Slittling very small screws

In the process of making Watch screws (14BA and smaller) from carbon steel, I have been experimenting with slitting them. Normally I use a
screw head file, but this can be somewhat time consuming so I tried a slitting saw in the lathe. I mount the screw in a tapped brass block clamped to the vertical slide and run in gently at centre height to the slitting saw.
This sort of arrangement I find works well when making larger screws (4BA and larger), but with a 8 thou slitting saw and slow backgear performance was somewhat hit and miss; sometimes a beautiful slot was cut, other times the slot was very Vee shaped with ragged torn edges and in one case the slitting saw lost a tooth (but the screw was undamaged)!
I have a feeling that this may be because I am using a cutter of too coarse a pitch (the finest saw I could find had a tooth spacing greater that the diameter of my screw head and normally I try to ensure that at least two teeth are in contact with the work. I should be interested to know if this is a plausible explanation?
Alan
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sounds plausible to me, IIRC when selecting a hacksaw / pierceing saw blade the guidance on TPI is to select one which will keep 3 teeth in the cut. I guess slitting saw blades would be similar. Have you thought of using dremel / clone cutting disks? Im not sure how thick they are, but might be able to thin them a bit anyway.
Dave
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Alan Bain wrote:

Yes, very plausible. Three teeth is standard.
http://cgi.ebay.co.uk/4-Diamond-QUALITY-Lapidary-Saw-Blade-1-2-Hole-20mm_W0QQitemZ300203774152QQihZ020QQcategoryZ4843QQcmdZViewItemQQ_trksidZp1742.m153.l1262
-- Peter Fairbrother
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Alan Bain wrote:

Backgear? Why? What dia is the saw? The center height of the lathe?

something smaller than my last suggestion: http://www.jlindustrial.co.uk/CGI/INSRCH?ns=1&oldNtt=&oldNtk=&oldURLVar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scrNtt=0.008&x%&y&Ntk=Keyword+Search&withinResults=true
but the teeth are still 1.5 mm apart.
-- Peter Fairbrother
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http://www.jlindustrial.co.uk/CGI/INSRCH?ns=1&oldNtt=&oldNtk=&oldURLVar 14D50FEB5C09CF0C92C78E24137111080A1C98164036961AA6CBE47CEE93D54968834E29341B56E0BF8B1DE42A19BC2A4A60BB2C668D9ABF07AA49FEC8AB8BF1376073548A1662FD0790ACE588A64ACBB604A9E32DCCEB03589A22949E39721959292B97CB1F236FFAB1C2ED0694C33068B9D01A98B39C4369F5D72F6CC04C620FB8FA32045C77F41D47410E7C0B412943AD2816C716718B702C6CF94BB9DE138541D5AE233F6918A55FB5E391DA4A12C691FB2AF0CC2CD928985CBCD71D2A7F134C35FED76B5E27273796687CF5FD5C5B97AA4A483295DD65D2858EFB9BE009C43D86FE8EA5A634D496313316F42A39780A4DA59F14E85C80597CB5037A24&scrNtt=0.008&x%&y&Ntk=Keyword+Search&withinResults=true
There are 1" diamond slitting discs on 2 mm arbors available. I don't have access to mine at the moment so I can't give a thickness, but it is far thinner than the Dremmel type of resin-bonded slitting disc.
Cliff Coggin.
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On Fri, 16 May 2008 08:59:35 +0100, Cliff Coggin wrote:

Dremel cutoff discs come in (approx) 0.05" and 0.025" flavours. The small diamond disc I have is also approx 0.025"
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[cut]
[cut]
Thanks for this suggestion; I hadn't thought of grinding type tools and googling around finds
http://www.eternaltoolshorology.com/diamond-discs.htm
which offers a 7 thou diamond slitting disk; looks ideal, thanks for the idea!
Alan
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The saw is 3" diameter. Lathe is 4" centre height with gap bed. Backgear was probably around 50rpm, so that makes a speed of 40 surface feet per minute and a quick look in tables suggests about 55sfpm for silver steel with an HSS cutter. Anyway that was my reasoning, it is was wrong then I would be interested to know!
Many thanks for the suggestions and pointers,
Alan
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Have a look at the Precitool range of carbide slitting saws.Not cheap for a home shop but very good and last a long time.We use them for slotting Stainless screws.
Mark.
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Alan Bain wrote:

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Alan Bain wrote:

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Hi Alan I think that the others have covered te main things, namely that the teeth on the cutter ned to be finer, also the cutter could be smaller with support cheeks. J&L list an .008" wide x 3/4" dia with 1/4" hole with 40 teeth, I am using a .010" one to slit brass 3 times at 120 degrees running at 10,000 rpm dry, not silver steel I know but it shows they work! I would also avoid plundging the cutter into the end of the job and pass the screw head under the saw, ie put the cutter in the lathe chuck and hold the screw shank in a holder on the cross slide and then wind the slide in to cut, plenty of coolant and you will get a perfect result. You will also get a flat bottomed slot. Peter
Alan Bain wrote:

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On Sun, 18 May 2008 10:14:34 -0700 (PDT), snipped-for-privacy@hotmail.com top posted:

Do you read books upside down?
Mark Rand RTFM
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The speeling in the title reminded me of a related mistake. Quite sometime ago the department secretary typed up a "Business Case for a Slitting Saw". Unfortnately she typed an "h" instead of an "l". Took quite a while before she was allowed to forget it.
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Speeling? :)
--
Mike Whittome

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