1750 RPM Grinder & Chisel Sharpening
 

I need to get the initial edge on new chisels (the "hollow grind").
Everything I've read says to use a slow speed grinder with aluminum
oxide wheels to prevent overheating of the steel (which ruins the
chisel).

I've been told that the grinder should not exceed about 1200 RPM. One
local woodworker actually keeps a cup of water next to his slow speed
super expensive Baldor grinder. He grinds for about 5 seconds, dips the
chisel in the water to cool it, and repeats the process.

I currently have an $70 Delta 1750 RPM grinder. I can get aluminum
oxide wheels for it, too. How risky is it to use it?

I'll have the cup of water to prevent overheating.....

Never Enough Money wrote:
I need to get the initial edge on new chisels (the "hollow grind").
Everything I've read says to use a slow speed grinder with aluminum
oxide wheels to prevent overheating of the steel (which ruins the
chisel).

I've been told that the grinder should not exceed about 1200 RPM. One
local woodworker actually keeps a cup of water next to his slow speed
super expensive Baldor grinder. He grinds for about 5 seconds, dips the
chisel in the water to cool it, and repeats the process.

I currently have an $70 Delta 1750 RPM grinder. I can get aluminum
oxide wheels for it, too. How risky is it to use it?

I'll have the cup of water to prevent overheating.....

1750 RPM is fine. Just take it easy, if you take a light enough cut
(with some practice) you wont even need the water. Remember a light touch.

Never Enough Money wrote:
I need to get the initial edge on new chisels (the "hollow grind").
Everything I've read says to use a slow speed grinder with aluminum
oxide wheels to prevent overheating of the steel (which ruins the
chisel).

snip

That's why I use one of those 1"x40" sanding belts.

Does a great job for this application.

Lew

I use a 1750 grinder with all my lathe tools. As long as you can keep the
bevel right it will work great. Using water is helpful but the whole process
shouldn't take but a few seconds.

Tim


"Never Enough Money" wrote in message
ups.com...
I need to get the initial edge on new chisels (the "hollow grind").
Everything I've read says to use a slow speed grinder with aluminum
oxide wheels to prevent overheating of the steel (which ruins the
chisel).

I've been told that the grinder should not exceed about 1200 RPM. One
local woodworker actually keeps a cup of water next to his slow speed
super expensive Baldor grinder. He grinds for about 5 seconds, dips the
chisel in the water to cool it, and repeats the process.

I currently have an $70 Delta 1750 RPM grinder. I can get aluminum
oxide wheels for it, too. How risky is it to use it?

I'll have the cup of water to prevent overheating.....

I thought a belt made a flat surface. The diameter of a wheel gives the
"hollow grind" which makes subsequent sharpening much faster.

I also have a 1" x40" belt but didn't think it would be better than a
grinder. Am I wrong?

Never Enough Money wrote:
I thought a belt made a flat surface. The diameter of a wheel gives the
"hollow grind" which makes subsequent sharpening much faster.

I also have a 1" x40" belt but didn't think it would be better than a
grinder. Am I wrong?


Never gave it a thought.

I use it to quickly sharpen things like scissors, scrapers, construction
chisels, etc.

HTH

Lew

I have been doing it for years. Never used a slow speed job. Pay attention
and there is no problem.

"Never Enough Money" wrote in message
ups.com...
I need to get the initial edge on new chisels (the "hollow grind").
Everything I've read says to use a slow speed grinder with aluminum
oxide wheels to prevent overheating of the steel (which ruins the
chisel).

I've been told that the grinder should not exceed about 1200 RPM. One
local woodworker actually keeps a cup of water next to his slow speed
super expensive Baldor grinder. He grinds for about 5 seconds, dips the
chisel in the water to cool it, and repeats the process.

I currently have an $70 Delta 1750 RPM grinder. I can get aluminum
oxide wheels for it, too. How risky is it to use it?

I'll have the cup of water to prevent overheating.....

I was just reading in Leonard Lee's book _The Complete Guide to
Sharpening_ about this. His power sharpening tool of choice for the
primary bevel is a vertical belt sander because it is cooler and
creates a flat bevel. Then he puts a microbevel that is one degree
greater than the primary bevel on using either the Eclipse or Veritas
honing guide and waterstones(800x followed by 4000x to 8000x).

Lee does not like hollow grinding at all.

