The "Unigrinder" WIP - another KISS knife grinder concept

How the "Unigrinder" concept was developed...

There is one old belt grinder in my woodworking shop, it uses 2.5” x 48” grinding belts and has a ½ hp motor which interferes with grinding on the left side of the contact wheel. Bought it about 20 years ago and have used it for many, many things in my woodworking shop besides knife making.

Got back into knife grinding, after about a 15 year sabbatical. Decided it was time to step up to full size belts, minimum of 1 ½ HP with speed and direction control, blade/tool rest that is solid and will actually work, real good belt alignment, low noise, smooth, etc. Looked seriously into my finances and realized it would have to be a low-budget affair using the equipment and materials that already have in my woodworking and turning shop.

Since I am really a beginner knife maker (meaning a small number of knives have been butchered over a long period of time), was not really sure what would work good or what was really needed in a grinder so the market was researched pretty well. Looked at the equipment and materials in my shop, took some measurements, thought about it a lot, and did some 3-D modeling. Based upon this, the following grinder evolved by trying to get back to the basics and keeping to simple solutions.

One of the tools available in my woodworking shop is a Powermatic 3520B wood turning lathe, a heavy duty wood turning lathe with a 1 ½ hp variable speed drive that can turn a 20 inch diameter disk over the ways. It would be a very easy to modify and a near perfect drive for the belt grinder.

Picture 1 above showing the Powermatic 3520B lathe in the corner of my shop.

Existing belt grinders have a number of different wheels; drive wheels, alignment wheels, large radius contact wheels, small radius contact wheels, flat plenums, etc. Rethinking and simplifying the belt grinder’s purpose, it was decided to go with one wheel that would expand slightly to grip the grinding belt. What could be simpler – one wheel, and a big one at that? :les:


Picture 2 above showing, at a slow grinding speed, the “Unigrinder” prototype for half of a 2 ½” x 48” grinding belt.

The only grinding belts in my shop are 2.5” x 48”, and the same evening that I started designing this grinder, an article was read that stated one guy who like to rip his grinding belts in half so that he had 4 edges to work with on a belt instead of just 2. It made sense, :what!: so the prototype was built for a 1.25” wide x 48” long grinding belt with the 90° quadrants built out of ¾” MDF and sized to fit my largest wood turning scroll chuck. Had to buy ¾”MDF and metric bolts to match the chuck, total cost was less than $20.


Picture 3 showing the semi-finished belt grinder prototype, without the tool/knife rest.

Above is a picture of the prototype in my shop, with the first test knife blade being ground with a 60 grit belts. The prototype has about a 15.24” diameter grinding wheel and will expand the 1/16” in diameter to grip the 48” long grinding belts used here. The quadrant segments were glued up ¾” MDF, trimmed slightly and drilled to fit the wood scroll chuck mounting holes. Once mounted, the lathe was turned on and the outside diameter turned true and the outside surface flattened with a 5” orbital sander. The quadrant width was turned to be slightly larger than the belt width. Belts used are the 60 and 120 grit blue Norton cloth backed belts. The rigidity of the backing made the slight wheel circumference gaps disappear.

Happy to say, the “Unigrinder” grinds good to me and hope some other people will try out the concept. Will post the updated concept for 2” x 72” belts over the next few days that can be easily made in a simple woodworking shop and total expected cost is about $300 for the 1.5 ho motor/driver combination and one sheet of ¾” MDF.



Pictures 4,5, & 6 show the wheel construction.

Next step is prototype for 2"x 72" belts that can be built in anybodys' woodworking shop for basically the cost of the motor and controller.

Hint, hint…if one has the motor and speed controller for it, then the woodworking lathe is not needed. The scroll chuck principles are simple…….you got it.

Will continue in several days when time permits.

Thank you guys and gals, here and in the other knife making forums and organizations. You have given me plenty of help and inspiration in the past, and this seems a simple way to try making up for some of it.

Rich S.

Good thinking, Rich. I used a lathe with MDF wheels for hollow grinding blades for a year or more until I could afford to build a 2"x72" grinder. I glued strips of sandpaper onto the wheel with rubber cement, that way I could easily change out the abrasives. It worked fine for quite a few knives, but I really love my 2"x72" now. Use what you've got until you can afford to upgrade has been my motto.

Good morning youall,
Previous post showed how the Unigrinder concept was developed, a simple prototype built, and used to test the assumptions.

