In article ,
Pete & sheri wrote:
I just went through a process of boring out 7 pulleys for a line shaft.
The original diameter of the bores was 1 7/16" and they had to be
bored out to 1 11/16". The depth of the holes varied from about 2 1/2"
to 4 1/4". I found that 1/2" diameter boring bars just aren't stiff
enough when sticking out much over 2 1/2".
Note that there are some boring bars (for lathes) which have a
solid carbide shank and accept carbide inserts. I use one on my lathe
(a little over 1/2" diameter, with flats to make it 1/2" for the
toolholder and to hold proper orientation), and those will extend an
amazing distance before chatter becomes a problem. I think that I've
run mine with a 6" extension. Solid carbide has a lot less flex than
steel of equal diameter. (They are also *quite* expensive. I lucked
onto mine on eBay a few years ago at a rather more reasonable price.)
The tools seem to vibrate and
cause a rough finish (using Bridgeports at a night school). I have an
old vertical mill that has a B&S #9 spindle, so I can't easily get a
3/4" head, but I sure would if I could!
Perhaps check whether a solid carbide boring bar (with insert)
could be fit to the boring head.
Or -- you could set up your lathe for "line boring" (where the
boring bar is supported between centers on a lathe, and the workpiece is
mounted to the carriage (a bit tricky with those pulleys, I suspect).
Or -- you could mount the pulleys in a 4-jaw chuck and bore on
the lathe, which is what I probably would do.
And the lathe (assuming one of reasonable size) could also use
larger diameter boring bars, such as perhaps a 1" diameter one, which
would be quite sufficient for the holes which you were starting with.
On the subject of imported boring BARS: I bought a set of those 9
cheapies from Enco. They must be some sort of soft carbide becuase they
dull very quickly. I can even sharpen them on an aluminum oxide wheel.
It sounds as though you wound up with brazed HSS instead.
Good Luck,
DoN.
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