Cutting Metric Threads

R

ronboult

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Can any one advise if you can use a Thread Dial to cut metric threads ( i.e. by releasing the half nut) if the lathe is fully metric and has a Metric Lead Screw?

Ron
 
Safest way is to always drop it in at the same number you started, if you want to experiment make a light cut, check your pitch, drop it in on different numbers with the cross slide backed off, stop the machine and wind the cross slide in to see if things line up, remember to disengage the split nut and wind the cross slide out before restarting, you can aways just leave the split nut engaged and just go from forward to reverse through the whole threading process.
 
Your lathe manual will tell you what numbers or positions you can engage to cut the thread. IE: Even or Odd.
It is always a good idea to test this as Don B suggests because sometimes the manual lies.
 
I don't use the thread dial, I drop it in and leave it. I even hang a big blue tape flag on it to remind me not to touch it out of habit (it's tough getting old). At the end of the thread, I note my depth, back it out and reverse it. Then I bring it back in + more for the next cut. I found that if I leave it engaged and try to reverse out while in the cut it screws up my threads because of backlash.
 
On my previous machine, Smith CB1239, I would run up to a dial indicator mounted on the way so it would move approx. one full revolution. I had fabricated a mount that spanned across the ways and would allow me to insert a dial indicator that would contact the apron. This would give me plenty of time to watch the dial indicator. Once it hit a predetermined point, I would shut the machine off, back out the crossfeed and reverse the machine. It had to be timed pretty damn close as there were no foot brake to stop the spindle instantly so by watching the dial closely I could get the same "coasting" on each pass.

I am assuming that is the way I will have to do it on my new lathe when I get it as I will not have a foot brake on it either.

Mike.
 
If everything is metric, of course you can use the dial.
 
ronboult said:
Can any one advise if you can use a Thread Dial to cut metric threads ( i.e. by releasing the half nut) if the lathe is fully metric and has a Metric Lead Screw?

Ron
Click to expand...

What brand of lathe do you have ?? If your lathe has a metric lead screw and is as you say fully metric, yes you should be able to release and pick back up on the dial....it should be the same as a standard lead screw cutting standard threads... check your manual, get a piece of round throw it in the chuck and try it out, check the thread pitch with a gauge....
 
While you can use the thread chasing dial on a metric lathe to pick up threads, there is an additional wrinkle vs the imperial/inch thread dial. Metric lathes generally include several (usually 3 sometimes 4) small gears that fit on the thread dial to pick up the leadscrew. Your lathe's manual should provide info on which gear to use for which metric thread.

Site with info on metric thread dial use on a mini-lathe:http://www.mini-lathe.org.uk/threading1.shtml Note that most common metric threads need a 16 tooth gear on the 7x12's thread dial.

The trick in the video mentioned earlier in this thread should work too - it just makes threading work as if you had kept the half nuts engaged to ensure sync.

I took the easy way out and added a dog clutch; threading works the same for metric or imperial - the threading dial was removed.
See: http://www.gadgetbuilder.com/Dog_Clutch.html

John
 
Last edited:
Hi
To those who have replied thank you very much for your time and effort.

The reason that I asked the Q. is that my reading on the Web didn't provide a definitive answer. My current lathe (Sieg SC4) is fully metric but doesn't have a thread dial so I can't just try it. From reading the replies it appears that the answer is not straight forward.

I am considering the purchase of a new lathe because of the issues I am having with the fitting of the chucks to my lathe ( See other posts).

Having a Thread Dial will be just one of the considerations in choosing my new lathe, hence my original Q.

I live in Brisbane Australia and although Au is nominally metric many of the lathes available are hybrids ( Imperial lead screw with 127 Tooth gear). Even some of the cross slide screws are Imperial with bastardised metric dials. Australia is a large country with big distances between major cities. Checking out what is available in other cities is just not feasible.
Cheers
Ron
 
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