Custom Waterjet Cut Parts

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Alan B
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Re: Custom Waterjet Cut Parts

Post by Alan B » Dec 11, 2017 4:24 pm

Another program to make part designs that I've been working with is OpenSCAD. I haven't tried it with Blue Saw yet, but it has been doing nicely for my 3D printer. It is free and runs on your own machine locally so you don't have to deal with slow servers and poorly timed updates.

Note - I later did some checking and it does not appear that OpenSCAD can produce a file type that BBS can use.

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Re: Custom Waterjet Cut Parts

Post by Big Blue Saw » Jan 15, 2018 1:53 pm

Here's your early notice: we have waterjet cut aluminum and stainless on sale next week. Be sure to get your designs ready a soon as possible. Read more about it on our website.

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Re: Custom Waterjet Cut Parts

Post by Big Blue Saw » Jan 23, 2018 11:38 am

The sale ends today, January 23, 2018.
http://www.bigbluesaw.com/big-blue-saw- ... steel.html

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Re: Custom Waterjet Cut Parts

Post by Big Blue Saw » Feb 21, 2018 1:48 pm

Next sale is on 5/16 inch thick aluminum and is coming Monday and Tuesday of next week (February 27-28). Upload your designs to order: https://www.bigbluesaw.com/quote .

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Re: Custom Waterjet Cut Parts

Post by cwah » Mar 22, 2018 3:24 am

Could you water jet some pinch or clamping torque arm on hardened steel or something similar?
Help me find my stolen electric brompton: http://bit.ly/1a0vbBC and Bosch Sinus B3 http://bit.ly/1eV0WQz

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Re: Custom Waterjet Cut Parts

Post by Big Blue Saw » Mar 22, 2018 12:07 pm

I'm not sure what you're referring to. Do you have a drawing of the part?

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Re: Custom Waterjet Cut Parts

Post by spinningmagnets » Mar 22, 2018 12:26 pm

Torque-arms are a requirement for a hubmotor. The more powerful the motor, the stronger the torque-arm needs to be. The problem with torque-arms is that they have to fit the bike frame, and there are dozens of variations that prevent one design from fitting them all.

There are several "universal" designs that are adequate for "most" frames and "average" power levels. But...once you spec an odd frame and throw in a powerful hubmotor. You have to draw and order it for yourself.

Here's my take on a pinching TA (https://endless-sphere.com/forums/viewtopic.php?t=74899):

Image

Image

Image

The axle slot is lower than the stock 26-inch wheeled-frame, but...I also moved the new axle location a hair back to reduce wheelies (longer wheelbase) and as a result, the stock chain could go from a 7-speed plus derailleur to a single-speed freewheel with no chain tensioner, just move the axle back in the slot to tension the chain.

Anyone who wants, please copy this, and use or sell as much as you like.

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Re: Custom Waterjet Cut Parts

Post by Big Blue Saw » Mar 22, 2018 12:31 pm

Thanks spinningmagnets.

We can definitely cut hardened steel or heat treated aluminum.

It looks like the torque arm consists of some custom parts plus off the shelf hardware. We could waterjet cut the custom piece if you had a drawing of it.

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Alan B
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Re: Custom Waterjet Cut Parts

Post by Alan B » Mar 22, 2018 1:43 pm

A note for people considering making torque arms or plates from hardened steel - the axles are soft steel, so the torque arm needs to be thick enough to avoid cutting through the soft axle given the force and power level. A hardened torque arm may also be difficult to make "pinch" the axle, the goal here is to minimize free play. Hardness isn't really a major goal. Torque arms are often made from stainless steel to reduce corrosion issues.

Water jetting is a great way to make one, but it needs to fit well, hardening the material makes it more difficult to file or grind the slot for final fit.

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Re: Custom Waterjet Cut Parts

Post by cwah » Mar 22, 2018 2:32 pm

So what should I do? I'm just tired of my nut getting loose all the time.

