ol3_m3 wrote:
On Dec 17, 5:51 pm, Chris wrote:

ol3_m3 wrote:

Need to enlarge the bore on a pc of bronze stock fron 1/2" to 3/4" the
length of the material is a bit over 12". any suggestions on where I
can find drill bits and reamer with extra long shanks? any tips on
keeping the hole concentric to the OD?

thanks

OM

first question, is the bore of the stock finished or just the rough
cored hole from extrusion?

second what type of finish do you require and size tolerance on the
finished bore?

very hard to keep a bored hole straight and true for that length
without dedicated gun drills or such

if you have access to a lathe , i would consider mounting a boring bar
between centers and boring with the stock mounted on the cross slide.

or alternately using same type of bar mounted in the tool post and
passing through a bushint in the headstock 9 making a sort of line
boring rig in the lathe.

i placed a roller bearing in a spindle through hole once and used a 6T
borring bar to bore a 32" long bore, held .001 for the length.

of course the bar was 3" diameter and i wa boring a 4" hole out to 4.125


need close tolerances, will be a sliding fit on the shaft it is to
fit over, is the stand for a precision grinder I am trying to build.

Bore the length oversize, fit accurate bushings to the ends, along
with wipers to keep the whole inside works clean.

On both size and location to decent tolerances is going to be a right
job to do. Never been around one, but it seems a job for a horizontal
boring machine, or a similar cobble-up from a lathe with a boring bar
between centers.

Cheers
Trevor Jones