Dropout Failure Experiements, and a call for Fork Donations

[Vanquizor]

I would be interested in seeing how much less force it takes to spin an axel the second second time (ie new fork but same axel)...

[dequinox]

I'm going to see what we can setup to generate a full spinout profile for each experiment, so we can see the torque on the 'Y' axles plotted against the axle rotation angle. This will be a lot more informative, comparing for instance how steel gives while alloy cracks, and will eliminate some subjectivity as well, but it'll take some time to figure out the best way to set things up.

Justin, quick question:

When you were testing the spin out torque on the dropouts with the torque-arm restraint, which was it that gave way and rounded out the most... the axle or the torque arm?

It seems to me that if the torque arm was the part that "ate it" then some improvements could be made by adding a simple tempering process to the manufacture of the arms. If we could get a manufacturer to laser/water cut out the torque arms from 1080 (or perhaps a T1 or 440c stainless ) steel, and then heat treat them for a Rockwell hardness of about 35-40... it would be much more resistant to "round-out" than your run-of-the-mill 1020 1/8" plate. Hopefully that hardness would also afford some "toughness" so that the torque arms wouldn't just crack out.

[Affliction]

I'm going to see what we can setup to generate a full spinout profile for each experiment, so we can see the torque on the 'Y' axles plotted against the axle rotation angle. This will be a lot more informative, comparing for instance how steel gives while alloy cracks, and will eliminate some subjectivity as well, but it'll take some time to figure out the best way to set things up.

Justin, quick question:

When you were testing the spin out torque on the dropouts with the torque-arm restraint, which was it that gave way and rounded out the most... the axle or the torque arm?

It seems to me that if the torque arm was the part that "ate it" then some improvements could be made by adding a simple tempering process to the manufacture of the arms. If we could get a manufacturer to laser/water cut out the torque arms from 1080 (or perhaps a T1 or 440c stainless ) steel, and then heat treat them for a Rockwell hardness of about 35-40... it would be much more resistant to "round-out" than your run-of-the-mill 1020 1/8" plate. Hopefully that hardness would also afford some "toughness" so that the torque arms wouldn't just crack out.

Hardened steel will fracture rather than deform so not really a good idea. The axle's are all soft steel so hardened steel would just destroy them.
Torque arms need to be springy so hardened steel is not the right solution.

[justin_le]

Justin, quick question:

When you were testing the spin out torque on the dropouts with the torque-arm restraint, which was it that gave way and rounded out the most... the axle or the torque arm?

It was the torque arms that suffered the most damage for sure. The axles are definitely harder than the stainless.

It seems to me that if the torque arm was the part that "ate it" then some improvements could be made by adding a simple tempering process to the manufacture of the arms. If we could get a manufacturer to laser/water cut out the torque arms from 1080 (or perhaps a T1 or 440c stainless ) steel, and then heat treat them for a Rockwell hardness of about 35-40... it would be much more resistant to "round-out" than your run-of-the-mill 1020 1/8" plate. Hopefully that hardness would also afford some "toughness" so that the torque arms wouldn't just crack out.

For sure, we'll get to know for sure early next week. The local waterjet shop where I've been getting the torque arms made happened to have some 01 tool steel in a 1/8" x 1.25" bar stock. He was planning to make a knife blade from it, but I was like, Nooooo! We need hardened torque plates instead! So I'm expecting those to be delivered this coming monday or tuesday and we'll see just how much of a difference that makes. It might be that the hardened torque plates just cut through the axles at only a little more torque than the axles were cutting through the softer plates, but we'll see.

Justin

[Affliction]

It was the torque arms that suffered the most damage for sure. The axles are definitely harder than the stainless.
Justin

The axle's are harder than stainless? I cut threads in these all the time and it's like cutting butter with my tap and die kit.
You can't drill stainless unless you have special drill bits and usually the bit is ruined once you're done.
You sure your torque arms are true stainless steel?

[liveforphysics]

It was the torque arms that suffered the most damage for sure. The axles are definitely harder than the stainless.
Justin

The axle's are harder than stainless? I cut threads in these all the time and it's like cutting butter with my tap and die kit.
You can't drill stainless unless you have special drill bits and usually the bit is ruined once you're done.
You sure your torque arms are true stainless steel?

The most commonly used alloy of stainless steel is 304.
It has a tensile strength of of 73,000ksi and a yeild strength of 31,000ksi

Other grades of stainless steel, like alloy 15-5, which is common in aircraft, have a tensile strength of 161,000ksi and yeild strength of 140,000ksi.

All the way up to L-19 stainless, which can exceed 300,000ksi yeild with the proper heat treatment. It's used only in fastener applictions, and it rusts very rapidly dispite being classified as a stainless steel, which technically only means it's >10.5% chromium by mass.



