# Let's talk belt grinders



## awake (Jun 7, 2021)

Figured I'd jump on the bandwagon with the "Let talk about ..." threads. I realize there are approximately 14 million videos and endless discussions about how to build and different designs of the ubiquitous 2 x 72" belt grinder ... I know this, because I consulted nearly all of them as I was developing a design that used the materials I had on hand to build my own grinder using a treadmill motor. In case you are interested, here is a quick overview video (made before I painted it):



On the one hand, despite the plethora of videos and discussions and even a few full sets of plans already out there, it was surprisingly hard to work out a design that suited my own needs and available materials. On the other hand, now that I am done, I am very pleased with the results - it can really move metal in a hurry when needed, but also seems to be capable of a great deal of versatility, even with the limited accessories that I have made thus far.

If anyone would find it helpful to see yet-another-set-of-plans, or to hear any of the design decisions that I found I had to make (and how I made them), I would be happy to share - but if this horse is already sufficiently dead, I will certainly refrain from beating it!


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## BaronJ (Jun 7, 2021)

Hi Andy, 

I doubt that you are beating a dead horse, as you put it !  I am interested in your work and your design.  Believe me I'm only too familiar with designing something and finding out that you need to make a change because you have overlooked a detail.

The problem with that is if you don't admit your mistakes no one can learn from them or suggest ways of overcoming a problem.

I'm sure that you have looked at the much modified "Brooks" TCG that I've built !  I've just got round to having a go at resurrecting a broken two flute slot drill that I cut the damaged end off with a Dremal.  This is where I now discover that a lack of clearance and some rigidity have reared its ugly head, necessitating a small modification.  OK I have to make a couple of parts, but isn't this what the hobby is about.

So don't fret about dead horses !  Enjoy the journey !


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## HennieL (Jun 7, 2021)

Great build - Belt grinders are hugely versatile, and mine is my most used machine in the workshop. 

Some comments/suggestions from a "frequent flyer": 

Get yourself a contact wheel in addition to the flat platen - a 300mm/12" diameter is ideal. The "rebound" from a wheel is mush less than that on a flat platen such as yours, making for more comfortable grinding, as well as enabling much more aggressive grinding.
Consider also using a 25mm/1" belt - especially on a wheel. Not only are these half the price, they also enable more precise grinding, eliminating to a large extent the 2" cuts made by the ends of the wider belt when not pressing with the same amount of force distributed across the platen.
Using good quality belts pay off more than the increase in cost - this goes for staying sharp, not creating deeper scratches due to uneven grit size, and just lasting longer.
See if you can mount a small dustbin or other container with water hanging below your table - it's then easy to just dunk the piece that your grinding whenever it heats up, thus protecting your skin and the temper of the tool that you are grinding.
Good luck with your future use.


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## ajoeiam (Jun 8, 2021)

awake said:


> Figured I'd jump on the bandwagon with the "Let talk about ..." threads. I realize there are approximately 14 million videos and endless discussions about how to build and different designs of the ubiquitous 2 x 72" belt grinder ... I know this, because I consulted nearly all of them as I was developing a design that used the materials I had on hand to build my own grinder using a treadmill motor. In case you are interested, here is a quick overview video (made before I painted it):
> 
> 
> 
> ...




Hmmmmmmmmm - - - - I would appreciate the plans and the project details - - - please.


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## bb218 (Jun 8, 2021)

awake said:


> Figured I'd jump on the bandwagon with the "Let talk about ..." threads. I realize there are approximately 14 million videos and endless discussions about how to build and different designs of the ubiquitous 2 x 72" belt grinder ... I know this, because I consulted nearly all of them as I was developing a design that used the materials I had on hand to build my own grinder using a treadmill motor. In case you are interested, here is a quick overview video (made before I painted it):
> 
> 
> 
> ...



I to also built a 2 x 72 grinder, I have added a 300 wheel along with the flat platen and a small wheel attachment.  What I want to add is a drill sharpening attachment for larger drills but have yet to decide on a design.  Don't know how I got along with out it.


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## timo_gross (Jun 8, 2021)

BaronJ said:


> Hi Andy,
> 
> I doubt that you are beating a dead horse,
> ....
> ...



Ha including oneself. To learn from my own mistake, I have to admit it was one in the first place. 

