Can you read the brand name on the back of the belt or is it too smeared? A scalloped joint makes sense, maximizes the area of the glue joint but allows a more gradual thickening. 

I wonder if a scalloped shear would work well, a whack with a hammer would save a lot of time and blades and you could make them as uniform as reasonably possible.

I was wondering about the practicality of gluing up so many at one time.

Frosty The Lucky.

It seems that this is known as a "sine wave splice". Here's some info from the 3M website:

Quote

A sine wave splice is constructed of interlocking fingers that enable the splice to travel smoothly over contact wheels, reduce hinging, and provide added strength to the joint area. Sine wave splices are typically used for coarser grades and wide belts as well as on belts that are going to be washed.

And from the Klingspor site (the "#4 joint" mentioned is just a simple butt joint):

Quote

Klingspor also has a nice little video about belt splices. Here it is cued up to the bit about this kind of splice:

 

48 minutes ago, Frosty said:

I was wondering about the practicality of gluing up so many at one time.

It was actually working very well, since the Gorilla Glue has a decently long open time. The only problems were the two described above, both of which could have been mitigated with better planning.

Thanks for the links John. I don't use mine enough to want to make belts though I have to say my 2" x 72" grinder is one of my most used power tools. A pain to build but a joy to have on hand.

Heck, I don't spend much time in the shop at all anymore.

Frosty The Lucky.

Update: I reglued the two belts that didn’t do well the first time. Step one was to sand off the glue residue on the new grinder:

Then on to glue-up, this time with a fence at the back for proper alignment:

 Which worked very well. 

The tricky bit is replacing the spring clamps with the caul, as the ends of the belts want to curl up and pull apart. Maybe doing it in segments would work better. 

We talked about this quite a bit when you first got started but at risk of repeating myself. Have you considered gluing the full width belt and splitting it into 2" belts afterwards? Keeping wide aligned is easier than narrow. Clamps would be more unwieldy but not much.

Frosty The Lucky.

I haven’t since I first started using the proper splice tape. Might be worth a try.

 In the meantime, I made up a batch of 80 grit belts. Went pretty well.

 Also, here are photos of a 36 grit belt before and after having the glue squeeze-out scrubbed off with a stiff wire brush:

 

 

How long do they have to stay clamped for the adhesive to set?

The one with the glue squeeze-out looks like it shifted too. That sort of thing was common when someone used too much adhesive in the rubber plant, the fabric would "hydroplane" on the excess adhesive and the joint would shear sideways. It was almost impossible to prevent the joint from shifting.

Frosty The Lucky.

According to the manufacturer, clamp for 1-2 hours, cure for 24 hours for full strength. 

One of the notable things about polyurethane glue is that it expands as it cures, and if unclamped, foams up and pushes the pieces apart. That’s not what happened here (this is one of the ones where the ends didn't come together in the first place), but it’s an interesting effect nonetheless. 

Sounds about right for a real cement, I meant to say cure, not set. I was intimately familiar with set and cure times for different types of rubber and adhesives from working in the rubber plant. Heck, we repaired our surf boards before then.

We didn't use polyurethane glues though but I remember how hot a topic it was on the old knife fora. Heck pre-covid there were a few fora devoted to nothing but gluing knife scales and arguing about it. 

I didn't spend much time reading them and never introduced myself though a number of IFI members were regulars so I PMed a few to say high.

Convinced me to use a flexible epoxy though, so . . . 

Frosty The Lucky.

Interestingly, the Sikaflex 11FC that Zurich Hofi used to glue his hammer heads to their handles is a polyurethane adhesive. I’ve used Gorilla Glue on hammer heads once or twice. 

Do you mean Uri Hofi? I can't find a Zurich Hofi online at all.

I don't glue hammer handles, I fit them after drying them well below average ambient moisture content and wedge them. The only ones I have that loosen up are commercial hammers. It takes longer but my hammers stay tight. 

Uri glued hammer handles because he didn't have time. He told me he sometimes put more than 100 handles on heads in a day.

Frosty The Lucky.

Gorilla Glue used to be marketed as a gap-filing adhesive.  Then one of the woodworking magazines pointed out that urethane foam has essentially no tensile strength.  The stuff will work as a gap filler or as an adhesive, but not both at the same time.

Darn autocorrect!

I’ve used Gorilla Glue on very small hammers (e.g., a small chasing hammer) to good effect. 

Now there's a head slapper! As many years as I've been cursing autocorrect, it still doesn't occur to me to think of it when I see odd words. Maybe it's because I LOVE a good straight line so much? If it came up with funnier odd words it'd be my favorite app.

Frosty The Lucky.

Come on, Frosty! Haven't you ever heard of Zurich Hofi, the well-known blacksmith-watchmaker?

