Question: Boring a larger hole on a piece too wide for a metal lathe

waldenc1

waldenc1

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I need to bore a larger hole in a table saw trunnion from about 16mm to 25mm to accept a bearing. For the life of me I can't think of a way to drill this hole. If I could chuck it up on my metal lathe --> easy done, however, the piece is too wide and won't be able to freely turn. I could reverse everything and mount the piece on my compound rest with a right angle attachment and put a boring bar in the chuck but that won't work (unless I had the exact size drill bit)

I don't have a mill but have just about every other machine and tool. I don't have the exact size drill bit to put in my drill press and even if I did I'm questioning the results. My mind has hit a roadblock and I can't figure out how to do this anyone have any suggestions? There has to be a creative solution to this or am I stuck just having to get a large drill bit and go at it on a drill press or reverse everything on the lathe?

Much thanks!
 
Others may have a better idea, but I'm thinking of putting a boring head in the headstock and **slowly** creeping up on the correct diameter. You may even leave space on the carriage to mount a sacrificial piece of stock between the boring head and the trunnion. Then you can check the diameter of the hole on the sacrificial piece before committing to the final cut in the trunnion.

Of course, this assumes you can get access to a boring head.

Another way may be to get close by extending the bit out of the boring bar bit by bit, then perhaps finding a 25mm Reamer to finish the job?
 
Pics might help. For a hole that large, an annular cutter might work unless the hole needs to be precisely sized for a press fit. In that case, boring it on a mill might be your best option. Lots of guys around here with a mill ... maybe ask for help?
 
Ah yes a boring head that should work! I don't have one but would much rather buy it than a dedicated drill bit I might never use again. I was stuck thinking that the bit, tool, boring bar would be on center in the chuck and for it to work needs to be off center ala a boring head ;-)

I had been thinking of making a small cutting tool and offsetting it in a 4 way chuck but then realized there is no way (or at least very tedious) way to adjust and creep up on the size.
 
I would second the motion to see pictures and have some idea of the requirements for relative precision both for location and size.
 
waldenc1 said:
Ah yes a boring head that should work! I don't have one but would much rather buy it than a dedicated drill bit I might never use again. I was stuck thinking that the bit, tool, boring bar would be on center in the chuck and for it to work needs to be off center ala a boring head ;-)

I had been thinking of making a small cutting tool and offsetting it in a 4 way chuck but then realized there is no way (or at least very tedious) way to adjust and creep up on the size.
Click to expand...
In the shop where I apprenticed, we routinely, for the most part, used solid boring bars and adjusted the tool out for size, using a dial indicator against the cutting edge to set size; cut and try, this, on milling machines and boring mills.
 
Here is the trunnion and hole that I need to enlarge. Where the shaft goes into the black cast iron trunnion I need to hog that hole from ~16mm to 25mm.

291609
 
benmychree said:
In the shop where I apprenticed, we routinely, for the most part, used solid boring bars and adjusted the tool out for size, using a dial indicator against the cutting edge to set size; cut and try, this, on milling machines and boring mills.
Click to expand...
Ok so I wasn't too far off in my thinking here I could always do a few test runs on a scrap piece of enlarging a hole with this method.
 
Is there another solution to your problem. I looks as though you may end up with a thin casting around the hole by opening it up. What is the reason for the larger hole size? If you must, I would suggest that the work be done on a mill.
 
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