Lathe setup, correcting taper.

L

litewings

H-M Supporter - Silver Member
H-M Supporter - Silver Member
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Dec 23, 2019
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So I've had the 1340GT lathe for a while now and have done some smaller projects. All has been good. When first setting it up in its home position I was very careful about getting it as level as possible. Since its had some run-time now decided to check level again in case of settling. All is still good according to the Starrett 98-6. Had some free time today so decided to cut a test bar to check headstock/ways alignment. Using 12" piece of 2.5" 6061, faced the ends, center drilled and relieved 8" between the bands to be test cut. Did the test cuts and had a .0031 difference in 9". I was able to get it to .0004 by adding twist to the bed via the adjusting legs on the bench. On the level now it shows about 3/4 of a line difference from headstock to tailstock ends. It's a mental thing, but I don't like having it out of level even though the end result is better.
Would it be better to adjust the headstock angle and keep the bed level? Opinions?
 
litewings said:
So I've had the 1340GT lathe for a while now and have done some smaller projects. All has been good. When first setting it up in its home position I was very careful about getting it as level as possible. Since its had some run-time now decided to check level again in case of settling. All is still good according to the Starrett 98-6. Had some free time today so decided to cut a test bar to check headstock/ways alignment. Using 12" piece of 2.5" 6061, faced the ends, center drilled and relieved 8" between the bands to be test cut. Did the test cuts and had a .0031 difference in 9". I was able to get it to .0004 by adding twist to the bed via the adjusting legs on the bench. On the level now it shows about 3/4 of a line difference from headstock to tailstock ends. It's a mental thing, but I don't like having it out of level even though the end result is better.
Would it be better to adjust the headstock angle and keep the bed level? Opinions?
Click to expand...
machine levels not always best, i stuck a 7 foot straight edge across the bed and sighted at the ends with a TOPCON level, cutting true now, also Abom 79 has a vid on levelling
 
I just went through the same exercise. I first adjusted the legs to get it to cut straight. A couple days later after having read too much I decided to use the Starrett and level it with the legs. I then aligned the headstock. My feeling with that is that I know the headstock will be aligned when the lathe is level.
 
parshal said:
I just went through the same exercise. I first adjusted the legs to get it to cut straight. A couple days later after having read too much I decided to use the Starrett and level it with the legs. I then aligned the headstock. My feeling with that is that I know the headstock will be aligned when the lathe is level.
Click to expand...

I have a feeling I'll be doing the same. Adding twist to me just seems wrong when there is another way that will not induce as much stress. Or am I over thinking it?
 
You'll find different schools of thought if you do enough reading. To me, with these lathes, you have the ability to make it level and adjust the headstock so I will do it that way. At least until I try something different. LOL
 
IMO the Starrett 98-6 does not have enough resolution to get it dialed in to the standards you are trying to achieve. You'd need a Starrett 199 to deal with your desired the accuracy. Also, it helps to have an alignment bar as shown here:
https://flic.kr/p/ST9RUG
Test bars like that are available on eBay for a reasonable cost and fit directly to the MT5 taper of the spindle.
tinyurl.com

5MT Lathe Alignment Test Bar MT5 Alloy Steel Over All Length 442mm 17-1/2 Inch 689274003735 | eBay

Overall Length : 442mm (17-1/2"). Shank : 5MT. We reply within 24 hours.
tinyurl.com
 
Putting that kinda twist in the lathe bed IMHO is a very bad idea. The bed should be straight. Does not need to be level, just straight. If the lathe still turns a taper after the bed is straight and no wear to be the cause. Then I would look at the head stock for the problem.

And you can use a Starrett 98. Must use finesse and just get a reading to be the same from front to back. Does not need to be on level, just the same reading.
 
+1 on the test bar. I think I have that exact one. It's not ground perfect all around. I had to use the average difference (Rollies-Dads?) method with the bar.
 
And remember that larger on the TS end is acceptable. I think it is .0002 or .0003" over 12".
 
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