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Thread: Best way to level a lathe
05-31-2010, 10:18 AM #1
Best way to level a lathe
Is there a relatively inexpensive way to level a lathe ? there are some inclinometers on ebay for under $50 but they only read the degrees in one tenth.
Something like this is what I had in mind.
LEVEL BOX DIGITAL ANGLE GAUGE INCLINOMETER PROTRACTOR 3 - eBay (item 180511337804 end time Jun-21-10 23:22:40 PDT)
I know a standard level with a bubble isn't a super accurate way to do it that's why i am unsure.
05-31-2010, 11:37 AM #2
1) what kind of lathe is this? Smart money says it's small, used. If a southbend then
definitely used as they have not made those in a while.
2) throw out any levels you own. Or sell them.
3) use the money to buy a copy of "How to Run a Lathe" by south bend.
4) follow the explicit instrucions therein on doing the "two-collar" test.
It's all you need to set your machine up.
05-31-2010, 12:55 PM #3
05-31-2010, 01:27 PM #4
05-31-2010, 04:20 PM #5
06-05-2010, 01:05 PM #6
Leveling a lathe for accuracy is a bit of a misleading concept. What one is actually trying to do is align the front and rear ways such that there is no "twist" which will cause tapered bores and O.D.'s when using a chuck. (Lathe beds are prone to this phenomenon due to their length, and the usual configuration of being fixed only at the ends.) A precision level can be placed across the top of the ways, front-to-rear, to check if the tops of the bedways are coplanar along their length (not necessarily "level"), and if not, adjusting the tailstock end of the bed to make them so. Whether this involves placing shims under the legs of a floor lathe, mounting feet of a bench lathe, or adjusting some kind of built-in mechanism, depends on the particular lathe in question.
But wait! Often, it's not actually a twist, but uneven wear to the bedways which is having the same effect. In this case, using a level may not resolve the problem, depending on the location/extent of the wear. In either case, using a level to align the bedways should only be considered an initial step. Final adjustment should be performed based on the results of the Two-Collar Test:
By using a bit of common sense, you can determine which way the tailstock end of the bed needs to be rotated. If the collar closest to the tailstock end is smaller than the headstock collar, then the bed needs to be rotated toward the front (CCW, viewed from the tailstock end), and vice versa.
Once you've got the spindle aligned with the bed, then you can check the alignment of the centers, as the former affects the latter. Here's how HTRAL describes the procedure:
06-07-2010, 11:29 AM #7
I bought a 8" machinist level and co-ax indicator. We'll see how it goes.
06-07-2010, 11:53 AM #8
The bed needs to start out with no twist. That's what you use the level for. If the bed is straight, and the lathe turns a taper, either the bed is worn or the headstock is out of alignment with the bed. (assumes you use good measurement technique and aren't trying to turn a 1/4" shaft sticking 6" out of the chuck.)
The "goodness" of the bed depends on the abuse and lack of oil its seen. The "goodness" of the headstock alignment varies between manufacturers and samples of individual lathes.
If the bed is worn, live with it or get it reground. If the headstock is misaligned, scrape it, shim it, regrind it or otherwise get it pointed in the right direction.
Once the taper is down to .0001-.0002 inches per inch, it's ok to tweak the bed slightly to correct it. If you try to fix the above problems by turning the bed into a pretzel, the carriage will no longer mate properly to the ways and you'll get instability and rapid wear of the carriage and bed.
You need a level and it should be a pretty good one.
06-07-2010, 11:54 AM #9
06-07-2010, 12:10 PM #10
I'm with the level-it-first crowd, based on personal experience with several lathes with not-too-worn-out beds. Just getting rid of twist in the bed has always gotten me close.
One additional advantage, for bench lathes, is that the bench itself will invariably move a bit over time even if it is all steel construction. With a precision level, it's a couple minute job to tweak the lathe bed back to level condition any time precision is needed.
06-07-2010, 12:36 PM #11
99 percent of all the machines discussed in this forum are used machines and will
have worn (to some degree) beds.
Simply slapping a good level on the tops of the V-ways really is just barely a start.
It will read true but the machine will turn and bore taper. That's no good.
06-07-2010, 03:10 PM #12
I just proved the validity of the above on my lathe (not that I doubted it). I had previously leveled it with a master precision level and I thought it was OK, but after reading this thread I decided to do the 2 collar test - it cut .0004" difference in diameters in 4 inches. A slight tweak on the leveling screw at the tailstock end, and it's now perfect. Way more perfect than I'll ever be! :-) Another one of the reasons I roam this forum!
06-07-2010, 06:05 PM #13
A ha, so you know how to use the leveling screws! I've stared at mine for two years wondering how they work and which way I'm supposed to turn them to get the results I need. Please fill me in on how I'm supposed to use them.
06-07-2010, 08:49 PM #14
There's a horrible secret here, and that is (no don't tell anyone!) that it's
really tough to figure out from first principles which way to turn the levelling
screws - and here of course, nothing is getting levelled, these are truly
*twisting* screws - to get the error to diminish.
Basically you try one one way, and see if the collar diameters converge. If they
don't, that is, if they get farther apart - then you go the other way.
I always have to write down the steps, such as, front screw in 1/6 turn, and rear
screw out 1/6 turn, and put the collar dimensions down in the next column,
to get it straight in my mind.
Same thing with shimming legs on a machine with tailstock legs. Never can
figure that out a priori.
06-07-2010, 09:07 PM #15
06-08-2010, 04:11 PM #16
Digital Level what 0.1 degree is?
0.1 degrees is about 0.100" per 57" or 0.010" per 6"
0.020" per foot
digital levels that read 2 decimal , 0.01 degree often vary 0.03 degrees and many are only rated to repeat 0.05 degrees
Any good Field Machinist needs to calculate shims or leveling adjustment amounts and needs to be able to figure out what a level reading means per distance.
A Starrett 98 red line level is 0.005" per ft per line increment and reading 1/5 of a line or 0.001" per ft is min reading possible and 0.020" per ft or 4 lines is normal max reading possible with a 8" level.
06-08-2010, 05:37 PM #17
Any good used lathe owner needs to know that plunking a level down on the tips
of the V-ways, and getting it to read just perfect all down the line,
can still result in a lathe that turns and bores taper.
No matter how good the level is.
06-08-2010, 07:45 PM #18