Thread: Headstock alignment

> I don't have a precision test bar or even anything to be used between centres.

- the headstock to bed alignment cannot be done using anything between centers. It is simply and very positively impossible.

> I had a piece of 19mm hardened shaft that I found in a nature strip collection. I used RDM (Rolles Dads Method) with the shaft held in the 3 jaw chuck, didn't even have a collet system then. I drew up a set of tables on the whyteboard and wrote down my measurements as I went. My aim was to get it better than the original spec which I did. Some people claim that RDM is only a rough and ready approximation, this may be the case but after the alignment I managed to turn a piece parallel to within 0.0001" over 8" which is plenty accurate for me

- RDM can be used successfully to shim the lathe bed such as to take out bed twist, without needing a precision level nor a test bar. But only if the headstock to bed alignment was previously done (at the factory) with a precision level and has not been changed since. In other words, a correct headstock to bed alignment is the prequisition for RDM to work. It is the same as aligning a lathe on a ship, where no level can be used: it is only feasible if previously the headstock-to-bed alignment was done on terra firma with a precision level.

- Leveling a lathe is the simplest and quickest method to ensure the bed is untwisted. And an untwisted bed is the prequisition for many of the lathe alignments. In use the lathe does not need to be level as long as the bed is and remains untwisted.

- Using the RDM to align a lathe whose headstock alignment is off, can result in forcefully twisting a lathe bed into a pretzel: when doing a test cut on a spool, it is always possible to shim the bed until the two spool diameters are exactly the same, but try to cut a shorter or a longer spool such as a long bar, and you may be surprised your lathe is actually cutting something like an hour glass shape instead of a linear taper or as you were hoping a parallel.

Chris

Originally Posted by cba_melbourne

- RDM can be used successfully to shim the lathe bed such as to take out bed twist, without needing a precision level nor a test bar. But only if the headstock to bed alignment was previously done (at the factory) with a precision level and has not been changed since. In other words, a correct headstock to bed alignment is the prequisition for RDM to work. It is the same as aligning a lathe on a ship, where no level can be used: it is only feasible if previously the headstock-to-bed alignment was done on terra firma with a precision level.

- Using the RDM to align a lathe whose headstock alignment is off, can result in forcefully twisting a lathe bed into a pretzel: when doing a test cut on a spool, it is always possible to shim the bed until the two spool diameters are exactly the same, but try to cut a shorter or a longer spool such as a long bar, and you may be surprised your lathe is actually cutting something like an hour glass shape instead of a linear taper or as you were hoping a parallel.

Chris

Hi Chris,

I'm not sure if either you have mis-understood me or I have mis-understood you.

The bed of my lathe was levelled with a precision level prior to HS adjustment. I don't understand how Using RDM to align the HS to the bed will introduce any further twist.

I didn't use the RDM to both align the HS AND level the lathe, as you say it can't be done as there are too many unknowns, you need one to use as a reference to the other. As explained above, I knew my lathe was level so the readings using RDM were used to align the HS.

Also, my precision level is not accurately adjusted to show true level so when I say level what I really mean is my lathe is levelled so as to have no twist and have the ways all in a single plane.

If i still have it wrong then I will need further explanation (in simpler terms) as I don't understand how I have gone wrong.

Cheers,

Simon

Simon,

this is the misunderstanding: originally the "Rollie's Dad Method for Lathe Alignment" (RDM) was intended to level a lathe bed when installing a new lathe in a home workshop, in the absence of both a precision level and a test bar.

Of course, once you know your lathe bed is untwisted, you could in theory reverse the RDM method and use the part of the RDM method that deals with averaging the measurements of a not perfectly straight bar held in a chuck. And this might even work in practice if you are dealing with an "american type" lathe whose headstock is scraped to the lathe bed and does not have the freedom to be moved and rotated in all directions. It may even work with the type of lathe with loose fitting headstocks, but only as long as you only try to lightly touch up or improve an alignment that is not really off to begin with. But it is absolutely hopeless if you try to realign after a headstock was separated from the lathe bed, or after a lathe had a transport accident. It can take several days and drive one into insanity trying to do an alignment that is hard enough with the proper tools, using the RDM method. You have to get it parallel horizontally and vertically, you have to match as good as can the tailstock height, and you have to match as good as possible the tailstock offset by translating the headstock front/back. That is 4 adjustments at the same setting, or at least 3 if you drop the last as too hard. Not easy with a floating headstock requiring torque shimming and possibly a roughly finished surface requiring a stack of paper shims that make this whole alignment somewhat "spongy". The required tolerances of this alignment are fairly tight.

