Big DIY Belt Grinder Build (planning)
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Author:  Fred [ Sun Jul 07, 2019 2:53 am ]
Post subject:  Big DIY Belt Grinder Build (planning)

I reached a point in the vice table build where I needed a belt grinder with flat table to do a nice job of what I was doing. Thought about asking a friend. Thought about buying one. Watched a load of YT vids. Remembered other YT vids that I had already watched. Saw some of the prices of new gear. And thought, I need to build one. I had previously discussed these with slackercam when over at his place one night, and that was what probably got me watching videos of them a while back, maybe 6 months ago or more. So I emailed the slacker and suggested a collaboration. No reply. SMS sent, he phoned me back, yep, keen to build 2 to some shared/agreed design. So I started thinking "what DO I want?" I was going to email him again, but thought I'd put it in public so others could add their 2c to the process, too. More eyes/minds = better, as evidenced in the vice table thread. :-)

The unit that inspired me months ago is called RM-48 Radius Master and is made in Australia. But it has a few minor issues: small table, small belt, 1.5kw/2hp, high price: $3400nz!! :-o and

It has a cousin with different features here:

There are also some more reasonably priced (Chinese) and bigger belted units available like these: under various brand names from various suppliers.

After that initial discussion months ago, some of the vids I watched include the epic fireball tools go kart belt grinder series:

Impressive unit, unique design, lots of nice features/details.

And this somewhat annoying series with multiple attachments:
Another approach to reconfigurable belt grinders:
Lots of DIY contraptions out there, varying degrees of convenience/quality/etc.

Looking at the RM-48 unit with 1200 belt in triangle configuration, the triangle is approx 400 on each side. To do the same thing with a 2m belt would be approx 650mm on each side, bigger, but still reasonably compact, more so than the long style configurations.

Things I want out of the unit:

  • Big belt, wide and long, long life and more versatile, 6" / 150mm by 2m are 90 for a pack of 3 in one grit from machineryhouse, didn't look elsewhere, this is cheap enough
  • Long flat platen under the belt on one side, ideally about 500mm would be nice, but whatever works out with 2m belt + wheel radii is fine
  • Easy/quick belt change for swapping out grits while working - open to design input here, haven't thought much about it except some sort of fulcrum point with one side near peak, other free
  • Assembly counter weighted / balanced around pivot points / shafts for safe/easy reconfiguration of grinding style
  • Spark collection/control is important for me in a very confined very flammable work area, well designed generous guards that collect and direct and control and deliver to a bucket of water perhaps
  • Variety of wheel sizes from say 12mm up to 200mm or so including 100mm, 50mm, and 25mm or there abouts
  • Belt tension works in any orientation, not purely motor weight/gravity
  • Max single phase draw, so about 10-15A @ 240V, 2.4kw-3.6kw, 3hp to 4.5hp absolute max
  • Three phase motor with VFD for speed control and soft start seems like a good idea
  • Table very stiff/rigid/flat both in terms of the surface and the mounting setups
  • Table adjustable distance to belt with small range, maybe fine thread adjusted?
  • Table adjustable angle from 90 to 135 (45 down) with coarse/quick and fine/slow adjustments
  • Table drilled on 50mm grid, for precision pins and precision angle setup using them
  • Table pivot centreline exactly on the lip of the bevel ground table inner edge by way of placing hinges on ends outside belt area. (Unique idea?
  • Platen position styles listed separately below:

Platen should be able to be used:

  • facing up for working above with downward pressure
  • facing forward vertically with table below for normal use
  • facing forward horizontally with table below for long parts
  • away with large wheel forward for soft inside radii
  • away with medium wheel forward for medium inside radii
  • away with adjustable wheels forward for various tight inside radii
  • away with one non-platen side facing forward (vertically)
  • away with one non-platen side facing up

So in summary, a swollen big boy's version of the radius master with hinge placement for the main unit swing such that one big table can more or less stay still and have the unit move around it.

Any all thoughts/critique/ideas/contradictions/abuse welcome! :-)

Author: [ Tue Jul 09, 2019 11:16 am ]
Post subject:  Re: Big DIY Belt Grinder Build (planning)

Here's a bit of a ramble of thoughts.

