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Precision Tailstock Alignment

I think I've got half a good idea, but need help with the other half!

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Scrim16/04/2011 01:54:20
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19 forum posts
I’d like my SC3 tailstock to be really accurately aligned to the headstock but there are four degrees of freedom to deal with: Vertical/Horizontal displacements and Vertical/Horizontal angular errors (technically called Yaw and Pitch I think).
It looks hard to adjust all four, but I have an idea to deal with the lot in one go.
Turn an MT2 taper (to match my tailstock) on a mild steel bar held at the headstock by any rigid means. The taper will be exactly concentric with the headstock axis of rotation so when the tailstock is fitted on it, it will also be precisely positioned on the headstock axis of rotation, as required.
The next step would be to somehow fix the headstock in this position relative to its base. It’s tempting to just fill all the gaps with shim and epoxy it solid, but it would be better if the tailstock could still be offset but easily returned to be exactly on axis at any time.
Has anyone seen an approach like this? I’m looking for ideas for this last step of the process.
David Colwill16/04/2011 06:25:47
670 forum posts
34 photos
   I do have a turner friend that aligns his tailstock by boring a hole the size of the barrel in a piece of scrap steel and setting so that it fits nicely when fed in this does take all of the above into account. There should be no problems with vertical alignment as this is usually very accurately machined. I'm not sure of the arrangement on an SC3 but I would be inclined to proceed slowly and methodically until you are sure where all the errors are.
   If you do have vertical errors one way of dealing with them would be to use one of the compounds like turcite which is used by machine builders to reduce friction on sliding surfaces and for what you are suggesting. There was an article about it in MEW but I can't remember when.
   Well good luck with it!
   Dave.

Edited By David Colwill on 16/04/2011 06:26:34

mgj16/04/2011 08:52:55
1008 forum posts
14 photos
First question is "How far has this been taken down?" simply because a misalignment is only a malignment relative to a datum.
 
So I suggest, if you think the headstock is out, (seems so from your post), that using a proper accuurate DTI you align the headstock axis with the bed, in both planes, with no strain on the bed.
 
Then you can bolt the machine down and bring the bed in proper alignment with the headstock axis with the usual test bar shimming and turning tests. Then you can align the tailstock in both planes by using an accurately centred bar.
 
Or, in your secend paragraph is there a transposition - for headstock read tailstock?
 
If you reckon the tailstock is badly out in all these planes, and its easy to measure, then yes, you can shim and lock up. Best way if the headstock is true or has been trued, might be to bore it off the headstock and fit sleeves or a replacement quill. Then you know it will be dead true, assuming the bed is true. (That is how they make them)
 
Assuming that the quill is true. Have you done a turnover test of a bar in the tailstock MT to check the alignment of the quill axis.(might be something as basic as a flake of metal in the MT and a problem solved by a wipe with a scraper.)
 
Personally I wouldn't start trying to turn test bars with MTs on them, (especially when I am not certain of my centres) though of course it can be done. For that sort of critical work I'd buy a good one properly ground to fine limits and then use a DTI graduated in .0001" or metric equivalent.
 
It just seems to me that there is quite a lot that is unknown in the original post, and I think I'd get myself into a position where I was pretty definite about the errors and where they are before I started locking stuff solid.
 

Edited By mgj on 16/04/2011 08:54:42

Mike16/04/2011 10:41:12
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713 forum posts
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About 3 years ago I bought a Clarke CL300, which I believe is similar to the Seig. I had terrible problems in aligning the tailstock, which seemed to settle in a different position by a couple of thou every time it was clamped to the bed. Eventually I bought the camlock tailstock from Arc Euro Trade. It fitted, spot on, straight out of the box, always clamps in good alignment, and I can now turn, parallel to within about half a thou over the full length of the bed. Makes me wonder if there aren't a few "rogue" tailstocks about.
Nobby16/04/2011 23:32:59
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587 forum posts
113 photos
Hi Guys
How about fitting a d.t.i. clock in chuck. then clock barrel of tailstock by turning the clock.
round the barrel it will show any misalinement . With power turned off.
Regards Nobby

Scrim17/04/2011 00:50:51
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19 forum posts
Thanks for all the replies. I should first correct an error in my original post - it should read: "The next step would be to somehow fix the

TAILstock in this position relative to its base."

I should really leave the precise setting of my tailstock until the bed and headstock are checked, but for now I definitely need to do some work on the tailstock as it's about 0.5mm low, which strains small drills and with larger drills results in over sized holes and the drill only cutting on one of its edges.
 
I'm aware of the usual methods of aligning the tailstock, but thought my approach might have advantages. I've realised though that it won't account for any error in the direction the tailstock moves when you turn its handle
 
Turcite sounds interesting. Where could I get it?
 

 
mgj17/04/2011 09:28:26
1008 forum posts
14 photos
Graham - I may have misunderstood your post.
 
