cheap mills, I ran across "mill/drills" and a lightbulb went off. I don't even have to put sideways force on the drill press I already have. I can just mill down a circle 2mm into the adapter, pull the mill up, slide the piece over and mill another circle until the whole face is at the same, new, level. As long as the table is flat and perpendicular to the chuck's axis, it should be reasonably precise.

I did bite the bullet & start making inquiries and found a shop that does custom motorcycle work that said yes.

Thanks all for the suggestions!

Don't mill on a drill press. The chuck is not secured for that kind of work and it can literally come out and fuuck you up.

Angle grinders and dremel with carbide head is a poor man's milling machine.

Also, if you didn't actually contact the machine shops in your area how would you know they won't do your work? I know, I know, it's terrifying to talk to actual humans in a field you don't understand but that's how progress is made.

I must've misunderstood the problem

My bike the axle spun a little bit in the Townie Electra. Basically the dropout's have been enlarged, now with my excellent skill set I've managed to put in a 1/4" or 1/8 plate x 1" x 5" from the motor axle flats, to the inside of the frame on one side, then hose clamps. 8)
...but a notched washer would work, fitted to the axle flats, then the frame pushed apart and motor slipped in. It can be a little bit of a hassle, trying to get the washer in place + frame separated + motor axle slipped into the dropout, but I do it everytime I have a flat (which is a lot! :lol: ) with that big plate of steel.

I have also put a notched washer for the notched axle to space out the frame from hitting the freewheel. Its an 8 speed I think so quite wide and too many gears for us ebikers. 8)

Whatever the problem is, you have to find a solution for the fix and do it yourself rather then get someone to do it for you. That way you can save your money and spend your saved money or more ebike stuff.

fechter said:

You might be able to put a washer on the axle between the motor and the frame and pull the dropouts apart to fit it in.

I have a milling machine here, but I'm not very good with it.

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morganw said:

I bought one of the Grin Tech. GMAC motors for an old full suspension mountain bike frame with 51mm I.S. caliper tabs. The disc ends up being 1.5-2 mmm too far to the left (outboard).

Click to expand...

Maybe a little late to ask, but what is the washer/spacer set up on your bike? Can you provide a picture? If it's the same issue as in this thread, then it may be as simple as you may have left out a washer that's designed to provide that 2mm of spacing.

https://endless-sphere.com/forums/viewtopic.php?f=3&t=99996&p=1465098#p1465098
http://www.ebikeschool.com/install-hub-motor-washers/

Hummina Shadeeba said:

Noisebridge in San Francisco is a free anarchist run work place with machine tools.

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Sounds like some very organised anarchists...

I am wondering how you like that motor. I'm thinking of getting one as well for an old, fully-suspended 26".
Have you gotten to try it yet?