Heavy Duty Torque Arm - Disc mount, clamping optional $35

[dmwahl]

Made from 3/8" (9.5mm) stainless steel and designed to bolt on to a standard IS disc brake mount. Can be used with or without an installed disc brake. No need to modify your frame, remove paint, epoxy, etc. Bolts on in a few minutes. I designed it for my KMX trike frame, but it should fit many other frames with an IS disc mount. Print the PDF below to verify your own frame will fit.

Features
- Standard IS disc mount geometry
- 3/8" (9.5mm) Stainless Steel
- 9.90mm wide opening, file to fit your specific axle for a precise fit
- Includes flats specifically sized to drill and tap hole for a 30mm M6 bolt (you will need to drill/tap yourself, it it NOT included). See here for pictures of a drilled/tapped part.
- No sharp corners to reduce stress concentrations and weak points

Use this PDF to verify fit prior to purchasing. It needs to be printed actual size on 8-1/2" x 11" paper (standard US Letter size), not scaled or sized to fit which is often the default setting.
Profile PDF - PRINT ACTUAL SIZE, NOT SCALED

File to 3D print the part to test out fit below. I made the file 3mm thick instead of 9.5mm (3/8") so it prints faster and uses less material, but the profile is identical. Note that many 3D printers don't have great resolution, so sometimes holes and internal cuts like this part can be a tight fit when made of plastic but a better fit when properly cut out of metal.

torque-arm-stl.zip

(448.9 KiB) Downloaded 329 times

Shipping
Price includes USPS shipping in the US. If you are not in the US, please PM me and I can figure out shipping for your country and send you an invoice via Paypal. I will not do things like mark it as gift, sample, etc to avoid you paying customs or other country specific fees. Countries I've already calculated shipping for are listed below.

Prices outside US
Canada - $40 for 1, $75 for 2
United Kingdom, Belgium, Sweden, Australia, Israel - $45 for 1, $80 for 2, $120 for 3


To purchase via Paypal, go here.
Price is $35 which includes US shipping. You'll need an address set up in Paypal, which allows me to automatically print a shipping label and expedites the process significantly. For non-US orders, pm me with your Paypal email address and I'll send you a request or give you my paypal email address.

1 in stock as of 15-MAY-2020.

Design thread here

I will support this as well as I can, but can't answer questions like "Will this fit frame _____?" or similar build specific questions. I've included a PDF to verify fit, as well as a .stl file to 3d print the design. Note that to save printing material, the .stl will print out thinner than the actual piece but with the same profile.

[dmwahl]

Bump. Still have plenty in stock, and will ship asap.

For reference, I torqued my axle nuts to 50 ft-lbs with a torque wrench and anti-seize on the threads, and they have not budged despite lots of tire shredding acceleration

[RLT]

I have had this bookmarked for several days.
Just haven't decided if they will quite work for any of my current (and currently stalled) projects.

[dmwahl]

I have had this bookmarked for several days.
Just haven't decided if they will quite work for any of my current (and currently stalled) projects.

What are you unsure of? I can post a file to allow you to 3d print the part if that would help. If what you're trying to do is relatively common, I'd consider creating another version of the torque arm to accommodate.

[teklektik]

Just a bit of a heads-up. The dropout alignment is slightly different than that of migueralliart's TAs - also For Sale here on ES. So - not interchangeable, but two different options...

Here are the two bolted up together. As mentioned in an earlier post, the buisness of dropout alignment is not part of the ISO spec and varies from frame to frame. I wanted to upgrade to the open slot design, but wasn't careful enough with the paper template.... (D'oh!)

(click to enlarge)

These are nice dropouts with a bit undersized slot so they can be filed for a good fit.

I might recommend slightly smaller holes for the 6mm bolts - they match the 'close fit' spec on my drilling chart but the hardened bolts I have are a tad loose.

[arkmundi]

Nice design & cut. I'm in the market for better torque arms. Will see if this might do it. Thanks.

[dmwahl]

I might recommend slightly smaller holes for the 6mm bolts - they match the 'close fit' spec on my drilling chart but the hardened bolts I have are a tad loose.

The screw hole diameter is 6.50mm nominal, and they tend to come in around 6.40-6.45mm. If it was too tight of a fit you'd never get it installed and would have to drill them out to fit your specific bolt. Anyway, the intent is to provide a little bit of play so that variations from frame to frame are not a problem. The bolts are to provide clamping force, not precise alignment. If you remove a disc brake caliper you'll likely find the same thing, that the mounting bolts are a little loose in the holes.

[dmwahl]

Nice design & cut. I'm in the market for better torque arms. Will see if this might do it. Thanks.

Thanks, they turned out better than I hoped. What is your existing solution?

[arkmundi]

Thanks, they turned out better than I hoped. What is your existing solution?

I'm still working on it, but see http://endless-sphere.com/forums/viewto ... 5#p1052004 for what I'm doing. Having lost my aluminium frame drop-outs, I'm honing it. For now its two Grin torque arms hammered into place in the triangle of the frame, which will be U-bolted on once positioned.

