Headstock alignment

Hey folks...

Anyone got any best practice methods for lathe headstock alignment please?

I've got 50um per inch runout from the spindle. Measured with a 3MT test bar from RDG...

Cheers, Jay

To mind 'runout' means rotational eccentricity but I'm thinking that is not what you mean, you might need to elaborate with more details. Just for fun I Googled 'best practice methods for lathe headstock alignment', plenty of reading to wade through. Maybe start with LPR Toolmakers.

Tony

Edited By Tony Pratt 1 on 10/10/2022 18:00:15

I can't offer any advice Jay, but I think those who can would need to know something about the machine, ideally make and model and whether it is a flat, round or prismatic bed.

Brian G

It's a 1941 Logan 10" (Montgomery Wards 700).

Yes rotational eccentricity is what I mean (At least I think that's what I mean...)

I have a test bar in the spindle and getting and additional 0.05mm rotational deviation for every inch I move the DTI away from the head stock...

Jay

Before moving the headstock it may be wise to first eliminate any other possible cause of run-out.

• On a lathe that old are you sure that the MT3 socket in the spindle is clean and straight, has someone tried to clean it up and put it out of kilter with the spindle.
• Has the lathe been set up so that there is no twist to the bed which could account for the non parallel turning.
• Is the MT socket clean.
• How accurate is the test bar and is that clean and undamaged.

Moving the headstock should be a last resort this is 'Here Be Dragons' territory.

Move slowly and carefully, eliminate all other possibilities before unbolting the headstock.

John

Edited By Journeyman on 10/10/2022 18:34:31

It's ok, I'm a prat!

Read the LPR article... Thought "yep yep yep..."

Read it again and realised my error!

I'd just inserted the bar by hand. Took it out gave it and the socket a wipe and gave it a clump home with the wooden mallet. Now I've got 0.03 runout registering along the whole bar. Which although still needs dialing in, isn't near as dire as it appeared earlier.

Leaving the post up for others to learn from my shame!

Jay

.

Very honourable, Jay

MichaelG.

After I mod my 3-Jaw chuck to adjust precice at various diameters, I quickly learn I must remember to clean the jaws and scroll before attempting to dial it in, patience is a good thing.

Headstock alignment will have no influence at all over eccentric runout of a test bar as the lathe spindle is rotated.

Your .03mm runout is most likely due to either burrs or bruises or other distortion on the 50 year old tapered hole in the middle of your spindle. (Even reaming the hole will not guarantee it is concentric with the outer spindle diameter. The reamer follows the existing hole) Or a small piece of grit between the tapers. Or it's not being seated exactly evenly. Or, and this is quite likely, due to very poor manufacturing standards of hobby grade test bars by low cost far-eastern suppliers.

The best thing you can do with your test bar is toss it away.

If you want to measure spindle runout, run a dial indicator directly on the spindle collar where the chuck mounts and rotate the spindle.

If you want to check and adjust headstock to bed alignment, the best method for old lathes is detailed in the Myford ML7 Users Manual.

This method works best because it measures what the lathe is actually doing under real world circumstances. It takes into account bed wear (which can throw a sensitive level off kilter) and cutting forces etc (which can provide a different result from a perfect reading with test bar like yours in a static test.).

If you are trying to determine if the headstock axis is parallel to the bed, first check the test bar is not tapered. A tenth thou clock set up as a comparator on a surface plate would be a good weapon for that.

Next, any test you do must be repeated at (say) 4 rotational positions of the spindle (eg 12,3,6&9 oclock). That will eliminate much of the possible errors due to dirty, wonky, bent spindles.

Martin

Thanks for the input folks.

I'll make a proper test bar once I know I'm in the ball park, which is all the RDG bar is for. I've done a full rebuild so thought it was as good a way as any to line everything up initially.

It was the initial reading that gave me a bit of a panic. Brain just went straight to catastrophic consequence before thinking to check the validity of the measurement... Such is the learning curve. So nice to have patient and knowledgeable folks here for a sanity check!

Jay

Edited By UncouthJ on 11/10/2022 13:33:37

Notice that the tightening of the headstock bolts might affect the alignment and if so, you might have to set the headstock very slightly off before tightening them. Patience is very important when carrying out these adjustments, never give in if it is difficult. The other check is having the DTI tip on top of the headstock, hopefully it will be ok without any bother.

Put your test bar between centres and check it for run out, I have one of the much maligned Indian test bars which came from RDG if I remember correctly, and it is well within its claimed tolerance. Blue up the taper on the test bar and rotate it in the headstock to see if you can mark up any high spots, ease them down with a hand scraper and keep bluing till you get good all round contact. I did this on my Mk1 colchester student, and it made a huge difference. To check headstock alignment put the DTI in the toolpost, and run it along the front centre of the test bar, reading should be constant when the headstock is in alignment, but also appreciate that this is subject to bed/carriage conditioin and you may see some jitters along the way. The overall reading from chuck to the end of the test bar is what is important. Repeat on the top centre of the test bar to check for any "nod" of the headstock, and please remember that all machine tools have a tolerance, and the further you go down the scale in initial cost and purpose of the machine, the greater the tolerance will be! The object of the excercise is not to get the machine bang on, it is to get it as close as you reasonably can, and then make parts! If the parts are good enough for purpose, you have won!!

Phil