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An unfortunate learnt something new lesson

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savarin

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As some will know I have been doing a lot of straight knurling in stainless steel of late.
I use a cam jack knurler to really apply the pressure required to get full depth knurls with no double tracking.
I'm very happy with the results but learnt a valuable lesson unfortunately the hard way the other day.
I wiped the finished knurl along its length with a rag to get a good look at it and all was well untill I picked up another tool whereupon I felt the splinters in my thumb that had gone clean through the rag.
BUT, I couldnt see them or even feel them lightly passing a finger over where I thought they were.
Nope, they hadnt gone, just so fine they couldnt be seen.
Even with a 10x loup I could barely see them, I swear they were finer than prickly pear hairs and even more irritating.
I checked a couple of the finished knurls that still had oil on them and there they were, long but ultra fine hair like swarf sitting in the grooves.
I usually use a very thin oil for lubricating the knurling and I think this flushes the fine swarf out but this time had run out and used a thicker oil.
A good wash got rid of them and the ones in my thumb appear to have eventually worn away.
 

T Bredehoft

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Fortunate you are that the wires in your thumb didn't stay behind to cause problems.
 

WCraig

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I've never knurled (is that a proper expression?) but I'd like to know more. I think I saw a video where the presenter brushed the freshly knurled and still rotating part with a stiff brush. I believe this was to knock off any swarf and such splinters. Is this a good approach?

Craig
 

NortonDommi

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WCraig, yes it's a good idea. I have a short narrow scratch brush that gets run over a fresh knurl running at slow speed then in reverse.
Savarin, #metoo.
 

savarin

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For cross hatch knurles I usually use a wire wheel running along both diagonals in a drill whilst the part is rotating first one way then the other.
This removes all the sharp edges. I havnt done it to these straight ones this time because they are quite small.
I will do next time.
 

mmcmdl

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One of my first experiences with stainless splinters was jumping up and sitting on a bench where someone was cleaning up welds with a carbide burr bit and die grinder . You won't make that mistake twice .
 

cathead

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Have you ever noticed that sometimes a knurl just doesn't cooperate very well? I have found that certain diameters
work better than others. If I am having a problematic knurl, I will machine off a couple thousandths and try again. Usually
it goes better on the second try tracking better and producing a nicer knurl. In theory, knurling is not a machining operation
but rather metal forming.

Savarin, sorry you got the splinters. We have all been there and it isn't much fun. That needely stuff is the worst.
 

BGHansen

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Savarin,

So glad to hear the outcome was just splinters. I started to cringe when I read "rag" and "knurling", was sure hoping the two didn't meet while the lathe was running. Thanks for the tip on the splinters.

Bruce
 

Superburban

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Have you ever noticed that sometimes a knurl just doesn't cooperate very well? I have found that certain diameters
work better than others. If I am having a problematic knurl, I will machine off a couple thousandths and try again. Usually
it goes better on the second try tracking better and producing a nicer knurl. In theory, knurling is not a machining operation
but rather metal forming.
Somewhere there is a math formula that takes into account the spacing of the knurling tool, that gives you the best diameter to start with to get a perfect knurl.
 

Shootymacshootface

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Sometimes you have to wait 2 or 3 days for the splinters to turn black to find them all. I know that you said that you were working with stainless. I would expect that to darken as well, unless it's a higher grade of stainless steel.
 

NortonDommi

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Somewhere in one of my safe places I have that formulae for knurling. Had a quick look through some old stuff and found an old article about knurling that might help someone. I'll see if I can find that formulae.

PopSciMech_2_262.jpg

PopSciMech_2_263.jpg
 

ch2co

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Thanks for the warning, Savarin. I woulda never guessed it. Havent seen this problem with all the aluminum and brass that I've knurled.
 

savarin

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Bruce, the lathe was stopped so I just ran the rag along the length as it was a straight knurl, I dont do that to cross hatch knurls. as you said, the thought of a rag caught up and spinning is a tad scary.
Shootymacshootface, they've turned black today, cant feel them but there they are just laying under the skin. 2 left.
I used to use the formula to turn the piece to the "correct" size but now if I see double tracking I just crank down harder till it looks correct. I dont think I could have knurled this stainless with a conventional (push) knurler.
 

MSD0

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As some will know I have been doing a lot of straight knurling in stainless steel of late.
I use a cam jack knurler to really apply the pressure required to get full depth knurls with no double tracking.
I'm very happy with the results but learnt a valuable lesson unfortunately the hard way the other day.
I wiped the finished knurl along its length with a rag to get a good look at it and all was well untill I picked up another tool whereupon I felt the splinters in my thumb that had gone clean through the rag.
BUT, I couldnt see them or even feel them lightly passing a finger over where I thought they were.
Nope, they hadnt gone, just so fine they couldnt be seen.
Even with a 10x loup I could barely see them, I swear they were finer than prickly pear hairs and even more irritating.
I checked a couple of the finished knurls that still had oil on them and there they were, long but ultra fine hair like swarf sitting in the grooves.
I usually use a very thin oil for lubricating the knurling and I think this flushes the fine swarf out but this time had run out and used a thicker oil.
A good wash got rid of them and the ones in my thumb appear to have eventually worn away.
I spend at least half an hour every week under a microscope with a scalpel blade and tweezers digging splinters out of my hands.
 

Asbestos

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When I was much younger I had a job at a Borg-Warner plant taking apart pieces of transmissions. we did this for about 3 weeks. About 4 days after we were done I woke up with one hand that was about 2.5 times the size of the other. It did not hurt but it was so swollen that I could not shut it. Doc poked around and pulled out a tiny metal splinter I did not even know was there.
 
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