Tail alignment and gear handle play

Hi

I have a couple of issues with a Sieg lathe.

One is the alignement of the tail, it is significantly too high. There are options to fix it. First is to shim the head, the other is lap the bottom of the top half of the tail. I had several people recommend each method.

The former is more easily reversable and less "damaging", but requires disassembling the headstock area and it would mean the V groove is sitting less reliably in the bed V.
The latter is easier in that disassembling the tail takes only a few seconds, but the risk is to make the tail not parallel with the bed. If I lap too much I can alwyas shim the tail, but fixing a non-parallel tail is more work... assuming it is parallel now.

So I'm not sure yet what method to go with.......

I also have some stickiness in the carriage hand wheel. I'll spare the details but I found it is from play in the hand wheel shaft in its apron bore. I don't have a way to bore the apron and add a sleeve or a ball bearing. I thought about sleeving the shaft, but not sure there's a good way to hold it...? Any suggestions?

Thanks!

Stick to the tailstock, if you have a complete disaster it's relatively inexpensive to replace.

Check it's not just stray paint between the two parts of the tailstock

There should be a groove between the bearing faces of the tailstock and the vertical spigot so you can take the height down without going anywhere near side to side alignment.

Neil

Thanks

So I shouldn't be too worried about misaligning the tail with the bed from uneven lapping i.e. making it angle up or down?

I think shimming the head is the least risky option and impossible to ruin anything, but more hassle to do and I'm not sure if it won't make it sit unreliably against the bed...? Those are the only reasons I thoguht to lap the tail instead.

I should have mentioned that this is already after removing any excess paint, checking for dirt, etc. in the tail.

Edited By Nitai Levi on 26/06/2015 17:33:17

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Nitai,

Neil's advice is very logical ... but I would check one more thing before making your decision:

Is the HeadStock spindle correctly aligned with the bed of the lathe ?

• If Yes, then proceed as Neil suggests
• If No, then get it right before you touch anything else.

MichaelG.

Shimming the head will stop it being properly registered with the inverted-V upon which the lathe's basic accuracy depends. That is why I would look at the tailstock.

I would be worried about introducing new alignment errors, though. I thought you were worried about 'twisting' the tailstock from side to side.

Perhaps you could quantify things. How big is the vertical error with the tailstock locked fully retracted and fully extended? If the errors are relatively small (especially the retracted error) then you should be able to correct them by scraping, using marking blue to find any high spots and aiming to maximise the contact area between the two parts of the tailstock. Bear in mind that the barrel needs to be clamped and the two parts solidly clamped together and clamped to the bed, so this will be a rather tedious operation.

To give you a guide of what to aim for, if you are aiming to meet the Schlesinger limits for finish turning lathes the error should be that the tailstock is 0-0.02mm (~0- 0.001" with any error in the tailstock high direction when retracted. With the tailstock extended 100mm an additional error of the same magnitude is allowable.

Neil

Thanks. I'll clarify a few things.

The tail twisting to the side is controlled by a dufferent surface as you say, so not an issue.
What I meant was the tail becoming not parallel to the bed, angling up or down from uneven lapping, since I can't really guarantee it is accurate except just being really careful...

By shimming the head, I meant to shim the side of it that sits on the flat side of the bed i.e. away from you when working on the lathe. Although the head might move a bit above the V on one side, it should still be able to use it for alignment. I was told by a couple of people that this doesn't change the alignment of the head and should be more accurate than lapping the tail.

I would rather lap the tail if I knew it would definitely be accurate, but I'm not sure it would be...

I need to make an adapter for my indicator to test more accurately, but the tail seems to be at least 0.3mm high (possibly a little more), which is a lot. I will fix the tail side alignment once it is at the correct height.

You also need to confirm that the axis of the tailstock is parallel with the late axis or tilting up or down. Check if the height error is the same with the barrel fully extended as it is with it fully retracted.

Les.

If you just shim one side of the head you'll introduce a twist into the bed which will make it almost impossible to turn parallel, as Neil said do any work on the tailstock. Take your time and do lots of measuring as you go.

How high is it?

Steve

Shaking my head in disbelief...

If you put a shim on the flat part on the bed (I hope I understand the construction of that lathe correctly), you will not only move the spindle axis a bit higher maybe, but you also rotate the headstock around the vee and so the axis moves also towards the operator side. Is it that what you want?

