Knurling tool build

rwm

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My plan to hold the knurls is to use a shoulder bolt with 1/4" shoulder. The head is 3/16" high. I think I can counterbore it 1/8" deep. Then I will have only 1/16" head showing or I can machine that off.
For the center pivot, I plan to machine a bushing 1/2" OD with a lip on the outside. This may be brass? I will center drill this and use a 5/16" screw into rectangular bar that will be held in the AXA tool holder.
Any better ideas welcome.
Robert
 

rgray

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My plan to hold the knurls is to use a shoulder bolt with 1/4" shoulder.
On knurlers I've built the axle for the knurl wheel takes a lot of abuse. I've built with O-1 tool steel which was then hardened and it was not good enough for the pressures of knurling. All mine now have hss axles.
the one for my manual lathe has small button head screws in the knurler body that retain the axle. They are in parallel with the axle, just off to the side so the head of the screw keeps the axle in.
The two for my cnc lathe have a groove ground in the hss and a single 4-40 flat head screw each retaining them at 90 deg or up and down where axles are horizontal.

When the axle is to soft and wears from knurling pressure it is then a problem to remove as metal is displaced and a groove ground into the axle.
 

rwm

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Wow, that is good to know. Maybe I should scrap my plan. How about using 1/4 drill shanks? Is the shank of an HSS drill hard? What about carbide?
Robert
 

rgray

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rwm

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I will plan to use an HSS axle of some type. I think I will not drill one of the axle holes all the way through and them use a small screw to hold the axle in place. I have some 10mm steel on order as well as some 5/8 keystock for the holder.
Robert
 

Cadillac STS

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Once you get it all sorted out why not upload the CAD files of the parts you worked on. That way someone with CAD/CAM software and a mill could load them in the system, make some G-Code with a post for their machine and make the parts.

I hope one or more do that with this simple project and post pics of the results!

Would be a nice way to share the work and let someone show off their CNC milling capabilities...
 

rwm

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I plan to upload prints if this is successful.
Robert

Yes, I could make the CAD file available.
R
 
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rwm

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I revised the drawing to get a better angle for the tensioning screw:

1584154852137.png

1584155526907.png

I think this is near final design version. Any ideas?
Robert
 
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rgray

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I think this is near final design version. Any ideas?
Robert
Maybe it's just the way the pictures look, but it appears like the original had a longer distance from the pivot to the pressure bolt fitting.
Where as your latest appears like the longer distance is from the pivot to the knurl wheel. That would give the pressure screw much less leverage.
Maybe it just appears that way to me. And maybe it would make little difference.

Also wanted to mention that when cutting hss blanks(or carbide) I just score them with a dremel cutoff wheel and then put them in a vise and break it off with a hammer. Saves time , brakes pretty cleanly, and avoids getting the piece so hot.
 

rwm

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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
 

petertha

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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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rwm

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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
 

petertha

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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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bretthl

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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
 

rwm

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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
 

rwm

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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
 

bretthl

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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.
 

rwm

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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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mmcmdl

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

bretthl

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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 may not be helpful - I snagged them from a set of mountain bike brakes I swapped out. I sort of wound up designing the width of the arms around those screws. Look at Bolt Depot online, they give detailed dimensions of their screws. If I recall knurls are about 3/8" wide with a 1/4" hole so something like this may work https://www.boltdepot.com/Product-Details.aspx?product=5031.
 

mmcmdl

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If that's what he needs , I'm staring at 10,000 of them . :grin: Robert , I have all sizes , if you need some let me know before 7am . I'll throw them in an envelope .
 

rwm

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If that's what he needs , I'm staring at 10,000 of them . :grin: Robert , I have all sizes , if you need some let me know before 7am . I'll throw them in an envelope .
That is very generous!
One question here: I know a 1/4" screw is not really .250". They are usually undersize. Would it be better to have the correct size axle? could the knurl wheel be wobbly?
R
 

mmcmdl

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Shoulders are .249 so you'll have a thou clearance .
 

rwm

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Shoulders are .249 so you'll have a thou clearance .
Ok then! I need the un-threaded length to be .625 minimum. .750" would be perfect. The smaller the head the better. Those mountain bike screws sure look nice. I will PM you my address!
Many thanks,
Robert
 

mmcmdl

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How many ? I have .750 body lenghts in hand . :grin:
 

rwm

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How about 3 so I have an extra for a Mulligan?!
Robert
 

mmcmdl

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I grabbed 20 or so . We throw them out by the buckets :)
 

rwm

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Don't go crazy! I will measure the best 2 and use them. I sent you a PM.
Also...first part (OK really second attempt at first part)

1584240686801.png

No chamfers!
I fly cut it to .378 but the thickness varies from .375 to .379. Should be adequate. I am not sure if my tiny mill is out of tram or I had a chip under the vice or what?! I also had a crash recently so I could have knocked the tram off.
Robert

Edit: I should note that the hole is actually centered and has been reamed to .500!
R
 
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rwm

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Another idea:

I have an aluminum dovetail that I made for my AXA toolpost. I am thinking of mounting this tool on that part instead of a regular tool holder. With one less interface the geometry should be better. I don't see a lot of force on the center pivot so I am thinking aluminum will be OK in this application. Otherwise I have a piece of 5/8" keystock (shown above.) What say ye?
Robert
 
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