Should a 6 x 48 belt sander leave a flat surface?

[Dan Forman]

I just set up a Rikon disc/belt sander, and tried surfacing a few pieces of wood: a chunk of 2x4 (wide surface) and a maple/ purple heart lamination about 4" wide. Both came away with slightly more material removed at the edges that at the center. Is this to be expected? I have no experience with belt sanders, but expected a truer surface.

Dan

[glenn bradley]

View the belt path from the side; that is, viewing across the narrow sanding surface with a drum to your left and a drum to your right. Press down on the belt with your finger and see how much it flexes. If the platen is lower than the height of the drums the paper will hang like a hammock (make a smile, bow, whatever) under pressure and do what you describe. It is not desired.

[Dan Forman]

Now that I finally figured out how to get the belt off, it appears that the graphite covering on the platen is level lengthwise (end to end), but is concave across it's width, which would account for convexity I'm seeing across the width of my trial pieces. The platen is higher than the drums, so it's not a hammock in length, but is in width.

Has anyone tried leveling one of these graphite platens with a large, jointed flat chunk of wood with sandpaper glued on? I wonder how long it would take to wear a hollow in it again, once flattened?

Dan

[Andrew Joiner]

What do you mean by flat?:D

http://www.sawmillcreek.org/showthread.php?t=107832

[Dan Forman]

What do you mean by flat?:D

http://www.sawmillcreek.org/showthread.php?t=107832

I saw that thread yesterday. :) As is, this sander could be used to finish the outside of a bandsaw box, but parts sanded on it could not be glued together, as the resulting surface is convex. I would like to be able to get a glueable surface, and also use it to true a few hand plane soles, as the standard methods I tried don't seem to work for me.

Dan

[Pete Bradley]

My 6X48 is one of the most useful tools I own, but I wouldn't use it if I was trying to get something dead flat. You'll find that the rollers are crowned, which over time tends to put a little crown in the paper also. It's also really difficult to avoid rounding the edges freehand. I'm not sure why the platen on yours is concave, but even if it wasn't I don't think you'd get the results you want. I'd probably hand sand on a granite plate or tile.

Pete

[Andrew Joiner]

A disk sander will probably get wood flatter than a belt sander, maybe flat enough to glue.

[glenn bradley]

I would like to be able to get a glueable surface, and also use it to true a few hand plane soles,

Hmmmm, this may not be the right tool for that but, I would look at getting the platen replaced if it is a new tool. If it is "new to you" (used) I am not much help on a method for flattening that surface.

[Kevin Godshall]

I was "given" and old Foley-Belsaw belt sander (6x89 belt), and have the same problem. The platen under the belt has been mistreated in the past and has a definite "hump" to it. Not quite sure how to fix it, but I've learned I can't use it to guarantee a true flat surface when I'm done.

[Brian Kent]

Mine had 2 problems.

1) Cheap sanding belts made a seam that would knock on the edges of the piece and make the wood slightly convex front to back. Very slight. Better sanding belts (3M) fixed that.

2) My graphite pad was worn and no longer flat. I removed it an turned it around so the un-worn edge was before the stop. That is just a temporary improvement until I buy a new graphite pad for about $20 from Grizzly.

For the first two years of regular use I relied on it for glue edges. I noticed the problems when I tried it for truing an old plane sole. It would create a convex sole that took a lot of extra fettling on a flat surface to correct.

Brian

[george wilson]

I use the best belts on my square wheel grinder.I can tell you that with a belt,no matter how tight,there is always some slight rounding of corners. Then,you have to finally lap the surface (when working in metal) to get the edges dead flat.

[Johnny Upton]

I'd get rid of the graphite, clean the platen and JB weld a ceramic platen liner (Fancy name for the glass used on Fireplaces) to the platen.

[Brian Kent]

Johnny, where would we find that? I only found much smaller sizes.

[Johnny Upton]

Brian -

The least expensive option is probably working with a fireplace store and have them cut a replacement panel down to fit.

You can also contact Darren Ellis (Not sure of the forum rules on links, please delete if not allowed)
http://home.comcast.net/~eellis2/EllisCustomKnifeworks/ceramicplatenliners.html (http://home.comcast.net/~eellis2/EllisCustomKnifeworks/ceramicplatenliners.html)

He doesn't stock 6" wide, but he will order it.

[M Toupin]

I've rebuilt two PM30 6X48 belt sanders over the years. Plattens take a lot of abuse from misaligned belts and folks pressing way too hard on the belt which wears the plattens. While yours is a Rikon, the basic premise is the same.

On both machines I rebuilt the plattens were worn badly. On the first one I had a buddy use a fly cutter to flatten it. The problem with this is the platten is only about 3/8" thick between the webs. Once you take a couple truing cuts there isn't much left. On the second platten, which was worse then the other, I used lab metal to fill on the wallow and true it up. I first cleaned the platten and then put a tin layer of lab metal on the platten and carfully covered it with seran wrap and then clamped the platten to a piece of MDF on my tale saw top. that made it pretty flat, but I still needed to true it up a bit. I glued several strips of 100g sandpaper belts to a piece of MDF and lapped it flat. The trick is to keep rotating the platten so you're putting even pressure on it and not wallowing out one side. It took about 30 min to get it flat.

I then glued graphite canvas to the plattens to eliminate any future wear. I knew the graphite canvas would eliminate the wear or at least greatly reduce it and would be easily replaceable. I was surprised to find the belt runs much cooler and the machine seems to have more power due to the reduced friction.

Mike

[george wilson]

My platens,on metal cutting Wilton square wheel grinder,are made of A2 steel,fully hardened,screwed over the original cast iron platen. They are in excellent condition.They are much flatter than any graphite can ever be. I can adjust belt tension to whatever I want,yet there is still some slight rounding near the edges of metal that is ground on it. Use of a disc sander,where the disc is glued down at all points,will give more perfect flatness,though the sanding scratch pattern will not be ideal.

[David DeCristoforo]

"What do you mean by flat?"

NOOOOOOOOOOO!!!!!!!!!!!!