Hi fellow home shop machinists,
Can somebody please refer me to a link on how to accurately grind 60
degree lathe bits. Consistancy is what I'm looking for. I need to
grind several single cut threading bits from blanks.

I currently hand grind. Now that I have a hand held microscope, I now
know that my points are not true 60 degrees when matched to a fish
tail guage.

I'm not threading for aerospace, but would like to acheive a perfect
60 degree point if possible.

Thank you in advance,

Rod
San Francisco

On Nov 21, 8:23*am, rodjava wrote:
Hi fellow home shop machinists,
Can somebody please refer me to a link on how to accurately grind 60
degree lathe bits. *Consistancy is what I'm looking for. *I need to
grind several single cut threading bits from blanks.

I currently hand grind. Now that I have a hand held microscope, I now
know that my points are not true 60 degrees when matched to a fish
tail guage.

I'm not threading for aerospace, but would like to acheive a perfect
60 degree point if possible.

Thank you in advance,

Rod
San Francisco

I forgot to mention that I'm using a standard pedastal grinder.

Rod
San Francisco

rodjava wrote:

Hi fellow home shop machinists,
Can somebody please refer me to a link on how to accurately grind 60
degree lathe bits. Consistancy is what I'm looking for. I need to
grind several single cut threading bits from blanks.

I currently hand grind. Now that I have a hand held microscope, I now
know that my points are not true 60 degrees when matched to a fish
tail guage.

I'm not threading for aerospace, but would like to acheive a perfect
60 degree point if possible.

Thank you in advance,

Rod
San Francisco

I'd make a simple jig to hold the bit at 60°.

--
Paul Hovnanian
-----------------------------------------------------------------------
Have gnu, will travel.

On Fri, 21 Nov 2008 08:25:45 -0800 (PST), rodjava
wrote:

On Nov 21, 8:23Â*am, rodjava wrote:
Hi fellow home shop machinists,
Can somebody please refer me to a link on how to accurately grind 60
degree lathe bits. Â*Consistancy is what I'm looking for. Â*I need to
grind several single cut threading bits from blanks.

I currently hand grind. Now that I have a hand held microscope, I now
know that my points are not true 60 degrees when matched to a fish
tail guage.

I'm not threading for aerospace, but would like to acheive a perfect
60 degree point if possible.

Thank you in advance,

Rod
San Francisco

I forgot to mention that I'm using a standard pedastal grinder.

Rod
San Francisco


Look up "center gage".

"L.S. STARRETT" SPRING STEEL CENTER GAUGES

Extremely handy for use in grinding and setting screw cutting
tools. Has a table of double depths of threads for determining size of
tap drills. Made of spring-tempered steel with satin chrome finish.
Gaging surfaces ground. Number of threads per inch scale. American
Unified National Standard, 60°

Cheers,

Bruce
(bruceinbangkokatgmaildotcom)

On Nov 21, 11:50*am, Bruce in Bangkok
wrote:
....

I never studied solid geometry. In an angle fixture, if I rotate the
bit say 5 degrees for side relief, how do I refigure the 30 degree end
angle?

On Nov 21, 8:50*am, Bruce in Bangkok
wrote:
On Fri, 21 Nov 2008 08:25:45 -0800 (PST), rodjava





wrote:
On Nov 21, 8:23*am, rodjava wrote:
Hi fellow home shop machinists,
Can somebody please refer me to a link on how to accurately grind 60
degree lathe bits. *Consistancy is what I'm looking for. *I need to
grind several single cut threading bits from blanks.

I currently hand grind. Now that I have a hand held microscope, I now
know that my points are not true 60 degrees when matched to a fish
tail guage.

I'm not threading for aerospace, but would like to acheive a perfect
60 degree point if possible.

Thank you in advance,

Rod
San Francisco

I forgot to mention that I'm using a standard pedastal grinder.

Rod
San Francisco

Look up "center gage".

"L.S. STARRETT" SPRING STEEL CENTER GAUGES

* * Extremely handy for use in grinding and setting screw cutting
tools. Has a table of double depths of threads for determining size of
tap drills. Made of spring-tempered steel with satin chrome finish.
Gaging surfaces ground. Number of threads per inch scale. American
Unified National Standard, 60°

Cheers,

Bruce
(bruceinbangkokatgmaildotcom)- Hide quoted text -

- Show quoted text -

Bruce,
I use a center guage aka fishtail.
Thanks for the suggestion anyway.