Ideally I want a torque arm that I can just install on my brake bolt
Help me find my stolen electric brompton: http://bit.ly/1a0vbBC and Bosch Sinus B3 http://bit.ly/1eV0WQz

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Re: Custom Waterjet Cut Parts

Post by spinningmagnets » Mar 22, 2018 4:21 pm

For a 2D shape, I have found that the Big Blue Saw drawing program is actually very easy to use. Its free to use, and free to get a price quote on the part that you've drawn.

I seem to remember there was a video tutorial on the website that was helpful.

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Re: Custom Waterjet Cut Parts

Post by cycborg » Mar 27, 2018 12:16 pm

Alan B wrote:
Mar 22, 2018 1:43 pm
A note for people considering making torque arms or plates from hardened steel - the axles are soft steel, so the torque arm needs to be thick enough to avoid cutting through the soft axle given the force and power level. A hardened torque arm may also be difficult to make "pinch" the axle, the goal here is to minimize free play. Hardness isn't really a major goal. Torque arms are often made from stainless steel to reduce corrosion issues.

Water jetting is a great way to make one, but it needs to fit well, hardening the material makes it more difficult to file or grind the slot for final fit.
So given these considerations, what are some specific steels available from BBS that would work well? I'm considering a non-clamping design, so for me file-to-fit is definitely a desirable characteristic.

Here's the material list.

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Re: Custom Waterjet Cut Parts

Post by Alan B » Mar 27, 2018 2:58 pm

I would select a stainless, they show 316 and 304. Looking at property differences 316 costs more but has marine grade corrosion resistance. 304 is probably adequate. Grin uses 1/4" thick stainless but I don't see a mention of alloy. Thicker would spread out forces more, as does putting one on both sides. I generally use the Grin torque arms, one on each side. But it depends on how much torque your motor has, and what the axle size is. Grin did a lot of testing which is documented here on ES, but their products are intended for normal hubmotors, and might not be sufficient for high power. I haven't done the calculations to determine what is sufficient. We have seen a few cases of really thick torque arms from aluminum alloy working, but that is not a common choice. Any steel should be fine if thick enough.

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Re: Custom Waterjet Cut Parts

Post by cycborg » Mar 27, 2018 3:31 pm

Thanks for the suggestions. Regarding this comment:
Alan B wrote:
Mar 27, 2018 2:58 pm
We have seen a few cases of really thick torque arms from aluminum alloy working
How thick is thick? My TAs will be doubling as spacers - I'm matching a 4 kW QS scooter motor to a swingarm that was built for a somewhat wider dropout spacing. I'm planning on a 5/8" block on each side.

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Re: Custom Waterjet Cut Parts

Post by Alan B » Mar 27, 2018 3:51 pm

Sorry, I don't recall, perhaps some searching can find it. 5/8 on each side sounds pretty thick.

Here's one thread on aluminum torque plates.

https://endless-sphere.com/forums/viewt ... e#p1133943

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Re: Custom Waterjet Cut Parts

Post by cycborg » Mar 28, 2018 8:55 am

Alan B wrote:
Mar 27, 2018 3:51 pm
Sorry, I don't recall, perhaps some searching can find it. 5/8 on each side sounds pretty thick.

Here's one thread on aluminum torque plates.

https://endless-sphere.com/forums/viewt ... e#p1133943
Thanks - I had seen Ron's "universal" design but didn't realize it was Al. That prototype is 3/8", so 5/8" seems reasonable for my application.

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Re: Custom Waterjet Cut Parts

Post by spinningmagnets » Mar 28, 2018 12:29 pm

When I am doing rapid protoyping, I often do much of my initial work with 1/8th thick fiber board (can cut with a razor), aluminum (1/4 inch, 3/8ths), plywood, etc...They are easy to cut and test, then move on immediately to Version-2.

Although some materials can be laser-cut, I like 304 stainless steel with a substantial thickness for a long-lasting part, once I'm satisfied with a particular design. For that, water-jetting works well, it provides a nice finish and no heat-warpage.