As far as amusing (or at least ironic) autocorrections go, I had one about four years ago when it turned "anxious" into the acronym for the school where I had my first fundraising job, which was arguably the most toxic, anxiety-producing institution I've ever worked for.

Getting back to the subject at hand, I took a look at the website for Sheldahl Corporation, the company that makes the tape I've been using. (They specialize in flexible materials, so they also make flexible circuitry, optical and protective films, and even a sunshield for the James Webb Space Telescope.) Here I found the interesting detail that the adhesives they make for abrasive belts (whether pre-applied to the tape or applied separately) are thermosetting polyurethane. While the specific products aren't appropriate for the home shop lacking the specialized equipment, I think this is a good indication that using the original Gorilla Glue (or the equivalent) puts us in the same ballpark.

Sure John, I'll be happy to engage auto-concoct and we can have a loooong conversation about him. 

I remember you talking about your experience with the institution of advanced in-fighting, bickeradge and backstabbitude. That's not the kind of typo I need, I have too many clingy albatross in my life I don't need to reminded of old ones. Let alone take on new ones.

Advances in adhesive chemistry is amazing and constantly changing. Heck, you can't find epoxy glue that behaves like what I remember, heck you can't even find the brands. Everything in the rubber plant was heat cure and some contained classified ingredients. Things we knew MUST be there just weren't listed in any meaningful way. So we made parts for military helicopters, what's the big deal, eh?

I'm really happy I left that job and moved to Alaska, two years with my hands in solvents and breathing the fumes made it a less than desirable position. Happily I only worked there less than two years and don't think I suffered much damage. No obvious symptoms anyway.

Frosty The Lucky.

When I worked in the art restoration studio, one of my co-workers specialized in the repair of glass and porcelain. Some of the epoxies she used had a refractive index so close to lead crystal (1.7-1.8) that you could barely tell it had ever been broken.

Of course, the pieces had to be held in perfect alignment for up to 24 hours during curing, so I was occasionally called on to build some oddly shaped brackets....

Boy does that bring back a memory! No, nothing personal but a science fiction story, maybe book from way back. "The Potsherd" or something like that. It was about someone who repaired pottery for a museum. Seamless, invisible repairs were the specialty of the protagonist. The author went into quite a bit of detail and it's been something I remember occasionally. Like now. . . . BLINK Light's ON  

It's a Phillip K. Dick novel, "Galactic Pot-Healer".

It's that brain thing again!

Frosty The Lucky.

Quick note: I was grinding something this morning with one of the 80 grit belts and caught a corner of the splice on the workpiece. I’m pleased to report that while the belt ripped, the glue joint did not fail.

No blood? No problem.

Isn't catching a corner an indication of a problem with the splice?

Frosty The Lucky.

The root of the problem was that I hadn’t split the belt evenly, so one side of the splice was a little wider than the other. In retrospect, if I had mounted the belt the other way around on the grinder, the wider corner would have been on a trailing edge rather than a leading edge and thus much less likely to catch. Oh, well; live and learn.

Yeah, it's all normal for figuring out how to do a new thing without mentor or proper equipment to copy. 

Thinking about it if you get a belt joint like this again I'll bet you could grind them even from the back side on the belt grinder. Might just make a frayed mess though.

No, don't say, "frayed knot."

Frosty The Lucky.

I watched this somewhat humorous video yesterday;

Maye some useful information in it for you.

Oh BOY another don't do THIS youtube expert! Have you tried this Gazz? Do you vouch for it's safety? You are aware a 2" x 72" or Square Wheel belt grinder put a LOT of power and speed into the belt, yes? Think recommending a HUMOROUS how to to inexperienced forum members is a good idea?

I've had a commercial 3M grinding belt split while in use. It didn't lay my hand open but I did wear a bandage for a few days.

My apologies if this is an over reaction but I don't find power tools the place for humorous how to.

Frosty The Lucky.

I've watched many of This Old Tony's videos and find them mostly informative.  In the one I posted, he does say that his attempts to make belts was a failure, so he is not really encouraging anyone to try it.  And he is dealing with 1/2x18 3/4x18 belts - hardly flesh rippers when failing in any case.  And yes I have been slapped by broken belts and it does hurt and these were on my little 1x42 grinders.  When they break on the 2x60 they just break without attacking the user, I think because most of it runs in an enclosure.  I don't have a 2x72 but have worked with them but can't recall any belt failures.  Without reading all of JHCC's posts, I don't recall if he made any comments about getting hurt by failed attempts to make his own belts.  In any case, working in blacksmith shop offers plenty of opportunity to hurt ones self or others which must be considered but can't be a prime focus.  I myself have a few scars that are reminders of what not to do and those experiences have taught me well.   Common sense must prevail.