Mechanics in Seattle/Dropout Filing

Z

zippybike

1 mW
Joined
Jun 17, 2020
Messages
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Hello everyone, I've been lurking for quite a while and have a few questions regarding my first e-bike build I recently threw together.
first bike.jpg

It's a 2012 or so Scott Scale 970 with a 1000w geared hub motor, CA v.2, Grin Torque arm V4. All electric parts were scavenged from my brothers e-bike when he crashed and bent his frame. I'm feeling good about the build so far, except for the dropouts. The motor axle doesn't quite seat in the pre-existing radius of the dropout, and I'm concerned about stress points on the sides causing fractures when going over bumps. I don't feel comfortable filing them out on my own because it seems like a pretty sensitive task that could affect alignment if done improperly. I've had bad luck with big bike shops so far here in Seattle, anybody have a recommendation for a shop/private tech that could file my dropouts/re-balance my wheel/make sure nothing on the bike is gonna kill me?

If filing is not necessary, let me know and I'll ride without worry :) Thanks for reading, this has been an awesome place to lurk (apologies if this is in the wrong section).
 
I would recommend a torque plate that bolts to your dropouts, that completely encloses the motor axle like a torque arm would. This thread has some examples, and there are others around the forum.
https://endless-sphere.com/forums/viewtopic.php?f=2&t=26444

Filing the dropouts significantly would weaken them, and also change the position of the wheel in the frame, relative to the brake calipers. IF it's far enough upward, it may require a modified caliper mounting bracket to allow using the rear disc brake, as the caliper may strike the rotor's edge.

Filing them just enough to change the shape of the top of the dropout to match the shape of the top of the axle may be beneficial; should be done with care/precision and by frequently checking fit with the axle. Both sides have to be even, or the wheel will sit at an angle.
 
Thank you for the response and advice. I have this torque arm installed, is it insufficient?

Torque arm.jpg

The precision required to file the dropouts perfectly is precisely what is making me nervous :p

Anyone had aluminum dropouts crack from this improper-seating issue?
 
You should be ok with that setup, as you have it now. If it was a larger 14mm round axle, then filing the dropouts 2mm deeper would result in the axle center on the new wheel being the same as the original 10mm axle on the bike. Your motor has a 12 mm round side, and 10 mm flat side. So not as much oversize, not as much not in place, as the big axle motors.

Currently your axle is only 1mm off center, likely not enough to cause brake alignment issues, even with a disc brake.
Only if you cannot adjust brakes to work with this as is, would you need to deepen the dropout. Without the good torque arm though, you would likely ruin the frame, or at least have the wheel loosen in a few blocks.

I think you are good to go as you are.
 
amberwolf said:
I would recommend a torque plate that bolts to your dropouts, that completely encloses the motor axle like a torque arm would.
Click to expand...

I don't think I fully understood what you were saying earlier, I can see the advantage of a solid plate. It would potentially keep the hard angles of the axle from jamming in the round dropout. My dropouts have a complicated geometry but I'll look in to it!


dogman dan said:
You should be ok with that setup, as you have it now. If it was a larger 14mm round axle, then filing the dropouts 2mm deeper would result in the axle center on the new wheel being the same as the original 10mm axle on the bike. Your motor has a 12 mm round side, and 10 mm flat side. So not as much oversize, not as much not in place, as the big axle motors.

Currently your axle is only 1mm off center, likely not enough to cause brake alignment issues, even with a disc brake.
Only if you cannot adjust brakes to work with this as is, would you need to deepen the dropout. Without the good torque arm though, you would likely ruin the frame, or at least have the wheel loosen in a few blocks.

I think you are good to go as you are.
Click to expand...

Awesome, thanks for the analysis! The disk brake works just fine, still tweaking the alignment. If I had a mill, I'd make a crescent-shaped shim to fill the gap just for peace of mind when going over big bumps. For now, I'll just have fun on the bike and start working on the lights and such.
 
A good hub motor ebike starts with strong dropouts. Pinch type or torque plates, each side, made with thick steel. So you can ride it fast at will, hard cornering, acceleration and braking never worrying.

Simple task, can be made with hand tools. Patience required. Well worth the trouble. Sooner or later you will do it, likely not after a fail. More than half ebike riders will upgrade the power and/or speed of their bike, most of the others are thinking about it.
 
MadRhino said:
A good hub motor ebike starts with strong dropouts.
Click to expand...

