Rotary platen creating flat spot by plunge

[Outdoor Gear Dad]

Hello all, Im finally starting to really dive into convex grinds. I am using the rotary platen to start conveying the 3/4 height flat grind. I cant figure out why, but I am getting a flat spot up by the plunge that I cannot get out with the rotary platen.

Any idea what I am doing to create this flat spot?

 

[Drew Riley]

Can you show a picture of what you're talking about?

 

[Outdoor Gear Dad]

Can you show a picture of what you're talking about?

Dang, I should have taken a picture..I was only able to work it out through hand sanding, but I attached a picture of where this flat spot usually occurs...Not matter how I try to attack it, its like I cant get it out on the rotary.

 

[Drew Riley]

I'm gonna assume it's just from where the belt flexes more on the edge of the platen. You might try tightening the rubber belt up a little more or using one of the shorter sides. You may have to "roll" the knife back and forth to get as much of a convex, but that may help.

 

[Outdoor Gear Dad]

I'm gonna assume it's just from where the belt flexes more on the edge of the platen. You might try tightening the rubber belt up a little more or using one of the shorter sides. You may have to "roll" the knife back and forth to get as much of a convex, but that may help.

Thanks for that....Out of curiosity how tight should the rubber belt be? I know its probably dependent on what you are trying to accomplish but is there a rule of thumb? Convex is relatively new to me.

 

[Drew Riley]

I don't use my rotary platen a ton, but I'd say that you'll generally want a little looser for softer materials and larger convexes, and a little tighter for harder materials. As for specific tensions, I'd say that's something you'll pick up on as you use it more. Try tighter vs looser on some scrap and see how it feels for different applications.

 

[imill3567]

I'm assuming you're using a side with no backer behind the belt? It's very hard to do a knife with a plunge without a backer platen in my opinion because the edge of the belt is too soft, but I believe other folks can do it. I also get a flat in that area because the belt isn't actually touching it, so really it's leftover flat.

 

[Outdoor Gear Dad]

I'm assuming you're using a side with no backer behind the belt? It's very hard to do a knife with a plunge without a backer platen in my opinion because the edge of the belt is too soft, but I believe other folks can do it. I also get a flat in that area because the belt isn't actually touching it, so really it's leftover flat.

Well I am using the Beaumont rotary platen. Each section has a rubber backer, but there isn’t a section that has a stiff backing like on the ameriblade rotary platen.

 

[imill3567]

Well I am using the Beaumont rotary platen. Each section has a rubber backer, but there isn’t a section that has a stiff backing like on the ameriblade rotary platen.

Yeah I was referring to the rubber backer as a belt. I have the ameribrade so that's the platen backing I was referring to. I find just the rubber belt to be not stiff enough for plunges.

 

[Outdoor Gear Dad]

Yeah I was referring to the rubber backer as a belt. I have the ameribrade so that's the platen backing I was referring to. I find just the rubber belt to be not stiff enough for plunges.

I’ve been debating trying out the ameriblade and I think this just sealed the deal. They are on sale right now too. Do you like yours?

 

[imill3567]

I’ve been debating trying out the ameriblade and I think this just sealed the deal. They are on sale right now too. Do you like yours?

I like the option of the backer platen for essentially a softer flat grind. I don't like that the frame is too close to the belt so in order to use a file guide you have to grind back the "triangle" shaped frames to give room for the file guide. If you already have a rotary platen it's probably not worth getting another but that's just my opinion. It's definitely not at the top of my list of must have shop tools but is nice for a couple specific things.

 

[Outdoor Gear Dad]

I like the option of the backer platen for essentially a softer flat grind. I don't like that the frame is too close to the belt so in order to use a file guide you have to grind back the "triangle" shaped frames to give room for the file guide. If you already have a rotary platen it's probably not worth getting another but that's just my opinion. It's definitely not at the top of my list of must have shop tools but is nice for a couple specific things.

Yeah would probably be easier to attach a piece of leather to one of my flat platens and call it a day!