Conversion of 4 Cycle Utility Engine to Steam

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vtsteam:
Thanks David for your ideas. I guess I do want bearing support near the ends and want a true bore all the way. I can't count on the fact that the holes seem to have met up well. It needs to be a true hole.

I read up on D bits in Hasluck -- the old style machinist's handbook. I've also made stationary boring bar bits out of 1/4" drill rod in the past -pseudo D bits, by flattening the end, hardening and tempering and grinding. But these are fairly flexible for even a 4" cut, and cut slowly.

After thinking about it for awhile and looking at a wood spade drill bit, I think I'm going to modify one of those into a boring bit. They are a little shy of 6" total length if you grind off the end spike, so I'll add to the other end -- it doesn't have to be tool steel there.

Probably I will end drill a piece of 3/8" square keystock and braze the spade bit end into the keystock to lengthen it. That square stock should fit in my lathe tool holder and provide good stiffness and support.

I'll turn the corners of the keystock round near the bit shank so part of the keystock can enter the drilled hole.

For the bit material I'll maybe use a 3/8" spade bit -- convenient for this size. It will be ground to a boring profile -- the back side of the flat will be ground away so it doesn't contact the hole sidewall. A cutting tooth will be ground on the contact side. Interestingly, the clearances of the end and side are already correct, so I can leave those.

I think spade bits will work well because they are a lot stiffer than the drill rod boring bits I've made -- I measured the shank of one I have in front of me now and it is .28" -- a little heavier than 1/4". And it must be hardened in a way to give it some extra rigidity, by comparison.

So basically I will be boring the hole to size, not drilling. I'll just be modifying a wood drill bit to do it.

Pictures tomorrow when I make it. Fingers crossed it will work out......

DavidF:
you can get some pretty long masonary bits as well, plus they are carbide tipped :clap:
I have some concerns about boring 6 inches with the tool only supported on one end. Were you going to bore then ream to final size?
Maybe you should make a trial run in something to test it out???

vtsteam:
A likely looking boring bar! I believe I found this one on the side of the road a couple years ago. Not a 3/8" but you get what you pay for, I guess.

vtsteam:
A little cleanup and marking out what I want to grind off.

vtsteam:
Finished implement of destruction -- drill bit brazed to a piece of key stock. Not pretty, but effective.

I drilled the hole out to 15/32" and 5 passes with the new "boring bar" got me to 1/1000th undersize. I didn't do the final pass because I was well frozen by then. It takes about 20 minutes per pass at the slow speed I'm turning the faceplate, and light cuts I was taking. Standing there in 35 degree temps watching the lathe go around eventually lost its charm and I headed up to the house to warm up and eat dinner.

But progress!!!! :ddb:

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