Subject: Half-Reamer, Info Needed!

From: [email-masked] (P.Feist)
Date: Thu, 19 Sep 1996 10:30:55 -0700

Hi; 

   I'm looking for information on how to make a "Half-Reamer". A
Half-Reamer is a reamer (naturally..) that is made with only one "Flute".
It is simply a cylinder of the appropriate taper or shape with half of its
diameter removed to provide a cutting edge.
   I had a chance to examine a half reamer several years ago, but didn't
have any background on cutting tool geometry, releif angles, etc. Now that
I do, I don't know how the thing was relieved to cut!
   BTW, Machinery's Handbook doesn't even mention this type of reamer.
   I need to make a cheap, easy rifle chambering reamer for a one-off
project, and thought this might be the way to go.
   Any information or *references* would be greatly appreciated, with
profuse thanks!

Regards
Paul Feist
Paladin Gun Repair
[email-masked]

---

From: Charles Lamont <[email-masked]>
Date: Fri, 20 Sep 1996 00:35:52 +0100

P.Feist writes
>I do, I don't know how the thing was relieved to cut!

I know this as a 'D-bit'.

It is, as you say, semicircular in cross-section.  The business end has
about 5 degrees front and side clearance.  There is no rake or relief,
but it still cuts - after a fashion. 
-- 
Charles

---

From: Henry Kratt <[email-masked]>
Date: Sun, 22 Sep 1996 19:31:41 -0700

Charles Lamont wrote:
> >have any background on cutting tool geometry, relief angles, etc. Now that
> >I do, I don't know how the thing was relieved to cut

The cutting is done on the front end of the reamer.  No cutting is done 
on the side as in a typical reamer or end mill.  

I use drill blanks/reamer blanks of HSS to make these, if they are the 
exact diameter needed, and grind away a fourth to half inch of the bit 
keeping the grinding above centerline.  For small reamers, say up to 1/4" 
the ground away part is .003 to .005 above center and up to .010 for a 
1/2" bit.  Opinion seems to vary on the ammount to be left above the 
centerline.  

Drill a relief hole .015 to .020 undersized. Then bore a hole the exact 
size needed for a short distance to lead the D-bit into the work.  then 
withdraw the bit at frequent intervals to get rid of the shavings.  

henry