Leveling Out Lathe Bed Twist

David_M · May 13, 2018

This lathe is cutting with less taper now. I should have done this sooner.

position1.png photo - David photos at pbase.com

position2.png photo - David photos at pbase.com

Has anyone used a granite cuboid/foundation for their lathe(s) to keep things true? I've seen it mentioned somewhere before.

steve-l · May 13, 2018

David, you should use the correct precision level. I think if you check the specs of both, you will see a glaring difference.

Spruewell · May 14, 2018

A good precision level (.001/foot minimum) layed across the bed in front of the spindle, then at the far end of the bed (and maybe a couple places in between) will be more reliable and accurate. Putting the level on the carriage may mask some distortions in the bed. Once the bed is leveled, then it’s on to aligning the spindle, then the tailstock.

David_M · May 14, 2018

This is a coincidence level with 1 arc-second (or better) accuracy. That should be .000582 in 10 feet.

steve-l · May 14, 2018

I think that's a great tool for aligning ship engine crankshaft bearings, engine mounts and propeller shafts, but it is still the wrong tool for your lathe bed.

Tyrone Shoelaces · May 14, 2018

David_M said:
This is a coincidence level with 1 arc-second (or better) accuracy. That should be .000582 in 10 feet.

Just out of interest how long does it take for the bubble to settle ? I had a 0.0001" in 10" " Hilger & Watts " box level and I sold it because it took me too long to level long machine beds.

I agree with a previous poster that placing the level on the saddle isn't going to give you ideal readings.

Regards Tyrone.

David_M · May 14, 2018

Hey Steve, I do have a level that is made like a Starrett 199 master precision level .0005/10" x 15" long. (Made in Europe) that I could use directly on the bed as Sprucewell mentioned. I've used that method many times, but if I use a level on the carriage don't I see exactly how the carriage twists as it moves along the bed?

I start at the headstock end of the bed, level the level's bubble, carefully move the carriage to the other end of the bed noting the deviation and correct it with the leveling screws. Repeating as many times as is necessary to no longer see bubble movement.

Ziggy2 · May 14, 2018

David_M said:
This is a coincidence level with 1 arc-second (or better) accuracy. That should be .000582 in 10 feet.

And how exactly does this correct bad lathe geometry? You're still cutting a taper right?

It sounds like you are stuck in the lathe leveling mode and not lathe geometry alignment.

dian · May 14, 2018

we dont know how long the lathe is. if six feet or more using the level is the only way i can think of. i would also like to know, why placing the level on the saddle is no good. isnt that the movement we are looking for? except if the saddle should rock, which should be checked also.

tnmgcarbide · May 14, 2018

surprised that no-one has chimed-in..."level doesn't mean shit"...blahblah...
"it could beblahblahh and still would cut straight"... blahbahfukyourmother,blah.

level is an easy way to setup a machine tool , and many of us have /could borrow a
precision level of some kind . having the machine level ... also means the table or the ways or whatever are reasonably level... meaning that we could
possibly use the same level for setups on parts that could not otherwise be
indexed to the same machine zero...

i suppose on a battleship or truck-mounted lathe -level is meaningless, so forget what i've said.

Demon69 · May 14, 2018

Tyrone Shoelaces said:
Just out of interest how long does it take for the bubble to settle ? I had a 0.0001" in 10" " Hilger & Watts " box level and I sold it because it took me too long to level long machine beds.

I agree with a previous poster that placing the level on the saddle isn't going to give you ideal readings.

Regards Tyrone.

I know what you mean about the super fine levels, take so long to settle out. Time imo is your enemy when trying to measure. Plus how accurate does a lathe bed in real world have to be? One whole division on a 20sec vial over 10" is only a .001"

.

Level on the saddle thing I struggle with a bit. Brand new machine with unworn surfaces makes good sense to go off the ways and maybe second check riding the saddle / TS base. When theres a bit of wear, unless youve confidence in some sort of reference surface on the machine, going of the saddle at least gets you quickly in the ballpark. Am I missing something?

I checked a friends machine (colchester triumph 2000) recently thats turning just under .004" taper over 6", fat at the free end. I checked level first riding the saddle. Using a .001" in 10" level, I got 0 / 1 div / 0. Chucked up some 3" steel and turned two equal diameter collars over 6" and got the following. The headstock was pointing up .002" and away from the operator .002" Which is pretty much what I expected due to some wear and headstock misalignment. At a glance the headstock looks easily adjustable so I suggested he bump it over when hes got time, would have had a go for him but it was getting late.

Cheers
D

David_M · May 14, 2018

Hey Tyrone,

I am here to learn. I don't mean to sound disagreeable, I hope I am not coming across that way.

My point is that if the bed has imperfections that the carriage doesn't react to them then I should not take them into account and I should only worry about the path that the carriage takes thus the level on the carriage. By the way I'm not checking level, just seeing if the carriage twists as it moves along the bed using the most sensitive level vial that I have.

