2x72" Belt Grinder as a Foundry-Related (Pattern-making) Tool

Here is what has had my attention the last 2 weeks or so. This is my slightly modified version of Jer Schmidt's 2x72" belt grinder design. It is well-designed and switches quickly from vertical to horizontal mode using a single knob and lever. For now, and maybe forever, it is powered with a harvested treadmill motor and MC-60 treadmill control. I may install a 3-phase motor and VFD if the treadmill motor does not live up to its billing. The grinder is heavily built and smooth-running. I would guess it weighs 175 pounds.

I have only 30 to 60 mins on it, but am very positively impressed. Included are a fixed 90deg table, tilting table, contact wheel, and small wheel sets. It is fast to change belts and to change tables for contact wheels etc. requiring 30 secs or less to do so.

You can see that it needs to go onto its mobile cart (a tool chest really) and to get the motor control into an
air-tight metal box and to get some wires cleaned up. But it is 95% complete.






I think this will be very useful in pattern making as putting a specified amount of draft on a surface and trimming parts to fit will be very easy.

I will not go into a long discussion here about making the tool here, but would, instead, suggest looking at a few of Jer's videos where he does a good job of describing the features and build of the tool.



Jer appears to be a very young man. But, the excellence of this design and his YouTube skills suggest he will make many contributions in his lifetime.

I did "improve" on his design in a couple places and would suggest that if anyone gets serious about building one of these grinders, they should get in touch with me for a discussion of those modifications of either design or fabrication technique.

If anyone is interested in belt grinder use tips, I would suggest looking up Walter Sorrells' videos for the thoughts of a professional knife grinder who can clearly and concisely instruct on grinder selection, belt selection, use, safety, etc. This applies whether you are going to be making knives (not me) or are otherwise utilizing a BG.

Denis

 

They are great machines to have, highly recommend having one for pattern making and for fettling castings too. I built mine from hand me downs after a friend bought a Radius Master: the contact wheel and idler wheel as well a frame and 12" sanding disc. The belt and wheels can rotate around the axis of main shaft so the belt can be horizontal and the idler wheel has a unique tracking mechanism so it can swivel 5 or so degrees like a ball joint depending on how the adjuster knob is rotated. That mechanism predates the Radius Master and some German made machines that now use it. The belt speed is 100 Km per hour on low pulley and the disc is 160 KM/hour (100 miles per hour).

 

One nice feature of Jer’s design is that the table need not be changed when changing from vertical to horizontal orientation. The belt/motor rotate on an axis coinciding with the table’s level requiring no adjustments, just rotation. Belt changes occur by just pulling that knurled lever to relax the idler tension. Slip the new belt on and relax the lever—-done. The various tables, contact wheels, and small spindle wheels are replaced by loosening a single toggle nut. He put a lot of thought in his first design in 2017 and then improved it 4 years later. It was those refinements that drew me to his design.

It is interesting that I came across Sorrell’s “buyers guide” video after I was 90% finished building my grinder. I was relieved when as he ticked off the important features for a good belt grinder, Jer’s design hit them all.

And, yes, the difference in metal removal and lifespan of a ceramic belt is stunning. They do have limitations, but for stock removal they are great. Finishing operations, maybe structured abrasives and zirconia. The number of belt choices can be a bit daunting which is why I recommended Sorrell’s video on belt selection.

Denis

Added: tables “plug into” the square tube socket. Rotation of belt from horiz to very is easy.

 

One safety feature that might depend on your particular machine layout is a steel bar in a few strategic locations to prevent the belt whipping abound at high speed if the join breaks. As belts sit unused the glued join can let go and it's not unknown for belt makers to be selling old stock like the new tool store chain that opened in my town with an entire batch of sun yellowed belts that all failed in under a minute. I've seen one nasty jagged scar on the upper arm of a person that needed several stitches and directly experienced a few near misses before fitting a bar at the back of the idler wheel. Is this particular to my machine's wheel geometry?, it might be although I see similar hinged sheet metal covers over the rubber driven wheel on several commercial machines too.

 

You bring up a good point Mark. I wonder about the appropriate location of safety bars however. For instance, in your case, if the belt breaks on let’s say the back portion of the travel when the belt is heading upward will that bar make much difference in how the belt whips over the idler wheel toward the operator? Or in my case with the two guide wheels on the platen should I locate a bar just as the belt arcs over that top wheel so that the belt is sort of constrained from flying forward toward me. The answer to this question does not seem entirely obvious to me.

