Rubber platen?

S

soundmind

KNIFE MAKER
Did I make a mistake to use rubber for a platen? Or is there a certain kind I need to get? Here's what happened to it while I was slowly grinding a guard down flush with a spacer. Thanks, Luke
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Honestly, there's nothing like that you can use on a platen that will last....even the stuff that Ken noted (that's intend for such use) will "wallow" out in VERY short order and create the same thing shown in your photo. Best thing I can recommend is to use a slack belt (as in remove the platen face) and use belt tension, along with grinding pressure to achieve what you want/need.
 
Thanks Ed, thanks Ken. I wasn't sure if I did the wrong thing or did the right thing and just the wrong way.

EdCaffreyMS said:
Best thing I can recommend is to use a slack belt (as in remove the platen face) and use belt tension, along with grinding pressure to achieve what you want/need.
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BTW I put this on initially to help me make flat grinds. I 'm not sure why I wasn't getting them on the bare steel platen. They kept coming out convex. Think it was the platen or grit size? When I purchased belts the lowest I got was 80. I wonder if I would have better results with a lower grit and either leather, what KenH posted, or just waiting until I can order a ceramic platen.
 
A platen needs hardened steel or any steel with ceramic glass. I put the glass on every grinder in the shop. It will wear and need to be replaced same as hardened steel does.
 
EdCaffreyMS said:
even the stuff that Ken noted (that's intend for such use) will "wallow" out in VERY short order
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I should have elaborated more on the graphite. It is NOT for hard grinding or it will wallow out for sure just as Ed says. It's used for final flat grind and helps hide some "not so perfect" grind defects as the OP mentioned. The graphite is good because it's so low friction, not at all like leather but provides a similar effect.

I use it from time to time, but my main heavy grinding platen is as mentioned before, a steel plate with glass glued on top. With the glass the platen doesn't need to be hardened since the belt never touches the metal, only the glass. For "crisp" grind lines a hard glass platen is required.
 
A couple of grinder manufacturers make a rotary platen that will work for this type of procedure, but it will last because the "backing" rotates with the belt. I've never used one, but I've seen them in action, and they work well.
 
I have a number of platens , steel , ceramic and when I want a soft platen I use a high density industrial felt 3/8 or 1/2 in thick . They hold up well and when they ware , peel them off and use contact cement and stick a new one on.
 
I use a high density industrial felt 3/8 or 1/2 in thick
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I'd forgotten about felt...and about a "rotary" platen...... I have both hanging on the wall behind the grinders....but it's been so long since using them..... I'd forgotten bout em. Either solution would work for what you're after..... but personally, I'd recommend the "rotary" platen. If you can't find pics, let me know, and I'll take pics of mine and post them.
 
Here's a link to the one I have..... https://beaumontmetalworks.com/product/rotary-platen-attachment/

WAY back, when Rob was first designing/testing these, he sent me a 3 wheeled version.....that just didn't work too well, then a couple months later I got this one...... It's essentially the drive belt for a snowmobile, on the grooved wheels. The different distances between wheels provides for harder or softer backing. It works really well for convex grinding of just about any variety.....although it does have a learning curve, and takes a level of finesse.
For me, it's there for special purposes, but I've learned that I have more control and flexibility by using a slack belt setup, and varying my grinding pressures. I have several different two wheeled grinder attachments, each with different distances between the wheels, that allow for varying degrees of slack belt stiffness. These are my "go to" setup for finishing handles and guards.
 
The rotary platen works quite well on handles. It can also make convex grinds a bit less convex than some you see that were done on slack belts.
 
So, I remembered why I had thought about the rotary platen setup. If you do corby bolt pins on handles, they are a beast to shape if you do a concave grind at the bottom of your handle, and not get a domed pin where the wood wears quicker than the pin. I always have to go back and do a decent amount of hand file work to flatten them out, and hand sand with a curved backer. The rotary platen is supposed to eliminate that problem.
 
One other trick that works well is using a worn out surface conditioning belts. I take my old ones and cut them up to the length of my platen. They are already 2” wide so they fit perfectly. A 2x72 belt will give me 10 strips. I have one platen dedicated for this. Just glue them on with spray adhesive and when they are worn out just peel and stick on a new one.
 
I've had a glass platen and coarser belts on my shopping list for awhile. I'll add rotary platen possibly for the future.

I have a few ideas for making some interchangeable platens. Ed mentioned different kinds in one his KMT videos (including leather and maybe wood?)

EdCaffreyMS said:
It's essentially the drive belt for a snowmobile, on the grooved wheels. The different distances between wheels provides for harder or softer backing.
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Is it the hardness of that belt or the tension between wheels that prevents the rubber from wearing out?
I have some used snow-machine drive belts I thought of using on my platen. They're in the neighborhood of 1" wide, serrated on one side. But horizontally, not diagonally. I thought they might not wear out fast and provide cooling. Just need to try it.
 
Is it the hardness of that belt or the tension between wheels that prevents the rubber from wearing out?
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The grinding belt goes over the top of the rubber belt....and the rubber belt rotates with the grinding belt. The different spacing between wheels is what provides different levels of tension.

Whatever you use, I suspect you're going to want a smooth face backing the grinding belt..... otherwise it's gona be like wagon wheels on cobblestones when you try to grind!
 
EdCaffreyMS said:
otherwise it's gona be like wagon wheels on cobblestones when you try to grind!
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That horizontal ribs would bounce the knife around?

I tried the ribbed side of a snow machine drive belt as a backer for hand-sanding and it didn't sand even. But on a platen I thought it'd help keep things cool, like I understand a serrated wheel to do - but no, the turning of the wheel and diagonal ribs must keep the sanding even with a wheel.

It'd would take a lot of fiddling to come up with a serrated platen.... anyway, thanks for letting bounce that idea off you.

I could still use the flat side of these snowmachine belts without much trouble. It's only worth it if the rubber on that belt isn't going to wear as fast.
 
hey guys........check out the Ameribrade website and have a look at their rotary platen.......i have just recently purchased 2 of their grinders and their rotary platen works great......there are 2 slack belt surfaces and 1 rigid surface......i am doing a lot more flat grind knives since getting this......one thing i noticed is that you have to keep the speed down or you will heat up the belt......it really does a great job at about 10% on the speed control.....another bonus is it works great for appleseed edges
 
Schreiber815 said:
One other trick that works well is using a worn out surface conditioning belts. I take my old ones and cut them up to the length of my platen. They are already 2” wide so they fit perfectly. A 2x72 belt will give me 10 strips. I have one platen dedicated for this. Just glue them on with spray adhesive and when they are worn out just peel and stick on a new one.
Click to expand...
Wow that's a good idea!
Thanks a lot Schreiber!
 
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