Good work with a worn out lathe.

Hi all,

In his book "Watchmaking" George Daniels states that "worn machines can do good work but only if the operator learns to master their idiosyncrasies."

I was wondering, how do you go about overcoming the inaccuracies of a worn lathe, such as spindle eccentricity, tailstock misalignment ( the lathes Daniels refers to oftentimes do not have adjustable tailstocks) and etc. This is purely hypothetical and is just something that's been nagging me.

Thanks,

Tom.

I would think that anyone who can use an imperfect lathe would already have a lot of experience

They would use compensation techniques and strategies in the course of a job, some of which would be quite ingenious

But the main element would be the knowledge and experience of the user

In my maintenance workshop we had a Colchester but the first lathe I had at home was give to me and it was 'home made' which I used to re-furbish a 2" traction engine it was a challenge at times but with a bit of thought and take your time it served me well.

H

As with any machine, it is important to know it.

Without that familiarity, it is easy to produce scrap on a brand new machine.

Think of the work produced by skilled craftsmen who lacked the graduated dials, and cutting tools with which we are familiar today, let alone DROs, and replaceable carbide tips.

We have had to learn how to cope with backlash in feed screws to produce accurate work.

Visiting the Manchester Ship Canal Company, was shown a LONG lathe. Used to turn repaired lock gate spindles back to original size. I was told.

The old operator retired, when he came back for a cup of tea with his mates, his successor asked "Do you ever get a notch in the job?",

"You do throw out the clutch when the crane goes overhead? There is a joint in the track, and jolt shakes the lathe and causes a notch"

Amazing work has been produced on ML7s, supposedly beyond the machine's capacity!

"Many a good tune played on an old fiddle"

You learn the peculiarites of a particular machine, and work out how to work around any shortcoming.

Howard

The Smart & Brown model A at the museum was destined for the scrap yard when Westland left Weston Super Mare. Fortunately it was offered free to the museum and has been in use ever since. Now 75 years old, it has 0.025" wear in the bed near the left end and there's not a lot we could do about that. The rack and leadscrews have been tilted to compensate for some of the wear. The saddle cuts deeper moving left for external and the other way when boring. When you get to know the way a lathe cuts, you can compensate pretty well and it is a joy to use which is why we are attending to the cross slide and compound on the Atlas to give them a feel closer to the S & B. The Atlas bed has no measurable wear and it can cut with precision without even attending to such things as "leveling".

He prefaces it by saying that it is false economy buying a secondhand lathe. There's a difference between worn and misaligned. Worn ways can be compensated for by various means. A misaligned headstock would be very difficult to deal with, to the extent that one would be essentially using the lathe simply as turns. Assuming a quality watchmaking lathe in the first place it is highly unlikely that the headstock would become misaligned, unless maltreated such as being dropped.

Andrew

I tend to agree with Andrew. I am not sure what you would do with a wobbly headstock, but one could cope with excessive backlash in the cross-slide.

Incidentally when I first met the great man, Mrs P asked him how he made his living. He simply said, "I am a watch maker."

Do you think spring passes has great value/potential-? Know your tol flex in uses...
I put my smallest boring bar(6mm Iscar) just like that in my new 50mm Vertex boring head and try to cut a brass piece around 22mm. The little bar surprised me, no funny noises. So I moved the advance up 0.1mm(10x indexes) meaning its suppose to cut 0.2mm(Both sides).
So I took inside measurements as best as I could....I found that it cut short of .2mm, but that I can make 7 spring passes to get it to cut nothing more. So in this case one can sneak up to a size using spring cuts rather than speculated adjustments and overshoot. So I think using spring passes might be of assistance.

Something I thought of before, is that in the case of a lathe turning a heavy chuck at some speed,how much influence can a sharp single point cutter/insert has on the running chuck with the centrificle forces present in the chuck taking a reasonable cut, compared to a mill with much less mass moving around but in this case the cutter moves and object stand stil(Clamped)l.

Edited By Chris Mate on 08/08/2023 23:07:33

My lathe tail stock has a little bit of play in the quill. I use this play to adjust the last 0.01 mm alignment by locking the quill a bit more or less.

The head stock isn't aligned perfectly. I can let the part stick out a bit more resulting a bit more bending during turning. That compensates for the misalignment when the tail stock is not used.

The chuck of the mini lathe has some run out. That is not a problem as long I don't have to remove the part.

The cross slide and carriage lead screws have some play. As long as I move them in one direction, it doesn't matter. For CNC turning I use backlash compensation and the movements are the same as I would do when manual turning.

A worn bed is not a real problem for short parts. When turning long shafts, emery paper can reduce the turned "tapers" to 0.

To an extent, a misaligned Tailstock may be caused by a twisted bed.

To cure this, use "Rollie's Dad's Method" (As told in Ian Bradley's "The Amateur's Workshop", and "Myford 7 Series Manual", and bu others elswhere  

For more serious mialignemnt more stringent methods might be required, such as machining the under side and fitting a plate to resoire the corrct vertical and horizontal alignment.

A friend bought a Myford ML4 which would not cut anything other than a taper.. One of the studs retaining the Headstock had been cross threaded and tightening the nut pulled things out of line. We made a crude jig (basaed on the centre distance of the other pair of "good" studs, and used it to open the damaged hole to tap it 3/8 BSF, before fitting a bush tapped 1/4 BSF. This allowed the correct alignment to be restored.

You may need to do something similar to bring things back into line.

Often, if there is enough metal, things can be corrected by opening up and bushing.

It might be possible that, with carefiul planning, the machine can "Pull itself up by int's own bootstraps" and produce the parts needed!

Howard

Thanks to all who've replied. Much obliged for the answers.

Tom