leadscrew sizes

J

jtg

Guest
I am always hearing about not getting a lathe with a leadscrew with 8 tpi.
Some people say get one with 4 tpi.
What are they referring to.
I do know the south bend 10L is 8 tpi but not sure about the rest.
Do you get better accuracy with the 4 tpi or what.
Any input would be appreciated as am now looking for a new lathe.
thanks,
John
 
Lathe leade screw pitch is mostly determined by the lathe size hence the leade screw diameter and pitch. With the proper gearing in the thread/feed box a 4 pitch and an 8 pitch would cut the same threads per inch.

On a smaller lathe with a 3/4" diameter 4 pitch screw would nearly cut the leade screw in two due to the double depth of a 4 pitch Acme thread vs.. the double depth of an 8 pitch Acme thread.

Now, getting into bigger lathes the leade screw diameter is not proportional to the lathe swing or horsepower. The screw strength is related but not proportional. For example, a 24" swing lathe of 20 HP and a 48" lathe of 35 HP might have the same diameter and pitch of leade screw.
 
leadscrew thread per inch

thank you very much for explaining the leadscrew sizes to me.
I was looking at a new victor 1440G lathe and noticed the leadscrew was 4 instead of 8 like on my heavy 10 and thought it may be a problem but now I see I was worried for nothing. They had a sharp 1440F that had an 8 tpi leadscrew like my south bend and although lighter than the victor was considering that because of the leadscrew.
This is a great forum to have knowledgeable people able respond to anyone's questions so fast.
thank everyone again
 
jtg said:
thank you very much for explaining the leadscrew sizes to me.
I was looking at a new victor 1440G lathe and noticed the leadscrew was 4 instead of 8 like on my heavy 10 and thought it may be a problem but now I see I was worried for nothing. They had a sharp 1440F that had an 8 tpi leadscrew like my south bend and although lighter than the victor was considering that because of the leadscrew.
This is a great forum to have knowledgeable people able respond to anyone's questions so fast.
thank everyone again
Click to expand...
You have a SBL Heavy 10 and are buying a Victor????? To be used as a spare I hope. Don't get me wrong, the Victor is not a bad lathe as imports go but it is not the quality or rigidity of the SBL.
 
leadscrew thread per inch

Yes I have a south bend heavy 10. I actually just sold my 10k and for awhile had 2 south bends.
The 10k was completely rebuilt by southbend just before they closed, actually about a year and a half before and was perfect but I got the bug to get the larger heavy 10 and found one in the east, I live in texas, and had it shipped here.
The problem is that i have about some runout on the spindle, it is the toolroom version with taper, etc, and it appears after adjusting the shims, the front bearing is worn out.
I am concerned I will be throwing good money away if i start replacing or rebuilding the machine as I personally have no knowledge of how to do these things and it would appear to be a costly project.
LeBlond who I called wants 12 thousand for a complete rebuild of the machine. That kills me because the machine is a beautiful piece of american craftsmanship.
 
jtg said:
Yes I have a south bend heavy 10. IThe problem is that i have about some runout on the spindle, it is the toolroom version with taper, etc, and it appears after adjusting the shims, the front bearing is worn out.
I am concerned I will be throwing good money away if i start replacing or rebuilding the machine as I personally have no knowledge of how to do these things and it would appear to be a costly project.
LeBlond who I called wants 12 thousand for a complete rebuild of the machine. That kills me because the machine is a beautiful piece of american craftsmanship.
Click to expand...
After removing all the shims, how much side-to-side movement do you have? i.e. If you put a 0.0001" dial indicator on the spindle nose at the base of the threads, how much movement do you have when you pry on the spindle nose with medium force?
 
leadscrew and runout

sorry i took so long to reply. i am on the road and typing on my brother in laws computer.
the runout when measured with a .0001 dial test indicator is 3 lines before the number 1 on a starrett dial test indicator that has numbers from 1 to 5 and back to 1 again at the top.
when i stick a broom in the spindle and measure on top of the cam lock coming out end of spindle it appears to measure about the same and sometimes all the way to the first number 1 and sometimes even to two lines past the number 1.
i do know that if i remove the bearing expander screws on the front spindle and leave the ones on the rear tight that the spindle still turns but if i remove the rear expander screws also the spindle will not turn.
i do know that with what shims i have in there now it is very hard to spin the spindle but if i add one more .0005 shim it turns more easily but the runout is also greater.
i may not be able to reply as fast due to being on road till tuesday but will definately try to read your reply to this and try to comment when i can but will for sure when i get home on tuesday for sure if not able to before.
thank you again
john
 
leadscrew and runout

Jerry,
I am sorry for the delay in returning to this thread. I have been in and out of the Hospital for the last 3 months or so with medical problems.
I have since purchased 2 brand new bearings with expanders from Joe at Plaza that he had.
I have installed on the spindle and now see how worn out my bearings really were. Now without opening the expanders the spindle will not move at all.
Before it had no effect at all on the larger front bearing it was so worn out.
My next project is to fabricate and install new bearing shims that I purchased for the lathe. It has become a time consuming job to try and find the right amount of shim stock for the spindle.
Any input on cutting new brass shim stock would be appreciated. I seem to keep messing the brass up with scissors.
Also does anyone know what is the correct amount of shim spacers that South Bend originally installed on their lathes.
John
 
jtg said:
Jerry,
I am sorry for the delay in returning to this thread. I have been in and out of the Hospital for the last 3 months or so with medical problems.
I have since purchased 2 brand new bearings with expanders from Joe at Plaza that he had.
I have installed on the spindle and now see how worn out my bearings really were. Now without opening the expanders the spindle will not move at all.
Before it had no effect at all on the larger front bearing it was so worn out.
My next project is to fabricate and install new bearing shims that I purchased for the lathe. It has become a time consuming job to try and find the right amount of shim stock for the spindle.
Any input on cutting new brass shim stock would be appreciated. I seem to keep messing the brass up with scissors.
Also does anyone know what is the correct amount of shim spacers that South Bend originally installed on their lathes.
John
Click to expand...
John, from what I gather in the shim adjustment instructions and looking at an exploded drawing of the headstock there would be 0.003" of shim under the end of each cap. One shim is 0.001", the other is 0.002".

The 0.002" is called a laminated shim (why-dunno). Anyhow, instructions say to remove the 0.001" for first the wear adjustment but to save the 0.001" to use later when additional wear requires another adjustment.

The second adjustment would be to remove the 0.002" shims and replace it with the 0.001" that was saved. Then I guess the final adjustment that would be available would be to again remove the 0.001" shims.

Mine has the first adjustment made, i.e. the 0.001" shims are removed. My spindle is still in great condition as to free-play. Since mine was made in 1944 and it has only required removal of one shim, I assume there would be thousands of hours of use between spindle adjustments.

We have some 3-step 13" South Bend lathes at Northeast State College that have been there for at least 25 years that have never had a shim removed according to maintenance records. But, they don't get used 24/7 either. These 13" SBL's look just like a Heavy 10 except slightly larger.

As to adjustment, and since you are using an old spindle and new bearings, keep adding shims, equally on each cap end, till the spindle turns freely. Then run the spindle at high RPM for a few minutes to make sure you don't get any heat buildup. Make sure you have oil in the bearing reservoirs and the wicks are clean. I use Mobil DTE light with 50% kerosene
 
Jerry,
thanks for getting back to me so fast.
I will start tomorrow cutting shim spacers and hopefully by friday try installing them a few at a time.
John
 
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