Grinder: How important is variable speed?

[Messinger]

Hi Gang. As a few of you already know, I'm building a 2x72 grinder. It's all done except the drive and tracking wheel assembly. The threads I've read seem to indicate that many of you do the majority of your grinding at around 1,800 feet per minute (belt speed). Well, If I direct-drive a 4" drive wheel that's exactly the speed I'll get (I've got a 1725rpm 1.5hp motor). I had been planning to use step pulleys to get variable speeds, but If I direct-drive a 4" wheel I can save $150 in arbors, pillow-blocks, and step-shieves. Another benefit is I can significantly reduce the grinder's bench-top footprint by going direct-drive.

What do you think? Save $150 and a bunch of bench real estate and have one speed (1,800 fpm), or spend extra & give up more shop space to go multi-speed? (Don't suggest DC or 3-phase variable speed - it's not in the budget at this time - maybe later) Thanks guys!

-Ben

[fitzo]

Thousands and thousands of knives have been ground on single-speed grinders. Variable speed only becomes mandatory once you've ground a blade on one.....

It helps, and it is the cat's meow, but IMHO, it's not at all essential. I used a singlespeed Bader 2 for 20 years.

[Don Robinson]

Hi, Ben.

You'll need about 3,000 sfm on your grinder.

I know this is blasphemy to say, but I don't have any use for variable speed. For me, it's always full speed ahead with a sharp tool.

[Don Cowles]

...and I'll throw in my two cents worth, too.

If I were in your shoes, I would go for the variable speed, although, you could always add it later if you are using step pulleys.

Variable speed gives me what I need the most of: more control. Mistakes can happen very quickly - and deeply - at higher speeds. I think Steve Johnson said he rarely (if ever) runs his grinder at over 50% speed.

[Don Robinson]

See what I mean, Ben? Blasphemy!

Hello there, Don Cowles.

[KandS_KNIVES]

My grinding mistakes, deep ones, went to almost zero, when I added speed control to my grinders.


Ken Beatty:cool:

[Tod]

Being able to slow your belt down, particularly when doing the fine grits, really helps. It makes it much easier to grind after heat treat without overheating things.

[Bob Warner]

I'll throw in my vote for variable speed. I used a single speeed home built grinder for a long time. ThenI got my variable speed and it is a very different world. I used to put on a 400 grit and make one quick pass and then cool off so I did not get the blade hot and ruin the heat treatment. Now, I just slow the belt down and grind without getting the blade hot at all. No more blue spots on the blade, no more redoing the heat treatment.

Do you need it? NO

Do you want it? Absolutely

[SVanderkolff]

Ben
I just got my KMG a couple of months ago and had it set up with 2 sets of 3 sized puleys. As I am just learning to hollow grind I found that even at the slowest speed that could give me it was still too fast so I invested in a third step puley and slowed it down even more. I figure once I get comfortable with it at the slow speed I can speed it up later but mistakes were happening just too fast. I definetely vote for the variable speed.
Steve

[Messinger]

Thanks for suggestions everyone. Sounds like I'll be doing myself a big favor by going with a variable speed setup.

-Ben

ps - Steve, good luck with the hollow-grinding. I'm sure you'll get it down to a fine art. I have no doubt. Your flat-ground blades look great. Your drop hunter and maple bird are two of my favorite fixed-blade designs.

[Kevin Wilkins]

I'd vote for variable (2) speed grinder. You dont really need it for blades, but if you only have the one machine, the slower speed makes working grips and other softer, easily burned up materials a LOT easier.

But it's better to get a good one speed grinder than a crap 2 speed grinder...

[Jason Cutter]

I just got my new 72x2inch grinder 2 days ago and I am now wondering how I got by without one !! This one was built by a fellow knifemaker / toolmaker and is variable between full speed and about 1/2 speed. It uses 2 different size drive pulleys to achieve this, I just change the belt position to change the speed. The 1/2 speed just adds SO MUCH CONTROL, its not funny. Especially for fine control work.

I suppose it helps to have the appropriate power motor. I know some makers use machines that rely on speed to keep things moving. The 1hp motor on mine seems to do the job right . Jason.

[Bob Sigmon]

Jason,

Congrats on the new grinder. How are you going to stuff it into your workshop? Let's see some pics. You were megaprolific on your old setup, you should really be cranking them out now. . . or you'll have more time for your garden!


Btw - I vote for variable speed. I'm just learning to grind and it does help me control and fix mistakes rather than adding to the scrap pile.

Bob Sigmon

[Khyber]

Greetings

Well, as I read the above commentary.. now I think to myself.. I am working on a grinder project, because I cannot afford the 2 grand for a grinder that some knifemakers told me I need to spend to get started.

Nonetheless, I endeavor to persevere in building my own, and I have to consider the multiple speed option now. I have a 1hp AC motor coming, (ebay), and I believe I can make a grinder with it. So with variable speed in mind, should I make the grinder with multiple pulleys?
Or should I work harder on finding a variable speed 1-2HP motor (that i have NO idea where to round up, they seem rare)

Charles.

[Bob Warner]

As with all tools in my opinion, you should try your best to get the tool that you REALLY want if at all possible.

I have had several home built grinders over the years and made a lot of knives with them. It works, single speed and homemade contact wheels and NO pulleys. That is what I could get at the time, so that is what I used.

Later, I got a KMG and also bought a DC 1.5HP variable speed motor and controller. It was a stretch for me to get it but it is definately worth it. I can go from smoking speed to a complete stop with the motor. I can get a very slow rotation of only a few RPM's and the wheel turns no matter how hard I push against it. It is awesome to have that control.

So, If you build your grinder, good. If you can only get a single speed at this time, good. Just keep the design variable enough to change out your motor from single speed to pulleys or even a DC motor. Get or build the best you can now and upgrade as you can.