I've found that for small chucking reamers they tend to flex enough that any
tiny misalignment doesn't matter, but for larger ones it results in a very
small oversize in the reamed hole. Gunsmith's deal with this by using a
floating reamer holder. I was thinking of making something similar for any
old size chucking reamer.

I was thinking the base of the tool would be a straight shank ER collet
chuck and an MT extension. For my 1440 lathe something like an MT4-MT2
extension adapter bored out for a sloppy lose fit with a 3/4 shank collet
chuck. Drill a loose fit hole through the adapter and a press fit hole in
the shank of the collet chuck, and press in a pin. Then it can float anyway
it needs to in order to just follow the hole, and the pin will keep it from
rotating with the part. The ER collets would be able to hold a wide range
of shank sizes. I was think ER25 or maybe ER32.

Stupid idea? Better cheaper way to do it? I don't know.

On Tue, 28 May 2019 15:16:59 -0700
"Bob La Londe" wrote:

I've found that for small chucking reamers they tend to flex enough that any
tiny misalignment doesn't matter, but for larger ones it results in a very
small oversize in the reamed hole. Gunsmith's deal with this by using a
floating reamer holder. I was thinking of making something similar for any
old size chucking reamer.

I was thinking the base of the tool would be a straight shank ER collet
chuck and an MT extension. For my 1440 lathe something like an MT4-MT2
extension adapter bored out for a sloppy lose fit with a 3/4 shank collet
chuck. Drill a loose fit hole through the adapter and a press fit hole in
the shank of the collet chuck, and press in a pin. Then it can float anyway
it needs to in order to just follow the hole, and the pin will keep it from
rotating with the part. The ER collets would be able to hold a wide range
of shank sizes. I was think ER25 or maybe ER32.

Stupid idea? Better cheaper way to do it? I don't know.

Reading some in the old text books may give you some guidance. Like
this one which has a chapter on Floating Reamer Holders:

https://archive.org/details/toolschu...wdrich/page/58

--
Leon Fisk
Grand Rapids MI

"Leon Fisk" wrote in message ...

On Tue, 28 May 2019 15:16:59 -0700
"Bob La Londe" wrote:

I've found that for small chucking reamers they tend to flex enough that
any
tiny misalignment doesn't matter, but for larger ones it results in a very
small oversize in the reamed hole. Gunsmith's deal with this by using a
floating reamer holder. I was thinking of making something similar for any
old size chucking reamer.

I was thinking the base of the tool would be a straight shank ER collet
chuck and an MT extension. For my 1440 lathe something like an MT4-MT2
extension adapter bored out for a sloppy lose fit with a 3/4 shank collet
chuck. Drill a loose fit hole through the adapter and a press fit hole in
the shank of the collet chuck, and press in a pin. Then it can float
anyway
it needs to in order to just follow the hole, and the pin will keep it from
rotating with the part. The ER collets would be able to hold a wide range
of shank sizes. I was think ER25 or maybe ER32.

Stupid idea? Better cheaper way to do it? I don't know.

Reading some in the old text books may give you some guidance. Like
this one which has a chapter on Floating Reamer Holders:

https://archive.org/details/toolschu...wdrich/page/58

*********

Great reference and it quickly addressed a couple of my concerns. My simple
design is basically the second diagram they show.