An Education on Grinders?

K

KB1SYV

Guest
Hey Guy's,

Do we have anyone on this forum putting out material kits for the NWG like PolarBearForge on Blade Forums? I need some education on this motor thing. I'm looking at single and 3 phase 1.5-2.0 hp electric motors on ebay. I see here that the recommended frame is 56C. How about 56H? Basically, what different frames can I get away with that are compatible with this grinder? When talking single phase, what is the recommended rpm's? 1800? 3450? I'm not much of a fabricator, so the frame compatibility is important. I just want to know how much leeway I have and what the differences of each frame type really are. Now, is the 8" wheel for heavy metal removal and smaller wheel for detail work? I see some setups without the big wheel, so I was wondering what it was used mainly for? Would you recommend the multi-platen setup or the standard platen version?

Thank you in advance for your time and advice.

Jeff
 
Jeff,

I'm on the learning curve on this topic as well. I'm building the Polar Bear Forge ("PBF") kit and want variable speed, having used a Grizzly that I thought was too fast and one speed.

The PBF Kit calls for a 56C frame motor, as you note, and ideally with a base. I don't know what a 56H is and have noted that there are a lot of variations of the 56.

At any rate, if you want variable speed you'll need a three phase motor and a VFD. The VFD's are expensive and selecting one is very confusing. So I will default to the one sold by Beaumont Metal Works with its KMG.

As to RPM, since the PBF grinder is direct drive I've read that a 3450 rpm (AC three phase) motor should be used. A single phase motor will not allow variable speed at constant torque.) If you don't have a 220 volt 60 hz single phase power source (in other words you only have normal house current) you're limited to 1 1/2 hp motor. The VFD will convert that to 220 volt for a three phase AC motor.

I hog 1/4 annealed steel with an 8" wheel- the same wheel that I use for hollow grinding-just change the belts.

Jay
 
Hey Jay,

I'm really not sure yet which way I want to go, single or 3 phase. It's a money issue. I can learn to grind using a single speed and it would be cheaper. What's the pro's and con's to a single speed? If I learn to grind at the speed I have, why would I need to change it? I am finding some good deals on motors, but they are not 56C, so I need to find out what these other frame configurations are and if they are compatible to the PBF Grinder. I probably won't have the choice due to lack of funds, but I'll probably have to do the single phase route. I just need to get more info. I'm familiar with the variable speed stuff, and I'm limited to 110v on a 20amp breaker. I still don't really know the function of the bigger wheels as opposed to the smaller wheels either. If anyone could clarify what their function is in idiot terms so I can understand, that would be cool!!!

Thanks,

Jeff
 
Last edited by a moderator:
Jeff,

I'm no expert but I think the only difference with the wheels is the radius of the hollow grind.

Many use an 8" wheel for hollow grind. I was at the shop of Michael Kanter (adammichaelknives.com). He uses only a 10" wheel. You can check out his knives on his web site. My friend has a KMG with an 8" wheel and that's all he uses except for the platen. I think the smaller wheels are just for a tighter radias.

At any rate, I like you, am concerned about cost and good wheels are expensive. I would think either an 8" or 10" is all that you would need. At least that's what I'm going to do.

If you don't want to hollow grind the least expensive is the flat platen.

Jay
 
On single phase and three phase. Most people have single phase running into their houses and shops. Three phase motors are cheaper but of you want to run a three phase motor with a single phase power supply you will have to buy a converter which will offset the difference between a single phase and three phase motor.

Variable speed control is expensive just about any way you want to look at it.

I would consider a 3450rpm motor on a direct drive set up as too fast. You can learn to use it but you will have problems with overheating with the finer grade belts. With pulley drive you can increase the ratio of the pulleys between the one on the motor and the one on grinder to reduce the belt speed. Get a motor with a speed of around 1600rpm and you can use a step pulley system to give a degree of speed adjustment.

Drive wheel size does effect more than the diameter of for hollow grinding. It will also effect the belt speed. All other things being equal, the bigger the wheel diameter the higher the belt speed.

Doug Lester
 
Thanks Doug- that makes sense now that you mention it; the size of the wheel would determine the speed of the belt at the contact point. I also appreciate your comment on the motor speed. I was all set to buy a 1750 rpm motor, but then I read Boss Dog Mickley's comment that he would use the 3 phase 3450 rpm motor on his new direct drive grinder (at least I think that's what he said.) and I think that is what Beaumont recommends for direct drive, but these are for variable speed set ups.