Rod
San Francisco

On Nov 21, 9:02*am, rodjava wrote:
On Nov 21, 8:50*am, Bruce in Bangkok
wrote:



On Fri, 21 Nov 2008 08:25:45 -0800 (PST), rodjava

wrote:
On Nov 21, 8:23*am, rodjava wrote:
Hi fellow home shop machinists,
Can somebody please refer me to a link on how to accurately grind 60
degree lathe bits. *Consistancy is what I'm looking for. *I need to
grind several single cut threading bits from blanks.

I currently hand grind. Now that I have a hand held microscope, I now
know that my points are not true 60 degrees when matched to a fish
tail guage.

I'm not threading for aerospace, but would like to acheive a perfect
60 degree point if possible.

Thank you in advance,

Rod
San Francisco

I forgot to mention that I'm using a standard pedastal grinder.

Rod
San Francisco

Look up "center gage".

"L.S. STARRETT" SPRING STEEL CENTER GAUGES

* * Extremely handy for use in grinding and setting screw cutting
tools. Has a table of double depths of threads for determining size of
tap drills. Made of spring-tempered steel with satin chrome finish.
Gaging surfaces ground. Number of threads per inch scale. American
Unified National Standard, 60°

Cheers,

Bruce
(bruceinbangkokatgmaildotcom)- Hide quoted text -

- Show quoted text -

Bruce,
I use a center guage aka fishtail.
Thanks for the suggestion anyway.

Rod
San Francisco

Many (most?) machinists' use the centre gauge and hand-grind the tool
to this gauge. Tedious. But practice makes perfect, or at least
better.

Next step up would be a bench grinder with adjustable table and
fences. Some are advertised in Home Shop Machinist. Or roll your own
as they say. An acquaintance of mine built such a device using a pool
pump motor and a 5" dia. cup wheel.

The cat's meow is a tool and cutter grinder, commercial or home-made.
With this you can make perfectly good AND bad tools under perfect
control:-))

I have a Quorn T&C grinder that I finished from someone's start. It
is overkill for lathe & shaper tools, but most versatile for all sorts
of cutter sharpening.

An alternative would be to look for a single lip cutter grinder such
as made by DECKEL. These are designed to grind from solid single lip
engraving cutters, and to sharpen them. It is quite easy to adapt one
of these to grind lathe tool bits, not only for threading, but also
parting blades with proper relief, grooving tools for Circlips and
Orings, etc. and accurate angles on turning tools for difficult-to-
machine materials.

These grinders are sometimes advertised on Ebay, Kijiji, or Craig's
List. Prices vary up to $2000 or so, but in this economic climate I'd
offer $500 for one in good shape and complete.

Let us know what you decide and how you make out.

Wolfgang

rodjava writes:

Can somebody please refer me to a link on how to accurately grind 60
degree lathe bits.

Part of the problem is that the angle you're grinding is a compound miter.
You don't grind a 60 degree angle to get a 60 degree cutter when a
clearance angle is involved. Perhaps someone has algebraic formulas to
compute this, but I am lazy and just model the tool shape and let the CAD
software solve numerically:

http://www.truetex.com/tool_grinding.pdf

In this example, for a minus 10 degree clearance angle, to get a 60 degree
cutter, you actually grind a 62.95 degree angle.

On Nov 21, 11:04*am, Richard J Kinch wrote:
rodjava writes:
Can somebody please refer me to a link on how to accurately grind 60
degree lathe bits.

Part of the problem is that the angle you're grinding is a compound miter..
You don't grind a 60 degree angle to get a 60 degree cutter when a
clearance angle is involved. *Perhaps someone has algebraic formulas to
compute this, but I am lazy and just model the tool shape and let the CAD
software solve numerically:

*http://www.truetex.com/tool_grinding.pdf

In this example, for a minus 10 degree clearance angle, to get a 60 degree
cutter, you actually grind a 62.95 degree angle.


Indeed, to machine grind a threading tool you have to know the
compound angles to use on the various angle scales of the grinder:-))

To hand-grind proceed as follows:

1) on a blank toolbit grind the front relief angle; make this 12
degrees or so from the vertical if the tool holder holds the tool
horizontally. Use an adjustable protractor for this.

2) blue this ground surface (the relief angle) and scribe a vertical
line in the middle. Mark the 60 degree angle on top.

3) now grind the LHS surface (flank) of the threading tip so that the
ground surface front edge forms a line parallel to the line scribed on
the front relief. Carry on grinding until the LHS approaches the
scribed line on the front. During this operation use a protractor to
ensure that this second surface forms a 30 degree angle with the LHS
vertical surface (long edge) of the tool bit.

