Not sure where you’re coming from.? When is it turning tapers chuck mounted or tailstock supported

There are plenty of threads on here about lathe alignment (often called lathe levelling). DO NOT undo the four headstock bolts that hold the headstock to the bed – Here Be Dragons.

The long bar is useless as either an indicator or as a means of alignment. Need basically to take any twist from the bed caused by uneven floor before doing anything else, this is done without use of the tailstock.

Once untwisted the tailstock can be checked for alignment .

John

If I were you I would:

Check the bed for straightness with a sensitive level. Adjust to suit (if it's possible). If you have no level or it's not adjustable (maybe it's on three feet) just carry on down this list.

Chuck up a stout piece of ally in the chuck (perhaps 2" dia and 6" long) take skim passes and check for parallel. If the bed is not twisted and the part dosn't turn parallel then you have no choice but to loosen the headstock and adjust.

Once you have it turning parallel time to adjust the tailstock. Measure the tailstock ram with a micrometer. Turn the piece in the chuck to the same diameter. Bring the tailstock up to the part you have turned.

Put a mag base on the saddle with a tenth-reading dial gauge. Put the dial gauge against the side of the ram and move the saddle so it crosses over to the turned bar. It should read the same. If it doesn't adjust using the off-setting adjuster until it does.

Now do the same but running the dial gauge along the top of the parts. If the tailstock is low shim between the body and base to suit. Check the ram is level with the dial gauge or very slightly rising (never falling).

If you do all that you'll be about as good as you can get.

STOP! STOP! STOP!

You are putting the cart way before the horse and getting several separate issues mixed up. Moving your headstock is an absolute last resort and should be avoided if at all possible. It is rarely needed.

Your tailstock is adjustable and is usually adjusted to match the headstock, not vice versa.

First, you need to realise there are two taper turning causes, with two tests and two solutions:

1. Bed Alignment.  Stick a piece of 1" diameter bar in the chuck with about 4 to 6" sticking out. NO tailstock centre in place for this test. Take a fine finishing cut along the length of it and measure the job for taper. It should be within a thou or less (0.025mm). If it's not, the adjustment is made by shimming ONE of the mounting feet where the lathe attaches to the bench, at the tailstock end. This "twists" the bed to get it aligned to your headstock spindle axis.

2. Tailstock Alignment. Stick a short piece of bar in the chuck and turn a 60 degree point on it as close to the chuck as possible. Then put a known good centre in the tailstock and slide it up so the two points almost meet. Pinch a thin steel ruler between the two points, with the quill extended about the amount you normally use it at. The steel ruler should stand up vertical and also should lay square to the main lathe axis when viewed from above. If it does not, adjustment is done by adjustment bolts or screws in the tailstock base that move it from side to side. If the tailstock centre is lower than the headstock centre, you will have to put shim between the base and main body of the tailstock to bring it up to headstock spindle level. Further fine adustment is made by turning a piece of 1" diameter bar 6 to 12" long between centres and measuring the resulting taper after a fine cut. Adjust tailstock offset until less than a thou of taper.

The best and simplest written/pictorial description of how how set up your lathe's bed alignment and tailstock alignment I have seen is in the front of the Myford ML7 Owners Manual. PDF copies are available free all over the net. It applies to all lathes, not just Myfords. You should read it carefully before adjusting anything. It gives two ways of doing the bed alignment, using either an expensive precision level, or by the simple turning test outlined in 1. above, which is all I ever use in the home workshop. Then they describe the tailstock alignment by turning test as in 2. above.

The test you have described with a very long piece of unmachined bar does not really give an accurate reading of anything. Ditto mounting a DTI on the toolpost at this stage. Do the above tests 1 and 2 before adjusting anything and you will at least know where you are starting from . At first blush it sounds like your main problem is a tailstock that needs adjusting. You may possibly not have to do any more than that.

Edited By Hopper on 11/05/2021 04:37:28

Do the tests Hopper suggests and make sure the tool is sharp so you get zero deflection of work and tool

You say the tailstock is forward of the "dent" you make with the ctr this can simply be cured by adjusting it horizontally and this will likely get rid of the taper you describe turning as the tailstock end will now be thicker.

From the same test you say the tailstock is low. So pack up the tailstock, can't see why you are packing the head up as that will make it worse.

Edited By JasonB on 11/05/2021 07:45:17

BTW, how much taper are we talking about on this 5" long job? What are the diameters at each end as turned?

Robin, your 'roller' is actually a tube, I would suggest taking out all the bits & pieces & let the stand sit directly on the concrete floor, then just shim/pack the corner[s] to remove rocking & also bring level if you want. You can then proceed to add appropriate shims between the lathe bed tail stock end [front or back] & the stand so the lathe cuts parallel. I strongly suggest you read the Myford manual so you understand what is going on. P.S. Just replacing the wood block with a roller tube may or may not eliminate lathe bed twist.

