Metal for torque plates

[cal3thousand]

Hi all,

I'm working on a project for my wife (rear MAC 7T on e-suede frame) and need some advice on sourcing supplies.

Trying to get some steel to make torque plates that will have an integrated bike trailer hitch. Any advice on where to look for metal and what metal to use?

So far, for my needs, I'm thinking 2 torque plates 1/8" thick each (only ~1.5kW of power). Should I be looking for a local metal shop or would a local hardware store carry this thickness?

[Kin]

How are you making the plates? As in, what sort of equipment do you have access to? I just ask this because you want the torque arms to be really tight. You can design your torque arm to be tightenable, but many people also try to just have very tight torque arm from the get-go and not have to develop a way to tighten the sidewalls.

I ask this question first because steel isn't that easy to cut nicely. I machined my torque arms in Aluminum with a CNC first just to make sure I didn't screw up the G-code*, because it was going to take a lot of effort to cut the stainless steel. Torque arms don't require a lot of material though, and so I just used some scrap. You want to use a steel that's harder than the softer steels, but I don't see why you would need an insanely hard steel (someone else nicely pointed out that the concern with ultra-hard steels might be the axle, often made of softer steel, deforming).

*Honesty's sake: G-code I don't know. The guy at work who runs the CNC machine helped me machine the file I made.

[John in CR]

Cal,

Whatever you do don't copy Kin and use aluminum, because it's just not the right material. Steel is what you want, and you want to make them the clamping type, so nothing too hard, since you have to drill holes. Any metal shop will have scraps you can use, and then they can help if you need something welded. Scrap yards are another perfect place. My new favorite material for use in my clamping torque dropouts (I make them part of the bike.) is steel from broken leaf springs. It's cheap, but a far better alloy of steel than just mild steel. If you do go that route don't use sections that look deformed where a mounting plate compressed it during years of service, because that area can be work hardened and virtually impossible to drill a hole.

How thick? That depends upon how much axle you have to work with. There's almost no such thing as overkill when it comes to torque arms and dropouts. I've had slot type that were .5" thick mild steel wallow out over time due to the back and forth forces of regen. All of my latest ones are about .75" clamped width on each side of the axle, and my new test motor is probably getting a full 1", because those are high power motors.

It also depends on your motor. Some of the smaller ones have small axles and narrow flats, and those axles are often lower quality steel. Even though they are lower power they still warrant substantial width to help ensure the axle doesn't spin, since there's less contact surface length. Those with thru axle wires also warrant more width, because the wire side axle is inherently weaker and can't be clamped as tightly or you can crush what is essentially a hollow tube.

Build it so you don't ever have to worry about it, and a clamping type gives you piece of mind that axle nuts don't even matter. One of my bikes runs 12kw and has and axle nut only on one side, and it's only there so the threaded axle isn't a sharp protrusion to clip a shin.

John

[dogman]

For that power level, 1/8" could be thick enough. But as said above, make em as thicker if you have the length on the axles to do it. The thin torque arms can just end up cutting a groove into the axle threads.

1/4" mild steel strap about 1.5" wide is easy to find, and easy enough to cut with simple tools. Make your hole undersize, and file to fit the last mm.

[Kin]

Oh shit. Excuse me, for any confusion. I did NOT use Aluminum for the torque plates! ***I AGREE DONT DO THAT.***

I cut out of Alu to TEST the file I made which I subsequently cut out of stainless steel. This was to mark the point: Stainless steel is hard to cut. Everyone's advise above me is more practical, anyway, for making the torque arms without a CNC. That's good, I do not have experience doing it without over-fancy tools, but it certainly can be.

[John in CR]

For that power level, 1/8" could be thick enough....

Torque arms have nothing to do with power level and everything to do with torque. Even at 500W a Mac in a normal size bike wheel can put a lot more force on the dropouts than the motor on my cargo bike that runs at over 5000W. It took 3 years and 6 months with regen, but that motor managed to deform 1/2" steel on each side. 1/8", though common in store bought torque arms, is wholly inadequate and that's why the store bought torque arms on every used motor I've purchase were wallowed out. That's also why Grin has gone to 1/4" stainless steel torque arms.

Torque arms are the one part of a DIY build where "enough to get away with" is a mistake. They use space that is otherwise useless. The weight is negligible. Thicker requires no extra work and little, if any, extra cost. Thick even allows for extra tolerance which is important for those built with hand tools. Failure can be catastrophic and take the form of the wheel separating from the bike.

One thing that I take back is the clamping requirement. I missed that it's a geared hub, which can't put force in the other direction. I prefer the slot type for fabbing with hand tools because it's easier to get a really good fit. Just pick up some scraps of 3/8 or 1/2" steel plate. If you're lucky enough to find something strong like stainless or leaf spring steel then 1/4" would be ok. Decide on a general shape and cut your slots first. Use an angle grinder till you get quite close to the perfect fit deep in the slot and a file to finish it off for a tap on fit. After the slots are cut, then cut the material to final shape and make your bolt hole(s).

