..and put a generous chamfer on the end of the stock to help start the thread..

Fully agree with doing it in the lathe if you can. Alternatively, I have done it with the rod held in a bench drill chuck and the dieholder flat on the table to keep things true, turning by hand of course.

To my eyes the threaded section of the rod pictured seems to be actually bent, which is easy to do when hand threading something that small without a guide.

Mike.

Could you screwcut and then finish with the die? (I realise that the half nut problem may prevent this).

Use a split dies and start with it fully open.

Don’t. Buy in a bolt and cut off the head.

Does the half-nut engagement work at all?  If so cut a rough thread with a single pont tool before going over wit the die.

Edited By not done it yet on 20/11/2021 14:12:01

Just had to redo some studs for similar reason, was making 22x M3 so trying to rush it and made a mess of half of them. Hold material in a collet if small, chamfer end of material, apply lubrication cutting oil, ensure split die is fully open, push die holder against end of part squarely, rotate to cut thread manually back off every couple of turns to free die of swarf string. The swarf can cause the die to move off centre if pushed too hard.

When using a die making the first thread or so produces seriously unbalanced forces because there is nothing supporting the inside of the die opposite the cutting edges. This force imbalance tends to tip the die off line during the formation of the first thread so a drunken thread results as the die stabilises following the line of the first thread.

The coarser the thread the more pronounced the effect. Coarsness being defined by helix angle not absolute pitch or TPI. High TPI or small pitch on a small diameter can be coarser than a much lower TPI or larger pitch on a larger diameter.

3/16 BSW is very coarse. Small diameter doesn't help because the slender shaft and even slenderer core diameter isn't terribly stiff.

Hence the need for firm die support. Either a die holder system with a decent size, nicely stiff, rod up the middle or something cruder like a flat ended pusher in the tailstock chuck. Pusher has to be just small enough to push directly on the die when its held in the diestock. Need to figure out something to stop the diestock turning yet still permit it to slide as one hand is occupied turning the chuck whilst the other operates the tailstock feed. As methods go that is maybe a bit on the crude and primitive size but I did many threads that way before being able to afford better equipment.

Objectively the best answer is a Coventry die head but its hard for the normally impecunious Model Engineer or Home Shop Worker to justify the cost.

D'oH moment. Make sure the die is in the holder the right way round. Put it in backwards and the clearances will be wrong way round so it won't want to cut. Which really doesn't help with going straight.

Clive

Edited By Clive Foster on 20/11/2021 18:04:11

Collet Chuck in the Tailstock and the die in the 4 Jaw maybe?

regards Martin

It is crucial that the die is started true, as the handles are usually used to check the die is square to the rod then it is important that the die stock is well made and the seating for the die is true with the handles and the die is seated properly in the holder. Once the die has started then check it is running true in at least two positions as you turn it. Once started correctly take care not to tilt the die holder as it will wander if uneven pressure is applied. I would review the equipment you are using and take great care to start the die true. Up to a point you can correct the start but if you are a couple of threads in and not true then start again.

Mike

Just a thought because simple mistakes happen, but are you certain it is 3/16" and not 5mm rod? 5mm is a too tight tight fit in the die, but this can be fixed by taking 0.2mm off the diameter with the lathe. Taking a little more off reduces the amount of work the die has to do without significantly reducing the thread's strength. If it is 3/16" same trick applies – reduce the diameter by taking a few thou off.

Also helps to pre-cut a groove of about the minor diameter ( 0.1342" ) where the thread ends on the rod. If the metal is squeezing as the die turns, the gap provides space for the overflow. It also lets the die cut the full depth without wedging up at the end. Another trick is to reverse the die to do the finishing cut because the chamfered input end can't reach all the way up to a face.

Dave

If you have a piece of steel turn this down to the size of your bar about 2" Long then bore a hole that will be a good fit on your 3/16 bar . When you have done this bore a hole in the end the same size as your Die this will then give you a Guide to to keep the whole unit straight .or if you have a larger size die holder thie can be done in the revirse with the held in your die holder and the die in the die holder after you have extented the 3 screws

Hope this helps and that it can be understanded I have made this and used many times

Good luck Bee M