Knurling tool build

rwm

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I have a poor quality pinch type knurling tool that so far has not done well. I believe the machine that cut the arms was out of tram and the arms are crooked. After looking at prices I decided to make my own.
I am thinking about something like this:

1583545762253.png

To get started I bought these:

1583545839928.png

1583545853758.png

My plan is to make this tool kind of like a Kant Twist clamp. I will have a 3/8" thick piece on the inside and 1/4" arms on each side of that.
So I have an issue I need guidance with. My original plan to hold the knurling wheel was to braze or weld flat pieces on the sides of the 3/8" arm and then cross drill these. (The knurls are 3/8" wide.) Welding is not a great option due to inevitable warp and the fact that the inside of the slot is inaccessible. I tried a test piece with silver solder but I could easily make the joint fail with a wrench. Would brazing be stronger? If so, what rod and flux for mild steel? I have bronze rod and nickel silver. How can I get the braze material to flow into a joint between flats? Should I "tin" each piece first and then joint them?

Robert


EDIT for completion:
I will add the prints to this first post to make them easy to find. These may get revised over time. The prints for the 1/4" CRS parts are 1:1 so you should be able to print these on paper to duplicate the cuts.
(Rev 3/26/20)
1585011783835.png
Robert
 

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brino

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Sorry I have no answers/advise, but....... oh boy, oh boy oh boy.......I am looking forward to this build!

popcorn3.gif

Thanks for sharing it!
 

mmcmdl

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I made a very nice scissor type knurler years back . I still have it and sold the Eagle Rocks . This one was made from solid Almar and heat treated . A very keen eye spotted it on one of my threads recently . :grin: I like the Kant Twist clamp style also , lot easier to make .
 

rwm

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The one I posted above is Accutrak. I think it is machined out of solid stock. After I saw the pic my brain clicked on and said "Kant twist".
Robert
 

C-Bag

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Nice render. I would think pinning and bolting the wings would do it. Or get a piece of 1 1/2" thick steel plate and mill it ;)
 

rwm

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My toy mill is not going to be able to cut that slot. Hence plan B. Plus that is a lot of steel to subtract.
I just made a test joint using nickel silver. It flows at a much lower temp and made a very solid joint. That may be the way to go. My brazing rod is coated with blue flux. Is there a specific flux I could/should put inside the joint in addition?
Robert
 

C-Bag

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I'm not an expert welder but I've done a lot of different kinds of welding, brazing and soldering. But not a lot of silver soldering. I just got a stick of silver solder that has blue flux too and it did not flow like my buddy described. But he also told me the usual braze flux would work and it didn't flow either but I got patches to at least stick. So I looked online and everybody seemed to like Harris STA-Silv black flux so I ordered me a tub. Not tried it yet so dunno. But I'd rather braze something like that. I'm not sure if it was tig welded it would warp that much.
 

rwm

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I have the Harris black flux and the white. So far better luck with the white. I don't think the 56% silver solder will be strong enough. The nickel silver rod is tough stuff.

I have another design problem. If I attach the wings I will have no way to put in the pivot for the screw. (It would go in the upper holes above.) I could make those holes .375 and just slide a cylinder in there but that would limit the size of the screw I could use. I was planning on a .375 screw but I may have to use .250? That would be kind of wimpy for this. I may have to redesign. Thoughts?
Robert
 

rwm

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Upper pivot could look like this:

1583590875298.png

This would go into the top holes above. It is only 3/8 diameter. It would fit a 3/8 screw on the flats with a 3/16 guide that could have a C clip on the backside? Pivot is not super strong but should carry the load? My original thought was brass but maybe I will go with steel for strength.

Robert
 

John O

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How does this type knurler work?
To me it looks like the upper wheel is fixed to the tool post needing the tool post height adjusted for top wheel height. When the lower wheel is tightened it will push the work up.
Should the top wheel be pivot as well?
 

rwm

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Outer arm (2):

1583591852662.png

I'm just guessing at dimensions here. I think I will cut these out of cardboard and play with them. I could model the assembly in Fusion if I were a real machinist!

Robert
 

rwm

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How does this type knurler work?
To me it looks like the upper wheel is fixed to the tool post needing the tool post height adjusted for top wheel height. When the lower wheel is tightened it will push the work up.
Should the top wheel be pivot as well?
The "bolt" in the center is a pivot for both arms. The center height does not have to be perfect. The straight part that goes into the tool post is not fixed to the upper arm. See this:
1583592120758.png
Robert
 

rwm

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Before I start building this thing I would appreciate any comments you may have for improvement especially if you see something that won't work! Any suggestions other than Nickel Silver brazing?
I may or may not take your suggestions but all are invited!
Robert
 

DavidR8

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@Rvm you’ve got some mad modelling skills!


Sent from my iPhone using Tapatalk
 

rwm

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Fusion 360 is awesome. I'm a total beginner. Notice I didn't put the screw in there between the pivots....
R
 
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mmcmdl

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Fusion 360 is awesome. I'm a total beginner.
That gives me hope ! :grin: You seem to have it down , I haven't used CAD in 20 years now . We had UG back at the DOD shop . One of these days I would love to have the time to try the 360 out . Your models are looking great Robert . :encourage:
 

rwm

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First part:

1583676170715.png

It's a fail. The hole is way off center because the drill must have skated :bang head:
I center punched, spot drilled and then drilled the hole. It is worse than the pic shows and too far off for me to be happy. My scrap pile is getting larger! Without a mill, I am also going to have trouble with the 3/4" holes in the arms. I may have to reduce the size of those or bore them on the lathe. I think making a fixture and using the lathe may be the best solution.

Robert
 

rwm

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So I just realized that the lower arms are about 1/4" too long to swing on my lathe :bang head: . Do I redesign?!
Robert
 

C-Bag

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I don't expect you'll see it my way but progress, not perfection. I'd use that first part and if it offends your need for perfection I'd trim the outside to center the hole a little. As long as the knurl wheels are in line with each other and track together the esthetics don't matter on a prototype. Just because a company makes something doesn't mean they made it perfect the first time. And I'll bet you $$'s to donuts they have a pile of prototypes that got tossed.

I was very frustrated with my old HF benchtop DP until I bought one of the cheap XY tables for it. NOT for milling but to be able easily adjust my clamped parts to get right in the center of my mark. Also using screw length drill bits instead of jobber length drills has made a world of difference. I've learned the weak spots in my layout and how to minimize the errors.
 

rwm

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I just redesigned the lower arm to be about 0.3" shorter. Took me about an hour but I am learning a lot about fusion. This design change allows me to swing the part on my 10" lathe. Otherwise the 3/4" holes would not be possible. I know the upper arm I made will work but I will probably remake it at some point. Here is the new drawing:

1583684887032.png

Robert
 

rwm

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Problem number next. I learned the tolerance on flat steel is 0 to -.006. Mine is .369 thick. That will be a problem with the knurls which are .3745. Anyone got a small piece of metric 10 x 25 flat bar they can part with? I can machine that down to .0375 easily. If not I know McMaster does!
Robert
 
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