Colchester Chipmaster tailstock shimming

This topic has 19 replies, 11 voices, and was last updated 19 April 2025 at 13:22 by Peter_H.

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16 April 2025 at 21:10 #793589
Peter_H
Participant
@peter_h
Equipment.
320mm test long bar, ground 25mm diameter, centre drilled each end.
Testing points – 10mm from each end of the bar, and traverse between.
Measuring gauge – Mitutoyo 0.001mm digital dial guage with 10mm convex probe.

I have a 1963 vintage Colchester Chipmaster lathe with an 8″ Set-Tru 3 jaw chuck and a dodgy tailstock. I trimmed the Set-Tru chuck until it was running true within 1um (half a tenth!). To be clear, this is purely rotating by hand and at no point did I start the motor. I’m sure the measurement would have worsened if I had, but it stayed stable rotating by hand through the tests.

The tailstock measured 150um (6thou) out horizontally and -400um low (16thou). Centre drilling and drilling has got bad recently so I decided to do something about the tailstock. Like most tailstocks there are two parts, a base which you can lock to the bed as required, and a body which houses the quill. The horizontal error of the tailstock can be zeroed out by moving the body side to side with two opposing screws. It rides on a transverse key, in this case a body 90 degree Vee and a base Vee groove. The body is supported on the Vee groove at the front and pad at the rear, about 30mm long and the width of the tailstock, at the rear. There are also two small pads near the middle but the Vee and the main rear pad are the two places you can tailstock.

There is an opportunity here to trim differential to remove any non-parallelism between the quill bore and the bed, but it seemeed ok here. I found some double sided adhesive tape on Amazon which is only 0.05mm thick (2 thou) so I decided it would be a lot less awkward to stick the shims to the base first, grease the lower surface of the body, and mate them. In this case I needed to raise the body of the tailstock by 400um (16thou). I thought I would be conservative and correct it by 14 of the 16thou and see how it looked. With 2 thou tape, it gave me 12thou shim for the rear. The front needs a little more thought. The shims are going on a 45 degree inclined surface (each side of the Vee groove). So the shim will lift by more than it’s thckness, so we need a thinner shim. School trig tells us the factor is sqrt(2) = 1.414. With the shim stock kit I had, I settled on 12thou for the back and 8th for the vee groove sides for a 14thou lift.

I cleaned the base and body surfaces with acetone, guillotined the shims and applied oversize adhesive to them them and trimmed to size. Stuck each one in place and held hard for a while. Greased the body mating areas and reassembled. I now trimmed the side to side error as best I could. I fitted a ground MT3 centre in the tailstock, and I turned a 60 degree centre on a piece of ally bar in the chuck, and mounted the test bar between the centres. I fitted a 10mm diameter probe with a convex bottom to the dial gauge. These are good for smoothing out grooves and scratches, etc. I clocked the bar horizontally at the sides and vertically at the top, traversing the bar with the gauge holder fixed on the lathe cross slide. Luck shone on me again and the horizontal error along the bar was 1 to 2um.

The vertical component which was our mnain target was down from 400um to 65um (about 2.5thou). If I was doing a lot of turning using the tailstock I may consider improving that, but for the majority of use which is drilling and centre drilling it is fine. The drill used to jump and make you think it would break but it’s fine now.

Peter
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16 April 2025 at 21:32 #793592
Michael Gilligan
Participant
@michaelgilligan61133
Good thinking … Well done, Sir

MichaelG.
16 April 2025 at 23:15 #793612
halfnut
Participant
@halfnut
Well done. From the factory the tailstock would have been set a thou or two high to allow it to come into line with wear. So a small amount of vertical error is not critical, as you have found.
17 April 2025 at 07:39 #793627
John MC
Participant
@johnmc39344
Well done for sorting that huge error out.

I’m intrigued as to where the vertical error came from? Wear, manufacturing error or something else? If its wear what is the rest of the machine like?
17 April 2025 at 11:02 #793659
Peter_H
Participant
@peter_h
The bed certainly has wear. I’ve never tried to quantify it, but the edges of the bed that the tailstock and saddle ride on are just about discernibly low compared to the unused part. The wear is going to come from decades of sliding the saddle and tailstock up and down the bed. The saddle is a big flat object with a fairly linear moving force so should contribute fairly even wear. The tailstock gets pushed forward slightly digging the leading edge in, and then pushed back digging the trailing edge in. This is conjectured to lead to curved wear of the tailstock base and wear of it’s mating surface on the bed that is worse toward the average position of it. In practise, a lot will be down to poor maintenance. Fine swarf and grit on the bed and lack of lubrication will take it’s toll. No wipers on the tailstock either. Maybe I’ll put some TPU filament in the 3D printer and see what I can come up with.

