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[How do I?] the chicken and the egg situation

buster

Iron
Registered Member
#1
I have a Jet 13 x 40 lathe with apparent minor misalignment somewhere between the head-stock and/or chuck and longitudinal centerline. I have done some of the usual checks and adjustments and test cuts and now I have these questions.
1. Assuming the chuck is perfect but the head end is askew, how can I confirm this condition?
2. Assuming the head end is perfectly aligned, how can I tell the chuck is wonky?
3. If both chuck and head end are off, will grinding the jaws fix both issues at one time?

I have turned a piece of stock over about 12" of its length and my dial indicator shows about 2 thou variatio along that length - not too shabby. BUT initially, there was considerable eccentricity in the raw stock before turning, so how in the world do I find where the culprit lies?

I have also chucked up a piece of T G & P 1-3/4" dia and it shows run-out! Wa-a-a-a-ah!

I feel like the GEICO gekko with a flat tire - "Please - somebody help me!!!!"
(I'm near Monreo Michigan if you are hearing my cries)
 

Reeltor

Active User
Active Member
#2
Buster,

I think (yes, that is a dangerous situation) that you need to chuck something that is ground round in your lathe chuck to see how much runout you have at the chuck. I have seen many people use a end mill and indicate off the shank.
I wouldn't grind anything on your lathe; you have some more investigating before you take a drastic
un-reversable step.
You said that you did the usual checks/steps; is the bed of your lathe level?
I'm sure the real experts will advise you on your next steps, good luck and have fun :)
 

Ulma Doctor

Infinitely Curious
Active Member
#3
Hi Buster,
i'm assuming you have a 4 jaw chuck.
chuck up a ground dowel or other precision ground rod and check the runout
if you have a prepared test bar, chuck it up and then you can mount a test indicator in the toolpost and indicate the test bar, that will test alignment in respect to centerline
 
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T Bredehoft

Active User
H-M Supporter-Premium
#4
Pity, Temperance is just across the border from Toledo, I used live in Toledo, but no longer. Pity.
Have you had, or do you know that the headstock was apart? If not assume good.
Indicate the face of the chuck. Indicate the diameter of the chuck. If both are good, look to the jaws, if not look to the mounting of the chuck.
 

RJSakowski

H-M Supporter - Premium Content
H-M Supporter-Premium
#5
I would start at the beginning. Use a test indicator to check the headstock Morse taper socket for runout. This will tell you if you have a bent spindle or bad bearing. Assuming good, next check the face of your mounting plate for runout. Also check for any nicks, burrs or chips that might interfere with proper mounting of the chuck backplate. Then remove the chuck form the D1-4 backplate and check runout on the registration surfaces. From there, mount the chuck and run runout and taper tests.

It is common for 3 jaw chuck to have runout, Set Tru type chucks being the exception. Taper is a matter of squaring the headstock to the ways of the lathe. Most often, this is done by leveling the lathe and or adding shims to remove any twist in the lathe bed. In extreme cases, the lathe headstock may be misaligned with the bed of the lathe, in which case, the headstock would have to be loosened and shifted to bring into alignment.
 

Silverbullet

Active Member
Active Member
#7
First 2 thousandth out in twelve inches , let's not get hysterical lots of things can contribute to that , tailstock not aligned to the head stock . Or if you didn't lock the cross slide it may have backed off during the cut. At worse you could live with it that's not much . The compound could be worn on the ways . Lots of things can happen to LATHES to cause the run out, the chuck is the starting point , three jaw chucks usually aren't the best for accuracy.
Are you building things for NASA , hobbyist tend to think every lathe should be exact to the sixth decimal . There not and never will be count yourself lucky if that's the worse problem that comes up. Learn the LATHES limits and work with them , a quick filing on the high section and your gold.
 

buster

Iron
Registered Member
#9
Thanks to all responders - I think I'm going to go back to basics. I found one of the feet under the head stock end a bit 'loose', so I shall start over with leveling in X and Y axis. The chuck I'm using was new a year ago so wear there should be negligible.
I have checked face of chuck mounting plate and it runs quite true, maybe a couple of 10ths variation but if I find out of level I'll still redo.
As far as building for NASA I say why not aim high? - they started out with some pretty hokey stuff. Oh but I forgot - they had alien life forms from Roswell to assist!
B
 

Tozguy

Active User
H-M Supporter-Premium
#10
When it comes to inspection of potential alignment problems I refer to the inspection record sheets provided by the manufacturer.
Not only do they show a drawing of the test set up but they often give the allowed tolerances. This is one example from Grizzly: http://cdn0.grizzly.com/pdf/G4003G_Inspection_Record.pdf
There are others, my lathe came with a three page certificate of inspection that also shows the various test set ups.

I get a lot out of these sheets as they help to understand where to start and what sequence to follow.
 

olcopper

H-M Supporter - Premium Content
H-M Supporter-Premium
#11
Also, keep in mind that .002 is less than the width of a human hair----having said that, have you chucked up a round item and tried to see if there is any movement in the headstock, if you can't feel it, then put an indicator on it just to be sure.
olcop
 

Splat

Active User
H-M Supporter-Premium
#12
Buster, first get the lathe on firm footing and level it as best you can. Next do a 2-collars cutting test. Search for it here if you don't know what that is. Once you've got that done to your satisfaction align the tailstock to the headstock. Again, search for that if you need to as that's been discussed here as well. Good luck.
 

intjonmiller

Active Member
Active Member
#13
I feel the need to point out, for those who may find it interesting, that eggs predate chickens by eons. :)

I bought an MT3 test bar on eBay from AtoZ tools (outfit that ships from India, directly from their factory). I don't know of any better way to verify the condition of the headstock (along with RJ's recommendation to indicate the actual spindle taper; use an inspection scope if you can get your hands on one to visually verify the condition while you're at it). The test bar is just a precision ground morse taper on one end and 12" or so of parallel ground bar that extends from it. If it has runout there's something wrong with the headstock somewhere. If it is not parallel to the bed you can go from there to determine if it's headstock alignment or bed twist. Then when you get to the point of tailstock alignment you know that you only have to correct its offset, and not bed twist. Minimize your variables by starting at the headstock and working from there. No sense creating a twist in the bed while trying to correct for what is actually a headstock (or, in other situations, a tailstock) issue.
 

tertiaryjim

Active User
H-M Supporter-Premium
#15
You can make the checks needed with an indicator.
First, the indicator will be mounted on a bar at least 8" long and rotated while mounted to your lathe spindle.
It can be clamped in a chuck or collett.
Soo, you'll need to make certain that the bar and indicator won't sag or have other errors.
Simply chuck the bar with indicator close to the lathe spindle, indicate to the inside of the tailstock spindle with
all locks snug on the tailstock. Record the readings.
Move the bar out 6" and set the tailstock back the same, read again. Since any bed twist will be too small to register in such a test, unless it's a pretzel,
you will see any misalignment of the head.
Don't worry about reading on different areas of the morse taper. Your only looking to see the difference in the sweep readings.
This will show lateral and vertical alignment problems.
I must agree with others that the footing needs to be better.
Just a piece of 3/4" plywood to spread the load out with some 4"x 4" x 1/4" thick plates will make a large
improvement in the setup.