Personally if its something as important as a tool post stud it would be better scewcut even if you do it to about 85 to 90 per cent depth then finish off with a die die for depth and form.

Hi, I agree with Clive, if you do it in the lathe, and if you use a die, use a tailstock diestock, or a squared end rod or tube pushing on the die and not on your hand diestock during starting the threading operation, and get the die started the full thickness at least before finishing with your hand diestock. You will need to advance the tailstock barrel at the same time as turning the lathe chuck though, to keep a square pressure on the die. I very often put the die in my hand diestock, the wrong way round, so to speak, so the full width of the die can be pushed with a blank end Arbor in the tailstock.

Regards Nick.

Definitely do it in the lathe with the dieholder or the tailstock pushing on the die/holder to keep it square.

Make the OD much smaller, to make life easy for yourself. I would go down to at least 9.9mm or a bit less, maybe even 9.8, for a 10mm thread. Remember, you only need 65% thread engagement before it starts to significantly affect thread strength. So struggling along tying to cut a full thread form with a die is pointless.

Make the chamfer on the end at least as big as the thread depth before you start.

Edited By Hopper on 13/11/2022 02:46:04

You may find the part rotates in the chuck once the die is on a couple of turns particularly if it's an old chuck so may need to move it to the vice but at least the thread will have started square with the tailstock die holder

If you absolutely had to do it with a hand-held die holder, here are are couple of ideas:

Make the part you want to thread longer than its finished length. Turn enough of it down small enough so it is a snug fit on the minor diameter of the die, the length being enough for the full depth of the die. This allows the die to locate centrally over the stock and will help stop it tilting. If you have enough material, make the chamfered part that increases from minor to major diameter much longer (maybe twice the depth of the die), so it gives the die a very good lead in. It is wasteful of material but not as wasteful as scrapping the whole part.

Find a tube that is larger than the OD of the thread. Hold in a(n unplugged) drill press (you might need to drive a wooden dowel in the end of the tube so it fits a 1/2" chuck). Load the quill handle (elastic strap) so the tube presses on the die. Turn the handles of the die holder.

You can also take inspiration from electrical conduit thread cutting dies: they have a parallel portion on the holder that goes over the OD of the conduit in advance of the cutting die which centres and guides the die. This works for conduit as it only comes in two sizes but some have an iris mechanism which make them a little more versatile.

See:

https://img.ffx.co.uk/r/700x-q85/tools/AK317DH.jpg

https://www.tlc-direct.co.uk/Images/Products/size_3/COSDG.JPG

Anything and everything you can do to keep the die and material to be cut in the proper relationship will help. The setup needs only two free degrees of movement – rotating and moving in the direction of the thread. Wobbling around freehand in space will make it difficult to produce good threads

Good quality cutting oil is a must.

Martin C

Forgot to mention that I think single point screw cutting is cheaper than buying dies, buying or making tailstock die holders or hand die stocks. One tool will do lots of threads when single point cutting so is a cheap option.

Edited By Martin Connelly on 13/11/2022 08:30:15

Single point most of the work then finish with the die to tidy up

Costs real cash if a beginner has to buy a grinder and HSS or carbide inserts and a holder, when a one-off job can be done with a die.

I've long since coughed up the cash for single point AND dies because:

• Single point removes most of the metal in a perfect helix,
• If the rod is bendy, single point can take several light cuts, and then
• A die is used to finish off, doing hardly any work following a straight pre-cut helix, only shaping the root and tip and paring the flanks to size.

Martin's technique sounded good to me, and I suspect either or both of:

• A poor start with the die not at the required 90°. I find it difficult to start threads accurately by hand and use a mechanical aid whenever possible. Lathe and tailstock, or mill and vice, pillar drill and vice, or home-made tap and die stand.
• The die is in poor shape. They work best when new and are fairly easily blunted by swarf mincing, over-sized rod, work-hardening metal, or the cut wandering off-axis. I've done OK with mid-range taps and dies, but the 'too cheap' variety are unreliable – a mix of OK for light use and too poorly ground or heat-treated to be worth having.

Dave

It's wonky because trying to start it with a die is rarely successful for straightness, plus you have to use a lot of force to cut 100% of the thread

So above 6mm it tends to be a lot easier if you get the lathe to do 80% of the work and the die does the last 20% kinda thing

The bigger the job, 8 10 12mm, the less successful a die will be at the start

If you want to do a straight start with a die then put the job into the lathe chuck and hold the die with the tailstock barrel when you wind it on