4) now grind the RHS flank the same way, using the centre gauge to
check the 60 degree thread angle, while ensuring that the front edge
meets the edge of the LHS flank. Keep the centre gauge parallel to
the top of the tool bit during this check.

5) use a hand stone to put a small flat at the tip of the tool. For
exact work the width of this flat should be 1/8 of the thread pitch.

6) for cutting brass, cast iron, leaded cold rolled, C1144 aka
stressproof, no rake angle is required. For machine and tool steel an
8 degree or so rake angle helps a lot. This angle should be ground so
that it runs back at right angles from the LHS flank without affecting
the elevation or horizontality of this LHS top edge. (It's easier to
show than explain).

Doing it this way ensures a side relief angle without having to
measure it. This tool is suitable for cutting a single start right
hand thread.

Wolfgang

On Nov 21, 11:44*am, wrote:
On Nov 21, 11:04*am, Richard J Kinch wrote:

rodjava writes:
Can somebody please refer me to a link on how to accurately grind 60
degree lathe bits.

Part of the problem is that the angle you're grinding is a compound miter.
You don't grind a 60 degree angle to get a 60 degree cutter when a
clearance angle is involved. *Perhaps someone has algebraic formulas to
compute this, but I am lazy and just model the tool shape and let the CAD
software solve numerically:

*http://www.truetex.com/tool_grinding.pdf

In this example, for a minus 10 degree clearance angle, to get a 60 degree
cutter, you actually grind a 62.95 degree angle.

Indeed, to machine grind a threading tool you have to know the
compound angles to use on the various angle scales of the grinder:-))

To hand-grind proceed as follows:

1) on a blank toolbit grind the front relief angle; *make this 12
degrees or so from the vertical if the tool holder holds the tool
horizontally. *Use an adjustable protractor for this.

2) blue this ground surface (the relief angle) and scribe a vertical
line in the middle. *Mark the 60 degree angle on top.

3) now grind the LHS surface (flank) of the threading tip so that the
ground surface front edge forms a line parallel to the line scribed on
the front relief. *Carry on grinding until the LHS *approaches the
scribed line on the front. *During this operation use a protractor to
ensure that this second surface forms a 30 degree angle with the LHS
vertical surface (long edge) of the tool bit.

4) now grind the RHS flank the same way, using the centre gauge to
check the 60 degree thread angle, while ensuring that the front edge
meets the edge of the LHS flank. *Keep the centre gauge parallel to
the top of the tool bit during this check.

5) use a hand stone to put a small flat at the tip of the tool. *For
exact work the width of this flat should be 1/8 of the thread pitch.

6) for cutting brass, cast iron, leaded cold rolled, C1144 aka
stressproof, no rake angle is required. *For machine and tool steel an
8 degree or so rake angle helps a lot. *This angle should be ground so
that it runs back at right angles from the LHS flank without affecting
the elevation or horizontality of this LHS top edge. *(It's easier to
show than explain).

Doing it this way ensures a side relief angle without having to
measure it. *This tool is suitable for cutting a single start right
hand thread.

Wolfgang

Wolfgan,
I can't thank you enough for your detailed and well thought out
instructions.

The miter calculations for clearance angles in the pdf file is very
helpful too.

Thank you
Rod
San Francisco

On Nov 21, 11:44*am, wrote:
On Nov 21, 11:04*am, Richard J Kinch wrote:

rodjava writes:
Can somebody please refer me to a link on how to accurately grind 60
degree lathe bits.

Part of the problem is that the angle you're grinding is a compound miter.
You don't grind a 60 degree angle to get a 60 degree cutter when a
clearance angle is involved. *Perhaps someone has algebraic formulas to
compute this, but I am lazy and just model the tool shape and let the CAD
software solve numerically:

*http://www.truetex.com/tool_grinding.pdf

In this example, for a minus 10 degree clearance angle, to get a 60 degree
cutter, you actually grind a 62.95 degree angle.

Indeed, to machine grind a threading tool you have to know the
compound angles to use on the various angle scales of the grinder:-))

To hand-grind proceed as follows:

1) on a blank toolbit grind the front relief angle; *make this 12
degrees or so from the vertical if the tool holder holds the tool
horizontally. *Use an adjustable protractor for this.

2) blue this ground surface (the relief angle) and scribe a vertical
line in the middle. *Mark the 60 degree angle on top.