It is the dynamics of the bed and carriage and every thing else together that determines the path of the tool bit's point relative to the centerline created by the spindle's and tailstock's positions.

Talking about the sensitivity of the bubble, at the Brunson school they show you on their transits that if you go past your target to continue rotating the transit in the same direction until you get back. Rotating it backwards throws it out of level even though they have the best bearings available.

Demon69 · May 14, 2018

tnmgcarbide said:
surprised that no-one has chimed-in..."level doesn't mean shit"...blahblah...
"it could beblahblahh and still would cut straight"... blahbahfukyourmother,blah.

lol, give it time

David_M · May 14, 2018

Ziggy2, it is cutting fine now after the adjustment.

David_M · May 14, 2018

Dian, that is interesting that you mentioned saddle rock. I don't have that on this lathe, but I can see how you could get it if you had twist in the bed for an extended time.

If editing had a global "find and replace" I would search for "carriage" and replace it with "saddle" in my posts in this thread.

RC99 · May 14, 2018

David_M said:
My point is that if the bed has imperfections that the carriage doesn't react to them then I should not take them into account and I should only worry about the path that the carriage takes thus the level on the carriage. By the way I'm not checking level, just seeing if the carriage twists as it moves along the bed using the most sensitive level vial that I have.

It is the dynamics of the bed and carriage and every thing else together that determines the path of the tool bit's point relative to the centerline created by the spindle's and tailstock's positions.

I think you got away with doing it this way due to a relatively unworn lathe. Those HJ Kingstons (Chin Hungs) are really well made and quite an accurate machine.

The general rule is the bed is the datum. Everything is aligned to it. So you level the bed and go from there.

Tyrone Shoelaces · May 14, 2018

David_M said:
Hey Tyrone,

I am here to learn. I don't mean to sound disagreeable, I hope I am not coming across that way.

My point is that if the bed has imperfections that the carriage doesn't react to them then I should not take them into account and I should only worry about the path that the carriage takes thus the level on the carriage. By the way I'm not checking level, just seeing if the carriage twists as it moves along the bed using the most sensitive level vial that I have.

It is the dynamics of the bed and carriage and every thing else together that determines the path of the tool bit's point relative to the centerline created by the spindle's and tailstock's positions.

Talking about the sensitivity of the bubble, at the Brunson school they show you on their transits that if you go past your target to continue rotating the transit in the same direction until you get back. Rotating it backwards throws it out of level even though they have the best bearings available.

You don't sound disagreeable in any way. My thinking on this is that to the best of my recollection the bible of machine tool alignments ( The Schlesinger Test manual ) shows you how to level your lathe by working from the bed-ways.

This is a machine tool industry standard that your lathe will almost certainly have been manufactured to even today. There's no harm in trying out the level on the saddle just out of curiosity, I've done it myself, but primarily you should be working from the ways.

All the best with it, Tyrone.

Richard King · May 14, 2018

I say set the level on the saddle to test the tool path. I use a .0005/12" or finner level to compare HS end to TS end. Using saddle is just like using a King-Way. One has to stop the saddle in the same direction to eliminate the possibility of rock. After doing that to get it close I do the 2 collar test and tweek the bed of a Vee & Flat bed and head if it sets on Flats and has a rotation pin. Also the machine needs to be relatively level so the oil reservoirs work properly.

I was been aligning lathes this way for over 50 years as a proffesional Machine Tool Rebuilder SUCCESSFULLY and it works. Of course the bed is worn near the chuck in 99.8% of lathes. One may have to split the difference on the final 2 collar twist as boring a hole will be double the error you remove on the OD. Or bore on back side of part ID. Setting level on the bed IMHO is a waste of time to eliminate TWIST. I do like machind perfectly level when rebuiling as i Stack the saddle, cross slide, compound, etc. To speed up the work in rebuiling and rebuilding.

I just used this saddle method - 2 collar method in a LeBond lathe in the CA Scraping Class # 1. I will post some pics in the morning from my laptop. Rich

steve-l · May 14, 2018

David,
At face value, there is nothing wrong rolling the carriage to observe change in level with one exception. Many lathe beds will dynamically twist a few thou as the weight of the apron approaches midway between the bed support legs. This dynamic twist will have little or no effect on cutting a taper, but it is measurable. Why reinvent the wheel? Use the proper tool the proper way.

DMF_TomB · May 14, 2018

many machines you rough level with a .005/foot level first. its used to calculate shim amounts. finer level if off scale got no way to calculate shims
.
sure you get it within .001/ft or 1/5 of a line division then switch to finer level. of course if you got a level with both vials .005/foot and .0002/10" you read the more sensitive vial when you are close enough to not be off scale
.
frame level i used 100 more often once i put the .005/ft level vial on it. the Starrett 98 level vial (.005/ft) bolted on cost more than the .0002/10" frame level
.
as a Millwright i often improved my tools. they level adjuster is a custom made 127 ipt fine thread pushing against rubber o-ring to calibrate level vial within seconds usually

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