DIY is not cheap because the wheels are so darn expensive. I paid 200 bucks just for 4 wheels from Beaumont Metal Works. I am in the process of designing a simple DIY that uses inexpensive parts. I'm targeting 200 bucks total without the motor. The only thing I can't find is an inexpensive drive wheel that fits a 5/8 inch shaft.
I really like the "knifemaker sander" from Grizzly. I think it's probably around $400 plus shipping. It runs 2x72 belts and when you ever decided to upgrade to a nicer unit, this one still works great for woodworking, etc... There is also an unused shaft coming out the left side that can take a buffing wheel or whatever.
Ah, found a pic of it...
Just my two cents worth here. Even though I have a KMG that I use everyday for knives, I still use my Grizzly sander a lot.
I was just thinking about the difference between the 6X48 that I have and the 2X72 that seems to be the standard. If you go by the surface area of the belt, mine has twice the surface area. What makes the narrower belt attractive?
The 2 inch belts make it easier to get into tight spaces plus there are more belts available for 2x72. That being said, you can make a knife on anything. There are some guys making knives totally on disk grinders.
One of the most important things for me to have correct is the platen. A lot of grinders don't have the proper width (that is the same exact width as the belt running over it) and will be too wide which doesn't allow for grinding right up next to the belt. Also, the platen should align under the belt while running and be square to the belt as well. If you look for these items you'll quickly rule out 3/4 of what's available.
While I understand what Dave is saying and agree with his points.....most grinders have the ability to track the belt back and forth across the platen. You can hang the edge of the belt off of the right or left side of the platen so that you get into corners and such, or it can be perfectly in line on both sides of the platen when you don't need that. That feature is NICE!!!
It also depends on how serious you are about grinding, little features, such as a flat platen with sharp even corners that line up to both sides of the belt are very important if you grind all day and expect to get something done. The other critical feature is HP, a lot of wide belt grinders and some of the narrow ones are seriously underpowered.
Thanks for all the responses. Other than the Multi-Tool, is there anything I can hook up to a 8", 3/4 HP bench grinder? I have another 1/2 HP motor around here too, and just don't want to buy a motor if what I have will suffice for occasional use. Except for the Multi-Tool, no weld DIY, or more $$ than I can invest in it, everything I've found online has an integral motor. $200 is probably gonna be my limit for now. Thanks for all the advice.
Funny that we are talking about the details of the trim(edges, exact width) of a metal part...on a machine designed for altering metal parts. Doesn't seem like you'd need to buy a different on over a platen that a belt sander can easily make.