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What am I doing wrong???

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Mark Harrison 118/10/2009 20:47:11
18 forum posts
Hi all, I am trying to cut a thread in a 3mm brass bar, I am using an m3 0.5 die but it's just not cutting a thread. At best it is chewing the end of the bar up. What am I doing wrong???
Paul Boscott18/10/2009 20:59:22
99 forum posts
21 photos

Hello Mark

One of the possibilities may be that the split die is not adjusted correctly you should test the setting by running it down an existing 3mm thread.  It should be just tight without removing any metal.


Mark Harrison 118/10/2009 21:05:08
18 forum posts
Hmm don't have a 3mm thread but could you please explain how I set up a split die?
JasonB18/10/2009 21:29:20
23076 forum posts
2771 photos
1 articles
Most dies have a slight lead taper, this is on the side with the size engraved on it, make sure byou have this side facing the work.
Your diestock will have 3 screws, place the die in the stock and tighten the middle one until it just starts to expand the die, then just wind the othe two in until they touch the die. You can then  start threading. Turn the die one full turn forwards and half back and so on to break the chip off (not really needed with brass)
Now try a nut on the thread, if its too big slacken the middle screw & tighten the outer ones to close the die and cut again, repeat until you get a good fit.
A small chamfer on the end of the rod will help the die to start
PS you are not trying to thread 1/8" bar by mistake ?

Edited By JasonB on 18/10/2009 21:31:00

Rob Manley18/10/2009 22:36:43
71 forum posts
14 photos
Oh and make sure you aren't using a die nut (hexagonal in shape and non adjustable) Oh and a quick warning about adjusting dies they should only require minimal adjustment from stock - close them up too tight  and they will break into two halvs. 
The Harper19/10/2009 00:29:01
18 forum posts
12 photos
Further to the above, make sure the brass rod is 3mm dia and not 1/8" (3.17mm) as the die will find this too much for it to cope with. Infact, anything above 3mm will make it awkward to get a start, also make sure you put a chamfer / lead on the front of the rod too as this will help the die to get going.
Cheers and good luck
Mark Harrison 119/10/2009 08:49:39
18 forum posts


Hi all and thanks for the posts, I have tried adjusting and it does not appear to make any difference. Checked the rod and it is 3mm so I am now stumped. Above pictures show the bar and Die I am using, if you can spot any issues please let me know.
Many Thanks

Edited By Mark Harrison 1 on 19/10/2009 08:52:04

IanT19/10/2009 10:24:49
2006 forum posts
212 photos
Hi Mark,
Two things - try backing off the two outside 'holding' screws mentioned above and opeing the die a little more with the centre screw (then just nip up the holing screws)  This will enlarge the die slightly. Then use the drill chuck nose (mounted in your tailstock - with the 'jaws' wound back into the body - to keep the die square as you apply a small ammount of pressure on the back of the die. Keep the die steady as you turn the chuck (that's holding the rod). This should form a slighly over sized thread - but it will get it started correctly.
Once you have done this - try a nut on the new thread - it will probably be too tight. Ease off the centre screw on the die slighly (half turn), ease, then re-tighten the outside screws and thread the rod again. Use the nut as a guide to correct size again. It should thread on using 'finger' force.
This appraoch should work. If it doesn't - I guess the die is faulty in some way and should be replaced. 
NJH19/10/2009 10:30:54
2314 forum posts
139 photos
Hi Mark
All previous advice is good but from your 'photo i would place the split in the die under the silver screw and tighten this first to expand the die.Failing this follow Ian T's latest advice!
Ian S C19/10/2009 10:50:20
7468 forum posts
230 photos
Hi mark,move the gap to the 12 0'clock possition and use the silver screw for adjustment,checkthat you are starting from the correct side of the die- like a first/second tap the first few threads are tapered off to start the cutting process not all dies have this indicated in writing,but its a bit difficult starting it the wrong way!IAN S C
Mark Harrison 119/10/2009 11:02:03
18 forum posts
Hi all, Right.. I have now tried forwards, backward, split compressed and split open and even tried the chuck method and it just wont cut a thread at all?????? Must be a faulty die?
NJH19/10/2009 11:34:44
2314 forum posts
139 photos
Looks like it.
Is this a one off requirement for a length of 3mm brass thread?  - You could pick up a piece of 3mm brass studding for about £3.   Even so the die is always useful of course ( as long as it works!)
David Clark 119/10/2009 11:36:48
3357 forum posts
112 photos
10 articles
Hi There
Stupid questions.
Is it a left hand die?
Have you tried it on an existing 3mm bolt?
regards David
Mark Harrison 119/10/2009 12:08:24
18 forum posts
Managed to find an old 3mm bolt and ran it through a few times.....sorted. must have been a blocked thread on the lead in of the Die, one thread now cut.
Thanks all for you help
Jim K19/10/2009 14:12:23
44 forum posts
Just for the record if you have the problem again try reversing the die in the holder maybe the die is stamped on the wrong side. i have had this problem with dies before.
Ian S C20/10/2009 10:54:10
7468 forum posts
230 photos
David C,you beat me to it,I was just about to suggest a possible left hand die,but sounds like the problems been solved.IAN S C

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