Rolled Bevel vs Micro Bevel vs Hollow Grind

[David Barnett]

I'm pretty confident I could design what I want for less than $500 maybe less than $300 depending on what type of deals i can find on the components.

Oh, if it's just for sharpening and a bit of slack belt shaping, yeah, under $300. You bet.

[Winton Applegate]

I am very frightened by the turn this thread has taken, power grinding and all and will all too soon succumb to my natural fear and panic impulse to run away and over the horizon like a terrorized rabbit but first let me say that if you do make a power belt sander don't use small pulleys; go larger and they will run cooler and treat the bearings better. I have one bench mounted belt sander with small V belt pulleys. The pulleys get so hot that the bearings actually start to seize and slow the works down. Blister hot if you touch them. No amount of belt tension adjustment makes much difference. I admit to using it heavier than say for a woodworking chisel but you guys are talking
three phase ?
and one horse power ?
. . . and he ran away in a small cloud of dust . . . all that could be seen was feet and a little white tail disappearing into the heat haze.

[Winton Applegate]

Ok that was a nice little run. Exercise does wonders for stress, fear and the mentally unhinging effects of discussing drastically different sharpening methods.
I'm better now.

Hi Derek,

I am not responding just to you but just generally chiming in on wheel size, wet grinders, speed etc.

James Krenov used quite a small radius wheel on his hand crank clamp on the bench hand grinder (god I hate those things; I admit it . . . he was just tougher than I am ) then one or two Arkansas stones to finish up. Of coarse he was working high carbon blades only. Arkansas stones lay down and die when I use them on my A2s.

The Tormek is quicker

Couldn't be anything slower on the planet than my Delta wet grinder (huge wheel diameter as well). And to make it just over the top frustrating to use the wheel has a hard spot in it as well. Goes grrrrrinde . . .bump . . . grrrrrinde . . . bump . . . grrrrrinde . . . bump.
I have considered buying a new wheel of a different brand for it but can't quite shell out the money. It would still turn too slow.

My first impression of the Tormec was that it was WAY over priced and I spent the money on the stones that I have. Some how I couldn't bring myself to "grade" the stone back and forth between coarse and fine. I assume you don't do that and just leave it coarse. Seemed like a racket. "Lets get the customers to grind their stones back and forth from fine to coarse and fine again until they wear them down in no time."
I just couldn't do that. Several times a day ? People do that ?

[dan sherman]

three phase ?

The motor needs to be three phase, so that you can vary the speed using the VFD.

and one horse power ?

most decent bench grinders are between 3/4 & 1 1/2 hp. I think 1hp is plenty powerful enough for sharpening.

[Sam Takeuchi]

I think 1hp is plenty powerful enough for sharpening.

Way and beyond plenty. When a hand cranked grinder can get the same job done, I think even a 1/3hp grinder would be plenty for grinding woodworking tools, even for HSS tools.

[Derek Cohen]

My first impression of the Tormec was that it was WAY over priced and I spent the money on the stones that I have. Some how I couldn't bring myself to "grade" the stone back and forth between coarse and fine. I assume you don't do that and just leave it coarse. Seemed like a racket. "Lets get the customers to grind their stones back and forth from fine to coarse and fine again until they wear them down in no time."
I just couldn't do that. Several times a day ? People do that ?

Hi Winton

Technically, I did not set out to purchase a Tormek. I bought a cheap Grizzly-type Scheppach version. The writing on the case was in German, which was a con because it was made in China. Poorly made at that. The wheel wobbled, and the cheap rest could not be set up reliably. I returned it to the store. The owner was quite apologetic and offered me a big discount on the run out Tormek 2000 model (the green version that was replaced by the blue). So I returned home with a still-expensive Tormek, but with my conscience appeased a little. Within a few days I no longer felt guilty. This is a class machine, and worth every penny. That does not make it a viable proposition for many. I am fortunate to have one.

