Well, I spent the week mulling this over, poring over the plans, and decided that I didn't have my machining sequence optimized. What I failed to do, was interpret the relationship between the position of the steam chest floor and lip in relation to the cast boss on the inboard end of the steam chest. If I want the gland centered in that boss (and I really do), then it is best to machine the steam chest to that feature. That means boring the cylinder, then drilling at least a center hole position in the boss, and referencing from that.
Well before tearing down, I measured the height of the boss, then measured the lip and floor of the steam chest, and found that if I want to center the gland in the boss, I still have 0.024" of steam chest to machine away. That gives me enough material to go back to the lathe, machine the bore and outboard face, and then come back and true everything up and keep going, so no harm done.
I decided that since it was all set up, and that I am pretty sure I can get the faces of the cylinder true to the lathe chuck, I might as well drill the bolt holes. So I did, using the cover as a template.
So on to boring.
Except - that's a pretty new operation to me, and I haven't had a lot of success with it. Time to change that.
I spent a good bit of time on saturday reading up on making boring bars and bits. I discovered in the old, mostly crappy lathe tool kit that came with the lathe, that I had a 3/8" boring bar, with a 1/8" square HSS tool blank in it. Perfect!
I made several cutting tools, and had several attempts at boring out a piece of aluminum rod that I had left over from a project. It already had a 20 mm hole in it, so this gave me a good practice piece.
After several dismal attempts I shut up shop and spent a few hours doing more research. Armed with some internet pictures and some advice from books etc, I returned to the shop this morning, and had another attempt at grinding a tool. This is really tricky on a small tool blank, and doing it freehand, on my bench grinder which has very curved edges on the wheels, but I made this thing.
It doesn't look very impressive, but the clearances and rakes are more or less kind of sort of where they need to be.
A few test cuts in aluminum showed that if I make 2 cuts for each diameter position, I can get a good finish. My reading suggested this was necessary, to account for boring bar flex. The first cut tends to be a bit rough, but the second one cleans up well.
I still didn't want to rush on to my cast iron cylinder just yet, so I gave it a go in a piece of stainless pipe I had laying around.
The finish actually felt very good to me, so since I had everything set up I took a deep breath and decided to have a try at cleaning the bore.
Here is my set up
As you can see, I cut off the excess piece of tool blank from the far side, and I have to have a goodly amount of overhang of the tool bar. The bore has plenty of material to take out, so I felt OK making a start with a light cut to see how things went. If it went poorly I could abort and still save the part. I set up the cylinder in the chuck by using parallels behind it on the machined face, and pushing it against them using a dead center in the tail stock. This had the part running very true in terms of the machined cylinder faces relative to the chuck.
After a couple of passes, I judged that everything was proceeding satisfactorily enough, that it was time to make a bid for the 1.000" bore.
To help, I noted the crossfeed dial position each time, and measured the bore using a bore gauge and micrometer, noting the nominal cut taken and any error. I wanted to get a feel for variation in diameter so that I could account for that as I got close to size.
It worked out well. Certainly I sneaked up on the bore size, but I got it, and I think the finish is acceptable. (Hard to tell from the blurry picture).
The icing on the cake was testing the bore with this aluminum plug. The plug measures 0.999" on my micrometer, and it slid evenly through the whole cylinder, with no detectable play, and no binding as I pushed it through. So I'll call the bore good. I may hone it at some point, but I'll be honest, I feel like my machine set up efforts, and taking the time to test new techniques are really paying off.
Since it was all set up so nicely, I decided to face the cylinder to length on the outboard end. I did this by measuring from a scribed center on one of the side port bosses. The inboard end will be machined to length from this new turned face.
Finished outboard end. The machined away boss that end is not used on this engine.
Colour me happy.
While in the shed, I have also made a start on cleaning up the base. Just by using emery paper on my surface plate. I need to take a little bit more off, just enough to make the underside flat with some clean metal all around.
While digging around I found a nice piece of 3/8" thick aluminum, left over from some work project or another. I'll flatten the top of it, and use it as a jig plate to hold the base casting.
I also found this lovely piece of cold rolled steel, a chunk of which is going to be used to make some new boring bar holders, based on the documents kindly sent to me by Baner.
So, some success. I feel good about all this. Next step is to machine the inboard face and gland to length, then I'll get back to the steam chest and finish that.
One thing that is very apparent, is that I really need to make the grinding table for my bench grinder. I have Howard Halls book - Tool and Cutter Sharpening (Workshop practice series 38) which has a nice design in it. That will really help for getting cutting bits made properly, once and for all.