Maybe I'm Finally Figuring Out How To Use The Rotary Platen...

ddavelarsen

ddavelarsen

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Dec 7, 2000
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Dunno how many of you have one of Rob's rotary platens but for me it's been one of the best tool investments I've ever made.

However, I've had a heck of a time figuring out how to convex grind a blade on it. I was all the time getting uneven plunges and too "thick" a convex curve.

Well, practice practice practice; and think about what's happening.

I'm one of those grinders who wales away on the rough grind, just hogging off as much steel as I can. That approach doesn't lend itself to the flexible support. The trick for me seems to be very simple: Light to light moderate pressure and a fresh belt. Using this combination I've finally gotten a grind the way I want it to go - or headed in the right direction at least. Nice crisp lines and a slight convex surface. We'll see how this develops. I haven't quite got it the way I want all the way to the edge, but I can see it coming eventually.

I'd be interested in hearing how others use theirs too, everything I've been able to do with this fine tool tells me I must be missing a whole lot more. One thing, I'm not sure how much tension I can put on the belt; any guidelines?
 
Dave, I don't have the rotary platen, I have the slack belt attachment. I bought the basic set-up without the contact wheel. I did get a used 10" wheel from Nathan House and I can't wait to try it out. :D I do all my grinding horizonally. As I work the convex grind up the blade, I add pressure to the belt as I'm moving the blade across the belt. The attachment I have does a wonderful job doing convex grinds. I'm not sure if that helps in your situation but I thought I'd share. The tighter the belt tension the less curve I get in the grind.
Scott
 
Dave, you can get the tension pretty tight. Use the narrowest flat area that you can. Keep playing with it.
Here's one I did last year - 3/16" S7 with 10" blade. Grind from edge to spine is 2 1/4".
 

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You KMG guys have it made. Someday. Someday me too. I HOPE; sooner the better. Don't think I don't love my Coote. I do and will keep her. A KMG is my want though.

RL
 
Scott, that's very much how I'm going about it too.

Kit, that is one beautiful grind on that knife! I'm not there yet. :D

Roger I know what you mean, I'm still using my first grinder for stuff too. Some things are just good reliable tools that you live with happily forever...
 
Dave, thanks for making me go back to Kit's post. I had originally scanned past too quickly. Very nice and wonderful to see another S7 by someone I know can do it. S7 is over looked for knives of that type I think. The wood on that one is superb too. The grind makes me want to retire and take up dumpster diving. Oh well, I'll just keep practicing I guess.

Dave, do you love that KMG as much as you do that bird looking thing in your avitar :cool:.

RL
 
Roger I have a BIII, which is probably as good a machine as the KMG but had I known at the time I'd have bought the KMG; I think it's a better value and is built like a freakin tank. Nice thing is, everything is interchangeable between the Bader and KMG, so when I do get one I'll be able to switch out all my tooling between them.

But no, nothing is as sweet as Uma's leggy sister Emu. :D
 
I don't care. That is one cute birdie. For a while I wondered if it was a self shot; but then I finally knew better :)
 
Dave good luck with your convexing :D I've learned the amount of belt tension and pressure applied while grinding has helped me.
Kit that is an awesome knife, I too am curious about the curved plunge.
Scott
 
On the plunge, beats the heck out of me :)
Just the right amount of tension (luck) and starting with a good sharp belt.
The wood is Koa burl that Tom Mayo sent me a few years ago.
BTW, the blade was hardened before I ground it.
 
I've always had to take the convex all the way to the spine. I tried -hard- to get a saber grind and couldn't. Also, I do most of the hogging on a wheel or flat platen before I go to the rotary or it seems to take forever.

Are you getting a clean grind line? If so, I need to have another look at it. I do use it for every knife when I put an edge on.
 
Tracy, I have learned to grind a nice sharp line. It takes light pressure and a sharp belt. Goes against my intuition not to lean into the grind, but that's exactly how it gets too convex and how I washed out the grind lines.

I'll try to get some pics of the false edge on the current knife, which is where I finally figured this out.
 
If I'm hijacking, just say so, but Roger, how does that coote hold up? I'm saving up, and I don't want to be stuck with a sears/craftsmen 2x24 forever. Would it be worth the $550 to get a coote with a nice platen, 10'' wheel, and nice, new motor? Or should I stick with the 2x24 until I can get a KMG.
 
This is a good thread. My rotary platen from Rob just came in the other day. I haven't even taken it out of the box yet. At least now I know more or less how to get started with it. I like convex grinds. Someone on this forum (I think) showed me how to build a "soft" platen using a mouse pad, glued to a piece of thin sheet metal, and attached to the regular platen. The mouse pad was lined with some graffite belting I had. It worked good, but left dimples all in the blade. I'm hoping this will take care of that. I also bought a big nice supply of fresh new belts. All in all, about a $650 week! Wife hasnt' seen the bill yet, that's why I can still type.
 
Robert you're going to love this thing. You'll wonder how you ever lived without it. This has to be one of those Renaissance breakthroughs that will eventually seem so obvious history will wonder that it took so long to be invented. I use mine virtually every time I make a knife, for something. Fantastic!

If you're smart and well-adapted like me, you'll buy your wife something she's been hinting about for a while... :D
 
Personally I think he's fibbin', Dave. If Carrie was gonna smack him around for buying toys he'd be a battered and bloody mess by now. That man's got some serious equipment! ;)

Robert may wanna smack me for saying this, but his dad is going in for some serious back surgery Thursday and I'd ask everyone to send some good vibes that way. Thanks.
 
Good vibrations have been delivered. Good luck to your father Robert.

And quit yer whinin about the Mrs! :D
 
Kit Carson said:
Dave, you can get the tension pretty tight. Use the narrowest flat area that you can. Keep playing with it.
Here's one I did last year - 3/16" S7 with 10" blade. Grind from edge to spine is 2 1/4".
Click to expand...

Freaking WOW! That's an awesome knife!

Kit, you are THE MAN!

John

PS: I think I have KMG envy :(
 
Robert has one of the best equiped shops in Texas and if Uvalde wasn't out in the middle of...well you just can't get there, I'd love to go play with some of his toys. (Not that there is anything wrong with that.) For those of you that don't know, Robert teaches classes how to make rocking chairs in his shop. He has been featured on several TV shows.

In order to stay on topic, Robert will enjoy using his new rotary platen very much I'm sure.:D
Good luck with your Dad Robert.

Dave, you've convinced me to give the rotary another go to get a grind line.
 
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