Bear in mind, heat-treated 7000-series aluminum is as strong as the softer grades of steel, but lighter. Using a water-jet doesn't add any heat, so the heat-treatment is perfectly preserved. Aluminum is fairly easy to cut and drill in your own garage, but when I'm feeling lazy (or I just don't have the spare time), water-jetting aluminum might be the best material and method for a certain application.

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Re: Custom Waterjet Cut Parts

Post by Alan B » Mar 28, 2018 3:32 pm

Just comparing 6061-T6 to 304 steel, in most characteristics the steel is 2-3x better than the aluminum. Tensile stength is about the only property where some aluminum alloys approach the steel, however in the case of a flatted steel axle exerting force on the slot in a torque plate we aren't operating in tension, we are operating in material deformation which is a shear property where the steel is 2-3x better.

I'm not an ME, but I think in this particular use-case (the axle slot in a torque plate) that the 304 has significantly better performance than the 6061. But if enough 6061 is engaged with the axle it should do the job. 5/8 wide aluminum on both sides sounds like a lot, but it may only be equivalent to two Grin standard torque arms.

I've used a lot of 6061-T6 and it is great stuff. The 7000 alloy material is amazing, but it is very brittle and not that easy to work with. Of course waterjetting it would be fine, that's basically a cold grinding operation. I haven't tried drilling holes in 7000, it is a challenge drilling in 6061 but it machines pretty well with sharp tools and appropriate lubrication.

https://www.makeitfrom.com/compare/6061 ... less-Steel

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Re: Custom Waterjet Cut Parts

Post by spinningmagnets » Mar 28, 2018 4:30 pm

There were certain applications where I needed "X" amount of strength, in a plate that was as thin as possible. In those cases I went straight to stainless steel and water jetting.

My concern using stainless on torque plates was how the axle steel was actually softer, and extra thick SS is expensive...thin SS might wear into it with heavy regen. I didn't want to experiment because it would take time and money.

If your torque plates are on the outside of the frame, and you have plenty of axle length...common carbon steel is more affordable, but extra thick aluminum is easy to cut when prototyping. Thick steel is good for the final product, but thick steel is a real pain when prototyping to cut, drill, and tap threads...

I guess the type of material and thickness also just depends on how much power you'd be using...

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Re: Custom Waterjet Cut Parts

Post by Alan B » Mar 28, 2018 4:52 pm

One advantage of the aluminum torque plates is they will take the damage before the axle does. If you keep a close eye on them and do careful testing, increasing the torque gradually, you should be able to see damage before a failure. Hopefully.

If the stainless or hard steel torque plates are not thick enough the axle will take the damage, and you will have to replace an axle. Which can be done but might not be fun.

If it were my ebike I would figure out how to do the calculations, or find a mechanical engineer who could do them, and have some idea of what might happen.

I think there are a few ME's around ES, perhaps one of them could make a thread on doing this calculation. I think it is pretty simple, but I don't know all the details at this point. Knowing the torque and radius/width of the flat should lead to a pressure estimate to compare to shear strength...

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Re: Custom Waterjet Cut Parts

Post by Buk___ » Mar 29, 2018 2:54 am

Alan B wrote:
Mar 28, 2018 4:52 pm
One advantage of the aluminum torque plates is they will take the damage before the axle does. If you keep a close eye on them and do careful testing, increasing the torque gradually, you should be able to see damage before a failure. Hopefully.
The problem with aluminium for this is that it age hardens. Even if it has sufficient ultimate shear strength and area of contact to resist the maximum calculated torque, over time the material will embrittle to the point were the next peak loading will cause it to fail catastrophically, even if there were no visible signs of damage.