[dmwahl]

I'm still working on it, but see http://endless-sphere.com/forums/viewto ... 5#p1052004 for what I'm doing. Having lost my aluminium frame drop-outs, I'm honing it. For now its two Grin torque arms hammered into place in the triangle of the frame, which will be U-bolted on once positioned.

From your video it looks like you're basically rebuilding the dropouts? These should work well for that since they're designed to take the torque load off the dropouts and transfer it to the frame, which can take a lot more. Try the paper template and see if it fits, I'll post a .stl so you can 3D print it if you have access to one. (Note that most 3D printers don't have the best resolution, so sometimes holes and internal cuts like this part can be a tight fit when made of plastic but a better fit when properly cut out of metal.)

[EDIT] I added a .stl file (zipped) to the first post in this thread so you can print out a copy if you want. It will be thinner than the metal part to save material, but the profile is the same.

[RLT]

Nevermind

[dmwahl]

Bump

[markz]

This is just for one torque arm? one on the brake/cable side?
Why dont people use 2 on both sides? Just no where to mount, due to no IS brake holes?

[dmwahl]

This is just for one torque arm? one on the brake/cable side?
Why dont people use 2 on both sides? Just no where to mount, due to no IS brake holes?

Yes, price is for one, on the brake side. You can still mount your brakes, just need bolts that are 10mm longer than stock. People don't use 2 largely because it's rarely, if ever, necessary. The spacing on the torque arm is much tighter than on your frame, so any axle rotation will be resisted by the torque arm instead of your frame dropouts. It also provides a nice big flat surface for the axle bolt to clamp onto, which is where a lot of the resistance to spin-out comes from, not just from resistance to spreading.

[spinningmagnets]

I ordered an un-drilled unit, and then I drilled it myself. I can verify that this is made from quality metal, very hard. I wanted to satisfy my curiosity, but I now recommend ordering it pre-drilled.

edit: in response to the post below...yes, it was hard to drill through. A drill press would have made it easier to get straight, and there a fluid called "tap magic"...I don't know whats in it, but it really is worth it. Much better than WD-40. The bits drill faster, and the bits last longer.

Drilled hole to 0.217-inch, Bolt allen wrench is 0.158, Bolt shank is 0.188

[markz]

I assume it was very hard to drill through the metal.

[mchlpeel]

Am i right in thinking that the caliper holes come pre drilled but the clamping hole does not?

Would you consider drilling and tapping the clamping hole for some extra $ ?

[dmwahl]

Am i right in thinking that the caliper holes come pre drilled but the clamping hole does not?

That's correct.

Would you consider drilling and tapping the clamping hole for some extra $ ?

I'll consider it, but it won't be for at least a few weeks. I have a drill press but would need to buy the bits, taps, etc. If you know a machine shop or machinist, they would probably charge the same, if not less, than I would.

What are you doing that clamping is required? Most bikes are fine without as long as the axle nut is sufficiently tight.

[mchlpeel]

well i intend to run 3000w through the rear so assumed that clamping would be required?

[dmwahl]

Torque is the problem, not power. FYI, for my trike I estimate about 90N-m, using the ebikes.ca motor simulator, and tightened the axle nuts to 55ft-lb with anti-seize on the threads. I can lock the front brakes and hit the throttle at 100% and all it does is spin the tire. No problems with the torque arm.

[dmwahl]

Sllikskills did a very nice 6kW build with this torque arm, check it out here

[hydro-one]

its not about the axle nut tightness. its about the clamping of the axle flats. you dont even need axle nuts in a properly designed system , and sorry one torque arm is not a properly designed system and will fail early on a high powered setup . especially if you are using regen. You NEED two torque arms . and ideally with clamping. now on lower powered setups without regen you might be ok for along time.

[999zip999]

Beautiful. Me like. Makes it easier with ebike choices with high power hubs.

[dmwahl]

its not about the axle nut tightness. its about the clamping of the axle flats. you dont even need axle nuts in a properly designed system , and sorry one torque arm is not a properly designed system and will fail early on a high powered setup . especially if you are using regen. You NEED two torque arms . and ideally with clamping. now on lower powered setups without regen you might be ok for along time.

And what prevents the flats from opening up? It's as much clamping pressure on the fork or torque arm face as it is the inherent ability of the flats to resist opening. When you tighten a nut you're stretching out the bolt (or axle) which provides a clamping force between the nut/washer and the surface it rides against. That friction, as well as the pressure provided by the flats against the axle are what keeps it in place.

While I haven't tested my torque arms to failure, Justin (ebikes.ca) did some testing where he torqued axle nuts to different levels with the same torque arm and measured spin-out torque. See here for the results. It's clear that axle nut torque plays a big factor, so the suggestion that a properly designed system wouldn't need axle nuts is a bit ridiculous. An over-designed system may not need axle nuts, but a proper one can certainly make good use of them.

[doublethink]

Still have more of these?