How different is a single speed motor vs a variable

Tony Manifold

Tony Manifold

Well-Known Member
I am looking to buy this grinder: http://www.suremak.com/grinder.html

There is an option for either a single or variable speed. I am not sure how much more the variable is but any more than a hundred or two will be seriously stretching my budget. Just how important is the variable speed?

Either one will be better than my 4 x 36 but I would like some opinions to help me decide how much more I would be willing to spend on the variable.
 
True variable speed is going to be way outside your budget - probably $600 - $800 more. Within your budget, you could get a pulley setup which would give you some speed steps. I have never known anyone who was sorry they got variable speed. Single speed is often the starting point for budget reasons. That is a valid choice and still way better than a 1 x 30 or whatever - but the day will come you'll want variable.

Why? Well Variable speed is easier to learn new techniques such as hollow grinding. Variable speed will increase belt life with finer grits. Variable speed will allow you to grind handle materials without burning the material. Variable speed will retain a better resale value.

Hope that helps.

Rob!
 
Rob is right, I'd expect a variable speed setup to be as much as the basic grinder itself.

Variable speed would be nice, but using a 3 step, or 4 step pulley allows a full range of speeds for MUCH less. Get the basic grinder, pick up a cheap 1hp motor from Craig's list or somewhere for $50 or less. Add cost of a pair of step pulleys and you've got a good selection of speeds for $100 or so over basic grinder cost.

I've got my 2 hp motor with a 4-step pulley setup for around 1200 SFPM, 1750 SFPM, 3400 SPFM, and 4800 SFPM. I never use the 4800 SFPM - just faster than I need. A better setup would be around 1,000 SFPM for low speed.

edit: On reflection with that 8" drive wheel a 1:1 pulley setup will give about 3600 SFPM which is great for hogging/profiling with 36 grit, but won't be too good for fine grits. It will need slowing down for precision work.

Ken H>
 
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A VFD is costly but not that much. I sell the best out there for $448.00 for a 1.5 or 2 hp motor and $350.00 for a 1 hp and below. And those prices include free shipping.

If one is doing a step pulley set up he will probably spend over $100.00 for the parts. Put that toward the cost of the VFD and consider that it reduced the price by $100.00. With the VFD you will also get better torque (power) smoother running and quieter.

In addition to the reasons for variable speed mentioned by Ken you can slow down when grinding post heat treat and have less problems with messing up the temper.
 
Wayne, that $448 doesn't include the motor - does it? Add in another $250 for the 2hp motor - aren't you at $700 for VFD motor for 2hp? The 3 or 4 step pulley is about $20 each for the pulleys, and $10 or so for a Vee belt. These are cheap pulleys and might not run as smooth as a high dollar pulley, but they will work just fine. Find a cheap used 1 to 2 hp 1725 rpm motor for $50 or so, and for $100 total cost you're in business with a grinder and a choice of useable speeds. With motor mounted on a hinged plate, speed changes take maybe 10 sec each.... OK, waiting for motor to stop, make that 30 sec each. With that design grinder you're limited to a 1725 RPM motor.

The problem is that darn 8" contact wheel really limiting the choice of belt speeds. To get a decent slow speed for fine grits and for grinding HT'd blades, you'd need at least a 6" pulley. The standard step pulley size is usually around 4" max, and that still gives 1800 SFPM or so. As Wayne and others say, a VFD would be best for that grinder, but - a VFD setup costs more than the grinder!

Ken H>
 
The 5" step pulley will put you at calculated 1445 (count it 1400) SFPM. That's with the 2" to 5" pulley and the 8" drive wheel. Still faster than I like for fine belts, but certainly workable.

Your speed range would be 1445; 2710, 4817, and 9032 SFPM.

Now, "IF" you could get that grinder with a 6" drive wheel, it would give you: 1084; 2032; 3613; & 6774

That would be a good selection of speeds - you'd never use the top speed, but the others would be good. Have you considered the Beaumont grinder? Seems like the basic grinder without motor/pulleys is $750 or so? OR - some of the other "basic" 2X72" grinders. I guess the grinder you linked to is the least expensive because it comes with platen and contact wheel?

Ken
 
It also ships from Canada which is a big plus. I could tack a couple hundred more on to the price if I bought from the US. It looks like I could swap out wheels too.
 
Years ago when I started and was broke! I purchased two step pulleys from the local Ace hardware and I think the brand name was Chicago? These were Air/heating pulleys and the come in 1/2" and 5/8 ths and 1" I think the shaft sizes where? measure yours.

Those and the old fan belt off of my truck and I was up and running. I would use link belt now and if you have the money get the VFD and motor from Wayne. At the time I just found a 1 horse open motor in the classifieds for $50.00 and later up graded to a 2hp. The TEFC motors are preferred but you can use a open motor, just realize you might burn it out with grinding dust.

Just to let you know I purchased a Hardcore products grinder with a Variable 2hp and I still use that old 2hp open motor and it hasn't burned out in 10 years of weekly use.

Look on craig'slist the paper and there are still some old electric motor shops in some towns?

Have fun and stay safe with your new tool.
 
As Laurence says - the TEFC motor is preferred, but an open frame motor is going to last a while. I'm using an open frame motor (free from a scraped air compressor) and when it goes out, then I'll look to see what I can find. Might use air pressure to blow thru the frame of an open frame out from time to time to blow as much dust as possible might help the life an open frame motor. It sounds like Laurence's open frame motor is still going strong after 10 yrs?

By all means, "IF" the budget allows, go first class with a VFD setup. As an old sailor once said about cruising, better to go on a shoestring than sit around home waiting to get everything first class.

Ken H>

Ken H>
 
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Tony Manifold said:
It also ships from Canada which is a big plus. I could tack a couple hundred more on to the price if I bought from the US. It looks like I could swap out wheels too.
Click to expand...

Added to the value of our dollar (About 91 cents US even before exchange fees) there are brokerage fees to deal with - not to mention Sellers who got burned shipping to Canada and will no longer ship here. On that note, Kudos to the ones who still do.
 
To really answer your question,
There are many knives made on single speed machines but every knife maker I have every talked with that got a single speed has said, I WISH I had enough to go variable. speed with direct drive machines or asked me about setting up a step pulley system for a belt drive.

The finer the grit of the belt, generally the slower you want to run it. Each grit of belt will have a sweet spot or sweet speed is a better way to put. The belt does it's best job of finishing and lasts the longest at a certain speed which will also depend on the operator and the material you are finishing.

Do the adjustable with a set of step pulleys aand some link belt.
 
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