Heat treating O1 platen?

[weo]

Hello all. I'm finally getting around to making my large diameter (36"radius) platen for my grinder. Starting piece is 1/2" thick O1. The mounting holes are drilled and tapped and I'm wondering if I should grind the radius before or after heat treating to minimize chances of warping.
Thanks

 

[Stacy E. Apelt - Bladesmith]

Depends on your equipment. If you have a wet grinder, I would suggest post-HT. If you are using a regular grinder, do the basic grind pre-HT and then true it after.

The way I calculate it, on a circle with an 18" radius ( 36" wheel simulation), an 8" chord (8" platen length) the chord height is .45"( 17.55" apothem ) … which is the thickness at the height of the arc at the center of your platen. You need to add at least .250" to that to accommodate the holes that are tapped in order to take into account that the thickness reduces as it approaches the ends. I figure that if they were 3/4" from the ends, which is normal for most platen attachments, the holes would only be around .100" deep at that point in the arc, so the extra .250" thickness added would be the hole depth.

To turn that into something that makes sense to most folks:
To make a 36" radius platen, you would need 3/4" steel ( or thicker).

I just waked out and measured one of Nathans 72" radius platens. The ends are almost .450" thick and the center is .650" thick. The holes are 3/4" from the ends and the steel is about 7/16" thick there. To make a 36" arc, you would need 1/4" thicker steel that that.

I did some quick math and you could make a 72" radius platen from your 1/2" thick blank, but the tapped holes would be barely 1/4" deep.

 

[weo]

Thanks Stacy.
I'm not sure I'm following you. Here's a pic of what I made, with the center at 1/2" and the outside edges are 1/4"


I have an OBM grinder and the flat platen that bolts to the bracket is 1/4", are you saying this isn't enough?

Also, my buddy Dave suggested that instead of heat treating the platen I look into some ceramic tape. Anyone know anything about this?

 

[Stacy E. Apelt - Bladesmith]

My error, I read 36" wheel instead of 36" radius. What you have will work for a 72" wheel replica grind. Nathan makes them a bit thicker and has deeper bolt holes, but you should be able to get enough 1/4-20 thread in a 1/4" deep hole to hold it snug.

 

[Stromberg Knives]

Mine is made out of O1 and I did my HT before the shaping. Use a sharp belt and keep the platen cool while shaping. It's a pretty solid piece of steel and will absorb a good amount of heat.

 

[Stacy E. Apelt - Bladesmith]

Stromberg's photo made me think of another thing.

Mount the blank on the platen arm and grind the radius with the arm as the radius pivot. It should be pretty easy to drill a 1/4" hole at the end of the tool arm and screw it into a 2X6 that is held vertical.Have a buddy hold the 2X6 as you swing the arm up and down and slowly grind the arc into the steel. It will grind down the bolts as it goes.