Not a dead horse, rather a work horse. (work horeses are still used, even today; Not dead)
Most videos I saw on youtube focus on the machine and barely on any process technology and consumables

Belt types
wear on belts
grid choices
cooling methods
grinding techniques
A lot of talk that I would love to read about, because I do not know any of it.



HennieL said:


> Great build - Belt grinders are hugely versatile, and mine is my most used machine in the workshop.
> .....



I cobbled something together loosely following basic principles explained by MrPete222 in his videos, almost embarrassing to show a foto. It works good enough to become the famous "temporary solution".  And it was not annoying enough to make the big fix yet. 
Then I learned about the 2x72" "US fashion". Because It was hard to find those belts locally, I was reluctant to built a machine with a difficult supply of consumables. Purchased plans from Jeremy Schmidt, but never built the thing, now he came out with metric update. (even more interesting to me)

My machine is using the belts that I can get everywhere.
Since I have the belt sander, the bench grinder is hardly ever used again.
I should have been the 2nd power tool to get after a simple drill.

Linking the cutter grinder thread to the belt grinder thread.
I saw some interesting 2x72" belt offers on the internet for diamond coated belts. Somewhat expensive, but they possibly will cut carbide tools, preferably with a contact wheel I am guessing here. Would be curious if anyone tried that.


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## HennieL (Jun 8, 2021)

timo_gross said:


> Most videos I saw on youtube focus on the machine and barely on any process technology and consumables
> 
> Belt types
> wear on belts
> ...



Timo,
We can spend hours discussing the points you mentioned above. To keep things simple, though, let's just talk about the various types of belts, and the grits used - from a knife making point of view, but applicable to most metal working.

As I stated earlier, it pays to use the better quality belts, as theu not only last longer, but impart less heat into that which one is grinding. I only use ceramic belts for steel, but use cheaper alox (aluminium oxide) belts for grinding wood. I prefer some Norton and the VSM (part of Pferd) ceramic belts, but also use some Klingspor belts (these are USA and German brands available in South Africa, and availability might vary in other parts of the World...).

Belts are graded in the "weight" and type of backing - "J" type being very thin and flexible, "X" type being much thicker and stronger, and "Y" weights being very thick, stiff, and strong. I prefer my "hogging" belts used for large-scale steel removal to be 36 grit Y-weight belts, and do my "normal" grinding on 80 grit X-weight ceramic VSM's or Nortons. As far as type of backing material goes, paper is cheap and nasty, and cloth (linen) is much better - I've never had a cloth-backed belt break in use, whilst paper belts snap regularly, and can be quite frightening (and dangerous) when breaking at 3000 RPM.

After doing the initial grinding (with whatever grit one chooses), all the following finer grits are just refining the scratches left by the previous grit. I do my profiling with the 36 grit, the shaping with an 80 grit, and then go through 180, 400, 600, 800, 1000 and 1200 grit belts before moving on to hand sanding with 1200, 1500, 2000 and 3000 grit wet/dry paper (I prefer 3M, it's just miles better than anything else I have ever tried...) in order to achieve a mirror finish on my knives. Obviously, on many tool holders, etc that I make I stop at 600 or 800 grit. Wood goes from 36 grit to 100, 180, 400, and (occasionally with some hard woods) 600 and 800 grit.

Something to keep in mind when using ceramic belts is that they are "self sharpening" in use - but require some pressure and speed in order for the blunt grit particles to break and produce new cutting edges - if you "nurse" your belts they quickly go blunt, but can be quickly revived by some hard grinding.

OK, enough for now...

Hennie


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## awake (Jun 9, 2021)

Thanks, all, for the encouragement to proceed. Here is the first installment. My goal here is not only to provide the plans I wound up designing, but more importantly to include some discussion of the alternatives that I considered, the design decisions that proved to be less-than-obvious from watching other videos, and the things I would do differently as a result of learning-by-making my design.

First, a word about influences on my design. Feel free to skip this and go to the next post which will have the first pages of the plans ...

<TL/DR warning on>

Probably the most important (and obvious) influence on my design is the Revolution grinder by House/Work, aka House/Made (Brian House: Revolution DIY 2x72 Tilting Belt Grinder Plans ►► INSTANT DOWNLOAD), but there are many differences in my design occasioned by the materials I had available and by the use of a treadmill motor. Note that I did not purchase the Revolution plans (or any others), so the influence is by way of watching videos and observing features that I liked. There are some other designs on the internet / in YouTube videos that have similarities to the Revolution design, and those no doubt contributed something to my warped thinking as well. I should note that Brian's plans are really inexpensive, so there is no good reason not to go with his proven design ... unless, like me, the challenge of making one's own design, making use of scrap / scavenged materials on hand, is a major part of the fun. 

