Knurling Help Needed

This topic has 7 replies, 6 voices, and was last updated 15 October 2011 at 22:32 by JohnF.

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14 October 2011 at 21:57 #5704
Hugh Gilhespie
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@hughgilhespie56163
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14 October 2011 at 21:57 #76300
Hugh Gilhespie
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@hughgilhespie56163
I managed to acquire some
rather battered Dickson S2 tool holders recently. They were missing various
bits, including the height adjustment thimbles and so I have been turning some
new thimbles from 7/8^th silver steel. Everything was going
swimmingly – I even managed to find a decent 3/8^th BSW tap for
threading the thimbles in the odds and sods box – and the first one I made was
lovely. However, on the next three the knurling was awful! I used an old Jones
and Shipman two wheel ‘push-in’ type tool that usually gives good results.

As far as I could, I used
exactly the same procedure for knurling all four thimbles. Lashings of CT90
cutting fluid and as far as I can judge, about the same amount of pressure for
cutting/deforming.

So, what arcane knowledge
of knurling am I missing? Do I need to shake hands with bent fingers, mutter
magic incantations or what? Every time I
think I have made some progress with this machining malarkey summat turns round
and bites me.

Any and all advice
gratefully received.

Baffled of Brixham
14 October 2011 at 22:38 #76301
NJH
Participant
@njh
Hi Hugh

|”Do I need to shake hands with bent fingers, mutter

| magic incantations or what “

Yes that might help but I’ve always had much better results with the clamp type knurling tool !

Regards

Norman
14 October 2011 at 22:44 #76303
Clive Foster
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@clivefoster55965
The first one being good and subsequent ones poor suggests that a bit of swarf has become embedded in one of the knurls, lashings of cutting fluid reduces the chances of this happening but its advisable to check and scrub between jobs.

Verify that both knurls are spinning freely. Lots of pressure on small bearings so older units will be worn and can drag badly. Especially after Lawyer Murphy has inserted a couple of small pieces of swarf in positions exquisitely chosen to maximise problems.

I have a two wheel push knurl tool made by Pratt & Whitney of slightly unconventional configuration which seems rather better behaved than the usual sort. As usual with this style of tool the knurl carrier is pivoted so as to equalise the pressures on each however the pivoting arrangements are offset vertically so that one knurl contacts the work pretty much on centre whilst the other is pulled upwards onto the work. In the conventional tool the knurl carrier pivots pretty much on centre height so one knurl is above centre and one below. If the forces don’t balance out pretty well right from the start you have problems with the conventional tool. In contrast the P&W version is clearly unbalanced when you start but rapidly pulls itself in to making equal depth knurls. Its also tolerant of a nervous approach, standard practice with the conventional system is to be very firm when engaging.

That said I find that a hand held, “nutcracker style” three wheel tool gives good results without arcane practices or extreme verbal encouragement despite a rather low rent appearance. The two wheel clamp down type are generally well spoken of too. Both of these have the advantage of removing the heavy forces from the lathe. Important as many of the lighter machines aren’t really strong enough to generate the heavy shove needed to hold a knurling tool up to the work.

Clive
15 October 2011 at 10:49 #76316
KWIL
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@kwil
Just a simple question, why use silver steel? It does not deform as well as BMS.
15 October 2011 at 16:53 #76329
colin hawes
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@colinhawes85982
I agree with Kwil knurls work best on soft steels.

Colin
15 October 2011 at 19:14 #76338
Hugh Gilhespie
Participant
@hughgilhespie56163
Hi Chaps,
Thanks for the advice. Norman & Clive, I do have a clamp type knurl tool that I bought from ArcWarcoChronoRGDtrade but it is so badly made that it is virtually unuseable. I guess the answer is to make one myself to suit .
Ken – In best mountaineering tradition, because it was there! I happened to have a length of 22 mm silver steel that wasn’t doing anything so into the lathe with it. I did have some ideas about hardening the height thimbles until I actually thought about it and realised it would be a complete waste of time – difficult to think of a part that has less stress than these.
Regards, Hugh
15 October 2011 at 22:32 #76347
JohnF
Participant
@johnf59703
Hi Hugh,

Agreed soft materials do knurl easier but you should have no difficulty with silver steel. Knurling is not an exact science and the fact that you are using S2 tool hoolders suggests that you have a fairly substantial machine so a straight feed tool should not cause you a problem.

I use a Marlco pinch type tool [on my Myford] and I think these are one of the best available but when in industry most knurling was done with a tool similar to yours. I always found it best to feed in from the front of the work–as if you were making a cut with a tool–with the tool set to about half the depth of the knurl then increase depth whilst moving the carriage/top slide back and forth untill full depth reached. This should give you a good start and if the wheels do get out of step then start from off the work again with a little more depth.

Good luck John
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