Leadscrew Freeplay

J

Jay Cutright

New member
Someone with a South bend heavy 10 that cuts great threads check your leadscrew freeplay and tell me what you have.
I set an indicator on the end of the leadscrew, engauge the half nuts and rock the saddle handwheel left and right while watching the indicator. My lathe has .001 freeplay I'm wondering what some of your lathes have.
 
Jay Cutright said:
Someone with a South bend heavy 10 that cuts great threads check your leadscrew freeplay and tell me what you have.
I set an indicator on the end of the leadscrew, engauge the half nuts and rock the saddle handwheel left and right while watching the indicator. My lathe has .001 freeplay I'm wondering what some of your lathes have.[/QUOTE

.001 is very good all most all manual lathes that use half nuts for threading will have some so called free play. Most will have more then .001 even when new.

Chet
Click to expand...
 
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coyotechet said:
Jay Cutright said:
Someone with a South bend heavy 10 that cuts great threads check your leadscrew freeplay and tell me what you have.
I set an indicator on the end of the leadscrew, engauge the half nuts and rock the saddle handwheel left and right while watching the indicator. My lathe has .001 freeplay I'm wondering what some of your lathes have.[/QUOTE

.001 is very good all most all manual lathes that use half nuts for threading will some so called free play. Most will have more then .001 even when new.

Chet
Click to expand...

I think it may be to tight. I have a Chinese made machine here that cuts a better looking thread with .008 play at in the leadscrew than it does at .000
My 10L cuts good looking threads but not as good as I think they should be. I restored this machine and set the leadscrew freeplay as close to zero as I could get it before I put the gear box back on it. I'm now thinking a little freeplay in the leadscrew can allow the cutting tool to float a little through imperfections in the leadscrew and result in a better thread quality.
My lathe was built in the time that South bend put one gear box screw under the head stock so it will take a bigger investment in time for me to experiment on it and thought it'd be worth while to find out what tolerance other people's machines have.
Click to expand...
 
Jay Cutright said:
coyotechet said:
I think it may be to tight. I have a Chinese made machine here that cuts a better looking thread with .008 play at in the leadscrew than it does at .000
My 10L cuts good looking threads but not as good as I think they should be. I restored this machine and set the leadscrew freeplay as close to zero as I could get it before I put the gear box back on it. I'm now thinking a little freeplay in the leadscrew can allow the cutting tool to float a little through imperfections in the leadscrew and result in a better thread quality.
My lathe was built in the time that South bend put one gear box screw under the head stock so it will take a bigger investment in time for me to experiment on it and thought it'd be worth while to find out what tolerance other people's machines have.
Click to expand...

Also check to see what freeplay you might have at various points on the lead screw. Might be a bit more sloppy near the chuck as most threading may be done here
Click to expand...
 
HiWall said:
Jay Cutright said:
Also check to see what freeplay you might have at various points on the lead screw. Might be a bit more sloppy near the chuck as most threading may be done here
Click to expand...

My half nuts are adjusted as snug as I can get them without binding on the leadscrew, the play I'm measuring is the leadscrew its self, freeplay can be checked anywhere along the lead screw with the half nuts engaged. The adjustment is the leadscrew nut inside the gear box.
Click to expand...
 
Jay Cutright said:
Someone with a South bend heavy 10 that cuts great threads check your leadscrew freeplay and tell me what you have.
I set an indicator on the end of the leadscrew, engauge the half nuts and rock the saddle handwheel left and right while watching the indicator. My lathe has .001 freeplay I'm wondering what some of your lathes have.
Click to expand...

Since you only cut in one direction it is not all that important actually.

As long as it tightens up the same way each time it engages and the lead screw comes to the same position.

A lot of this is similar to the 'tricks' we use that allow a 1911 to be loose enough to cycle but come to the same
relative position when 'in battery' each rime before firing.
 
brickeyee said:
Since you only cut in one direction it is not all that important actually.

As long as it tightens up the same way each time it engages and the lead screw comes to the same position.

A lot of this is similar to the 'tricks' we use that allow a 1911 to be loose enough to cycle but come to the same
relative position when 'in battery' each rime before firing.
Click to expand...


+1
 
Jay Cutright said:
Someone with a South bend heavy 10 that cuts great threads check your leadscrew freeplay and tell me what you have.
I set an indicator on the end of the leadscrew, engauge the half nuts and rock the saddle handwheel left and right while watching the indicator. My lathe has .001 freeplay I'm wondering what some of your lathes have.
Click to expand...

I have a 1944 Heavy 10 but I put a new half-nut on it a few years ago. About 1/32 play. Unless you have a ball screw you will have some end play. Look at your half-nut. You can tell if it is badly worn. Otherwise don't sweat it.

