Mount Trapezium

[uuu]

If you can use tailstock support, it feels more comfortable.  Not always possible, I know.

Wilf

[redhouseluv]

Thanks Wilf, good point, I didn't think of that!

Today I'm going to make a start on the cylinder. Strangely neither the drawing or the build log give the ports depths or angle of the steam passages.

The drawing is 1:1 so I think I'll measure the depths and use a protractor for the angle, hopefully, that'll work out?

I'm getting 0.441" depth and 12 - 15 degrees or 78 - 75 degrees depending on which way you measure

[Jasonb]

Not sure if I have ever seen the angle given on a drawing, It is usually a case of eyeballing it.

Depth may be restricted by the flute length of your 2.5 or 3/32 cutter but it is only the edge that affects valve events so you could happily mill the slots shallower and then use a series of slightly smaller drilled holes, the 2.3mm would do and match the passages.

I'm also not averse to drilling the passage sparallel to the bore and making the ports deeper to meet them. On a display engine it won't affect efficiency or max power.

[crueby]

I like the parallel passages like Jason showed, if there is enough space at the cap to cover the hole end as it may be farther from the bore - whether parallel or angled you don't want to risk the drill breaking through, and measure the drill depth first and dont exceed that, if you connect up with the port you should feel it break through, but if not you dont want to go too far.

[redhouseluv]

Parallel ports, I've never seen or considered that on anything that I've made so far. I guess that takes a lot of the uncertainty out of the getting the angle correct. I presume I 'cut out' where the steam passage starts doesn't need modifying at all (blue circles see last pic).

I finished boring the cylinder with a good fit table end and to the cylinder cover; however I'm confused as to how the cylinder fixes to the table and cover to the cylinder? The drawing says 9 holes at 2.3mm with is 8BA clear and only the holes above the ports to be tapped for the cylinder cover. The table also has 8BA clear holes - I would have thought there would/should be studs going into the cylinder otherwise how does everything fasten?

I have added some of the diagrams the general arrrangement one looks like studs to me?

[crueby]

Correct on the little section between the parallel hole and the cylinder bore, on mine I use an end mill to make that little cut. If you going to drill the hole at the angle, I would still use an end mill to make that cut, to connect the drilled hole to the bore.

[Jasonb]

You have 9 clearance holes where you can get to the other side of the flanges and three tapped holes where the port block gets in the way at the bottom. Personally I would be inclined to tap them all for studs at the top which it looks like the GA shows
You might want to turn that rectangular top 90 degrees.

[redhouseluv]

 I'm glad you think the same about the studs and I wasn't going mad!

Yes, I'll will remember to turn the top after a few more operations and before final fixing - well spotted, BTW 

[uuu]

You might want to consider making the threaded hole nearest the three port holes a dummy.  A nut on a stud that only projects into the cover, not the cylinder.  So the danger of breaking through is removed.  And it gives the gasket an easier job of sealing around the port holes.

I recognise the break through danger is reduced if you opt for the parallel port idea.

Wilf

[redhouseluv]

today ..... the top flange machined to size, port surface machined, followed by the ports. This is the first time I've made the ports into fresh metal, previously it has always just been a clean up of a casting.

Each port was machined by drilling 3 holes to a depth of 0.440" and then milling across to join them up to a depth of 0.375". Still have to steam pockets and passages to go, needs a fresh head for that!

[redhouseluv]

I was about to cut the steam pockets when I looked at the drawings again - see attached. The pockets are 0.156"deep and cut in to the cylinder by the same 0.156"

However the other image shows a rectangular pocket rather than a round one and there are 3 holes in it, what's that about? I've only seen round pockets so far (not an issue, but just different I guess), but what are the 3 holes, surely I'm not making 3 steam passages.

Am I looking at the drawing incorrectly or just getting myself into a pickle or both?

[uuu]

Yes - three steam passages.

20191204_092933 by Wilf, on Flickr

Some people subscribe to the "bigger is always better" philosophy, and merge the three holes into a slot.

Wilf

[PaulR]

... surely I'm not making 3 steam passages.

I smell fear 

As long as they connect with the steam chest slots and don't break through into the cylinder bore the exact course doesn't matter. I seem to recall I once made an engine (without any milling facility) and just filed the 'pocket' so it was perpendicular to the passages and therefore easier to start the drill.

[PaulR]

Yes - three steam passages.

What's that little notch on the opposite side for in your photo Wilf?

[Jasonb]

Use a 2.5 or 3/32" cutter to cut the recess to the width and setback shown.

Some of us like more than three