# Lathe setup, correcting taper.



## litewings (Feb 26, 2020)

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?


----------



## stuarth44 (Feb 26, 2020)

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?


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


----------



## parshal (Feb 26, 2020)

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.


----------



## litewings (Feb 26, 2020)

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.



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?


----------



## parshal (Feb 26, 2020)

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


----------



## davidpbest (Feb 26, 2020)

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.  *








						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
				



*


----------



## cascao (Feb 26, 2020)

In this video you will see some good tips


----------



## chips&more (Feb 26, 2020)

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.


----------



## parshal (Feb 26, 2020)

+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.


----------



## ddickey (Feb 26, 2020)

And remember that larger on the TS end is acceptable. I think it is .0002 or .0003" over 12".


----------



## benmychree (Feb 26, 2020)

The Starrett #98 is definitely not sensitive for machine leveling, it is intended for millwright work; the 198 is 10 times the sensitivity.  The 98 is good for getting the job withing the range of the 198.  The ways should be level, if the lathe still cuts with taper, other means should be pursued, such as scraping for alignment under the headstock or shimming.  It is best to not have a twist in the bed.


----------



## RJSakowski (Feb 26, 2020)

Before checking for turned taper, I check for perpendicularity of the cross slide travel to the spindle axis.  If the travel isn't perpendicular, you will cut a dome or a dish depending upon which way the the misalignment runs.  Since the carriage isn't moving on the ways, a twist in the bed will have minimal effect on this cut.  On my lathe the only way to adjust this is to adjust the headstock.

I check for proper alignment by mounting a boss on my faceplate several inches from the center.  I set up a dial or test indicator on the cross slide and rotate the faceplate so the boss is to the front and horizontal with the spindle axis and adjust the indicator to intersect the boss with the cross slide retracted.   I zero my indicator and rotate the faceplate with the boss to the rear and horizontal and move the cross slide so the indicator again intersects the boss..  If the reading is zero, the cross slide is perpendicular with the spindle axis.  If not, the difference divided by the separation between the two measurement points is the amount of taper.  To ensure hitting the same point on the boss , I place a small marker dot on the boss.

Once this is done, I next adjust turned taper, checking by Rollie's Dad's method or by the two collar test.  Finally, I adjust my tailstock using a modification of Rollie's Dad's method or by the two collar test.


----------



## parshal (Feb 26, 2020)

Not to hijack the thread but the discussion about the accuracy of the Starrett 98 vs 199 got me searching around.  While the graduations on the 98 are .005" the spacing between the graduations is quite large.  I'm sure one can easily use that to a finer degree than .005".

Poking around for used 199's I found you can get a brand new Mitutoyo 960-613 for $375 which is cheaper than the other two less accurate models.  It's accuracy is .00017".  I can't imagine trying to level a lathe with that.  I'd be chasing my tail for hours.  LOL


----------



## RJSakowski (Feb 26, 2020)

parshal said:


> Poking around for used 199's I found you can get a brand new Mitutoyo 960-613 for $375 which is cheaper than the other two less accurate models.  It's accuracy is .00017".  I can't imagine trying to level a lathe with that.  I'd be chasing my tail for hours.  LOL



The Mitutoyo 960-613 has a sensitivity of .00024"/12" as compared to the Starrett 199 with a sensitivity of .0005"/12".  I'm not sure what the accuracy spec refers to; possibly the flatness of the surface?


----------



## parshal (Feb 26, 2020)

RJSakowski said:


> I'm not sure what the accuracy spec refers to; possibly the flatness of the surface?



Me neither!

Am I wrong in interpreting that to mean it's twice as sensitive as the Starrett?  And, it's under 8" vs 15" which might be a bit more conducive to leveling a lathe.


----------



## RJSakowski (Feb 26, 2020)

I


parshal said:


> Me neither!
> 
> Am I wrong in interpreting that to mean it's twice as sensitive as the Starrett?  And, it's under 8" vs 15" which might be a bit more conducive to leveling a lathe.


It is twice as sensitive as the 199.  A problem with a shorter base is that it will be more prone to error due to imperfections or debris under the base.  My level has a sensitivity of .0005"/10" and is slightly less sensitive than the 199 but it has an 8" base.  For measuring across the ways, it is fine as the span is less than 8" on my lathe.  If I were leveling a mill table, I would prefer a level with a longer base.


