On Fri, 16 Aug 2013 19:50:21 +0200, asalcedo
wrote:


'The Other Mike[_3_ Wrote:
;3108109']On Fri, 16 Aug 2013 17:21:28 +0200, asalcedo

wrote:
-

Following up from my previous thread.

I am going to try and tap a 7/32" BSW countersunk screw 10 mm long

I have found the following dies:

'7/32 BSW dies'
('7/32 BSW dies'
(http://www.tap-die.com/contents/en-u...BSW_dies.html))

'Rotagrip - 04) 7/32 x 24 BSW HSS Die 13/16\" Diameter'
('Rotagrip - 04) 7/32 x 24 BSW HSS Die 13/16\" Diameter'
(http://tinyurl.com/pzecw2y))

A couple of questions:

1. Which blank can I use?
2. I have a 25mm die holder from a metric tap and die set. Do I need to
get a 13/16" die holder for the dies above?-

You can't buy countersink screw 'blanks'

Holding countersink screws and machining a new thread on them is not
straightforward so you need to machine from solid

What you are trying to do requires machine tools not a diestock and a
die. At
the very least a lathe, preferably a milling machine as well to cut the
slots
for the screw head. Think a minimum of 750 quid, a few months to learn,
jigs
to hold the blanks and part machined screws and quite possibly a ****
end
product.

A 13/16" die holder is needed for 13/16" diameter dies.



What is wrong with buying the as near as dammit 12 24 UNC screws off the
shelf
at 60p a piece?


--

I have indeed ordered the 12 24 UNC screw from the place you pointed me
to, a2stainless.com (they have been close for holidays and delivery will
be delayed)

But I wanted to give a try as well to making a 7/32 BSW, if it were
easy.

So, is it not possible to make the screw using the 7/32 BSW die from a
tap and die set starting with an M6 slotted countersunk screw where I
had removed the thread and holding it tight on a vice?

You need to remove the thread, keeping the bolt exactly round and parallel,
reducing it in size to the major diameter of the thread you are trying to
produce

7/32" BSW or 12 24 UNC are 0.216" or 5.48mm.

Given that an M6 x 1 thread is 6mm diameter and 5mm at the root you cannot
produce a 7/32 BSW thread from this as by the time the M6 thread form is removed
the diameter of the bolt is 0.48mm smaller than that of the diameter needed for
the new thread.

Also, and excuse my ignorance, other than to clean a thread or rethread
a slightly worn out one, what use are the dies in a tap and die set for?

For cutting new theads on usually round material, exactly what you want to do
but you are starting from the wrong start point.


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