- How do you think you'll most commonly use the machine? With the belt vertical or flat? One of my all time favourite tools is a basic linishing attachment for a bench grinder. Like this . I think using the belt flat can feel more natural depending on what you're doing.
- Wide belts are good but the outer edges tend to flare out and it makes grinding across the entire width of the belt inconsistent. Maybe a really nicely made machine wouldn't have this but the belt can only be so stiff and due to the crown on the rollers you end up with the tension being less at the outer edges. I bet that gokart wheel one suffers badly from that. Good for bulk material removal but not so great for precision work. A narrower belt requires less crown and therefore has less variation in tension. I feel more attracted to a precision machine than a giant beast for mowing material away quickly. Spending a few more minutes on a job is fine if it's for a hobby and not commercial. Smaller belts are also cheaper to replace when you inevitably get rough and damage it.
- VFD 100% sounds like the way to go. I haven't found the correct terminology to find these on aliexpress. 240V single phase in and 415V 3 phase out. Let me know if you know the correct cheat code.
- Don't be mean to Jer. He's not annoying. Definitely no more so than you :lol2:
- Wheel sizes to match common (roll hoop) sizes would be beneficial too.

Author:  Fred [ Tue Jul 09, 2019 12:38 pm ]
Post subject:  Re: Big DIY Belt Grinder Build (planning)

Good question. I think mostly in vertical mode with table, but on a variant of sizes/shapes of steel, some of which would be much wider than a 50mm belt. You could say that those parts could be ground on the platten with the belt flying sideways, but I'd respond that then you have to provide the opposing force which is difficult or a block on the table which leads to trailing/leading edge wear and is worse than any belt-stretch related unevenness that could be accounted for by moving the part from side to side while grinding against it.

Re belt inconsistency, I have a couple of comments/questions:

1) If the two rollers each side of the platen are *not* crowned then surely anything done to the belt either side of that will not manifest in a meaningful issue in between? Thus the drive wheel or other wheel(s) could provide the tracking crown.

2) With a platen behind the belt, and pressure up against it, surely any inconsistency in tension is fully overwhelmed and replaced with the flatness of the platen, whatever that happens to be?

Agreed that speed is not an issue, wider belt for wear and for wider parts. Longer belt for wear/cooling/platen length.

Smaller belts are cheaper, but fairly linearly, 30 bucks each for 150, 10 buck each for 50, etc. Is that really inevitable? They come in packs of three from machinery house anyway, so there's always a spare :-D

Re VFDs, Amazon has them in droves, eg this grunty one: not sure if it's legit, or not, but there's a lot, and half of them are "eligible for shipping to communist countries" :-D

I notice now that output voltage == input voltage, so a 380v 50hz 3phase motor will only be getting 230v X Hz 3 phase power from VFD + 230v input. Guessing that's fine, but worth noting.

Banggood responded well to VFD too. Still boycotting aliexpress due to being ripped off.

Jer, the tone of his voice, the lame humour, you know what I mean. He's alright, I watched a few of his vids without dying. But some of it is hard to swallow!

What are common rail hope sizes?

ehb, anything to add? :-D Toxic Jeff? Rob R33?

Author:  Fred [ Tue Jul 09, 2019 1:05 pm ]
Post subject:  Re: Big DIY Belt Grinder Build (planning)

This has some good info in it:

Author:  Fred [ Wed Jul 10, 2019 10:11 am ]
Post subject:  Re: Big DIY Belt Grinder Build (planning)

Cam, watch from this timestamp on:

Note belt flapping around a bit loosely between the wheels until he applies his parts. Then the belt is touching the platen where ever he is holding his work against it, and away from the platen whereever he is away from it. IE, the tension appears to have no bearing on the profile of the belt, but the work piece does.

Also, if you think about it, putting more tension through the middle would, if anything, cause elongation of that region, and a tighter set of edges than the centre.

I look forward to a rebuttal by an engineering wizz, either Germany, or Auckland :-D

Author:  ehb [ Fri Jul 12, 2019 12:07 pm ]
Post subject:  Re: Big DIY Belt Grinder Build (planning)

Aw man, belt grinder...

