EERF file

The finished product is essentially the same depending on which version of the EERF you get. The EERF grinder requires you to provide the steel and cut out the pieces yourself (or have it done for you). The GIB has already been cut out and is shipped to you ready to assemble. Unless you have a good source to get the water jetting done, I think the GIB is the best value. At least where I'm at, you can't buy the steel and get it cut for the price Polar Bear Forge is asking for their kit. Both versions have been built by a lot of guys and I can't find a report of anyone being dissatisfied with either.
 
kcgmann98 said:
The finished product is essentially the same depending on which version of the EERF you get. The EERF grinder requires you to provide the steel and cut out the pieces yourself (or have it done for you). The GIB has already been cut out and is shipped to you ready to assemble. Unless you have a good source to get the water jetting done, I think the GIB is the best value. At least where I'm at, you can't buy the steel and get it cut for the price Polar Bear Forge is asking for their kit. Both versions have been built by a lot of guys and I can't find a report of anyone being dissatisfied with either.
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Thanx! I was mainly looking at the functionality of the two and if there was any real difference in the end. Tge GIB looks great.
 
There are files foe the home made kmg. I would look at those. It will be stout and should work great.
 
There are several DIY grinder plans available from various online sources. Most of them you have to pay for. The EERF (FREE spelled backwards) grinder is just a set of plans available for download for free. Some very kind gentlemen have provided the plans in a CAD file that can be given to a fab shop to cut the pieces from 1/2" plate steel. Polar Bear Forge sells the GIB (Grinder in a Box) which is just that. They have already cut the steel and drilled most of the holes. They ship it to you in a USPS box. Both grinders share the same DNA. In both cases you will have to drill a few holes, tap a few holes and bolt and/or weld everything together. In both cases you have to provide the motor, VFD if desired, hardware and wheels.
 
Aneat, First, I am not an electrician but I have read all the info I could get about faster motors vs slower motors and most of the guys who have electrical training say the slower motors will give full hp at slower speeds better than the faster motors. You will notice that most of the non direct drive grinders like the KMG will use a slower motor and pulleys and jackshaft to get 3450 Rpm to the 4 inch drive wheel which gives less than 4000 sfm. If I was using a direct drive grinder I would probably use A 1725 Rpm motor and an eight inch drive wheel if I could find one. 4 inch drive wheels are common so I would use a 3400 rpm motor. One thing is for sure...you don't need more than 4000 sfm to make good knives and in fact it might keep you from getting the blades too hot.
 
Think about what you want VS for....faster grinding or slower grinding?


That alone should tell you that a 1750RPM motor is preferable. There are other technical reasons, too.
 
Can you guys run down the belt FPM speeds on the low and high end that are preferable?

I am looking at a VFD direct drive.

I think the KBAC VFD's have 100 steps in speed control, somewhere I saw that they do 0.6 hz steps, don't know if that is true or not. So that would determine how slow you could go with a VFD, then you could hash out the speed range available with the controller, motor, wheel combo.
 
0 to 120Hz is the normal range for a VFD. That translates to 0 to 200% motor speed. As a matter of practicality, 0 does not work, but something like 3Hz is reliable.

A 4" drive wheel moves approx. 1 foot of belt per revolution ( 12.5" to be more exact), so 1750RPM=1750FPM. At 200% that is 3500FPM belt speed. That will do most any grinding task. On the lower end, 3Hz will run the grinder at a bit less than 90FPM, which is very slow.

If you need more speed at the top end, use a larger drive wheel. 6" will give you 50% more belt speed. That would make the top end 5250FPM. If you regularly need more speed than that, I think you would be better off with two grinders.

I run my grinder at slower speeds fifty times more often that at faster speeds.
 
bladsmth said:
0 to 120Hz is the normal range for a VFD. That translates to 0 to 200% motor speed. As a matter of practicality, 0 does not work, but something like 3Hz is reliable.

A 4" drive wheel moves approx. 1 foot of belt per revolution ( 12.5" to be more exact), so 1750RPM=1750FPM. At 200% that is 3500FPM belt speed. That will do most any grinding task. On the lower end, 3Hz will run the grinder at a bit less than 90FPM, which is very slow.

If you need more speed at the top end, use a larger drive wheel. 6" will give you 50% more belt speed. That would make the top end 5250FPM. If you regularly need more speed than that, I think you would be better off with two grinders.

