999zip999
100 TW
I'm very happy with nord-lock washers.
BMC Hub Motor - customer support - stripped threads
- Thread starter tkollen
- Start date
cassschr1
10 kW
So just what is this thing called Exactly....Common hardware store had this? Like menards ,home depot, lowes?
ET4041
1 mW
I checked Home Depot, Canadian Tire. Nothing there, not even just the nut. Can OP post where he got his?
tkollen
10 mW
It is called "Threaded Insert" and you won't find it at Home Depot or any other hardware store, especially not the M20-1.5 size. After a lot of research I finally found it at Reid Supply Company (http://www.reidsupply.com), Item No: KLI-66170 at $10.63 a piece. The insert comes with 4 protruding pins for the case an insertion tool is used. Just break them off. They are unnecessary for this application.
In order to get the insert flush with the axle end I did replace the original washer and lock washer with M20's and screwed the inserts by hand to the dropouts. On the cable side I had to cut off ca. 5mm of the insert and grind off ca. 5 mm from the nut (this nut is thicker than the original nut) in order not to block the cable hole.
I bought the M20-1.5 nuts from The Nutty Company (http://www.nutty.com) and M20 Stainless Steel washers and lock washers from http://www.fastenal.com.
In order to get the insert flush with the axle end I did replace the original washer and lock washer with M20's and screwed the inserts by hand to the dropouts. On the cable side I had to cut off ca. 5mm of the insert and grind off ca. 5 mm from the nut (this nut is thicker than the original nut) in order not to block the cable hole.
I bought the M20-1.5 nuts from The Nutty Company (http://www.nutty.com) and M20 Stainless Steel washers and lock washers from http://www.fastenal.com.
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cassschr1
10 kW
Thanks for the detailed post on these. Gonna use these for the sloppy threads on my 5404.
Joe Perez
100 W
Forgive the thread necro, but I just wanted to say a big thanks to tkollen for discovering this threaded insert.
With the DocBass torque plates installed, I have relatively little thread engagement on the wire side of my axle, and it's all on the section that has the cutout to allow the wire to turn. Thus, the amount to which I can torque that nut is extremely small before it skips the threads. It's not stripping the threads per se, just deforming the axle a tad (due to the cutaway) and jumping a groove.
I plan on attaching this insert to the exposed portion of the axle using either JB Weld or DP-420 (I'm open to suggestions) to reinforce and lengthen it, which should provide me with better thread engagement.
With the DocBass torque plates installed, I have relatively little thread engagement on the wire side of my axle, and it's all on the section that has the cutout to allow the wire to turn. Thus, the amount to which I can torque that nut is extremely small before it skips the threads. It's not stripping the threads per se, just deforming the axle a tad (due to the cutaway) and jumping a groove.
I plan on attaching this insert to the exposed portion of the axle using either JB Weld or DP-420 (I'm open to suggestions) to reinforce and lengthen it, which should provide me with better thread engagement.
agniusm
1 MW
Are you not using any torque arms on your bike?tkollen said:
Chalo
100 TW
Joe Perez said:
No, something is stripped. Threads don't open up and then just return to normal.
If you're lucky, it's only a matter of the nut being poorly toleranced and soft, and the axle is still OK. Get a better fitting nut, preferably one that had threads closer to the face of the nut. (I use automotive lug nuts on my X5 hub; the original nuts were disgraceful.) You have to have three full threads engaged to apply full fastener torque, and that's with normal threads rather than the flatted-axle junk we live with.
From where I stand, gluing torque arms on and then tolerating loose/non-existent axle fastening is stacking up two terrible ideas. Basically, you have glued the wheel onto your bike. Would you ride a bike with pedals that were glued to the cranks rather than screwed in?
Joe Perez
100 W
Perhaps I didn't adequately explain the specific issue which I have.Chalo said:
This is the least-bad image I could find from the web which illustrates the area of concern:
You can see how at the very end of the axle, there is a significant cutout on one of the two flat faces. The purpose of this cutout, I assume is to allow the wiring to bend into it and exit the axle at a right angle.
Now, because of the added thickness of the torque plate which I have, that is precisely the area which my axle nut winds up engaging. As a result, the axle has, in fact, been crushed slightly inwards in that exact area. It is visible to the eye, and measurable with a micrometer. As I apply torque to the nut, it has the effect of squeezing that area, which does in fact deform and allow the nut to skip.
It's not, as you say, that threads are "opening up", rather the axle itself is compressing due to the cutout and the thinness of the material in that area.
My proposed solution, therefore, is to install an insert of the type posted by tkollen around the axle over this area, and secure it with DP-420. Provided that the insert is reasonably strong, this should have the effect of better distributing the load which is imposed by the nut, and preventing the deformation of the axle.
No, but only because the force vector is entirely different. Pedals are stressed in shear at the point where they attach to the crank. I would also not trust a welded joint here, and for the same reasons.