The following are some observations from running the prototype:

The prototype wheel was turned flat, smooth, perpendicular, and of uniform width by turning the lathe drive on and cutting the wheel down with normal wood turning tools. With the belts used, the small gaps could not be felt while grinding, both radial and lateral run outs were small, which means you could grind good sharp corners.
Several things became obvious with a bit of use. One of the first questions to arise is with the belt overheat due to the lack of air on both sides of the belt to cool it (between the wheels.) Long-term experience will show if this concern is warranted, but don’t think so.

Another question arose on how to align the grinding belt so that the edges ran true in straight. Short term, believe the solution would be to have with small piece of plastic or thin plywood and hold it against one side of the wheel. Slide the belt over to the contacts that surface, and rotate the wheel so that that surface is constant and consistent. That should align the belt edges on both sides.

One annoying characteristic of the prototype was the sound and lack of a soft grinding surface on the MDF wheel. For practical purposes, believe the quadrants should have some kind of rubber or plastic contact glued to the outside, similar to the rubber used on steel contact wheels.

Guess that is about it for this post.
Will post full size model for 2 x 72" belts.
Thanks.

One of the interesting points experienced is that while a large radius contact wheel would work good for grinding the blade profile in the cutting surfaces, it wouldn’t work too good for knife handles and other things with small radii. Reflecting on that problem, it seems the best solution would be to have another Unigrinder wheel that would be approximately ½ inch thick with us semi-circular profile. A 5/8”or ¾” wide section of a fairly limp grinding belt could be used and would probably make the good small radius grinds.

The lathe drive used to power the prototype as solid bearings and provided minimal lateral and radial run out. If an electric motor was to be used for the drive, a solid construction and tight bearings are required to minimize run out.

“UNIGRINDER” model for 2 x 72” grinding belts.

Sorry for the boring reads above, but it lays the background for this installation, which is how to build a full-size working grinder. This is the interesting stuff and while it may not be a grinder for everything, believe it can be quite useful in a knife makers set of tools.


Picture 1 showing 3d view of “UNIGRINDER” from the left front.

Picture 2 showing 3d view of “UNIGRINDER” from the right front.
Base is 2 layers of ¾” MDF for mass and resistance to vibration, as is pink tool/blade rest.
Possibly hinge tool/blade rest on left hand side, so it hinges up out of the way. Should work well with most blade grinding jigs.
VFD/speed motor controller behind motor.
Motor is sized at 2 hp, 3 phase, 230 v ac motor to match controller, 3600 rpm.
(1800 rpm would be slightly better, but controller will handle that. 583 rpm equates to 3,500 fpm
Belt speed, suggests that normal working speed will be about 150 to 400 rpm.)
Brown support box is sized as a kitchen cabinet, with the Unigrinder base bolted to the cabinet.

Picture 3 and 4 showing the expander disc controlling the outside diameter of the wheel.
Picture 3 shows how rotating the expander disc slides each of the quadrants out slightly, increasing the overall diameter to grip the grinding belt tightly.
Note that a belt of 71 7/8” length will wrap exactly once around a 22.8785” diameter disc.
A belt of 72” length will wrap exactly once around a 22.9183” diameter disc.
A belt of 72 1/8” length will wrap exactly once around a 22.9581” diameter disc.
Thus, there is only about 1/32” in diameter difference of each 1/8” difference of belt length.
The rigidity of the cloth backed belt covers the 1/16” or so gap between quadrants without being able to sense a bump at the gap.

Picture 5 shows the wheel parts, except the shaft coupling to the wheel and the expanding disc locking knobs.
The green quadrants slide in and out in the base wheel slots. The expander disc controls the quadrant position. Quadrant locking threads and knob not shown for clarity.
The quadrants are made up of ¾” MDF glued together, with a ¾” hardwood piece fastened on back to ride in base wheel slots. The dowel sticking out of the quadrant is imagined to be aluminum bar, with a threaded hole out to front. The quadrant locking knobs would be threaded into these dowels, and the friction between expander disc and dowels to keep quadrants in position, keeping the grinding belt tight.
Note that the wheel parts are setup for small shop building using ¾” MDF and 1” aluminum pipe. Serious and commercial construction would probably use a combination of steel coupling with cast and machined aluminum wheel segments and discs, to cut down on costs and rotating mass.

Buyouts used to detail the 3Dmodel are:

1. 2 hp ac motor and controller, 230 v, 3 phase, 5/8” keyed shaft, … $270 approximately thru dealerselectric.com. (No intentions implied, find your own source that you like.)
2. 5/8” keyed sprocket with 10T…..$5.30 thru surpluscenter. (Again, this is just one means and source, find whatever make you happy.)

That is about it for this segment on the Unigrinder.

