Little Wonder

[Old Man Aaron]

Hell of a process. Always a pleasure to see how you do it.

[Trevor Thompson]

Hell of a process. Always a pleasure to see how you do it.

Trevor

[Trevor Thompson]

Creating the straps is long winded - there is little room for error! The first one I made didn't quite work out - but it did enable me to fine tune the process - so that the second one worked.

So missing out the drilling and milling bit for the moment, the second one having its inside bored out to the final size, 16.24mm:

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You might just be able to see that the strap is just fitting inside the slots in the chuck jaws, and that is really useful to make sure it is held firmly without crushing it. I made a "go/no go" gauge to act as a dummy eccentric so that I could finish the bore to exact size without fitting it to the actual axle:

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The gauge is inserted fully - the next bit which is clear of the strap is the "no go" bit which should not go into the strap. Since all of the eccentrics are identical (16.18mm - or at least really close to that) it will work for all 8 straps. The first 2 straps:

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The one on the right is the first one and you can see that I milled the cutouts for bolts far too deep. I should have been able to spot that from the drawing but somehow couldn't really get my head around that bit - at least not until I had seen it in the flesh. The right hand one is the second, and that looks much better. The inside face which contacts the eccentric has been polished using a polishing cloth mounted in a Dremel and used carefully while the chuck was rotating backwards. It is a close sliding fit on the eccentric - and was easier to achieve than I had expected. The one good strap mounted on the eccentric:

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The key bits to get right are to mill the cutouts to the correct size, and then position the holes for the bolts centrally. There is little room for the holes to run out. It seems safer to tap the holes while it is 3mm wide, and then reduce the thickness of the strap to 2.5mm. I drilled the centre to 12mm diameter before cutting the strap in half and bolting it back together - because drilling it out when it was still one piece seemed to put less strain on the strap - and particularly the 10 BA bolts. I also found that gripping the strap in a vice with the centre line exactly lined up on the top of the vice jaws, and sawing with a junior hacksaw along the top of the vice was the easiest way to make that cut accurately. Not good for the jaws - but it worked.

Just another 7 to make.

Trevor

[Trevor Thompson]

The first 4 eccentric straps are complete:

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They are a reasonably close fit on the eccentrics, but they do rotate - as in they will remain stationary when the axle rotates. I think they will be fine when they are run in. Of course having the eccentric rods attached and being connected to the rest of the valve gear will hold them in line and make it easier for them to rotate freely. I will have to line up the bolt heads when I finally fit them - or the corners of the heads will catch on the other straps.

Just another 4 of them to make, and I am making them together as one "batch". Outside diameter to size, bored out sufficiently to get the boring bar in, and the width reduced to 2.5mm:

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You can also see that I have scored guides to show where the pockets have to be milled out, and where they have to be cut in half.

Trevor

[Trevor Thompson]

Milling the pockets for the bolt heads on the 5th strap:

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drilling the holes 1.4mm:

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and cutting it in half:

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four more tapped and fitted together ready to bore to final internal diameter:

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Soon be able to start on the eccentric strap rods to connect them to the expansion links.

Trevor