I used to work in a gear shop and had to repair gear shafts that had been
centerdrilled and had more then the .001 runout that the print called for.
I used a steadyrest with ball bearing rollers and that gave me dead true
runout. It is best to collet or chuck on a small part of shaft and let the
steadyrest pull the shaft to dead true. Then I hand ground a 30 degree
angled tool to form one side of the centered part. Imagine half of a
centerdrill without the drill part in front of the angle. If you blue up the
center of the part you can see it cut the high point of the runout till it
is dead on.
Jim

" Jim Sehr" wrote in message
...
I used to work in a gear shop and had to repair gear shafts that had
been
centerdrilled and had more then the .001 runout that the print called
for.
I used a steadyrest with ball bearing rollers and that gave me dead
true
runout. It is best to collet or chuck on a small part of shaft and let
the
steadyrest pull the shaft to dead true. Then I hand ground a 30 degree
angled tool to form one side of the centered part. Imagine half of a
centerdrill without the drill part in front of the angle. If you blue
up the
center of the part you can see it cut the high point of the runout
till it
is dead on.
Jim

I agree with you. Boring with the use of a steady rest is an
intrinsically accurate operation.

On Thu, 8 Jul 2004 20:06:39 -0700, " Jim Sehr"
wrote:

I used to work in a gear shop and had to repair gear shafts that had been
centerdrilled and had more then the .001 runout that the print called for.
I used a steadyrest with ball bearing rollers and that gave me dead true
runout. It is best to collet or chuck on a small part of shaft and let the
steadyrest pull the shaft to dead true. Then I hand ground a 30 degree
angled tool to form one side of the centered part. Imagine half of a
centerdrill without the drill part in front of the angle. If you blue up the
center of the part you can see it cut the high point of the runout till it
is dead on.

In the last year or so we've had to recenter several inspection
arbors. Basically the same, except after putting in the steady rest,
we indicated the compound to 30 deg., then ground with a Precice
grinder, small CBN wheel. Used the normal bronze against the arbor,
gives less runout than BB would.
Lennie the Lurker

How small a centerdrill could you grind?
Jim
wrote in message
...
On Thu, 8 Jul 2004 20:06:39 -0700, " Jim Sehr"
wrote:

I used to work in a gear shop and had to repair gear shafts that had been
centerdrilled and had more then the .001 runout that the print called
for.
I used a steadyrest with ball bearing rollers and that gave me dead true
runout. It is best to collet or chuck on a small part of shaft and let
the
steadyrest pull the shaft to dead true. Then I hand ground a 30 degree
angled tool to form one side of the centered part. Imagine half of a
centerdrill without the drill part in front of the angle. If you blue up
the
center of the part you can see it cut the high point of the runout till
it
is dead on.

In the last year or so we've had to recenter several inspection
arbors. Basically the same, except after putting in the steady rest,
we indicated the compound to 30 deg., then ground with a Precice
grinder, small CBN wheel. Used the normal bronze against the arbor,
gives less runout than BB would.
Lennie the Lurker

Using a 1/8" wheel, the pilot hole was the controling factor. As they
were already in, we could do those with a 5/32" pilot hole without
problems, but have also re-drilled the pilot and reground the entire
center when needed. IT's not an ideal solution, depending on the
condition of the diameter in the steady rest, it may come in to
tolerance, in our case .0002", or it may not. If the arbors were an
off the shelf item, buying new probably would have made more sense.
Some came in to nothing detectable with a .0001" indicator, others
would not come in to less than .001".

I would imagine that using a tiny point, and with enough rpm to turn
it, doing very small centers would be possible, not that I would want
to be the one to do them. PITA as it is.



On Thu, 8 Jul 2004 21:36:44 -0700, " Jim Sehr"
wrote:

How small a centerdrill could you grind?
Jim
wrote in message
.. .
On Thu, 8 Jul 2004 20:06:39 -0700, " Jim Sehr"
wrote:

I used to work in a gear shop and had to repair gear shafts that had been
centerdrilled and had more then the .001 runout that the print called
for.
I used a steadyrest with ball bearing rollers and that gave me dead true
runout. It is best to collet or chuck on a small part of shaft and let
the
steadyrest pull the shaft to dead true. Then I hand ground a 30 degree
angled tool to form one side of the centered part. Imagine half of a
centerdrill without the drill part in front of the angle. If you blue up
the
center of the part you can see it cut the high point of the runout till
it
is dead on.

