Stuart Twin Victoria (Princess Royal) Mill Engine

[JasonBModerator @jasonb]

As the change in look is quite sudden it may have been a tiny hard spot or inclusion that just took the edge off the tool, should all come out when you hone or lap.

[Ramon WilsonParticipant @ramonwilson3]

Just got home Doc – to find a good result

I would agree with Jason on the differing colour – if you can't feel it by lightly running a finger tip over it it's minimal and will easily disappear with lapping, though as said, I would think that's hardly neccessary but if you get satisfaction from lapping then certainly go for it.

That's the first one done – you'll be an old hand at it after the second

If that hole is open then a drop of JB scraped in and swiped off with a scalpel before it's fully set will eliminate any tendency for the sharp edge to affect whatever piston packing you decide to use.

[Dr_GMJNParticipant @dr_gmjn]

Thanks for the comments both. I’m getting more of a feel for grinding tools now, and I can tell what sounds right or if something’s wrong. Cutting seems to have a distinctive sound that corresponds to a good surface finish and nicely formed chips, whereas even slight rubbing changes it.

I checked the bore again, but I can’t detect any ridge with my finger, plus each end gives an identical vernier reading, so it can’t be anything serious I think.

I did think about filling the screw hole break-throughs, I wondered if there was a chance the tiny bit of JB Weld might fall out though. I’ll try it before lapping anyway.

So tomorrow I should get the other cylinder done, then it’s on to end facing with a mandrel. Apologies if I asked previously, but a few questions:

1) I assume the mandrel should be long enough to fit in the Chuck and to within perhaps 5mm of the end to be machined? The cylinder is quite long, so I did wonder if it should be stepped near the machined end, and have tail stock centre for support?

2) What’s the best material to use?

3) Should it taper at the Chuck end to fix it, or should it expand using a bolt?

4) Should I face, drill and tap the Chuck end first, so I can mount it in an angle plate on the mill, for determining the cylinder axis somehow?

[Ramon WilsonParticipant @ramonwilson3]

First off Doc, if the bores are not identical (unlikely) make any mandrel you do to fit the larger bore and do it first – the mandrel can be relieved to fit the smaller bore.

Best to make the mandrel from mild steel – aluminium could be used but you do run the risk of galling.

I would make the one for facing the ends an expanding mandrel the end of which is just inside the cylinder end – the cylinder wants to be as close as posssible to the chuck jaws. There should be no need for tailstock support.

A second mandrel – a plain much simpler one – just a length of mild steel faced off one end and tapped for bolting to the angle plate the other end drilled and tapped for a clamp bolt. You could modify the expanding mandrel to do this of course but it's best left for something else in the future. If you can turn this second mandrel from something larger in diameter to give a larger flange for the bolting surface against the angle plate even better. Same thing goes regarding the largest first bore. With the cylinder ends faced it can be clamped in any radial position using a pre turned 'washer'

I just use 6mm capheads for these tasks.

The chances of a JBW repair to that hole coming out are virtually nil. Though not JBW I used a similar product -Loctite Metal Set – to do a similar repair to one of my Twin Vic's cylinders and that ran for a few years on steam at displays before many more on air without a hitch. JBW came along much later – every bit as good and far more cost effective!

It's a 'Control Line Distraction' day today – back later then

Ramon

[JasonBModerator @jasonb]

Just one thing when making the mandrel which you will probably have to make from 30mm stock is to turn the part that fits the cylinder down to say 10thou oversize, drill, tap and then remove from lathe to saw the slots.

You can now put it back into the chuck and finish turn using the cylinders as a ring gauge, this way the arbor stays in the chuck after finish turning and is therefore concentric

[Dr_GMJNParticipant @dr_gmjn]

Thanks again both.

I was going to ask about that: after slitting the expanding mandrel, the final sizing cuts will obviously be intermittent for a bit?

And I think I’ve asked before, but the expanding mandrel bolt hole should be drilled, then tapped with a first tap so that the thread tapers to nothing and gets pushed out with the bolt? Maybe taper the end of the bolt too.

Re. Ramon’s point about the bores being identical – I noted down the exact micrometer reading for the bit protrusion for the last cut, which I will use again for the second one. I’m assuming that if I’m taking a similarly shallow final cut, the bores should be the same? I guess final depth of cut is the thing that could change that? I think the perfect 1.0000” bore on the first was a fluke; I’d calculated the need for one more cut, but instinct told me to creep up on the diameter and triple check just to be sure. The readings made me smile anyway.

Ramon – As well as this, I’m trying to finish a 1:72 Airfix Swordfish floatplane that I’d pretty much given up on in February, it’s one of those that’s fought me every step, but I put so much effort into additional details that I couldn’t just leave it. So I’m splitting my hobby time at present. Plastic and iron is a nice contrast at least.

Cheers.

[JasonBModerator @jasonb]

Yes using a taper tap is usual . As for sizing I tend to use the part to gauge final fit of the mating part

[Ramon WilsonParticipant @ramonwilson3]

I see no reason why the taper from a taper tap could not be used but I have always used a caphead screw of varying diameters for the expasion bolt. I have een countersunk screws used for this too but the angle is really too obtuse to ease the torque required.

