Re: cam tailstock lock modifications for SB13


Agreed. Jim is spot on the money. 

From: <> on behalf of Jim_B <jim@...>
Sent: Monday, May 11, 2020 3:40 PM
To: <>
Subject: Re: [SouthBendLathe] cam tailstock lock modifications for SB13
Yes I agree the thread is relevant, but only to the extend that it must be coarse enough to do the job. 

A fine thread will not work. 

Let's say that we need 0.010” of space between the lower clamp and the underside rails of the bed for the tailstock to move properly. 

(Is that a good number? I don't know, I know on my beat up bed I would need more.)

I want that space to show up when I move the locking nut 1 flat, maybe 1-1/2 flats. Then one turn of the screw would move the nut 0.060”
Thats a 16.7 TPI thread. so anything less than 16.6 TPI will not work for the quick on/off use we are looking for. 

The washer thickness or position of the square nut would not matter, We would need more than 1 flat to get enough space. 
Now my SB-10L has a 13 TPI thread. Thats 0.077” per turn or about 0.013”  per flat. If your bed is in fair condition that should be enough, So   should 14 TPI, or 12 TPI or 10 TPI  and any usable thread coarser than 16.7.

A 20 TPI thread, OTOH will not work. It will lock down the tailstock but not in 1 flat. 

So, Yes the thread pitch is important as long as its coarse enough. 

On 11 May 2020, at 14:56, wlw19958 <wlw-19958@...> wrote:

Hi There,

Sorry I have to respectfully disagree.

Fine.  You can disagree.  I still maintain that the thread pitch is immaterial.  Of course
one can calculate the amount to decrease or increase based on the pitch but it doesn't
matter what the pitch is.  One can change the thickness to suit no matter what the pitch
is.  You are getting bogged down in the minutia that hasn't the constituent value of a
large pile of legumes.  You have to step back to see the larger picture. 

Good Luck!
-Blue Chips-

Jim B.

Jim B

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