paul
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Posts: 8
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Post by paul on Apr 11, 2008 20:05:45 GMT
With the 'clapper' engine on hold awaiting a valve and elbow engine awaiting materials I decided to build the opposed single acting twin version of 'Scotty' - 'Double Scotch' - so called because it has two scotch yokes, one controlling the valve and one the movement of the pistons. IMHO the original design needs some changes in the steam passage/valve area - producing a 90mm x 5mm diameter bore good enough for the valve pistons is difficult; long series drills are needed but it's then too long for reaming and too narrow for boring! The designer suggests drilling carefully from each end then reaming all the way through. Pah! I had the remake the part twice as the this hole in the first one came out a little skewed - it would probably have worked but would have irritated me no end - no fun when you have no mill and need to make the frame from 10mm thick steel (I don't have aluminium as called for in the plans). In the end I decided to make a bigger hole and fit a piece of commercial brass tube (6mmx0.5 wall) as a sleeve. Crank, main bearing and piston rod are made, next the cylinders.  |
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paul
Member
Posts: 8
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Post by paul on Apr 13, 2008 16:50:43 GMT
Made the 'spool valve' assembly from 1/8" silver steel turned down to 3mm at each end to take the 5mm dia valves, loctited in place - the plans call for soft soldering discs to brazing rod - doesn't sound that accurate to me  Still a bit too firm a fit at present but at least my modification seems like it'll work.  |
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paul
Member
Posts: 8
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Post by paul on Apr 26, 2008 16:33:52 GMT
After a pause in operations work has resumed... Got the cylinders sorted and the steam/air passages, the base such as it is, and the bearing for the main yoke on the front. Due to an errant hacksaw there's less material at the top of the frame than in the plans which meant filing down the correct size cylinders that I'd turned in the 4-jaw. Ho hum. Roughed out the valve yoke from aluminium but I'm not keen on it - maybe I'll make another from steel sheet...callouses are developing nicely.    |
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paul
Member
Posts: 8
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Post by paul on Apr 29, 2008 19:52:44 GMT
Pistons are in although righthand one is a bit tight despite hours of oil and brasso ;D Once the yoke is on I should be able to solve that little problem though.  |
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Post by jgb7573 on Apr 29, 2008 20:07:20 GMT
Keep 'em coming Paul. Much better than spot the difference! ;-)
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Post by dickdastardly40 on Apr 30, 2008 10:36:03 GMT
Paul,
I've just acquired a box of treasure with some long series drills in. Not sure of the sizes OTTOMH but if you need one in future your welcome to borrow for the cost of postage.
Good progress so far, love seeing what you do without extensive machinery.
Al
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Post by circlip on Apr 30, 2008 11:18:02 GMT
And you'll learn far more WITHOUT big iron at this time Paul. Have you thought about a PERSPEX one next time?? Regards Ian.
And yes Al, some of us have seen your latest acquisition, ------ at least TWICE, give up crowing ;D ;D ;D
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Post by dickdastardly40 on Apr 30, 2008 12:43:42 GMT
Crowing was not my intention Ian, sorry if it came out like that, I don't wish to be a boor.
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paul
Member
Posts: 8
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Post by paul on Apr 30, 2008 15:08:50 GMT
Thanks all.
circlip: let's go 'round his house and relieve him of that obscene amount of freebies posted elsewhere. At least he spared us the pictures this time ;D ;D
Al: Seriously, thanks for the offer but I'm ok for the time being - I bought a 4.5mm and a pack of 10 (!!) 6mm long series bits. If anyone wants a postage-cost-only 6mm just holler, I can't see me using them all in a lifetime!
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Post by circlip on Apr 30, 2008 17:01:07 GMT
Al, look at the smileys.
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paul
Member
Posts: 8
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Post by paul on May 2, 2008 21:12:01 GMT
Made the connecty-bit today. Rusty block, filey block, drilly block, filey block is how it goes...  |
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Post by modeng2000 on May 3, 2008 5:29:33 GMT
Paul, the picture repetition rate is too fast for my tired old eyes.
What I can see looks great.
John
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paul
Member
Posts: 8
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Post by paul on May 3, 2008 8:22:07 GMT
Fixed that John  |
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Post by modeng2000 on May 3, 2008 13:51:30 GMT
Thanks Paul.
John
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paul
Member
Posts: 8
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Post by paul on May 3, 2008 20:38:51 GMT
Soldered the yoke to the piston rod and after much cajoling got the engine to turn by hand. Yippee! Also started making the combined flywheel/eccentric, watch this space.
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paul
Member
Posts: 8
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Post by paul on May 5, 2008 19:41:16 GMT
Made the flywheel/eccentric. First time I'd tried turning anything off-centre in the 4-jaw and it didn't com e out too badly - the diameter and thickness of the eccentric part is spot on but it's a tad further off-centre than the plans call for  I don't think it'll make much difference though as I can take up the difference in the manufacture of the valve yoke thingy. This engine is getting pretty heavy for it's size; I put it on the scales and it came in at just under 2lb! Maybe I should have used that aluminium girly metal after all LOL.   |
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Post by jgb7573 on May 6, 2008 8:10:48 GMT
Would that be a British Standard tad or one of these new-fangled mertic ones? |
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Post by dickdastardly40 on May 6, 2008 10:18:17 GMT
Nearly 2lb, that's almost an imperial bag of sugar (my partner understands bags of sugar but not tads)
The flywheel looks especially good.
Once you get the thing working there's plenty of scope to lighten the gross weight by drilling holes or sculpture if that sort of thing provides bouyancy to your dinghy.
Setting up to turn eccentric (the job not yourself) can be a skill all of it's own, good show on your first try.
Al
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paul
Member
Posts: 8
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Post by paul on May 6, 2008 12:05:32 GMT
Would that be a British Standard tad or one of these new-fangled mertic ones?  It was supposed to be 2.5mm off centre but it's nearer to 3 so it's a decimo-imperial fractionlet. I couldn't think of a way to measure the offset other than make a fine punch mark in the right place then use a centre in the tailstock to get it aligned, then run a tool across it to make sure the whole face was true. It took ages and I almost changed plan - a separate eccentric disc fastened on to the flywheel would have been easier to make but then I'd have the same problem positioning it before fixing. Hmmmm..... Al, the flywheel is a bit rough and ready to be honest; I got chatter aplenty while trying to scoop out some of the material and the mass-reducing holes are a very strand shape when viewed closely, not 'triangular' and certainly not round, but they'll do I had to loctite the air/steam inlet on top as there isn't enough 'meat' to put a thread in above the valve tube and I couldn't get the thing hot enough to silver solder, so I wouldn't be surprised if I manage to break it off at some point! |
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Post by jgb7573 on May 6, 2008 12:19:38 GMT
Nice one Paul. Should you ever have to do something similar, you might think of putting a 2.5mm packing piece under one jaw. That should work with a 4 jaw. And there are probably lots of other ways of doing it too.
The job's looking good though.
John
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I don't think it'll make much difference though as I can take up the difference in the manufacture of the valve yoke thingy.
It was supposed to be 2.5mm off centre but it's nearer to 3 so it's a decimo-imperial fractionlet. I couldn't think of a way to measure the offset other than make a fine punch mark in the right place then use a centre in the tailstock to get it aligned, then run a tool across it to make sure the whole face was true. It took ages and I almost changed plan - a separate eccentric disc fastened on to the flywheel would have been easier to make but then I'd have the same problem positioning it before fixing. Hmmmm.....