Very light but deep boring

daveog

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Hello,

I have a 12” piece of 2024 aluminum tubing that is 1.5” OD and 1.370” ID that I need to open up to 1.375”. It’s just a 0.0025” cut but I need it to be uniform and clean. I’ve considered getting a heavy 1” boring bar and holder and also a 1.375” shell reamer. But, I have a 5/8” shank coolant-through steel boring bar in hand. Do you think boring 6” one way then flipping it in the chuck and doing the other end would be a viable method? I’d rather use my tooling on hand as opposed to buying more if it can work but I don’t want to experiment with a $30 piece of tubing either.

Thanks!
Dave
 
I thought this was a pretty cool setup that Kieth Fenner used. You would have to build a jig to make it work, but it would cut true all the way through. About 27:49 into the video
 
I agree, line boring is the simplest way. I would weld or bend a setup, that has a flat bottom, and a tube larger then the one you want to bore out. design it to either mount to your compound, or if possible, directly to the carriage.The have set screws like Keith has on his setup. Keith has shown that method to do line boring a few times. Several years ago, I made a small mount to attach to my compound, and try it for myself. Mine was just some steel plate welded to an inverted L, with a solid bar ion the top. The bottom had a hole to mount it to my compound. I used drill bits mounted in the chuck to make the original hole, then a home made boring bar. Even though my setup was flimsey, taking it slow it all went great.

If the tube will fit inside your spindle, I have also seen a video where the person made a long boring bar, and hole it in the tail stock, and a steady rest right in front of the chuck. I have not tried it, but I would make the boring bar so it just leaves enough room for the chips to squeeze out. I can see a lot of flex when the bar gets towards the far end of the tubing.
 
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That is a neat setup, but more setup than I really want to do. What about using a shell reamer and doing half way from each side?
 
Does the hole need to be straight?

I was thinking about those, but have never used one. I would think you could make your own long handle, and ream it in one shot. How well do they follow a long hole? would making a pilot to guide it be worth the time?
 
I don’t know anything about them. I think a pilot would be a unnecessarily difficult with such a large hole to begin with. I’m only trying to remove 0.005”.
 
From your first post it sounds like you have a lathe with a bed long enough to fit everything, so maybe you could take some decently sized mild steel round stock and stick a HSS cutter in one end to use as a boring bar? It would probably take a while going very slowly, but there's minimal material to take off anyway.
 
I think the problem with “improvised” boring bars not held in a tool post is the ability to accurately adjust depth of cut, especially when my cut will only be 0.0025” deep. I can’t manually set and measure a cutter in stock that well. I’m wondering if a 1” boring bar and holder going just over 6” from each and and meeting in the middle would work. I need it to be perfectly straight and concentric with the OD.
 
I might be misunderstanding, but it sounds like you're imagining the cutter coming out of the bar above the centerline of the work. You could just drill the hole for the cutter off centerline of the bar, so it's about on centerline of the work. Of course no matter what, the bar will have to be narrow enough to fit into the pipe.

Or instead of improvising a holder, you could either weld a piece of square stock toward the back of the bar to fit into your current holders, or mill that profile in the same spot. That way everything is still on centerline, and you can save most of the bar afterward.
 
Also please someone stop me if this is an incredibly stupid idea. In my head it makes sense.........
 
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