Laser Cut M12 Torque Arms ??

The Torque Arm on the left is from eBikeLing and it is stamped (the tooling marks are obvious). The hole measures 10.25mm by 14.0 mm on the front face. It is a bit larger on the rear face (another result of having been stamped out).

The one of the right is a six year old Torque Arm from BMSBattery and it was actually "Laser cut". The hole measure 10.03 mm wide by 12.05 long .... the hole size is the same for both faces.

Why does this matter you ask:


Question:
Does anyone in the US or Canada sale Laser Cut M12 Torque Arms ?
BMSBattery still has them listed but shipping is over $20 for a pair.

"All of our torque arms are currently laser cut in the USA and assembled and finished in Canada."

https://ebikes.ca/product-info/grin-products/torque-arms.html

I was hesitant to spend the money on the Grin torque arm, especially considering shipping to and from Canada is absurdly overpriced. In the end I'm glad that I did though. It's very very well made.

Well here is an interesting approach I had not seen before.
https://www.ebay.com/itm/392746794025


Maybe I do not get out often enough

Those are safe only for low power. You need to cut them yourself in thicker steel if you build high power. Cut them off a piece of 4’’ angle stock scrap and make the axle hole a tight fit specifically for your motor axle, one on each side. The job may look complicated but really, it is pretty easy to do with an angle grinder, hand drill and 2 files. And, you will have them finished long before the shipping delay of weak commercial torque arms.

MadRhino said:

Those are safe only for low power. You need to cut them yourself in thicker steel if you build high power. Cut them off a piece of 4’’ angle stock scrap and make the axle hole a tight fit specifically for your motor axle, one on each side. The job may look complicated but really, it is pretty easy to do with an angle grinder, hand drill and 2 files. And, you will have them finished long before the shipping delay of weak commercial torque arms.

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I ONLY run low power
... but they are expensive as well :|

The ebikeling v2 ones say laser cut, and looking at the pics, they don't look like stamped steel. Can't speak to the tolerances or thickness.


The ebikeling ones on Amazon look like they may be v1? The arm portion of those looks stamped.

E-HP said:

The ebikeling v2 ones say laser cut, and looking at the pics, they don't look like stamped steel. Can't speak to the tolerances or thickness.
The ebikeling ones on Amazon look like they may be v1? The arm portion of those looks stamped.

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The picture of the eBikeLing torque arm in the picture above is what was actually delivered in their kit this past Friday. Their website and Amazon listings are likely put together by marketing types who do not have a clue or don't care or both.

E-HP said:

The ebikeling v2 ones say laser cut, and looking at the pics, they don't look like stamped steel. Can't speak to the tolerances or thickness.

Click to expand...

The one Ebikeling kit I installed for a customer last year (a 500W geared rear hub kit) spun the axle right through the flats on the cheesy torque arm.

A friends kit came with a very thin and loose fitting torque arm. He bought a thicker torque arm from Grin, it fit much better and has worked just fine for the last 5 years.

I bought a Grin torque arm for my MAC, it looks very good and fit well but I didn't use it. To fit the bike, I built a torque arm for each side, overall thickness is 9/16", no problems so far. On the motor wire side, the torque arm I built uses a pinch bolt to squeeze the axle in the torque arm.

We use a Grin torque arm on my wife's bike, it has worked well for over a year.

somehow got a double post

It took some practice, but I learned to make a torque arm with simple tools pretty easy. Not only could I shape the TA to fit the rear dropouts of a particular bike perfectly, but I could make them so tight I could have a real struggle to get them on the axles.

I used a cordless drill and a small triangle file to cut the hole, which got easier and easier with a bit of practice. I found that I had a great deal of variation in the actual size of 10 mm flats on axles of various motors. The small ones of course, were the problem.

As I went, I tried to come up with a design that was a variation of Grins universal TA, but instead of a single bolt on the pivot, it would have two bolts. One bolt hole was set in the design, then after adjustment, the second hole would be drilled to fit the particular installation on a particular bike.

