Flattening door with wide belt sander

[Ted Wong]

Hello All,

I built a set of frame and panel doors and one of frames has a bit of a wind to it. I was contemplating using a wide belt sander to flatten it out under the assumption that wide belt sanders can do this because the feed rollers are not under pressure. Is this assumption correct or should I be looking at other methods to flatten the frame?

[Harold Burrell]

Personally,m I would be scared to death to try it with a belt sander (I'm not to be trusted with one myself. I tend to hogg off too much.) Do you have any hand planes???

[Peter Quinn]

How thick is the door? A wide belt does have hold downs under spring or pneumatic pressure but typically they don't apply the kind of down force you get with a planer. The sander may just hold down a 3/4" door and let it spring back like a planer would, but thicker doors (1 3/8" for instance) tend to not bend under e hold downpressure, somyou can often shave off a slight crown then flip and flatten. Your success will depend on the size of the doors and the severity of the problem. I have managed to improve a few slightly warped doors on the sander, but its no guarantee .

[Rick Fisher]

Hey Ted..

I have a 25" Wide Belt sander and can tell you that it is the exact right tool for the job. On a job like that, the biggest problem is keeping the gravity pressure off the door while its being fed through the sander.

My sander doesn't have front and rear conveyor rollers( rollers in front of the conveyor and behind) , its a cabinet door machine, sanding a large door is an even bigger problem, but its possible with patience.

With a slightly cupped panel, or slightly warped, you feed the piece through on the slowest speed, and slowly lower the belt into the wood. Right away, you will notice its sanding one side of the panel, but not the lower portion.. If your careful, in a few passes, you can make the surface 100% flat. Its amazing.

A wide belt does not push so hard on the product that it forces the wood flat. If you pushed that hard, you would shred the belt .. The configuration is actually all wrong for that type of pressure. They work by putting the stock through on a moving sticky table, unlike a planer.. the material is actually carried through, not fed through with rollers.. There are upper rollers but they basically apply enough pressure to the wood that it sticks to the conveyor belt..

Wide Belts rock.. They eliminate hours of sanding in minutes, and flatten wide panels beyond what is possible otherwise.. I have run multiple strips through mine and can report that kickback can be amazing.. Something a planer would never do .. If one strip of wood is a hair thinner than the one next to it, the upper roller will not affect it and the sandpaper will propel it towards the operator with the same vigor as a table saw..

A 37" Wide belt would be a fantastic machine for entry doors.. You just need a method of keeping gravity off the door while being fed in and fed out.. A slight dip will dig a hole in the door or trash a $30.00 belt in a split second. A planer would never do that due to the strong rollers but a wide belt needs support ..

With only a 25" Wide machine, I will sand wide glue-up's in halves, and then use a domino to join the two halves together.. I end up with one precise ( due to the domino) glue line to clean up .. A scraper and 5 minutes is all it takes.. If the halves are jointed after sanding, the panel is still 100% flat..

[Peter Quinn]

Another issue to consider is the " flats" or reveals involved. Some cabinet door and passage door styles have a reveal perpendicular to the face of the door which then becomes the sticking profile as it bumps out to hold the panel. Thi is usually between 1/16" to 1/8". If you sand enough off the face of a warped door the flats in the high corners can become slight to the point that it is very visually obvious. So the door will be flat, but it doesnt look right. Same thing applies to raised panels. Watch out for that effect.

[Steve Griffin]

I've done this a number of times using a quick sled of veneered ply or raw mdf. Spot glue some shims so the door doesn't rock and screw a stop block or two to secure the door.

This is only good to make a minor improvement though, such as for inset doors which you want to line up just a little better with the frame.

If it's really warped you're out of luck and need to make another door. Not fun, but always worth it. (I've always said woodworking would sure be easier if it wasn't for wood.)

[John A langley]

Ted - I have to agree with Harold. Wide belt is not the machine to use. I have not seen one that will do what Rick says they will do.. My 37" widebalt has pressure rollers front and back. Without the pressure rollers you would have chatter like grazing. Again I don't know what kind of machine Rick has. Now to address your problem, first if it is slight and you are using Euopean hinges you might bee able to adjust it out. More than likely the twist is in the stile rather than in the rail. I have removed stiles from cabinet doors before by cutting the stiles off just before the tongue then removing the rest with a chisel and then putting a new stile on. If it is in your rail I'd probably build a new door.

[Sam Murdoch]

Rick is exactly right! Maybe not all "wide belts" will do this but a professional model with the option of platten down or up is the perfect tool. You can just kiss off the high spots of one side with no perceptible distortion whatsoever. The rubber pad is what pulls the work through the machine and the table can be raised ever so slightly to set the work into the belt to achieve very light passes for good results in no time.