I am in the bad books of the US agent as I insist on the Tormek being a grinder and not a sharpening system. I only use it on the coarse setting. I would not want to use a blade that is honed on the stropping wheel - just polished serrations. Sharp serrations. I like the Tormek because it is very predictable, reliable and safe as a grinder. My 8" dry grinder still gets used, but generally for roughing out rather than final grinding. Everyone has a system they feel comfortable with. As I wrote earlier, there is no one "right" system.

Regards from Perth

Derek

[Jim Koepke]

I think even a 1/3hp grinder would be plenty for grinding woodworking tools, even for HSS tools.

but... but... My grindstone is from an old mill and weighs in at 3 tons...

jtk

--just for laughs folks...

[dan sherman]

Way and beyond plenty. When a hand cranked grinder can get the same job done, I think even a 1/3hp grinder would be plenty for grinding woodworking tools, even for HSS tools.

It depends how fast you want to remove material, the faster you want to remove material, the more power you need.

[Sam Takeuchi]

It depends how fast you want to remove material, the faster you want to remove material, the more power you need.

As far as woodworking tools are concerned, you never press down the tool on the wheel hard enough to bog down even a 1/3hp motor. Perhaps more power can be useful in metal working or auto repair, but for woodworking tools, it's utterly unnecessary. In fact, if you look at Baldor's grinder catalog (that's more than decent line of grinders), 6" & 7" grinders are between 1/4hp and 1/2hp. Even 8" grinders are only in 3/4hp range (with price tag of nearly $1000) and those are designed with more than plenty of power for most use, including metal grinding. I know there are cheaper grinders with 1hp available elsewhere, but it doesn't change the fact it's way over powered for the use concerned here, regardless of material removal speed.

Out of many problems and issues people often write about, grinder not having enough power is one thing I've never seen so far on woodworking forums. Have you ever come across an occasion where you needed that much power?

[Winton Applegate]

I only use it on the coarse setting

Derek,
See, I know you are logical and practical. Seems like I remember that story now from quite a while ago about the swapping of the grinders.

Ha, ha, take this with the humor it is meant to be
At work today I was thinking WHY my flat stones sharpening is "the only right way" and why the power grinders are "all wrong".
Because . . .
this is Neander and it is for HAND tool wood working.
Ha, ha there you see ?

[dan sherman]

Out of many problems and issues people often write about, grinder not having enough power is one thing I've never seen so far on woodworking forums. Have you ever come across an occasion where you needed that much power?

let me try and explain this in a different way. You can remove more material in two ways. You either feed the work into the grinding medium more aggressively, or move the medium past the work faster (higher sfpm at the wheel face or belt). Like you said Baldor ups the power as the wheels get bigger. they sell 3600 rpm grinders with 6,7,8 inch wheels that yields the following.

6" ~5654 sfpm
7" ~6597 sfpm
8" ~7539 sfpm

the 8 inch has the potential to remove more material at a given feed rate, but it is also easier to stall, as the large wheel creates a larger lever arm, thus it needs more power to maintain the sfpm.

I have needed the extra power before, when you're grinding stuff like M2, M35, M42, & T15 it's pretty easy to bog down the grinder.

[Sam Takeuchi]

Yes I know about the pressure and surface speed, and I understand why larger wheeled grinder need more power in general (and that larger grinders are generally designed for...well, larger and heavier tasks which also require more power). That's why I was separating woodworking tools (where you have to balance the speed, heat and temper, and can't go ham-handed grinding) and metalworking. And that's where my emphasis on "woodworking tools" come from since that was the primal concern here. Your grinding tasks include steels that are uncommon in woodworking tools, but if you go back, you recommended 1hp grinder and sharpening of woodworking tools. That's where I pointed out that it's over powered. And it is.

I don't have experience with those steels you mention as they are not common in woodworking tools, but I do have M2 blades for plane and HSS turning tools. I can hardly bog down a 8" 1/2hp grinder with reasonable use. I'm sure if I ram it hard, it can, but who does that? Other commonly available woodworking tool steel are not going to survive the kind of grinding that bog down a motor. Between cooling and aggressive grinding, that's not going to remove materials any faster.

