Stuart Twin Victoria (Princess Royal) Mill Engine

Yes, I was thinking just do the upper sides anyway.

I might try levelling it by screwing two studs into the adjacent valve chest holes, and resting them on the top of the vice. Then, once centred, it should be a case of moving the casting left to right. OK I’d lose the consistent tool height by having to insert a drill for re-centering, but for this it might be fine.

Put some primer on the caps - they look OK I think:

Continued with the cylinder fittings by making the exhaust pipe flanges. Again, the oval extrusions supplied were too small and a different profile to the mating pads, so I machined them from solid brass bar using the r/t:

Drilling holes first for datums:



Machining the flanks:



Machining the ends:



Tapping the bore:



Made a threaded mandrel, and screwed up to the chuck jaw ends for turning the boss and facing to size:





Finished:







Next is to machine the oversized profile of the cylinder pads to match them.

Set the cylinders up in the r/t to profile the exhaust flange pads. I thought I’d do this while the offsets and angles were fresh in my mind. First set centrally, and checked for flatness:



Then machined the flanks:



Then re-set with the ends central, and machined them:



Now they’re equal:



And a perfect match to the flanges:





I opted for 90 degree corners so I can recreate the radii with Milliput, and blend any slight height mis-matches into the body of the castings.

'Hyper detailing' eh Doc? A very nice result indeed

It will be a few months yet before I follow your lead but the Phantom grows steadily.

Keep it coming

Best - R

Thanks Ramon. I thought I’d do it, since all the other profiles are matched.

Once the cylinders are primed and done, I need to spend some time on the Airfix Vulcan. Started it in November last year, but it’s such a terrible kit I’ve not been motivated to finish it. Fed up with the sight of it.

Started on the valve chest covers this evening.

This is the cast iron block I’d got for them:



The plan was:

Surface the top of the block. I tried lots of methods, but the best turned out to be the shell mill:



Then profile the sides to size. This is where things started to go wrong. My mill doesn’t like milling anything but aluminium. It’s horrible on steel and iron. This was the result with my 10mm and 12mm end mills:





Unless the cuts are small tenths of a mm, it squeals like a pig, judders, and is generally unpleasant to use - especially side milling. Anyway, nothing new there.

So tried again using the shell mill to chomp away at the sides and remove the damage:



Then swapped to my dwindling supply of end mills to refine the sides and get the final dimensions (shell
Mill doesn’t give straight sides). Trouble is, by that time it was undersized, so effectively all the work was for nothing. I decided to use it as a trial for the milled recess in the top surface:



A few lessons learned there, but the 6mm, 1mm corner radius cutter worked well enough at a 1mm depth of cut.

So I’ll put this evening down to experience.

Plan now is:

1: Turn the block upside down and re-surface.

2. Profile all sides to within 1mm with the shell mill.

3. Profile to final size with an end mill (using minimal cuts).

4. Mill the recess in the top.

5. Co-ordinate drill the holes.

6. Hacksaw it off the main block.

7. Put back in vice and shell mill to thickness.

8. Repeat using the remaining profiled block.

Edited By Dr_GMJN on 06/07/2022 22:52:52

I'd actually face one side and saw a bit off, repeat 3 more times. Face the opposite sides of your 4 pieces.

Now with a 3 flute 6mm dia cutter bring the 4 pieces to overall size, using a stop and parallel packing so you can repeat the sizes. Use the side of the 6mm cutter and start with say a 4mm height x 0.5mm stepover cut. Reason for the 6mm is the spindle speed can be higher which means the motor is running where it will have more power, also more mechanical advantage for the machine with a smaller cutter and cutter will be shorter so more rigid.

Then recess the two covers, turn the chests then stitch drill out the waste and mill the cavity

Also suggest you position the parts over to one side of the block rather than in the middle then you can saw off most of the waste down one side prior to milling.

Disappointing about not being able to easily mill steel or cast iron without problems, and should not really be the case. What is the black finish on those broken end mill cutters? Are they carbide? Maybe try different brand of cutters, or HSS etc. Sometimes 4 flute cutters are a bit more solid too. And did you try slowing the rpm right down for cast iron?

Edited By Hopper on 07/07/2022 08:23:34

Sorry Jason, I don’t follow. I’m making the two top covers for the valve chests. I’ve already finished the chests themselves - they were Stuart castings I bought ages ago.

