Thread Size

[Dingo Dog]

Blokes

In thread size, what size is 12 gauge. My thread size tool has 12G stamped onto it, its the only one in the bunch. Have looked up on Google without much success, I need to make a replacement bit for a Myford 4 jaw chuck. have nothing in my threading chart at all.


DD

[markpest]

G'day DD

Not sure about 12G, but Tap Drill Sizes provides details of #12 screw size, but recognises both 24 and 28 TPI. You mention Myford 4 jaw chuck - Myford have traditionally used Pratt Burnerd chucks. I had good dealings with them 25+ years ago in providing replacement jaw screws. Would it be worth chasing as a spare? Pratt Burnerd International - Products - Manual Chucks

[franco]

The Myford spindle nose thread is 1 1/8" diameter 12 threads per inch, using the Whitworth thread form, i.e. 55 degree thread angle with rounded crests and troughs. There is a bit of information here:

SPINDLE NOSE TAP at Lautard.Com

where he states:
"The spindle nose thread is the same on all Myford Series 7 lathes produced from 1946 right through to the end of 2000. If you own a Myford ML-7, Super 7, Sigma 7, ML7-R, or even a ML-10 or Diamond 10, the spindle nose thread on it will be 1-1/8 x 12 tpi right hand Whitworth."

As pointed out in the website, taps are available, but very expensive - much cheaper and probably more accurate to cut your own 1 1/8 X 12 TPI thread on the lathe on which it will be used.

Frank.

[pipeclay]

A 12 G is .216" DIA,can be UNC,UNF,UNEF,UNS,thread count can very from 24,28,32,36,40,48 and 56 TPI.

[Dingo Dog]

Blokes

The 4 jaw chuck that came with the lathe has been damaged due to being forced closed with swarf on the threads. Removing the jaw thread inserts if that's what they are called I was going to make two new ones out of a couple of bolts threads, have a couple that are 12G. On inspection of the the chuck threads I found that there are a couple that have been damaged. Chunks missing etc. Now all I need is a bottom tap to cut the internal threads back into order. Well that's the plan anyway, just needed to know what 12G was, my local Venables specialist bloke should be able to get me a bottom tap to recut the damaged thread.

DD

[pipeclay]

Does the 4 jaw chuck you have use a Standard V thread form for the Scroll ( the jaw thread insert).
What size Chuck is it.
Seems odd to have this type of thread form if it is for the Jaws.
Does the item you wish to replace have provision in the end of it to take your Chuck Key.

[Dingo Dog]

Pipeclay

Its a 125mm chuck, yep, checked the thread size again, it is 12G.
I dont need to make new screw threads now, as I intend to purchase a bottom tap to re-cut the damaged thread.

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[wbleeker]

Some of the screw pitch gauges I have seen are marked as per the ones in Question IE 12G where they should say 12 TPI , I am pretty sure I have a set like that. A ruler is an easy check for a thread like this six threads per half inch.
Will