There should be enough details that people can think this through and build their own grinder. The tool/blade rest seems kind of silly, lacking most adjustments. Believe that if the builder knows what jigs he wants to use and how he grinds, he can build his own tool/blade rest to satisfy himself. And yes, this would be easy to do with steel and aluminum, but that’s outside the simple woodworkers shop and abilities.

Now I guess, it’s time for me to go build my own full-size grinder. Maybe one of you readers can build one with me or even beat me there and we can compare notes.

Thank you guys and gals,

Rich S.

Great way to build a hollow grinding wheel. :les: I have a small jet lathe but I don't think a 22. something inch wheel would fit on that little jet I have? More like about half of that, Ill have to measure it.

I want a wheel or that 22" diameter or larger for some Japanese culinary knives. Hmmm?

Thank you for sharing!

You know, the Unigrinder setup (either belt or stone solid)is probably quite easily the most prominent grinder of choice everywhere except the US. One fantastic Scandinavian bladesmith by the name of John Neeman uses a solid stone unigrinder......and the work that leaves his shop is nothing short of awesome. Same with most Japanese bladesmiths. Functional, practical and as old as time.

Freeman,
Had not thought about it that way, but you are sure right.

2 x 72" belt grinder, version C...

Got started cutting and gluing three-quarter inch MDF for the full-size Unigrinder prototype for 2 x 72” grinding belts. Playing with the parts made me skeptical on some of the details. My biggest concern was if somebody walked into the shop and somehow plugged the Unigrinder into a 230 V outlet, thus bypassing the speed control and having the 1.5 hp motor try to turn that big wheel at 1750 RPM. Yes, it is a very unlikely scenario, but needed to be considered. Would the MDF base wheels stand up to the forces at high rpm? There was another problem with locking the individual pieces together transversely, to eliminate vibrations and keep the belt running smoothly and straight.

So, back to moving electrons around using SolidWORKS, sure is cheaper than cutting steel and wood. Used a combination of materials in this case, where each was more appropriate.

Version C of the Unigrinder as a ¾” steel base wheel plate, cut to a shape that minimizes rotating weight. Welded on two ½” bolts (A325) to align and clamp the sliding pieces in their places. Another ½” diameter rod welded on to radially position the quadrant sections. A small 1/8”is screwed on to lock the wheel assembly onto the motor shaft.

The quadrant sections went to ½” plate, shaped again to minimize rotating weight and vibrations. For the prototype, again used a glued up section of ¾” MDF for the outer grinder surface, because it is cheap, uniform in density, and cuts/scraps/sands easily into the desired profile and outside diameter. The glued up MDP sections bolt onto the steel sections with five ¼” bolts. The equalizer wheel went to ¼” plate, with a centralizer. Am showing four screw knobs, which hold the quadrants into their expanded position and make the belt changing easier.

Overall, lots better machine, but now the steel plates need to be sourced from a flamecutting/waterjetting company. Will take more time.
Spent much time considering the material to use on the outer grinding surface quadrant rims. Would have liked to use aluminum, but don’t want to find aluminum caster and make the forms. The MDF rim sections can be cut, shaped, and glued in any woodworking shop. Bolted on, they would be strong enough. Also cheap, and replaceable. And easy/cheap to cover with any softening surface that is desired, from thin rubber strips to thicker vinyl or felt.

Attached are pictures from SolidWorks showing this improved version.

Anybody with some ideas or concerns? Thoughts?

Why not just machine the rims out of solid 2" thick aluminum, rather than casting? That diameter could be swung on a Bridgeport mill with a rotary table pretty easily.

Guess the real reason for not using 2" aluminum or building up the thickness with multiple layers of thinner plate is that I'm not personally experienced, and comfortable, with aluminum.
Do not have the capabilities for machining metals in my woodworking shop, except for limited numbers of holes. Also do not know any venders from past experiences.
The cut steel and limited welding are normal for my work, thus, know venders and companies that can do this cheaply and timely.

There are ways to cut those parts out of aluminum with woodworking machines. You could cut the pieces out on a bandsaw, better if you can slow the speed down, but more important to have a fine metal cutting blade. I have cut aluminum and brass on my woodworking bandsaw and table saw. Yes be careful!!
You could set up a pivot point and swing the arc on a woodworking edge sander, I have done so with great accuracy. I actually set up two pivots. Make a table that pivots off the machines table with a stop of some sort. On this secondary table set up your pivot point for your piece. You can really dial in the accuracy with a set up like this.
Routers and router bits will cut aluminum as well, you must slow the speeds down to under a 1000 rpm's.
You do need to be very careful and if your out of you comfort zone don't try it!
Any machine shop could make those parts as well.
If I can help by being more specific with these methods, just ask! Larry