Re: C to B 9" workshop conversion.

Steve Wells

The stack up height of the A/B apron for the cross feed was set with the apron cross feed gear they are marked M for minus and P for plus, a common line card listing would be M 10 for minus .010
The cross feed nut should wear first by design, but after many years the screw can wear in the center and you can expect to have to replace the nut and screw if backlash is over 10 to 20 K. I would replace the nut first and inspect the screw and if you can see sharp threads or measure wear, replace the screw threads. It's not difficult to do either and you refit everything and you will probably never do it again if it's oiled and maintained.
Steve Wells 

----- Original Message -----
From: john kling
Sent: Sunday, November 03, 2013 4:06 PM
Subject: Re: [southbendlathe] Re: C to B 9" workshop conversion.


Thanks for the information. I am trying to approach this with my own attempt of order. My first step is acquisition of the A and B apron. The cross feed screws seem to be a bottleneck as well. I have what I believe is a model 415 (single arm banjo and top oilers). I assume there is no additional problems here. When one has excess backlash (I do not have this problem) is the greater problem of wear normally found in the bronze "nut" or in the steel screw?

From: Steve Wells
To: southbendlathe@...
Sent: Sunday, November 3, 2013 3:55 PM
Subject: Re: [southbendlathe] Re: C to B 9" workshop conversion.


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 -----
From: john kling
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.

From: "armne@..." <armne@...>
To: "southbendlathe@..."
Sent: Saturday, November 2, 2013 1:27 PM
Subject: Re: [southbendlathe] Re: C to B 9" workshop conversion.

  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.
MSC also carries some stock but they are expensive.
Here is some leadscrew rod.
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.
Jim B.

Were do I buy accurate amce thread stock.
Thank You

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