Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

I've decided that having the bearing caps ready when I do the next stage of machining on the base will be a good idea, so I made a start on those. Mostly just cleaning up and squaring up.









Now I have them set up and ready to receive the bolt holes:








I decided to add the stepped feature to the bearing caps. Not really necessary, and most builds I have read leave this out, but I figured why not give it a try?





Then I moved on to machining the bearing area on the base casting. I have been having trouble getting my head around how to locate the surface of the bearing area when at an angle. I couldn't figure out how to locate it relative to the center of the bore in the cylinder mounting. But then when I was at work I saw one of our machinists setting up an extremely complex item, and he was showing me how to use gauge blocks and pins to set up different features. Armed with this fresh insight, I was ready to have a crack at this base casting again.

I set up my angle block, getting it mostly square to the machine using a 2-4-6 block in my vise, which I had already trued up. I used the dial gauge to verify squareness of the angle block.



....and checked angle using this caliper. This was a gift from a small business I helped out with some design work. It's a handy tool, but not sure I'd splurge on it normally.



Before setting up the base casting, I used a pin gauge to verify the bore diameter in the end of the casting, and then used the pin gauge to measure height of the rail surfaces relative to the bore.



I didn't take a picture, but I did the same thing to establish the center of the bore relative to the guide rail edges.

Then I moved it to the mill and finished the set up - I clamped it to the angle plate and then clocked it to verify squareness again.



In this next picture, you can see a gauge block and a pin gauge in place against the machined surface where the guide gland goes. Using this, I was able to touch off against the top of the pin gauge, and establish a height to the top of the bearing surfaces. I could also calculate the position of the center of the crankshaft. Easy as it turns out - just some trigonometry. In the picture you can see a spot face and center mark I made some months ago, when I was trying to figure out how to do this. I made the center mark as a visual aid.



 Anyway - decided to have the courage of my convictions and went for it.





The bearing caps fit reasonably well.



One thing to notice is that because of an earlier error when machining the face where the cylinder mounts, the bearing caps are not perfectly located. I did not properly interpret the intent of the design and did not locate the mounting face of the cylinder correctly relative to the datum on the print. As a result I have had to machine more away from the bearings on the base casting than is ideal. I knew this was going to be the case, at this point I am continuing on, correcting things as I go, with a lesson learned. This should still work - it will always look a bit odd, but it's only my third engine, and 1st casting set. There are bound to be learning opportunities along the way. The next one will be better, for now forge ahead.

I'm pretty happy with how the bearing caps fit anyway.

I clamped the caps in place one at a time, and spot faced through the bolt holes, before drilling a tap hole for the screws, and tapping the threads.



Then screwed the caps in place.



After that, I cleaned up the outside and inside faces.



Normally the clean up would be done after bolting the part flat to the table - but I decided this was as valid a method as any, and looks a little "different". Odd? I don't know - put my own slant on it. Slant. Get it?

Anyway, I also dusted off the front edges of the caps to make them match up to the base casting a little better.





After that, I removed the part from the angle plate, and decided this was good a time as any to spot and drill the bearing caps for the oilers.



This is where it sits now. It is FAR from perfect. It can, at best, be described as adequate, but while that is true, there are a lot of successes on this part, in terms of setting up square and true, and learning how to indicate off available surfaces to establish geometries. I am actually very pleased. I was at least savvy enough to not just press ahead assuming everything was right, but measured the part to find out where I was at - as such I think I can recover it and make a working engine.



The two slide rails for example, are off center. But I now have the option to machine the wider one to match the narrow one, and get them both centered. Alternatively I'll machine the guide to suit. Once in place the difference in rails will not be obvious. So I need to give that some thought. Either approach means making mating parts fit what I have, and not achieving parts that are "made to print", which is a goal of mine - but I'm making progress, and enjoying myself. Therefore, I deem it a success, at least on some level.

Next - get the casting set up and drill and ream the bore for the crank shaft.