Bench grinder mounted diamond blade sharpener

I've looked through the many (dozens?) of different low speed lapping machines folks have come up with. The "legit" ones are too pricey for my taste, and I was hoping to come up with an easy way to sharpen scraping blades that doesn't take up a lot of room in the shop and that I can put away easily when I'm not using. My idea, maybe a silly one, is to built a little rig to spin diamond lapping plates at slow speeds that bolts up to a standard bench grinder. I (like many I'm sure) have a handful of bench grinders kicking around so this seems like a decent idea?

I did some fooling around in CAD and came up with this initial design. Has a few CNC aluminum plates for the bracketry and an aluminum disk for the lapping plate holder. A single sealed bearing is used as the low speed spindle. A flat belt running around the grinder spindle and the outside of the lapping spindle gives a reduction of 12:1. A few laser cut steel plates welded together are used as the work surface, and can be tilted up 30 degrees or down 80 degrees (my idea there is that it can fold all the way down for flat storage). Like several others online I was thinking the diamond plates could be held on by magnets. Given the low forces I was thinking the magnets alone would be fine to hold it in place and stop it from slipping?



I haven't modeled all the hardware although it should all be stock items. I found a cheap idler pulley on amazon which is modeled in here as a simple fixed tensioner. If I could find an appropriate soft rubber vacuum cleaner belt I suppose I could just stretch it on and go without a tensioner.

This is sized to fit a cheap (terrible in fact) 6" chinese bench grinder I had sitting gathering dust. It has 3x 8-32 threaded holes on a 2" circle on the end for mounting the wheel guard. I have no idea how standard this is. Ideally this would fit a multitude of different bench grinders.

Thoughts, criticism? If this worked maybe I could do a run of parts kits for folks to make their own and/or open source the design. There doesn't seem to be a straightforward way to DIY such a thing currently.

arsenix said:

tensioner. If I could find an appropriate soft rubber vacuum cleaner belt I suppose I could just stretch it on and go without a tensioner.

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I don't see anything silly about the idea. Undoubtedly, once you actually make the prototype you will find some ways to improve the design. But, if you could come up with a really functional DIY system (might take a few iterations before you really get it tuned) that many folks could implement, I think you would be doing a real service. The idea of making a kit of laser cut parts would also be a good one once the design is shown to work well. I was part of a group in the PNW consisting of about 35 folks who had kits of parts laser cut for pretty cheap and made a very powerful, robust and convenient belt grinder designed by Jer Schmidt of Etsy fame. (I do not think there is a commercial 2X72 belt grinder that is better) By getting a large group to buy kits the price of each kit was much better than for a set of 1 to three kits.

One suggestion:
With respect to a belt to drive the unit, I would suggest consideration of polyurethane flat belting available from McM among many others. This belting can be easily cut to length and solidly DIY joined to make long-lasting, quiet, strong, and smooth running belts. No tensioner will be needed with a polyurethane belt.

Denis

arsenix said:

Given the low forces I was thinking the magnets alone would be fine to hold it in place and stop it from slipping?

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I used a single pin with a matching hole drilled in the disks, but it likely wasn't required and you can always add it later if you notice it slipping.

Using the OD of a diamond wheel..(or a plate-mounted diamond face side wheel.)
Mount a motor behind your beach grinder with a pully to the opposite side wheel perhaps the left side ..With having your fine diamond wheel mounted on the right side of the bench grinder.. the drive motor spins the bench grinder at a low RPM for fine finish sharpening... The bench grinder becomes a belt drive spindle.

When you need roughing pop off the belt and use the left-side diamond wheel at the bench grinder RPM.

For years I used a Baldor double end grinder used to sharpen lathe tool bits. It ran 3400 RPM and the carbide got hot. Before that my dad used a plain old bench grinder and we mounted a flat face diamond wheel on it, diamond side facing out. We brazed an extension onto the side of the tool rest so we could do the side. That worked well. We used a 600 grit diamond wheel.

When I taught a class in Sweden I took my Glendo diamond lapper wheels with and we mounted them in a lathe chuck and used the top of the compound as a rest. Set the RPM at 400 and that also worked well. Lots of ways to do it.

dgfoster said:

With respect to a belt to drive the unit, I would suggest consideration of polyurethane flat belting available from McM among many others. This belting can be easily cut to length and solidly DIY joined to make long-lasting, quiet, strong, and smooth running belts. No tensioner will be needed with a polyurethane belt.

Denis

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This is interesting. I was looking at the Buna belts but I believe they have nylon in them (ie they likely don't have much spring). Are the polyurethane belts just poly? Ie I could tension it up a bit? That would be nice. Simplifies the design a fair amount without the tensioner. I did work on the tensioner a bit and have simplified it, but that adds a number of parts and is likely $25-30 in parts alone so it would be nice to skip it. The tensioner is also a belt guide currently though. I'm unsure if the belt would track consistently without a crown in one of the wheels.

Ah. Richard nice to hear that a full speed grinder will also work in a pinch! Maybe for scraping this doesn't matter quite as much? With lathe tools a good carbide grinder certainly makes a difference.