Tony

Edited By Tony Pratt 1 on 11/05/2021 15:13:01

If not already done the cabinet stand should preferably be bolted to the floor. These stands are not particularly stiff compared to the lathe bed and trying to shim the tailstock end of the bed to the cabinet is just as likely to move the cabinet as untwist the bed.

As Tony says above, get the cabinet as level as needed (doesn't have to be perfect and you may want to slope the tray to the suds drain point) shim under the cabinet feet to stop it rocking then bolt it to the floor. You now have a solid immoveable foundation from which to untwist the lathe bed. Loosen the tailstock end bolts between cabinet and bed, slide in shims as required, tighten bolts and test. Repeat as necessary turning and checking the test bar between tries. If the right hand end of the test piece is bigger than the left hand end put a shim under the front tailstock foot and of course 'vice versa' shouldn't take more than a couple of goes to get it bang on.

John

Hi All,

here we go down the rabbit hole again! A couple of observations:

First, never enter this rabbit hole unless the lathe is not producing the parts you need to the accuracy you require.

With an engineers level, check across the bed at either end, and shim the cabinet untill the readings are as near identical as possible. you need to shim at four points, front and rear, at the headstock and tailstock end. The idea of this is to twist the bed into as near perfect alignment as possible. this process is best done over a few days to allow the bed to settle, and then be checked again, when you are happy with this, proceed as follows

It is pointless to try to align using the three jaw chuck, the very best of which are usually at least 3 thou out WHEN NEW!

Remove the chuck, check and clean the spindle bore, fit the bush and a known good centre, and then put a DTI on the spindle, and then on the centre.

If there is run out on the spindle, tighten headstock bearings to eliminate it.

If there is runout on the centre, remove the centre and bush, check the bore again, check the bore in the bush, and re seat the bush and the centre.

Buy a test bar,, remove the centre from the headstock and fit the test bar in its place, and check with dti at the remote end, you may need to remove and reseat the test bar till you get the absolute minimum possible run out.

Place the DTI on the saddle with its foot on the front of the test bar at centre height, and wind the saddle from the headstock towards the tailstock, If the headstock is misaligned you should see the DTI needle move steadily in one direction, if the reading is erratic, you may be looking at bed wear.

Take note of the runout at the remote end, rotate the spindle 90deg, and try again, note the reading and repeat till you get the spindle back to its original position.

You should now have a good idea about headstock to bed alignment, and will be able to make a decision as to whether you need to realign the headstock front to back, and whether the bed is worn or not

Now move the Dti to the top of the test bar and test from headstock towards the tailstock to see if the test bar is parralell to the bed, again be aware that you are looking for a constant downward or upward trend, and any erratic movement in the needle may be bed wear.

You now have a good idea whether you need to shim the headstock to correct any "nod" in the alignment.

You will usually find that by slackening the headstock bolts slightly, and bumping the headstock with a soft faced mallet in the desired direction, front to back alignment can be corrected.

Sometimes, selective retightening of the bolts can correct up or down nod, but if not you will have to shim, or scrape, but it may be a case of removing the headstock, cleaning the plate it sits on, identifiying and removing any dings or burrs with a flat stone or small scraper.

Now you have the spindle sorted and the headstock alignment as accurate as possible, you can move on to the tailstock. Whilst any of the above tailstock methods will work, I usually put my best centre in the tailstock, and with a dti on the side of the test bar, wind the centre into the centre drilling whilst watching the reading. Any discrepancy here can be corrected with the tailstock alignment screws.

Now repeat with the DTI on top of the test bar, and you will see if you need to shim the tailstock, by how much, and whether it needs to nod down or up.

Now move on to the turning tests ans see what results you get!

I must add that this is the way I do it, based on as much logic as I can muster at the particular moment. I am not suggesting that you go this far, indeed, you should only correct a fault if it occurs, and not go looking for trouble, because it is all to easy to imagine there is a problem. As I said at the top, only dive down the rabbit hole if your machine is unable to make the parts you want to the accuracy you require, and I will add to that that most lathes and associated chucks/tooling etc benefit from a complete strip down, clean, debur, lubricate, and carefull reassembly

The best of luck!

Phil

New here but always interested in this topic…
Am I right to roughly assume the following:
-As soon as you bolt the lathe Headstock-to-Bed combination(Maybe new from factory) down to something, in most cases the cabinet, your bed twist is linked to that, if all that weight is placed on the cement floor the Bed straightness/twist is linked to the cabinet and weight pulling it down to floor, so the bed is naturally not as straight as at the factory without the cabinet as grinded. So now you always forced to shim it at some stage of the fitment.

I my case I fitted a 12mm steel plate(70Kg) between cabinet and lathe bed, forcing me to shim it at the bed end points to cut a testpiece sticking out straight, luckily not at the headstock side, it took some time(Long).
I bolted the cabinet to the floor as well, but did not do my adjustment at the floor due to the plate stronger than the cabinet

Edited By Chris Mate on 12/05/2021 19:46:47