Ivan
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| posted on 22/5/07 at 07:20 AM |
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Can't cut threads
I feel embarrased asking this - but I'm struggling to cut a 8mm thread with a die - I get it started then after about 3/4 of a turn it strips -
what am I doing wrong? - using MS rod about 7.8 mm diameter.
I am starting the thread then backing off slightly then cutting about 1/10th of a turn then backing off etc.
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mackei23b
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| posted on 22/5/07 at 07:32 AM |
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When I've cut threads, I normally have a bit of pressure on the die at the start so that it takes to the rod there after I let the die pull
itself.
The other thing, I normally do 1.5 - 2 turns before backing off at the start.
One final thing, if the die is blunt, it can also have the effect of chewing the rod.
Hope this helps.
Cheers
Ian
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nib1980
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| posted on 22/5/07 at 07:42 AM |
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don't take this the wrong way, but you haven't got the die upside down have you? most a a leading face.
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flak monkey
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| posted on 22/5/07 at 07:43 AM |
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Use some cutting fluid or oil to lubricate the die and rod.
You also need to make sure the die goes onto the rod squarely.
Its hard work, but you'll get there. Give it a bit of welly 
David
Sera
http://www.motosera.com
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02GF74
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| posted on 22/5/07 at 08:19 AM |
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good luck - I 've tried and it is very difficult to get a square thread. Depending on what it is you want it to screw into or hold together,
that may be acceptable.
To start it off, put the rod in a drill press and file a conical end - you can always cut that end off afterwards, unless you have cut the rod to
length.
the way to guarantee a squrre thred is to use a lathe.
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David Jenkins
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| posted on 22/5/07 at 08:22 AM |
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As nib1980 says - make sure the die is the right way up. There should be writing on one face of the die; in most cases this should go towards the
rod.
It helps to have a little bit of a chamfer at the end of the rod (just 1mm or so) to get the die started.
I was taught to do 1/4 turn, then back until it clicks (when the swarf is broken off), then another 1/4 turn, etc.
Try as hard as you can to keep the die totally level for the first few turns, with a steady downward pressure to help it start cutting. On 7.8mm rod
you shouldn't have to try too hard.
Just make sure that you're not doing the dumb trick I once did - I just couldn't get a thread started once... until I found that I'd
picked up a left-hand threaded die!
HTH,
David
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owelly
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| posted on 22/5/07 at 08:29 AM |
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Have you got the stock set right? For the first cut you need to tighten the middle screw first to spread the die. Then on the second pass, unscrew the
middle one, tighten the outer two.
http://www.ppcmag.co.uk
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britishtrident
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| posted on 22/5/07 at 09:41 AM |
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quote:
Originally posted by owelly
Have you got the stock set right? For the first cut you need to tighten the middle screw first to spread the die. Then on the second pass, unscrew the
middle one, tighten the outer two.
More or less what I was going to say --- a "split" die is required.
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Ivan
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| posted on 22/5/07 at 11:29 AM |
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Hi All - thanks for the advice - eventualy got it right by turning the first 7mm down .5mm that got it started properly  - unfortunately my die
isn't split so can't set penetration so after all the hastle find the thread is too tight on the nuts - will have to buy a split die
 
Must learn how to cut threads on a lathe some time, although I think my gearbox is Imperial so not sure if you can cut metric threads.
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MikeRJ
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| posted on 22/5/07 at 11:50 AM |
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quote:
Originally posted by owelly
Have you got the stock set right? For the first cut you need to tighten the middle screw first to spread the die
And if it's a cheap carbon die, it's then time to buy a new one as it will most likely be in two pieces!
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David Jenkins
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| posted on 22/5/07 at 11:52 AM |
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I don't bother to use the feeds to cut small threads on my lathe - I just use the nose of the tailstock to hold the die stock in line, and turn
everything by hand. I either rotate the die-stock, or pull the chuck round, while GENTLY feeding in the tailstock, just enough to keep things
straight.
Well worth putting the lathe out of gear, or ensuring that the mains is completely off (pull the plug out) before trying this!
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trikerneil
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| posted on 22/5/07 at 11:58 AM |
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When cutting threads on a lathe using a die I don't feed the tailstock, just push it along by hand keeping a steady pressure towards the
headstock while turning the chuck by hand.
Otherwise there is a chance of cutting a thread which has a compound pitch of the die and tailstock threads.
HTH
ACE Cafe - Just say No.
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daviep
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| posted on 22/5/07 at 02:48 PM |
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If I'm using the lathe, I hold the the die stock in the four jaw and the bar in a chuck in the tailstock and just leave the tailstock free to
travel, lowest speed and bob's your uncle!!
Tapping: hold the job in the chuck, revolving centre in the tailstock. Hold the tap against the job with the tailstock and use a spanner to stop the
tap rotating, lowest speed and go for it.
To cut metric threads on an imperial machine you need a 127 tooth change wheel in the gear train somewhere.
Regards
Davie
[Edited on 22/5/07 by daviep]
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David Jenkins
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| posted on 22/5/07 at 02:50 PM |
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quote:
Originally posted by trikerneil
Otherwise there is a chance of cutting a thread which has a compound pitch of the die and tailstock threads.
HTH
I wasn't talking about pushing hard with the tailstock spindle - just enough to keep the die straight.
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thomas4age
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| posted on 23/5/07 at 02:27 AM |
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Most of the time at least up to M6 threads
I lock the die in my small vice, and put e rod in a small battery power hand drilling machien (whatsitcalledagain?) and then run the drill slowly
using a little presure and when it grips let the die pull the rod through.
I've never tried doing thet on M8 but suppose that would work also,
only the the rod is not connected to for instance..... euhm the car? would take a serious drilling machine and strong arm to pulle that of 
grtz thomas
If Lucas made guns, Wars wouldn't start either.
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JB
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| posted on 24/5/07 at 05:43 PM |
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Cutting Male Threads
All good advice and tips.
However the best advice I can give is design so you do not have to cut male threads! Home cut male threads are generally awful, they are full of
stress raisers and the material not really strong (otherwise you wouldnt be able to cut it)
If I need a male thread I will buy a stud (or bolt) and use that into a tapped hole using 638 Loctite to hold it in.
If it was a threaded adjuster (ARB drop link for eg) I would use tube with welded in tapped threaded inserts.
John
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iiyama
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| posted on 27/5/07 at 08:48 AM |
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If its not a split die, its the wrong one for the job! If its a 'die nut' then these should only be used to clean up threads that are
already cut.
As mentioned before as to how to use one, you should be using a split button die.
If its broke, fix it. If it aint broke, take it apart and find out how it works!
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Ivan
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| posted on 27/5/07 at 02:19 PM |
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Tried to buy a split die at my local Nut & Bolt shop on Friday - don't have in 8mm.
Anyway have subsequently found that running the tap that came with the die set I used through the female part I was using sorted the problem.
Obviously I have an an off-standard set.
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