Flattening using a belt sander

[transatlantic]

I have a panel glued up that is going to be a table, and as the stock wasn't all the same thickness (it was purchased PAR, but there is a 1-2mm difference between boards) it now needs flattening. Due to the size, I don't want to attempt this with a hand plane, as I know I'll make a mess of it (I also forgot to align the grain between boards).

I know it's common to use a router sled for this, but I was wondering if it could be achieved more easily with some kind of belt sander sled? The idea being that it could potentially be much faster as you're working a larger surface, as well as allowing you to use a finer grit for the final pass.

My idea is to have the belt sander with dowels through it (for left/right movement), attached to rails to slide on. The height adjustment would be with feet attached to the rails.

The feet idea isn't great, as it means adjusting things in four places, but does allow for finer control. Perhaps this could be replaced by wedges under the rails, so then you only have to adjust 2 things. Or pehaps the height adjustment should be on the beltsander part itself, ideally with a single hand screw to adjust.

It clearly needs more thought, but can you see any pitfalls?

 

[dzj]

It might work if the dowels are rigid enough, but I've never seen a set up like this.
If you are having doubts about doing it free hand, you have the whole of the under side of the
table top to practice on. It's not that hard, just keep the belt sander always moving, go through the grits
and you'll be fine. Perhaps knock off the highest bits with a hand plane.
Good luck.

 

[Jacob]

Looks like a non starter to me!

What you want is a belt sander with a frame. It keeps it level and avoids digging in.
This sort of thing:

If you've already got the belt sander it may be available as an accessory, otherwise buy one with a frame.
40 grit to get it flat then work through the grits in leaps of 20 to 40, but no bigger leaps.

 

[transatlantic]

It might work if the dowels are rigid enough, but I've never seen a set up like this.
If you are having doubts about doing it free hand, you have the whole of the under side of the
table top to practice on. It's not that hard, just keep the belt sander always moving, go through the grits
and you'll be fine. Perhaps knock off the highest bits with a hand plane.
Good luck.

Yeah - I guess depending on how wide I make it, steel tubing might be a better idea. I will give it a try free hand, but I know exactly what will happen. I'll get one spot nice and flat, and then end up having to redo it becuase I messed up a different spot and then before you know it :

I did see those frames but could only find the Festool one and that was £130 for the frame on its own!

Why do you think it's a non starter? Assuming I can come up with a good height adjustment mechanism, it could be a cheap portable collapsable alternative to a drum sander.

 

[Ttrees]

Id get some FLAT plate of some sort and scribble black crayon all over it ,
rub it on your wood and use a hand plane or maybe a no 80 scraper if your not comfortable .
It would be a good way to check whatever method you use to surface the top
provided your not deflecting the top that your working on in the process .
Good luck

 

[AJB Temple]

Back in the day when I first started, I made a 2" thick utility room work surface about 3ft wide and 12ft long out of iroko that I t&g'd together myself using a 1/4" router. I levelled it by using an Elu belt sander because these were the tools I had. I am still using that belt sander 25 years later). Go carefully, keep the belt platen flat against the surface (don't letter rollers dig in in other words) and go through the grits as Jacob says. It really is not difficult at all if you don't rush it.

A hand held electric planer is also not expensive. I have recently (this week) bought a Triton unlimited depth rebate planer which is 3" wide that I am using for cleaning up awkward places on green oak, such as big tenons. This cost £90 on next day delivery (Sunday in my case) and is a useful tool It also has a sanding drum. You can set it to cut 0.2mm minimum depth and it will work fine especially if you are not confident with a bench plane. It is triple bladed and gives a very good finish. I might review it here!

 

[RobinBHM]

It is possible to do the dimensioning sanding by going diagonal with the grain, then work through the grits with the grain.

Sanding all with the grain is more likely to end up with a washboard effect.

A sanding frame helps or use a belt sander with a large platten, like the makita 9404

I think your idea would be frustrating in practice as sanding only takes off tiny amounts and any flex in the jog could be more than the cutting amount.

 

[Jacob]

....

I did see those frames but could only find the Festool one and that was £130 for the frame on its own!

Bosch do them for some of their machines. Not cheap but very useful. Mine gets a lot of use - old floor boards, parquet, table tops etc

Why do you think it's a non starter? Assuming I can come up with a good height adjustment mechanism, it could be a cheap portable collapsable alternative to a drum sander.

Dunno it just looks a bit Heath Robinson. Why bother if you can get a sander with a frame?

 

[profchris]

I think you might be surprised how easy it would be to hand plane this flat (assuming it's a normal sized table, not one of those refectory jobbies).

Plane at 45 degrees to the grain direction, taking fairly coarse shavings to start with, and you'll soon remove the ridges. Once you're roughly flat you could carry on with the 45 degree planing, taking lighter shavings and finishing off with the belt sander (or a scraper plane if your wood will scrape). Or if you're good at planing go with the grain for a final finish, but I note you haven't matched grain direction (what I'd think of as runout, which might be in opposite directions on adjacent strips), so I'd go for the first option.