Table top trauma

[Dru]

Hi All,
I'm really impressed by the support of this forum, and I'm posting my first message here today.
I'm tackling a table top for the first time, and I've made a couple of errors in the sanding process.
Firstly, there are four boards in the table top, and I've managed to create on one of the boards a series of white lines about 300mm apart running across the board. I think it is probably caused by me not running the sander up and down the top evenly, but instead working on an area and then moving on to the next area - I'm told it's good to learn from mistakes! So my problem is how to get rid of the lines. I've tried sanding across the lines from one end of the board to the other, with heavy duty grit, but they don't seem to want to shift. Someone suggested I try wetting the timber to lift up the fine fibres, but I haven't tried that yet. Someone else suggested a wire brush approach - but that sounds a bit aggro.

My other concern is not as obvious, but the four boards are not as flat as I'd like them to be when I put a straight edge across them. There's an undulation that I seem to have created, and I'm wondering whether I can try to remove the undulation by using a belt sander across the grain (ie to break down the undulations) with, say, 150 grit, and then return to the correct up-down sanding approach, working up from an 80 grit, etc, to remove the grit lines that would have been caused by the "across" sanding. Would that work at all, or am I getting into more hot water?

Any thoughts would be gratefully received. Many thanks.

[3 toed sloth]

Hi Dru & welcome.

I assume the white lines are grooves and depressions from uneven sanding. What you need to do is remove enough timber from the entire surface of the board, so that the white lines disappear. So you could say you need to focus on the whole surface except where the white lines are.

Also try the search link, up the top.

[Ed Reiss]

Hi Dru ...welcome

Yep, that's exactly what has happened...hills and valleys. You didn't mention if the boards have been glued up yet, if not then the best way is to joint one surface flat (with a jointer) then run it through a planer to get the other surface flat. My assumption is that you don't have a jointer or a planer...maybe one of your mates has them you could use.

Now, if the top has already been glued up, assuming that it's now too large for the jointer and planer, it's going to be a lot more difficult. Running the belt sander carefully at a bias (crosswise) where the hills (what your calling the white lines) are should get you in the ball park to a "fairly" flat surface, but nowhere near dead flat.

There may be options that others suggest.

Good luck with your project.

[artme]

G'day Dru and welcome to the house of the knowledgable one!

Got yourself some good advice already.

[Teredo]

I'm curious as to how you managed to create those white lines across the grain of only one board, unless you sanded all the boards individually before clamping them together ?
Wetting the upper surface of the table will create an upward bulge in the boards if you slacken off any restraints, allowing you to get a "better go" at the problem area but when the boards go back to equilibrium moisture content, you will have a depression that could be painfully obvious, especially if you plan to apply a high gloss finish.
The only really satisfactory solution to your problem is to plane the whole surface to a new datum that removes the damaged area.
Using a 4ft spirit level as a straightedge, and a smear of dark acrylic paint along the contact face, work the straightedge back and forth across the surface leaving witness marks on the high spots. Remove these with a hand scraper. I find a 12" planer blade makes an ideal scraper for flatting off uneven surfaces. Repeat until you've worked your way down to the damaged area, and scraped the scratch marks out.

[Dru]

Thanks alot, Teredo, and the others. I'll certainly try the suggestions and see if I can improve the situation somewhat!

[jerryc]

Dru,
I'm a great believer in establishing EXACTLY what the problem is before attack.

One way to see if the problem is related to high and low spots is to use a light beam at a shallow angle to the top. This should indicate part of the problem if it is uneven surfaces. Assuming it is so, a very simple way is to use a chalk stick and draw lines at diagonals each way across the table.
I then use a jointer plane because it has a long base which bridges the highs. You should aim to just remove the chalk marks. Most belt sanders are too short and will tend to follow the highs and lows. However if you are careful it can be done with a belt sander by carefully blending down the high spots. This does mean taking care and not using heavy grits. Work diagonally across the surface and don't dwell on single spots. At regular intervals rechalk the surface, chalk is cheap.

What you should be aiming for is to reduce the highs down to the low spots, not to take off the entire surface. Why make work for yourself and waste wood?


Jerry