Thinking of making UHMW insert for hollow grinding blades

K

kawzak

Joined
Jan 9, 2025
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I want to be able to hollow grind a blade. I clamp my blade in my angle tool/jig and flat grind at a specific angle on the sander table now. So -if I make a piece of UHMW plastic w/slight radius that will go between the back of the sander belt and the upright metal back, then use my angle tool/jig I think that might work. Other than a specific built sander w/a 4”-6” diameter wheel for the belt to go around and a platform there to do this ,I don’t want to redesign my sander ( I could, but don’t want to). So-any suggestions, will be appreciated
 
I'll just throw out that UHMW has a low melting point if I recall correctly from my days in the food industry. It's commonly used as liner material due to its low COF (slippery-ish). Can't really picture in my mind what you have going, but be careful if the application is close to hot metal. I think your kinda trying to make a radiused platen of sorts using plastic as a backing with a belt flying over it. If that sounds right....no bueno, sir. Potentially flying materials and such.

P.S. That voice you heard that made you post here first ....listen to that guy. He's powerful in knife making.
 
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It won't work for many reasons.

Some of us have radiused steel platens that simulate a large wheel, but making a small radius platen would not be a good thing. Just us a contact wheel the radius needed.
I have 6",10", 12", and 14" contact wheels. You don't need that many. Most folks do fine with one at 10" or 12". You can use a jig with it similar to your flat grinding setup, but you will soon learn to hollow grind freehand if you give it a try.

Hand sanding after grinding takes some patience but is fairly straightforward. You can make or buy a curved backer for your paper but folding it up and using your fingers works just fine.
 
Ah, freehand. Can’t do that. I have Parkinson’s. The blade would look like one of those wavy daggers from Egypt ( Lol). I wasn’t thinking about heat build up, so recon your right. I have a simple belt sander. This is a hobby, not a profession. I would like to make a hollow ground blade, but without some sort of mechanical advantage I’m stuck. My straight angle blades turn out pretty good ( IMO) , but that’s only because I made a clamping tool to hold the blade and set the angle. I just slide it back/forth on the platform. It’s Robust and works well. I dip the whole thing into a small bucket of water so nothing gets too hot. I use to build equipment, robotics, and had access to a full machine shop. That all went away once I started to shake badly. Thanks for your advice.
 
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Radius platen (steel) is what I use. I have a 24" radius and it turns out a beautiful shallow hollow grind that is close to a flat grind, but not. I use a rubber eraser (bigger size from Walmart, not the one on the end of a pencil) to hand sand, though I may purchase a radius sanding block.

edit: when talking platens, don't try to outsmart Sergeant Safety. G10, plastic, micarta...all easy to make in your shop, terrible idea for a platen. Use steel for the radius platen, hardened.
 
Yes, a radiused platen makes a wonderful shallow hollow grind. It makes urasaki easy. The problem is tahy start to create a lot of drag and friction when they get below a 24" radius. That is equivalent to a 48:" contact wheel.

An 8" radiused platen (16" contact wheel equivalent) would be great for hollow grinds, but the tight turn would heat things up like crazy. It might (???) work if done with a full water spray setup.

You should be able to use the fixture that you currently do flat grinds with to do hollow grinds with a 12-14" contact wheel. They have special micrometer adjusted grinding jigs for doing hollow grinds. They are pricy, and most folks who get one never use it because it is too much work to set up and adjust. I have one in a box somewhere in the shop.
 
I agree dont use UHMW.
I work in automation, and it's really only good for light, incidental contact. PV kills it.

I too was thinking like you, but I was thinking Teflon material. I still have some, but stopped going in that direction.

I think I have a similar platen as navman navman
I love mine. It's flat, but I could see how a Large radius might work, too.

I'll offer an outside the box thought.....
What about trying a tapered disk?
That "should" give a non-flat grind.

I imagine it would be pretty easy to set up fixed fixturing for one to guide against.
 
I’m sorry to hear about your condition. May I ask what kind of sander/grinder you have? If it’s not a 2x72 you may need to fab or get creative.
 
A tapered disc won't create a hollow grind of any amount. It may also be hard to work with a grinding jig.

Tormek has several jigs the hold a knife blade for hollow grinding. Take a look at some for ideas on using with a contact wheel.


BTW, I don't think I gave you a proper welcome.
Welcome to Shop Talk.
Fill out your profile so we know where you live and something about you. It helps with answers and offers of assistance or equipment/supplies.
For instance, If I knew you were near me, I have an unused Tormek I would give you if it would help you do hollow grinds.
 
Thanks so much. I appreciate all the input. I’ll look into a curved platen. I think I can mount a roller w/brgs right above it to hold the belt. Gave me some ideas. Thanks. I’ll go into my profile and give some more info on myself. Typing depends on timing of my meds. Sometimes it takes me a 1/2 hr just to type a paragraph. Also I’ll need to figure out how to post pics. Thanks.
 
After going out and looking at my sander, and then pics of curved platen plates, I think I can make me one out of 1/8” CRS and bolt it on almost too easy ( I’m ashamed to say). Had I looked at curved platen plate on the internet before asking to begin with I wouldn’t have had to bother you guys so much thanks again.
 
You can make a temporary platen out of a oily hardwood if you want to try it out. And it will work better with finer grit belts.

Hoss
 
Just a thought, but I have had friends who could not type due to palsy, and they used a speech recognition typing program.
 
Windows and Mac have that feature built in as do iPhone and Android. Usually under accessibility settings or similar. On a desktop computer you’ll need a microphone, but those are built in on laptops and phones.
 
Thanks for the suggestions. I do have an I-phone but Unfortunately I studder some. It’s frustrating, but easier to just type -when I’m in the middle of my meds. Even if I have to do over and over. FWIW autocorrect gets to be entraining !.
 
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