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miro13car
100 kW
Welcome to ebike "China brand" technical standards.
Of course they are made in China so is my high tech SONY digital camera. The same camera is made in Japan also - no difference.
The differnce is hubs are made in China sweat shops, not in Western company China factories, hence "China brand"
but cheap
no wonder he doesn't answer calls, he is swamped , probably will close shop once made enough money.
Maybe at the beggining BMC were decent quality until somebody Chinese decided to save some cents on production unit.
how much did you pay?
Of course they are made in China so is my high tech SONY digital camera. The same camera is made in Japan also - no difference.
The differnce is hubs are made in China sweat shops, not in Western company China factories, hence "China brand"
but cheap
no wonder he doesn't answer calls, he is swamped , probably will close shop once made enough money.
Maybe at the beggining BMC were decent quality until somebody Chinese decided to save some cents on production unit.
how much did you pay?
More likely closing shop due to losses on returns, failures and defect units.
Joe Perez
100 W
Here's a much clearer image of my own axle, so that you can see exactly what is going on:Chalo said:
You can see clearly how the end of the axle has deformed inwards such that it's now on a taper. This reduces the depth of engagement between the threads on the axle and the threads on the nut, and there is sufficient elasticity that the axle can be dynamically squeezed a bit more when the nut is threaded onto it. Once the nut reaches a certain torque, the axle becomes so deformed that the nut literally skips a thread, like the needle on a record player skipping a groove.
The threads themselves are undamaged (both on the axle and the nut), it's the underlying structure of the axle which has deformed.
So the goal is to reinforce this section with a bonded, rigid collar that spans the entire circumference of the axle, absorbing the compressive force of the nut and transmitting only torsional stress to the axle.
Joe Perez
100 W
I just wish I could come up with some way of doing this that doesn't render the motor permanently closed, by preventing the axle from being driven out of the side cover...
Chalo
100 TW
I gotta say-- that slotted part isn't a thread per se, even though threads are cut into it. Because of the opening, it won't be able to hold normal thread retention forces, even with an insert stuck on it. When real fastener tension is applied, it will scoot out of the insert the same way it escaped your axle nut.
Seems like time for a thinner torque arm (no epoxy, Gorilla Glue, or wheat paste required, just mechanical fasteners) and a credible attempt to pick up some functional threads on that axle.
Seems like time for a thinner torque arm (no epoxy, Gorilla Glue, or wheat paste required, just mechanical fasteners) and a credible attempt to pick up some functional threads on that axle.
Joe Perez
100 W
Hence the need for a strong epoxy to bind the collar to the axle. I don't like the fact that it will render the motor permanently closed, but I can't think of a viable alternative at the moment.Chalo said:
Well, if you have any suggestions for how to remove the torque plate which is there presently (bearing in mind that it's quite seriously affixed to the frame with DP-420), I'd be happy to listen. I have considered trying to shave it down using an angle grinder, but I can't see how I'd maintain any reasonable degree of straightness and flatness.
voicecoils
1 MW
Joe Perez said:
Could you possibly modify the torque plate to turn it into a axle pinching type? That would hold that side of the axle in without relying so heavily on the nut.
Like this with a bolt through it:
The extreme thickness of those doctorbass dropouts, combined with reasonably thick aluminum dropouts hasn't left you much thread engagement to work with!
Chalo
100 TW
Joe Perez said:
The shear strength of DP420 on sanded and solvent prepped steel, according to 3M, is 2700 psi at room temperature. They also publish figures showing that is shear strength at 180F is 10% as high as at room temperature. We know from experience that these motors get kind of warm.
Assuming that the Ezee motor axle is made with one of the weakest plausible steels-- 12L40 in a fully annealed condition-- then the yield strength of that axle is 40,000 psi-- not likely, but possible. And it yielded in its application already. I guess I don't see why you are planning a solution around a material that's between 0.25% and 7% as strong as the material that already failed. If it succeeds wildly, beyond all specifications, then the axle that squeezed in and escaped its nut will just do the same thing to the insert you glue on with puckey.
I think you simply have to use the part of the axle that isn't cut away.
As for how to unstick that thing you glued on your frame, just use 3M's data to your advantage: Get it too hot to touch, and whack it with a mallet. It'll probably just pop off.
Chalo
Joe Perez
100 W
voicecoils said:
Were I to do it over again, I might well do that. As it stands, the plate is pretty thoroughly stuck to the frame, such that converting it to a pinch-type is not really practical.
I've considered Chalo's suggestion (heat it up and whack it) however I'm not really keen on pouring large amounts of heat into an aluminum bicycle frame.
Perhaps I shall assemble a test fixture by gluing two pieces of steel together and then subjecting them to heat with the MAPP torch, to see just how much it takes to get them to separate.
I also spent a little time eyeballing the plate last night, and I'm starting to convince myself that I might actually be able to use a metal cutoff wheel in the angle grinder to slice it in half, thus decreasing its thickness. A byproduct of this operation will be large amounts of heat, so we'll just take that as it comes.
