How do I assemble my crankshaft?

[John Hill]

I am making good progress on my double acting "steam" engine, the cylinder is bored, piston complete, valve chamber and valve spool made and two chunky flywheels turned from exercise weights.

Now the crankshaft, I will be using 3/8" for the shaft as thats what size I have for the main bearings. The crank throws will be from 12mm square stock.  I am at a loss at how to make a low friction eccentric so I will be using a crank for the valve rod too.

What choices do I have to fitting the short pieces of 3/8" into the short pieces of 12mm in an adequately rigid manner?  OK I know  I could use solder but heat would prevent using bearings for the big end and the valve rod,  I can press it together and/or use Loctite et al  but maybe there are other ways I have not tought of?

[bogstandard]

John,

I don't know if this will help you, but when I want to mount a roller bearing in the big end, this is the method I use. Make a split crankshaft.

This gives you an idea of how to do it.

http://www.homemodelenginemachinist.com/index.php?topic=862.msg5946#msg5946


John

[sbwhart]

Hi John

I was going to suggest that you pinned them but it looks like John B beet me too it, if you have a look at page 1 of my loco build you can see where I pinned the webs of the crankshaft.

As for making the eccentrics they are quite straight forward.

For the tumblers you just turn up a good length of bar (more than you need) to diameter, then you off set it by simply holding it in the three jaw with a packing piece in one of the jaws, (thickness half the throw) this gives you the off set and drill the hole for your crank, then simply part off the discs, and drill and tap for a grub screw to fix it too the axle.  For the sheaves you use the length of bar left over from the tumblers as a gauge to get the bore right, make from two bits of material clamp together, bore out in the four jaw, when you un-clamp them bob your uncle you have two halves of the sheaves. Then just hack the outside to the shape you want.

Hope this makes sense  , again if you look at my loco build you can see how the sheaves were made.

Cheers

Stew

[John Hill]

Thanks John, Stew  thats enough new material to get the gray matter past TDC and on the go again.