(0.001" freeplay? It wasn't that tight when new.)




.
 
JerrySharrett said:
I have a 1944 Heavy 10 but I put a new half-nut on it a few years ago. About 1/32 play. Unless you have a ball screw you will have some end play. Look at your half-nut. You can tell if it is badly worn. Otherwise don't sweat it.

(0.001" freeplay? It wasn't that tight when new.)
.
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Jerry, I think I have it to tight. I clamped the leadscrew in a vise (with brass jaws) and setup an indicator on the gear box then tightened the leadscrew nut until I had the .001, I really believe I'll see an improvement if I go back and give it some clearance.
 
Adjusting half nuts

Hello Jay
Out of curiosity, I have a question that maybe you can help me with. How do you go about adjusting the half nuts on a south bend lathe?


Thanks, Chet
 
coyotechet said:
Hello Jay
Out of curiosity, I have a question that maybe you can help me with. How do you go about adjusting the half nuts on a south bend lathe?


Thanks, Chet
Click to expand...

That's a great question Chet! ? Replace them with new old stock half nuts to the tune of about $350.
I was thinking about my big 16" machine that I adjusted all of the clearance out of. This big grizzly is the reason I'm thinking about my heavy 10, I adjusted some clearance into the leadscrew and half nuts and improved the thread quality. I was thinking I went through an adjustment procedure on the 10L until you asked.
 
Jay Cutright said:
Jerry, I think I have it to tight. I clamped the leadscrew in a vise (with brass jaws) and setup an indicator on the gear box then tightened the leadscrew nut until I had the .001, I really believe I'll see an improvement if I go back and give it some clearance.
Click to expand...

Jay, your leade screw is of Acme design. Like a Vee thread they need a working clearance . If you only have about 0.001" end play you must have adjusted the half-nut to where it has no radial clearance. Acme threads need a different working clearance than a Vee thread. Same with the British Whitworth. The Whitworth is designed to be loaded from one direction only.


i.e. Back it off a few thousands from "tight".



.


.
 
JerrySharrett said:
Jay, your leade screw is of Acme design. Like a Vee thread they need a working clearance . If you only have about 0.001" end play you must have adjusted the half-nut to where it has no radial clearance. Acme threads need a different working clearance than a Vee thread. Same with the British Whitworth. The Whitworth is designed to be loaded from one direction only.


i.e. Back it off a few thousands from "tight".



.


.
Click to expand...

Jerry, I believe you have misunderstood me. I'm measuring the end play at .001 by measuring from the end of the leadscrew, not the saddle, just the leadscrew.
I noticed yesterday that whith the indicator on the saddle I get .007 so the half nuts do have some clearance.
 
Jay,

If I'm understanding you correctly, you have an indicator touching the end of your lead screw, and you get .001 when you push the lead screw from side to side, meaning moving it parallel with the bed of the lathe. Correct?

Justin
 
HiWall said:
Jay Cutright said:
Also check to see what freeplay you might have at various points on the lead screw. Might be a bit more sloppy near the chuck as most threading may be done here
Click to expand...

Some things you and Chet mentioned here got me out in the shop looking this machine over again instead of going by what I remember.
The measurement you mentioned checking is what I would consider the clearance the half nuts have on the leadscrew. I was thinking when I reassembled this machine I went through an adjustment procedure on the half nuts but I was mistaken, I did that on my big grizzly. It produces better threads with some clearance in the half nuts and the leadscrew, I learned something this week.
Now I'm back on my 10L, I have .007 play at the saddle and I know .001 of that is the leadscrew itself so have some clearance in the half nuts and it is consistent throughout the length of the leadscrew.
The leadscrew does not bind so I'm leaving it alone.
Click to expand...
 
Jay thanks for the kind reply makes a lot scene. Having the lead screw adjusted at the gear box to tight could create a bend in the lead screw.
Glad you found what ever it was and got your Heavy 10 fixed to your liking.

Chet
 
This is a little off the topic, but I thought I would mention it for enthusiast to be aware of.

On lathes such as the South Bend, you have a plain bearing thrust That controls the end play in the spindle.

If you have noticed that when threading off center, the tool seems to wander from one side of the thread to the other, (whether internal or external), your spindle thrust is probably too loose. It needs to be just snug enough so that it does not build heat, but not so loose as to allow the spindle to drift back and forth in it's bearings.

It's easy to adjust with the nuts at the rear of the spindle.
 
Jay,

I think you have likely figger'd this out, but I doubt that one thou in lead screw play is causing your threading issues. I'd be inclined to look at such things as tool rigidity, gib tightness, the compound being cranked towards the work or locked down, etc.

Justin
 
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