Some alloys of SS are as soft as mild steel and drill very easily. Some alloys are as hard as a tool steel drill, and require carbide tooling (or other means).

[GrayKard]

Excellent info so far! I can't wait to see the data from the next set of tests.

What I would want to know is if dual torque arms offer twice the resistance to spinout or do they give more or less protection than that. Not two arms with one reversed for regen but two mounted the same direction.

Gary

[dequinox]

The axle's are harder than stainless? I cut threads in these all the time and it's like cutting butter with my tap and die kit.
You can't drill stainless unless you have special drill bits and usually the bit is ruined once you're done.
You sure your torque arms are true stainless steel?

The reason you have a difficult time cutting stainless is its tendency to work-harden. A drill bit trying to push through stainless steel produces a lot of pressure, and like when you bang a welding rod flat with a hammer at room temperature, the surface of the stainless becomes harder and more resistant to cutting. Only stainless has a much much higher tendency to react this way to machining than mild steel or even the higher carbon alloys. You shouldn't be ruining drill bits if you use a proper cutting fluid, feed rate, and speed with a decent drill press. Even with a regular bench top you should be able to get a few holes drilled before the bit goes dull and you have to sharpen it again.

You might try using your tap and die on a SS bolt the same size as the axle sometime...there may (and I say may because I haven't done this myself) be a noticeable difference in the machine-ability. Something like a 1080 steel might be soft if it isn't heat treated...but try machining it after a good temper is put into it. The higher carbon stuff has higher tensile and yield strengths, but that doesn't necessarily vary directly with its machining characteristics.

For sure, we'll get to know for sure early next week. ... It might be that the hardened torque plates just cut through the axles at only a little more torque than the axles were cutting through the softer plates, but we'll see.

Cool, I'm glad that thought already crossed your mind and it sounds like we'll be informed of the characteristics sooner than I thought! You may also want to keep an eye on the profile of the cut edges. A perfect corner (that is, un-rounded) can have a higher tendency to form stress fractures. Slightly rounded corners may help that quite a bit. You probably don't want the torque arms to be too hard...in fact I hypothesize that the R/C hardness should about match that of the axle. Ideally there will be no friction wear on the torque arm/axle at all if the nuts are tight and the axle doesn't move much relative to the dropouts...but sometimes people forget as you've pointed out.

The most commonly used alloy of stainless steel is 304.
It has a tensile strength of of 73,000ksi and a yeild strength of 31,000ksi

Are your units kg/in^2? I can't remember off the top of my head what ksi is...

What I would want to know is if dual torque arms offer twice the resistance to spinout or do they give more or less protection than that. Not two arms with one reversed for regen but two mounted the same direction.

Two torque arms would double the ability of the torque arms to hold a moment, and probably the total ability to hold a moment by 20-30% (thats a S.W.A.G.), but the real limit relates to the ductility, shear strength, and hardness of the axle and torque arm material. It's a lot like how a crescent wrench doesn't get dented when you strip a nut or bolt head with it...the material of the bolt head didn't have enough hardness so it mushed over instead of tightening further. Does mounting a torque arm backward make a different for regen? I'd be interested to know if it does because I want to play with this on my next build (a few years out of course).

[Affliction]

The reason you have a difficult time cutting stainless is its tendency to work-harden. A drill bit trying to push through stainless steel produces a lot of pressure, and like when you bang a welding rod flat with a hammer at room temperature, the surface of the stainless becomes harder and more resistant to cutting. Only stainless has a much much higher tendency to react this way to machining than mild steel or even the higher carbon alloys. You shouldn't be ruining drill bits if you use a proper cutting fluid, feed rate, and speed with a decent drill press. Even with a regular bench top you should be able to get a few holes drilled before the bit goes dull and you have to sharpen it again.

You might try using your tap and die on a SS bolt the same size as the axle sometime...there may (and I say may because I haven't done this myself) be a noticeable difference in the machine-ability. Something like a 1080 steel might be soft if it isn't heat treated...but try machining it after a good temper is put into it. The higher carbon stuff has higher tensile and yield strengths, but that doesn't necessarily vary directly with its machining characteristics.

Ever try and drill through a bearing race? It's near impossible even with Tungsten carbide bits. Yes I know all about cutting oil and how not to ruin a drill bit. On hardened metals I use the old "smoke wrench" to make holes. Then I use a die grinder to make the final shape.
Running a die on hardened steel is a futile effort, you just end up wrecking your tool.
I cut threads all the time and I was just mentioning how soft the axle threads are by the ease of cutting a different pitch for repair.
Hub motor axles appear to be very soft metal.

