Advice on lathe for home shop

It’s 9” between the two collars . I’ve got that front foot floating right now, I read a similar comment on a different thread last night, hopefully it does settle a bit over time
 
GSweldmech said:
It’s 9” between the two collars . I’ve got that front foot floating right now, I read a similar comment on a different thread last night, hopefully it does settle a bit over time
Click to expand...

Keep in mind to do an accurate 2 collar test the bar isn't supported on the tailstock end, and the stock shouldn't extend more than 4 times it's diameter from the chuck. That would mean you would need a piece of stock at least 2-1/4" in diameter to keep it from flexing at the tailstock end due to tool pressure. If your stock was smaller I would do another test using the mentioned parameters. Most manufacturers state that a work piece should not extend more than 3 times it's diameter without support. The most I've ever heard of is 5 times the diameter.

I do know that I can't hold tolerance on my 13" Sheldon with anything over 4 times it's diameter without support. I've experimented with many different materials and many different speeds and feed rates. Without support results are very similar to what you're getting. With support I can easily hold .0003". If I'm extra careful I can get down to .0001. However tolerances this tight aren't necessary for more than 90+% of the work I do.
 
projectnut said:
Keep in mind to do an accurate 2 collar test the bar isn't supported on the tailstock end, and the stock shouldn't extend more than 4 times it's diameter from the chuck. That would mean you would need a piece of stock at least 2-1/4" in diameter to keep it from flexing at the tailstock end due to tool pressure. If your stock was smaller I would do another test using the mentioned parameters. Most manufacturers state that a work piece should not extend more than 3 times it's diameter without support. The most I've ever heard of is 5 times the diameter.

I do know that I can't hold tolerance on my 13" Sheldon with anything over 4 times it's diameter without support. I've experimented with many different materials and many different speeds and feed rates. Without support results are very similar to what you're getting. With support I can easily hold .0003". If I'm extra careful I can get down to .0001. However tolerances this tight aren't necessary for more than 90+% of the work I do.
Click to expand...
This is somewhat encouraging, I’m doing this with a piece that started off at 1-1/2” diameter ( the biggest I had on hand) so I’m about 6 times the diameter. I’m taking cuts of .005” , I wouldn’t think that the piece would flex with such a small cut. I made a few more attempts to dial things in further yesterday and I was getting worse results that on Sunday. Maybe this is a result of the piece being down near 1.3“ and flexing more. I will get a chunk of 3” the next time I’m at my steel supplier, I’ve been using standard mild steel is there a preferred grade I should be using for this test?
 
I suggest doing a spring pass on the two collars. And, you want as little tool pressure as possible. I found the shape of insert affected the outcome as well. Smallest radius yielded the best results. I was down to 0.0002 over 8.5" or so (if I recall correctly) on a diamond shaped insert.
 
I’ve been thinking about this , if the work piece is flexing away from the cutter wouldn’t I have a larger diameter on the tail stock collar? I’ve got the opposite, my tail stock side collar is smaller.
 
Did you watch the video I posted? He goes over it really well. It helped me get it done.
 
You must log in or register to reply here.
Back
Top