Cutting a thread up to a shoulder
by John
A problem with some thread dies is that they have such a large “lead in” that they are unable to cut a thread up to a shoulder.
A 3/8″ x 32tpi die. Note the large lead in taper.
This results in the thread stopping a long way from the shoulder… undesireable in some situations.
This is a thread made with the die in the previous photo. I wanted it to go right up to the shoulder, but this is as close as it gets. About 2mm gap.
The screw in this upsidedown photo does not allow the shoulder to seat properly.
The solution? Modify the tool.
Here is the tapping die, held onto a magnetic chuck, within a machined steel disc to increase the magnetic attachment force.
So I ground off the top 1-2mm of the die. My surface grinder is out of action, so I used the tool and cutter grinder. A bit rough but it worked.
This is the die after grinding the surface. Note that there is no lead in. I ground the unlabelled face so I did not lose the specs of the die.
And the screw after using the modified die. The thread now goes right up to the shoulder. Incidentally, this is a zoomed photo using an iphone. Not bad?
So that does the job.
The downside is that in future the thread must be started with the unmodified side of the die, and finished with the modified side. Adds some time. And the die is thinner and a bit weaker.
A pity that the dies are not manufactured with one “no lead in” face.
The particular set of ME dies will now all be modified in the same way.
johnsmachines 
Have you noticed that the lead angle on the “front” side of the die is about 45 degs but on the back it is significantly less. That might have worked for you.
john f
LikeLike
On these particular ME dies the lead distance was about 3 threads on both faces so reversing the die did not assist.
LikeLike
Hi John,
The usual thing in this case is to use the back of the die to thread to the shoulder after starting the thread with the front.
The lead on the back of the die is much less than the front and is usually good enough for most work
David
LikeLiked by 1 person
Not with these particular ME dies, unfortunately.
LikeLike