BTW, I did a rough test of the quill alignment relative to the bar and was pleasantly surprised. Same setup, I just moved the tailstock back and brought the quill forward to engage the bar again. This would also incorporate errors due to change in wear in different parts of the bed. From the quill reading zero, back to reading 80mm, the tailstock end of the test bar showed no discernible horizontal error, and only 0.015mm (1/2 thou) vertically. It really must have been my lucky day!.

Peter
17 April 2025 at 12:33 #793691
parovoz
Participant
@parovoz
Thanks for that ! ! ! I too have a dippy chippie with a droopy tailstock. Bed definitely a bit worn, carriage gets a little stiff at the tailstock end. It does bore very true though…. I’m definitely looking to shim the tailstock in the near future when I give the machine a general overhaul. I did the variator a few years back and I can now work the machine without ordnance grade ear defenders 🙂
17 April 2025 at 12:40 #793693
Martin Johnson 1
Participant
@martinjohnson1
Well done Peter. I did a similar fix on my 5.5″ Kerry with similar results. Luckily that has no 45 deg surfaces to worry about so plain shim just stays put.

I subsequently bored out and sleeved the quill (to repair a scored morse taper) all macined in situ on the lathe. That should in theory give a perfect result but theory seemed to be on holiday that day. Anyway it’s better than it was but not perfect.

Martin
17 April 2025 at 19:50 #793786
old mart
Participant
@oldmart
The tailstock of the museum’s Smart & Brown model A has a mass of shim stock between the halves to get things lined up, we would not dare to offset it. Having the taper turning attachment means that the shims will not be disturbed anyway. Having mills I could easily adjust the surfaces and add a single thick spacer, but prefer to let sleeping dogs lie. I have replaced the tailstock of the Atlas 12 X 24 lathe with a NOS Chinese one which has a lever lock.That meant making a new base to fit the Atlas bed. With careful milling, I got the quill lined up in all directions without any shims at all.
18 April 2025 at 09:54 #793860
John MC
Participant
@johnmc39344
I’m finding it difficult to believe wear is the problem. The saddle and tailstock work on different parts of the bed. there is near zero load on the tailstock when its moved so will not wear, unlike the saddle, so wear is extremely unlikely to be a problem.

I would be looking at for other reasons, distorted bed for instance.

My Chipmaster is a mid-1970’s machine, was there ever a change in bed design?

For interest, attached are the accuracy charts for my machine.
18 April 2025 at 10:23 #793862
Alan Jackson
Participant
@alanjackson47790
I had a similar problem with my Chipmaster. I added a 6 thou shim at the 45 degree guide this then got the tailstock barrel parrallel to the spindle axis but it was still about 6 thou too low. I then made a No 3 Morse taper male insert and bored a No 2 Morse taper female hole in the male Morse 3 insert, the Morse No 2 bore was offset 0.015″ eccentric. This was the inserted into the Morse 3 tailstock barrel and rotated to match the vertical spindle centreline, then it was pulled into the tailstock barrel by a hollow bolt. The horizontal adjustment was made via the normal adjustment setting. This gave me a Prefered Morse No 2 tailstock because all my parts from my previous lathe were No 2 Morse. I also added a rack drive to the tailstock.

Alan
18 April 2025 at 10:30 #793865
halfnut
Participant
@halfnut
If there is 16 thou of wear on the bed, you should be able to see that by laying a 12 inch steel rule along and looking for daylight. A piece of white paper held in the background helps make the daylight easier to see.

