Headstock Re-alignment Problem - Help Requested

[Taylon]

Hello to you all,

With regard to my attempted re-build of my TDS viceroy lathe, the head stock had to be removed to gain access to a seized gear change shaft and now has to be re-installed. The main chuck shaft on the taper roller bearings has been installed but when the headstock is affixed to the bed there is some misalignment.

I have a MT3 parallel test bar that is 250mm long from the end of the Morse taper section. When this bar is installed into the chuck shaft there is run out of 0.05mm at the end of the test bar and 0.005mm at the chuck end. Secondly, when a DTI with magnetic base is clamped to the carriage and the DTI run along the length of the top of the shaft there is 0.03mm difference between the reading at the chuck end to the tail-stock end of the test bar. The tail-stock end of the free end of the test bar being higher. The horizontal alignment has been corrected and is within 0.005mm.

Hence it is my understanding that the headstock is misaligned. Furthermore if a fixed centre is placed into the tail-stock and then bought up to the centre point in the end of the test bar, the test bar deflects downward by 0.06mm as measured by the DTI on the end of the test bar. Thus my conclusion is that the headstock centre line is about 1.5 thou lower than the centre line of the headstock.

Are these normal tolerances for this type of lathe? Your help and comments are requested.

Kindest regards, John R.

[Andy B]

Hi John,
Your conclusion does not tie up with your reported measurements, in my mind.

"Secondly, when a DTI with magnetic base is clamped to the carriage and the DTI run along the length of the top of the shaft there is 0.03mm difference between the reading at the chuck end to the tail-stock end of the test bar"
If you now rotate the headstock spindle / test bar by 180 degrees, do you still get the same difference?

Similarly with your horizontal measurement - do you maintain 0.005mm after rotating 180 degrees? Given your runout figures, I don't see how you can.

First I would check that the MT bore in the headstock spindle is totally clean and free from burrs - it only takes a very small burr in here to kick the test bar off centre. Assuming your test bar MT is clean, use some engineers blue to test the mating bore.

I went through a similar process with my 280VS - mark the headstock in line with the highest runout point, then check the vertical and horizontal variations along the length of the test bar with that mark in 4 different positions (90 degrees rotation between each).

Hopefully that will enable you to draw your own conclusions - but please come back if you want another 2p worth!

Andy

[Taylon]

Dear Andy,

Thank you for your helpful reply.

However, the deflection caused by the tail-stock centre being engaged with the end of the test bar produces the same downward deflection irrespective of the angular position of the headstock shaft. Therefore, the tail-stock and headstock must be ms-aligned in the vertical plain. Do you not agree?

The test bar has been thoroughly cleaned and as you pointed out there appears to some marks/burrs in the headstock MT3 and tail-stock barrel. To than end I have ordered and purchased finishing MT3 taper reamer to try and remove any burrs from the MT3 bores. The headstock chuck shaft does not appear to be hardened as an ordinary file appears to remove metal (done from the back gear end), Therefore an HSS reamer should work to clean up the MT3 bores.
Do you agree?

The run-outs specified in my previous post are the maximum noted and are obtained when the chuck shaft is at the 1 o-clock position and the minimum is at the 7 o-clock position (relative zero point). The horizontal alignment achieved has been done at angular position midpoint of the run-out given by adjusting the tail-stock horizontal slide bolts.

What are you conclusions?

Kindest regards, John R.

[dazz]

Hi

I would suggest removing the headstock and re-checking the mounting surfaces for grit and/or corrosion.
The slightest contamination between the surfaces would be enough to cause measurable misalignment.

I purchased a 3MT finishing reamer for exactly the same reason.

Remember that everything flexes when doing measurements to fine tolerances. For example, as a DTI moves long the length of the test bar, the leverage of the force applied by the probe will vary with length causing the bar to deflect. Take a measurement from both sides of the bar and average the results to eliminate deflection errors.

The conclusions depend on any assumptions you make. It appears that you are assuming that the bed is straight (no bed wear) and aligned (not twisted). These might be valid assumptions but if they are not measured, you can't be sure. Measuring straightness of the bed needs intrumentation you probably don't have in your workshop (I know I don't).

The old-school way was to use a tightwire micrometer. To make measurements relative to the tight wire involved bringing a micrometer head up to the wire and using a continuity tester to determine when you just touched the wire. You could make one of these if you wanted to go down that path.

When I rebuilt my lathe, I made the assumption that the bed was straight and that the headstock was aligned. I have only adjusted bed twist and tailstock offset.