I'll think on this a bit and maybe cut some chips on it. With the CNC parts, this might be harder to fab for folks that don't have one. Those parts could certainly be laser cut sheet metal too although it would be a bit more finicky to assembly nice and square.

Poking around online it is clear there are MANY different bolt patterns on the ends of grinders. I think the bolt pattern on this cheap chinese one is more unique than standard. I'll check the other grinders I have to see what they have. I'm not sure this worthless one has enough power to even spin this diamond disk and it may go in the trash after all!

We've been discussing this for years. You can google Glendo or carbide grinder alterantives and then type Practical machinisst. Like the one below.

Also on Hobby Machinist forum. Google it and put hobby machinist instead of Practical Machinist. Like this one where the one guy makes a wood box lapper.

Hate to be a debbie downer but ... nope. This micketty mouse thing will never be as good as a leaonard-lap, doesn't have the sideways stroke, it's as flimsy as a six year old's first treehouse, anyone who really wants one can find a real one for $500 or less, the wheel alone is more than your cheapskaters will pay, it's an idea without a need.

Since it's nothing but playtime on the computer, that's cool, like everyone has to draw up a radial engine but product ? not going to fly.

arsenix said:

This is interesting. I was looking at the Buna belts but I believe they have nylon in them (ie they likely don't have much spring). Are the polyurethane belts just poly? Ie I could tension it up a bit? That would be nice. Simplifies the design a fair amount without the tensioner. I did work on the tensioner a bit and have simplified it, but that adds a number of parts and is likely $25-30 in parts alone so it would be nice to skip it. The tensioner is also a belt guide currently though. I'm unsure if the belt would track consistently without a crown in one of the wheels.

Ah. Richard nice to hear that a full speed grinder will also work in a pinch! Maybe for scraping this doesn't matter quite as much? With lathe tools a good carbide grinder certainly makes a difference.

I'll think on this a bit and maybe cut some chips on it. With the CNC parts, this might be harder to fab for folks that don't have one. Those parts could certainly be laser cut sheet metal too although it would be a bit more finicky to assembly nice and square.

Poking around online it is clear there are MANY different bolt patterns on the ends of grinders. I think the bolt pattern on this cheap chinese one is more unique than standard. I'll check the other grinders I have to see what they have. I'm not sure this worthless one has enough power to even spin this diamond disk and it may go in the trash after all!

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My diamon sharpener uses nothing more than an o-ring for a drive belt. It works great.

QT: (Ah. Richard nice to hear that a full-speed grinder will also work in a pinch! Maybe for scraping this doesn't matter quite as much? With lathe tools a good carbide grinder certainly makes a difference.)

In the ballpark of 6000sfpm is the wet grinding speed and will give the best wheel life and OK surface finish for the size of the grit.
Slow-wheel use will give the best finish but is more like honing and not the best for keeping the wheel flat, or wheel life.
The best might be having two speeds around 6000sfpm when wet grinding for taking stock and a slow speed just for finishing that last .0005 to .003.

I used to production run single-point radius tools with a Baldor and would kill the motor to take the last tickle at a slower speed to make the required surface finish spec.
A two-speed drive motor, or a second motor set on a door hinge gravity base, pulleyed to make slow speed might be good.
Using a plate-mounted wheel or a type 1 one can just hand-nick a groove in the OD of the wheel and put the belt in that groove.
Here find a handy wheel speed chart

arsenix said:

This is interesting. I was looking at the Buna belts but I believe they have nylon in them (ie they likely don't have much spring). Are the polyurethane belts just poly? Ie I could tension it up a bit? That would be nice. Simplifies the design a fair amount without the tensioner. I did work on the tensioner a bit and have simplified it, but that adds a number of parts and is likely $25-30 in parts alone so it would be nice to skip it. The tensioner is also a belt guide currently though. I'm unsure if the belt would track consistently without a crown in one of the wheels.
!

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If you are unfamiliar with the orange polyurethane belting materials (as I was a few years ago), I’d suggest purchasing a foot or two and getting a feeling for how it works. I have a polyurethane belt on a T+C grinder powered by by a 1HP 3-phase motor and VFD I retrofitted. I chose that combo as the drive is nearly vibration-free and allows a wide range of RPM adjustment. The belting will take quite a bit of tension. I guarantee no tensioner will be needed. A little crown on one or both wheels will improve tracking.

Prototyping your design will reveal where it shines and where it will require refinement. Undoubtedly you know, no matter what endeavor you choose, there will be naysayers. Some folks specialize in it. No one who listened to them ever made a new and useful design. Your final setup may only vaguely resemble your conceptual drawing. But, either try to work it into a solid and useful tool or agree that ”it can’t be done.” The worst outcome is that you will acquire some useful knowledge and had some fun along the way, but not have made a tool that works as well as you had hoped. More likely, if you persist, you get the trifecta—-fun, knowledge, and a useful design.

Denis

I've never used one of these but it looks interesting (for brush type motor only and limited HP)

If you're using a full speed grinder you need to take great pains to make sure the face of the plate is running true or the lap will skip on the insert you're sharpening. Also to go from a good lap to a wrecked one take just a moment's innatention. You dig it in, you trash it. Running at 3-400 rpm doesn't pose these problems.

