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I don't have a useful bench grinder and since I've been getting comfortable with the Carruth scraper and working with more metals for jigs and stuff, I've been thinking I need one. So I'm going through the usual optimization problem - searching for used grinders, looking at wheels, etc. The CBN wheels Woody mentioned on another thread look like an excellent idea to me but they're not cheap. Cheap grinders are available but there are a lot of complaints about stamped steel washers where they should have machined flanges. And finally, there are 6" and 8" grinders. I naturally started gravitating toward the 8" grinders because they seem like more serious machines.

But then ...

Slow speed ==> slower heat buildup ==> better for sharpening tools.
(My first consideration since I don't care how slow other operations may be but I don't want to de-temper tool edges).

For a given motor speed the grinding surface on a 6" wheel is going to be moving past the tool rest at 3/4 the speed of the surface of an 8" wheel. So wouldn't a 6" grinder be better for sharpening?

Example for the typical 1750 RPM "slow speed" bench grinder:

Linear Speed, inches/second = (RPM/60 * pi) * Wheel Diameter = ~ 90 * Diameter
For 8" wheel LS = 720 in/sec
For 6" wheel LS = 540 in/sec

8" CBN wheel, 80 grit @ $140
6" CBN wheel, 80 grit @ $110

Norton Al Ox wheel:
8" @ $41.55
6" @ $21.95

Is there some other reason why an 8" grinder is better that I'm not thinking of? Is it harder to find a high quality 6" grinder than 8"?

I really have no idea which is better or worse for the scraper but an 8" has less of a curve than a 6" that may make a difference. The 6 inch will make a deeper hollow grind.

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Thanks John. I didn’t think of that. Would that be a deal breaker on edge tools, for instance, turning tools?


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You prevent overheating edges during grinding by dunking the tool into a cup of water every few seconds.

I heard from others that 6" would be fine for most edge tools. I mainly was just adding to the points you had. Hollow grind drives me crazy with the way I use paring chisels for guitar work, but I think it is just me; others swear by the method.

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Stronger edge (less concavity = stronger edge), and faster, cooler grinding (larger wheels with higher edge speed and more mass/surface area to dump heat). We seldom have to dip tools we grind with the 8" radiused-face CBN wheel from Tool for Working Wood. We have both the $100 1/2 hp and $200 1 hp 8" Rikon low speed grinders, and both work well even for heavy grinding with CBN or Norton 3X (I did a framing slick and two framing chisels Friday...these had not been touched in a decade, but cleaned up in about 15 minutes of grinding and honing). The Veritas tools rests are handy, and make square edges such as on the thicker StewMac scrapers easy, but we have found the grinding jig sold as part of the system to be unnecessary.

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For the times they are a changin'

- Bob Dylan

Interesting. So I think you're saying that speed counts - 1750 RPM is better than 3500 RPM but the extra 33% slower you get from the smaller wheel is less important than keeping the hollow grind shallow?

I was almost ready to pull the trigger on the small 8" Rikon at ($99 Woodcraft right now) when I got all balled up in slow-speed vs. diameter vs. cost vs. wheels ... Maybe the $99 8" grinder with the $140 CBN wheel is a good, reasonably cost-effective solution?

Thanks.

With CBN, we would use standard speed grinders if the wheels were rated for more than 3000 RPM, but few are. Higher speed = faster grind, assuming the extra heat can be addressed, and with CBN wheels, heat is less of an issue because much of it is dumped back into the wheel itself. Our experience has been that the $99 1/2 horsepower Rikon works well with 8" 3X and CBN wheels, although with any budget brand grinder, some care in getting the wheel centered helps.

_________________
For the times they are a changin'

- Bob Dylan

If I didn't already have a wet wheel grinder I might check this one out: http://www.walmart.com/ip/WEN-10-2-Dire ... sem#read-m

I don't know anything about it except what I've read in the ad. The motor is kind of small (1.6 A) but it is only turning the 10 inch wheel at 115 rmp, so it might be o.k.
I have some old WEN tools. They don't appear to be "industrial quality" but they work O.K. I don't know what they are like today now that they are made in China - like most tools.

Surface feet per minute (SFPM) is what we're looking at.
A wheel with with a 1 foot circumference turning 100 RPM would be 100 SFPM

Went looking for one of my old slide rules and thought, everything is on the internet
here ya go
http://www.carbidedepot.com/formulas-turning.htm

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Say what you do, Do what you say.

Wow. That’s really cheap!



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Yep. Everything is on the internet. Including you guys, happily. Thanks.