Also, to make sure the bed is untwisted in the first place you already need a good and usually expensive level to begin with. Why then try to save on a real test bar, that usually sells cheaper than a level?

Lastly, a test bar at the same time verifies that the internal taper of your headstock is colinear with the spindle axis. Normally, the spindle taper is the reference when manufacturing the spindle. I know that many of the least expensive Chinese made lathes have tolerances of 0.02mm and more between spindle taper and chuck mount. Chris

Originally Posted by TED C

I am very interested in this thread,
I too have a lathe with a suspect mis aligned headstock, It will turn a 3 thou taper 4 inches out from the chuck or collet.
The lathe was purchased new, [al960b] no crashes and it has not been abused.
Ted

Ted the AL960 has adjustment bolts at the rear
mine was the same
have a look at this thread

https://www.woodworkforums.com/f65/my...-taper-147402/

but remember to ensure your lathe is level (no twists in the bed) before any adjustments...you will need a machinists level to do this

I can't believe you people are listening to this nonsense. As long as you have the right equipment and the bed is level it's not difficult at all, just time consuming. As for impossible to line up if the headstock has been removed, what a load of rot. It is a simple adjustment, why do you think some manufacturers include the means to do so. Next you'll be telling us that tailstock alignment should never be messed with.... Absolute nonsense.

Originally Posted by tongleh

As long as you have the right equipment.

I dont recall anyone saying it was difficult "as long as you have the right equipment".
I doubt you do but thats up to you.

Besides, I thought you had taken your bat and ball and left??

Stuart

Originally Posted by Stustoys

Besides, I thought you had taken your bat and ball and left??

I must have missed something. Obviously a post has been deleted.

Originally Posted by tongleh

I can't believe you people are listening to this nonsense. As long as you have the right equipment and the bed is level it's not difficult at all, just time consuming. As for impossible to line up if the headstock has been removed, what a load of rot. It is a simple adjustment, why do you think some manufacturers include the means to do so. Next you'll be telling us that tailstock alignment should never be messed with.... Absolute nonsense.

Yo do not listen.

What I say is that HS alignment requires a precision level and a proper test bar. Then it is only time consuming, especially if you expect to end up with an unchanged tailstock height.

Without a precision level, HS alignment is not possible at all.

With a precision level but without a proper test bar it can be quite challenging and very time consuming on a well finished lathe, or near impossible if the lathe has a poorly finished headstock underside and/or needs paper shims.


Why do manufacturers include the means to adjust the headstock? Certainly NOT for the user. The means are only there to aid during the assembly of the lathe in the factory. I know of no lathe maker, not a single one, that would include HS alingnment in their user manual.

You do not need a test bar, you can take careful cuts on suitable sized pieces of steel and align it that way... Takes awhile but it is attainable...

Not a big fan of test bars, well cheap ones that is all we can afford anyway...

Hi RC,
So effectively you are making a test bar.

Though you may well be out horizontally to make up for any out of vertical parallel between the spindle axis and bed.
But as you now have a test bar you can clock the top and check.

As always it depends just how close is "fit for purpose".

Stuart

Colchester lathes do have a headstock alignment procedure in some of their instruction manuals as I am sure other manufacturers do, see page 11 of Master 2500 in the following link.

https://docs.google.com/uc?export=do...MWdiTE90a1NWQQ

Originally Posted by tongleh

I can't believe you people are listening to this nonsense. .....

Apparently 'banned' has some meaning apart from the obvious.

So apparently you can still post while banned? Admins?

I aligned the headstock on my lathe, several years ago when I bought it in pieces for $80 so I had no choice. I borrowed a machinist level and used my dial gauge and did not have problem just lost a couple of days.