I build the 4×36 grinders on the side line for extra income. Personally I use a 100 x 915 grinder with a .75HP motor to build the big grinders.

It works a treat! I like the broad belt for squaring off the tubing corners. One of the most used machines in my shop.

The best part is that I don't have to use 3 phase or variable speed. Just switch on and go. The belt stays in line with minor adjustment. I use ceramic belts for roughing and then switch over to the Alu ox belts for finishing or finer work.

I can stall the machine with grinding big surfaces, but not easy, so I reacon a 1.1KW would work fine.

Personally, I would not go with a VFD. You do lose power and it is overkill and expensive. The only reason people use them is to start slow in getting the belt to run true. If you want I can upload a pic of mine.

If you build your own, just use a single phase motor with a 2 to 1 reduction on the pulleys or get a 2 pole motor that runs at 2800RPM and use equal size pulleys.

Lots of designs for belt grinders on Youtube, etc.

I have a 2" wide belt grinder with a 1/2 HP, 2850 motor which is OK for light grinding but way too under powered for any decent work. I can easily stall the belt if I push too hard. Would prefer something with at lease a 1 or 1 1/2 HP motor.

Paul.

I use an 8" bench grinder with a commonly available "Multitool" brand attachment that runs a 2" x 36" belt and an 8" or 10" sanding disc on the end, with rest, which is real handy for squaring pipe etc. Whole rig cost me $40 at a garage sale but you can buy them brand new for a few hundred dolalrs so may be worth it if you are using it that much. The Multitool quality is professional level. Never had any problems with it. If you google Multitool Belt Sander plenty of pics there give a better idea.

Hi. Have built a 4 x 36" with a 750w motor. It used a rotor and bearings from an old motor as a drive roller with a 8" disk on the end. Belt drive with idle pully to tension. Works in either vertical or horizontal position.

Basically the power needed to drive a machine tool is related to the metal being cut and how fast you want to remove it. A small motor can do the same amount of work as a big one, it just takes a lot longer!

How much work is required to remove a cubic millimetre of common metals:

Aluminium Alloys – 0.3 to 1J
Brass and Bronze – 1.3 to 3.2J
Cast Iron = 1.1 to 6J
Steel = 1.9 to 9.2J

It takes about 2 Joules to remove a cubic millimetre of mild-steel and a Joule is a Watt-second.

Examples:

Grinding 100 cubic millimetres off a mild-steel bar would take a 500W belt grinder:

(2.0 * 100 ) / 500 = 0.4 seconds

A 2500W belt grinder could do the same job in:

(2.0 * 100) / 2500 = 0.08 seconds

Knife grinders work with hardened steel, say 8 Joules per cubic millimetre. Shaping the blade of a largish knife, which might include grinding fullers, means removing a lot of metal – perhaps half a blank. A 200x6x40mm blank might need 24000 cubic millimetres to be removed. On a 500W grinder:

(8.0*24000) / 500 = 384 seconds

With 2500W

(8.0*24000) / 2500 = 76.8 seconds

Makes sense for someone making lots of chef's knives out of old farrier rasps to own a powerful grinder. The same machine isn't an intelligent choice for someone doing occasional light work in brass and mild-steel, or someone who needs the grinder for sharpening rather than serious metal removal.

When buying tools I always ask myself what it's for. Usually there's a huge gap between what I want, (a pristine tool-room Dean, Smith and Grace), and what I need ( a mini-lathe ). 45 years ago an old chap bent my ear about the inexpensive Japanese socket set I'd just bought. He told me cheap rubbish like that is a waste of money because it won't last. 8 or 9 old-bangers later, the set is still in perfect condition today. Buying the quality socket set recommended by the old chap would have been a complete waste of money.

But I do recognise that pride of ownership is important to many. If spending time and money on good tools is your thing, go for it! But don't tell the wife or your accountant!

Dave

1HP per inch of belt is accepted wisdom for knife grinders if you are going to do a lot of grinding. I know people who have more HP but they make a living from grinding. I have a Goset grinder which is 1.1KW for 2" which is fine for me https://www.youtube.com/watch?v=tuTNe1YDab0. I have used 1hp for 2" and it wasn't always quite enough. (I have a home build 2HP 2", and an under-powered 1HP 4" which both get some use, and a couple of the DIY store 4" (one converted to use 2" belts) which just gather dust).

If I was making a grinder, I would go for 2HP and stick with 2" for knife making. You don't tend to use the whole 4" width evenly when grinding bevels and you don't often need to flatten stock much wider than 2". 4" belts are more expensive. You go through a lot of belts. Longer the better- as they will run slightly less hot and will be cheaper per inch of belt (you pay for the joins).

I'd even consider using narrower belts.

I am fortunate to have a spare motor and VFD which are now on my 4×36 linisher. Whilst it is a bit cobbled together (the original integral motor burnt out) I would recommend having a variable speed system. Obviously it depends on what sort of use the machine is put to, but for flexibility working with a variety of materials, from CI, hardened steel, plastics, aluminium etc, the ability to alter the cutting rate is indispensable.

At really low speed its possible to flatten and adjust (with a high degree of control) say the surface of a CI angle plate to a state ready for scraping.

One day I would like to make a more versatile belt grinder/linisher/sander (or whatever the right name is) so that items like instrument front panel can be 'brushed' using a slippery hand held pad to press the belt (underside of the loop) into contact with the workpiece. Another useful feature would be to have the platten the same width as the belt itself so that its possible to sand/grind an internal corner.

For home workshop or ME use a VFD is definitely worth having

Ian P

Peter F, the machines shown in your two pictures look brilliant!, I want one!

Do they exist, one looks a photograph but the first one could be a rendered 3d model. Either way do you have nay more info or links?

Ian P

The tracking wheel moves up and down to tighten the belt but can also be angled to track the belt on the rollers.

A good series of videos has been posted on Youtube by Geremy Scmitdt about building a 2×72 inch belt grinder which can be used in a vertical or horizontal position.

He has made lots of different attachments and has a set of plans for the grinder.

Paul.

Just as an aside, it's interesting how unguarded belts on lathes bring howls of warning — or provisos such as "removed for demonstration purposes, don't do this at home" — but some of these beautifully made belt sander machines look as if they are just waiting to snatch somebody's shirt tail as they walk past, and that seems to be ok. I just have to wonder why that is?