Sam

[John A langley]

Sam - I am assuming by the highlighted wording that I've upset you and maybe Rick in the process. First, I didn't mean to imply that Rick didn't know what he was talking about. My SMCI Sandy 1 may not be a professional sander in some circles. But I've got it dialed in and it does a good job and I''d just as soon not change anything like it is being suggested. But I do think there are better ways to do what the OP is asking. I have a tendency not to get as technical as some of youi guys do. The one thing I have learned about this forum, there is more than one way to do things and I suppose that I should have made my suggestion and left Rick out of it.

[Sam Murdoch]

Yes John, I was responding to your line - "I have not seen one that will do what Rick says they will do" . You did not upset me - my bold italics may have been more emphasis than needed (since edited out)- but I did want to make it clear to the OP that in fact some wide belts will do precisely what he wants. If he has access to such a wide belt I can't imagine an easier fix - though it will result in a door that is thinner than he intended and other potential issues with profiles etc., but that wasn't his question. Sorry I raised my voice :(.

Sam

[J.R. Rutter]

I think that it depends how you have your sander set up, and what kind of feed belt you have. The only way that I have found to reliably flatten a door that has some twist is to put shims under the high corners. I just use sanding disks. They stay in place between the door and the belt.

[Rick Fisher]

I have a small SCM sander ..

I came back here to clarify some of the things I said.. My experience in sanding warped or cupped panels has been smaller stuff than doors.. I build a bunch of Sofa Tables with 19" - 20" wide tops.. If they develop a slight cup, the wide belt will remove it easily and leave it flat.. As I said, you can see it working with each pass, the machine sands the high spots first .. keep going until its sanding the whole panel.

I have never tried to flatten something as big or long as an entry door..

[Peter Quinn]

IME when you start messing around with reducing your hold down pressure on the wide belt strange things can start to happen. Chatter,, snipe at one or both ends, the occasional groove. across the width of the board. You can,pull up the platen and take light passes searching for that fine line where you hold the work down enough to sand well but not so much that it just holds the work down to the table. But a lot still depends on the size and thickness of the actual work being processed and the severity of the problem. For instance a 20" wide 3/4" door 42" length with some twist is going to be hard to fix. If you put it on a flat work table and you can push the twist out with a single finger, and this is a realistic scenario that has occurred in my work, the wide belt will hold it down too. The 37" machine where I work has to handle everything from 16' counters up to 3" thick down to sanding veneer or 1/4" applied beads. The hold down pressure is adjustable, but certainly not on the fly. Even with the platter up there is enough spring pressure to hold flat lanky cabinet doors and thin panels. And thereis only about 5 1/2' of table, so just like a jointer, there is an upper limit to what can be flattened anyway. Shimming thhe bottom can help if you can read the high spots. We have guys come in all the time looking to have various things 'flattened' on the wide belt. Some requests are realistic, others are impossible. One guy brought in a wrecked maple counter 1 1/2"" thick, 30" wide, 14' long'. I sighted maybe 7/8" of wind over its length, he wants it flattened so it sits better on the island where it will live. Well, when it gets down to about 5/8" it should be easy to pull down with screws! Ive seen guys come in with doors, table tops, work benches, every manner of things. Not every thing can be saved. It's called a time saver, not a miracle maker.

[Rick Fisher]

Great post Peter.. I think you summed up what I was trying to say.. I remove cups that are a mm or 2 ... When I am finished, the board is 4mm thinner ( 2-sides) .. To remove 1/4" or 3/8" would not be reasonable, and probably not work.

I have never adjusted the upper rollers on my sander .. I just take off the smallest cut possible and lower the platen all the way..

The conveyor is obviously adjustable and the platen is the part that touches the wood.. if you adjust the platen all the way down, you have sorta adjusted the rollers.. Unless other machines rollers adjust with the platen ? Mine do not..

I can say that on a 19" x 60" wood top with a slight cup or bow.. the process works perfectly.. Laying on the bench, you can put a straight edge anywhere and see no light.. One of the best features of a Wide belt is that perfectly flat surface .. I run 150 Grit on my machine .. A quick touch with 220 with a Random Orbit and its done.

[frank shic]

hey ted, how did you get access to a wide belt sander? i would be more than willing to pack everything up and drive a few miles...

[John A langley]

Frank = You can use mine. I 'm only a few miles. LOL But anybody close I'd be willing to help with the wide belt.`

[frank shic]

anyone in northern california??? lol thanks john