Thread: Hercus radius turning tool - project

I assume you meant 3mm X 0.6 (3mm X 0.5 is easier to find). Why not use 1/8" (3.175), course or fine, you have more than enough depth there for thread in the body of the toolholder, may as well get the thickest thread possible and the taps and dies shouldn't be that hard to find in that size. You can leave the top of the bolt at 3.8mm with a slight taper to be on the safe side.

Yes that is correct, 3mm X 0.6, sorry I didn't represent it clearly. I also have the 3mm X 0.5 but the problem will certainly be the same, total garbage tap & die set. My only real option is to buy better stuff. I have a wonderful collection of taps & dies which came with my lathe, a bucket full actually, but nothing anywhere near this small. I'm going to have another play with it hopefully tonight, and pending what happens I'll probably be opening my wallet one way or another.

Instead of buying a full set, I buy a decent quality set of taps, 3 in a set, taper, intermediate, and bottom at the same time I get a die, preferably an adjustable
one. The carbon steel ones are only good for cleaning up threads, I've found.
Kryn

OK so I had a go at threading on the lathe.. Put the metric change gears on and went for it. Resulting in confusion and frustration! Trick for new players I suppose, the thread chasing dial and metric don't mix on a non metric lead screw. Or whatever the case is.
Had a bit of a google, seems I need to just stop the lathe and run it backward and forwards without disengaging the half nuts? Will give that a go tonight and see what happens, I'm cautiously optimistic that I may have some success.

Originally Posted by ratters

OK so I had a go at threading on the lathe.. Put the metric change gears on and went for it. Resulting in confusion and frustration! Trick for new players I suppose, the thread chasing dial and metric don't mix on a non metric lead screw. Or whatever the case is.
Had a bit of a google, seems I need to just stop the lathe and run it backward and forwards without disengaging the half nuts? Will give that a go tonight and see what happens, I'm cautiously optimistic that I may have some success.

Hello Ratters,

I too have an imperial lathe with a set of metric transposing gears. Most of the metric threads I have cut have been fairly short in length, that short that I would court disaster if I used power feed. It is upsetting to watch your threading tool slowly carve its way into a shoulder because the lathe doesn't stop fast enough.

To overcome this problem, I turn nearly all metric threads by hand using an expanding mandrel and a hand crank installed in the back end of the spindle. Laborious work at times, especially if the pitch is coarse and the material tough like 4140, but the results are controllable. With a bit of hand and eye coordination it's possible to cut a thread with no runout groove.

If you do use power feed just make sure that any backlash in the gear train is taken up before any successive cut.

Good luck
Bob.

Well the threading actually turned out OK thank goodness, I set the pulleys at the slowest speed + engaging the back gears so it was perfectly manageable speed-wise, although I know what you mean Bob, cutting into the shoulder..



However, the curse of the chinese tap & die set was not over... I thought I was being super careful, taking only small cuts about a 1/4 turn, backing out completely to clear out the swarf, but no, it turns out the tap was infact made of cheese. I was hoping it wouldn't come to this but I suppose I will buy a decent HSS tap to finish the job.

Hi Ratters
sometimes if I am cutting a thread up close to a shoulder I will grind a tool to fit a boring bar and come in on the back of the screw starting at the shoulder, running the lathe in reverse and cutting the thread away from the shoulder.
When returning to the starting point I get close under power and turn the chuck to get back to the exact starting point.
I have even put marks on the chuck and spindle to get even more accuracy
You must not forget backlash while doing this though.

Phil

With respect to your broken tap, at least you have something to hold onto to get it out.

Whenever I can (and especially when tapping more demanding materials like alloy steels and stainless) I use Trefolex (there are other similar products out there) to lubricate. Check your hole size too - if you are tapping M3x0.6 I would expect a hole diameter of 2.6mm. It's tempting to say that 2.5mm (tapping drill size for M3x0.5) is close enough but it is amazing how much extra torque that 0.1mm requires.

Michael

Yes I forgot to mention, had that tap out in no time, got a pair of pliers onto it and it came free without too much hassle. I was using trefolex too, spray-can variety, but you need to see this tap & die set, its total crap, the tap handles don't even hold the taps without slipping. I bought it a long time ago for a quick and dirty job but its all I have in small metric sizes. In regards to the drill size, yes I only have a 2.5mm drill, so I guess it would have contributed to the broken tap.

So I managed to get past the tapping/threading issues and have the toolpost almost done. I still need to make one more screw and also need to attach the toolpost to the slide. I'm quite happy with the way it's turned out actually, I decided to mill the sides to match the angles of the carbide inserts and I think it looks quite good. Next it's onto making a handle of some sort to rotate the tool and then of course the tool will complete itself when it's first project is a ball knob for the handle

Originally Posted by ratters

OK so I had a go at threading on the lathe.. Put the metric change gears on and went for it. Resulting in confusion and frustration! Trick for new players I suppose, the thread chasing dial and metric don't mix on a non metric lead screw. Or whatever the case is.
Had a bit of a google, seems I need to just stop the lathe and run it backward and forwards without disengaging the half nuts? Will give that a go tonight and see what happens, I'm cautiously optimistic that I may have some success.

Hi Ratters

What you can do when you want to cut a metric thread on the imperial lead screw with the chasing dial is start the thread at any number on the dial and when you get to the end of the cut back the tool off and disengage the nuts and turn the machine off, when you reverse the lathe spindle (as long as you have a reversing motor or by hand), engage the half nuts when it comes to the same number and run it back in reverse which will hold the same place on the thread as the chasing dial will only turn a small fraction past the number once it is disengaged and the machine is stopped.

Steve

Doubleboost recently had a bit on this method. First he said it was impossible, then someone pointed out this method so he tried it in his next video. Worked fine.

Here's a link

https://www.youtube.com/watch?v=doxU4sR0xuE

Dean

Small update since last time, I made the handle, just a straight bar with threaded ends and some flats milled on it for tightening. And I may put a bend in it but I want to see how it goes first as it is. Very close now to actually using the tool, I just have the attach the toolpost because its just sitting at the moment. Hopefully the next post here will be the finished item and action shots!
Cheers

Well its 99% complete and works great, very solid and smooth with no chatter! One thing I will say though, and I'm sure other people will probably attest to, there was a fairly decent learning curve and to be honest I still haven't got the hang of it properly. It was confusing trying to work out how to position the tool, relative to how the final size of the ball would end up. Any tips on how to set up? The last thing I will do is bend the handle up a bit but other than that its more or less finished. Sort of debating on bluing it now, the mild steel is already rusting despite being covered in oil.

Hi Ratters, What a great result. The brass ball looks excellent, have you tried to turn a steel ball ?

Keep up the good work.