Threading again

**Steamwhisperer** · 10th December 2011, 06:16 AM

Originally Posted by morrisman

The general rule of thumb is
55 degrees is 0.64 x pitch
60 degrees is 0.61 x pitch

So for 55 degree at 7tpi it would be about .091" depth ?

Hi Mike,
That would be correct. The only reason this would differ is for the different classes of fit but for general purpose those figures work well. If possible I always do the nut first and use it as a gauge.

Phil

**tanii51** · 10th December 2011, 08:17 AM

hmmm what is the class of thread used for a lathe chuck thread and spindle
john

**pipeclay** · 10th December 2011, 09:36 AM

More than likely it would be something like 3 or 4 G but it wouldnt really matter that much if it is 6G.
I think each number represents about .01mm clearance.

**Michael G** · 10th December 2011, 03:16 PM

The class of thread for a lathe spindle is not as significant as you might first think - Accurate location of the chuck on the spindle depends on a couple of register faces. One is a cylindrical surface adjacent to the thread which is usually the major diameter of the thread or a little larger; the other is a land at 90 degrees to that which is usually just slightly proud of the surface the spindle comes out of - the closer to the bearing the better. These two surfaces define the spindle locating points. The thread is mainly there to hold the chuck in place.

Michael

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