Well, for sure a machine that I wished to have for a long time!
Building it has been in the picture, but considering how I usually get lucky with cheap old industrial machines, I've been putting DIY off.
Sorry that I can't chime in on this much - I really don't have a stationary belt grinder. Yes, this has to change. :)

What I think about belt tension: Enough so it doesn't slip and then a tad more. :) That's what I gathered from using my handheld belt grinder.
I sometimes clamp that one to the workbench too, but a horizontally running belt without table against it is awkward to use. What I'd like would be a vertical industrial machine with at least 120 mm belt width. I've been watching the market for two years but nothing in my price range has come up. :(

When building yourself, interchangable rollers with common pipe diameters would be awesome, so you could notch out pipe ends.

Concerning power: I love 380 V three-phase. Use it wherever possible.
Concerning VFDs: Haven't used many yet - only a couple from Omron and a cheap chinese one that came with a milling spindle. Configuration is a bit of a bitch with all of them, but they're all still running good (all have been >7 years in service).

Author:  Fred [ Sat Jul 13, 2019 6:23 am ]
Post subject:  Re: Big DIY Belt Grinder Build (planning)

That's a good point re swapping out contact wheels. If the Aussie one was emulated, you could build 2+ carriers with 3 sizes on each, and add sets of 3 as you needed more. Quick change the carrier and go?

3 more VFDs than I have! :-D are you running them 230x1 in, 380x3 out? or 230x3 out? Would heavily affect the power output of the motor if they can't step up.

Longevity is going to be down to design/build and use, semiconductors always fail in the end, but a very far off end if done right. This is why China TIGs scare me! Ditto cheap inverter MIGs.

Glad you like them wide, too! :-) The place I bought my drill press doesn't do 120 or anything else between 100 and 150.

Re belt sanders and clamping... ... 2892769280


Author:  Fred [ Mon Jul 15, 2019 2:39 am ]
Post subject:  Re: Big DIY Belt Grinder Build (planning)

One minor detail, the platen should be made of hardened non-mild-steel and polished with radiused ends. Maybe a slab of truck leaf spring ground and quenched?

"Jer" was saying if he did a lot of grinding at one table height, it wore a step into his platen! This implies that his belt is harder than his platen, or abrasive on the back.

Author:  Fred [ Mon Jul 15, 2019 8:28 am ]
Post subject:  Re: Big DIY Belt Grinder Build (planning)

Tracking designs/styles:

Typical: 1 wheel angle-to-flat adjust
Dual plane: and
Eccentric: Radiusmaster with lever on eccentric hub as seen here and here: (first 30 seconds) and and

Names of owner/designer of radiusmaster and tracking mechanism design: John Lewis Price and Peter "Tompin" ?

RM48 Patent: ... ewis+Price

23. A tracking adjustment mechanism for correcting the tracking of a belt on a belt drive assembly, the mechanism including an axle assembly operatively mounted to a support, the assembly including an axle upon which a contact wheel is mounted for rotation, the axle including opposed end bearings one of which provides for at least limited pivotal movement of the axle, the other bearing including an eccentric thereon which is operable by a lever so that rotation of the eccentric causes pivotal movement of the axle in the other bearing thereby adjusting the position of the axle relative to the support carriage.

Reading around more, stiffness, fine adjust, quick adjust, lack of play, etc are crucial to precise tracking.

Those two dual plane machines are both alloy, ie, more expensive and weaker for a given physical size. And lighter, which is a negative in this context IMO. Steel all the way.

Home sick as a dog, watching mexican drug running videos, and belt grinder videos. Hence this :-p

Author:  ehb [ Mon Jul 15, 2019 2:41 pm ]
Post subject:  Re: Big DIY Belt Grinder Build (planning)

Fred wrote:
One minor detail, the platen should be made of hardened non-mild-steel and polished with radiused ends.

That's true. The dust alone around the machine is abrasive. That's why machine shops often have a separate grinding room, because that dust quickly destroys the ways of all precision machines.

What comes to mind is a steel called "Hardox", but I haven't checked prices and availability yet.

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