[dequinox]

Ever try and drill through a bearing race? It's near impossible even with Tungsten carbide bits. Yes I know all about cutting oil and how not to ruin a drill bit. On hardened metals I use the old "smoke wrench" to make holes. Then I use a die grinder to make the final shape.
Running a die on hardened steel is a futile effort, you just end up wrecking your tool.
I cut threads all the time and I was just mentioning how soft the axle threads are by the ease of cutting a different pitch for repair.
Hub motor axles appear to be very soft metal.

Perhaps the axles Justin has are of a different alloy than the one's you work with. That might explain the stainless torque arms getting mutilated while the axle was less affected. I wouldn't in a million years try running threads on a piece of metal without first applying a proved annealing process...nor would I ever suggest it. I was hoping the "try machining it after a good temper is put into it" comment would be understood as a bit sarcastic.

[justin_le]

Hub motor axles appear to be very soft metal.

I would say it appears otherwise. In your case you are chasing threads with a die on an already threaded axle, of course it's not going to take much force. The hub motor axles are all heat treated, Nine Continent I know spot checks them with a Durometer (I didn't ask what the actual spec was, but will do that), and if you make a torque plate from regular cold rolled steel and spin it out, the hub motor axle will carve threads into your steel, and will itself be barely damaged. Perhaps "very soft" compared to carbide or whatever, but as far as machinable steels go they appear to be more on the harder side.

Justin

[Affliction]

Hub motor axles appear to be very soft metal.

I would say it appears otherwise. In your case you are chasing threads with a die on an already threaded axle, of course it's not going to take much force. Justin

This is not quite true. I am not chasing pre existing threads at all but rethreading to a coarser pitch as a means of repair of stripped threads.
Chrystalite axles are threaded 12mm X 1.25 pitch, I'm simply cutting new deeper threads that pretty much eliminate the original threading.
I find 12mm X 1.5 pitch a good solution to repair stripped axle threads. I must have done a good dozen axles now on wilderness energy and Chrystalite hubs. They all seem to cut easilly with no burring. I usually have burring occur on harder bolts. ex I have to make more threads on a bolt not threaded to the head. On harder bolts I seem to get a really rough cut.

[patrickza]

This is not quite true. I am not chasing pre existing threads at all but rethreading to a coarser pitch as a means of repair of stripped threads.
Chrystalite axles are threaded 12mm X 1.25 pitch, I'm simply cutting new deeper threads that pretty much eliminate the original threading.
I find 12mm X 1.5 pitch a good solution to repair stripped axle threads. I must have done a good dozen axles now on wilderness energy and Chrystalite hubs. They all seem to cut easilly with no burring. I usually have burring occur on harder bolts. ex I have to make more threads on a bolt not threaded to the head. On harder bolts I seem to get a really rough cut.

Do you have a thread somewhere about re-threading the axles. I partially stripped my crystalyte 5305 hub when I first installed it. I'm using alonger bolt now so it works, but I'm keen to know how it can be repaired. Thanks.

[Affliction]

Do you have a thread somewhere about re-threading the axles. I partially stripped my crystalyte 5305 hub when I first installed it. I'm using alonger bolt now so it works, but I'm keen to know how it can be repaired. Thanks.

Chrystalite 5 series has a 14 mm axle. I havn't had to rethread any 14 mm axles so far and I'm not sure what the original thread pitch is either.
My best guess without seeing it is it's probably 14mm X1.5. The way thread pitch steps up you have to take into account not only the width between threads but also the depth as it's equal to the width ex. 1.5mm between threads is 1.5 mm deep into the bolt.
You need to pick a coarser thread pitch that mostly eliminates the old depth of the thread but not too coarse.
My best guess is you need to go 14mm X 2.0. Find some automotive lug nuts and recut the axle to that size.

[justin_le]

First set of results graphed here:

Nut Tightness on Spinout Torques.jpg (53.25 KiB) Viewed 1067 times

Tightening the nuts to 90 N-m, we were so sure it was going to strip the threads, but it didn't, and something quite non-linear happened between this and the 60 N-m test that increased the torque required to cause axle spinout by a substantial amount.

Will do a thorough description of the test procedure later.
Justin

[el_walto]

Would you recommended tightening the eZee hub motors to 90Nm? I'm afraid I might strip the threads, or even crush the aluminum dropouts on my bike.

I'm curious as to what is the maximum torque a standard axle/bolt starts to strip at.

[lester12483]

Its pretty simple

Your bike must have steel forks

Your ebike then must have a torque arm

Its not safe for a hub motor to be over 700 watts. Way too much torque.

[dogman]

I tend to agree about the steel dropouts. At least for installing without tourqe arms. This first graph is a no tourqe arms test.