I love Jeremy Schmidt's design (Gen 2 Tilting Belt Grinder | Jer's Woodshop), but ultimately decided not to go that route. Again, his plans are extremely affordable, so if anyone likes this unique design, there is no good reason not to buy the plans and use a proven design. I certainly learned from watching his videos, but ultimately I did not wind up using any part of his approach. For anyone who has not studied hours of YouTube videos (not saying that I have ... cough, cough), Schmidt's design is quite different from just about every other grinder out there, in that his belt path is in-line with the main tube and tooling arm, rather than being to the side. (To say it another way, the main tube/arm sits "inside" the loop of the belt.) A second major difference is his unique design for rotating the grinder, which allows the tool rest to remain in place while the belt assembly rotates - very clever.

Another interesting feature of Schmidt's approach is the choice not to use square tubing, but instead to build up the main tubes by welding up plate. Not quite the same but in a similar spirit are many variations of a "no welding" design that bolt together the main tube from plate, such as this freely available example: http://www.knifehelp.net/media/docs/GrinderPlans.pdf. (There are also "no weld" designs that do use square tubing, such as this set of inexpensively priced plans: No Weld Grinder Plans Hard Copy Nearly 50 pages.) I did think long and hard about going the route of building up the main tubes, but materials on hand include lots of 1/4" thick plate and virtually no supplies of thicker plate. I would have needed to weld the 1/4" plate, since I would be reluctant to trust the small fasteners I would have to use on its edges ... but then I was worried about too much warping. Meanwhile I had what appeared to be a good telescoping match with 1.75" square tubing and 1.5" square tubing on hand, so I went that route - details in the next post below.

<TL/DR warning off>

On to some actual plans!


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## awake (Jun 9, 2021)

First, the main tube(s) of the grinder - this seems to be the heart of any 2x72, the tubing into which accessories and tool rests will telescope. A simpler design will have a single main tube, and the tool rest will fasten directly to the arm that supports the platen or other accessories - nothing wrong with that design. Some designs use a separate plate as the primary structure of the grinder, to which the main single tube or dual tubes are bolted or plug-welded - nothing wrong with that either, except that it involves additional material. I decided to go with a design in which two main tubes are welded together face-to-face and they form the main structure without any additional plate:






There are some important notes in these plans; I won't repeat them all below, but do want to call particular attention to a few things regarding the choice of material shown above. The odd-size 1.75 x 1.75 x .125" tubing let me create the telescoping effect I wanted using 1.5" square tubing for the tooling arms ... but using .125" wall material has important implications:

On the positive side, the resulting machine is heavy enough to be completely stable in use, but not so heavy that it cannot be moved without a hernia.
On the negative side, it is necessary to add thickness anywhere that one needs a thread - either by welding on a nut (as shown above, to accommodate the bolts that lock the arms into place) or by welding in an additional plate (as will be discussed in later plans).
Even more on the negative side, the thinner the material, the more easily it will warp when welding. To try to minimize warping, I did *not* weld continuously down the seam between the tubes; I welded 4 1.5" long beads evenly spaced across the joint. (Of course I tack welded it together first while firmly clamped, to keep the tubes aligned.) But even so, it still warped - not enough to be visible, but enough to destroy the lovely close fit that I had between the interior of this 1.75" tubing - after grinding off the internal weld seam - and the 1.5" tubing I was going to use for the arms. It was such a lovely fit before welding, but afterwards it would go no more than an inch in before jamming. I had to skim around .020" off of each face of the 1.5" tubing before it would again pass through the welded 1.75" main tubes, and the final result is a lot more wiggle than I had first thought I was going to achieve. It still works just fine once the tooling arms are clamped in position, but it is annoying to have one's perfect plans ruined.
What were the design challenges, and what would I do differently with this part of the design?

