Belt Grinder

downsizingnow48 · Mar 2, 2019

This is not about welding except I figure many of you interested in welding might be interested in a 2x72 belt grinder.

Our girls have been asking for handmade knives since I retired, which sounds like a good thing to do, and obviously an excellent reason to get a new tool.

I studied the internet for a couple months. There is a forum called BladeForums which is a gold mine of information on these belt grinders. It is the knife-making equivalent to TBN for tractors.

I wanted to make the grinder from scratch, which lots of folks do. But I have so many projects stacked up. I finally decided to buy it from an outfit called The Belt Grinder in Minnesota. It is wonderfully well made, everything CNC machined. I got the 2hp 3 phase Leeson motor from Surplus Center and the Variable Frequency Drive from KB. It took a day to make a bench and wire up the motor and VFD. I already had 240v power at various places.

I haven't got to knife-making yet. The first job is to clean up the main rails of the new backhoe thumb I am making. At a belt speed of about 3600 feet per minute, with a 36 grit ceramic belt, the grinder chews through 1/2" steel very fast.

Right away I can see a need to lay the machine on its side, there are many operations that pretty much require that. So will rig up a simple hinge.

I ordered it without a work table. The knife making work tables are all pretty small. But for what I do I wanted something bigger. So I made a 8x24 table from a piece of 1/2" aluminum plate left over from something else. It works very well.

I have been using hand held belt sanders instead of bench grinders for some time now. Now that I have this 2x72 machine, I am probably going to sell the old Baldor 6 inch grinder which I haven't even turned on in over a year.

yomax4 · Mar 2, 2019

Cool choice on the grinder. I know the company in MN. I'm glad to hear that your girls are interested in the home made knives. mine are the same. I just watched a video of a bundle of cut pieces of welder liners were melted to make cool Damascus knives. Enjoy !!

Big Barn · Mar 3, 2019

That’s a nice looking grinder!

It will be nice to lay it on its side to use horizontally. That was my plan with my Burr King but it got way too complicated so I just built a pedestal and mounted it conventionally.

radios1 · Mar 4, 2019

good job. and you're lucky to have 3 phase in your house, most people can't..

Big Barn · Mar 4, 2019

radios1 said:
good job. and you're lucky to have 3 phase in your house, most people can't..

downsizing is using 240V to run the 3 phase motor with aid of a VFD. A great setup.

downsizingnow48 · Mar 4, 2019

Yep. It is pretty much magic to me. There is one block in the VFD where you hook up the single phase AC inputs, in this case the two hot leads from the 240 wall outlet. There is another block where you hook up the three leads from the 3 ph motor. In between the VFD converts the single phase to three phase, and provides frequency and voltage control to operate the motor at various speeds. So it is a nominal 1800 rpm motor that the VFD can spin from zero rpm to close to 3600 rpm. More magic. Very beneficial for a grinder, you can get the exact belt speed to suit what you are doing from polishing to hogging.

Fallon · Mar 4, 2019

downsizingnow48 said:
Yep. It is pretty much magic to me. There is one block in the VFD where you hook up the single phase AC inputs, in this case the two hot leads from the 240 wall outlet. There is another block where you hook up the three leads from the 3 ph motor. In between the VFD converts the single phase to three phase, and provides frequency and voltage control to operate the motor at various speeds. So it is a nominal 1800 rpm motor that the VFD can spin from zero rpm to close to 3600 rpm. More magic. Very beneficial for a grinder, you can get the exact belt speed to suit what you are doing from polishing to hogging.

Technically a VFD converts any input (1 or 3 phase) to DC. Then it converts DC back to AC, usually 3 phase at whatever frequency you want. It just turns transistors on & off really quickly. That way you end up with a stair step voltage curve that approximates an AC sine wave. Just imagine turning on & of a switch on 12v DC really quick. If something was smoothing out the output & it was on only half the time you'd end up wit about 6v DC. Just vary the amount of time you leave the switch on or off to match a sine wave & flip the polarity half the time with another switch & you get AC.

joeu235 · Mar 7, 2019

I know very little about 2 x 72 grinders. Do they really need a 2 hp motor?

downsizingnow48 · Mar 7, 2019

joeu235 said:
I know very little about 2 x 72 grinders. Do they really need a 2 hp motor?

I am just getting started so not an expert by any means. I studied these grinders for a couple months before buying. I would say the companies that sell complete grinder packages range from 1 hp to 3 hp for motor options. 2 hp seems to be pretty common which is why I got it.

downsizingnow48 · Mar 11, 2019

Got the hinge made, works well.

Photo 1 - Grinder in vertical position. You can see the brace that holds it in place and a hole in the bench, which is what the motor rotates down into in the horizontal position.

Photo 2 - Grinder in horizontal position. I made a work table out of 1/2" aluminum 6x18.

Photo 3 - The hinge. There is an adapter plate of 1/2" aluminum that bolts to the machine base on one side and to two pillow blocks on the other. I got the pillow blocks for $7 ea. Then the main hinge frame, welded up from scraps laying around. The hinge pins are 1" bolts left over from something else.

All the bolts that go through the bench have large heavy duty plate washers on the bottom side to keep the fasteners from sinking into the wood.

First project is final shaping on my new backhoe thumb, and bevelling of the cross pieces for welding.