I agree, I'd love to have some beefy brackets to be safe and worry free. I'm concerned about the geometry of my dropouts and unsure how to make something that fits and bolts. Here are my dropouts:IMG_20200618_170256.jpgIMG_20200618_170318.jpg

I see some holes to potentially screw in to, but I'm not sure how to handle the machining (besides getting some box wrenches and bending the hell out of them lol) This frame might be easier to do as a mid drive, I didn't have a hub conversion in mind when I bought the bike.

999zip999 said:
? Has your brother found out his bike has been cannibalized ?
Click to expand...

Haha yes, he's been helping me with some of the electrical aspects. It's a custom setup so I need his advice from time to time.
 
The title threw me off, I thought there was a mechanic or mechanics in Washington that were filing for dropout.

I guess I should post something useful.
I normally use 1/4" steel plate and take a grinder to make a slot for the axle, then more notches to hold a hose clamp.
The dropouts on my bikes have been chewed up pretty badly, on the ole busted frame Townie, I did a bunch of wonky things. Like slip the 1/4" steel plate T.A. inside the one dropout because the aluminum frame slot for the axle was so mangled. It took a bit of effort but not much and once it was in, I would just hammer the tire until the tire was somewhat aligned. It worked!
 
markz said:
I normally use 1/4" steel plate and take a grinder to make a slot for the axle, then more notches to hold a hose clamp.
Click to expand...

It's nice to know I can make something with just an angle grinder, I'm really short on tools. It's also nice to know workarounds are possible if I do have a spinout :p

999zip999 said:
Just get a second T.A
Click to expand...

Will do as soon as I design one/buy one that could work.

Any thoughts on a spacer of this design? I know it wouldn't be a replacement for a torque arm, but it would fill the gap caused by the different radii.... I'd also add a torque arm/plate on top of it. (First part ever modeled in CAD, be kind)

Dropout.jpg
 
zippybike said:
It's nice to know I can make something with just an angle grinder, I'm really short on tools. It's also nice to know workarounds are possible if I do have a spinout :p
Click to expand...
Yes, there are a lot of examples done that way in that torque arm picture thread. Depending on what you start with you can even just use a drill and a set of files, if you have patience. Sometimes you can get lucky and even make something out of existing hardware you havent' even realized you have laying around.
 
From what I see in your last few photos, I'd be a little concerned myself. That axle and washer/nut are almost at the halfway point. It probably won't pop out, but the operative word here is "probably". If it were my bike, I would pull out a simple file and file the dropout enough to make the axle go snugly into it, or at least more snugly than it is now. You have lots of material on the dropout, a tiny bit of filing isn't going to affect the strength.
 
markz said:
Heck, even a wrench would work!
Click to expand...

My thoughts exactly :p

momus3 said:
From what I see in your last few photos, I'd be a little concerned myself.
Click to expand...

I was worried during my first ride, I'd like to have more to grab on to myself. One of the dropouts is 2 pieces of metal bolted together, advisable to file? Looks like it might be getting close to that hole. Here are pictures of both dropouts without the axle:
dropouts.jpg

I decided to take the hub motor off to see if there was any damage, and I did find some marks appearing where the hard angles of the hub meet the rounded dropout:
damage.jpg

I 3d printed my spacer to see how it would fit, it works great but doesn't leave much meat for the axle to grab on to:
spacer.jpg

Thanks for all the replies and assistance, I hope to be back on the road soon!
 
So I've decided to just go with a solid torque plate. It will take a lot of filing to get it to fit the complicated curves, but seems like the most secure option as amberwolf was saying. I'd have one open side and one closed side, here's an example of the open side:

plate.jpg

Any thoughts on where to attach it? I could weld a 90 degree piece to reach the threaded hole located right below the bracket, or I could drill a hole to the right of the axle, or both?
 
You can make both sides closed, for more secure mounting. Put the torque plates on the axle first, then the axle in the dropouts, then bolt the plate to the frame, then put the washers and nuts on the axle and tighten down.

Slightly more complicated to install, but simpler to make as long as you clamp both plates together when making them, to drill and file them perfectly parallel to each other. :)

You should be able to drill thru the dropout area of the frame to bolt the plates to, as long as the screw or bolt doesn't stick thru where the moving bits of motor are, or disc rotor, etc., and aren't in the way of the washers / nuts on the motor axle seating onto the plates.

Thick steel or aluminum works; thicker is better because there's more surface area for the axle flats to apply torque to, spreadng out the pressure.

Make the axle hole as perfect a fit as possible, so ti cant' rock back and forth. Even better if it's so tight you would have to gently tap the plates onto the axle (or even an interference fit, but that's difficult to do by hand). Make sure the hole is shaped like the axle, not the dropouts, but that the flats are aligned with the dropout flat edges.


