- Joined
- Jun 6, 2014
- Messages
- 183
Just a PSA on my dumb move to hopefully save someone else down the line:
I am starting the construction of a small "cox" style engine from a casting. Last night I excitedly put the casting in the lathe and proceeded to begin boring out the journal when the main shaft bearing will go. Everything went well until I went "DOH!" I can't measure it.... The whole in question is recessed beyond the reach of my calipers, and I do not own a set of bore or pin gages to measure the diameter with. I was also set on machining two bores and two faces all in the same setup.
The finished bore should be 0.687-0.688" and will have a bronze bushing pressed in. Fortunately, there is enough stock in the casting and thickness in the bushing that this number can have an "ish" added on as the bushing hasn't been started yet. I ended up opening the bore until I could just barely tap in a cutter I have with a 5/8" (mic'ed at 0.624") shank. I then gently removed the cutter and cut blind until the dial on my compound said I had taken off another 0.030" radially (0.060" diametric + 0.625"=0.685") This should be acceptable, but if needed will leave me a few thou to ream or hone out.
If I were to do it again, I would turn a stepped pin with diameters of ~0.665", ~0.675", 0.680" and finally 0.685" I then could have mic'ed the pin and known where I was based on when I hit each step. For the last two I would be able to creep up on them until I had a tight running fit and be close enough for my purposes.
Below is a picture of the casting in the setup, and a really bad picture looking down the bore after I started cleaning up the as cast surface.
I am starting the construction of a small "cox" style engine from a casting. Last night I excitedly put the casting in the lathe and proceeded to begin boring out the journal when the main shaft bearing will go. Everything went well until I went "DOH!" I can't measure it.... The whole in question is recessed beyond the reach of my calipers, and I do not own a set of bore or pin gages to measure the diameter with. I was also set on machining two bores and two faces all in the same setup.
The finished bore should be 0.687-0.688" and will have a bronze bushing pressed in. Fortunately, there is enough stock in the casting and thickness in the bushing that this number can have an "ish" added on as the bushing hasn't been started yet. I ended up opening the bore until I could just barely tap in a cutter I have with a 5/8" (mic'ed at 0.624") shank. I then gently removed the cutter and cut blind until the dial on my compound said I had taken off another 0.030" radially (0.060" diametric + 0.625"=0.685") This should be acceptable, but if needed will leave me a few thou to ream or hone out.
If I were to do it again, I would turn a stepped pin with diameters of ~0.665", ~0.675", 0.680" and finally 0.685" I then could have mic'ed the pin and known where I was based on when I hit each step. For the last two I would be able to creep up on them until I had a tight running fit and be close enough for my purposes.
Below is a picture of the casting in the setup, and a really bad picture looking down the bore after I started cleaning up the as cast surface.