Headstock - tailstock alignment

Hi,

I recently purchased an EMCO Compact 5 lathe from a deceased estate. I've always enjoyed using my hands although that is not how I earn a living. Hopefully this addition to my garage, which already has more hardware in it that meets with the approval of someone else residing at the same
address, will keep me occupied and out of mischief for many happy hours.

I believe that I got the lathe at a good price as the previous owner had
purchased it in 1984 but had never used it. It was still in the original
packaging! The date of manufacture was in October 1982.

When I machine a length of steel mounted between a dead and a live centre, I get a few thou difference in the diameters near the headstock and near the tailstock.

I conducted the following test:

1. Put a dead centre in the headstock.
2. Put a live centre in the tailstock spindle.
3. Brought the tailstock close to the headstock and locked it.
4. Brought the points of the two centres together by using the tailstock handle while holding a 6" steel rule between centres.
5. When the rule was clamped between the centres it remained perfectly vertical, but was twisted, indicating an apparent misalignment of the headstock and tailstock in the horizontal direction.
6. I repeated the above while
a. Rotating the spindle,
b. While rotating the dead centre within the spindle,
c. While rotating the live centre point, and
d. While rotating the entire live centre within the tailstock.

The steel rule always indicated the same misalignment throughout each of the above tests.

I don't think that the bed is twisted and that shimming will help. To try and check for this I conducted another test:

Turned a piece of steel about about seven inches long held between a dead centre in the headstock and a live centre in the tailstock. The diameter measured at the tailstock was 11 thou (yes, that much) less than that about 0.5" from the headstock end. I couldn't turn all the way to the headstock end as the last half inch was occupied by the lathe dog.

I then repeated the above but with a piece of steel about 2 inches long. The discrepancy was again 11 thou'.

This would seem to indicate that bed is not twisted and the tailstock was too far forward (or the heastock too far back) by 5.5 thou'.

This seems inconceivably excessive. Does anyone have any ideas/suggestions? I’m reluctant to start filing anything or doing anything that cannot be undone.

Thanks

Ron

Welcome Ron.

I can't help with adjustments but I think you have undertaken and posted enough tests (and far more completely than many)..

I would agree that the error is in the horisontal plane..what adjustent is avaiable to you I can't say..

1 does the tail stock run on dovetail and gibb strips?

2 could these be adusted..slacken one side tighten other..net result movement across spinde

regards Jason

Take the tailstock off the lathe, take it to bits and give it a good clean and inspection

Maybe there's a bit of fettling needed, you did say it's not been used yet

Emco Austria made good accurate bits, don't know about any foreign ones though

Hi Ron,

If I remember correctly the Compact 5 lacks the ability to adjust the tailstock sideways (as you might do when you want to turn a shallow taper). So if it is so and you want to correct this you will either have to try to scrape the tailstock - not an easy job. Or rebore the tailstock and fit a new (and larger dia. tailstock barrel). Another solution might be to make some arrangement to adjust the position of just the tailstock centre - maybe something like this?

Regards

Thor

Edited By Thor on 09/03/2013 05:55:43

Edited By Thor on 09/03/2013 05:56:08

Edited By Thor on 09/03/2013 05:56:29

Edited By Thor on 09/03/2013 05:56:56

Hi Ron,

Welcome to the forum.

For a lathe that's 350mm between centres a 'few thou' may be in spec.

What really matters is how big is the error over the length of the longest section you will need to turn parallel. If you are making a crankshaft, even one a foot long, if the journals are only an inch wide then your error will probably be insignificant.

That said, there has been recent discussion about how to set up a lathe to turn parallel - if it doesn't meet yourt needs after the above checks, it may be the bed has developed a slight twist over time and you can get rid of this by mounting it on a rigid base and carefully shimming one of the feet.

Read this thread end to end! The error at the start of that thread is 0.5mm in 200mm, so that would be about 35 thou over the length of the Compact 5 - perhaps ten times worse than your result.

Hope that helps,

Neil

Hi Ron
Firstly welcome to the forum, Lucky you brand new and stll in wrapings, I wonder why he never used it. Now at the date you mentioned do not think this is a Far East machine do you have any doc's.
Do not start fettling, firstly get a nice big tub of white spirits and mix with oil, rubber gloves and lots of rag. Give it a good clean up and assemble if you have not done already. Put a bit of bar stock in ensuring there is a centre spot.. If amid all the bits you got a gauge clamp it on and run it over the bar,
Please PM me if you need any help
Bob

OOps sorry double clicked.