3) now grind the LHS surface (flank) of the threading tip so that the
ground surface front edge forms a line parallel to the line scribed on
the front relief. *Carry on grinding until the LHS *approaches the
scribed line on the front. *During this operation use a protractor to
ensure that this second surface forms a 30 degree angle with the LHS
vertical surface (long edge) of the tool bit.

4) now grind the RHS flank the same way, using the centre gauge to
check the 60 degree thread angle, while ensuring that the front edge
meets the edge of the LHS flank. *Keep the centre gauge parallel to
the top of the tool bit during this check.

5) use a hand stone to put a small flat at the tip of the tool. *For
exact work the width of this flat should be 1/8 of the thread pitch.

6) for cutting brass, cast iron, leaded cold rolled, C1144 aka
stressproof, no rake angle is required. *For machine and tool steel an
8 degree or so rake angle helps a lot. *This angle should be ground so
that it runs back at right angles from the LHS flank without affecting
the elevation or horizontality of this LHS top edge. *(It's easier to
show than explain).

Doing it this way ensures a side relief angle without having to
measure it. *This tool is suitable for cutting a single start right
hand thread.

Wolfgang

Richard,
I would like to thank you for the tool grinding pdf. I mistakenly gave
thanks to Wolfgang for this file.
The geomotry is very helfful.
Thank you.

Rod
San Francisco

On Nov 21, 2:04*pm, Richard J Kinch wrote:
...
*http://www.truetex.com/tool_grinding.pdf

In this example, for a minus 10 degree clearance angle, to get a 60 degree
cutter, you actually grind a 62.95 degree angle.

Thanks, that is what I was looking for, 10 and 63 degrees.

On Fri, 21 Nov 2008 08:58:06 -0800 (PST), Jim Wilkins
wrote:

On Nov 21, 11:50Â*am, Bruce in Bangkok
wrote:
...

I never studied solid geometry. In an angle fixture, if I rotate the
bit say 5 degrees for side relief, how do I refigure the 30 degree end
angle?

Not sure what you are asking but the usual procedure for cutting
threads is to grind a tool bit to a 60 deg. point with normal side and
end relief. If you want side rake then grind it as once the sides are
ground changing the top surface doesn't change the side angles.

The tool is then set with the center line of the tool at right angles
to the surface being threaded. The compound is set to 30 deg., or very
slightly less.

Using the cross feed the tool is advanced until the tip of the bit
just touches the work. Either a threading stop is then set or, more
usually, the cross feed dial is set to zero.

Feeding the tool into the work is then done by use of the compound
while the cross feed is used only to retract the tool between cuts.
The zero setting on the cross feed dial, or the threading stop, makes
it easy to return to your base setting.

As tool feed is done at 30 deg. to the work surface it means that the
threading tool cuts only on the forward edge resulting in a smoother
cut.

Setting the compound to slightly less then 30 deg. means that as the
tool is advanced by the compound the path is not exactly parallel to
the rear edge of the tool resulting in a very light, scraping, cut
being taken by the rear edge of the tool bit. Some argue that it
results in a smoother thread.
Cheers,

Bruce
(bruceinbangkokatgmaildotcom)

On Fri, 21 Nov 2008 13:04:13 -0600, Richard J Kinch
wrote:

rodjava writes:

Can somebody please refer me to a link on how to accurately grind 60
degree lathe bits.

Part of the problem is that the angle you're grinding is a compound miter.
You don't grind a 60 degree angle to get a 60 degree cutter when a
clearance angle is involved. Perhaps someone has algebraic formulas to
compute this, but I am lazy and just model the tool shape and let the CAD
software solve numerically:

http://www.truetex.com/tool_grinding.pdf

In this example, for a minus 10 degree clearance angle, to get a 60 degree
cutter, you actually grind a 62.95 degree angle.


Yes you do. The tool is set horizontal, i.e., parallel with a line
drawn across the ways. No back rake is normally used. Top rake is
usually not used.

Having said that if very large threads are cut one might grind a
roughing tool with top relief and rough the thread nearly to depth and
then set a finish tool to cut the last few 1/1000's but it is not
usually done.

Cheers,

Bruce
(bruceinbangkokatgmaildotcom)

"Bruce in Bangkok" wrote in message
...
On Fri, 21 Nov 2008 08:58:06 -0800 (PST), Jim Wilkins
wrote:

On Nov 21, 11:50 am, Bruce in Bangkok
wrote:
...

I never studied solid geometry. In an angle fixture, if I rotate the
bit say 5 degrees for side relief, how do I refigure the 30 degree end
angle?

