Knurling tool build

The center pivot is almost the same distance from the threaded pivot as it is from the knurling wheel. I feel like that will be fine. I wanted to keep the screw as short as possible so that it wouldn't flex. Thank you for the tip on cutting HSS! I will use that!
Robert
 
My gut feel if I understand the assembly is that this 'T' joint (orange sketch) is going to be a weak spot because its a relatively small surface area and all the shear force of the tension screw (which is considerable) will be concentrated here. How were you contemplating joining the components?

One idea if you wanted it to keep it 'components' focused vs. entirely milled from solid stock or brazed or something, is to extend the outer sandwich segments a bit (green sketch). That will give you more contact area &/or allow for pins or cross bolts or something. You will have to prove out the scissor action based on diameter range, probably cant go quite as close to the center action as I've sketched.

The scissor knurlers I've seen are made from pretty tough stuff. Part of the reason why clones or pseudo-knockoffs give so-so knurling results is they lack rigidity & flex under load, even when good knurl wheels have been swapped in. This can be from combinations of arms, axles, mating surfaces... Anyways my advice is err on the side of more meat = more stiffness & good sliding fits on everything that moves.
 

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Thanks Petertha. I was worried about weakness at this joint. As a test, I first silver soldered together two pieces of mild steel with similar overlap to my design. This joint easily failed with a wrench on one piece. I then used Nickel Silver rod and brazed them together. I clamped one piece in the vise and beat the other with a hammer in the "shear" direction. The metal deformed from the hammer but the joint held! Your idea is sound, however. At present, I do not have the capacity to do the milling (that will soon change!) from solid steel. If the current plan proves too fragile, it will not be too hard to re-make the arm in question on my soon to be new mill.
Robert
 
Just more food for thought. With a drill press you could insert alignment/shear pins like so. Not sure if in conjunction or to replace silver soldering.
I've shown what might have to be the corner lopped off to accommodate the scissor action if necessary.

Why do the corners of the center bar have to be chamfered like you have? I don't see that they interfere with anything
 

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I built this type last year and it has worked well. Need to design for some serious side forces and have a decent tool holder. I wouldn't get too caught up in the fasteners, just use hardened caps screws.

knurling tool 1.jpg

knurling tool 2.jpg
 
Very nice work! I have a cheap version of that. Are your knurling wheels running on the threaded part or is that part unthreaded?
Robert
 
Just more food for thought. With a drill press you could insert alignment/shear pins like so. Not sure if in conjunction or to replace silver soldering.
I've shown what might have to be the corner lopped off to accommodate the scissor action if necessary.

Why do the corners of the center bar have to be chamfered like you have? I don't see that they interfere with anything
The corners may not have to be chamfered. I originally designed like that because I didn't know how much clearance I would have. I will check on the CAD.
I plan to use at least one temporary hole and screw to fasten the wings for brazing. Your idea with 3 would no doubt be very strong.
Robert

1584232128032.png
 
Very nice work! I have a cheap version of that. Are your knurling wheels running on the threaded part or is that part unthreaded?
Robert

Unthreaded. I cut down a pair of longer cap screws to align the unthreaded portion with the knurls.
 
Great idea! Consider it stolen. Can you give me a source or part number? I am having trouble finding screws with the correct unthreaded length. McMaster is not very specific about this. I would not want to try to thread a hardened screw.

This view removes one of the wings so your can see the knurl wheel. No interference issues without the chamfers.

1584232518022.png

Robert
 
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Robert , I scrap 1000s of grade 8 bolts every week . What do you need ?
 
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