Thread cutting

I have been having some trouble in cutting some M.E. threads on 1/4" and 3/8" brass rod using dies. I thought perhaps it was because I was using the rod at its original diameter, forcing the die to take care of the rounding of the crests of the threads. With the idea of discovering how much to remove from the diameter of the brass rod, to remove the crests of the threads. I measured the diameter of several four flute M.E. taps. They are all between two and five thou over the marked size! Is this normal, or are they just not very good taps? Should I be turning the material to slightly less than the nominal diameter to help with the external threading?

Regards Maurice

Hi Maurice

Normally when threading your material is the same size as your dies so it would help if you told us what sort of dies your using HSS or carbon, are they split dies, are you doing it in a lathe or vice and what is your exact problem ?

H

I always tend to turn the material to nominal size, rod should be easier as its usually a thou or two under size

I have tried two carbon and one HSS dies in a tailstock die holder. The material is "ordinary" brass rod from the now defunct GLR Metals. The threads always look thin and a bit torn. Even with the die fully expanded the result is a loose fit in a tapped hole. Sometimes it works ok. but I can't get consistent results. I have just been told that I should be screw cutting to start off, and only finishing with a die. Is this accepted practice?

Maurice

I rarely screwcut ME threads only if I want large ones that I have not got a die for so that would be over 5/8".

Have a try with the dies in a handheld diestock, it may be they are not machined true to the backface of the die.

These are a few things I have done in brass since christmas all done with dies and a tailstock holder, run on under power @ 50rpm while holdinmg the dieholder.

These have 3/16, 1/4, 7/16 and 1/2 X 40, threads are tight a sthey are greasers and I don't want teh grease finding its way out the thread.

And these have 3/16, 1/4, 5/16 and 7/16 x 40

Maurice

Cant add much to what Jason has said I cut ME threads in brass both in the lathe and by hand in the vice without a problem nice lead in bar, some thread cutting paste and back off often. Just a thought have you tried to thread brass from another source, could it be the material ?

H

Hi Maurice

I don't know where you got the info about GLR Metals being defunct but I have just been in contact with Richard at GLR and they have never stopped trading.

Regards

Stan

I stand corrected over GLR, I have been misinformed . I will try again with the theading; thanks for all the advice

Regards Maurice

GLR now trades as GLR Kennions

They have had some changes over the decades and that may have included changes of owenership. Starting in Hertford near Kennions whose casting range they picked up they moved ot Hoddesdon in the '80s, then up to Doncaster (when they were the supplier for Chronos material stock BTW) and more recently down to Epping. The recent move may have occasioned some disruption in service that was construed as ceasing trading . They are now only mail order however. ( I hope the above is reasonably accurate)

I have to admit having rather forgotten about them and not been to their premises since getting a materials 'starter pack' from them at Hertfored in about 1982. I think they used to come to the ME shows back then.
They should be persuaded to put an advert on this site to raise their profile.

Still got a box of paxolin sheet offcuts bought at GLR thirty years ago at their shop near Hertford East Rail station (hard by Kennions shop!). Gradually going but will see me out for bits halfway between wood and metal.

Did visit in Hoddesdon after I moved North twenty years ago.

john

Threading I find is like a lot of model work, it's down to feel and keep a close eye on taps especially as you cant slack them off like a die. Use all three stages. Watch for how much they're springing. If in doubt retract completely and clean as much of the chippings and cutting compound away as possible. Then start again. Threading like most things is down to practice. Having said that I had a tap wind it's self into a spiral once (I think it was a second stage tap) where it had missed being tempered I assume.

Jesse.

