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Stuart Twin Victoria (Princess Royal) Mill Engine

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JasonB22/06/2022 12:58:41
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5mm H7 reamer which is quite a common tolerance will be fine with 5mm stainless rod which can be a little under nominal anyway. That's what I used on the Real I'm describing at the moment, one of ARC's Machine type.

Dr_GMJN22/06/2022 17:37:26
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OK thanks both. I'll get some 5mm rod and a reamer.

Ramon: I think Jason mentioned PTFE tape for the packing for the 10V. It was a bit stringy and tricky to deal with at first, so I twisted it, then plaited three lengths of it to give some bulk. It was then easy to use and works very well.

Cheers.

JasonB22/06/2022 18:22:17
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Yes you need to do that if using tape, the actual PTFE packing is more solid like like a thin rope or cord and there are also square section ones available.

Ramon Wilson22/06/2022 18:27:28
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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 Wilson22/06/2022 18:31:51
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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_GMJN22/06/2022 22:27:27
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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 Wilson23/06/2022 07:40:51
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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!

yes

Dr_GMJN23/06/2022 22:55:52
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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:

JasonB24/06/2022 06:55:30
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Looks good and yes I would add the fillet.

Ramon Wilson24/06/2022 07:33:14
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Nice result and plus one for the fillet.yes

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

JasonB24/06/2022 07:41:57
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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.

Hopper24/06/2022 09:29:22
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Looking good, Doc. Which mill is that you have there? SX2?

Dr_GMJN24/06/2022 14:09:04
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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...

Hopper24/06/2022 22:41:36
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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_GMJN24/06/2022 23:08:56
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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_GMJN26/06/2022 15:30:20
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Started to reinstate the cylinder/cap fillet radii using Epoxy filler (Milliput), and ball sculpting tools. Quite a satisfying job:







Dr_GMJN26/06/2022 22:56:45
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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.

JasonB27/06/2022 06:55:01
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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_GMJN27/06/2022 12:31:49
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Thanks Jason. I might try it in the r/t, although setting up to be level and central three different times will be interesting.

JasonB27/06/2022 13:03:39
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You could just set up to do the flanks and central large radius and file the ends.

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