Sieg C0 alignment

Hi I have just purchased a used sieg c0 micro lathe

the problem I have got when I turn 3/8 dia brass rod

to a length of 30mm just taking a light cut it is 2 and a 1/2

Thou out which I think is excessive.

could someone please advise me how to cure this

Thanks in advance

Martin

Hi Martin,

Your question is not clear. Can you please give more details.

Paul.

Martin,

As Paul suggests: We need more detail of both the test configuration and the result.

MichaelG.

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P.S. ... Just spotted that little Portmac in your album

Tony, at lathes.co.uk has expressed an interest in these.

Edited By Michael Gilligan on 12/10/2015 08:57:51

Sounds clear enough to me. Turned brass 3/8 dia by 30mm long and found he had a taper of 0.0025. Be better to keep the units the same. Either metric or imperial. An idea of the depth of cut would be good too.

First question - if you leave the same cut set and keep running the tool along several times does the taper reduce? Use slow feed.

John

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Edited By John W1 on 12/10/2015 11:10:18

With a wee lathe like the C 0 you might find the you get better results if you run it with a centre in the tail stock. I'd run the lathe at around 1000rpm (vary the speed up down 'till it feels right). Your tool must be SHARP, and try using one with a flat top.

Ian S C

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• Held in the chuck ?
• With or without tailstock support ?
• Between centres ?
• Which direction is the taper ?

Just a few of the things that are not clearly stated.

MichaelG.

Very probably no centre over that length and probably intelligent enough to try without one in if there was anyway.

The taper direction does matter but if it's in the wrong direction he needs more equipment than he probably has to find out just what the problem could be. I'm hoping it enlarges away from the chuck.

John

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Had a wee job to do today, and did not want to remove the work that was in my main lathe, so I used the Super adept, it was to make a tool makers reamer for a plastic wheel I was making for a sliding door. the reamer .380" dia x 1 1/2" L, held in the 4 jaw chuck a bit of steel from the junk box, probably rebar, about 1/2'dia, took it down to size without tail stock support at .015" per cut to .005" over size, it tapered toward the chuck .002", I finished it with a long angle lathe file. Ian S C

Edited By Ian S C on 13/10/2015 12:22:11

I wondered if he has loose bearings Ian. Same setting recuts are a sure sign providing the bar isn't bending. Past that it can be difficult to find out what the problem actually is. I'm reminded of some one that reckoned his tail stock was out so lapped it and then from what he found looked to be really down to a warped bed which would also give a taper turning without the centre in.

Files / emery cloth may well be the best answer.

Anyway the person seems to have gone. Maybe he found something more positive in the early postings some where else.

John

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John, yes take a second, or even a third cut at the final setting should reduce the taper. I tried the Super Adept again today on a bit of 316 stainless steel, the item was hollow so I drilled that on my big lathe, then took it down to size .010" at first then .015" toward the end. the little bar was 5/8" dia, it went to 1/2" dia for 1/2", then 1/4" dia for 3/4". It was only gripped by the chuck, the 3/4" length as tapered .002" with the large dia away from the chuck. Tool HSS. So wee lathes can cut stainless, you just need time, I'm glad I'v got an electric motor on mine, not a foot motor as they had back in the 1930s.

Ian S C

It is taken as read that tool is on centre height, and everything is clamped firmly, and without play in the Cross Slide gibs, Topslide gibs and Headstock bearings?

If turning between centres, (unlikely over a 30mm length) the Tailstock could be off centre. (See later)

It could be that the lathe is mounted so that the bed is twisted.

If the latter, the lathe needs to be levelled, to remove the twist. To do this:

Either a sensitive level needs to be used at Headstock and then at the Tailstock end of the bed, or follow the procedure given on Page 42 of the Myford Series 7 Manual. Whatever method is used, the adjustments (possibly shimming the feet) need to be reiterated until the twist is removed by the level reading remaining unchanged, or the lathe turns parallel.

Heaven forbid that the Headstock is not aligned on the axis of the bed! Check this with a suitable alignment bar

(As large as possible diameter piece of Silver Steel may suffice; but measure the diameter at both ends before, just to be sure that it is parallel)

Clamp the Silver Steel in the chuck, (DO NOT TURN THE CHUCK) Mount a DTI in the Toolpost at centre height, and set to Zero at the headstock end. Wind the saddle to the tailstock end. The reading should still be Zero, assuming that the Silver Steel is the same diameter at both ends.

