Building a mini grinder

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Randy3000

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Jun 3, 2017
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Since i only make small folding knives, I'm thinking very hard about making a small grinder and disk sander. Thinking about a 1x42 belt and no smaller than a 5" disk. Something like this but with a disk sander

I know generally you want high speed for grinding and low speed for sanding. So I'm thinking about rigging the sanding disk on a large wheel. I know that rpm times circumference of the wheel gives you the linear velocity of the belt at the drive wheel, and then at another wheel in the system you divide that velocity by the circumference to get that wheels rpm. So by looking at specs off of sanders and grinders being sold, i can figure out what motor and wheel sizes i need.

So here's my questions. I assume the wheels not directly connected to the motor have to have a little play in them. Is this play enough to make the sanding disk wobbly? Will pressing stock up against this disk cause the belt to slip off? Should i put the sanding disk on the main drive wheel? Should i make a totally separate wheel for the sanding disk completely independent of the belt grinder? I've seen homemade varieties of all kinds, and no one talks really about which design is best. And by best i mean that isn't so problematic in use you wish you just bought the real deal.
 
I would just buy the "real deal." You can get a 1 X 30 with a 5" disk for under $100.
I would get a 1 X 42 and a separate disk sander.
 
If a belt sander is good enough to bevel blades and clean up bolsters then I'll go that route. it seems like putting "grinder" in the description adds a few hundred more dollars!
 
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I fantasized about building a 1x42" KMG.
It must have been the funding crunch that fueled the fantasy at the time.
 
At least up here one of the Chinese tool places sells a 1x42 with a 6 or 8" disc for something like $150. I recall seeing one that was about $220 that was a 2x42 with 6 or 8" disc also.
I haven't used them (my small belt sander experience is limited to the Kalamazoo 1x42 and craftsman 4x36) but they looked decent enough and those were Canadian prices. Might be worth looking at somewhere like grizzly
 
I have a previously mentioned 1x30 +5" combo and the 5" isn't big enough, even for Pocket knives. Remember than you usually only use the outer third of the disc, or at least I do. One end is moving the wrong way, and the middle doesn't move as fast.

If you can build a mini KMG that would be fine but an off the shelf 1x30 is flimsy and rickety.

Something you might do is buy a variable speed bench grinder and use that to power your machine. You get variable speed and more power than you would in a 1x30.

Overall I think it's more about build quality than belt size. Though bigger belts last longer since the work is spread out across more surface area.
 
boy&hisdogs said:
I have a previously mentioned 1x30 +5" combo and the 5" isn't big enough, even for Pocket knives. Remember than you usually only use the outer third of the disc, or at least I do. One end is moving the wrong way, and the middle doesn't move as fast.

If you can build a mini KMG that would be fine but an off the shelf 1x30 is flimsy and rickety.

Something you might do is buy a variable speed bench grinder and use that to power your machine. You get variable speed and more power than you would in a 1x30.

Overall I think it's more about build quality than belt size. Though bigger belts last longer since the work is spread out across more surface area.
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And larger belts tend to heat up more slowly, or that's been my experience. I guess it could also be the larger platen needed for a wider belt that helps dissipate heat.
 
The disk size comment is making me think i need at least an 8" disk. I have lots of free handle material in wood, antler, and bone so i really have a need to be able to make stuff flat easily. A good choice of disk sander will really save me money in the long run by not having to buy handle scales.

I'm concerned about too wide a belt. I'm afraid I'll run into situations where i need to take material off a blade near the tang, but too wide a belt will result in uneven bevels or taking material off the tip accidentally. I feel a narrower belt will be easier to control where i take material off. Also, in making multiblade folders i have a need to taper blades, they aren't usually an even thickness. I think the narrower belt will be easier to achieve the taper i need. With blade sizes in the 1.5"-2.5" range usually, 1" can't be too small i think.

So I've been looking at 1" belt and 8" disk, and the grizzly has been getting bad comments about holes not lining up, so I don't know about that. Maybe i should buy the tools separately?
 
Randy3000 said:
The disk size comment is making me think i need at least an 8" disk. I have lots of free handle material in wood, antler, and bone so i really have a need to be able to make stuff flat easily. A good choice of disk sander will really save me money in the long run by not having to buy handle scales.

I'm concerned about too wide a belt. I'm afraid I'll run into situations where i need to take material off a blade near the tang, but too wide a belt will result in uneven bevels or taking material off the tip accidentally. I feel a narrower belt will be easier to control where i take material off. Also, in making multiblade folders i have a need to taper blades, they aren't usually an even thickness. I think the narrower belt will be easier to achieve the taper i need. With blade sizes in the 1.5"-2.5" range usually, 1" can't be too small i think.

So I've been looking at 1" belt and 8" disk, and the grizzly has been getting bad comments about holes not lining up, so I don't know about that. Maybe i should buy the tools separately?
Click to expand...

In my experience combo tools never do each job as well as a standalone. Buying two machines will be more expensive but it's also a waste of money to get a "deal" on something that's junk.

That grizzly 1x42/8" combo still has the crappy little platen that the HF and many other 1x grinders have. You might be able to build a better one, I built a "better" one for mine with thicker steel and a piece of tile but it still flexes a little, which would be pretty bad for things with tight tolerances like a multi blade pocket knife.

Again, I think a mini KMG home build and standalone disc will be the best grinder combo in the end.
 
You can run narrower belts on most machines. I often split belts to 1" or even 1/2" wide for handle shaping with my 2x72. It ends up being a lot more economical than using my 1x42.
 
I have an old Craftsman (I think) 1x42 w/ an 8" disc. It's hard to find PSA discs with decent abrasive in that size, but I use it a lot for hogging off or flattening handle material after gluing. I use the belt slack with no platten for handle shaping. Despite having a KMG, the combo machine sees action on just about every knife - I just don't use it on steel anymore!
 
daizee said:
I have an old Craftsman (I think) 1x42 w/ an 8" disc. It's hard to find PSA discs with decent abrasive in that size, but I use it a lot for hogging off or flattening handle material after gluing. I use the belt slack with no platten for handle shaping. Despite having a KMG, the combo machine sees action on just about every knife - I just don't use it on steel anymore!
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Take a look at a place that sells autobody supplier. Their big sanders take 8" discs, and discs from them usually cost about what buying sheets to cut into 9" discs do, but without all the screwing around
 
After a lot of deliberation, i finally just bought the grizzly 1"x42" belt and 8" disk sander combo. It arrived late this afternoon. I assembled it without any problems at all. Overall i was pretty happy with the machine out of the box, seems very solid and everything fit together correctly, the only plastic parts are the guards. Started it up and everything ran smoothly and is not very loud. We just moved into our first house, and my wife can sit in the living room with no tv on and can't hear it at all in the garage. That works for me! She goes to bed about 3 hours before i do so that is 3 hours of work time i never had before, she can't hear anything I'm doing!

Going to work on my first stockman, at 10pm, pretty happy about that.
 
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