Slittling very small screws

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Subject Author Date
Slittling very small screws Alan Bain 05-15-2008
Posted by _ on May 16, 2008, 9:40 am
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 On Fri, 16 May 2008 08:59:35 +0100, Cliff Coggin wrote:

>> Alan Bain wrote:
>>> 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
>>
>> Backgear? Why? What dia is the saw? The center height of the lathe?
>>
>>> 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.
>>
>> 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=25&y=15&Ntk=Keyword+Search&withinResults=true
>>
>> but the teeth are still 1.5 mm apart.
>>
>> -- Peter Fairbrother
>
> 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.

Dremel cutoff discs come in (approx) 0.05" and 0.025" flavours. The small
diamond disc I have is also approx 0.025"

Posted by Alan Bain on May 16, 2008, 4:21 pm
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>On Fri, 16 May 2008 08:59:35 +0100, Cliff Coggin wrote:
>
[cut]
>>> Alan Bain wrote:
[cut]
>> 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.
>
>Dremel cutoff discs come in (approx) 0.05" and 0.025" flavours. The small
>diamond disc I have is also approx 0.025"

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


Posted by Alan Bain on May 16, 2008, 4:17 pm
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>Alan Bain wrote:
>> 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
>
>Backgear? Why? What dia is the saw? The center height of the lathe?

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


Posted by mark@ems-fife.co.uk on May 16, 2008, 4:17 pm
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> 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

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.


Posted by on May 18, 2008, 5:51 am
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Alan Bain wrote:
> 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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