In the last year or so we've had to recenter several inspection
arbors. Basically the same, except after putting in the steady rest,
we indicated the compound to 30 deg., then ground with a Precice
grinder, small CBN wheel. Used the normal bronze against the arbor,
gives less runout than BB would.
Lennie the Lurker


Lennie the Lurker

In manufacturing they use a center hole grinder, lots of different
models available, here is one I found on a search
http://www.machineryvalues.com/xdetails.cfm/QN/126727
Not overly complex, usually a dead center, steady rest and a cone wheel
grinding wheel. But if refurbishing a center in a shop the above
practice is the way to go.
I the last shop I was in we had a lot of arbors for grinding Turbine
Disc Blades. The arbors were 4140 but we installed hardened bushings in
the ends of the arbors and then bored the angles and used carbide tipped
centers on the grinders. The bushings were fixture parts from Carr-Lane
(cone locator bushings)
http://www.carrlane.com/Catalog/inde...3C3B285356415E

wrote:
Using a 1/8" wheel, the pilot hole was the controling factor. As they
were already in, we could do those with a 5/32" pilot hole without
problems, but have also re-drilled the pilot and reground the entire
center when needed. IT's not an ideal solution, depending on the
condition of the diameter in the steady rest, it may come in to
tolerance, in our case .0002", or it may not. If the arbors were an
off the shelf item, buying new probably would have made more sense.
Some came in to nothing detectable with a .0001" indicator, others
would not come in to less than .001".

I would imagine that using a tiny point, and with enough rpm to turn
it, doing very small centers would be possible, not that I would want
to be the one to do them. PITA as it is.



On Thu, 8 Jul 2004 21:36:44 -0700, " Jim Sehr"
wrote:


How small a centerdrill could you grind?
Jim
wrote in message
. ..

On Thu, 8 Jul 2004 20:06:39 -0700, " Jim Sehr"
wrote:


I used to work in a gear shop and had to repair gear shafts that had been
centerdrilled and had more then the .001 runout that the print called

for.

I used a steadyrest with ball bearing rollers and that gave me dead true
runout. It is best to collet or chuck on a small part of shaft and let

the

steadyrest pull the shaft to dead true. Then I hand ground a 30 degree
angled tool to form one side of the centered part. Imagine half of a
centerdrill without the drill part in front of the angle. If you blue up

the

center of the part you can see it cut the high point of the runout till

it

is dead on.

In the last year or so we've had to recenter several inspection
arbors. Basically the same, except after putting in the steady rest,
we indicated the compound to 30 deg., then ground with a Precice
grinder, small CBN wheel. Used the normal bronze against the arbor,
gives less runout than BB would.
Lennie the Lurker


Lennie the Lurker

--
James P Crombie
Slemon Park, PEI
Canada
Machinist - 3D Cad Design - Amateur Astronomer

http://www.jamescrombie.com

On Fri, 09 Jul 2004 12:18:15 -0300, Machineman
wrote:

In manufacturing they use a center hole grinder, lots of different
models available, here is one I found on a search
http://www.machineryvalues.com/xdetails.cfm/QN/126727
Not overly complex, usually a dead center, steady rest and a cone wheel
grinding wheel. But if refurbishing a center in a shop the above
practice is the way to go.

Time for some massive snippage her

The machine shown, I've seen them in Case, is more used in a
production setting, used between heat treating and the final grind
ops. More to take care of any nicks or dings and any possible
distortion that happend in heat treating. (The V block and destaco
clamp sorta give this away.) Beyond that point, concentricity is held
from the center, which for production is probably the only practical
way. I picked up the "steady rest and tool post grinder" method from
watching the machinists regrind centers on some very expensive splined
inspection arbors. These arbors were all made with a stub on the end,
hardened and ground, which I assume was ground to be concentric with
the spline PD and the center from which the spline had been cut.

I would have loved to see how they set up the hobber to make these
arbors, .004" taper over 12" of length, probably some tolerance on the
PD, but almost nothing for helix. I assume there was some grinding of
the spline after HT, but have no idea of how that would have been
done, don't think I want to, either.
Lennie the Lurker