Clearly an axle hard enough and a nut that allows tightening to 90 helps. I don't know that it would be good to squeeze alloy that hard either, but I would never run a powerfull motor on alloy drops anyway. The established safe method for installing powerfull motors to alloy frames is a custom made steel tourqe plate, that effectively replaces the alloy rear drop with a steel one.

About the 700 watts, I don't agree. But that is about the limit for running without tourqe arms.

I would say that 700 watts is about the limit you want to put on a bike and sell it, and be liable for though.

[el_walto]

I'm really curious as to what point aluminum forks will snap.

I have 1100W geared on this fork right now, with a not so thick torque arm: http://www.chainreactioncycles.com/Imag ... l/7846.jpg

Previously i had it on the most crappy fork in the world, i would not recommend this fork to anyone as it comes with a lot of wobble right out of the box: http://northernbeachescycles.com.au/sho ... %20sf8.jpg

[dequinox]

I tend to agree about the steel dropouts. At least for installing without tourqe arms. This first graph is a no tourqe arms test.

Clearly an axle hard enough and a nut that allows tightening to 90 helps. I don't know that it would be good to squeeze alloy that hard either, but I would never run a powerfull motor on alloy drops anyway. The established safe method for installing powerfull motors to alloy frames is a custom made steel tourqe plate, that effectively replaces the alloy rear drop with a steel one.

About the 700 watts, I don't agree. But that is about the limit for running without tourqe arms.

I would say that 700 watts is about the limit you want to put on a bike and sell it, and be liable for though.

Yeah you probably don't want to be sending one of those out the door unless you throw two torque arms on it!

I will be curious about the aluminum dropouts also...it seems like they would be slightly more common on ebike conversions since a lot of people like to do dual suspension frames.

[The Journey Guy]

This is a very informative thread for me, because I am just starting my first ebike build, using a X5303 motor with a 48v 40a controller.

I have read with great interest the thoughts and results in these pages full of information. Something keeps coming to mind, and maybe someone can comment on my thoughts.

The way I generally understand it, and keeping the situation where the axle nuts are loose out of the picture, all these shear results and metal smear results happen when there is
almost max torque (N) applied, correct?

What I keep asking myself is this: What if when I use the throttle, I start slowly, and gradually increase my speed? Then my fork dropouts will never see max N values, correct? If I am
cruising along at say 25mph, and then go to 3/4 throttle, the forks will not see as much N force as when I go from a dead stop to 3/4 throttle. Or am I wrong about that?

In other words, if I don't do burnouts, and if I don't go from a dead stop to max throttle, there is a good chance that I might never stress the dropouts to their fail point, yes?

[dequinox]

Yes if you spread the torque out over a longer time period you will not be seeing a very high peak torque on the dropouts. The opposite is true as well...if you start out slow and then hit 100% throttle in an attempt to do a front wheel burnout...you may end up doing a faceplant.

[Mark_A_W]

Its pretty simple

Your bike must have steel forks

Your ebike then must have a torque arm

Its not safe for a hub motor to be over 700 watts. Way too much torque.

Not necessarily, it just has to be engineered properly. The forks are ally, the reinforcements are STEEL. And the end is closed over the axle - this is important even if I have an axle spinout I will not lose the front wheel.

I have over 10,000km, with 1300w, and mucho abuso on these forks. I've broken 2 frames, 2 rims, seatpost, rack twice, pedal...I've lost track....but the forks keep on trucking.

[Affliction]

Not necessarily, it just has to be engineered properly. The forks are ally, the reinforcements are STEEL. And the end is closed over the axle - this is important even if I have an axle spinout I will not lose the front wheel.

One thing I got to give to Aussies is their ingenuity! Our consumerist north american society could never figure this stuff out.
I've modded my front forks and I don't use torque arms! And I'm well over 800 watts on my front hub.
Bikes just aren't designed to handle hub motors. There needs to be a new standard for E-bikes.

[dogman]

Mark wins the best tourqe arm award again. This pic gets reposted all the time.

Re Journey Guy. Yep, how you use the throttle can affect the tourqe load on the dropouts. But the single most important thing is how the nuts and washers fit into the dropouts. There is much anectdodal evidence that poor fit of the oversize motor washers and nuts into the cups of alloy front forks are responsible for many of the alloy front fork failures. When the large washer spans a space under it, the forces when the nut is tightend spread the dropouts. But should this happen, Marks design of tourqe arm would keep the motor on the forks and prevent a faceplant.

Personally, I would not run a motor on alloy front forks without something as substantial as Marks setup. Call me fraidy cat, but my broken up shoulders are just now getting fully healed from my last face plant 20 months ago. But on the rear, I would not hesitate to run an x5 on an alloy frame with good tourqe arms or toruqe plates to back it up.

Tight nuts do help, on my Fuji, I run an x5 with no tourqe arms on a steel frame. No problems so far, and I don't baby the throttle.