Also, it’s possible the tailstock is not the original from the factory, having been swapped over the years by previous owner. Weirder things have happened to old machines.
18 April 2025 at 10:57 #793874
Bazyle
Participant
@bazyle
For other in this situation I suggest first removing an inverting the tailstock and then seeing if the sliding surfaces are dead flat from even wear or convex from extra wear at front and back. With such a big heavy unit and oil on the surfaces it may not be able to ascertain this from rock left to right in situ.
18 April 2025 at 11:00 #793876
Diogenes
Participant
@diogenes
18 April 2025 at 11:27 #793883
Alan Jackson
Participant
@alanjackson47790
Diogenes, It is home made, I first made it for my previous lathe but it was so useful for both small and large drills etc that I transfered it to my Chipmaster. It has 5 inches if travel for just under three turns of the capstan.
18 April 2025 at 11:30 #793885
Peter_H
Participant
@peter_h
Both sides of the bed have the raised Vee so I can’t see across. Besides which, I can’t get down that low anymore :). My theory, not that it matters much, is that the wear is in the tailstock rather than the bed. The bed is hardened, the tailstock isn’t (is it?). My main evidence is that the error is the same wherever the tailstock is on the bed, and the corrected figures don’t change with tailstock position either. I’ve heard it said before that the tailstock sliding surface can wear in a convex manner, and scraping it flat can only be a good idea, if you can scrape. The important thing for me is the result of how it is in use. As long as the tailstock clamps in the same relative place on it’s curvature then all should be OK. Also, by luck or whatever, the quill seems level and aligned to the rotation axis within the limits I managed to achieve. In a machine this old there is no one culprit, everything will have wear to some extent. The tailstock has the same serial number as seen anywhere else on the lathe.
18 April 2025 at 12:05 #793897
Peter_H
Participant
@peter_h
John, my counter argument would be that the bed ways are induction hardened and ground after the casting has been seasoned. The tailstock hasn’t been hardened to my knowledge. I can’t see how or why the bed should distort as long as the machine is levelled. The bed itself shouldn’t wear as much as the saddle and the tailstock. The saddle has end wipers and has way oiling points. The tailstock has neither. The idea I read was that the tailstock mating face will wear convex as it is being “dug in” at the front when sliding forward and v.v. the rear. I have no idea if it is true. I’ll keep an eye on the alignment but at the moment I’m happy with it, whatever the cause.

Peter
18 April 2025 at 12:39 #793901
Pete Rimmer
Participant
@peterimmer30576
18 April 2025 at 13:29 #793920
Bazyle
Participant
@bazyle
Thanks for tip 3 <sigh> I’ve been putting this off for my 70 yr old Boxford for too long.
19 April 2025 at 12:54 #794093
John MC
Participant
@johnmc39344
Still struggling to see how the tailstock base has worn so badly, wear to cause the stated error would be believable in a heavily loaded part but the tailstock base in not highly loaded.

If “muck” gets between base and bed, even with many years of use, what must the rest of the machine be like?

Also, because the load that the tailstock sees when being moved, is its own weight plus tooling, hardly anything in reality, it will tend to ride up over the “muck” rather than grind against it. On the other hand, the saddle and slides sees considerable load when being used so “muck” can be very detrimental.

I would not assume that the relatively soft tailstock base will wear before the hardened ways.

Looking at rectifying the problem again, I would suggest using thin shim and sticky tape is not the way to fix it. The base, where it rest on the bed needs to have 2 – 3mm removed parallel to its top face. The “lost” metal replaced with steel strip screwed down on to the base, then machined until the error in alignment is corrected.

Shim suck down with sticky tape is no good because the interface will be subject to high load every time the tailstock is clamped. Likewise, gluing the shim in place will also introduce a relatively flexible member in to the structure of the machine.
19 April 2025 at 13:22 #794097
Peter_H
Participant
@peter_h
Well, struggle if you must John, but looking at the lathe and the bed and how it performs I can’t see what else it could be. Whatever it is, shimming it seems to fix it, which will do me. I think you are getting the wrong mental image of this “glue”. For health reasons I would not have achieved the job without it (tremor). It is 0.05mm thick double sided tape, comprising 0.03mm polyester tape with a fine coating of adhesive each side. So it represents 2 thou out of the 14 thou I’ve shimmed it. The base and body of the the tailstock are tightened together good. Force compared to operating the clamp?. No idea, probably between 20% to 60% to pluck a number out of the air. Even if all the adhesive gets squeezed out that still leaves 12 thou of steel shim and 1 thou of polyester out of the original 14 thou. If that happens in the next 3 or 4 years, (about 30 hours use) I’ll redo it. If it happens again after another few years, I’ll either be gone or too old to care!

It’s great to do things right, and I don’t doubt the method you describe would do a more permanent job. I’ve spent my life being a perfectionist and I still enjoy turning things to a few microns when they don’t need it but there comes a time when illness and age win out and a more pragmatic approach is forced on you.

Peter
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