Need Help

M

MGP

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Ok here it goes i have small Grizzly 11x26 Lathe i recently moved it and trying to get it setup im having a problem. I chucked up my test barrel in a 4 jaw and indicated with a range rod to within .0005" cut new 60 degree centers ,then put in between centers with plate and a dog to hold the barrel. My Problem is with the 8" test barrel im cutting 6-1/4" length of the barrel. Measureing with my mic at the headstock the barrel od is .9776" in the middle it is .9780" and at the tailsock it is .9794" so i have .0018" difference tapering from the tailstock to the headstock but what i find weird is when i run my indicator on the top of the barrel zero the dial at the headstock and run it along to the tail stock it is .003" difference.Run my dial on the side of the barrel zero the dial at the headstock and run it along to the tail stock and it is .0005" difference and when i do the same on the bottom of the barrel it is
.0011". Can someone give me a start on what to do i cant remember when i first set it up 3 or 4 years ago. Thanks Mike
 
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does your book tell you the steps to go thru? on my Jet it has very detailed instructions on setting the chuck and tailstock when one is out one way and tells you which one to move when it's out the other way. I figure your grizzly has the same type instruction set.
 
Lathe help

G'day Mike

What you have described in your post sounds fairly normal for a reasionable quality lathe.

You can adjust the tail stock over to correct for the difference in diamiter. As you described your barrell is 0.0018 larger at the tail stock. So the tail stock should be moved over towards the tool by HALF this ammount or 0.0009. Be aware that this is a fairly small error and is quite common in small lathes. Put your dial indicator on the side of the live center shank (as close to the job as possable) and zero it. Then start undoing the screws and adjust the tail stock to give the required 0.0009 offset. With errors this small it can be quite fiddly and may require several attempts. Keep taking the SAME SIZED light cuts (say 10 thow) and Check again, readjust as required.
Don't worry if you can't get it spot on. On machines like this it is a fluke if you get it exactly parrallel. And even more flukish if you can repeat it.
You can always use a little emery cloth to bring it to the final size.

As for running the indicator over the top of the job, you didn't say weather it is higher or lower at the tailstock end, none the less is dosn't realy matter as you can't adjust it up or down anyway.
Most lathe tail stocks are set a little high when the machine is cold and as the head stock heats up it will "Grow" higher and match the tails stock hight more closly.
As for the 0.0005 on the side of the barrell this could be a combination of sloppyness in the lathe carrage slides, the surface finish of the job and swarf on the lathe bed.
A very old and wize machinist once told me that you can't do an acurate job on a dirty machine. And with this i have to admit i am anal about cleanlyness.:D

Cheers
Leeroy
 
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Another factor in small lathes is deflection. Most people really have no idea of the forces involved in taking a cut on steel. Smaller lathes can deflect the tailstock to an alarming degree, especially with a heavy cut. To check to see if I have an alignment or deflection problem, I have a precision ground mandrel for truing actions that I place between centers and run a test indicator from the headstock to the tailstock. If the reading on the indicator is steady, the tailstock is properly aligned and the problem is deflection. To correct for deflection, you must use very sharp cutting tools and sneak up on your final dimensions with final cuts as small as .001". Tedious, but necessary if you want good accuracy from the smaller machines.
 
Lathe set up

You said you just moved the lathe, have you checked to make sure it's level along the bed? After a move it may take some little run time for it to find it's final position and a slight twist in the bed can cause tailstock miss-alignment. A small lathe is surprisingly easy to twist, just put a dial indictor on a bar mounted between centers and lean on the tail stock a little and you'll see.

Dennis
 
Dennis D. said:
You said you just moved the lathe, have you checked to make sure it's level along the bed? After a move it may take some little run time for it to find it's final position and a slight twist in the bed can cause tailstock miss-alignment. A small lathe is surprisingly easy to twist, just put a dial indictor on a bar mounted between centers and lean on the tail stock a little and you'll see.

Dennis
Click to expand...

yep..i'd start here. run and check, run and check....let it settle in.
mike
 
Thanks Guys

I ordered mounting pads for the bench is this a bad idea? I was going to level the bench again with these mount pads and start over leveling the lathe? Thanks Mike
 
Leeroy said:
G'day Mike

What you have described in your post sounds fairly normal for a reasionable quality lathe.

You can adjust the tail stock over to correct for the difference in diamiter. As you described your barrell is 0.0018 larger at the tail stock. So the tail stock should be moved over towards the tool by HALF this ammount or 0.0009. Be aware that this is a fairly small error and is quite common in small lathes. Put your dial indicator on the side of the live center shank (as close to the job as possable) and zero it. Then start undoing the screws and adjust the tail stock to give the required 0.0009 offset. With errors this small it can be quite fiddly and may require several attempts. Keep taking the SAME SIZED light cuts (say 10 thow) and Check again, readjust as required.
Don't worry if you can't get it spot on. On machines like this it is a fluke if you get it exactly parrallel. And even more flukish if you can repeat it.
You can always use a little emery cloth to bring it to the final size.

As for running the indicator over the top of the job, you didn't say weather it is higher or lower at the tailstock end, none the less is dosn't realy matter as you can't adjust it up or down anyway.
Most lathe tail stocks are set a little high when the machine is cold and as the head stock heats up it will "Grow" higher and match the tails stock hight more closly.
As for the 0.0005 on the side of the barrell this could be a combination of sloppyness in the lathe carrage slides, the surface finish of the job and swarf on the lathe bed.
A very old and wize machinist once told me that you can't do an acurate job on a dirty machine. And with this i have to admit i am anal about cleanlyness.:D

Cheers
Leeroy
Click to expand...


It is .003" high at the tailstock.I am anal about keeping my lathe clean also. Thanks Mike
 
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