The "swing" left to right of the tailstock can easily be applied using the alignment screw, or by putting a second screw in near the front to take up any slcak in hte guideway.
Interesting to see that the quill should run high, because work tends to lift - unless one is doing something on a rear toolpost.
 
I actually went and checked both lathes last night, and they are running a lot closer to true than those figures suggest, though I accept that there will be errors due to oil films and wear, and of course the bed is set to turn true. But there is no rise, either lathe.
 
Scrim - are you sure you want to go slapping Turcite or whatever over the machine. If you know the error, then a shim between TS base and top will do the trick. Superglue them in place. If you need to tilt it fore and aft, then you put differing shims front to back. that way you will get it all aligned perfectly and without permanently deforming the machine just in case one of the measurements was wrong.
 
I had to do the same under the pedestal of a Warco Super Major mill. One very thin shim fixed it . A packet of steel shim is about £25 and is a lifetime buy.
Les Jones 117/04/2011 12:38:23
2171 forum posts
149 photos
Hi Scrim,
Could it be that the headstock is high due to dirt between it and the bed rather than the tailstock low ? What is the history of the lathe ? Knowing that would help people with making suggestions.
Les.
Terryd17/04/2011 14:05:56
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1935 forum posts
179 photos
Hi Scrim
 
Graham is absolutely right about the lathe being returned if reasonably new. It is not 'fit for purpose' under the terms of the Sale of Goods Act 1984 - as Amended. Under the terms of the law a manufacturers guarantee period is often meaningless and could be disregarded when considering if a product is 'fit for purpose'. If the lathe is reasonably new I suggest that you research the Act and then decide on your course of action.
 
I am often amazed at the number of people who do not know their legal rights in this respect and accept faulty or substandard goods. Even if it is not relevant in this case, it is worth getting to know the terms of the Act for future reference.
 
Best regards
 
Terry
mgj17/04/2011 20:50:52
1008 forum posts
14 photos
Gray - Swing. Yes I can see that it shouldn't be down to the alignment screws on the tailstock. Also, I can quite see that, if there was to be an error, you'd want it towards you. Depends on the type of bed. If it has vee guides than you are rather limited by that. If you have the Myford flat bed, with a gib strip, then were it out, you could possibly use those to get it right, if hte error was radial around the axis, and not simply a lateral misalignment.
 
Also I suspect that the pemissible error may well have something to do with quill stroke and size of machine? A given angular error will give varying indications depending on travel?
 
On both my machines, a 6 x36 long bed Chinaman, and the Myford, these errors are quite difficult to detect.
 
I wonder if these things shouldn't be very close to true, but if there is an error then it should be in a particular direction . Anyway - I for one m very happy with pretty much true to the limits of my measurng equipment. Both machines turn mighty straight, mighty parallel!
 
 
 

Edited By mgj on 17/04/2011 20:52:26

Terryd18/04/2011 01:34:52
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1935 forum posts
179 photos
Hi Scrim,
 
I had a similar problem with drilling and itr turned out to be a badly set i
up Jacobs chuck, I changed the chuck and the problem disappeared. I disassembled the original chuck, cleaned and reassembled it properly, added a new arbor, scraped out the crap from the tailstock female taper and it worked perfectly
 
Terry
Nobby18/04/2011 10:48:29
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587 forum posts
113 photos
Hi Guys
I have a 1to2 sleeve its acurrate only in one postion so i have marked the top so I know the correct way round
Nobby
Nobby18/04/2011 23:06:30
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587 forum posts
113 photos
Hi Guys
I thought this may be of interest talking about tailstocks Heres the fabricated one I made for my Super7 Mk 1 note the rule & adjustable pointer
Nobby

mgj19/04/2011 17:55:28
1008 forum posts
14 photos
Gray - I don't think we disagree in principle..
 
My only point is that before we go slapping stuff onto, or chomping bits off a machine irreparably, we are very sure of hte error (if any).
 
Nobby had mentioned an MT socket that is out. The other classis is that if the lathe bed is not bolted true (set to turn true by a turning test,) then a clock on an extended tailstock quill will give a false indication on a tailstock tilted up or down, depending on direction, and drills will jam and cut funny sized holes..
 
I think one also must accept that a .5 mm error is huge when we are talking of hundredths, and it should or could have been detected by even the most sozzled partygoing oriental on a Monday morning. So something is amiss, and the likelihood is that it doesn't originate in a China. (that doesn't mean it doesn't or can't - it means that on the blance of probabilities... because most kit is built on CNC machinery these days)
 
Before I started attacking this lathe, I'd like to see it set up within .0001" on a test bar and clock. (or by turning test, the permissible error on one collar being +/-.0002" max) Once one has the bed dead straight, which takes a lot of effort and time, its amaxing how things tend to turn straight an other errors disappear, because one can set hte tialstock accuratley (and easily).
 