Not sure what you are asking but the usual procedure for cutting
threads is to grind a tool bit to a 60 deg. point with normal side and
end relief. If you want side rake then grind it as once the sides are
ground changing the top surface doesn't change the side angles.

Sorry, that's not true. As you move the edge away from center, it most
certainly does change the angle.

Worst thing is it also eliminates the tool from cutting on the back side,
which is a vital function performed by threading tools. That's the reason it
is fed at less than half the thread angle, and not at half angle as you
suggested.

Threading tools should not be ground with rake unless calculations are
introduced to compensate for the change in angle. It is minor, but it does
exist. Remember, too, that rake eliminates the ability of the tool to take
a full cut, which is very desirable when cleaning up a thread as it nears
size.

Harold

matthew maguire writes:

Try to section "parallel" to the tool top and see if the result changes.

Compound miters with two degrees of freedom are tricky. Hard to argue with
CAD models that give correct results. The -10 degrees must be measured
normal to the resulting cutting edge axis. Maybe your assumptions are
different.

Jim Wilkins wrote:
On Nov 21, 11:50 am, Bruce in Bangkok
wrote:
...

I never studied solid geometry. In an angle fixture, if I rotate the
bit say 5 degrees for side relief, how do I refigure the 30 degree end
angle?

Hi Jim

Compound angles are calculated thus;
Primary angle = arctan(tan A x cos B)
Clearance angle = arctan(sin A x sin B)

The formula will give you the "RESULT" of a secondary angle being
introduced. So...

If you set your vice to 30 (60 degrees included) primary angle "A" and
then adjust for 10 degrees clearance "B" the result would be
(arctan(tan(30) x cos(10)) = 29.621 degrees primary angle or about .756
(.378 x 2) degrees short of the 60 you need.

If your "laying out" a tool to grind offhand, then just lay out the 60
and set the table for clearance and grind to the layout line.

Matt

Richard J Kinch wrote:


http://www.truetex.com/tool_grinding.pdf

In this example, for a minus 10 degree clearance angle, to get a 60 degree
cutter, you actually grind a 62.95 degree angle.

Hi Richard,

I looked at your PDF forever trying to figure out why you show 20
degrees total clearance against a 60 angle needing 3 more degrees and I
come up with about half that....

Try to section "parallel" to the tool top and see if the result changes.
This is just confusing the heck out of me....

On Sun, 23 Nov 2008 01:06:04 -0600, Richard J Kinch wrote:

matthew maguire writes:

Try to section "parallel" to the tool top and see if the result changes.

Compound miters with two degrees of freedom are tricky. Hard to argue with
CAD models that give correct results. The -10 degrees must be measured
normal to the resulting cutting edge axis. Maybe your assumptions are
different.


No use to the OP, but the way I do it is to set the bit to the correct half
angle from horizontal in the vice (30deg in this instance). then tilt the vice
to give the clearance angle. Then grind on the surface grinder. Since the vice
is being rotated about the same axis as the 30deg angle, the two settings are
completely independent. As I said, no help with a bench grinder, but trivial
on a surface grinder or T&C grinder.

Addendum:- Make a side table with guide rail for the bench grinder and the use
a cup wheel. Then the correct angles can be generated with ease.


Mark Rand
RTFM

Mark Rand writes:

No use to the OP, but the way I do it is to set the bit to the correct
half angle from horizontal in the vice (30deg in this instance). then
tilt the vice to give the clearance angle.

I guess that depends on what coordinate system "set the bit" and "tilt the
vise" means. That is, what are the axes of tilt and rotation in relation
to the planes of the table and the grinding surface, and whether these
angles are independent vs compounding. On a Baldor or Chinese tool
grinder:

http://www.harborfreight.com/cpi/cta...emnumber=46727

The table tilt axis is parallel to the plane of the grinding surface, so
the (half) angle on the sliding miter is not the (half) angle ground on the
bit, unless the table tilt is at 0 degrees. The point of my CAD
computation was to solve for the miter angle (62.95 degrees) that yields 60
degrees on the bit when compounded by a -10 degree tilt on the table.

Jim Wilkins wrote:
On Nov 21, 11:50 am, Bruce in Bangkok
wrote:
...