I run a Baldor carbide grinder full speed with a cheapo 1200 grit lapping disk from ebay, cooled with kerosene. Work fantastic, zero issues with overheating or skipping. Blades are just as sharp as when I used to use a jerry-rigged low speed setup. The only problem is that the disks come with a 5/8 mounting hole that has to be opened up to 3/4 to fit the Baldor.

OP: I like your idea, it is a creative way to make a low speed grinder. It does seem like a lot of engineering though and there are simpler ways to solve this problem. I think you should decide if you're trying to design and sell a product or if you're just trying to sharpen blades.

Hey, you're in Milpitas, you can swing by and try the Baldor if you want.

Richard King said:

Also on Hobby Machinist forum. Google it and put hobby machinist instead of Practical Machinist. Like this one where the one guy makes a wood box lapper.

Glendo lapper clone

After taking Richard's class, I was sold on both 1) getting a Biax and 2) figuring out how to sharpen carbide better and faster. There was a Glendo lapper available and it sure made sharpening easy! I found used ones on eBay for about $700 and thought that I would make a clone to save money...

www.hobby-machinist.com

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I have read quite a few threads but hadn't seen this one. I am aware there are around 1 million of them. Thank you!

I had also considered picking up a three phase bench grinder or motor and just slowing it down with a VFD. That won't get me 1:12, maybe 1:5 with decent torque.

Nice info here. It sounds like the slower speed diamond grinders are mostly useful because 1) more accurate/fine finishing can be done despite any small amount of runout on the wheel 2) temperatures are lower which requires less cooling which is typical for the DIY setups vs a professional wet grinder. Generally though even running a 6" wheel the "ideal" RPM isn't that far off what a normal bench grinder runs (3200 RPM). With adequate cooling it sounds like running a 6" wheel straight on the bench grinder isn't as off-ideal as I had thought, and I shouldn't be afraid to run higher speeds. There are also inexpensive 4 and 5 inch diamond wheels which might be even more suitable for the higher speeds.

The poly belt is a great idea. Without the tensioner this unit could be smaller and eliminates a number of parts. I could also consider a poly o-ring, since I think I could cut an OD groove easier than I can crown a pulley.

It also seems to me that a lot of these parts could likely be plastic rather than aluminum which reduces the cost. I don't 3D print (yuck), but some of the parts could even be made that way. The forces and temperatures involved are quite low.

Appreciate the feedback and ideas. Despite the fact that these issues have been discussed many times I still managed to pull some new information from folks

jwearing said:

I run a Baldor carbide grinder full speed with a cheapo 1200 grit lapping disk from ebay, cooled with kerosene. Work fantastic, zero issues with overheating or skipping. Blades are just as sharp as when I used to use a jerry-rigged low speed setup. The only problem is that the disks come with a 5/8 mounting hole that has to be opened up to 3/4 to fit the Baldor.

OP: I like your idea, it is a creative way to make a low speed grinder. It does seem like a lot of engineering though and there are simpler ways to solve this problem. I think you should decide if you're trying to design and sell a product or if you're just trying to sharpen blades.

Hey, you're in Milpitas, you can swing by and try the Baldor if you want.

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Nice! That is an excellent testimonial. If i can run at full speed I could rig something up much simpler. It sounds like the whole concept of a low speed grinder may be unnecessary for my use case.

On the product front, I'm always more inclined to "build rather than buy" since I do this stuff for the fun of making things. When I build something that others might find useful I'd love to make more than 1 (economy of scale and all). Many times my projects are way too niche to be of interest to others. I naturally suffer from "too many projects" syndrome though like many who hang out here, with my work taking much of my brain bandwidth.

I am in Milpitas! Would love to try your setup! I'll shoot you a PM.

When I used a Baldor grinder I used wheels that bolted to a steel back faceplate. It had a rubber backing sheet and 4 flat head screws that we tighten as we indicated the flat diamond face of the wheel with an old dial indicator. When I taught a class for our old member Shane Carr Or screen name Collector up in Canada all he could find was a 260 grit diamond wheel he put on his Baldor and it worked. It had a dripper too. Back when we used a Baldor we dripped coolant on the blade. On my Glendo, I use a 260, 600 and 1200 grit wheels, for roughing, to finish so I don't ruin a 1200 for all. I use penetrating oil or spray soap to cool the blade and see that the blade rake is hitting the whole radius.. What sucks is Glendo no longer makes the lappers. The guys in Austria that now teach my classes made a lapper for BIAX factory that has a 600 grit and 2000 grit ring on one flat face wheel they had made special,. at 5:00 minute mark on this it shows it. They also have blade holders that have pins that rotate the blade at different radiuses and hook a vacuum to suck up the carbide dust..

I forgot to mention the back of the table should be higher then the front near the wheel so your sharpening and seeing the top side of the blade, On the one on the video the wheel is turning clockwise and the back of the table is high in back 5 degree's blade rake for regular gray iron. If your scraping steel use 20 to 30 use a positive rake and Turcite/Rulon a neg. 12 degree rake on a BIAX 1/2 moon blade 60mm tip radius