Acceptable finish

I grind to 220 and then use a Scotch Brite belt.

kuraki said:
One is the rotary platen with a glass platen behind the longest length.
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What a great idea!!!
I never thought of this solution, but always felt it was a shame you couldn't use the long space for true flat grinds. I think I will be out in the shop this weekend with a piece of heavy aluminum angle stock and measure for a piece of pyroceram.

Now, if you can find a way to make the bearings in the rotary platen last longer, you will be a true genius;)
 
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Not my idea, I got it elsewhere, but definitely don't go without glass. The belt will practically melt running on anything else.
 
I may put a screw-in TC on the platen back to keep track of the temperature.

Friction was one of my concerns. Obviously, I would back the platen off for most use and run the belt slow when using the platen for flat grinding.

Out of curiosity, is the platen addition on a rotary unit any different/better than a good glass backed platen on a regular flat platen? I already have several types of flat platens I use.
 
Different how? I used the same glass I use on a typical platen, and I only operate my rotary at 200 to 800 SFM. (Over 800 SFM is where heat really starts to build on mine, but under that I can almost run indefinitely) I never move it in or out, even if I'm using the unbacked rubber portions. I have it set to just make contact, only slightly proud of the wheel tangent. There's less tension on my rubber belt than on my grinding belt, so when rotated out of the way there's very little pressure/friction between the rubber belt and glass.

If you're asking how it's affect on grinding is different, it's vastly different than a sanding belt on glass platen. Even though the belt is very stiff, the ribs act like a cushion. It's a very very slightly convex grind. I imagine it's just like putting a leather or felt pad behind your belt, or doubling up belts like Nathan suggested. Just less maintenance.

I really only use my rotary platen for 3 things at this point. Convexing edges with the belt only portion, finishing bevels with the platen backed belt, and the occasional grinding of surfaces with dissimilar materials like a guard/wood joint, but in that instance only where the surfaces are linear or near linear. It's next to worthless (in my opinion) for the front of a guard where the guard meets the handle in a tight radius, and I use a slack platen and scalloped belts there.
 
" ....If you're asking how it's affect on grinding is different, it's vastly different than a sanding belt on glass platen. ...."

Thanks, that is what I was asking. I'll have to give it a try.
 
valknut said:
Best thing that helped me was the disc grinder. I come off the grinder at 120, go to the disc at 320, then hand sand 320 and 600.
Using the disc grinder takes all the vertical scratch Mark's out and theres np problem with a stray 60 or 120 grit scratch(s)
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I have my disc, but find it challenging to get up to the “curve” near the spine without blowing through it. How do you keep from having that problem?

Jeremy
 
I do the same as kuraki. I definitely suggest using a carbide file guide. It let's you really get into the plunge area. But yeah stay away from the top curve of the plunge
 
I made a "poor man's 'Moen' platen" similar to what Kuraki is describing. I used a 36" micro-v belt on a 6"x12" frame.

Here's a pic on my instagram: https://www.instagram.com/p/BfCXo6egvSl/?utm_source=ig_web_copy_link

It definitely reduces if not eliminates belt bump and cuts down on the finishing efforts. I'm still playing with it and trying to figure out belt progressions/types that work best with it, but I think it's definitely worth trying out.
 
I handsand a finish on the flats, belt finish the bevels then touch it up with surface conditioning belt. yes that belt bleeds onto the flats but I go back and very quickly fix the flats by hand ( 5 minutes). majority of my time is spent getting the hand sand finish on the flats before I grind in the bevels.. after bevels there is very little to do. Ive started to get 220 grit lengthwise finish off the platen then handsand 320 or 400ish before bevels.

 
Why not just sand the flats on the platen? Flats are easy. On the full tang knives that I do, I sand the flats mostly on the platen to get them right initially and then "overrun" if I am hand saying the bevels. ON the feet that I have done with belt finish on the bevles, I do final clean up on the flats with the platen regardless of which way the scratches are going.
 
knife to a gunfight said:
I made a "poor man's 'Moen' platen" similar to what Kuraki is describing. I used a 36" micro-v belt on a 6"x12" frame.

Here's a pic on my instagram: https://www.instagram.com/p/BfCXo6egvSl/?utm_source=ig_web_copy_link

It definitely reduces if not eliminates belt bump and cuts down on the finishing efforts. I'm still playing with it and trying to figure out belt progressions/types that work best with it, but I think it's definitely worth trying out.
Click to expand...

I use something similar here in production grinding. We've ground thousands of knives on it. Once the belt broke in it quieted down. I run it up to about 3000 SFM at extended run times without any problems controlling heat with a platen chiller.

This allows me to skip rubbing the grit off the splice joint. Nice smooth grinds.
 
jdm61 said:
Why not just sand the flats on the platen? Flats are easy. On the full tang knives that I do, I sand the flats mostly on the platen to get them right initially and then "overrun" if I am hand saying the bevels. ON the feet that I have done with belt finish on the bevles, I do final clean up on the flats with the platen regardless of which way the scratches are going.
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I've done it some on the platen but if you do not go into the platen perfectly flat then you can round the tang. Yes it could be such a tiny amount but still visible after gluing up the handle.
 
Im beginning to think that the rotary platen with a backing like knife to a gunfight posted is the way to go. You need a backing with some cushion to get an even finish.

I'm going to be honest, I straight up can't get a good finish on a flat platten. After I make that jump from 120 to 220 ceramics or gator belts, there's just not enough backing and I always end up missing spots or with an uneven finish.

The rotary platen is great and I can get solid finishes but because of the slack, you can only grind blades of a certain height before the concave becomes too great and you hit the spine of the blank on the belt. For example, trying to grind a 2in Chef is a no go because the spine will hit the belt.

Its time to get a backing set up for my rotary platen.
 
Nathan the Machinist said:
I use something similar here in production grinding. We've ground thousands of knives on it. Once the belt broke in it quieted down. I run it up to about 3000 SFM at extended run times without any problems controlling heat with a platen chiller.

This allows me to skip rubbing the grit off the splice joint. Nice smooth grinds.
Click to expand...

Yep this is the next step for me. Adding cooling. I have to believe it will work even better at higher SFM, once the heat is mitigated.
 
Nathan the Machinist said:
I use something similar here in production grinding. We've ground thousands of knives on it. Once the belt broke in it quieted down. I run it up to about 3000 SFM at extended run times without any problems controlling heat with a platen chiller.

This allows me to skip rubbing the grit off the splice joint. Nice smooth grinds.
Click to expand...

That's good to hear. I haven't noticed a problem with heat, but I typically keep it at 30% or below on my VFD, and I'm using an aluminum platen backer to help control heat a little better than the steel backers I normally use. I'll have to play with bumping the speed up though, and I'm sure I'll need to work up some kind of cooling if crank it up like you are.
 
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