It was surprisingly hard to determine the optimum length of the main tubing. The motor will prevent the tooling arms from extending out the back, so whatever length is used must accommodate various tooling arms when they are pushed in (e.g., to free the belt) and still provide secure fixturing when they are extended (e.g., to tension the belt and to position the tool rest). Most of the designs I looked at seemed to go shorter on the main tubes; for example, I think the Revolution uses 10" length of tubing. I modeled the finished grinder in CAD with the basic flat platen and tried to anticipate exactly how much room I needed ... I was really thinking I would go with 14" main tubes, but got nervous since everyone else seemed shorter, and I wound up cutting them down to 12". Now that I have it all assembled, I really wish I'd stayed with 14" - in use, the tooling arms stick out a long way beyond the support of the main tubes. Again, it all works just fine ... and maybe when I get around to making a contact wheel, I'll discover that I need the shorter length ...
If I ever build a Mark II design, I will strongly consider accepting the weight penalty to go with 2 x 2 x .25" tubing. The .125" wall tubing seems plenty rigid and stable, but it is an annoying extra step to add thickness where threads are needed, and I would hope that .25" wall tubing might stay more stable when welding, preserving a closer fit between the main tubes and the tooling arms. Maybe ... perhaps someone here can offer a witness on that point? I note that the Revolution design does not seem to suffer from warping, but then again, it is not welded up face to face as I have done, but rather the tubes are plug-welded to a thick plate which also forms the mount for the motor.


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## awake (Jun 9, 2021)

Next, the pivot and pivot-lock plates. I decided to go with a design that allows the grinder to rotate from vertical to horizontal. Will this be useful? I think so, based on some preliminary testing.




Again, I won't repeat all of the notes included in the plans. The 1/4" thick plate seems more than sturdy enough for the job, as does the .5" pivot (which will ride on a 1/2" bolt).

The major design challenge here was where to position the pivot point. The 1" distance from the left edge is determined by the choice of 2 x 2" square tubing as the support pillars (that will be the next page of the plans). But should the pivot point be centered on the center-line of the main tubes? It was hard to tell for sure from the videos, but as best I could tell, the other designs that were similar to this one set the pivot point slightly below the center line. Is that essential for balance? I agonized over this decision for far too long.

Finally I decide to try a center-line placement, but only tack-welded the plates in place on the main tubing assembly until I could test the balance with the treadmill motor attached. The result, as best I can tell, is perfect - I really don't have to lock it in place; it rests very stably in either vertical or horizontal position. (I guess if for some reason I wanted to tilt it, say, 45°, then I would need to lock it in place!) No doubt some lengthy calculation might determine that a slightly different placement would be even better, but this is more than good enough.

In terms of welding these plates to the main tubing, some things to consider: the weld is going to need to be on the "outside" edges and on the ends, but not in the "inside" area where each pair of pivot plates will surround a support pillar. This requires some care to avoid pulling the plates out of square during the welding.

The strategy that worked for me was to use a length of 1/2" all-thread, along with nuts, washers, and shims, to assemble the pivot plates together with the support pillars in the correct spacing, then to position the plates on the main tube and tack the ends of each plate. Adjust as needed, then do the outside welding passes.

Next up are the plans for the support pillars and the base plate - but I need to finish "prettying up" those pages first. I made a complete set of plans as I built this grinder, but I didn't bother to put in all of the labels and certainly none of the notes or the CC copyright. Stay tuned ...


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## awake (Jun 11, 2021)

Here are the plans for the base and support pillars:





The main tube assembly shown in the previous post will attach to the support pillars via 1/2" bolts and will be locked with a 3/8-16 bolt so that the main tube assembly can rotate. Note that most of these dimensions can be adjusted to suit. Certainly the base plate can be made larger or smaller, or made from something other than 1/4" plate. The height of the support pillars is somewhat arbitrary; the only "must" is that the motor must clear when the main tube assembly (to which the motor will be attached - as will be shown in plans yet to come) is rotated to the horizontal position. The pillar tubes do not have to be 2" square, and the spacing between the the pivot point and the lock threads could be something other than the 1.25" shown - but of course, any changes here must be matched by changes to the pivot/lock plates in the previous page of plans. One could probably go with a smaller pivot diameter, maybe down to 3/8", or certainly a larger pivot point (I think the Revolution design uses 5/8"), but the 1/2" shown and built seems to me to be "just right" in proportion to the rest of the build, and provides very robust and smooth rotation. One could definitely go with a smaller lock bolt, as the unit is very well balanced and needs very little locking force - but I wanted to use the same size for all of the lock bolts, and I think anything smaller than 3/8-16 will be too small when we get to the tooling arm and the "D" plate.

