Stuart Twin Victoria (Princess Royal) Mill Engine

[Dr_GMJNParticipant @dr_gmjn]

Thanks both. Ramon – I guess there’s the Related Hobbies section for plastic?

Jason – Yes, I could do that. If I get time I’ll measure the relative end lengths tonight and see how they compare. I probably also need to make some aluminium pad arrangement for the carrier to tighten against. I think it’s a bit big for this job really. It only just touches the drive spigot too, so I might lengthen that with a sleeve or something.

Also going to turn a small pad to JB Weld to the saddle for the stop/gauges to seat on; the surface at present is a bit flaky with paint etc, so I guess the depths may change slightly depending on the exact position the gauge blocks on the saddle face. The face might not be parallel to the end stop bolt either I guess.

[Ramon WilsonParticipant @ramonwilson3]

I have no idea Doc. I think I posted something on here in the past regarding plastic modelling distraction but it may have been on Model Engine Maker.

Re a stop button, yes it's a good idea to fit one as A, the surface is a bit hit and miss and B fitting one gives you some room to hold a slip in.

I managed to drill my saddle and glued in a hardened button – I found the right spot by turning a point on a piece of steel that fitted the stop block and used it as a centre punch.

Definitely worth doing

[Dr_GMJNParticipant @dr_gmjn]

Thanks Ramon. I’ll get on with that later.

If you’re measuring from a pre-faced face, what’s the best method of determining the face datum with the tool tip? I’ve been feeding the tool – by hand – to touch the (stationary) work, then adding the slip gauges in front of the stop. Not sure it’s accurate though, because I’m getting a few thou difference between the slip gauge thickness and the measured resulting step.

Edited By Dr_GMJN on 05/09/2022 09:01:24

[Ramon WilsonParticipant @ramonwilson3]

You may find once you've fitted that button things will improve some.

With the lathe stopped I touch the tool on the end of the workpiece, set the stop with the required slip(s)s, and lock firmly. Back the tool off slightly with the top slide and then, keeping the saddle up firmly to the stop and slip(s) and holding in place with the handwheel – with the lathe now running – bring the tool back up to just witness touch the face, taking a skim down to the centre if thought necessary.

That should see you within a thou or so given any tiny slack in the system.

If your slips are 'worn' as some of mine are and they don't wring that well I make the pile up and just lay a piece of masking tape on to keep them together until the pressure from the hand wheel takes the strain.

[Dr_GMJNParticipant @dr_gmjn]

Roughing now complete. The diameters are all within 0.001” to the drawing, and 0.0005” end to end, which I was reasonably happy with, and the lengths within a few thou of each other and the drawing. The mid length is spot on to the drawing.

I think I can improve on all dimensions using the saddle pad, and Ramon’s datum technique which worked very well. For finishing, if I swap the shaft round for the final diameter cuts without touching the diameter setting, and using the same width settings, in theory I suppose everything should be identical.

Surface finish is excellent with a 0.002” finish pass, and some light work with fine abrasives/polish. So far so good I think (centre section left un-machined since it’s only 0.004” over-sized on radius):

The depth stop pad is currently set in place with JB Weld:

Edited By Dr_GMJN on 05/09/2022 23:25:47

[JasonBModerator @jasonb]

Do be carful taking your "Roughing" cuts to within 1 thou of final size as if there is any slight bend in that bar or your ctr holes are off or your 3-jaw not 100% concentric it will leave you almost nothing to true up once you have it mounted between ctrs.

10 thou would have been better to leave on diameter.

[Dr_GMJNParticipant @dr_gmjn]

Sorry Jason I meant relative to the roughing drawing. I did a roughing and finished version just to make sure I didn’t get anything wrong.

There’s 0.010” on radius and length for all the diameters (hopefully I can get to final diameters in two passes) apart from the central portion, which is what it is, as stock. In theory there’s 0.004” on radius for that, to bring it down to 14 mm diameter. Mixing units, but I find it easier to visualise small increments in thou (because of using imperial feeler gauges on spark plugs from a young age I guess).

Next job is to check the tailstock setting with a dumbbell test bar. Hoping its OK to use aluminium for that?

[Ramon WilsonParticipant @ramonwilson3]

Doc,

When you machine between centres and swap end for end you should check the datum again as, unless you are certain they haven't, the centres may have slightly differing depths – that will affect the position slightly relative to the bed stop.

Any material is fine for the test bar

[Dr_GMJNParticipant @dr_gmjn]

Posted by Ramon Wilson on 06/09/2022 08:52:15:

Doc,

When you machine between centres and swap end for end you should check the datum again as, unless you are certain they haven't, the centres may have slightly differing depths – that will affect the position slightly relative to the bed stop.

Any material is fine for the test bar

Yes I asked about that a few posts ago. Jason suggested a feeler gauge may be needed between the gauge blocks and stop at one end or the other. I can determine this during initial setup I guess, and use it for all stop depths.

Edited By Dr_GMJN on 06/09/2022 09:50:42

[Ramon WilsonParticipant @ramonwilson3]

[Dr_GMJNParticipant @dr_gmjn]

Spent ages adjusting the set-over of the tailstock, with it locked in place longitudinally, ready for turning the shaft. Managed to get it to zero on the calipers, turned out to be 0.0002” diameter difference with the micrometer. That’s over about 3.6”:

Hopefully that will be good enough because it got the stage of fractions of a turn tightening or loosening one adjuster shifted it from + to – size.

