Stuart Twin Victoria (Princess Royal) Mill Engine

[Ramon WilsonParticipant @ramonwilson3]

Yes it's the square section type I use on pistons Jason but I'm not sure there's anything corded/braided that would be small enough to use directly on rod glands – I'm not aware of any that is.

[Dr_GMJNParticipant @dr_gmjn]

Posted by Ramon Wilson on 22/06/2022 18:27:28:

Whatever you are happy with Doc. I haven't tried it so can't really comment but if Jason has used it successfully then carry on – one things for certain it'll be a lot cleaner than using graphited yarn!

I like the braiding BTW but I did you have to use a fair bit of tape to get that bulk?

Best

Ramon, from memory I just cut 3 lengths of plumbers PTFE tape, twisted each one a bit to get rid of the flat form, then loosely plaited them. This was enough to hold them together while stuffing them into the grooves. Snugging the bosses down made a good seal, which is also smooth and low friction. I’ve only used the 10V on air, but it appears to run well enough.

[Ramon WilsonParticipant @ramonwilson3]

Thanks for that Doc, I'm going to give that a try on the marine engine glands.

There is one thing to consider with PTFE as a packing material and that is if the model is run on steam then PTFE can swell and tighten things up. Like you though I only build to run on air and as friction, or rather lack of it, is important for low speed running at low air pressure then 'every little helps' as they say!

[Dr_GMJNParticipant @dr_gmjn]

This evening I drilled the discs and screwed them to the caps, and roughly marked them out using the aluminium test piece as a template:

Then roughly hacksawed them to shape:

Then, after much calculation of angles and offsets, setting up, and double checking, made a start on milling the profiles:

Initially used a 10mm end mill, but it didn’t seem to like it, so I switched to a 6mm version, which cut very nicely:

Once the sides were done, slid the fixture to each end stop in turn, and milled the end radii:

I crept up on the correct cut depths, finishing with a 0.01mm final pass both in depth and side:

I’m glad I took a lot of care with these, because they’re right on the ragged edge of having enough metal to remove. In fact in some areas the JB Weld remains:

Despite the look, it’s smooth, and will be painted anyway.

So that’s the first cover done. Still needs a quick de-burr, and a few passes with a file to get rid of any swirls in the pad (they look worse than they feel), plus perhaps a Milliput fillet radius round the boss:

Next one tomorrow hopefully:

[JasonBModerator @jasonb]

Looks good and yes I would add the fillet.

[Ramon WilsonParticipant @ramonwilson3]

Nice result and plus one for the fillet.

It looks like you were using a carbide EM which precludes the idea but if you use a HSS cutter you can radius the teeth by hand on a bench grinder to give a radius. I have a tin of several such modified cutters – very useful at times

All looking good Doc – hope that second one goes as well

[JasonBModerator @jasonb]

Or you can buy them with the radius already on the corners I use these quite a bit on the CNC to leave a fillet, I have both and it is a good way to use up blunted ones, you can grind concave and convex corners for beads etc. Freehand grinding will do and any slight errors will be averaged out by 3 or 4 teeth and it's a casting we are trying to replicate after all.

[HopperParticipant @hopper]

Looking good, Doc. Which mill is that you have there? SX2?

[Dr_GMJNParticipant @dr_gmjn]

Thanks all.

Jason, Ramon, I do have some cutters with corner radii, but they are a bit small. Also, I wasn't convinced that there was enough sound material in the corners of the castings to machine consistently. In the end I went for sharp corners, and I can then add whatever radius fits.

Hopper – thanks, yes it's an SX2P. It has it's issues – I really need to adjust the gibs again to reduce stiffness, but sometimes it's best just to stop fiddling and get on with making something…

[HopperParticipant @hopper]

Posted by Dr_GMJN on 24/06/2022 14:09:04:

Hopper – thanks, yes it's an SX2P. It has it's issues – I really need to adjust the gibs again to reduce stiffness, but sometimes it's best just to stop fiddling and get on with making something…

LOL yes I am well familiar with that syndrome. Looks like it's the ideal size for this type of work though. Nice.

[Dr_GMJNParticipant @dr_gmjn]

Posted by Hopper on 24/06/2022 22:41:36:

Posted by Dr_GMJN on 24/06/2022 14:09:04:

Hopper – thanks, yes it's an SX2P. It has it's issues – I really need to adjust the gibs again to reduce stiffness, but sometimes it's best just to stop fiddling and get on with making something…

LOL yes I am well familiar with that syndrome. Looks like it's the ideal size for this type of work though. Nice.

Yes, it’s spot-on for size, and makes a great pairing with the ML7 for the things I want to make. However the ML7 is far nicer and smoother to operate. I think there’s something amiss with the gibs on my SX2P, maybe if I had the skills to scrape them they’d be much better. Locking the axes is also a bit vague and spongy feeling, and often moves the DRO reading by 0.02mm or so. Anyway, it is what it is.

[Dr_GMJNParticipant @dr_gmjn]

Started to reinstate the cylinder/cap fillet radii using Epoxy filler (Milliput), and ball sculpting tools. Quite a satisfying job:

[Dr_GMJNParticipant @dr_gmjn]

I’ve been working on the exhaust pipe flanges tonight, while I’ve got the r/t set up. I’ve nearly finished one. I re-drew them to be the maximum best-fit size on the pads. I say best-fit, because when one fits perfectly on its pad at the bottom, there’s excess metal on the pad at the top. This is despite using the plan dimensions for the port and stud holes. Basically the cast pads aren’t symmetrical.

On the opposite cylinder, it’s a better fit, but still some excess.

Is there a trick to re-profiling the pads to get them a perfect fit to the flanges? I can only think to scribe round them and file back the excess, or even make a dummy flange from steel to use as a filing guide?

Thanks.

[JasonBModerator @jasonb]

Scribe and file has worked for me or if you want it more exact mount the cylinder on the rotary table and do the same as you did for the glands.

[Dr_GMJNParticipant @dr_gmjn]

Thanks Jason. I might try it in the r/t, although setting up to be level and central three different times will be interesting.

[JasonBModerator @jasonb]

You could just set up to do the flanks and central large radius and file the ends.

[Dr_GMJNParticipant @dr_gmjn]

Posted by JasonB on 27/06/2022 13:03:39:

You could just set up to do the flanks and central large radius and file the ends.

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.

[Dr_GMJNParticipant @dr_gmjn]

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

[Dr_GMJNParticipant @dr_gmjn]

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.

[Dr_GMJNParticipant @dr_gmjn]

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.

[Ramon WilsonParticipant @ramonwilson3]

'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

[Dr_GMJNParticipant @dr_gmjn]

Posted by Ramon Wilson on 01/07/2022 07:28:02:

'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.

[Dr_GMJNParticipant @dr_gmjn]

Re-built the fillet radii with Milliput, same as the caps and valve faces:

[Dr_GMJNParticipant @dr_gmjn]

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

[JasonBModerator @jasonb]

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.

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