The picture shows an earlier design, with adjustment built in. Better to replace the adjustable slot with one hole drilled where it is needed to fit a particular bike.
Please, somebody copy this and produce some lazer cut ones to sell to ES members.

E-HP said:

The ebikeling v2 ones say laser cut, and looking at the pics, they don't look like stamped steel. Can't speak to the tolerances or thickness.

The ebikeling ones on Amazon look like they may be v1? The arm portion of those looks stamped.

Click to expand...

Yeah I use a similar torque arm well just the plate that connects to the Axle Flats. Then I have it screwed into the frame. They do OK but I can feel little bit of movement if I go from heavy E break to throttle.

dogman dan said:

It took some practice, but I learned to make a torque arm with simple tools pretty easy. Not only could I shape the TA to fit the rear dropouts of a particular bike perfectly, but I could make them so tight I could have a real struggle to get them on the axles.

Click to expand...

If I wind up having to make my own then I will have to buy the 1/4 inch SST plate to make them from. That will cost me almost as much as a set of torque arms. I also do not relish the thought of trying hack-saw said plate. Of course if I did it then they would be specific to the installation and a simple piece arm on each side of the front fork.

Fortunately I had one 'new old stock' on hand and one used one to serve my immediate need. I will have to address the problem in the future when/if it comes up .... but one thing is certain: I will NOT be using any crappy, lose fitting, stamped torque arms.

In some ways, stamped offers slightly better material properties than cut, the metals grain is more compressed on the faces but any gain from that will be cancelled out from the dishing so in reality there's no net gain. "Laser cut" is more a marketing term than anything, water jet would give just as good accuracy and a well set up plasma or even flame cutter can be just as good (but they're very rarely so meticulously maintained).

It shouldn't cost a whole lot to get a couple cut, waterjet will probably be the easiest to source and setup will make up the bulk of the price with something so small so getting 2 cut probably wont be much cheaper than getting 20 cut, maybe worth getting the extra and selling them on? Get them cut slightly undersize though, draw it out with clearance all round and then bring the flats closer together. Easier to hand finish accurately that way as you don't have to worry about where the flats meet the curves and when you're hand finishing, give them a squirt of fast drying paint as you're doing them (rattle can primer for ex. engineers blue is what's usually used but paint works ok). Then, when you try them on the shaft, the paint will show where it's fitting tightly so you'll know exactly where to file without leaving too much clearance elsewhere.

Kind of crazy flats are still used, they might have been good enough for sturmey archer 3 speed hubs but that doesn't scale up well to the 50kw monsters they're still being used on! Keys would be better and at the very least you'd expect taper lock bushes or some similar positive fixing method to be the norm by now :/

LewTwo said:

Torque Arms(2048).JPG
The Torque Arm on the left is from eBikeLing and it is stamped (the tooling marks are obvious). The hole measures 10.25mm by 14.0 mm on the front face. It is a bit larger on the rear face (another result of having been stamped out).

The one of the right is a six year old Torque Arm from BMSBattery and it was actually "Laser cut". The hole measure 10.03 mm wide by 12.05 long .... the hole size is the same for both faces.

Why does this matter you ask:
Sloppy 00 (2048).JPG

Question:
Does anyone in the US or Canada sale Laser Cut M12 Torque Arms ?
BMSBattery still has them listed but shipping is over $20 for a pair.

Click to expand...

Easy. Fill the gap caused by the sloppy tolerance by forcing in a bit of cut off hose clamp, into the slot between the axle and the motor.

Tommm said:

Easy. Fill the gap caused by the sloppy tolerance by forcing in a bit of cut off hose clamp, into the slot between the axle and the motor.

Click to expand...

You sound like the eBikeLing tech support guy. I would rather have some made correctly to begin with. Besides if you look at my builds then you will realize I do not use radiator clamps.

LewTwo said:

Tommm said:

Easy. Fill the gap caused by the sloppy tolerance by forcing in a bit of cut off hose clamp, into the slot between the axle and the motor.

