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

Anyway, pressing on today. I set up with a very close fitting rod to let me locate the center of the bore.



Using the two clamps allowed me to adjust the level of the top machined surface of the steam chest (and therefore the base of the steam chest).

I aligned the V blocks supporting the rod to the Kurt vise using other V blocks - which worked really well. I did double check that the faces of the cylinder were parallel to the X axis of the table.



Clearance was a problem with this set up. It worked out fine for the larger slot, although I had to extend the milling cutter a way.



Got the slot done. I also noticed that I could clean up the one side of the chest a bit more, and put radii in the two corners. I may well do that at some point. Should have done a better job up front.



Of course - having finished it, I realised that the supplied drawings specify the slot with from the outside quadrants of the radius at the ends of the slot - whereas at work we always dimension slots from the center of the end circles - which is because that is most useful to the mill operator. So unfortunately this slot is too wide. However, I think it will still work. I'll make sure the valve suits the slot. And in future, I'll be more careful to check all dimensions on supplied prints as to how they are defined.

I'm also disappointed about the ridges in the slot, which are a result of milling the slot in stages. I wonder what I could have done to avoid these ridges? I locked down the cross slides when milling this, but maybe there is a backlash adjustment I need to make? Need to give that some thought.

So on to the smaller slots. And here I got in to some difficulty. I simply could not get close enough with my quick change collet holder, so had to resort to using the standard Jacobs chuck for milling the two small slots. I may have to obtain some standard R8 collets - or a better approach might be to make / modify some clamp bars to a lower profile for small work.

I did have to move clamps around throughout the process, but I managed to get the job done.







Finished:



Not the prettiest. Improvement needed of course. However, depth of the short slots was only 0.005" over nominal - so getting the hang of dealing with quill backlash, which is encouraging, and everything seems to be in the right place.

Close up of the ridges



I don't think these will affect the operation of the engine, but obviously I'd like to improve on that.

To finish up for the day, I put the side holes in.





I now face the challenge of making four porting drillings, at 20°, to port the two small slots to the bore. I started looking at the use of an angle plate I have, but did not get very far. I think I want to use the tight fitting rod to find the bore center to locate the ports. Anyway - more thought needed, and hope to put some time in on this tomorrow after getting my chores done.



I've got this, but I'm not seeing a way of using it and keeping access to the bore, which I need in order to position the ports. I think.




Thanks for looking. As usual - mixed feelings. Some things went OK, other things didn't turn out as well as I hoped, but I think I'm still looking at a functional cylinder to get to a working engine at this point. However, I'm desperately trying to make really nice looking parts, not just functional ones. I'll get there.