I have several bench sanders:
1" X 42" belt with a 9" disc on the side.
2" X 42" with a 6" disc.
2" X 72" belt -(no disc attachment)
4" X 36" belt with 6" disc.
A 12” disc sander.
I don't have a 1" X 30". I think the types of belts available are too limited to be of a lot of use in knife making. However there is a wide variety of grits and different types of abrasives like silicon carbide and Alumina Zirconia for metal working for the 1 X 42. The extra 12” in length of the belt makes the belts last longer, and it helps keep the belt and the work cooler.
My 2 X 72 is the sander that has the most types of abrasives available with the widest range of grits available from 24 grit to 4000 grit. This size machine seems to be the choice of knife makers and has the widest range of belts available.
My 2 X 42 is a gutless Sears bench top belt sander. It is so underpowered that about all I use on it is the 6” disc sander & I don’t do that very often.
My 4 X 36 was the first sander I bought. It is also a Craftsman and it is a decent sander. When making & sharpening knives I really don’t need such a wide belt so about all I use it for ay more is to sand wood for handles or to shin out a set of handles when they are too thick. It is handy to have from time to time but not a necessity.
I also have a 12” disc sander that was given to me. I use it occasionally to remove a lot of material in a hurry.
Of all these sanders I find the most useful to be the 2 x 72 & the 1 X 42.
Here is a link to the Grizzly 2 X 72 like mine:
http://www.grizzly.com/products/G1015
If I were going to buy a new 1 X 42 I would probably buy a Grizzly. I like the quality of their equipment. No, they aren’t made in the USA, but I don’t know of any 1 X 42 that is now days. Here is a link:
http://www.grizzly.com/products/1-X-8-B ... nder/H8192
The key for me to the usefulness of the 1 X 42 is the variety of sizes of grit, different types of abrasives and different weight of backings available in the belts for this machine. All 1 X 42 sanding belts are not created equal! I have found cheap belts are a waste of money.
I hope this helps a bit in deciding which one(s) you get. It really depends on what you are going to do with the sander.
If you are just fixing up a few knives, sharpening a few knives, etc, the 1 X 42 would be adequate. If you want to do a lot of work on knives, re-handling, rebuilding & repair I think you will eventually be best served with a 1 X 72.
A disc sander is useful, but a 6” on the side of the 1 X 72 is adequate for most things you will need while fixing knives.