Heres a short example made for a I/C cylinder head

I have several capheads from 8 ba to 6mm which have had a 60* included angle turned on them. The mandrel is roughed out to with .5 and 1mm on diameter drilled and tapped. the head needs to be no more than 8mm or so wide – the relief is there for nothing more that to enable the jaws to spring easier.

Removed, the slots are put in (by hacksaw) then returned to the lathe and the hole heavily centred with a centre drill. Insert the screw until it just nips up then turn the diameter to suit the component. This way the expanding bolt can be flush and is expanding with equal force across the four 'legs' and requires little torque to establish a firm grip. The mandrel is uniform in diameter throughout it's length but the component does need to be as close a sliding fit as possible.

Even with careful measurement given the nature of the boring bar you will do exceptionally well to achieve to identical bores but – you never know

My car's packed, I need to do my lunch and I'm off out 'circulating' – 'plastic' comes later

Best – Ramon

[Dr_GMJNParticipant @dr_gmjn]

Thanks Ramon. Re identical bores, you said before “..if the bores are not identical (unlikely)..” which I thought ‘hmmm, that’s optimistic! I assumed you meant to say they would be different, so no problem.

Plenty to do so I’ll report back as and when. I think I need to get a bit of mandrel steel on Monday, but first the other bore.

[Dr_GMJNParticipant @dr_gmjn]

Second cylinder setup – pretty much a case of undoing the bolts and substituting the part. Vertical slide just needed to go down a fraction.

Uneventful, and managed to get it the same diameter as the first, the last cuts were dust, but anyway the bore looked a constant colour apart from the very end near the steam port.

So after all those questions, in the end it was fairly straightforward, and it’s another process I’ve used. Thanks for all the info and help.

Next job is making the mandrels.

[Ramon WilsonParticipant @ramonwilson3]

That's an excellent result Doc – both finish and dimensionally

When you finish turn the mandrel do as Jason suggested and use the cylinders to size the mandrel but in case there's the slightest difference in bores try both each time and do, as said, the larger one first.

You should be well pleased with the outcome – looks like you've made a real good start to a nice long journey

Ramon

[Dr_GMJNParticipant @dr_gmjn]

Posted by Ramon Wilson on 01/08/2021 21:27:34:

That's an excellent result Doc – both finish and dimensionally

When you finish turn the mandrel do as Jason suggested and use the cylinders to size the mandrel but in case there's the slightest difference in bores try both each time and do, as said, the larger one first.

You should be well pleased with the outcome – looks like you've made a real good start to a nice long journey

Ramon

Yes, very happy with that, glad it’s done. I wouldn’t have tried to size the mandrel using the dials – I was going to use the angled topside method to enable very small cut increments when I get close. Cheers.

[Dr_GMJNParticipant @dr_gmjn]

Made a start on the first mandrel. I’ve had this before with mild steel, but no matter what tips or speeds or feeds I try, I can’t get a good finish. I got EN1A from my local supplier – he knows his stuff so I’m confident it’s right.

The sound varies along the cut, sometimes it sounds fairly smooth, but then there will be an intermittent grinding crunchy type sound, as if the material properties vary along the cut.

Any thoughts on what’s going on? Cheers.

[JasonBModerator @jasonb]

Double check that the tool is not slightly too high and make sure tip is not damaged or worn

[Ron LadenParticipant @ronladen17547]

I don't know but is the rearward angle of the tool OK for that type of insert, I use CCMT inserts and mainly have the leading edge of the insert perpendicular to the work.

Just wondered.

What I should have said is the insert the right tool for general turning and finishing to size.? 

Edited By Ron Laden on 05/08/2021 07:56:53

[Dr_GMJNParticipant @dr_gmjn]

Thanks both. I’ve tried brand new inserts to no avail. The end was faced with that tool, and it seemed spot-on for height.

[Dr_GMJNParticipant @dr_gmjn]

I tried a GT insert intended for aluminium as a last resort, and it worked great; much better surface finish. I’m using 0.002” per Rev feed, and the fastest spindle speed on the ML7.

Now got the mandrel slotted, drilled, tapped and turned to the size of the larger cylinder (even though they measured the same Ramon was right, one is larger by a tiny amount).

I was wondering if it was really necessary to finish turn them in the same Chuck position as for facing, since for facing I guess concentricity isn’t important?

Cheers!

[Ron LadenParticipant @ronladen17547]

With EN1A I quite often use a GT insert not just for the finish but the turning down as well depends on how much material needs removing and the depth of cut I go with.

[JasonBModerator @jasonb]

Not critical.and the only way you could really do them at the "same chuck setting" would be with a between ctrs mandrel so you could cut both ends at the same setting.

I thought that was a DCGT under the swarf, if you were sneaking up on a close fit to the cylinder with shallow depth of cut then the "blunter" DCMT was getting pushed out of the cut and then springing back in, then out again and so on. The sharper DCGT can take much finer cuts as can sharp HSS.

