Thankyou – an interesting range of possible causes, and of course there may be more than one!

Bernard –

I’m not sure why “of course” a button tool is sharper on its right-hand side when it was new to this operation and I was sometimes cutting both ways with it.

The connecting-rod’s small end was on the tailstock-centre and there the 6mm button was about right for the blend radius. At the other end, with a much bigger fillet, I roughed it out with a button tool but finished it with an HSS radius-tool free-hand ground to approx 1/4″ radius.

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Dave, and others –

Vibration… I did notice a curious change of behaviour approaching the small end, and this appeared to be partly from some sort of resonance, though likely combined with the rapidly-changing geometry between the tool and the slender part of the work.

There was some signs of “bouncing” at times when trying to take a cut <0.005″ deep, but most cuts were from 0.005 to 0.010″ deep. I didn’t risk heavier than that.

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A point I don’t think I made earlier is that although the rods are made from the same stock bar, the finish is distinctly different between them, but I could not pin this down. It could be from tool wear.

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The lathe’s bearings –

Well, this is an old machine that may have had a fairly hard life. There is a slight step between the flat surfaces of the bed, up onto the corresponding parts of the gap-filler; but generally it does not seem too badly worn. I don’t know its origin for certain, but I think came from a Gas Board maintenance workshop so was probably not used on long-term production-work.

It may have suffered worse when used occasionally but fairly heavily by several of us, including me, in the workshop we used for a small school-club miniature-railway. When that project had to close, we dispersed equipment not earmarked for another railway elsewhere, and the lathe came to me. (None was school property. We had all donated or loaned all the tools and machines including this lathe ourselves, and practically everything was very “pre-loved”.)

When I installed it at home I was shocked to find no oil in the all-geared headstock. The moving parts were all heavily oily but more by luck than judgement. So if the headstock bearings are worn or out of adjustment it’s not really surprising.

My first action was to buy a lathes.co facsimile manual for the machine.

The second was to replace the old, massive 1ph motor with a Newton-Tesla 3ph motor and electronics….

Third? Give the headstock a drink!

To my delight the previously horribly noisy machine now runs very quietly for its size. (The old motor having been bolted to the cabinet had probably contributed generously to the racket.) Saliently, the headstock does not sound unduly noisy. I tend to run the machine at fairly modest speeds, though with the speed-control knob up in the green sector on the label, but the headstock does emit an odd ticking noise I need track down.

So I think some of your posts above point to my giving the headstock a good looking-over.

I am not sure as I write if the spindle bearings are adjustable, but I will investigate that. Obviously cutting away from the headstock will unload the bearings, possibly just enough to let the spindle, hence work-piece, to float axially.

Though to be fair to the lathe, I must also consider possible play in the set-up, including within the elderly live-centre in the tailstock.

Lots of possibilities to investigate!

I think that combination or accumulation of causes very likely.

I did try other tools including one of those lozenge-shaped inserts with a 55º tip, but I don’t think it made much difference.

Since I was using cuts <0.010″ deep on a small diameter on a heavy machine I didn’t think the force from a new button tool would normally be significant but it may well be on a slender work-piece. Cutting rightwards gave a better finish though still with the banding, hinting perhaps at the effect of bearing play or saddle wear.

Wear might include on the rack and pinion teeth as they are used for the power-feed, as the drive-shaft is geared to the hand-wheel shaft. I wonder if uneven wear or damage on the hand-wheel drive-gear or rack-pinion, or swarf trapped in it, might give the racoon-tail effect. This might be enhanced by the rack teeth being more worn on the leftwards-cutting flanks.

The more irregular finish I see much more frequently is probably from general, unevenly distributed wear and tear. I will though examine the saddle to see if it can yaw despite being guided on Vee-ways as that could give the regular pattern.

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Speeds and feeds – The spindle speed did not seem to affect it much.  I was using a very fine feed, not as fine as is possible with the change-wheels and 3-speed feed gearbox, but still probably <0.003″ / rev. I’d need examine the wheels I used, and consult the manual, to be able to calculate the actual feed.

The 3-speed gearbox, with a 1:1 central ratio, reduces the overall feed a bit but not much, only 1.25 or 1.5 :1 if I recall correctly. As it drives the lead-screw as well it may be more useful when trying to cut some awkward screw-pitch.

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I still don’t discount the way I had mounted the connecting-rod though. It was driven between-centres at a slight angle to the lathe’s axis, and by a chuck jaw pushing a stud screwed into the big-end.

I don’t know if this arrangement might give some peculiar effects if the drive is rigid. When using a set-over tail-stock does the work need swing back and forth with each rotation? A normal cranked drive dog typically has quite a bit of play in the catch plate or a faceplate slot; a straight dog pushed by a cylindrical pin as on the Myford lathes would allow considerably more oscillation than needed. This stud-driven set-up might have cramped any such swinging.

On the other hand, the banding’s pattern is far coarser than I’d expect from this source. Each revolution equates to only a couple of though of tool travel.

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So I think the first ports of call are dirt trapped in gear teeth, and general wear and tear. These would affect using any type and size of tool on any metal, but the pattern I saw was quite unlike the much more common, irregular “bouncing” finish.

Thankyou Michael, Gray –

I did notice that although my rods are of “mild”-steel they might be less “mild” than the oddment I used for the soft centre, because the latter ended up with a step worn on it. Better that, than harming the work.

I’d not expected that wear to happen. The idea of a soft centre turned in-situ was a blend of accuracy and the difficulty mounting a proper centre. The spindle nose has been damaged by some numpty in the past putting a rough step inside it, probably by careless use of a boring-tool.

Still, this was my first attempt at this form of taper-turning!

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I’ve often obtained better results with an HSS tool than carbide; even on good-quality material. That’s not a fault of carbide tooling per se; and I have not found it needs terrifying spindle speeds as many think, but the inserts are made for narrow ranges of materials and cutting conditions, and we might not always have quite the right combination.

Especially for we whose Goods Inwards Quality Control is, umm, variable. I salvaged some former cable-drum tie-rods. This “any old iron” will give fair results with HSS where fine surfaces are not functionally necessary, or the parts will be painted, but a carbide tool simply tears it to bits.

Thankyou Fulmen.

Yes- quite a few people have suggested a finer and sharper cutter.

I did keep watch on the centre pressure. It did ease very slightly at times, probably from the soft centre creeping back in the chuck, or the tailstock clamp not quite up tight enough.

I don’t think there’s anything wrong with the lead-screw (not used on this operation anyway) and feed-shaft; but the rack and pinion are badly worn and if the pinion has worn unevenly, or had swarf jammed in it, it could well produce a varying feed. It is difficult to examine closely as it is deep inside the saddle, but just visible by shining a light into the gloomy recesses.

The rack and pinion would be very difficult to replace. I do have a collection of Harrison L5 spares (courtesy of a private seller on this forum) and I will have a look, but I don’t think they include a rack, and probably not the pinion either.

Where a fine and accurate feed is needed, I’ve not investigated if it can be gained from the 1/4″ pitch lead-screw. The machine’s designers intend it for screw-cutting only, so a fine feed may not possible with the standard change-wheels.