John, if you are referring to the apron lead
screw, there were three specs: standard; tool room and military. the military
spec being the best.
these were sorted as they were ran in production.
If you are referring to the 7/16 LH acme for the cross feed, the normal (old
way) was measurement over 3 wires to an SBL internal spec for back lash with
the nut and or assembly. On a 7/16 acme you would use .05164
wires
and the internal spec was .451 +.000 and
-.003. So .003 backlash was allowed. The stock for the screw on a non ground crossfeed was turned
to .4375/.4370. on a ground screw, the turn was .4475/.4455 and then ground to
.4375/.4370. South bend didn't use a standard Q9000
screw standard such as 4G or 5G (rub fit) the
screw fell in-between those numbers but was listed on the control sheets as
4G.
A 3G screw if roll threaded will make it into the
back lash specs just fine. My screw material is roll threaded 3G, and I'm
almost out of stock, but I will soon be running the original South bend
automatic screw machine that made these cross
feed screws, I have the only one left from the factory thanks to Ted. and I
have it running, but need to set up the collet for the blank stock and set the
cutter blocks up, I have the finish tool block done, I need to do the
rougher bit now. Just takes a lot of time...
Steve Wells
----- Original Message
-----
Sent: Saturday,
November 02, 2013 7:15 PM
Subject: Re:
[southbendlathe] Re: C to B 9" workshop conversion.
Varying accuracy are claimed for different models of SB lathes
lead screws. Also the different suppliers of acme stock makes
assertions about high accuracy. What is involved and how is accuracy
measured for threads?
I guess I am asking
for some one to put on a pedogogue's hat.
Thank you Jim,
I have cut acme threads to fit a worm amce cast iron nut on my
tail stock.
Alec Ryals
From:
Jim B.
To: southbendlathe@...
Sent: Saturday, November
2, 2013 8:41 AM
Subject:
RE: [southbendlathe] Re: C to B 9" workshop conversion. [2
Attachments]
Steve
Wells has some very special, accurate and polished 7/16-10 LH stock for
rebuilding cross feeds.
The
compound is 3/8-10 RH
You can
find accurate stock for that here.
http://www.roton.com/
MSC also
carries some stock but they are expensive.
Here is
some leadscrew rod.
http://www.mscdirect.com/product/01206184
Of course
you can roll your own. You only need some rod and to grind an ACME threading
tool.
I have
made some for my Burke Mill in/out feed and its been good for 5 years now.
This also
gives you the ability to “fit” the thread to a worn nut.
Were
do I buy accurate amce thread stock.
Thank You
Alec