Once again I went with .125" wall tubing, simply because I have a lot of it on hand. 1/4" wall tubing would certainly make it easier in terms of threading for the lock bolt, but again with added weight. The .125" wall tubing seems to be plenty robust and rigid, but as shown I did need to add a 1/4" backer plate in the area where the 3/8-16 thread is - this is extremely easy to do using a couple of plug welds, so long as one has access to suitable welding tools / techniques. The exact size of the backer plate is not critical, so long as it is narrow enough to fit inside the tube, short enough to clear the pivot hole, thick and wide enough to provide plenty of "meat" for threading, and long and wide enough to provide sufficient room for the plug welds.

Next up: the tension arm and its associated parts.


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## GrahamJTaylor49 (Jun 12, 2021)

Many thanks "Awake", have printed off the drawings and will start getting the materials from
some of my customers scrap bins. Will let you know how I get on.


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## awake (Jun 12, 2021)

GrahamJTaylor49 said:


> Many thanks "Awake", have printed off the drawings and will start getting the materials from
> some of my customers scrap bins. Will let you know how I get on.


Great, glad to hear it! I'll try to keep the pages coming along. Be sure to note the many options that you have for materials - one of the main reasons I am documenting this is to describe the design decisions that I went through so that hopefully others can either build my design OR be better equipped to design their own.


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## awake (Jun 12, 2021)

Here is the next page of the plans, and the first of several parts that go together to make up the tension arm assembly. First is the "tension arm support pillar" that holds the tension arm and allows it to swivel:






I think this one is fairly self-explanatory, but a couple of notes on design decisions. First, this is a place where the Revolution belt grinder very strongly influenced my design. Like the Revolution, I chose to go with a design in which the tension is applied by an extension spring at the back of the tension arm. Using a compression spring on the front of the tension arm is certainly an option, and might allow a more compact assembly. I did not care for the design in which the tension is achieved by a compression spring inside a set of telescoping tubes - this did not seem to me to offer sufficient rigidity to ensure precise and repeatable tracking.

Given the decision above, the next question is how tall to make the support pillar, and whether to angle it (as shown) or make it vertical; this decision is dependent in part on 1) how long the tension arm will be (9" in my case); 2) the desire to keep the tension wheel relatively horizontal with the upper idler of the D-plate when the tension arm is fully tensioned; 3) the desire to keep the tension wheel relatively far back - a few inches in front of the drive wheel on the motor, but well inside the front/rear boundaries of the main tube assembly. Honestly, I don't know how essential any of that is, but I hoped it would give me the best combination of flexibility with different attachments, rigidity and precision of tracking, ease of use of applying tension, and so on. It may be that there is a better way to achieve these, but I have to say that so far I feel very pleased with how this design has worked in all of these areas.

One other note: I have shown provision for an eyebolt to be welded into the support pillar to serve as a means for attaching the tension spring. For my own build, I actually used a flat metal tab with a hole drilled on the end, welded in at the same angle and approximately placement as shown in the plans. Either should work fine, but were I to do it over, I would go with the eyebolt for simplicity. Note that one can weld the tab or eyebolt in place on the support pillar before or after welding the pillar to the main tube assembly. I am not sure which order is best; I welded the tab on first, before welding the support pillar in place.

Up next: more parts of the tension arm assembly.


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## goldstar31 (Jun 12, 2021)

I bought a cheap( about £30  double.  ended sander/6" grindstone probably from either Lidle or Aldi in the UK.
By no means the best but adequate . A bit flimsy and underpowered but it does work. 

Whe I was in the supermarket,  I bought supplies of belts with assorted grits.

Next job for it is the new Quorn Mark3 castings.
Confession-  perhaps but I got a City and Guilds in Motor Vehicle Restoration when I retired 36 years afo, so I'm happy to take the excrescences etc off the castings. 

I also got a similar chear-y part plastic sander from the same sorce and I;m quite popular with my neighbours who are restoring eooden garden  rables and chairs unobtainable in the present pandemic.

I get paid in coffees and tots of whisky and -- vintage port.


Yummm


Norman


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## awake (Jun 13, 2021)

Page 5 of the plans is the tension arm and spring:





As shown, I decided to go with .25" wall tubing for this part, mostly because there are two tapped holes, and because I had a stick of 1.5 x 1.5 x .25" tubing of the right length. I don't know that the exact length matters, but I was aiming for approximately a 2:1 leverage for the spring acting on the bottom rear vs the 3/8-16 attachment point for the tracking wheel bracket on the top. For various reasons (aka poor planning), I wound up with a bit less (5.5" from the 1/2" pivot point to the tracking wheel bracket attachment point vs. ~3" from the pivot point to the spring attachment, for a ), but it seems to work just fine.

