Stuart 10V Build Log - Complete Beginner...

So I tried to find a sleeve of about the right size, but no luck. I also considered making a Pre-drilled bush to press in, and drill to size when fitted, but a) A small enough drill was very flexible and b) The very thin wall might collapse on fitting.

Anyway I fitted a plain brass plug:



Set it up as best I could again in the 4-jaw chuck and re-drilled to a size that was a definite clearance fit in the 5BA die:



OK, ok it’s not drilled exactly centrally, but there we go. I guess there was no guarantee the initial hole was spot-on either.



There is some float in the lower seal hole and nut, so I think the new valve rod (yet to re-make it) should be a good enough fit. If not I’ll drill out again and risk a pre-centred bush.

Anyway, lessons learned. Onwards...

Presumably the 3.1mm diameter valve rod is a suitable diameter for a 5BA thread?

From what I can find, the O/D on a 5BA thread should be 3.2mm, so a 0.1mm undersize should be safe in terms of threading (but maybe a bit sloppy?

Cheers.

The fit of the flanks matters more than the o/d. 3,1 should be fine. With a normal split die you can adjust how much you tighten down the two screws that bear on the free ends of the arc, in tandem with the centre screw that opposes them. start with the die slightly open, test the result, then tighten it down if necessary by a few degrees turn on the screws, and test again till you get a light friction fit. But if you go a little too far, a bit of slop's unlikely to affect function.

My 10V's a crude job in comparison with yours, but it's worked very nicely for 25 years.

Edited By Mick B1 on 23/07/2020 09:21:42

Thanks Mick - I'll do that with the die.

Your 10V looks fine to me, I'd be more than happy with that, the main thing is that it runs well.

Wing and prayer job, really - with a Unimat 3 and a cheap Chinese bench drill I still use. Couldn't swing the eccentric with its arm in the tiny Unimat for boring, so I had to cut it off and attach a separate turned arm instead. I interference-fitted a bronze tyre to the flywheel - but I can't remember all the other dodges I used.

Edited By Mick B1 on 23/07/2020 11:00:06

It is very common to use a 5BA thread straight onto 1/8" nominal stock (which can be a bit under size) and I expect just about all the 10V & H engines built do that, 2BA also goes onto 3/16" nominal and 7BA onto 3/32" even though they sizes are not what you will find on most charts.

Hi Dr_GMJN, I was sure your username rung a bell when you started posting but I couldn't place it, didn't realise it was from PH until I saw the Stuart build thread pop up in recent posts there.

Nice engine build so far, hopefully she'll run like a chipped 330D .

Re your post on the previous page about indexing, would highly recommend getting both hex and square Stevenson collet blocks from Arceuro, makes jobs like that really easy.

Thanks, yes those blocks look good. Spending money is going to be a bit tight next month unfortunately though!

So tonight I re-set the scrap valve rod in the lathe and sawed the threaded end off. I found that putting it in a collet gave me 0.0015” runout, so I stuck with that rather than messing about with the split bush and 3-jaw chuck:



Centre drilled, and turned down to size with a DCGT insert, then tried the 5BA die. This time it worked. I needed to turn a pointed grub screw to open the die though (it slid on without that, but I wanted to make sure, as suggested, it wasn't undersized):





There was about 1mm to spare. Flushed with success, I milled the valve plate to size:



And drilled and tapped it after centering using the edge finder:



Fit on the rod was spot-on.

So then onto cleaning-up the valve Itself and the rest of the parts. The sliding fit of the rod in the chest is pretty good, if a tiny bit sticky at the very top of the travel (but only in one orientation). Might need a bit of lapping or something to get it perfect. I think it’s Probably fine as it is though, becasue it shouldn't ever get to the very top of the bore I guess.



All seems to fit together well:



And I think the travel is OK for the ports too:



Just need to make sure the eccentric throw is spot-on.

So I made a start on the valve rod fork end:



Full disclosure:

I chamfered the end, drilled, tapped and lightly screwed the rod in with Loctite. Then brought the tail stock chuck in, and gently nipped it around the end of the rod to keep it aligned while the Loctite set.

Turned the chuck Slowly by hand to make sure it was true, the Tailstock chuck grabbed, and twisted the end off the rod.

I think I may take a week off from this project...

No. This is Victorian tech, so do what they did when they fell orf their 'orse.

Get straight on again, and ride!

If I had any spare rod I would! I was still congratulating myself on saving the first screw-up (by about 1mm).

Ill send for another rod next week.

I have a rule when modelling or whatever, that I correct screw-ups before moving on.

Hi Dr_GMJN , it's looking good. have a look in my album for some pics of my build, also my final run video..

**LINK**

George

Thanks George, your 10V looks beautiful and runs as well as it looks.

One question though - unless I've misunderstood the concept of how the slide valve works (which is quite possible), I thought it needed positive pressure in the valve chest, ie the air/steam feed would go into the valve block, to keep the sliding faces together, but you've got the exhaust there.

Is this correct - does the valve work with the inlet either side? I'd have thought the positive pressure acting on the pocketed side of the slider would tend to push it away from the valve port face, causing leakage?

Cheers.

I would have to look at the drawing again to clarify what 'guzinta' & what comes 'outa' where. My grey matter is decidedly slower than it was when I built it. I'm just pleased it still runs great.

George.

Yesterday morning I got a new rod (and some oilers and drain cocks from Stuart Models) and put it in the parts box. This evening took it out and started to machine it. Then test fitted it to the valve block and found I’d picked up the piston rod stock by mistake, which is too thick for the sealing gland. So started for the third time, this time on the right stock. Turned, lapped, threaded and re-set into the brass block. I didn’t turn the chuck this time. So back to where I was on Sunday.

Crumbs! It's a shock to realise mine is 20!

Neil

Creeps up on yer, don't it?

Valve rod forked end finished at last. I made some Hardened filing buttons to profile the end. Worked a treat:























Might have a go at the bearings next.

I got a bit distracted with other projects recently, but today I fitted the main bearings to the sole plate.

I set it up so that the plate would remain fixed to the mill bed when the bearings were un-clamped. This was so I could drill with tapping drills, clearance drills or whatever, then remove the blocks and go back to exactly the same co-ordinates for tapping.

I used the plate flange edges as datums, because that’s where the nuts and oilers will be viewed relative to. If there was an error in how central the bores are, and I took the bore centreline as a datum, the whole lot would look off.



Started by drilling through everything with a tapping drill:



Then opening up just the flanges to clearance:



Then removed the bearings and tapped the sole plate:



Then re-fitted the bearings using studs and nuts, and tapped the oiler holes:



I’m not sure if I should have gone all the way through to the bore with the tapping drill, but too late now. The oilers themselves have a constriction in them. I’ll have to find some fibre washers because they protrude into the journal. Good job I spotted that - could easily have caused some confusion/damage on test assembly:



I didn’t notice that the bearing mount holes were relieved under the sole plate. It looks like everything is on the right place though, so I’m confident the blocks were the right size, and were aligned properly in their pockets:



So that’s that: