Air cushioned platen prototype

rfrink

rfrink

Joined
Aug 1, 2000
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Although, this discussion is on another forum, I wanted to share it here for those that don't surf around the knife boards.

The concept was brought up to used forced air behind the abrasive belt to form a cushion between the belt and the platen plate. Just like an air hockey table.

After thinking about it for a day or so, I figured it would be easy enough to try out. So I went into the shop and cobbled up a prototype to test.

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The platen has been drilled with holes and mounts onto a manifold which supplies air to the holes. The manifold has a 1/8" npt port on the back.

I haven't had a chance to try this out yet. I'm hoping that it will provide a smoother flat grinding action by eliminating the belt thump, improve belt life, and lower the horse power requirements.

I hope to try it out on Monday when I get back to the shop.

What do you think so far..?


-Rob
 
That. Freakin'. Rules.

I can't wait to hear how it works. Keep us posted!

-d
 
Oh Boy!!! Another toy for my KMG.:thumbup: :cool: ;) :D Let me know the $$$ if it works. Any idea for the PSI range????
 
Anxious to hear how she works. I hate to be the devils advocate but I have a feeling you're not going to be able to keep the object (in this case, the blade being ground) off of the platen. I'm thinking that pressure against the belt will close off the holes under the contact points and cause it to push the belt further away in places where there isn't any contact thereby creating a less than flat surface. I hope to be proven wrong. I very much appreciate the R & D that you do for us Rob ! I'm very much hoping to be able to pick up a "Rotary Platen" from you, it is not a matter of if I will, but when. The "Rotary Platen" is, in my humble opinion, a must have accessory for what I'm doing.I need one now ;) :) I would like to say to any guys that are starting out, the quality of your grinds will improve immediately upon receipt of a KMG Grinder, along with shortening your learning curve. It is without a doubt the best purchase that I have made for my shop, Bar None ! Rob, don't take my negative feedback in the wrong light. Just trying to help with constructive criticism :thumbup:. Edit to add: I made some manifolds for a "drier" blowing hot air (similar concept) and to get a uniform air exhaust you might find yourself adjusting the size of your "orifice" as it moves away from the air source.
 
That really is a great idea! After flat grinding a batch of knives last night, the pyroceram I have glued onto my grinder got quite warm. Makes me a little nervous, as we've all heard stories of these breaking free and going into the wheel.

Hey Rob, is the platen hardened steel? It would be great if it was hardened D2! Keep up the good work! :thumbup:
 
rfrink said:
Just like an air hockey table.
Click to expand...


Hummm......I dont think it will work...
You have in mind the "puck",,and how the puck skims across the table. But I dont think thats what happens here...
The truth is that it will be more like placeing your hand down flat on the air hocky table,,,Your hand feels no air hitting it from underneath,all the air just goes around it..


I think the problem is that the air is going to spill out where it's the most easy...and not go at all where it's the most hard...

That means that any place where the belt is being pushed on by the guy holding the knife blade will be closed off just enough to convince all the air to just go someplace else and not go near the knife....

This would mean that the place on the platten getting the work and the most hot would also be the place left high and dry of the air movement, while parts of the platten not being pushed on by the blade would be wide open to allow the air to slip out....

I think the platten would need a way to "flow" the air somehow,,to make sure the full platten gets an equal amount of air flow....and cooling...
 
rfrink said:
ab-ppl%20002.jpg
Click to expand...
I think you would need to connect all the holes on the outside just under the sanding belt.
You would need a way for all the air to slip out of the platten in an equal amount no matter how hard you pressed the knife into the belt.

a bunch of small groves connecting every drilled air hole with the edge of the platten would allow air to sneak out in a controled way, thus cooling the platten no matter what force is being used....

Moveing air is cooling air.
The moment any air stops moving it is not cooling anything, all it's doing is heating up.
If you want a platten to be air-cooled, then I think you have to keep the airflow in movement at all times.
 
I think you have a really neat idea. Maybe to avoid what Alan is concerned about in his first post, that using larger grit belts than you normally would that are really "stiff backed" (technical term) and not applying alot of pressure is a procedure to use....or if you need to tweek it, more air pressure....maybe Alan has a good idea there in the post just ahead of mine....
Maybe we are thinking that the air cushion will hold the belt farther from the platten than you are planning...actually it only meeds to be held far enough away from the platten to reduce or remove most of the contact between the paltten and belt, and compensate for the splice "bump"...maybe a very few thousandths of an inch?
Please do keep us informed....its a neat idea.
 
I think you came up with an excellent first iteration that will teach you a lot, Rob. I bet the second try is lightyears ahead of the first. The cool thing will be that if you need to experiment with hole patterns all you have to do is plug the ones you want to with round toothpicks or match sticks. Save a little machine time that way.

Interesting concept. Nice execution.
 
Yep...I think everyone has excellent comments. I don't have any idea if it'll work or not either..and can only speculate.

For me, it is certainly easy enough to build this simple proto-type to test. I have a bin full of scraped prototypes that never flew...so this wouldn't be the first. Besides, I just like to "make stuff" in the shop.

But...What if it does work..? What if it is silky smooth...and you never feel the belt touching the platen??

Just think..maybe a year from now, we'll be talking about the ol' days. You know, ....before there were cell phones, I-Pods..and air blown platens...:D :D
 
It's a nicely executed idea, Rob. My concern is its affect on dust collection. Can't wait for your evaluation. God, I love new toys.....
-Mark
 
You won't know until you hook 'er up and see!

Though my first impression is in line with some others (that it will be easy enough to overpower the air jets just under the workpiece), the fact is, that it might be an improvement anyway--by reducing friction everywhere the workpiece is not pressing against the platen.
Also, you might be able to run the belt quite a bit tighter than usual which might help abate flatness problems (using stiffer belts as mentioned would probably do it too). I'm thinking with a tight belt, the air cushion could be extremely thin. Flatness should be better than the rotary platen, for instance.

Have to plug in and try it out to know for sure!
 
I think the belt has to be very tight for any design to work...
You need equal back pressure for there to be a more equal distribution of air flow...
any loose gaps would draw all the air away from other areas...

Like an air hockey table has to have all the air holes about the same size or the bigger holes would draw all the air from the smaller.
 
Man, this looks really good. I think it has potential. My thought is you're looking to get the belt to stand off the platen only a couple thousandths.

I wonder if this will affect the tracking when a load is applied?

Rob, you are one innovative dude!!! :thumbup: :thumbup: Please let us know how it works.
I'll probably be up for one too.

Kelly
 
Rob,
That will be sweet if it works like you think.
What was the other forum.
I would like to see the conversation?
 
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