Scotch All Round

[crueby]

New pot fitted and we're up and running again. Hope to get some progress tomorrow!

Great!  Let the chips fly!

[redhouseluv]

Back in business and it didn't take too long ........ is that a lathe I can hear running? 

[Kim]

Glad it's working again! 

Sounded like the pot to me.  Glad you were able to get a fix for it under warranty!

Kim

[PaulR]

Started off today's session by grinding up a new HSS tool for facing operations and it gave a lovely smooth cut - surely a good omen 

Shaved the cylinders to length, spotted them through the frames, drilled the steam/air passages and threaded the central holes. Slimmed down the ends of the cross member tube things so they fit nicely at each end then faced each side of the flywheel blank. Here's a test assembly with temporary fasteners. Next job will be drilling and reaming the cylinders and valve cylinders (I don't have any boring bars and the bores are only 6mm and 8mm anyway) and making a widget or two to clamp the frames for silver soldering.

I've been thinking about how the scotch yokes will be made. I've made two engines in the past with a 'button' on the crank disk and a simple slotted yoke (Elmer's 'Scotty' and the 'Double Scotch' engine). The slight issue with both of those is the yoke has no guide and tends to rock in the vertical plane although it doesn't stop the engine working. I don't have any milling capabilities at present so might fabricate them rather than filing slots. I had another idea which would reduce friction between the yokes/button - make the yoke from a pair of thin round bars with little connecting plates at top and bottom, a bit like a single tall bike chain link. They would still tend to rock but there'd be almost no surface contact with the button. Hmmm...

[PaulR]

Not much shop time today, just enough to do one of the valve cylinders. In the photo there's a piece of 6mm rod passing through it just to check size and alignment, both are ok. The internal finish is only 'adequate' but I think it'll be good enough.

[Roger B]

Glad you are back making parts now 

[PaulR]

Soldering the frames and tubes together seemed to go well until it had cooled down and I discovered that one of the frames had bowed slightly. I had a stub of crankshaft keeping things parallel and right next to this a single toolmaker's clamp. Everything seemed rigid enough but the excess metal on one side due to the clamp must have resulted in unequal heating and distortion. The net result is that the frames at one end are 0.5mm further apart than at the other and as a consequence the cylinders aren't coaxial. You can see the problem if you look at the far right cross-member/tube in this photo, there's less of it poking through the frame. That's not an issue but the distortion certainly is so I need to think about how it might be rescued (I've got an idea already but will to sleep on it).

[crueby]

Looking at the previous photo, looks like the cross tubes all have shoulders at either end? If so, then at the one end the lengthwise bar must not be up against the shoulders? If so, could it be re-heated and a clamp applied to push it back against the shoulder to straighten it?

[PaulR]

Looking at the previous photo, looks like the cross tubes all have shoulders at either end? If so, then at the one end the lengthwise bar must not be up against the shoulders? If so, could it be re-heated and a clamp applied to push it back against the shoulder to straighten it?

Possibly, if I can get it hot enough to melt the solder again - I've never tried that. However there also seems to be some curvature near the centre. I'll have a look with fresh morning eyes!

[PaulR]

Looking at this again it's worse than I originally thought, basically one frame seems ok but the other is curved, diverging at both ends. I'm going to have to saw off the tubes, drill out the ends and, if I can straighten the bent frame, do it again. Next time I'll try to clamp some blocks between the frames to stop any distortion. 

[PaulR]

One step forward, six steps back, four steps forward...

Sawed off the toobes, tidied up the solder/brass, straightened the frames - both were distorted. Made 4 new tublings (steel this time, I didn't have any suitable last time round) and drilled one - they're too long to get a 1mm drill through in one go so have to drill from each end. Three more to drill then make whatever clamping blocks are needed to get the soldering right next time.

Blurry photo:

[redhouseluv]

It's tough when you have to go back and redo something or mess something up along the way - if it's any consolation, I joined that particular club today! 

I must admit I still get very frustrated when it happens, but I hopefully it'll happen less over time.......maybe

[PaulR]

It's tough when you have to go back and redo something or mess something up along the way - if it's any consolation, I joined that particular club today! 

I must admit I still get very frustrated when it happens, but I hopefully it'll happen less over time.......maybe

Yep, I should have known better to clamp the work more securely - I've made the same mistake before, hopefully this is lesson learned! At least it was only the simple tubes I have to remake so not too bad.

[PaulR]

Almost finished drilling the tubes when I broke a drill and couldn't extricate it so had to make another one (tube that is, not a drill bit )

Finally got the tubes ready, used a small toolmakers clamp, two nuts and bolts and some rods to keep it all square for soldering. Don't know why but I kept getting blowback from my little torch tonight (probably the number of vortices created by all the rods and clamping widgets)  which meant I had to stop and relight it half a dozen times. Anyway, all went ok; I've measured at various points along the frames and there's a total variance of 0.13mm or about 5 thou in old money which should be fine. Having a bit of a pickle at present, photo t/f.

[PaulR]

Everything seems all square now (piece of rod through valve cylinders to check). I seem to have spent far too much time on this simple assembly, which with hindsight isn't the best design. hopefully I'll have some more progress to show soon.