Edited By Springbok on 09/03/2013 08:17:09

If your Emco has no lateral tailstock adjustment and you need the accuracy you could try putting a boring head in the tailstock to compensate for the error without machining/scraping.

The Emco is a small lathe? so whilst a boring head might counteract the discrepancy it might also reduce the available space too much in which case you could make an offset tailstock centre.

Paul

Edited By _Paul_ on 09/03/2013 08:33:56

Hi Neil,
I do not agee with your bed twist suggestion. I think Ron's next to last sentence states exactly what the fault is.

Ron,
I would like to complement you an the concise way you presented the information and the logical way you did your tests. I do not know your lathe so I cannot make any suggestions to fix the fault.

Les.

Bit of swarf/dirt/paint in the V groove under the tailstock base?

Russell

Les

My fault for speed reading the thread

Apologies to Ron.

Neil

Hi Ron, Welcome to the club, please do not start trying to alter the machine as has been suggested, it is unlikely that a manufacturing error is the problem -- not impossible but unlikely.

However first I would use a Morse taper test bar if you have access to one to check the head stock alignment with the bed -- unlikely to be out but this is the first thing to check. If you don't have a test bar chuck a piece of silver steel [ground stock] and use a dial gauge to ensure it is running true, should there be slight run out mark the bar at the high / low points then check the alignment using the carriage.

assuming all is OK I would then mount a dial gauge on / in the spindle / chuck and clock the tailstock bore -- don't forget about "gravity droop" on your clock top and bottom readings. It is more the side to side you are interested in. This should of course be correct within 0.0002 TIR or better.

If it is incorrect you have a problem if it is OK then suspect the tooling centre's some of the imported ones are not so great but I have not seen one so far out as your error would suggest.

Hope this helps a little. John

PS you could always contact Pro Machine Tools I have always found them helpful [ have a Maximat 11 and FB2 mill]

Hi John,
I think Ron's test 6 shows that the problem is not with either of the centres.

Les.

Ron.

If the lathe will turn a short bar to a reasonable level of parallelism without tailstock support, then you can be a little more confident in the bed not being twisted.

I would first make sure that no burrs or dirt exists between the tailstock and bed before doing anything else.

Maybe if the tailstock checks out OK, it might be a case of dirt/burrs between headstock and bed before final assembly at the factory, but if this is the case, then it will probably show up in the above test without tailstock support.

Martin.

Ron,

Remember, Gray is a toolmaker, follow his advice to the letter.

Oh what a lovely little baby lathe want one for my grandson.

Bob

Full marks for your initial tests Ron as they tell us that twist is not the reason for the error. If it were, the error would be larger with a longer test piece. There is though one other test worth doing, assuming that you have not already done so. This is to repeat the test with the longer (or shorter) test piece, but repeating it first with the tailstock barrel fully home, then again with it fully extended.

If you still get nominally the same degree of error you will have proven that the tailstock barrel is moving parallel to the lathes axis. Whilst this is very likely to be the case you will have eliminated with certainty one of the posible problem areas, that is, the barrel moving at an angle to the lathes axis.

I see Graham that your Compact 5 appears to have a tailstock made in two parts, being keyed together allowing it to be moved backwards and forwards. I assume this is a modifictaion that you have carried out as other pictures of the Compact 5 do not show this. Looks well done, as one would expect coming from yourself.

Harold

Hi

I am overwhelmed by the number of responses. Thank you. I will be performing several more tests in the next week or so. Unfortunately the necessity of earning a living prevents me from spending more time in my workshop.

To try and answer some of the comments:

AAy1 and Russell: I have already taken the tailstock off to check if there is any junk at the interface with the ways. It is clean and smooth. I still have to dismantle the tailstock completely.

John: What is a Morse taper test bar? I also don't quite follow your suggestion of mounting a dial gauge in the spindle/chuck and clocking the tailstock bore. Couldn't any discrepancy also be caused by problems with the headstock or my ability/inability to correctly mount the dial gauge?

Martin: I didn't think of dirt where that headstock contacts the bed. I'll check it out. Regarding your suggestion of machining an unsupported piece of steel - couldn't any discrepancies be caused by poor mounting in the chuck? I've only got a 3 jaw chuck and have yet to acquire the 4 jaw.

Harold: I will follow your suggestion re repeating the test with the tailstock spindle fully extended and not extended.

Gray: What is the significance of doing a test between dead centres? I would have thought that the tests done demonstrate that the dead and live centres are concentric throughout?

Many thanks

Ron