----------



## mikey (Feb 26, 2020)

The sensitivity of a spirit level refers to the change in slope required for the bubble to move one unit on the vial. The more sensitive the level, the less slope required to move the bubble one unit. For example, my Kinex level is sensitive to 0.02mm/M, or 0.0002"/10". In contrast, a Starrett 199Z Master level is sensitive to 0.0005"/foot, so about half as sensitive as my Kinex. It can take up to a minute for the bubble to settle on one of these levels so be patient when using one, and try not to have other machines running nearby when you do.

In general, I follow a sequence when setting up or checking my lathe

 I start by confirming that the headstock is aligned with the ways. You can do this with test bars or Rollie's Dad's Method or whatever you like. I prefer to prove the position with test cuts on a 4-6" long bar supported by the chuck alone. If the diameter all the way down the bar is the same, the headstock must be aligned with the ways.
Level the cabinet next. I move the saddle to mid-position and adjust the feet on the cabinet so the lathe is zeroed in both X and Z.
Level the lathe. I use my Starrett 98-6 sitting on the cross slide, perpendicular to the spindle centerline and set there with a square. I start at the headstock end and adjust the studs under the headstock end to get it level, then do the same at the tailstock end. Once completed, I lock the lathe down to the cabinet.  Then I switch to my Kinex and repeat, this time adjusting the feet of the cabinet. Because the lathe is mostly leveled already, it takes just a minute adjustment of one of the feet to bring the lathe into level according to the level.
Then I do a 2-collar test to finalize the level. Most of the time, this just requires a tiny tweak on one of the feet and the lathe is level.
Finally, I use a test bar that was cut on this lathe to align the tailstock to the spindle and I'm done.
Regardless of how you do it, I suggest you begin by making sure the headstock is aligned with the ways. Everything else that follows depends on this one thing being right.


----------



## litewings (Feb 27, 2020)

Reading these replys which reinforced my thoughts on twisting the bed is not fix and merely a bandaid, I'm back to leveling the machine today and adjusting the headstock to remove the taper. Thanks as always for the input.


----------



## RJSakowski (Feb 27, 2020)

litewings said:


> Reading these replys which reinforced my thoughts on twisting the bed is not fix and merely a bandaid, I'm back to leveling the machine today and adjusting the headstock to remove the taper. Thanks as always for the input.


Twisting the bed needn't be a bandaid. The important takeaway is that two wrongs don't (necessarilly) make a right.  All other options should be exhausted first and bed twist used as a final tweak.  In using a level to adjust for taper you are assuming that the lathe had been made correctly to begin with and that wear during use had not created a condition that leveling couldn't cure.

In the end, the ultimate test is whether or not you can make parts to your specification.  If you still have a taper when turning after leveling, it does you no good to have a level machine.  OTOH, if your machining operations are cutting true, why should it matter if you had to twist the bed to make it happen.

It is wise to remember that any and every manufacturing operation has some error associated with it.  Tolerances are set up to define the product and if the product is within the tolerance specs, it passes out the door.  Good manufacturing has tighter tolerances, poor manufacturing has looser or non-existent tolerances. 

Another important point is that we must analyze what surfaces are important to our alignment.  For example, my lathe has a prism on the front way and a flat on the back way that define the location along the bed.  I cannot assume that the flat just in from the prism is parallel to the prism.  Nor can I assume that the top of the prism is parallel to the working surfaces of the prism.  Nor can I assume that the prism itself was ground parallel.  Setting a level on the wrong surfaces and leveling might not produce a straight cut even though the level indicated that the lathe was leveled.


----------



## litewings (Feb 27, 2020)

Project complete. Re-leveled the lathe again. Probably in better level condition now than it was before. Adjusted the headstock to .0002 in 9".  I'm happy with it and will sleep better knowing the bed is not twisted to a point of excessive stress. Going to use it as is for a while to let things settle in and then recheck.


----------



## ddickey (Feb 27, 2020)

Which end is larger?


----------



## litewings (Feb 27, 2020)

Tailstock


----------



## ddickey (Feb 27, 2020)

You're good then.


----------