If tests like that have been done, and we aree sure htat the bed is right, and the tails stock is then checked and shows not a constant "error" but divergence, then there is a problem. But until then I think I'd be a mite cautious.
 

Ian S C20/04/2011 03:05:20
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7468 forum posts
230 photos
Some were, some time in its life between China, and its final place, did the tail stock get changed for one on another lathe, that now has one that is out of line in the opposite direction? ian S C
Scrim21/04/2011 17:11:18
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19 forum posts
I'm having trouble posting here for some reason. I'll try again:
 
Hi, Sorry for the delay in getting back. I agree that the error in my tailstock is excessive and I should have thought about asking for a replacement but at the time of purchase of this, my first lathe, I was a bit overwhelmed with all the other issues. Also, my experience of the number and extent of problems with my Super C3 left me expecting very little. To give an example, my first experience of improving part of my lathe was to work on the dovetail and gib in the vertical slide accessory I'd also bought at ARC Eurotrade. There was a big problem with the set screws that position the gib as their threaded holes were drilled too high so that the gib sat not flat against the opposing dovetail surface, but tilted at an angle. The result was that the gib made only a line contact with the dovetail face instead of pressing on it with its whole surface. I questioned the boss, Ketan, at ARC Eurotrade about this. He passed on his top mechanical chaps opinion that it wasn't worth trying to fix this problem on the vertical slide. I ignored this and redrilled/tapped three new holes and then a few spent days with silicon carbide grits lapping the dovetail/gib surfaces together and it now has a truly superb action.

After that experience I could easily understand why ARC's preparation service for my Super C3 included redrilling/tapping the set screws for my cross slide gib - it clearly had the exact same problem! I also noted the same saddle gib screw fix on the Super C3 shown on 'The Society of Model and Experimental Engineers' (SMEE) stand at the Alexandria Palace Model Engineering show earlier this year, so sadly it seems they mass produce them with this fault as standard! Ketan says it's a long hard slog getting them over in China to improve anything. The guess is that the jig they use to drill the set screw holes is out by millimetres due to extreme wear. Operating a wobbling drill press sitting with it on bare unsurfaced ground is a potential cause! I should point out that some parts are made exactly accurate as as far as my new Mitutoyo caliper can tell, so the range of machining quality very variable.

Returning to the tailstock: I decided to practice my intended technique for hand grinding the saddle to fit the bed by grinding the lower section of my tailstock to fit the bed first. As supplied it only made contact at one point on each of its three contact faces so there was plenty of room for improvement. Having already begun this regrinding I don't feel in a good position to ask for it to be replaced and anyway, I'd just have to repeat the very laborious bed fitting again (you do it with cut strips of silicon carbide sandpaper...).

OK, so this situation is a joke, but on the other hand I got a compact lathe with the new quite sophisticated high torque at low revs speed controlled motor for a small fraction of the cost of something like a Myford, which would be too big for me anyway. The best way to get the Chinese to get their act together is for some other up and coming county to outclass them at a competitive price. Meanwhile people will grin and bear it as alternatives are limited when so too is cash.

Thanks for all the input. I’ve had a suggestion that after checking everything else I might lower the headstock instead of raising the tailstock and this would certainly result in a much tidier solution that I’d foreseen, so I may follow that course.
Scrim21/04/2011 23:26:52
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19 forum posts
Ah! Normal posting has resumed!
 
 
Ian S C22/04/2011 09:22:51
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7468 forum posts
230 photos
Hi Gray, since I,v been on the web I,v desided that it's impossible that the retailers of these machines have not read these threads, and surely with the negative advertising, they shoul be pulling their socks up. Can't of course do anything about private sales on the net, or other places. I have not heard any complaints in NZ (there will be), but I have noticed an improvement over the last twenty years in the stuff coming out of China, my mill and lathe are Taiwanese. Ian S C
Les Jones 122/04/2011 09:31:30
2171 forum posts
149 photos
Hi Scrim and Gray,
I would be very cautious about attempting to machine the bottom surfaces of the headstock. Even with access to a good milling machine getting the relationship between the" V" groove and flat surfaces will require a lot of care. Even if this is attempted I would suggest checking that the headstock is seated correctly on the bed and checking that the axis of the spindle is aligned with the bed. If it is not aligned then measurements should be taken to enable this misalignment to to be removed when machining the base of the headstock.
Les.
Scrim22/04/2011 16:24:07
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19 forum posts
I think the theory that my tailstock got swapped with someone elses, somehow slipped through the system seems most likely. I very much appreciate offers of help (I live quite near Alexandra Palace in north-east London) but I'm fairly confident that my bed fitting technique is good.

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