I've never worked with these, but accumulated a few i anticipation of 
doing so. I liked the simplicity of them, and their reputation for 
flexibility in use. Over the past few days I've managed a bit of cave 
time, and am rehabbing, sharpening and right-sizing some as per Paul 
Hasluck's Handyman's Book. I found Dunbar of little help, and Lee 
doesn't seem to mention them.

I've made some progress, getting some of the larger bits cutting nice 
clean holes, and adjusting their sizes a little, but the holes they're 
producing aren't flat-bottomed. They have shallow domes in the center. 
This doesn't seem critical at the moment, as I can always pare or rout 
the bottoms if need be, but I was wondering if I should aim for 
flat-bottom holes?  I'm thinking that can be achieved by filing the 
'horizontal' cutter or router edge furthest from the center, to bring 
the edge nearer to square with the center of rotation. Most of them seem 
to droop or angle downwards.

Also I'm wondering about the bevel angle for the upper surface of the 
router. Does30 degrees sound good?

Finally, some of the horizontal cutters have a back bevel, sometimes 
quite large, and it seems to me this is just wrong, because it will 
reduce clearance there. Should I aim to eliminate it completely?

Any comments or advice on any of these points would be welcome. I'm 
hesitant to tackle the smaller bits until I understand these bits 
better, as there's more room for error on the big ones...

Don

Don

If you look at the construction of the bits, the horizontal cutters are
typically angled to begin with to provide as much sharpening edge as possible
and as much support as possible. This does produce the slight dome and that’s
normal. You can also find some that will cut a flat surface but they were made
for that purpose.

The skew cuts across the grain more efficiently and that’s the reason for the
shallow added angle. You do have the option of sharpening to reduce the skew but
that will increase the force needed during drilling if you’re using a wood
framed bit brace.

I’ve read different numbers on angles, which I believe has more to do with the
type of wood being bored than with any rule as well as, again, whether you are
using a wood framed brace or a metal framed brace. Shallow angle for wood framed
and a slightly more aggressive for a metal frame. But still, these are fairly
delicate bits so in general, look at the existing angle of the cutter and just
sharpen the edge only as much as is needed, forgetting about angles.

Gary
...............................
Gary Roberts
http://toolemera.com
http://toolemerabooks.com

"I'ld rather read a good book, than write a poor one." Christopher Morley




On Apr 23, 2014, at 3:31 PM, Don Schwartz  wrote:
> 
> I've made some progress, getting some of the larger bits cutting nice clean
holes, and adjusting their sizes a little, but the holes they're producing
aren't flat-bottomed. They have shallow domes in the center. This doesn't seem
critical at the moment, as I can always pare or rout the bottoms if need be, but
I was wondering if I should aim for flat-bottom holes?  I'm thinking that can be
achieved by filing the 'horizontal' cutter or router edge furthest from the
center, to bring the edge nearer to square with the center of rotation. Most of
them seem to droop or angle downwards.
> 
> Also I'm wondering about the bevel angle for the upper surface of the router.
Does30 degrees sound good?
> 
> Finally, some of the horizontal cutters have a back bevel, sometimes quite
large, and it seems to me this is just wrong, because it will reduce clearance
there. Should I aim to eliminate it completely?

On 4/23/2014 3:31 PM, Don Schwartz wrote:
>
 > I've never worked with these, but accumulated a few i anticipation of
 > doing so. I liked the simplicity of them, and their reputation for
 > flexibility in use. Over the past few days I've managed a bit of cave
 > time, and am rehabbing, sharpening and right-sizing some
 >
 > Any comments or advice on any of these points would be welcome. I'm
 > hesitant to tackle the smaller bits until I understand these bits
 > better, as there's more room for error on the big ones...
 >

Not sure about actual advice... I have a bunch of centre bits and I
do use them from time to time.  Of note are a part box of NOS
Marples 5/8 inch centre bits I picked up at one of the Tools Of
The Trade sales.  If you want pictures of a bit that has never
seen wood I can try taking a few.

Is GIC back up yet?

-- 
Darrell LaRue
Oakville ON
Wood Hoarder, Blade Sharpener, and Occasional Tool User

On 4/25/2014 8:40 AM, Darrell & Kathy wrote:
> On 4/23/2014 3:31 PM, Don  Schwartz wrote:
 >>
 >> I've never worked with these, but accumulated a few i anticipation
 >> of doing so. I liked the simplicity of them, and their reputation
 >> for flexibility in use. Over the past few days I've managed a bit
 >> of cave time, and am rehabbing, sharpening and right-sizing some

OK, so GIC seems to be up again (thanks!) but kinda slow in
responding.  Here are a few pix of my centre bits.
Turns out I mis-remembered regarding these.  I seem to
have a set of NOS Marples bits here.  1/2 to 1 inch in eighths.
I thought I had just some 5/8 NOS and a random assortment
of other bits making up the set.  Nope, it looks better than that!
You can still see the purple tempering colours on some of them.
Also see the file marks where they were sharpened.

http://galootcentral.com/components/cpgalbums/userpics/10074/100_5106.J
PG">http://galootcentral.com/components/cpgalbums/userpics/10074/100_5106.JPG
http://galootcentral.com/components/cpgalbums/userpics/10074/100_5105.J
PG">http://galootcentral.com/components/cpgalbums/userpics/10074/100_5105.JPG
http://galootcentral.com/components/cpgalbums/userpics/10074/100_5104.J
PG">http://galootcentral.com/components/cpgalbums/userpics/10074/100_5104.JPG

-- 
Darrell LaRue
Oakville ON
Wood Hoarder, Blade Sharpener, and Occasional Tool User

I have used center bits on occasion, and have more than a couple
sets worth.  Just got another, in fact. The ones I have range from
1/4 tp 1 1/2 inches.

They were reinvented around the '60s as "high speed bits" for
electric drills, incidentally.

I find them very useful.  I'm glad I didn't read about their use
before working with them.  One pundit assured his readers that
center bits don't work in end grain.  They do, exceptionally well.
One of my favorite uses for them is drilling out broken dowels in
old furniture when making repairs.  They're my first choice for
this job.

Peugeot hand tools was still making center bits (metric) in the
1980s.

Mike in Sacto