Using metric dies

[cumbriasteve]

Wanted a M8 thread on a bit of steel this morning and things did not go well.

Lessons learnt are don't leave your good set of Dormer dies in a wooden box for 5 years without checking if damp is affecting them.

Next lesson learnt is it takes nearly an hour to polish up a dozen rusty dies back to a decent standard.

I HATE tools being damaged

Anyways, back to the problem:

I turned the stock to 8mm (with a lead in) for the 8mm die, I am presuming that is right and because I did not have a split 8mm die could not get a start, turned the stock down to 7.9ish...give or take a midge and managed to thread it but have a shallow looking thread, luckily it's a test run until I find some decent bar.

I was using trefolex as well.

I think I know the problem is the lack of a split die to start the thread, are the experts in agreement or have I got the dia of the bar initially wrong, it's been more years than I can remember since I did similar work.

 

[optima21]

I dont think a split die makes much difference for starting a thread, for an M8 thread I'd turn the bar down to 8.0mm, I dont think 0.1mm undersize would make that much difference.

for starting a thread in the lathe I'd normally use a hand held die stock and push it using the body of a 1/2 chuck (in the tailstock), against the back of the diestock. I'd then turn the chuck with the workpiece in it by hand to start the thread. I'd keep the pressure on the diestock with the drill chuck in the tailstock for the first few threads.

that's my way of doing it

was the cutting edge of the die damaged, or were you using it the wrong way round, as they have a lead on them too.

 

[cumbriasteve]

was the cutting edge of the die damaged, or were you using it the wrong way round, as they have a lead on them too.

The m8 is a cheap one, the only size missing from my good set so I suspect that had something to do with it.

 

[arther dailey]

I normally put a small 45degree taper on the end of the material to allow die to bite in.works for me.

 

[Dee J]

If you used the die and ended up with a shallow thread... Was it the peak or root diameter that was wrong? Would an M8 nut fit? If the root diameter is wrong then the die is damaged. If the peak has been cut down too much is there some obstruction in the die? Or was your starting material too small?

 

[cumbriasteve]

If you used the die and ended up with a shallow thread... Was it the peak or root diameter that was wrong? Would an M8 nut fit? If the root diameter is wrong then the die is damaged. If the peak has been cut down too much is there some obstruction in the die? Or was your starting material too small?

The nut goes on ok and it's the peak, probably just the bit I took off to make it start easier has caused that, only a small amount but makes a visible difference.

Have just bought a new die of good quality for when I do the real project.

 

[Hood]

An M8 will be round about 7.8mm OD when cut.
Are they dies or die nuts? If the latter they are really only meant for cleaning threads.

 

[cumbriasteve]

Are they dies or die nuts? If the latter they are really only meant for cleaning threads.

They were dies

 

[Robotstar5]

When I'm threading conduit, I put a 45° nick in the tube with a file, this gives the die an easy start.

 

[brightspark]

funny u should mention it I turned some brass down to 8mm a week ago. went to thread it in lathe using a hand die holder and lined it up with tailstock and cranked it over .it didn't particularly like it and wouldn't start took a couple of more thou off it and it went strait on . never ever had any bother before