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spuddevans:
Not too much to report on today, I've only had a little time in the workshop and spent most of it just standing there wondering :scratch:

The bit that has got me wondering is the Block mounting plate

I was going to PM Bogs to ask him this, but I figured I may not be the only one who, when building this, has not got the exact materials that I thought I had, so I thought if the answer could be put into the main build log then anyone could find out.

As you can see on the plans it calls for 2-2.5mm brass or steel sheet and I thought I had some 2mm brass sheet, but it turns out after measuring a part that didnt have a beaten edge :doh: (note to self, always check to make sure when using verniers to make sure the jaws lie flat and square to the bit being measured) it is only 1.62mm (1/16") thick. Now I have got some 2.5mm ali' plate that is big enough, but before hacking my way into that I wanted to know if (1) would the 1.62mm brass be too weak/thin? and (2) if that is the case, would the ali do instead?

So If anyone has an answer please chime in and I will be eternally grateful :bow:

Tim

kvom:
Bogs' drawing suggests not going any thinner, whether for rigidity or dimensionality I can't say. I made my plates from 1/4" brass that was flycut a few thousands on each side.

Note that when the plate is thinner, the piston will be higher in the cylinder at TDC, as will the valves. You might need to do some calculations to see if that causes a problem. You will have the weight of the block plus the steam chests supported by the four columns on the edges. If the plate is able to flex from the weight or vibrations then binding could occur.

In short, I'd probably use the Al plate myself.

spuddevans:

--- Quote from: kvom on August 09, 2009, 11:23:37 AM ---.......In short, I'd probably use the Al plate myself.

--- End quote ---

That is what I am expecting to do, I guess I'm just vainly hoping that the brass would do. But like you say about the weight and vibrations, it'll probably be better to err on the side of caution.

Thanks Kvom :thumbup:

Tim

bogstandard:
Tim,

Kirk has it almost spot on. 1/16th is really a little too thin to support the weight of the whole top end, and the friction induced forces going up and down. Brass or steel was chosen for it's rigidity. Steel because it is rigid from the off, and brass after it has worked hardened, will be strong enough to do the job. I am not too sure that the ali, with it's natural softness, would be up to the job, you would have to suck it and see. 3mm ali would be much better.

If it was flat enough, you could use two layers of the brass plate, say loctited together (not soldered, that would soften the material too much). The amount of bolts holding things together on the top end would ensure it acted like a single thickness.

You will hit the same problem when the bottom plate is made. So your choice has to be made at this time.

By going thicker, the only things that really have to be taken in consideration are the bolt lengths and the four column lengths. The bolts would need to be longer than the difference in thickness from 2mm, and the columns, shorter.

John

spuddevans:
Thanks John, I think I'll pick up some 2mm brass for both the top and bottom plates, I think that will be the best solution all round.

I think I was grasping at straws once I found out the brass was thinner than I thought.

Oh well, I live and learn a bit more.

Til I get my brass sheet there's a few other things I can be getting on with until I get it.

Thanks again for helping me :thumbup:

Tim

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