If I can halve the thickness of the plate, then along with the added thread engagement afforded by the use of an insert as compared to a regular nut and washer, I should be able to reclaim 2-3 threads' worth of engagement, getting me back onto the non-cutout section of the axle.
dnmun
1 PW
i doubt if anything can be done anymore since the axle is crushed already so the nut will never fit. when you look at a new motor then find one that has enuff axle length to allow the nut to seat on the axle and not on the cut out part.
dont use a torch... a plain electric heat gun will get it hot enough imo. ( if you opt to remove them )
Joe Perez
100 W
Haha, what's with this "when" business? I'm far from ready to give up on this unit.dnmun said:
The only electric heat gun I own is a 250 watt Weller 6966, which I use for heat-shrinking small tubing. The torque plate would just laugh at that.Ypedal said:
For the moment, I'm going to adopt a two-phase strategy. Plan A will be to shave down the thickness of the plate by ~50% and count on the combination of that, along with the added "reach" of the new insert (as compared to the Chinese nut used originally, in which the thread does not go all the way to the "bottom"), and hope that the extra 2-3 threads' worth of engagement that this gets me will be sufficient.
Plan B, if that fails, will be to attempt removal of the torque plate via heat. Who knows, it may well be that the heat generated by Plan A will cause this to happen anyway. If it does, then that's even better- I'll be able to take it to a machine shop and grind it properly.
If both of those fail, Plan C will be to epoxy the insert to the axle.
plan C is a bad one... :lol:
250w.. not good enough but a 1500w heat gun would do.
250w.. not good enough but a 1500w heat gun would do.
Joe Perez
100 W
That's why it isn't Plan A.Ypedal said:
I have faith that it would work, I simply don't want to fuse the motor shut.
I know for a fact that you are not the first to be bitten by this issue: I had the identical problem torquing down my first BMC and similarly solved it by just picking up a few more threads. I am confident this general strategy will be effective.Joe Perez said:
The real failing here is that there is no max torque spec for the BMC axle nuts - regardless of the poor axle design. In the end, with good torque arms (which you have), there is really no reason to torque the heck out of the nuts - certainly not to the extent that the size of the axle nut might suggest. I have two BMCs with 4500 mi on them and after getting a reality check as you did torquing one down the first time, I have not any difficulty using reduced mounting torque. The only change I made was to swap out the stainless nuts supplied with the motor for softer sacrificial nuts to ensure that any over-torque would result in damage to the nut not the axle. The softer nuts are still pristine and the motors have never decided to part company with the bike....
Joe Perez
100 W
No kidding.teklektik said:
Just for kicks, I dropped in my old motor (Amped DD) and was really surprised to see how much longer the axle was:
So that's why I never had this problem with my old motor. Can't quite figure out why the MAC / BMC axles are so short.
Anyway, making some progress. It turned out to be fairly easy to make a straight cut sideways through the plate. Here's an in-process shot:
When I was just about all the way through, I decided to see how much the not-inconsiderable heat of the grinding operation had affected the DP-420. Stuck a flat screwdriver into the groove which I'd created, and while it took some effort, I was able to pry the plate off of the frame. I forgot to bring home the infrared thermometer this weekend so I don't know how hot it actually was, but when I sprayed some water onto it with a little squirt bottle, the water sizzled. So it was at least 100 degrees C, and probably quite a bit more.
This actually turned out to be of benefit, as after finishing the cut in the vise on the workbench, I was able to use my micrometer to accurately measure the thickness of the plate in different areas, and use this as a guide to doing some light finishing work to make it properly flat and true.
Starting thickness was .380 inches, and finished thickness was .175-.180 inches. So I've successfully reduced the thickness by a little over 50%, picking up almost exactly 5mm, which translates to 3.3 threads.
I found another way to pick up a little more thread engagement. Previously, I'd had to install a shim about 1.5mm thick between the inside of the dropout and the hub, to prevent the brake caliper from rubbing on the hub. Turns out that the part of the frame to which the caliper was mounted had raised features a little over 1mm in height, spacing the caliper inwards (towards the wheel.) So by grinding those flush, I can eliminate the shim and gain back that thickness as well.
Anyway, the plate is now back on and curing. Removing the residual epoxy from the dropout took quite a bit of work with the 80 grit abrasive-bristle wheel, so I still have a fairly high degree of confidence in this stuff.
Yeah, this bugs me about bikes in general. Being an engineer by profession and a shadetree auto mechanic of 20 years, I'm accustomed to there being a torque spec for everything. Granted, there's no good way to put a torque wrench on a nut that has a bunch of wires poking through it, but at least it would put me in the ball-park.
When I first put this together, I used quite a bit of force on the nut, which I'm sure is partly responsible for the deformation of the axle. I keep having to remind myself that even though the lug nuts on my car are the same size, the 85 ft/lbs which I use to tighten them is not appropriate in this application.