Reason I did it like this was I’ve had trouble getting stuff like this all square, so I thought by facing and profiling in one setup I’d be guaranteed as accurate as the mill table.

I also thought it’s easier/safer to grip the work like that for most operations - again in the past work has moved while trying to grip a c. 3mm plate in the vice.

Thanks Ramon. I think they’re carbide cutters.

Over the years I’ve had the mill, it’s never cut ferrous metals very well. In that time I’ve tried a whole range of feeds, speeds, cutter collets, cutter diameters, and machine fettling to no avail.

+1 I suspect the cutters too. That the shell cutter did a reasonable job suggests the machine is reasonably stiff and the motor is adequately powerful. It's not surprising that a smaller hobby mill isn't rigid enough to take aggressive cuts out of steel, or to get through the hard skin sometimes found on cast-iron, but they do work.

Maybe unlucky with the material too: not all metals machine well, which is why I always look for 'free-cutting' in the specification when buying, and am not surprised if a bit of unknown scrap proves difficult.

Could be a case of:

Awkward material + iffy cutters + light mill + inexperience = misery

Dave

Edited By SillyOldDuffer on 07/07/2022 09:19:48

Though by the size of the lump you were cutting the chests too. In that case just face, saw, face and saw again to get two slices then face opposite side before doing the edges.

Look like ARC Premium cutters to me with the dark coating being TiAIN and I've not had any problems with them either HSS or Carbide..

Ron who chips in here sometimes also has an SX2P and manages these materials OK with the same cutters

It's not a bit of scrap DAVE but CI block from a supplier which won't have a skin either.

That's a good point.

I can mill steel and CI on the vertical slide on the Myford and that is a pretty flimsy, flexible, "make-do" sort of a set up, so would have thought a proper mill would do the job, as it does with the shell cutter so must be capable as you say. Very weird.

Thanks Jason - problem is - how do I do the edges to get them all square. I've had trouble in the past gripping thin work like this, and how do you cut and re-orientate to guarantee squareness? The block sides aren't perfectly square I don't think.

Yes, it's GD 250 iron, from my usual supplier who is very good.

Thanks S.O.D. you're probably spot-on about the real causes of the issues. I have no baseline for expectations for a mill like this, because I only embarked on this hobby a couple of years ago.

Jason makes an interesting point about using small cutters, running fast. My assumption was that larger cutters would be stiffer, hence give less issues.

Regarding the problems with the end mills. Are you taking off much metal both with the side teeth and the end teeth on the same cut? I've tried to minimise this type of operation on my fairly light-weight hobby mill ever since GHT advised against it in ME years ago. He was writing about milling with a vertical slide. It seems easier on the cutter and certainly improves the finish, especially with steel.

Edited By Clive Brown 1 on 07/07/2022 11:17:37

The one thing that struck me looking at this mornings photos was the dust being produced, can't really call it chips or swarf.

This suggests to me that the cutters have become blunt and are no longer cutting as they should, possibly due to being used on Stuart Castings that some say have hard spots, This could also explain why the insert cutter works as that is less likely to have been blunted than what I assume are HSS cutters.

Now I don't have an SX2P to test on but the SX2.7 is the next one up and not as rigid as my X3, to compensate for the slightly larger machine I chose a bit of low quality cast iron (old gym weight) and took a few cuts. used a similar type of vice.

First with an ARC Premium 6mm HSS cutter, I only have 2-flute in this size but it will do to demonstrate, a 3-flute would be better. Worked out the spindle speed for a modest for me 20m/min cutting speed. Ap - vertical height of cut 5mm as suggested but I upped the Ae- sideways cut depth to 0.6mm which is 0.1D. Fed at what seemed right and looking at the time on the video it's approx 150mm/min would be around 225mm/min if a 3 flute at that spindle speed.

Next took a similar 5mm x 0.6mm cut with a 10mm dia 3-flute cutter from the same source and cutting at the same surface speed though spindle obviously less.

Finally upped the anti and went with Ap of 10mm and Ae of 1mm with the 10mm cutter which is the often quoted cut in makers suggested feeds and speeds.

So if the 2.7 is happy taking 10mm x 1mm cut the next size down SX2P should given sharp cutters be able to remove 1/4 of that eg 5mm x 0.5mm

Edited By JasonB on 07/07/2022 13:03:43

Clive, no, just one or the other usually.

When I milled the cylinder cover bosses I made a final cut simultaneously on the side and base, but only something like 0.02mm.