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Alan Worland	25/01/2012 21:00:48
247 forum posts 21 photos	This afternoon I decided to make some 0ba studs for my new project - I thought it shouldn't take too long - wrong! I had a rummage through my material stock and found some nice .25 inch stainless rod, faced and turned the end down for a length of 5/8 (it turned lovely) Put the die in a holder and brought up the face of the tailstock chuck to keep it square. I locked the tailstock to the bed and pulled the work round in the headstock by hand and as the die fed on I kept it square with the tailstock handwheel. I dont think I have ever seen such a manky thread! (I used a light oil while cutting and relieved the chips) I turned it all off and tried again, nope! I tried various mild steel rods (I dont know what spec they are) most of which seem to turn ok. The best thread I cut is probably just about useable but shows a poor/shallow thread at the start ending in a full thread at the finish ie the entrance to the die. It's as though the thread is being destroyed by the rest of the die, which has had little use and looks fine? I have found another die and will have another go but does what I am doing sound ok? Its worked ok before! Alan
jason udall	25/01/2012 21:15:36
2032 forum posts 41 photos	Had simular . maybe over size "rod". m6 od is not 6.0 for example....
Jeff Dayman	25/01/2012 21:16:11
2356 forum posts 47 photos	Hi Alan, a) you need a good die for stainless, buy a new HSS one if yours is old. Carbon steel will not stand up to stainless for long. b) make the starting chamfer 20 to 30 degrees angle per side on the stock, and the end of the stock slightly smaller than the tapping size for the thread. c) give the die/dieholder a really good steady push toward the chuck when starting. d) use a good quality cutting oil, not diluted Good luck, JD
Alan Worland	25/01/2012 21:26:46
247 forum posts 21 photos	Thanks for the guidance! Jason, I have been turning the rod to the correct OD so the die is not removing excess material. Jeff, I am beginning to think my die is dull, it is only carbon steel (I think my other one is as well) and despite putting a good chamfer on the lead is does take a bit of 'getting going' Will get a rplacement and see if things improve! Alan
methusala	26/01/2012 10:06:38
32 forum posts	Hi Alan, Have you tried reducing the o.d of the rod by two or three thou, as this can help in getting a decent thread in harder materials. It wont lead to a sloppy thread, as the flanks on the thread will still be be in contact, but should ease the pressure on the die. Hope this helps. Colin.
Ian S C	26/01/2012 11:51:55
7468 forum posts 230 photos	I find that I get one shot a cutting a thread with a die on stainless, it work hardens, so you can't thighten up and skim a thou or two off to finish the thread as you can in other metals. It does play merry hell with both taps and dies, just don't try for high percentage fits. Ian S C
Martin W	26/01/2012 12:25:09
940 forum posts 30 photos	Ian If Allen has already turned the rod down to size will this not have started to work harden the surface of the SS. If so would there be any benefit in trying to anneal the turned down section prior to trying to thread it. I ask this out of complete ignorance re the work hardening of stainless materials as my only, cautious, attempt resulted in the tool bouncing off the surface of a piece of SS. That said I had no idea of the type of SS and my approach was tentative so the surface had ample opportunity to harden. Cheers Martin
AndyP	26/01/2012 13:15:07
189 forum posts 30 photos	It's as though the thread is being destroyed by the rest of the die, which has had little use and looks fine? Alan, I have an ME die that does exactly the same, works fine t'other way round though, ie with the face of the die without any markings on it presented to the job - worth a try? Cheers Andy
Roger Mawby	26/01/2012 17:39:04
1 forum posts	Hi Alan, I had a similar problem which I tracked down to axial distortion of the split die in the die stock caused by the screw opening up the die and twising each half in a different diirection. A bit like a spring washer. It was a poor quality 'cast' die stock witha poor seat for the die and rough ends on the adjusting screws. A decent stock resolved the issue. I have also found, like AndyP that some dies do seem to cut better threads when turned round! Mellie
Richard Parsons	26/01/2012 17:50:47
645 forum posts 33 photos	Hi Allan cutting an external thread in the lathe with a die can and is often fraught. I always (where I can) set up the gear box and turn the thread down to at least 50% of the finished diameter of the thread and finish it with at least two passes with a die. In the first pass I set the split die open (that is what the ‘centre’ screw is for). I then try it with the nut (or whatever). I then let the die close a bit –may be a turn of the centre screw or less- and repeat the process. A bit of a fag, but it is worth it. By the way 0BA is 6mm diameter by 1mm pitch. At a pinch you can get away with 25 tpi and by using an ISO metric tool to cut the 50% thread depth. Rdgs Dick
colin hawes	26/01/2012 18:00:31
570 forum posts 18 photos	A blunt die can sometimes be sharpened with a Dremmel type grinder if it has not been used for too long in a blunt state. Colin
chris stephens	26/01/2012 19:46:11
1049 forum posts 1 photos	After you tightened the screws did you tap the die home in the holder and did you clean any crud out first? There is no point in holding the die holder square if the die is on the p*ss. Do you have another holder you could try, as it might not be the die that is wrong. chriStephens
Alan Worland	26/01/2012 21:48:45
247 forum posts 21 photos	Had another go today with another die, not new but it looked ok, result! and far less effort required. Not perfect but a million times better - I have ordered myself a new HSS die. I might try them round the other way to see if things improve. I used to use the tailstock die holder but found that the cutting centre of the die didn't always match the centre of the holder so I now generally use a die stock with the tailstock brought up to keep it square and I always clean the holder so it sits properly. I usually open the die out fairly fully to cut, then try the fit and adjust for a nice close fit with the mating part. I have had bad experiences of die cast holders (with only one screw!) so last summer I managed to obtain some 'proper' ones from Boot Sales, they can be picked up quite cheaply. I did consider screwcutting the thread but the pitch put me off! having an imperial lathe with an imperial gearbox? I dont know what grade of stailess it was but it turned lovely - take an extra .001 off with no probs, anyway thanks for all your advice and suggestions - I got there in the end! Alan

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