Note that the bolt that will adjust the tracking wheel angle is a fine thread (3/8-24) to allow finer tracking adjustment. The plans may be a bit confusing on the threading for this bolt; basically, the side on which the knob should be is drilled for clearance, and the other side is drilled .332" and tapped 3/8-24 - the holes are in line, but .2" below the center line. I hope that makes sense ...

The only difficult design decision for this set of parts was the size of the spring. I bought some springs that turned out to be too weak, but found a spring that I could modify to produce the one shown in the plans - .094" wire diameter, .75" spring diameter, 23 turns plus the top and bottom hooks. I don't honestly know what the ideal tension is on the belt, but this seems to work well.

Up next: the tracking wheel bracket. Teaser: this part features a design element that as far as I know is unique to my build - and it works really, really well.


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## MrMetric (Jun 14, 2021)

Because we are beating on poor horses,   , I have a related question that you may be able to answer. I hope this doesn't devolve into an off-topic deviation from your very interesting thread. I am really enjoying it.  Anyhow...

In your search of those millions of videos, did you ever find a process _that works_ for repairing belts that are brand new but which have non-functional splices (i.e. that break)?  I've tried hide glue, super strong fiber tape, layers of this and that, etc... But everything seems to break after not all that much time.  Unfortunately, I bought a bunch of surplus belts, so I would really like to use those.


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## awake (Jun 14, 2021)

MrMetric said:


> Because we are beating on poor horses,   , I have a related question that you may be able to answer. I hope this doesn't devolve into an off-topic deviation from your very interesting thread. I am really enjoying it.  Anyhow...
> 
> In your search of those millions of videos, did you ever find a process _that works_ for repairing belts that are brand new but which have non-functional splices (i.e. that break)?  I've tried hide glue, super strong fiber tape, layers of this and that, etc... But everything seems to break after not all that much time.  Unfortunately, I bought a bunch of surplus belts, so I would really like to use those.


I wish I had an answer! I have wondered the same thing, as I have some very old 2 x 72 belts that I bought many years ago when I first began to think about building one of these. (Yes ... a long-delayed project!) As I understand it, the seams deteriorate with age, and two of the four have indeed separated. To be fair, they are aluminum oxide, and I was using them on metal as I first tried out the machine - wrong belt type for metal, as I now understand. But still, they did not last long before separating.

The millions of videos I have been viewing were almost entirely devoted to the machine design / build, rather than to the belts, so I didn't see anything there. I do have a vague memory of reading something on this topic many, many, many years ago, but on a woodworking forum ... I've been meaning to dig around a bit to see if I could find anything. Meanwhile, maybe someone else here can offer a workable solution!


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## BaronJ (Jun 14, 2021)

MrMetric said:


> Because we are beating on poor horses,   , I have a related question that you may be able to answer. I hope this doesn't devolve into an off-topic deviation from your very interesting thread. I am really enjoying it.  Anyhow...
> 
> In your search of those millions of videos, did you ever find a process _that works_ for repairing belts that are brand new but which have non-functional splices (i.e. that break)?  I've tried hide glue, super strong fiber tape, layers of this and that, etc... But everything seems to break after not all that much time.  Unfortunately, I bought a bunch of surplus belts, so I would really like to use those.



Have you tried 3M rubber solution or Evo Stick !  Both are a rubber based adhesive.  They work for me but then I don't over tighten them !

I did the same as you and bought a number of old stock belts that were well past their use by date.  The other trick that I have used in order to make use of them is to glue a piece to a length of wood and use them like a file.


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## goldstar31 (Jun 14, 2021)

John

I'm going on what is a Pelmanustic memory and may be wrong.
it is in fond memory of a member of the local club- who made a highly developed Quorn, was alway broke and ran  cars and repaired silencers with ---

SILICOME  SEALANT
No, I have never tried it  but from what I read can stand tempoeratures up to say 450C

However it is worth a try

Norman


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## HennieL (Jun 15, 2021)

MrMetric said:


> In your search of those millions of videos, did you ever find a process _that works_ for repairing belts that are brand new but which have non-functional splices (i.e. that break)?  I've tried hide glue, super strong fiber tape, layers of this and that, etc... But everything seems to break after not all that much time.  Unfortunately, I bought a bunch of surplus belts, so I would really like to use those.



