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.

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

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.

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.

On 18 April 2025 at 10:23 Alan Jackson Said:

.. …I also added a rack drive to the tailstock… ..

Alan

Is that home-brewed or a Colchester accessory..?

..looks neat & useful..

On 18 April 2025 at 10:57 Bazyle Said:

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.

This is an important observation and I wrote a long post about it yesterday which I promptly lost by clicking off the thread before it was sent.

Tailstock bases, just like saddles, wear convex due to the debris getting under the leading edges as they slide and eroding the surfaces underneath. The bedway also wears but at a much slower rate since the bedway is long and the wear is spread along the length of travel. For a tailstock this can induce downwards nod in the tailstock. The saddle can suffer quite a lot of wear before it becomes bad enough to affect your work but the tailstock obviously is much more sensitive.

Here are the steps I would take to remedy a badly worn tailstock base:

1. Remove the base form the tailstock and remove the key, de-burr all of the edges.

2. Put the tailstock base on the bed up near the chuck. This are will not be worn by tailstock use. Use a dial gauge vertically down on the flat top of the base and slide it under the dial to judge the amount of wear. This is a dummy check more or less just part of the investigative process.

3. Set your base inverted on a surface plate on 1-2-3 blocks or parallels and use a dial gauge on a stand to check how much wear there is on the flat/prism ways. for the prism just put a piece of ground metal stock like an end mill in the vee and sweep across it.

4. Scrape the base of the tailstock underside ways flat concentrating on the ‘highest’ end to bring the finished ways back to parallel with the top face of the tailstock base.

5. Relieve the centre 50% of those ways a few tenths by scraping to pre-empt future wear and prevent rocking/poor clamping.

6. Now your base should have top faces parallel to the ways. Repeat step 2 to check.

7. Re-build the tailstock and fit it to the machine.

8. Turn a piece of stock to the exact diameter of the tailstock quill, to the best of your ability to measure. Bring the quill up to the turned stock. Mount a dial gauge on the saddle and set it acting vertically down on the turned stock. move the saddle to sweep across from the stock to the quill. Note the difference in the reading. This is the amount you need to shim the tailstock top up from the base.

Of course this method discounts any wear in the quill or barrel which you can assess and attempt to allow for or just accept it as a best effort solution. You also have a choice of shimming the top with shim stock, or using turcite, moglice or just a good 2-part epoxy like araldite 2013 then scraping that down to fit which would be a more workmanlike solution but shimming is perfectly acceptable for a non-moving joint.

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.