Lorch Schmidt

Collet restoration

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I can say that all the collets with this machine have been carelessly handled in the past, people have not taken the care necessary to fit them into the key inside the mandrel bore properly, resulting in some quite severe bruising. I have with the aid of engineers blue and a very fine Swiss file removed the high spots and cleaned up the keyway.

By this action the internal key of the donor lathe has been almost worn away, fortunately the one on my machine is not afflicted in this way, so they fit well.


The Female step chucks below

have come up extremely well. As you can see so has the spindle nose adaptor, the collets are not so easily wrecked as the next ones.....

I have to apologize for this photo, I just could not get close enough to show how bad this was without loosing clarity. The Male step collets are all too easily ruined. All of these were to all intents and purposes fit for the bin, but because they are so rare, the challenge had to be taken, after all nothing to loose but time, and everything to gain if I won. In the above photo you can easily see how this collet has been badly strained, the gap is wide on the left and touching on the right, what is not so easy to see is that each of the three sections were also twisted, looking at the photo again the edge of the top portion is about 20 thou overlapping the edge of the bottom section. This is how I fixed them, unbelievable, maybe, I surprised myself on this occasion.

I turned up this holder or former, it is reamed to a snug fit for the shank of the collets which will ensure that no matter what I do to the head of the collet nothing will change on the shank. The nose is an exact replica of the internal of the collet inside the bored section, the collet being radiused and flared out at its end. To get this exact I finally hand scraped the internal using blue. The OD though is a little smaller than the internals of the collet, the length being about 30 thou short, hence the two brass shim washers. These were found to be necessary as the collets are not all exactly the same, there's a surprise. The nut is to pull the collet in.

This shows one collet bolted up, there is on this one a single brass shim. Something else was needed, the hole through the centre must be kept open, but each collet has a slightly different bore, so I used number drills to find the right sizing. I must add at this point, the need for feeler gauges. As one of these is fitted and slowly pulled in, you need to run a feeler gauge through each slot several times, to remove scale and muck, and keep doing it until nothing comes out, or you wont get the three gaps to close centrally. One other thing not shown that was done, was to monitor the gaps as I pulled the collet down, every time a gap looked wider than the others I gave it a wallop with a rubber mallet.

You can see here that having pulled the collet into the former, and indeed the nose of the collet has closed that the tail end where it has been forced in the past is still open, well what better a way to contract three leaves than with a three jaw chuck, this was then squashed until the gaps closed, as the collet pulled ever closer to the end of the former I slackened the nut on top a little. Yes it did leave some marks on the first step of the chuck, but it will get skimmed later. The drill bit is still in place below, keeping that end locked centrally.

The above photo needs to be viewed in conjunction with the one below as well. Here you can see my method of stressing the collet the opposite way to which it had been forced in the past and every time this was done it tried to make itself more central.

The view from the other side, by holding the very end closed and using the lathe I can reverse the process that I was doing on the former, some lube oil helped the process of course.

Well like I said at the outset, I surprised myself, they are mostly within within 3 thou, one is four thou, and that is in both plains, I also check the bore by running the clock on a number drill, but this is dubious at best as you cannot contract the end of one of these collets, but even that test was reasonable about five thou error. So when the Lorch is running, it will just be a case of skimming three to four thou off each step on five collets.

It sure beats throwing them away, and where can you get some more anyway. I truly hope this method may be of use to someone else. Needless to say this wasn't a single operation two of these collets were so bad that they flitted back and forth between the lathe and the former several times, each time the stresses were pulled more central by the process, neat trick huh.