torque arms / fixing in angular position

A lot torque arms are of a 2 part construction with one part fixed to the frame or fork and the other part onto the axle with the only thing fixing them in position is a single fairly small diameter bolt which has always seemed a bit of a weakpoint to me. Once you've used the flexibility of this system to find the correct relative positions of the two parts it would seem sensible to fix them in place rather than rely solely on a single small bolt so what are your thoughts on a diy solution such as silver soldering or brazing which should be possible with a gas torch for such relatively small parts? I know there are fans of certain epoxies here too so what are thoughts for this application?
(yes- I just noticed my torque arm bolts had loosened a little, I'd thought of it as a potential weak spot before then did nothing about it! It's taken several years for them to work loose but could easily get missed- with disastrous consequences since my bike is front wheel drive.)

alsmith said:

What are your thoughts on a diy solution such as silver soldering or brazing which should be possible with a gas torch for such relatively small parts? I know there are fans of certain epoxies here too so what are thoughts for this application?

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Usually these types of torque arms you mention are, so far as I know, of closed mouth design. So if you put them over your axle and then soldered them to your frame, how would you extract the axles from the dropouts afterwards?

http://www.endless-sphere.com/forums/viewtopic.php?f=31&t=29129

These torque arms are open mouth design, if you can use them I recommend them. www.youtube.com/watch?v=xQOC2BwiJDU I think that you could probably do fine with soldering or brazing on torque arms with the right technique, I can't say I know that a solder job will hold forever, and who knows how well you will perform the task or what materials you will use, but I imagine if people are having great success with an epoxy (seems plenty have) that a solder job would work out fine for an electric bicycle.

I'd clean all surfaces super well before joining metals. Remove all paint, dirt and oil from the mating surfaces for sure. This means using stainless steel brushes and acetone, maybe some serious sanding action going on to get through the initial layers of paint.

Then I'd line the parts up, clamp them in place with metal clamps http://www.amazon.com/gp/product/B00004SBBN/ref=as_li_tl?ie=UTF8&camp=1789&creative=390957&creativeASIN=B00004SBBN&linkCode=as2&tag=xbnijgbr-20&linkId=F7UN3NZLP56JNAFS like these. Paint the area with flux and then heat it up and so on. I really recommend that before all of this that you should practice the methods and techniques before doing the important one.

Personally, I think steel is the way to go for retrofitting electric bicycles due to ideas relating to fatigue limit. Welding steel is probably a radically more ideal way to go compared to soldering or brazing. What I am getting at is, you can probably find an old stick or flux core welder for super cheap that'll do work out on steel. The welds might not be 'stack of dimes' pretty, but an angle grinder with a flap disc can make any weld very pretty. The main thing here is if you are concerned about the strength of this application, which it sounds like you are, you won't achieve the penetration level when soldering or brazing to anything close to what you'll get with welding. I am sure this doesn't mean anything unless you really understand the process, but welding means you are melting some of the material together of two seperate pieces both at the surface and usually a fair bit deeper. This isn't like a surface glue, this means the pieces are fused together at a certain point, this is what I mean by penetration.

If you decide to stay with your current setup for torque arms, I assume you have a nylon bolt preventing the bolt from unturning itself. If you were really worried, you could probably look into something like a combination of ideas, this is likely an insane degree of overkill though. But there are things like nord lock washers and loctite that you could use all together that would make it insanely difficult for the nut to undo itself. Lots of options for preventing nuts from undoing itself. www.youtube.com/watch?v=mgwmuZuJ02I

I just welded one to prevent rotation at the bolt. Brazing should work. Epoxy would not be strong enough, unless you buried the whole joint in a gigantic blob of PC 7 or something.

If the TA can be secured in such a way that the strap or hose clamp cannot slip on the fork or chainstay, then you don't need to weld the joint. If oriented right, a front installed TA can be strapped to the fork such that rotation of the TA will pull down toward the fat part, and it can't slip.

If your bike is steel, you can weld a tab to it, and bolt the TA in place. With that bolt, then the TA can't rotate at the joint anymore. It can't slide up or down the fork that way no how.

No welder to secure the TA at the bolt? This is about a 30 second task for a welding shop or auto repair place to do for you, once you have it bolted down at the right angle. Should not be very costly to do, compared to a new bike frame!!!

Silver soldering or brazing will work if you have a steel frame. Remember that most of the vintage bicycles of the previous century were brazed together.

There are people that 'claim' they can braze Aluminum but I would not stake my life on it.
There are only two welding processes used to join Aluminum to steel: vibration and explosive.
A number of vintage aluminum bike frames were 'cemented' together (Miyata, Vitus, .Peugeot).
In the 1990s Honda was using an adhesive process to build their aluminum racing cars. They used that same process to build the first Honda Insights.
My point is that properly done adhesive (i.e. epoxy) is a proven process.

Personally, I think I would just get a bit of loctite 490 tape for the small screw that you referenced.

For aluminum, I'd replace the usual hose clamp with a far more slip proof clamp and two bolts. One bolt secures the clamp so it cannot slip. Then the other secures the arm to the TA.

But none of that needed, if you weld the TA itself. That's the easy route.

This one won't ever have the bolt slip.

Maybe I was a little unclear- I don't mean fixing to the frame, only that central pivotable (is that a word?) joint. Mine is fixed to a plate welded to the forks and bolted very solidly with two bolts. The motor is a Crystalyte X5 so uses the larger 14mm axle and it is a closed profile slot. There's not much spare metal around that central bolt.

(btw there's a torque arm on both sides, the axle half is stainless (type 2 from ebikes.ca), the longer top half was chosen from a different torque arm set)

Beautiful! In your case, since the second part of the TA is fixed to the frame with two bolts to a welded mount, it's impossible now for your TA to rotate at the pivot bolt.

No worries. I ran 4000w through a front hub attached the same way with no problems whatsoever. You did exactly the right thing to control a powerful motor like that one.

Yep-all good but that single M6 bolt.

I think I'm going to look try silver solder to fix that joint in place so it can't rotate or move- it melts at a lower temperature than a brazing rod, the fairly small size of the 2 arms will help to make sure it gets hot enough to solder with a good joint, and better yet I have some 4% Silver Solder, I think it will do the job but 'll look to see how it compares with other proportions can be had from 0.5% to 80%.

If you think about it, that bolt can't rotate anymore, because the other piece can't move up or down, or rotate in or out now with two bolts.

But nothing wrong with brazing it, soldering it, welding it, whatever. Belt and suspenders thing.

Saddly it did rotate spreading the flats on the forks a little. It was caused by the bolt backing off a little so allowing some movement.

That is the fault of a shitty fitting torque arm then.

And possibly use of regen?

Just a quick note that stainless steel takes some specialized equipment to weld...brazing may be impossible AFAIK.

No regen- it wasn't really enough of a gain to be worth the extra reverse stresses.

I don't think its a shitty torque arm- it's still in good condition and the movement didn't damage the arm. The problem is the bolt.

brazing shouldn't be an issue - most stainless steel types, with the exception of titanium or niobium stabilised grades, can be brazed. However I'm going to try silver solder.

If you don't have a c washer under that TA in the picture, That is the problem then.

Yes, C washers fitted. the tongue is not a problem.