I run my grinder at slower speeds fifty times more often that at faster speeds.
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I've never used a VFD, but watched some Youtube videos and stayed at a Holiday Inn express last night ;)

How do you make a 1750 RPM pump go 3400 RPM? You can do that? Without burning up the motor?
You can get 200Hz when being fed 60 hz? I'm not understanding this much apparently.

I know how to do the basic circle math here.

What I don't know is how many FPM to set the range up for. Mainly the slow speed. Since I've never used a variable speed before and know how many FPM it would do, I don't know what the low and high ranges should be. There's a lot of discussion about the high range but not for the low range. For instance 400 FPM doesn't mwan anything to me.

The answer of course is to calculate all the wheels out and see the ranges for your VFD-Motor-Wheel combos.

But it still wouldn't tell me what would be a really nice low speed to have?

Maybe you guys can chime in about what would be your perfect speed ranges?

This makes an arguement for a VFD and high-low pulley system to me for some reason.
 
Les, the way you make a 1725 rpm motor deliver 3400 rpm is by putting a 5 inch pulley on the motor and a 2.5 inch pulley on a jackshaft that drives the drive wheel at 3400+ rpm. Take a look at Kmg grinders on the Beaumont Metal specialties website. Polar bear grinders and EERF grinders use a direct motor connection to the drive wheel so the motors are usually 3400 to 3600 rpm motors. The VFD gives you variable speed and electronic motor protection. I have read that there are good reasons to use a 1725 rpm motor vs a 3400 rpm motor but I am not an electrician and many knife makers use Polar bear grinders and love them. I have a KMG and it works great for me but I have not ever used a direct drive grinder. I doubt that I would notice a difference especially if using a 2 hp motor. The fastest I grind is about 3600 sfm and the slowest is with the VFD set at 20% but I do not know the actual sfm at that setting on my Kbac 27 d drive. I think we are all splitting hairs about 1725 rpm VS 3400 rpm grinder motors The polar Bear and EERF grinders look like great equipment to me. I would opt for the heaviest and most solid looking grinder for the money. People have been making great knives on equipment for years that is not as good as the current crop of machines in my opinion. My only advice is not to go too light on hp...have at least a 1.5 hp motor and 2 hp if you can get 220 in your shop or garage. Call or go online to WayneCoe in Tennessee for motors and advice but get the 2 hp at the same price as the 1.5 hp and don't let him talk you out of it because like me you will buy a second 2 hp motor later that you could have had right off.
 
A VFD is a Variable Frequency Drive. It varies the frequency electronically from the input. It can also vary the output voltage. For knife grinder motors, it usually takes a normal shop input or 120 or 240VAC single phase 60 cycle, and outputs 220VAC 3 phase. Because 3 phase motors are not reliant on the 60 cycle current to make them spin, the frequency can be varied from almost nothing to about twice the rated input. This would be from 10 Hz ( hertz or cycles) to 120Hz. Many VFDs will go to 200 HZ, and some to 400 Hz, but that is pushing the motor beyond safe limits. A far as the motor goes, if it is a good quality motor, the bearings will be fine running at 3500RPM as they would at 1750RPM. The best motors for running 3Ph power are labeled "Inverter Duty". They are specifically wound to handle the higher and lower frequencies best.

You can NOT run a single phase motor on a VFD, it has to be a 3 Ph motor.

As far as figuring feet per minute on a belt, use this simple rule - If the drive wheel is 4" 1 RPM equals 1 FPM. On a 5" drive wheel 1 RPM equals 1.25 FPM. On a 6" drive wheel, 1 RPM equals 1.5 FPM.
 
River Oaks, I do not believe you can drive a 2hp motor with 110 volt power through a Kbac 27-d. You will have to have a 220 box installed. How do I know? well, I just ordered a 230 volt 3 phase 2 hp induction motor TEFC (totally enclosed fan cooled) to replace my 1.5 hp motor of the same type and I use a kbac 27 d drive. I paid an electrician to put a 220 box in my garage for this purpose. You have to make sure that the "jumpers" inside the Kbac are set to 220 power. Get the 1800 rpm motor unless you are you getting a direct drive grinder. See the motor wiring instructions on the Beaumont metal specialties website. They sell KMG grinders which use pulleys and a jackshaft to drive the belt. Ploar bear grinders have a direct mount motor in comparison.
 
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