Split dies

Hi Guys,

I've been using this type of die for many years and each time I ask myself :-

Should the side which has the labelling be the start of the cutting (ie if run down a bolt - finish up next to the bolt head) or should it be the end of the cut (ie facing away from the head)

I've tried both ways and I can't tell the difference, but a little voice keeps nagging me that it should.

Advise always welcome

regards

Bernard

If I'm reading you correctly; the start of the thread is the stamped / labelled side, the first couple of teeth are tapered to give you a shallow cutting starting action building up to a full depth tread at the end ( back ) of the die. If you need to go up to a shoulder you can either undercut next to the shoulder which will allow you to run the die past the initial tapered threads to the shoulder, or, once the initial thread is cut turn it round & run the die from the back to give you a full depth thread... my preference would be to undercut next to the shoulder ... if you get my drift.

​George.

sometimes they are tapered both ways so there isn't a right or wrong way. The only time that matters is when the die has been visibly ground off the back face, that is so you can flip it round once it's cut and use the full depth to proceed right up to the shoulder.

That is, if the die was cut straight the first time.

Michael W

Look at it from the common sense perspective. What die (or pair) is in the tool at present?

Ooh, can't read it because it is in the wrong way? Does that make it fairly obvious which way they should be installed?

Like buying a newspaper or a book and all the names/titles only being hidden inside somewhere!

I have to admit I hadn't noticed the difference in the taper, but then 4BA has been the largest die I've used so far

Thanks for all your replies

regards

B

Hi All

the start of the thread is the stamped / labelled side, the first couple of teeth are tapered to give you a shallow cutting starting action building up to a full depth tread at the end ( back ) of the die. If you need to go up to a shoulder you can either undercut next to the shoulder which will allow you to run the die past the initial tapered threads to the shoulder, or, once the initial thread is cut turn it round & run the die from the back to give you a full depth thread...

For the reasons above this is how a die should be made. Why on earth do some manufacturers taper the die on both sides? Barmy!

I've just bought a 40 t.p.i 5/16" dia from dgr (anagram) and I'm not impressed tapered on both sides. I'm making a piston rod guide and would like to reverse the die and run it up to the shoulder, undercutting is not an option. So I'm pretty pxxxxx at this moment in time. Rant over

geoff

Geoff

I have a set of cheap dies bought when I started model engineering and they are tapered both sides so when I need to get up to a shoulder I take the die to my bench grinder and adjust the profile of the non printed side. Simples.

Jim

A quick scan of my readily accessible split dies, from 5BA to 1¼ BSW, show that they are all tapered on both sides. The dies are mostly LAL with one stamped AM, which is going back a bit! The annotated side is tapered about 2 pitches and the other side about 1 pitch. I rarely use split dies, but I do sometimes turn them over to get a bit more thread. Whatever you do, you will never get a thread all the way to a shoulder with a split die. That would require a very thin edge to the die which would get broken off as it tries to cut full depth. Even thread milling will only get you within one pitch or so.

If a thread is needed all the way to a shoulder then you need to undercut, or counterbore, one or other of the threads. Or change the design, for instance a threaded spigot through a threaded bush.

For piston and valve rods and guides I prefer screwcutting to ensure squareness and a snug fit. I've never found it that easy to accuately adjust split dies.

Andrew

Hi Guys,

Thank you for your replies. Yes I appreciate that it is impossible to thread right up to shoulder, I just needed one more thread. Tapering on both sides would seem to apply to certain manufacturers. All my dads old dies, imperial and metric, and I've got hundreds of them, British made, are all tapered on one side.

Could I also ask for your thoughts on the following.

The die from GDR (anagram) is 1" o/d and 5/16" x 40 t.p.i. and has 4 cutting edges so you can measure the root dia

With the die out of the stock the root dia of the threads measured with the vernier is 0.265". With the die in the stock and the outer screws loose and the central tapered screw fully tightened the root diameter is .270.

From M.E. thread tables I find that the root dia of a 5/16" thread is .280 and has a thread depth of 0.016".

I think the die should measure at least 0.280" root diameter with the die out of the holder. Would you agree.

Not used the die yet, may well have to send it back.

geoff

As several posters have said, many dies have a tapered lead on both sides. They are fine except when threading to a shoulder. A die without the double lead allows you to turn the die around and cut the last bit of thread.

Just bought a new #2-56 UNC split die. Not only is it tapered on both sides which is bad enough, but the adjusting screw extends outside the die diameter so it won't even fit in the die-holder !!