You can replace the derailer hanger with one of the torque plates, if you can tap the threads for the hanger bolt in the hole for it in the plate. Then use the bolt hole for the hanger in the dropout for the plate.
 
Epic info, thanks for all the tips. The only reason I was going to keep one side open is to avoid snipping off the end of the motor harness, but if it makes it safer I will consider it.

Any advantage in using an axle-shaped hole vs a rectangular one?
 
zippybike said:
Epic info, thanks for all the tips. The only reason I was going to keep one side open is to avoid snipping off the end of the motor harness, but if it makes it safer I will consider it.
Click to expand...
Which connector do you have on the cable? Almost all of them will fit thru a hole the size of the axle, unless it's a really small axle or really huge connector.


Any advantage in using an axle-shaped hole vs a rectangular one?
Click to expand...
There's a discussion about that around here somewhere, but I can't find it at the moment. I don't remember if one was found better than the other. I expect it is a thread started by Justin_LE because he does a lot of experimenting to determine if there's a better way than existing methods, etc., but it could be by anyone, and might even be in the middle of a thread about something else. :( But it's probably about torque arms.
 
If you find that after filing the dropouts , you have what amberwolf describes here , you can go to the hardware store and buy slightly longer caliper mounting bolts ( 6 mm or 8 mm ) and small washers to fit between the caliber mounting surface and the bracket that is bolted to the frame .




amberwolf said:
Filing the dropouts significantly would weaken them, and also change the position of the wheel in the frame, relative to the brake calipers. IF it's far enough upward, it may require a modified caliper mounting bracket to allow using the rear disc brake, as the caliper may strike the rotor's edge.
Click to expand...
 
Sorry for the delays, wanted to have something to show before responding. Decided to do a few shop upgrades, been wanting some metalworking tools for ages.
Press.jpg
Used drill press, but recently refurbished with a variable frequency drive. Super slow is nice.
Saw.jpg
Good ol' HF bandsaw, surprisingly accurate when dialed in

Here's my first test torque plate, missing the small arm that will bridge to the nearby tapped hole
Test.jpg
And here is the fit. Notice how the plate cradles the axle just off the surface of the dropouts. I'm hoping this puts all the downward force along the angled area where the plate meets the dropout
fit.jpg

Any design changes suggested? I'm less comfortable trying a closed design.
 
That is very strong, stronger that I usually make but, you know you need to make both sides, right?
Otherwise, you risk axle twisting and eventually, wheel misalignment due to the weakness of the other side. Well, depending of the power of course.

That is how I like to do. Lighter (1/4’’ thick), with bolt-on mounts to the frame, integrated IS brake mount that permits a different axle positioning (1’’ lower, 2.5’’ backwards) than the original dropouts in this case, for geometry mod and use of a smaller wheel. The swing arm is a Santa Cruz Heckler mod.

203A79DD-F23A-474D-ABCD-61F168BCF892.jpeg
 
MadRhino said:
That is very strong, stronger that I usually make but, you know you need to make both sides, right?
Otherwise, you risk axle twisting and eventually, wheel misalignment due to the weakness of the other side. Well, depending of the power of course.
Click to expand...

I use two torque arms on hubs that have solid axle stubs on both ends. When one axle end is drilled out for cables, I don't bother putting a torque arm on it. It would fail structurally if the other side were to defeat its torque retention. I would use a tabbed washer if I had one, and of course tighten the axle nut properly. But there no point in using a torque arm that would squash the hollow axle if it were called upon.
 
A torque arm is enough in many case, and better used alone. I mean, it is very likely that a double torque arms installation has a slight difference of alignment, simply because it is difficult to attach them to the frame with reliable precision. Thus torque is applied to one of them first and forces the axle to the point where the second does hold.

I quit using torque arms after I had notice damage to one and had to make custom dropouts instead, on the first ebike that I have built. Since then, I have improved the fabrication and precision, and achieved very reliable high power hub builds.

I agree that hollow axles are a weak point that should be avoided in the design of hub motors. Even the common axle channel shouldn’t be. A bigger bearing should be used and the axle should have a wiring channel on its side instead of inside.
 
MadRhino said:
I agree that hollow axles are a weak point that should be avoided in the design of hub motors.
Click to expand...

Or use a large-diameter thickwalled "pipe" axle, whcih could then carry the wires thru it with plenty of room to spare and still be strong...it wouldn't use axle flats to transmit torque. But it also wouldn't fit in bicycle dropouts. ;)
 
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