That's probably why the belts were sold as surplus in the first place - long past their "use-by" date 

In my experience, it's not advisable to re-join belts purely due to safety - unless you are using them on a belt grinder with speed control turned all the way down... and then you might as well just hand sand. A belt that's running at optimum grinding speed can cause quite bad injuries when it breaks, and can even result in blindness if the tip hits your eye.

Another reason for not re-joining belts is that the "bump" created by the DIY joint is invariably thicker than that of the original belt, and the vibration caused by this leads to inaccurate grinding, and even faster wearing-out of the newly made splice.

Best to use them as hand-sanding belts as stated by BaronJ above.


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## BaronJ (Jun 15, 2021)

Hi Hennie, Guys,

I've not had any real issues with the belts that I've glued, yes there is a slight bump as the joint comes round, but you get that to some degree with a new one.

I find that if I clamp the glued ends of them in a vice overnight they don't easily come unstuck.  I use a scalpel to shave off the dried glue that oozes out of the edges of the join on the sides of the belt.

I think people use too much glue thinking that a thick layer will hold better !


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## awake (Jun 18, 2021)

Time for the plans for a couple of rather simple parts ... which may be the only unique part of my build - the tensioner bracket and tensioner pivot:









What makes this unique? The provision for setting the angle of the bracket on tension arm using two set screws. This turns out to be a very simple solution to a problem that I have not seen addressed on any of the many videos and articles I have perused. I can't say for sure that no one else came up with this idea first; it is such a simple idea that it seems hard to believe it hasn't already been used. But not only have I not seen this idea in any of my research; I haven't seen _any_ real solution to enable precisely setting the angle of the tensioner mechanism. Of course, every design includes a bolt or some such that applies against the pivot plate to set the angle in the vertical plane, but the problem is, any rotation of the tensioning mechanism on the horizontal plane (where it attaches to the tension arm) has a VERY large effect on tracking - far more effect for a tiny change than adjusting the pivot angle does.

The typical solutions are either to "be very sure to attach the tension mechanism straight with regard to the tension arm," or "spend time very carefully nudging the bracket back and forth until you get it just right." (See Brian House's video on tuning the Revolution belt grinder as an example of the latter approach.)

Given how sensitive the tracking is to this adjustment, I wanted a precise and controllable way to adjust the angle. What I came up with above is super simple - as shown in the picture on Sheet 7, the tension mechanism spans the tension arm with around 1/8" of space on each side; on one side this allows room for the tensioner plate to swivel on its hinge (vertical plane), allowing adjustment of tracking using the 3/8-24 bolt that goes through the tension arm and bears on the tensioner plate. On the other side, this 1/8" space allows room for the 1/4" set screws (grub screw) to be adjusted in or out, creating a rotation of the bracket in the horizontal plate, swiveling on the 3/8-16 bolt that attaches it to the tension arm.

In practice, this design decision has worked exceptionally well. If nothing else from my design is useful to anyone, I highly recommend using this idea, or coming up with something else that will allow for similar adjustment!


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## awake (Jun 25, 2021)

Now for the tracking wheel and its spindle:




There is nothing unusual about the tracking wheel itself, and many will prefer to buy one rather than make one. The main design decision here is how much crown to use on the wheel. I have no idea what the optimal crown may be; I simply started out with the crown as shown, in which the diameter at the center is approximately .060" (1.5mm) larger than the diameter at the ends. (If someone prefers, I can put in the radius of that curve ... but in terms of my own manufacturing, that dimension was not or will not be particularly useful.) I figured if that did not seem to work well, I would experiment with other dimensions for the crown ... but it does seem to work just fine, so I have not tried anything else.

In terms of the spindle arrangement, I have gone a route that is rather different from most that I have seen. Rather than simply using a bolt of the appropriate diameter, and using a ny-lock nut to secure the wheel on the bolt, I have made a spindle that first attaches firmly to the pivot plate via a 1/2-20 thread, and then holds the wheel snugly in place using a "cap" and a 1/4-20 button head screw. This approach would not make much sense for anyone who does not have a lathe to size the length of the spindle and cap combination to just the right length - but with a metal lathe, it is surprisingly easy to get this just right.