The problem with calculating this, is that the points on the tips of the threads where the axle flats are cut, give rise to point loadings which are -- at the extreme -- infinite:
pointLoads.jpg
pointLoads.jpg (26.94 KiB) Viewed 198 times
With aluminium's ultimate yield strength being anything from 50% to 5% of that for stainless or low carbon steel, it requires a considerably larger surface area to resist the repetitive point loadings.

The two best things you can do, regardless of your frame or torque plate material is:
  • Carefully. lightly radius the points of the threads where the flats cut through them, in the area that will contact the frame/TA.
    .
  • Ensure as small a gap (green above) as possible.

    If necessary, shim that gap with something tough but ductile and cheap enough to replace often.

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Re: Custom Waterjet Cut Parts

Post by Alan B » Mar 29, 2018 8:04 am

This is a for sale thread on blue saw's waterjet cut parts. This discussion should probably be moved elsewhere.

Steel is the safe choice. There have been so few aluminum torque plates that we don't have a lot of collective experience with them, but I'm not aware of any failures of this type in this application. It is not a simple shear situation, if the tips of the threads cause a local failure and the axle rotates slightly into the thick aluminum the forces are spread and new, unstressed aluminum is backing up the failed areas. So I would expect that it would mark the aluminum and find a new equilibrium if the torque peak is brief. This would appear to be a different situation than the usual where the materials fail and there is no backup material to take the load.

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Re: Custom Waterjet Cut Parts

Post by Buk___ » Mar 30, 2018 6:11 am

Alan B wrote:
Mar 29, 2018 8:04 am
This is a for sale thread on blue saw's waterjet cut parts. This discussion should probably be moved elsewhere.
S'fine. Move it anywhere you like including the bin. I tried to delete it, but it won't let me.

(I wish I had a copy of just one of the half dozen reports I've co-authored on aluminium failures due to work hardening. All catastrophic; two fatal.)

See also: Work strain hardening and brittle failure.

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Re: Custom Waterjet Cut Parts

Post by Alan B » Mar 30, 2018 6:55 am

Clearly aluminum can fail, and it can succeed (aircraft seem to be successfully made from it, as well as bicycles). If you have the professional credentials to evaluate this particular situation please state that, and it would be good to show scales on your simulations as well as share your assumptions for torque, axle dimensions, etc. How does the failure propagate when partial failure results in a large increase in the volume of aluminum involved in the interactions?

To be clear, I'm not recommending aluminum torque plates. The people who have used it have not reported failures, but I think the sample is small. All the commercial products I'm aware of seem to choose stainless or or other steels (though many of them are NOT thick enough, however they are made for standard low-torque hubmotors, not high powered units). It's up to the user to choose. Compared to front fork lips a pair of 5/8" thick 6061-T6 torque plates would seem to be very substantial, and the failure mode in a rear axle is significantly lower risk than a front fork failure, or most other bicycle frame failures, as the result is the axle spins, severing and shorting the motor wires, and blowing the controller. Spun rear axles generally do not result in loss of the rear wheel. Front spun axles are far more serious, but this appears to be a rear axle application. I certainly don't recommend taking any risks in a front wheel application, myself I replaced the alloy front forks in one bike with steel forks when adding front wheel drive making a 2WD bike. I have used 6061-T6 torque struts without problems, but they are at a much larger radius than the flats of the hubmotor axle and the stress is within rated limits there.

To the potential user, it is fair to state that there is at least some concern about using aluminum in this application.

Perhaps Ron can help us move this discussion to a more appropriate place than Blue Saw's for sale thread. We can move existing posts so the end result will be a clutter free for sale thread with a link to the new discussion, if that is the chosen plan.

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Re: Custom Waterjet Cut Parts

Post by Buk___ » Mar 30, 2018 11:34 am

Alan B wrote:
Mar 30, 2018 6:55 am
Perhaps Ron can help us move this discussion to a more appropriate place than Blue Saw's for sale thread. We can move existing posts so the end result will be a clutter free for sale thread with a link to the new discussion, if that is the chosen plan.
See https://endless-sphere.com/forums/viewt ... 1#p1368746

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