Up to now no one commented about 'lapping'. How do you plan to do that? With an oilstone maybe? To remove 0.3 mm with lapping you would need days or weeks imho...

I would advise you to find someone with a milling machine and mill away 0.3 mm on the sole of the tailstock, then (if done correctly) you don't have to worry about ending with a tailstock pointing towards the sky...or the other way...

Regards, Frank

There are a few more things to check before you start chopping into the tail stock.

Head / spindle alignment in regards to the lathe bed, you needs to check that the centre line of the spindle is parralell to the bed of the lathe as the spindle nose could be high / low or skewing off either side so check and correct this first.

I found on my C2 seig that there were burrs under the head stock where it contacts the bed causing the head to sit higher at the rear also check around the bolt holes that the mounting bolts for the head screw in.

Once you have that sorted then turn your attention to the tail stock and i would mount a dial test indicator up in the chuck and use that to sweep around the tail stock barrel , then just as a precaution i would fit a dead centre in the tail stock to confirm that the bore is concentric the the outside, if the barrel is no more that a couple of thou high that is fine but not low

I have read somewhere (may have been another forum or magazine) about shimming the head to correct alignment issues and it seemed to be a very tedious operation at best but they had no choice as the head was so out of kilter the lathe was unusable.

I also had issues with the carriage being sticky but mine was caused by paint under the gear rack which i scraped off and now the carriage is nice and smooth to operate also my apron already has a roller bearing for the hand wheel which surprised me !

As the apron can be removed without loosening the saddle you could mount the apron up on your face plate , lock the saddle down on the bed and use the cross and compound slides to allow you to bore out the hand wheel bore and fit a bushing or bearing.

Ian.

Just some observations since nothing I've read seems to cover them:

Is this a new lathe? if so, I'd send it back (or perhaps just the tailstock).

If it's a lathe that's been in use for some time, I'd have to wonder how it got this far before becoming a problem that needs fixing.

If the lathe has recently been rebuilt/refurbished and this problem has resulted, then you'd be better off finding out why than removing metal (or shimming).

Thanks everyone. I'll try to clarify and reply all.

Yes, this was confirmed. It is reasonably accurate that I don't want to change it.

I don't see why there would be a twist in the bed because of that.
I measured it a while ago and I have to make an adapter to make get a more accurate measurement, but it is approximately 0.3mm too high.

You're right that this would happen, but the side alignment of the tail needs to be adjusted anyway and would need adjustment once I disassemble it to adjust height, so the head moving towards the operator by a small amount is not an issue...
I was worried about this too but two people who have used both methods many times explained that shimming the headstock this way on this lathe is "standard" and would be the most accurate. Obviously the shims would have to be about twice as thick as the height misalignment.

My only way is to use a flat surface (granite) and put sand paper on it, sanding the tail on it by hand. Yes it's probably a bit slow... maybe even unrealistic... plus the risk of ruining alignment from the sanding, even if extremely careful...

Unfotunately not really a realistic option... unless it's the only option. I don't know anyone, would need to find someone in another city probably, have no idea if they are good and trustworthy (huge issue here) and this kind of thing is not really done here by shipping. there isn't a machining "group" here or anything like this... you almost have to know abotu someone by coincidence. There are a bunch of high level CNC machining places that wouldn't agree to do this or charge a fortune...

It's a new lathe and driving to return it (a hassle... no shipping) could result in another lathe (if it's in stock, probably not, as I need this very specific model) that has who knows what other issues. Especially after I spent almost 30 hours adjuting it already... maybe finding someone to mill it is a better option...

Thanks again

If you must shim the head then put a 0.3mm shim on the flat way and 0.212mm shims on either face of the V and it will lift it straight up with no rotation. So in practical terms 0.3mm on the flat and 0.2mm on the Vees and you won't be far off

Basic theory is whatever you pack the flat way with multiply that by 0.707 to get the thickness of the V shims.

Edited By JasonB on 27/06/2015 10:23:55

If you do need to remove metal from the tail stock, it sounds like a job for a surface grinder rather than a milling machine.

Ian S C

Have you had the tailstock apart yet? This may well be a 'stray paint' issue. Tailstocks are mass produced on jig and are intended to be interchangeable so an error of that magnitude may have appeared before machining and final assembly.

Also, how are you measuring the error? The standard way is to put a test bar between centres, and measure the highest point at each end. Repeat with the centres rotated unless their accuracy is above suspicion.

