Yippeeee!!! It's Rotary Platen Time!!

ddavelarsen

ddavelarsen

Joined
Dec 7, 2000
Messages
5,179
Yep, it came today and naturally I had to grind something... So I sharpened my knife! :D Man I can't wait to get this baby rolling!

Rob, thanks for the lightspeed turnaround and for building such a Tank!

Dave
 
Let us know how you like it. I hear thier great. I'll probably go bug George soon to try his out. Send some pix soon.:D :D :D
 
Hey Dave, I'm jealous now! I looked those rotary platens over at the Blade Show and was highly impressed. From what I hear it should be a breeze to get a slightly convex, almost flat grind on it!

Happy grinding!
 
J. George who???? :) :) :) I am still going thru a learning curve. When you are cleaning up your grinds on it slow down the grinder. I plan on finishing a bowie on it today. It is going to be bad once I get the hang of it.:D :D :D
Jerry A. loves it already. Right Jerry???
 
George. Yeah you. Maybe I misunderstood earlier. I didn't realize the rotary platen was a flat grinding item.
 
J. It is not exaclly flat where the wheels are the closes, but darn close. Where the wheels a the farthest apart you get a convex grind.
 
George or Rob, about how much tension do you put on the belt? I have it fairly tight but don't know whether it's too much or too little. Do you folks with experience have a standard yet?

Does belt tension affect the resistance in turning the platen? It does pull pretty hard, good thing for powerful grinders! I wonder whether there's a break-in period and it'll loosen up over time?

Is there an upper limit on speed? Should watch out for heating the bearings?

And Rob, how long should the belt last and should I keep a spare? If so I'll go ahead and order one.

Finally, I'm going to try using one of the rollers as a contact wheel. Any problems with that? Do the ribs on the belt influence the grind?

I've said it before and I'll say it again, this tool is going to revolutionize some aspects of knife making, particularly convex grinding. All the various firmnesses of platen make this thing incredibly versatile. You just gotta love it!

By the way, this baby was packaged to beat the band. It took some doing to get it out, and you can imagine I wasn't wasting any time. :D

One more thing: Two and a half one-pound coffee cans of silver coins will pay for your rotary platen. :cool: That's about a year's worth of end-of-day change for me. :)
 
Hello Dave,

You sound like a Kid on Christmas morning!

Of course the tension of the rotary belt will dictate the dgree of convex. i.e. more tension = flatter convex. Howvwer there is point where increased tension really doesn't provide more flatness. It is hard to describe where this point is....but a few things will to look for. High tension causes the rubber belt to conform into the grooves on the rollers. The conforming action of the rubber generates heat and the higher the tension, the more heat. So you should adjust the tension such that everything runs at a comfortable temp. Same with the speed. The belt is rated to run continously at 180F and the bearing manufacturers say 250F continous is acceptable. You find the point where the operating temp be stable to a "warm to the touch". Too much tension and speed and the temp will uncontrollably run away. You'll get a feel for it as you use it more and more. Heck if you destroy it...send it back.....or if it doesn't do what you thought...send it back. They are certainly unique tools. The best performance will come with using finer grit belts...say 220 and higher. It is really not a hogging tool that you can lean into without losing your grind, however you can rough out the grind on your hard platen...then swith over to the rotary platen for more delicate refining and finishing.

The closer you take the rough grind to your final shape, the flatter the bevel will be, For a flat blade, rough on your std platen say 80 then 120 grit, then use the rotary platen starting at 220 grit to finish.......or for a very sweet convex: rough grind to 80 grit on the std platen, then go to 120 with the rotary platen to reshape and blend...then finish with 220, 400 and smile! You will see the finishing benifits immediately and its ability to fix grinding mistakes from the hard platen. You'll quickly see that you don't need to be as precise on the std platen.


As far as rotary belt life....I dunno. I haven't seen any wear out yet. Similiar to automotive maintainence, I would expect them to provide at least 1000hrs of performance. That's like grinding and hour everyday for 3 years. This is speculation of course and time will tell. I have replacements in stock and they are avaliable at your local industrial suppliers as well.


No problem grinding on the wheels as contact wheels....this was one of the design goals.


Thats all I can think of right now....if I missed anything let me know.

Take care,
Rob
 
I have one of Robs "Rotary Platens" as well. Rob said it all. I really like the slight convex grind it gives and I can vary it for individual blade widths by simply loosening the belt tension and/or moving to the section with the wheel distance wider. It really shines with finish work and to take out deformations and scatched left by my flat platen. It is not a replacement for a flat platen. I use the flat platen to hog off the bevels and switch to the rotory to clean and finsh them. I made my ultra fine taxidermy blade the other night on it. I dont have variable speed on my burr-king but could still get great results because it is so forgiving. Be gentle and finese the finish on.

The automotive belt should go about 50,000 miles.
 
I was fortunate enough to get to try one of Rob's Burr King model prototypes!

I have been playing with it quite a bit and I really like it!

I'm planning on starting a thread dedicated to my report on it after some more testing. :)

Thanks Rob!
Nick
 
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