John

[Kin]

For comparison, I used ~8mm plates on my rear mac (1/8 inch is 3.175mm), because that's what would fit. Check what fits, and give yourself a little bit of spare thread room.

[cal3thousand]

How are you making the plates? As in, what sort of equipment do you have access to? I just ask this because you want the torque arms to be really tight. You can design your torque arm to be tightenable, but many people also try to just have very tight torque arm from the get-go and not have to develop a way to tighten the sidewalls.

I ask this question first because steel isn't that easy to cut nicely. I machined my torque arms in Aluminum with a CNC first just to make sure I didn't screw up the G-code*, because it was going to take a lot of effort to cut the stainless steel. Torque arms don't require a lot of material though, and so I just used some scrap. You want to use a steel that's harder than the softer steels, but I don't see why you would need an insanely hard steel (someone else nicely pointed out that the concern with ultra-hard steels might be the axle, often made of softer steel, deforming).

*Honesty's sake: G-code I don't know. The guy at work who runs the CNC machine helped me machine the file I made.

I don't have access to any quality machinery. Just hand tools.

That's why I was hoping to get away with 1/8" steel.

Cal,

Whatever you do don't copy Kin and use aluminum, because it's just not the right material. Steel is what you want, and you want to make them the clamping type, so nothing too hard, since you have to drill holes. Any metal shop will have scraps you can use, and then they can help if you need something welded. Scrap yards are another perfect place. My new favorite material for use in my clamping torque dropouts (I make them part of the bike.) is steel from broken leaf springs. It's cheap, but a far better alloy of steel than just mild steel. If you do go that route don't use sections that look deformed where a mounting plate compressed it during years of service, because that area can be work hardened and virtually impossible to drill a hole.

How thick? That depends upon how much axle you have to work with. There's almost no such thing as overkill when it comes to torque arms and dropouts. I've had slot type that were .5" thick mild steel wallow out over time due to the back and forth forces of regen. All of my latest ones are about .75" clamped width on each side of the axle, and my new test motor is probably getting a full 1", because those are high power motors.

It also depends on your motor. Some of the smaller ones have small axles and narrow flats, and those axles are often lower quality steel. Even though they are lower power they still warrant substantial width to help ensure the axle doesn't spin, since there's less contact surface length. Those with thru axle wires also warrant more width, because the wire side axle is inherently weaker and can't be clamped as tightly or you can crush what is essentially a hollow tube.

Build it so you don't ever have to worry about it, and a clamping type gives you piece of mind that axle nuts don't even matter. One of my bikes runs 12kw and has and axle nut only on one side, and it's only there so the threaded axle isn't a sharp protrusion to clip a shin.

John

You're right, I should go thicker. As suggested elsewhere, I will see how much of a torque plate that I can fit on the axle and reconsider my options based on my limited tools.

For that power level, 1/8" could be thick enough. But as said above, make em as thicker if you have the length on the axles to do it. The thin torque arms can just end up cutting a groove into the axle threads.

1/4" mild steel strap about 1.5" wide is easy to find, and easy enough to cut with simple tools. Make your hole undersize, and file to fit the last mm.

1/4" might be the sweet spot between what I can manage to make and what will keep the axle in check. I will definitely keep the axle cutout undersized and file to a fit.

For comparison, I used ~8mm plates on my rear mac (1/8 inch is 3.175mm), because that's what would fit. Check what fits, and give yourself a little bit of spare thread room.

So that's between 1/4" and 3/8"; sounds like a good range for me needs


Thanks for helping out guys!



BTW, while I have your attention, what's the best way of finding a shop that can adequately handle the cutting and welding? I've been Google map searching for "metal shop" or "metal supplier"

[Kin]

It sounds like, by the others' descriptions, this might be doable with hassle using something as simple as a dremel tool, the right disks, and a file. But going to a metalworking shop might also work.

I don't have experience finding such shops, but I do notice they exist a lot nearby universities, if you're in that kind of populated area. Frankly, i've been told all of California is of sufficient population density that I bet there's cause for a machine shop nearby. You can also see if your local "hackerspace" would have the equipment, if you want to get into this on a more extreme DIY level (there's always another level, it seems). But besides those terms, also look up "rapid prototyping" or just "prototyping" because companies that specialize in one time builds are usually working with small scale companies to fabricate their prototypes. Finally, if you're really having a hard time finding, this could be within the skill-set and tool-set of a good auto mechanic that knows how to do a bit of metalwork. If you know how to talk to people, that could very well be cheaper than a prototyping company.