Denis

 

I looked around a bit for injury reports and 2x72 belt grinders. There are not a lot, seemingly, though I did find this so-so video of a belt failure. If you slow down the playback to .25 speed and watch around the 4 to 6 second mark you can sort of see the movement of the broken belt as it impacts and passes beyond the table which I assume would be functionally equivalent to a safety bar. The belt whips outward as you would expect as it tries to make the corner around the wheel, but the table holds it back. So, that makes me think on the platten setup, a safety bar, if used, should be located just where the belt has passed around the wheel and is starting to descend. Broken belt flailing upstream of the bar would be restrained by such a bar. How did you decide to have it on the back and not front of the idler wheel?



The edge of a coarse ceramic belt would really cut if it were drawn forcefully across you hand of forearm, for instance.

Denis

 

Those are two different tables. One is a fixed dead 90 degree table and the other is a variable angle table. Both tables will be drilled and tapped (the angle one is already) so that auxiliary larger or specialized tables can be attached on top of the steel table. A radius grinder is also a simple add-on for either table

Next on the docket is to build the small wheel attachment that plugs into the rotating square tube. (The tables plug into the fixed tube. Here is a video of his original design.) The parts are cut and I will weld it up tomorrow if I don’t melt iron—-weather dependent. Two molds are freshly packed today and ready to go.

.

A few mins in he shows the small wheels for grinding concavities with radii as small as 1/8” possible with the right belt.

Denis

 

That's the first time I've seen such a belt failure, it's like there was a small tear on the belt that caught on his table. The less than ten failures I've seen have all been a clean break on the glued join and the belt has swung round either wheel like a cracked whip. The bar or the table catches the belt which comes to a halt as there's no tension. Crosslinked urethane is often used for it's high strength and heat resistance but has a shorter join life.

I found the photocopier repair shops will let me rob a retired copier for the small diameter (under 2") hard rubber rollers which are ideal for belt grinders.

This video shows a clean break I'm talking about at the 3:08 minute mark:



This video shows a similar belt path to mine as well as multiple belt fails possibly due to old glue joins.

 

Yes, the belt launches right off the top roller straight at him. So, maybe a bar just as the belt is making the downturn on the top roller would reduce the launch somewhat. Not sure.

Denis

 

A some commercial units have guards over 180 degrees of the wheel when it's not being used, so that'd be better protection and can swing clear for use.

 

The motor control is now boxed up and power cord properly installed

zzz

 

Here is a quick vid showing the grinder eating a piece 1x1x1/8” angle. I have gone to 2hp 3-phase motor and VFD. I really was not pushing it. Note that the motor does not slow. This was done using a 60 grit Cubitron belt. A 32 would have been more agressive. It is good to keep an eye on fingers as they could be ground quickly as well!



Denis

 

For as much metal work as you do, David, I’d push this one up the list. I was not expecting the difference in the feel of smoothly abrading steel with the belt vs the hop, hop, hop and relatively poor control of grinding with a wheel or disc. It’s just different (and BETTER!). I’d also give careful consideration to Jeremy Schmidt’s design and make sure another one bests it some way before purchase or construction of something else. Believe me, I’ve been checking out belt grinders and most aren’t much. Simple, yes. But limited.

Denis

 

It is now complete. It is on a mobile base which doubles as a tool chest as well as granite surface plate carrier. I am very happy with the machine.

The handle plugs into a socket in the base and usually will be stowed on the base out of the way. Two casters swivel and two swivel or are locked from swiveling as needed at the moment. It weighs 700 pounds altogether. So brakes aren’t needed.

I am using an AutomationDirect VFD (protected with a “roll cage”) and a 2hp 3-phase motor. It’s a great tool. I also made a small contact wheel attachment, tilting table attachment, and large contact wheel attachment. Each switches out in less than a minute. I tried a cheap VFD. It was defective, horribly and inadequately documented and flimsy. The AD worked perfectly as preprogrammed right out of the box. Its 650-page manual covers every possible application and question.



I won’t go into details here, but I have some suggestions for anyone making this grinder.

Denis

 

I broke my last belt grinder belt last week and the new belts haven't arrived yet.... I have never missed having a power tool so much .