I made the wheel first and pressed in the bearings (more about this below). Then I made the spindle out of some .750" hex stock; I made it to the dimensions shown on the drawing, tweaking the diameter for a snug sliding fit on the inner race of the 6201 bearings that I chose to use. (Of course, you could use a different bearing, and adjust the dimensions of spindle, cap, and wheel appropriately.) Finally, I made the cap, leaving the "shaft" portion a little bit long. Before parting off, I put the assembled wheel on cap and slid in the spindle; then while holding the spindle firmly against the end of the cap, I could slide the wheel assembly back and forth to see how much play I had. I carefully skimmed off the excess until I achieved a fit without any play - actually, I aimed for a couple of thousands of an inch of  very light pre-loading of the bearings. Then part off the cap, and voila! A lovely spindle.

A word about the tracking wheel that I am _actually_ using for the moment - I plan to make the tracking wheel out of aluminum, just as soon as I am able to cast one up (or as soon as I find a suitable chunk of aluminum to machine to size). To get started, however, I thought I'd try 3d printing a prototype tracking wheel, in part to give me a chance to try different settings for the crown. I didn't really expect it to last very long, but thus far, the printed tracking wheel has held up just fine in mostly light duty use - all that I have done so far on this belt grinder. (I also printed the idler wheels for the D-plate arrangement ... and I've worn out one set of those, when the bearings got hot enough to allow the bearing seats to distort. Not sure if that indicates too much pre-loading, or just the expected heating of the bearings, but I'll come back to this discussion when I get to the D-plate.)

I've attached the .stl file that I generated and used to 3d print the tracking wheel. I've also attached the OpenSCAD program used to generate this .stl file (contained in the roller.zip attachment, since the forum does not allow uploading a file with .scad suffix). Note that this program requires some OpenSCAD libraries that I have developed; these are contained in the libraries.zip attachment. (You will need to unzip the libraries into your OpenSCAD libraries folder.) The roller.scad program can generate a variety of wheels, with crown or without, for any size of wheel (diameter, length, bevels), bearing, crown, and so on - just change the appropriate parameters, which hopefully will be obvious in the program if you are at all familiar with OpenSCAD. Note that all measurements in this program are intended as mm. FYI, on my printer, printing this in PLA using 20% infill and .25mm layer height, setting the clearance to .1mm radially (.2mm or .008" for the diameter) gave me a nice light press fit for the 6201 bearings - this setting will no doubt need to be tweaked depending on the printer, filament, and layer height.


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## awake (Sep 25, 2021)

Here at last is the next installment in the belt grinder build. I apologize for the long delay - it has been almost exactly 3 months since my last post on this! Too much work, too little time for hobbies ... obviously, the world is very messed up. 

Here is the motor mount:




Nothing very exciting here, except that this is the part most likely to have to be customized to suit the particular treadmill motor that you are using. The motor I am using has a u-shaped bracket that creates two "ears" that stick out from the motor, 3.5" apart:






Each "ear" is approximately 5.5" wide, with mounting holes that are 4.5" apart. The motor is not centered over the mounting holes, but rather is offset .5" to one side. To say it another way, with the motor mounted sideways as shown above, the mounting holes at the top of each ear are 2" above the centerline of the motor, but the mounting holes at the bottom of each ear (not visible in the picture above) are 2.5" below the centerline of the motor.

The fixed mounting plate shown in the plan is welded so as to be centered on the main tube assembly vertically and flush with one edge (note the edge indicate in the plans). The offsets in the placement of the slots in the adjustable mounting plate shown in the plan, plus the off-center placement of the mounting holes on the motor bracket, allow me to choose whether the motor is mounted above, on, or below the centerline of the main tube assembly, simply by flipping either or both the U-bracket on the motor or the adjustable mounting plate upside down.

This was the key design decision that I wrestled with - reviewing various other designs, it seemed that the motor was sometimes mounted above or below the centerline, and I wasn't sure how much the placement would affect the balance when the grinder is rotated from vertical to horizontal. I wound up situating the motor centered on the main tube assembly, and the balance seems to be perfect.

At the risk of stating the obvious, the slots in the adjustable mount let me adjust the motor left or right, and allow enough clearance to twist just a bit either way, so that on assembly the drive wheel mounted on the motor spindle can be adjusted to precisely the same plane as the platen wheels - this is important to achieve smooth tracking.


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