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The newer high quality grinding wheels are a world different than the old ones which would burn your tools if you blinked.

Also - dressing the stones makes a big difference... Not only for squaring the wheel back up, but also to remove any glazing or contamination (like paint, plastic, aluminum, or brass on the wheel).... so make sure you have one of those tools handy as well..

...another benefit of CBN wheels is no dressing required...which is not the same as saying you can grind tools in the buff

_________________
For the times they are a changin'

- Bob Dylan

Oh.... Trust me.. CBN stones can be contaminated by aluminum, plastic, brass, and other stuff... And it more or less ruins them... I had to listen to the guys in the toolroom curse an operator for days after he ground an aluminum bar on their grinder running CBN wheels for carbide.... It was a brand new wheel - put on the day before... Ruined!

It happened often until they put a lock on the plug so nobody could do that again...

Sanders are for grinding aluminum and brass... The belts/disks are a lot cheaper and easier to replace...

I've been eyeing this one myself. If you are just using it for sharpening that is...

http://www.grizzly.com/products/10-Wet-Grinder-Kit-Anniversary-Edition/T10010ANV?utm_campaign=zPage&utm_source=grizzly.com

We have a nice Tormek in the shop - was the default grinder for bench tools until affordable CBN was available...it now is relegated to stropping carving tools. The issue with wet grinders is speed - even the Tormek takes a while to regrind an edge. The boss looked at a 10" CBN wheel for the Tormek (dry grinding), but no advantage there over the 8" grinder, other than slightly less concavity.

CBN is for grinding tool steels only, although I found out how to clean the wheel after loading it with mild steel.

_________________
For the times they are a changin'

- Bob Dylan

It feels like an eternity. I can't figure out how the guys in the youtube videos are getting a good edge in just a minute or two. The one video where the guy intentionally chips the chisel edge and has it working in a couple minutes... seems more likely I'll catch a unicorn.

I may look into this CBN wheel you speak of and offload the Tormek to some lovely craigslist patron.

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"I've been eyeing this one myself. If you are just using it for sharpening that is...

http://www.grizzly.com/products/10-Wet- ... rizzly.com"

That looks like a WrEN in a bear suit!

Grinding aluminum is always a bad idea. A coworker was using a cutoff wheel to cut aluminum angle and was wondering why it was becoming increasingly difficult to cut. The aluminum was clogging the wheel which can cause it to heat up and shatter. They do make special wheels for cutting aluminum ( I always used a carbide tipped saw blade).

So funny...got a note from the boss about 20 minutes ago:

"Tormek CL for $500, unless one of your Hab people wants it. Strop on bench works better anyway. Will shoot you link to listing."

Guess he ran out of reasons to keep it in the shop.

_________________
For the times they are a changin'

- Bob Dylan

I went up to Woodcraft today and bought the smaller 8” grinder (the $100 model). An employee helped me take it out of the box in the store and try it out. We messed around for a while trying to fine-tune the balancing of the wheels by realigning them on the axle but didn’t really make it any better. It seems pretty smooth to me but I have no real experience with a bench grinder so I don’t know how much vibration is too much. Another customer looking at the same grinder watched us and said it seemed significantly better than the General grinder he was looking to replace.

I’ll look for some YouTube videos about truing grinder wheels but can anyone tell how to know when I’ve made it about as good as it’s gonna get? I don’t really even know if it’s decent or awful right out of the box. Well, I’m pretty sure it’s not awful but that’s a low bar.


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You can remove both wheels and run the grinder to see if there is any vibration of the arbor bearings. The wheels provided by Rikon are terrible - dressing them will help, but plan on swapping both for either the Norton 3X or a CBN and 3X combination. The CBN wheels we have are both close-tolerance fits over bronze sleeve bearings...there is one layer of 0.0015" copper tape for fit.

_________________
For the times they are a changin'

- Bob Dylan

Thanks Woody. Ill try that. I’ll at least get the Norton wheels. Not sure yet if I can justify the CBN wheel but it does sound like a big enhancement.


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I see now that putting some decent wheels on my grinder can make it pretty handy, instead of just using it to sharpen my lawn mower blade. Off to LV soon!

Alex

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"Indecision is the key to flexibility" .... Bumper sticker

I have the 8" Rikon grinder and do not like it at all. The tool rests are terrible. I will soon be getting a nice vintage Delta grinder with cast iron tool rests and will get rid of the Rikon. I have decided to gradually replace all Asian made machinery in my shop with vintage American made machinery.