Actually Jack, the extra material is to make a couple more pieces that are required, but there would be no trouble making them up out of normal steel if I used it to replace a buggered up cylinder. It is for that reason I am making the cylinder first, just in case I need the option.
But I needn't have worried, making the cylinder went very smoothly, but I might still keep that piece of cast and make the bits out of some scrap steel I have, it seems such a waste of a good piece of precious material.
Away we go, my way of boring a cylinder.
First off, I am using a four jaw self centring chuck, not a 4 jaw independent. I find they are a little more accurate than a normal 3 jaw.
One of the first things you will notice are the brass shim protectors, you could use cut up drinks cans instead. Cast iron, although fairly hard to penetrate can have the surface bruised very easily by unprotected jaws, these are used to help prevent that. There is no need to go to white knuckle tightening up, they grip rather well without going that far.
The flange was faced to correct thickness.
By using different sized drills, I gradually remove most of the material to come out of the bore.
I left 3/16" to bore out. You can go much closer than that, but I like to use the run up to final size to gauge how the bar is cutting. Writing down the cut put on and seeing if it matches with the amount taken off.
The boring tool was set up in it's holder. Making sure that it will go all the way thru the part. I also set up the saddle stop so that it works just after the tool has gone all the way thru.
This is really sticking out a bit more than normal, but this is a 16mm diameter tool and I have found that they are more rigid than a normal steel one of the same size, so if normal cutting pressures are kept low (no big depth cuts) then everything will be fine.
So the sleeve was remounted into the chuck, but using a slightly different method.
The flange goes fully up to the jaws, to stop the sleeve being pushed inside the chuck as I put a new cut on. Secondly, the protectors are still used, but the jaws are only tightened just enough to stop the part spinning in the chuck.
If you tighten up too much, the outside walls will be pressed inwards and when the boring bar takes it's cut, it will be off the metal that has been pushed inwards and you will find that when the chuck pressure is taken off, you will end up with a triangular(if using a 3 jaw) or square (if using a 4jaw) shaped hole, not perfectly round. I hope you understood that.
If possible, I always try to bore thin wall items with the bored part being outside of the chuck jaws.
Anyway, back to cutting out this hole. I rough cut out at 0.025" cuts for the first few, until I got within say 15 thou of required hole size. Then remove the material until it leaves about 0,002" to be removed. The closer you get to size, the finer and slower the feed you use.
I do the final cut, measure that it is either spot on or very close to size, then using a very fine feed, take another half dozen cuts with no more cut on at all, just using the same setting as the final one used to get down to size. This is to take off any material that wasn't cut because of the tool flexing as it went down the bore.
All this lot took well over an hour, but hey, the job isn't going to get up and run away, so time shouldn't enter into the equation, other than the longer you take on it, usually the better results you get.
The bore, measured at either end was exactly the same, one thou oversize, so no tapered bore. I suppose I should have used my deep bore gauge as I was doing the job, but I couldn't be bothered to unpack my instrument cupboard to get to it.
The surface finish was smooth as silk. I love working with cast iron for that very reason, you can get fabulous smooth finishes on it.
The last pic shows the sleeve sitting on a bar of metal. Cast iron again, and that will end up as the piston. A job for next time.
Actually, the instructions that came with the engine suggests honing the bore at this time. Personally I think that is the wrong way to go on an engine such as this, so after the piston is brought down to size, it will be lapped in with the cylinder bore, that will give an even smoother and less friction of fit than honing could achieve.
Bogs