Threading brass rod should not be a problem,I think the trouble is caused by poor quality dies,probably carbon rather than HSS and no relief on the die teeth, which causes the die to jam on the thread,40/50 years ago carbon cut thread taps and dies of English manufacture cut good threads and the expensive HSS ones were used for production jobs, I have a lot of threading tools from that period and they still do a good job,for about 25 years carbon steel taps and dies from dodgy foreign manufacturers have appeared in this country and some are crap. The only solution is to buy HSS ground thread taps and dies but far more expensive and only buy the ones you need rather than sets.I have an ex army set of 9/16 to 1 inch whit taps and dies ,new and dated 1942 the 5/8 taps have cut around 100 threads and are still ok,but of course English manufacture. Also be careful when buying larger dies,say 1/2 inch whit,you may find that the outside diameter is very small and will only fit into a small die holder with short handles so that it is impossible the turn the die unless you are a giant,one solution is to use a tailstock die holder with a long tommy bar.

I have found what my problem is with cutting these threads in brass. I was advised to keep endwise pressure on the die while it is cutting, rather than let it drag itself into the work. This helped a lot withe the finish, but the result was still undersize. After a close look at all the equipment involved, I have discovered that the recess in the particular tailstock die holder I was using, is only about 6 thou bigger than the dies! I measured other holders I have, and these are up to 28thou bigger. Tried one of the others; perfect! I shall now bore the holder body to a larger size. This raises another question. Many years ago, there was an article in M.E. about making a set of die holders. The author raised the point that if the dies are manufactured with the cutting faces concentric with the outside, then when fitted to a tailstock holder in a clearance hole, they will be eccentric to the work. I can't remember what conclusion was reached. I can see that it's not a problem with something fairly long and flexible, as it can self centre, but not so if it's a short stubby piece of brass. Should the recess ideally be bored eccentric, and by how much? I can see that is not a critical issue as most threading is done with no problem, but I would be interested to hear what others think.

Maurice

Hand cutting this problem is not noticed, I think that the tailstock die-holder should be a loose fit on its shaft.

There are a few designs about for "floating" die holders which allow a little movement from the lathe axis to take up any eccentricity of the die.

J

I still have and use, a T/S die-holder supplied by Pete@GLR. It has a loose fit on the supporting T/S mandrel, giving a floating positioning that always seems to allow alignment with the work.

In recent months (2014) I have made a couple of purchases from the new owners of GLR Kennions with complete satisfaction.

I think it was GHT (George Thomas) who made a set of tailstock die holders with multiple screws to allow perfect centring and adjustment for each die.

Neil

To centre the die in the tailstock die holder really needs 3 screws to centralise the die, plus one to adjust the die opening.

Ian S C

Maurice. This might help. I have a copy of the DORMER Technical Handbook, purchased from Greenwoods at the Harrogate Exhb. The book contains vast amounts of information on all sorts of cutting tools. I would agree with one reply the quality of the dies is crucial. I purchased a set of ME dies from a recognised trader and they are poor quality HSS.Some of the dies are OK but several have faults as follows

1) the two dimples set at 90 deg for closing down the die are not in the same plane so when adjusted twist the die and consequently thin the threads.

2) The split in the dies are not symetrical ie the 90 deg 'V' is off centre or not at perpendiculr to the two faces

3) The lead angle on the dies is not sufficient.

DORMERS advise that and appropriate chamfer is applied to the bar to be threaded to form a centralising lead

Good quality dies to BS or similar standards should not be expanded as this causes rubbing.

You might find ( if the dies are of good quality the the lead chamfer is different on one face to the other If so start with the greates lead. This is usually the face with the makers name on it.

Hope this helps

Peter

Picking up on this old "thread", no pun intended. I have been struggling to cut M3 threads in mild steel. Brand new HSS split die M3 x 0.5 from Tracy tools in a tailstock die holder. Stock turned to 3mm with a generous chamfer for lead in. With the two side screws nipped gently just to hold the die, I struggled to get the die started and ended up stripping about the first 4 threads before getting a good thread form. Putting some cut on the centre screw to split the die, makes it easier to get the thread started, but there was a tendency for the thread to strip. I assume that there is a happy medium, but how to find it? I am putting pressure on the die holder and turning the collet chuck by hand with the lathe in neutral. I would be interested in tips on how to perfect the technique on M3 or smaller.

Would I be better without a split die to get a more precise size?

There are some good thoughts in this thread and I will be definitely be looking to check the die alignment in the holder

Thanks in advance any other suggestions