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Tom wrote: Sun Apr 09, 2023 10:47 am
Thanks, McMaster is always my first go-to. Love that place. Order by 4 and its on my porch by 10 the next morning. I did look at those when I first started hunting and wondered how 'twice as strong as ss' compares to the bolts I now have, and the tool does better with fully threaded bolts. I assumed real grade 8 bolts would be easy to find, so kind of forget about those. But so far they may be the most promising yet.
So, according to McMaster 316 SS = 70k tensile strength psi, 18-8 SS = 80k, and the alloy steel are 130k.
Thanks for that. When I switched from 316 SS to 'regular' bolts, they were very noticeably stronger. Now I'm wondering how "normal" bolts (grade 5?) bolts compare to that alloy bolt? The bolts I now have are probably stronger than the plastic, so my hunt for the grade 8 was mostly out of curiosity to see how strong I could make it. If that alloy is stronger than a grade 5 bolt, I may give them a try.
One of the previous cars was a very early Europa type 46, and that car used the half-shaft (with u-joints!) as a stressed member of the suspension. The connection at the gearbox was a splined yoke, and it used a pair of concentric roll pins to hold it in place. It was definitely a bit of Colin Chapman "added lightness" at work. Fast-forward: You can fit a dry-ice frozen/shrunken 1/4" roll pin through your plastic, and let it expand warms up to a tight fit. Then fit a smaller pin inside the first one to add shear strength and additional tension to the outer one.
Another option is to use an actual grade-8 1/4" capscrew, and grind the threads to the exact diameter your sprocket demands.
For some industrial applications, I've made larger three-pin tools that engage the 'teeth' on the sprocket. I use larger pins, and do a little work on them to fit in the recesses on the sprocket OD. ASSumes you don't have a belt or chain installed already around the teeth. The tools are always made with a cross-bar rather than the single-handle you are showing, and when made in metal I put a 1/2" square relief in the middle to use 'real' drive tools.
Next option is a tool that's like a strap wrench with a piece of old timing belt instead of the flat rubber typically used. Same deal -- works only when there isn't a belt already wrapped around the teeth.
Is there an industrial-sized filter wrench that fits your over your sprocket? With round pins added inside to engage the teeth on the sprocket? Or filled and with pins as you are showing to get the drive side of the tool already done.
Roll pins through an aluminum ring spanner? Plastic is fun and you have the tools to make things, but a metal ring spanner will easily hold spring-steel roll pins without risk of distorting the tool.
If you need something stronger and commonly available, how about using two hex wrenches instead of the 12-24 screws? A #12-24 screw is 5.6mm diameter, so a 5mm hex wrench should be close to the right size. You'll have to test fit and see what fits in the holes of the balancer sprocket.
Thanks for all the suggestions! Re one of dr. bob's thought, I'm actually working on a flywheel lock that engages a lot of teeth on the flywheel to see if I can come up with a plastic tool that holds 155 ft lbs at the front pully. I figure if there is roughly 300 pounds of force on the outer edge of the flywheel, if I spread that over enough teeth/contact area, maybe plastic can hold up.... My mechanical engineering degree is from YouTube, however, so I'll rely on a lot of testing for that.
As for the pin wrench, I love the Allen key idea. I'm sure I could make a metal pin wrench in metal without 'too' much trouble, but these 3D printed plastic tools are partly a design challenge for me -- with the primary goal of creating parts people can replicate locally with easy to find parts. Allen keys are available everywhere (more so than 12-24 screws even), and hardened, and even come in 5.5mm -- so seem like a great idea!! I'll give that a try at some point and report back.
