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Building a Belt grinder - advice please.

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Peter F24/04/2019 23:34:06
98 forum posts
23 photos

Having owned and sold one of those little 1"x30" belt sanders, you've all seen them, I got rid of it because it was appalling quality, but it was the first time I've owned one in my home shop, and it was very useful for the week I owned it.

My new project is to build my own belt grinder, but to standards I deem acceptable, this Knife making hobby has become very popular lately, and I like the versatility of the designs, with a tilting front section, but want one with a wider belt, like many people here, space is problem so it has to have a very small footprint, I think a 4"x36" or 100mmx915mm is possibly the way to go, as they are a very common belt, and about the size I want.

Here is the problem, many of the knife making community seem obsessed with machines that hog material off as fast as possible, like it's a competition or something, I've seen many comments by them talking about 3HP motors etc, is this really necessary? would a 1.5HP/1.1KW motor bog down? not be powerful enough? I'm not gonna push my body weight against it to prove to people how fast it can reduce metal to dust, but would like it to be reasonably capable.

I'm planning on using a 3 phase motor so I can have variable speed, I'm not an electrical expert so I'm unaware if how this affects the torque so thought I'd mention it.

TerryB25/04/2019 02:28:31
7 forum posts
17 photos

I build the 4x36 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.

Plasma25/04/2019 05:56:17
191 forum posts
20 photos

Hi Peter, are you using this machine to make knives? The Americans are obsessed with belt machines but Sheffield always used abrasive wheels running in water for grinding their blades, no fear of burning the steel.

Best thing about the machines that use is the variety of contact wheel and platens they can fit up front. Baldor do knife making machines of this type.

I made a 1/4 scale copy of one, I will dig it out and post a photo.

Mick

Paul Lousick25/04/2019 09:26:34
1043 forum posts
473 photos

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.

Peter F25/04/2019 10:16:23
98 forum posts
23 photos

Terry, yes I'd love to see what you've built, the plan was to use a face mount motor, and attach the drive wheel directly to it, I'm trying to keep the overall size to a minimum, what size drive wheel would you recommend for a 2800rpm motor? I've read speeds varying from 1500 to 4000 surface feet a minute for metal, abrasive dependent, but I'd be willing to go single phase at a similar SFM speed as you if you say it works ok, I've just seen 4x48" belts are quite common, I think I'll go with those.

Plasma, No I'm not making knives, Like terry said, it's for squaring up tube etc and general use, knife makers tend to prefer the 2 inch belts, I think it gives them more control putting bevels on the blade, but for me I think 4" would be much more useful as a general purpose grinder, love to see yours too.

Paul, yes, I've been looking at loads of them, which made me think of using some of their designs with a wider belt could create more of a 'tool room belt grinder' so to speak, thanks for confirming your experience with a 1/2HP motor, I think a 1 1/2HP motor is a happy medium, could I ask what size drive wheel your 2850rpm grinder uses?

Hopper25/04/2019 10:54:24
avatar
3512 forum posts
68 photos

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.

Ian Parkin25/04/2019 11:01:36
avatar
606 forum posts
166 photos

I built a 2x 72 grinder using a 3 phase 2hp motor 1440 rpm driven from VFD so variable speed

It can be stalled easier than i thought or rather the over current trip on the vfd trips out

I used a pallet truck wheel as the driver so 200mm dia

Kevin D25/04/2019 12:28:26
12 forum posts
86 photos

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.

imag0086.jpg

img_0848.jpg

img_0845.jpg

Peter F25/04/2019 13:17:34
98 forum posts
23 photos

Hopper, for me building it is a big part, I'm not so much in to model trains etc, I prefer making tools, and to be honest, the quality of commercial ones similar to what I want to build are in the £700 to £800 region,

Ian, was there any reason you went for a 1440rpm motor? all the info I can find points towards metal belt grinders needing much more speed than wood?

Kevin, how have you found the 750w motor?

SillyOldDuffer25/04/2019 13:39:33
4121 forum posts
831 photos

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


Ian Parkin25/04/2019 13:59:10
avatar
606 forum posts
166 photos

Peter

i went for the 1440 rpm motor so i can run it from 20hz to 100hz Or 570 rpm to 2800 rpm

so with my 200mm driving wheel i can go from 361metres/min to 1758 m/m (that’s 100km/hour)

Its been very useful so far i have built a mop shaft to take 200mm dia mops or wire wheels taking the drive with a rubber flat belt

jaCK Hobson25/04/2019 16:55:33
163 forum posts
20 photos

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.

Vic25/04/2019 17:33:13
2016 forum posts
10 photos

I have a much modified Record Power BDS 250 which gets a lot of use in my workshop. The standard belt size is 150 x 1220 but I’ve made an auxiliary platen for the machine and often run 50mm wide belts on it for tool sharpening. I sometimes make my own belts or split 150mm belts into three. Motor power is 0.8 Kw according to RP.

Peter F25/04/2019 17:35:20
98 forum posts
23 photos

Jack, thanks for your input, but I'm not using it for knife making, it's for general fabrication work, which is why a 4 inch belt is more useful for 'ME' what I want from the machine, I had a 1 inch grinder, and it was next to useless for what I needed, the machine I'm planning on building should be able to use 4x36 and 4x48, the former are cheap as dirt and widely available, the later are not expensive either really, but yes you are correct, if knife making is your thing, 2" is the way to go,

grinder

This is the style I'm planning on building, but with 4" belts, and 48" not 72" so reduce the size down, the design allows for different length belts, and I should be able to make it very compact, I'll be building the frame out of 10mm thick cold rolled steel not ally like the picture.

Not entirely sure what motor set up to use yet, but thank you to everyone for their input, it has been helpful, and those of you who mentioned, I'm still interested in seeing your machines,

Vic25/04/2019 18:48:13
2016 forum posts
10 photos

I’ve found this company good for abrasives belts as you don’t have to buy ten at a time like some suppliers.

**LINK**

I like the “no weld” approach of this design. smiley

**LINK**

Ian P25/04/2019 19:33:44
avatar
2078 forum posts
88 photos

I am fortunate to have a spare motor and VFD which are now on my 4x36 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 F25/04/2019 20:50:16
98 forum posts
23 photos
Posted by Ian P on 25/04/2019 19:33:44:

I am fortunate to have a spare motor and VFD which are now on my 4x36 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

Yes, I've changed my mind about half a dozen times, but I think a 3 phase 2hp motor with VFD is what I'll do, you seem to understand the concept of what I want to create, a versatile workshop machine, a 2" belt wouldn't be able to do simple tasks like make sure a bit of sawn off 50x25mm box section cut at 45 was spot on, the belt just isn't wide enough, this photo shows the kind of rest that makes that design so good.

dsc_1183.jpg

Ian P25/04/2019 21:08:11
avatar
2078 forum posts
88 photos

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

TerryB25/04/2019 21:22:50
7 forum posts
17 photos

Peter, there is a fundamental floor in the design of that first model. I made the same mistake on design.

When you build yours, make sure that the guide wheel (top wheel) moves through a horizontal arc to the belt.

I will post again with pics of my different designs and the pit falls.

Peter F25/04/2019 21:27:36
98 forum posts
23 photos

Ian, the first one I'm not sure if it's a 3d rendered model, but it is a real machine that is sold, both are just random pics I found on Google images, if you google 2x72" belt grinder, you'll get loads of this style of grinder, 2x72" seems to be the in vogue size in the knife making community, they are a very versatile design, which is why I want to make a similar design, but with shorter belt and wider, there's an American company that makes one that is in the region of $4000.

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