I never studied solid geometry. In an angle fixture, if I rotate the
bit say 5 degrees for side relief, how do I refigure the 30 degree end
angle?
For a nice visual on compensation using compound sine plates look he

http://www.auto-met.com/subtool/stcat/st_137.html

Suburban tool now owns Taft-Pierce metrology div. and has placed their
book of constants used for compound angle solutions (with illustrations)
he

http://www.subtool.com/st/imgs/BookofConstants.pdf

The following is a link if you want to buy software, (I'd use my money
to buy a Machinery's' Handbook).

https://www.penntoolco.com/catalog/p...categoryID=728

If you are looking for accurate thread profiles, then the tool grind is
just one part of it, using the three wire measurement process is easily
done with 2 sets of different diameter wires to determine the angle of
the thread you just cut.

Matt

On Sun, 23 Nov 2008 15:28:53 -0600, Richard J Kinch wrote:

Mark Rand writes:

No use to the OP, but the way I do it is to set the bit to the correct
half angle from horizontal in the vice (30deg in this instance). then
tilt the vice to give the clearance angle.

I guess that depends on what coordinate system "set the bit" and "tilt the
vise" means. That is, what are the axes of tilt and rotation in relation
to the planes of the table and the grinding surface, and whether these
angles are independent vs compounding. On a Baldor or Chinese tool
grinder:

http://www.harborfreight.com/cpi/cta...emnumber=46727

The table tilt axis is parallel to the plane of the grinding surface, so
the (half) angle on the sliding miter is not the (half) angle ground on the
bit, unless the table tilt is at 0 degrees. The point of my CAD
computation was to solve for the miter angle (62.95 degrees) that yields 60
degrees on the bit when compounded by a -10 degree tilt on the table.


Thought experiment for you:-

Set the sliding mitre to 30 degrees and the table to 0 degrees.

Grind the tool

You now have a tool with a 60 degree included angle.

Hold the tool against the sliding mitre and note that the cutting edge of the
tool is parallel to the face of the wheel (It'd better be, you just ground it
:-)


Now tilt the table up and down. Note that the cutting edge remains parallel to
the face of the wheel. Thus the correct angle to set the mitre to is 30 deg
(actually, it'd be 27.5 for a proper thread ;-)

Not too worried about the accuracy of the clearance angle. The included angle
of the thread is the important one!


regards
Mark Rand
RTFM

Mark Rand writes:

Now tilt the table up and down. Note that the cutting edge remains
parallel to the face of the wheel. Thus the correct angle to set the
mitre to is 30 deg

Now I'm confused. I think it depends on whether the miter tilts with the
work versus only the work tilting. Or whether you're north or south of the
equator.

On Wed, 26 Nov 2008 16:54:11 -0600, Richard J Kinch wrote:

Mark Rand writes:

Now tilt the table up and down. Note that the cutting edge remains
parallel to the face of the wheel. Thus the correct angle to set the
mitre to is 30 deg

Now I'm confused. I think it depends on whether the miter tilts with the
work versus only the work tilting. Or whether you're north or south of the
equator.


The mitre tilts with the work. The cutting edge (that you just ground in the
thought experiment) is already parallel with the face of the wheel. When you
tilt it, you are rotating it about an axis parallel to the face of the wheel.
Therefore you aren't changing that particular angle when you tilt the table to
give the relief.

It took me quite a lot of head scratching before I was happy with the concept
for some 29 degree and 40 degree included angle bits for ACME turning and gear
shaping...


regards
Mark Rand (east of the Equator :-)
RTFM

Mark Rand writes:

The mitre tilts with the work. The cutting edge (that you just ground
in the thought experiment) is already parallel with the face of the
wheel.

OK, I agree. I believe my calculation applies to a different case, when
you have a work holder that applies the clearance angle by tilting the work
up, while the miter stays in the horizontal plane perpendicular to the
wheel.

On Nov 26, 7:09*pm, Mark Rand wrote:
...
The mitre tilts with the work. ...
Mark Rand (east of the Equator :-)

I think I follow you. The test I use is to continue the change to an
extreme and see if it still holds true. In this case, tilt the table
almost vertical, so you grind an edge suitable for a wood chisel.

On Wed, 26 Nov 2008 22:44:12 -0600, Richard J Kinch wrote:

Mark Rand writes:

The mitre tilts with the work. The cutting edge (that you just ground
in the thought experiment) is already parallel with the face of the
wheel.

OK, I agree. I believe my calculation applies to a different case, when
you have a work holder that applies the clearance angle by tilting the work
up, while the miter stays in the horizontal plane perpendicular to the
wheel.


Yes, that would be useful for some things (3D mitres?), but a real pain for
tool grinding...


regards
Mark Rand
RTFM