Also made an aluminium split sleeve to protect the steel shaft from the carrier:

Found a neodymium magnet to hold the carrier to the drive peg. I’m sure there’s a more traditional method, but this worked fine – held it together while turning, but allowed the work to be removed easily too:

Runout on the turned parts is on average about 0.002”, easily lost in the excess material:

On to the axial error caused by the centre drillings, this was about 0.001”:

Might double-check the tailstock setting, then get in with finish turning the shaft next time.

[Ramon WilsonParticipant @ramonwilson3]

Ah Doc, you're moving into the modern age for sure – neodymium magnets indeed, whatever happened to the twist of copper wire

Nice touch and nice work

[Dr_GMJNParticipant @dr_gmjn]

Random question – the difference in length is about 0.001", but the smallest feeler gauge I have is 0.002". Is there any alternative, for example foil or paper I could use instead? I know these aren't critical lengths (to that tolerance), but it would be nice to see how close I can get end-to-end using these methods. Thanks.

[JasonBModerator @jasonb]

Why not just set it up with two larger sizes, whatever you use so long as the difference in the total is 1 thou it will do the job so you could use 8+3 when working on one end and 10 when cutting the other end.

[Dr_GMJNParticipant @dr_gmjn]

Jason, I don’t follow. The idea was to setup the offset of the saddle, using gauge blocks against the stop, with the tool just in contact with the end of the work. Then remove the block stack, machine to the stop, then swap the work around (without touching the stop at all). One end would need 0.001” shim, the other wouldn’t.

If I’m using two stacks and re-setting the depth stop, I might as well just use a single (correct) stack depth and re-set the stop to that for each end for each pass. I thought this would be more prone to error that leaving the stop alone completely, and just putting a shim in place when machining one end.

[Ramon WilsonParticipant @ramonwilson3]

I'm sure Jason means using a ten thou shim at one end between the stops and slip and an eleven thou at the other but to be honest Doc I think you are trying to spilt hairs here.

I can understand why you want to try but if you think about it you've already established you can get it within two thou – pretty good for the part I'd say but if you really are that fussed why not just back the topside off one thou on the closer end?

[Dr_GMJNParticipant @dr_gmjn]

I understood (I think) just after hitting submit!

yeah, probably not worth it, but interested to see if each end turns out identical.

[JasonBModerator @jasonb]

Yes as Ramion says set one end with your stack of blocks and a 10thou shim and use that shim when machining that end, for the other do it with 11thous worth of shim net result is one end the saddle will stop 1thou further from the stop.

I would have suggested using the Topslide Ramon but as you pointed out earlier it needs to be used at an angle so Doc can't do that without upsetting his length position.

[Martin ConnellyParticipant @martinconnelly55370]

It used to be the case that in order to call yourself a turner in industry you had to do some work between centres. So now you can say you have achieved that distinction.

Martin c

[Ramon WilsonParticipant @ramonwilson3]

Posted by Martin Connelly on 07/09/2022 17:00:22:

It used to be the case that in order to call yourself a turner in industry you had to do some work between centres. So now you can say you have achieved that distinction.

Martin c

A bit of trig soon sorts that Jason but I take your point

[Dr_GMJNParticipant @dr_gmjn]

Martin – thinking about it, yes this will be my first attempt at between centres turning, at least for a part rather than a test bar. I did between centres boring for the cylinders, which went OK.

Ramon, Jason, as you say the top slide needed angling, but even with trig, if I want to maintain a radial setting for the finishing cut at each end i.e. without touching the cross or top slides (which is why I want to swap the bar around), then moving the angled top slide would make this impossible.

Also, re. the one thou shim, as said it’s such a tiny amount, and not critical, I might just use a doubled up bit of fat paper which is about the right thickness. Just having one shim will reduce my chance of getting it wrong. If it’s accurate, great, if it’s a bit off at least it will be closer than a thou, which is fine for this. 
 

I do hope that switching the shaft around between centres at the same radius setting of the tool is an accepted method for getting identical diameters?

Or should I be competing one end at a time and then starting again at the other end?

Edited By Dr_GMJN on 07/09/2022 22:49:53

[JasonBModerator @jasonb]

Just be aware that if you sneak up to final size on the first end in small steps of say 1thou and then go to do the other end without moving the cross slide the effect of taking say a 10thou cut may not give the same diameter as the various cutting forces may deflect the setup or even draw the tool into the cut.

[Dr_GMJNParticipant @dr_gmjn]

Thanks Jason, the idea was to take incremental cuts to get to size, but take each cut identical at both ends by swapping around and leaving the tool alone. Should only be about 2 cuts, then a cut to size. The end diameters are the same as-roughed, so in theory all cuts will be removing the same amount of material, both initial cuts and the final one.

[Ramon WilsonParticipant @ramonwilson3]

Any turner worth his salt would not do the second end at the same setting without moving the tool Doc.

Both ends would be treated the same way making a note of the cross slide setting as the first end is finished and treating both independently, making careful measurement of the second end.

Pre CNC (oh! how easy it is to forget how short a time that was) it was the skill of the turner to make repetitive parts sometimes to very fine tolerances – a mic was all he had.

You are doing fine

[Dr_GMJNParticipant @dr_gmjn]

Thanks Ramon. I’m interested as to why you wouldn’t do it with these same setting though? I assume between centres turning is very accurate – and repeatable in terms of taking out and replacing the work.

I currently have +0.010” on each radius, so I was planning on cuts of:

-0.006”

-0.002”

-0.002”

All determined from the cross-slide dial after measuring the diameter after the first roughing cut.

The absolute size of the diameters isn’t critical, since I’m boring the other parts to fit.

It would be nice to see if I can get them identical end to end though.

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