Click to expand...

You sound like the eBikeLing tech support guy. I would rather have some made correctly to begin with. Besides if you look at my builds then you will realize I do not use radiator clamps.

Click to expand...

That's funny, I think I am more like the aliexpress bargain basement tech support.

I meant you need a thin sheet of metal, for which purpose a sheet cut off of the end of the hose clamp will function fine, for example. If you already understood it, sorry, it is the nature of explaining by text.

LewTwo said:

Tommm said:

Easy. Fill the gap caused by the sloppy tolerance by forcing in a bit of cut off hose clamp, into the slot between the axle and the motor.

Click to expand...

You sound like the eBikeLing tech support guy. I would rather have some made correctly to begin with. Besides if you look at my builds then you will realize I do not use radiator clamps.

Click to expand...

My Grin TA is pretty tight already, but I hammer in a small piece of razor blade in, sharp edge first so there's no movement. Takes a while to get off though, for maintenance.

E-HP said:

My Grin TA is pretty tight already, but I hammer in a small piece of razor blade in, sharp edge first so there's no movement. Takes a while to get off though, for maintenance.

Click to expand...

Hmmmmmm ... that is surprising . I would have thought the Grin torque arms would have been on tolerance to begin with. Of course they have gone over to the "universal 14mm" approach. They do make a special smaller torque arm for the Bafang G311 motor.

The eBikeLing motor and BMSBattery torque arms went on the "weight weenie" bike to replace the the Bafang SWXU motor. That bike is just not a pleasant ride. Houston streets are just too rough for a rigid frame and high pressure 700x25C tires.

LewTwo said:

E-HP said:

My Grin TA is pretty tight already, but I hammer in a small piece of razor blade in, sharp edge first so there's no movement. Takes a while to get off though, for maintenance.

Click to expand...

Hmmmmmm ... that is surprising . I would have thought the Grin torque arms would have been on tolerance to begin with. Of course they have gone over to the "universal 14mm" approach. They do make a special smaller torque arm for the Bafang G311 motor.

Click to expand...

I think they also have to deal with the tolerances of the Chinese axles as well. It would be nice if they sold an oversized/advanced (undersized) version that could be touched up with a jeweler's file. Wouldn't be that hard to tweak the manufacturing process to make a builder's version of the TA at virtually the same cost.

Reading back on this thread, the best advice for "regular" power would be the grin TA. Mine have fit tighter than any other production TA.

I never used anything but scrap 1/4 inch mild steel to make a TA. Never went to lawn mower blade steel or anything. If tight, its strong enough. But I never ran much more than 3000w on them.

Tight is the thing. Thats a cool trick, pounding in some razor blade.

Another approach would be to take a cheap ass TA, weld some bead into the hole, then file back out to fit tight. Tight is the only thing that matters, not how strong the steel is. At some point, you'll just twist the axle off if your loads are big enough.

Which brings you to pinching torque plates if you want seriously tight. Some immensely long threads about this idea.

dogman dan said:

Another approach would be to take a cheap ass TA, weld some bead into the hole, ...

Click to expand...

I dare say that many, maybe most, of us do not access to a welder.
LOL ... I doubt my 40 year old townhouse even has the excess electrical capacity to run one.

Well a bit of good news for the folks in the UK.

Hammer-ebikes
Ian Hammon, hammer-ebikes@outlook.com
http://www.hammer-ebikes.com
Phone: 07754032024

They have a line of Torque Arms (appear to water cut). They also sell them primarily on EBAY.UK
Shipping cost to the US are prohibitive (more than the Torque Arms themselves).

Thats a nice looking torque arm, if it fits your motor tight.

Lots of people have wire feed welders, and cheap ones run on regular house current. But the cost of a motor is higher than hiring somebody to put a spot of metal in a cheap ass TA.

I'm writing this for the many others that read this, looks like you found a good one that won't be stamped out with a too large hole.