Another option is an online place. Pololu, Ponoke, and Bigbluesaw.com are places I know that do 2D cutting, which is optimal for what you want. You probably don't need to weld the torque arms, assuming you use Scotch-Weld DP420 (look at Doctorbass's thread).

For all the hassle it will be to have a local shop make the torque arms, is there some reason why you do not want to do something prefabbed like the Grinn's torque arm? I don't know much about your frame, I surmise that might be relevant.

As always, here with excess information. Wait for the other posters to get a concise and useful response :p.

[cal3thousand]

It sounds like, by the others' descriptions, this might be doable with hassle using something as simple as a dremel tool, the right disks, and a file. But going to a metalworking shop might also work.

I don't have experience finding such shops, but I do notice they exist a lot nearby universities, if you're in that kind of populated area. Frankly, i've been told all of California is of sufficient population density that I bet there's cause for a machine shop nearby. You can also see if your local "hackerspace" would have the equipment, if you want to get into this on a more extreme DIY level (there's always another level, it seems). But besides those terms, also look up "rapid prototyping" or just "prototyping" because companies that specialize in one time builds are usually working with small scale companies to fabricate their prototypes. Finally, if you're really having a hard time finding, this could be within the skill-set and tool-set of a good auto mechanic that knows how to do a bit of metalwork. If you know how to talk to people, that could very well be cheaper than a prototyping company.

Another option is an online place. Pololu, Ponoke, and Bigbluesaw.com are places I know that do 2D cutting, which is optimal for what you want. You probably don't need to weld the torque arms, assuming you use Scotch-Weld DP420 (look at Doctorbass's thread).

For all the hassle it will be to have a local shop make the torque arms, is there some reason why you do not want to do something prefabbed like the Grinn's torque arm? I don't know much about your frame, I surmise that might be relevant.

As always, here with excess information. Wait for the other posters to get a concise and useful response :p.

I thought about prototypers, but figured it would be expensive. I live in LA, so I should be able to find someone capable. University suggestion is good, maybe I'll find someone in school that wants a pet project.


There's a couple reason's that I don't want to go pre-fab. 1) And the reason I need welding; this piece needs to be an integrated torque plate AND bike trailer hitch coupler. 2) I don't like the look of the pre-fab torque arms. 3) I like to complicate my life, learn things, and socialize.

[iamsofunny]

You can use steel bar stock 1/2" thick and weld three pieces together rather than cutting a slot. You'll have to make some sort of trailer hitch thing anyway and stick welders are pretty cheap.

[cal3thousand]

You can use steel bar stock 1/2" thick and weld three pieces together rather than cutting a slot. You'll have to make some sort of trailer hitch thing anyway and stick welders are pretty cheap.

That could work, but I cannot have any more machines (tools are OK as I can hide them from the wife )

I've found a gentleman that will weld disc brake tabs on the frame already but he's far away and I'll have to take a day from work to venture down there. I guess I should call him back up and see if this stuff is within his scope (It should be). It would be nice to have it done locally or have the pieces cut before I get down there for him to weld everything else.

Thanks for replying.

[amberwolf]

One source for some nice 1/4" steel that is hard enough to use but soft enough to cut, drill, and file, is the steel support from some computer desk chairs that holds the back to the seat.

Also on those chairs is often some 3/16" to 1/4" steel that is used for the legs, under plastic covers.

[dnmun]

why even try to fabricate them if you don't have tools or workshop? you can buy the torque arms from a number of sources.

if you are mounting a front motor in dropouts with the lawyer lips then you will need to buy the C washers to mount inside the dropout recess.

justin sells them, he invented them. absolutely essential for alloy front forks with lawyer lips.

[Kin]

why even try to fabricate them if you don't have tools or workshop? you can buy the torque arms from a number of sources.

He said he needed some sort of combo hitch-torque arm.

[cal3thousand]

After talking to the welder and finding out he doesn't have tube stock small enough for the frame mounted basket idea I have, I decided to just order some metal online.

Measurements last night confirmed I have enough room for 3/8", but I settled on 5/16" x 3" Cold finished 1018 (site says it's good for plates and spacers etc). I got 4 - 3" squares for under $11

Also ordered some 1.25" OD x .109" wall DOM Steel Tube for the hitch portion. 2 pieces for under $4

Shipping is the only thing that sucked on this order. Hopefully I will get 2 sets of plates out of this.

EDIT:

used www.speedymetals.com

[iamsofunny]

if you find a machine shop, waterjet shop, laser shop you can get free metal (if they give you permission) if you want to climb into the recycling bin and break off a chunk from the sheets, but not all sheets have thin enough edges to get free chunks from

You should buy a welder and when the woman nags you, just go ape-sh&t and tell her, "I'm the man and you are merely a woman. I command you and you will listen because men are superior in every way and you will not dictate my actions."

Then point to the kitchen and says "sandwich. now".

SHe will love you