[dan sherman]

I don't have experience with those steels you mention as they are not common in woodworking tools, but I do have M2 blades for plane and HSS turning tools.

It depends on what kind of woodworking you are doing.
http://www.d-waytools.com/tools-skews.html

And besides if it's cheap more power is always better.

[Brian Ashton]

let me try and explain this in a different way. You can remove more material in two ways. You either feed the work into the grinding medium more aggressively, or move the medium past the work faster (higher sfpm at the wheel face or belt). Like you said Baldor ups the power as the wheels get bigger. they sell 3600 rpm grinders with 6,7,8 inch wheels that yields the following.

6" ~5654 sfpm
7" ~6597 sfpm
8" ~7539 sfpm

the 8 inch has the potential to remove more material at a given feed rate, but it is also easier to stall, as the large wheel creates a larger lever arm, thus it needs more power to maintain the sfpm.

I have needed the extra power before, when you're grinding stuff like M2, M35, M42, & T15 it's pretty easy to bog down the grinder.

I would have to disagree with this presumption that surface speed allows you to remove more material faster. Remembering this thread is about sharpening tools, not pushing a piece of scrap steel into a grinding or cut off wheel as hard as you can. Even then you will find that you can't grind all that fast either… If you have a cut off machine try forcing the wheel as hard as you can on a piece of steel, to the point where the metal glows red. It gets to a point where you stop cutting altogether. The heat build up is so high that the cut off wheel is actually floating over the hot metal and not removing anything or very little. Obviously this doesn't apply to a thin piece where the PSI over comes this.

I have for decades ground all my tools at very low RPMs. For about the first 20 years I always suspected that grinding at sub 300rpm was much quicker than grinding on a standard grinder but couldn't be bothered to put it to a test. About 8 I had mentioned this on a forum down here and was told I was full of it… So I took an old chisel and put it to the test. Conservatively, I figured it might be 10% faster. To make sure I wasn't being biased I usually allowed the chisel to over heat every so often to a light straw colour when using a standard grinder to maximise time on the wheel… And made sure I didn't discolour it when using my slow speed grinder. I was quite surprised at the results when it was all done. Slow speed grinding allowed me to remove material on average 40% faster.

There are at least two factors here at work, probably others but I can't be bothered to figure them out. First, at slow surface speeds basic physics says heat will be generated at a much lower rate. Therefore the steel, having a high heat coefficient, is more efficiently able to conduct the heat away from the edge and dissipate it before a critical temperature is reached; allowing you to keep the steel at the wheel for longer. Second, when you try to remove material using sand paper or grinding the slower the grit is passed over the wood or steel (or vise versa) the deeper it's able to cut thus removing relatively larger amounts of material in each pass. So when you combine these two factors you end up removing material much faster and more efficiently at slow surface speeds (> 450 sfpm) compared to very high speeds such as what you have listed.

I'm sure there is a formula that will determine how many seconds you can keep a piece of steel pressed up against a grinding wheel, at a specific pressure, at a variety of speeds before it reaches 300 degrees… So if someone wanted to really get stuck into it they could determine the optimum speed…

[Tim Put]

I've got a Tormek, a 6" variable speed grinder with a (regularly dressed) 60g grey wheel, and a Viel belt grinder with belts down to 46x Zirconia. Because of the pressure that can be safely put on a tool when it's in a water bath, the Tormek with a diamond dressed wheel (not the grading stone; follow Derek's advice, not the aforementioned US Tormek rep) is the fastest of the three for major regrinding. It is however the slowest to setup and take down. But then again it's also the cleanest (least dusty/gritty).

The Tormek with a "coarsely graded stone" using the carborundum stone it comes with is the slowest of the three. In that case even hand powered methods compete with the Tormek.