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Making a Toolpost T Bolt

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bogstandard:
Darren,

For the size of lathe you have, 25mm is starting to get large, 10mm should by done without even breaking into a sweat.

Have you turned the bar down to 10mm beforehand, as I have seen people trying to die down with the bar up to 2mm oversize. It don't work unless you are a gorilla.

John

Darren:
Hi John,

I turned the bar to 10mm dia to make a 10mm thread. But try as I might either the belt on the lathe slips ( the motor is held by an electrical brake) or the work slips in the collet.

I just can't seem to win on this. Using the 10mm tap gave the same probs, I only just managed to tap the thread on the nut.

I was thinking if I could make a spindle lock and go from there, ??

25mm, not a chance, not on this lathe as it is anyway.... :scratch:

Darren:
Out of interest what sizes do you guys on here "power" tap or thread with taps and dies.

I find that threading under power works far more successfully than hand tapping. On the lathe I've done from 4mm - when the belt slips at around 10mm.

sbwhart:
Hi Darren

I've never cut a thread under power not that I'm saying you shouldn't do it I just havn't had the balls to try. I've watched it done many times the last chap I saw do it was John and he made it look very simple. My new Sieg mill has a tapping function I'll have to get the curage up and try it.

I was talking to a chap at the model eng club and he was saying he taps down to 8ba using a cordless screwdriver, this seams a bit risky to me just think  :scratch: :- you've just spent a month machining up a cylinder, the last job tapping it for the cylinder covers and you break a tap

 :bang: :bang: :bang:

For a bolt

Regards your 10mm thread I don't know what you know about threads but basicly you have:- major dia, effective dia, minor dia:-

Major is the bigest dia:-  if you look at the thread specifications this is below the stated size I'e for a 10mm thread major will be say 9.8 ish

Effective dia is the half way size

Minor dia is the smallest or the diameter at the root of the thread.

For a nut this is the same but you have to think in reverese

Also from the specifications the sizes for nuts and bolts have built in clearances to allow fit.

A trick a lot of machineist do is to truncate the thread to make it easyer to machine for your 10mm thread you could machine your bar to say 9.7 this will leave a small flat on the top of the thread but it wont effect the strength of the thread to much, you can do the same trick when tapping by going the next size up with your tapping drill this reduces the load on the tap.

I hope this helps

Cheers
 :wave:
Stew

bogstandard:
With this new lathe Darren, I have tapped and die'd easily up to 12mm, and I suspect I could go a lot larger. At the moment, 8BA is the smallest I have done in internal and external. Normally I would use my vertical tapping stand for any smaller sizes.

For the smaller sizes, it is all to do with 'feel', larger, brute force.

When you have 40 or 50 holes to tap, you soon get over the fear of using power, otherwise you very quickly end up with sore and aching hands. But like everything, technique and lubrication are 99% of the job, and like Stew has said, get the material to the correct size first.

This chart I put in the downloads section gives you the acceptable range of drill sizes for threading. If the going gets tough, you can try a slightly larger size.

http://madmodder.net/index.php?action=downloads;sa=view;down=8

John

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