I was just reading in Leonard Lee's book _The Complete Guide to
Sharpening_ about this. His power sharpening tool of choice for the
primary bevel is a vertical belt sander because it is cooler and
creates a flat bevel. Then he puts a microbevel that is one degree
greater than the primary bevel on using either the Eclipse or Veritas
honing guide and waterstones(800x followed by 4000x to 8000x).

Lee does not like hollow grinding at all.


I agree, it removes metal from behind the cutting edge. the OP could look at this:
http://www.leevalley.com/wood/page.a...84&cat=1,43072 and add
the motor.

--
Alex - newbie_neander in woodworking
cravdraa_at-yahoo_dot-com
not my site: http://www.e-sword.net/

On 1 May 2005 14:55:09 -0700, "Never Enough Money"
wrote:

I need to get the initial edge on new chisels (the "hollow grind").

You certainly don't need a hollow grind on anything except razors, and
they're different again.

That said, I'd be lost without a powered wheel for initial shaping on
boot-sale pre-war chisels.

Everything I've read says to use a slow speed grinder with aluminum
oxide wheels to prevent overheating of the steel (which ruins the
chisel).

Aluminium oxide (white) and a "half speed" grinder are a good start.

The woodturners are probably the experts though, as they do a lot of
sharpening with this type of equipment (rather than finishing with a
bench stone). They're now using pink stones rather than white, as they
run cooler.

It's also worth finding a grinder (or at least spindle) that can take a
40mm wide stone, not the 20mm or 25mm that are more common at the cheap
end. You can always upgrade the stone later, so long as the spindle is
long enough.

I've been told that the grinder should not exceed about 1200 RPM.

Nice idea, but impractical. Induction motors don't run at that speed, so
you'd need reduction belt drives. A 4 pole induction motor will run at
1750 rpm (1425 in the UK) and that's close enough for a cheap direct
drive grinder. 2 pole motors run at around 3000 rpm and so the really
cheap metalworking grinders are too fast for this.


One local woodworker actually keeps a cup of water next to his slow speed
super expensive Baldor grinder.

Not the best idea. You're better cooling with airflow (which the stone
provides) or cooling much more frequently than this. 5 seconds is just
enough to set up hot/cold cycling that's going to avoid drawing the
temper, but may also give rise to microcracking in a hard steel.

I currently have an $70 Delta 1750 RPM grinder. I can get aluminum
oxide wheels for it, too. How risky is it to use it?

Sounds fine.



Read Leonard Lee's book too.


--
Cats have nine lives, which is why they rarely post to Usenet.

Andy, thanks for the thorough answer. One minor update to your RPM part
of the answer:
"Nice idea, but impractical. Induction motors don't run at that speed,
so
you'd need reduction belt drives. A 4 pole induction motor will run at
1750 rpm (1425 in the UK) and that's close enough for a cheap direct
drive grinder. 2 pole motors run at around 3000 rpm and so the really
cheap metalworking grinders are too fast for this. "

Garrett Wade is selling one that runs at 1120 PRM. How do they do that?
http://www.garrettwade.com/jump.jsp?...oductID=101879

On 2 May 2005 05:46:43 -0700, "Never Enough Money"
wrote:

Garrett Wade is selling one that runs at 1120 PRM. How do they do that?

It doesn't appear to have any reduction mechanism, so I guess it's a 6
pole induction motor (which fits with the claimed speed). That's simple
enough to design, the only problem would be finding enough orders to
make it worthwhile for the motor maker to tool up for this "special".

It's the frst one I've seen, but I doubt it will be the last. Once one
does it, others tend to follow.

Use the 1750 machine. As others have wisely said a light touch with short
contact period will work fine. If you haven't already, you will soon learn
with things are getting warm. Most tool grinding operations happen with
very brief contact anyway.

Sharpening technology is like a lot of over shop techniques - there are
thousands of ways to spend or save your money.

I agree, it removes metal from behind the cutting edge.

If you are comparing to a single bevel then that is true. But if you
are comparing to a primary/secondary bevel method then it depends how
you do it. Hollow grinding followed by flat honing like Krenov
recommends seems like better geometry in my investigation. Link below.

--------------------------------------------------------------------------------------------------------
What I've learned about sharpening plane blades
http://members.shaw.ca/petermichaux/...harpening.html

On 1 May 2005 14:55:09 -0700, "Never Enough Money"
wrote:

I need to get the initial edge on new chisels (the "hollow grind").
Everything I've read says to use a slow speed grinder with aluminum
oxide wheels to prevent overheating of the steel (which ruins the
chisel).