To check the tailstock alignment, you really need an alignment bar, that will fit between the centres on your lathe. A possible alternative is, again, a piece of Silver steel, (because it is likely to be parallel over its length) of the largest diameter that will pass through the Headstock mandrel, should be mounted in the chuck with as little protruding, as possible and centre drilled.

Turn the Silver Steel, end for end, and again with the least amount protruding from the chuck, centre drill.

You now have an Alignment bar! Mount it between Centres in the Headstock and Tailstock, without excessive force, but definitely without any play. Mount a DTI in the Toolpost, so that it is on Centre height, and set to Zero at the Headstock end. Wind the Saddle to the Tailstock end, and note the reading. Hopefully it is still Zero. If not, a + reading indicates that the Tailstock body needs to be moved, on its base, ( AWAY from you to give a Zero reading). A - reading needs the Tailstock to be moved TOWARDS you.

Return the Saddle to the Headstock, reset Zero and recheck at the Tailstock end. Repeat the checks and adjustments, until the DTI reads Zero at both ends. You should then be able to turn parallel between centres.

Hope that all this is not "Teaching Granny to suck eggs", and will be of some help in sorting the problem.

Howard

Lot's of good advice there but the first thing I'd check is that the chuck is seated properly.

Rod

The chuck is unlikely to hold the silver steel dead on but that could be used to check to some unknown n thou.

It is possible to make a pretty good between centres test bar but it's fiddly. A fixed steady and a sensitive dti is needed. On a lathe this small just make it as long as possible. The usual length of a piece of silver steel should be ok on larger lathes. Diameter is tricky. To prevent sag due to weight some are hollow but hopefully that wont be a problem for say 12in of 1" bar. This method will work providing the tail stock isn't insanely out. The centre drill tip will probably break if it is. I'm assuming slides have been set sensibly. Not too loose.

Grip a short part of the length say circa 1/4" lightly in the 3 jaw and set the steady. Carefully set the steady to get the bar running to ideally no dti movement at all with a 1/10 thou reading dti. Tighten the chuck and check again. Done well so far and the reading wont have changed. Face the end of the bar. For a pro look turn the OD down a bit for say 1/4", chamfer the end and turn a recess in the end to protect the centre hole as well from knocks. Then carefully centre drill it. Not too deep, say up to the cone on the drill being around 1/8 - 3/16" dia. Slowly so that the drill can make the hole central even if it's only cutting on one side and for if the tail stock is a bit flimsy. The drills are stiff enough to do this in reasonable sizes. It's the whole idea behind them.

Then do the same thing to the other end.

To use it set up between centres. Using the cross slide run the dti across the top of the bar at several places along it's length. The reading should all be the same. If they are just different in the middle and variations on that the bed is warped. Say reading are taken at 1in intervals a pure angular error will show the same change of readings each time the dti is moved along. There is not much point in just running a dti along the side if the top readings are well out as the dti finger will be at different heights along the bar. A vertical slide could be used to rule this aspect out. The cross slide should be locked when doing this test. Say there is some error along the top it's possible to calculate what this means in terms of reading changes cause by the dti finger being at different height on the curved surface of the test bar so the degree of error in both directions can be estimated. Using the cross slide to test the top has removed any errors due to the test bar being round.

Then it becomes a case of what to do to correct them if needed. This might just be an estimation of what to do so the same test can be done again and adjustments refined. Maybe even making a new test bar before that but in real terms the method I described is likely to produce a pretty accurate bar.

Perfection I suspect is unlikely in many cases. Lathes are not super high precision devises. That's what grinding machines are for or more usually emery and files in our case. The other problem with lathes is wear.

Catches. Loose head stock bearing might make that end look low. The morse taper may be out compared with the axis of the spindle. Morse taper errors are likely to be insignificant due to the length of the centre being used - not so when a morse test mandrel is used. Loose bearings will cause the same cut setting to repeatedly remove material but be careful as the cut might be bending the bar.

Use of a morse taper test mandrel is very similar. This often have a draw bar socket in the morse end so that the spindle can be pulled back firmly into the bearings - not just firmly into the morse socket.

A more usual method of correcting taper when a centre is in the end of work - change the tailstock offset to correct it. This can come into things when staining the bed is used to correct shorter length turning test as they usual are. The usual light cut on 2 rings. Correcting these by straining the bed at the end is likely to throw the tailstock out so offsetting can correct that. There are complications. Personally I feel bed straining is pointless on most lathes and really applies to lathes that are stood on massive iron castings. The usual steel cabinet will give over time if the adjustment made that way is really significant. It's only intended to correct very very minor errors.

John

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