Jay
 
Doug,

I was thinking that a 72" belt is a 72" belt and it would travel at the same speed no matter which size wheel was used. But that's why I like this forum...I always learn something.

Jay
 
There is another option for a variable speed, my Bader has a DC motor, with a controller, not sure what you call this controller, but it runs on 220 volt AC to the controller, and is converted to DC going to the motor. It is 1-1/2 hp and works great. The motor is a Baldor, I can get some info from the controller if anyone is interested. Not sure how cost would compare to three phase motor and a controller.
 
Doug Lester said:
On single phase and three phase. Most people have single phase running into their houses and shops. Three phase motors are cheaper but of you want to run a three phase motor with a single phase power supply you will have to buy a converter which will offset the difference between a single phase and three phase motor.

Variable speed control is expensive just about any way you want to look at it.

I would consider a 3450rpm motor on a direct drive set up as too fast. You can learn to use it but you will have problems with overheating with the finer grade belts. With pulley drive you can increase the ratio of the pulleys between the one on the motor and the one on grinder to reduce the belt speed. Get a motor with a speed of around 1600rpm and you can use a step pulley system to give a degree of speed adjustment.

Drive wheel size does effect more than the diameter of for hollow grinding. It will also effect the belt speed. All other things being equal, the bigger the wheel diameter the higher the belt speed.

Doug Lester
Click to expand...

The grinder that PolarBearForge sells is setup for direct drive no pulleys. I built one and I'm using a 1800 rpm 220 motor. You can check out some pictures on my web site. It went together fairly easy but you need to have some tools drill press and taps Jamie has a good Tutorial on his site on how to assemble it. http://dougwhitesworkshop.com/index.php?option=com_content&view=category&id=42&Itemid=66 If you have any more questions email or PM me.
 
whiteeugene said:
The grinder that PolarBearForge sells is setup for direct drive no pulleys. I built one and I'm using a 1800 rpm 220 motor. You can check out some pictures on my web site. It went together fairly easy but you need to have some tools drill press and taps Jamie has a good Tutorial on his site on how to assemble it. http://dougwhitesworkshop.com/index.php?option=com_content&view=category&id=42&Itemid=66 If you have any more questions email or PM me.
Click to expand...

Thanks Doug. Does that mean that I would be okay with a 1 hp single phase 1750 or 1800rpm motor with the PBF Grinder?
 
Grinder

KB1SYV said:
Thanks Doug. Does that mean that I would be okay with a 1 hp single phase 1750 or 1800rpm motor with the PBF Grinder?
Click to expand...

I would think at least a 1 1/2 1750 or 1800rpm I was going to suggest that you look at the posts on Blade forum but when I went to look up the links it looks like you are already reading it. I think that that would be the place to get information several people on that forum were involved in the design. When looking at motors be sure and keep the shaft size in mind I purchased all my wheels from Tracy I'm sure there are other places but $$$$ count when you are building also look under tutorials Wayne Coe just did one on belt Wobble and wheel alignment it was a great help to me.
 
Sorry to butt in your thread, had to add my two cents! I have been using direct drive motors for years on my grinders and they work fine as long as you figure out what speed works for you, Bader grinders makes different sized drive wheels to get different speeds. the smaller the drive wheel the slower the belt speed. I had a 3450 rpm motor with a two inch drive wheel and the belt speed was very do-able. I recently changed most of my grinders over to DC variable speed. My 1hp runs my horizontal small wheel grinder, has plenty of power and runs on 110v. my 1-1/2hp runs on 220v and both controllers can be wired for 110 or 220. Nothing beets a variable speed grinder!!
I was told to stay away from three phase. As for contact wheels, most use 8" because that's what comes with there machine when they buy it, it all depends on the width of your knives and how far up you want your grinds to go. I have an assortment of wheels, but the majority of my hollow grinding is done with a 12" wheel. I like to get my grinds to go almost all the way up to the back bone of the blade. Thanks for hearing my two cents!
Sincerely,
Clint Sampson
Sampson Knifeworks
 
I'm not thrilled with direct drive but with a slower motor it should be ok. The big argurement against the Grizzly, which is also direct drive, is the speed of the motor. The next biggest is that the motor gets in the way of working from the left side with anything smaller than the 10" drive wheel. Make sure that the motor gives good clearance on any direct drive grinder.

Doug Lester
 
You must log in or register to reply here.
Back
Top