I've been told that the grinder should not exceed about 1200 RPM. One
local woodworker actually keeps a cup of water next to his slow speed
super expensive Baldor grinder. He grinds for about 5 seconds, dips the
chisel in the water to cool it, and repeats the process.

I currently have an $70 Delta 1750 RPM grinder. I can get aluminum
oxide wheels for it, too. How risky is it to use it?

Just one guy's opinion, but I sharpen my bench and lathe chisels on a
regular old Delta bench grinder with the original wheels, and after a
little practice, it has worked well for me for some time. I *do* dunk
the chisels between grinding passes, and do *not* grind for as long as
5 seconds. With a slower speed, I'm sure you can keep the tool on the
wheel a little longer, but with a standard grinder, one quick pass is
all you get before quenching it, or you will burn the blade. A light
touch and a bit of patience rules the day here, but it's certainly
possible. After gettting the hollow grind in, I just touch it up
quick on my whetstones, and they're plenty sharp for me.

I'll have the cup of water to prevent overheating.....

Aut inveniam viam aut faciam

Andy, I'm trying to understand how 60 hertz and the number of poles
maps to RPM.
I'm not too bright when it comes to motors so please indulge me an
ignorant question.

I'm visualizing an amature and 4 windings in the stator. Now 60 hz
going in seems to mean that the strongest e-field (or B-filed) woudl
change at 4 tiems that rate. This would give 240 RMP. So I must be
missing something...what? Please avoid the tempatation to say "A
brain."

"Never Enough Money" wrote in message
oups.com...
Andy, I'm trying to understand how 60 hertz and the number of poles
maps to RPM.
I'm not too bright when it comes to motors so please indulge me an
ignorant question.

I'm visualizing an amature and 4 windings in the stator. Now 60 hz
going in seems to mean that the strongest e-field (or B-filed) woudl
change at 4 tiems that rate. This would give 240 RMP. So I must be
missing something...what? Please avoid the tempatation to say "A
brain."

for openers you missed the difference between HERTZ or cycles per SECOND and
Revolutions Per MINUTE. So you are only off by a factor of 60 for openers.
But that only applies to synchronous motors.

del cecchi

In article ,
"Del Cecchi" wrote:

"Never Enough Money" wrote in message
oups.com...
Andy, I'm trying to understand how 60 hertz and the number of poles
maps to RPM.
I'm not too bright when it comes to motors so please indulge me an
ignorant question.

I'm visualizing an amature and 4 windings in the stator. Now 60 hz
going in seems to mean that the strongest e-field (or B-filed) woudl
change at 4 tiems that rate. This would give 240 RMP. So I must be
missing something...what? Please avoid the tempatation to say "A
brain."

for openers you missed the difference between HERTZ or cycles per SECOND and
Revolutions Per MINUTE. So you are only off by a factor of 60 for openers.
But that only applies to synchronous motors.

del cecchi

It applies to induction motors too. There's a slip frequency, but the
seconds/minutes mixup is still valid.

In article .com,
Never Enough Money wrote:
Andy, I'm trying to understand how 60 hertz and the number of poles
maps to RPM.
I'm not too bright when it comes to motors so please indulge me an
ignorant question.

I'm visualizing an amature and 4 windings in the stator. Now 60 hz
going in seems to mean that the strongest e-field (or B-filed) woudl
change at 4 tiems that rate. This would give 240 RMP. So I must be
missing something...what? Please avoid the tempatation to say "A
brain."


1) you multiplied where you should have divided

2) you forgot to account for the number of seconds in a minute


60 hz == 3600 cycles/minute

4 pole motor == 3600/4 == 900 rpm.

"Never Enough Money" wrote in message
oups.com...
Andy, I'm trying to understand how 60 hertz and the number of poles
maps to RPM.
I'm not too bright when it comes to motors so please indulge me an
ignorant question.

I'm visualizing an amature and 4 windings in the stator. Now 60 hz
going in seems to mean that the strongest e-field (or B-filed) woudl
change at 4 tiems that rate. This would give 240 RMP. So I must be
missing something...what? Please avoid the tempatation to say "A
brain."


If you have an hour or two, this has to be one of the fun places to spend
it.

http://www.sea.siemens.com/step/default.html

Thanks for the good answer, Robert.

Useful site. Thanks for the reference.