[Dr_GMJNParticipant @dr_gmjn]

No it wasn’t a GT insert for roughing where I got the poor finish. I doubt a GT insert would have survived it, so nothing lost. Here is the mandrel, the marks are where I ran the cylinder along it a few times with some polish just to free it up a tiny amount:

I ran out of M8 capheads, so had to use a countersunk screw. Seems to work fine though – it matches the countersink I put in the end of the mandrel.

Edited By Dr_GMJN on 06/08/2021 08:15:00

[Ramon WilsonParticipant @ramonwilson3]

Just check the mandrel is dead true and face off the piston rod end first then reverse and do the other end – that way if the second end is slightly out of square it has no effect on anything – unlikely if the mandrel is running true but you're hedging your bets.

I very rarely use any form of carbide tooling on my Myford S7 and certainly not for finishing cuts. I know the Aluminium inserts are highly recommended from some quarters but a freshly ground HSS tool will provide a superb finish and especially so on EN1a. GCQ steel is another kettle of fish – difficult at best of times. If I remember correctly from when I had mine the ML7 top speed is only 800rpm – no where near high enough for carbide to work efficently except on much larger diameters and then that places great strain on what is a relatively lightly built lathe. (And yes I have hogged off some serious amounts of swarf with deep cuts and high feeds in my time – thing was the machine was built for it and had the horsepower to cope with it).

Personally I believe the biggest mistake a newcomer to the hobby can make – on small hobby type machines – is to be led down the path of using carbide tooling in preference to learning how to grind an efficient HSS tool but it is only my opinion.

Regards Doc – Ramon

[Dr_GMJNParticipant @dr_gmjn]

Thanks for the comments Ramon. For HSS on steel, would it be the same geometry as for the boring bar pretty much? I cant grind exact angles, but it was about 10-15 degrees relief on everything? I need to make some profiles tooling later on for this model, so it would be good to know.

Re. Doing the piston rod end first – why would it make any difference? I can’t think how the first setting would give any better perpendicularity to axis result than the second or third or fourth (or 100th!) end? I could understand if I was facing the piston rod end on the same setup as boring, then turning round, but in this case it’s a completely different fixture from the start?

Cheers.

[Ramon WilsonParticipant @ramonwilson3]

The main percieved problem to the newcomer to grinding HSS tools is having to create a tool as per 'text book' with 'perfect' angles. Obviously there are optimum angles where the tool performs best and differing angles for different materials but it is only the tip of the tool that does the work – a long perfectly formed angled face is fundamentally redundant for the most part. So if that newly ground tool doesn't quite work as hoped the cutting area can easily be tweaked – much as you have just found.

Of course it's much easier to take out a preformed insert and off you go but A, for the most part they are working well below their design parameter in feed and speed. B, they are expensive for what they are and can chip easily instantly spoiling the geometry that cannot be reclaimed by grinding. Yes they can be tweaked on a green grit or diamond wheel but it's not ideal. C, For the most part the type of machines used by most home users are not capable of sustained working to the speed and feedrates required. In other words, to my mind, they are always working well below par for the most part. That said I do use carbide occasionally – roughing out the EN24t crankshafts for instance but the finishing cuts are always done with HSS.

I'm pretty sure if there was a range of tooling available that held pre ground HSS inserts in similar fashion they would soon be the favoured choice – which brings me full circle to reground HSS cutter shanks in a mild steel holder

I confess I am very idle when it comes to grinding tools. I do have an awful lot of pieces of HSS the ends of which have been hacked at in some way mainly before I acquired them I should add but it's a rare occasion when I grind a few pieces to 'text book shapes'. Once done they are pressed into service over all materials – just tweaking the cutting edge to suit.

 

Regarding the cylinder as I said – you're hedging your bets – if the mandrel is running true as it should be you are correct – it doesn't matter what end is done first – but – if you do the rod end first and you are unfortunate to have the mandrel move for any unseen reason you have the important end done and out of the way. Just a way of approach, nothing more.

 

Regards – R

Edited By Ramon Wilson on 07/08/2021 09:42:36

[JasonBModerator @jasonb]

HSS inserts are available from Warner and Little machine Shop, a few over on MEM like them plus a few here.

The need to "work" the carbide applies a lot more to the **MT as they do not have any where near as sharp an edge as the **GT inserts which will happily take 1thou cuts. Even on teh MT if you go for the "LF" or similar ones they will take quite light cuts as they are designed for "Light Finishing"

Doc , if your GT inserts are not surviving taking that bit of 1.25" down to 1" then something is not right.

[Dr_GMJNParticipant @dr_gmjn]

Thanks both – I’ll have a look at those HSS inserts.

I didn’t actually try the GT insert until the final passes, so on the mandrel I make for the milling operations (later today hopefully), I’ll see how it performs on much deeper cuts.

Ramon – I’ll check concentricity before I face the rod end; I’ve been messing about working the cylinder in and off it so it could have moved I guess. I’ve got to take a skim off the diameter for the second cylinder, so I’ll immediately fit it and do the rod face. I’d better mark the cylinders L & R.

Cheers.

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