You can 'eyeball' the facing tips of two dead centres for a first estimate.

If you are really pressed, and are sure of how much metal to remove, then the easiest way is to fit a flycutter in the headstock of the lathe and mount the upper part of the tailstock on the tool post with the lower surface facing the headstock.

Alignment will be critical. You can use a DTI held in the 3-jaw chuck and feed the tailstock past it to ensure the cut will be exactly parallel to the existing surface, but you also need to ensure the surface to be machines is aligned vertically as well.

You will need exceptional care and light cuts, but the machining should be straightforward.

My approach would be to remove somewhat less metal than necessary and finish by hand scraping. Bear in mind you say the error is 0.3mm which is not an accurate enough measurement to determine what to reduce the error to around 0.02mm by any procedure.

Neil

Edited By Neil Wyatt on 27/06/2015 11:06:28

Hi Naitai

Like you, and a couple of months ago, I discovered that the vertical alignment on my lathe (Warco180) seemed to be out by quite a long way.

After spending a while worrying about this , and after taking some measurements and advice from people on this forum, I came to the conclusion that it wasn’t as big a problem as initially it might seem. Search for the thread ‘Vertical Tailstock Alignment’ and have a read.

I ended up convincing myself that to all practical intents and purposes , and at least for my needs, it didn’t matter. I’ve used the lathe to make an IC engine that ran, and that’s good enough for me.

David

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I'm feeling left-out.

MichaelG.

Nitai,

Depending on when your machine was actually made, the process for finishing the underside of SC3 headstock has changed...generally for the better, without going into details.

The more questions you ask about scraping and finishing, the more different answers you will get. Try to keep things simple without over thinking. There are more than half a million mini-lathes in the world now, all with variable issues, and most are being used, with and without adjustment.

Keep it simple and play with the two halves of the tail stock - scraping/shimming in between the two to make the adjustments you need. Only play with the underside of the head stock if you really feel adventurous and if you know what you are doing. Do not try to do all things in one go. The key is to take small steps to see what is acceptable to you.

For the carriage, consider what Ian - XD 351 said and re-look at ARC SC3 Dismantling and Reassembly Guide pictures 31 to 33, 83 to 87, if you havn't done so already.

It is a big deal or a problem only if you make it so. You have a good machine for the price you have paid. If anyone suggests that you should not have to do any adjustments, then I would politely suggest that they are simply mistaken. Every mini-lathe in the world will have variable adjustment issues. There are too many variables to take into consideration, to include transit and climate settlement effects on the machine in the environment it will be used. At this price level, a machine tool fitter is not supplied with the machine for installation, and this is not a tool room lathe.

Good luck and don't worry so much.

Ketan at ARC.

OK I just measured again and the tail is not high by as much as I remembered. The puppitast shows approx 0.265mm difference (hard to be sure because it's also not aligned side-to-side), so I'm guesstimating between 0.130mm and 0.135mm high. Still far more than I want it to be. So it's still a question of lapping the tail (as I desribed) or shimming the head (might shim the V as well like JasonB suggested). I had a less reliable puppitast holder before which is probably the reason for the error and why I wasn't sure.

MichaelG, sorry, it got a bit much with trying to quote every post I answer to
If I didn't mention it already, yes, the spindle is accurate with the bed, at least as accurate as I expect and need it to be.

Neil, yes, I disassembled the tail a few times already to check things. I removed anything that could affect this, like paint, dirt, etc. There actually wasn't any that affected it and it made no difference.
I'm measuring it by putting a puppitast in the head stock and checking the tail. To verify, I tested both the quill bore and a dead center.
Eyeballing two dead centers is how I initially checked, before more accurate tests.

Edited By Nitai Levi on 27/06/2015 11:29:40

Edited By Nitai Levi on 27/06/2015 11:32:21

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Thanks for the info. ... That's good to know !!

In that case, I would very strongly recommend that you leave the HeadStock firmly attached, and treat it and the bed as being a single unit. ... Any "fitting" work should be confined to the TailStock [for the very good reasons identified by Neil].

MichaelG.

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P.S. ... Ketan's observations are [as usual] very reasonable. ... If you really want a much better-aligned lathe then I would recommend looking for a decent old Pultra; unless, of course, you can afford the more modern Levin or Derbyshire equivalent.

Edited By Michael Gilligan on 27/06/2015 12:11:04