Marking material to find high spots?

[Will Blick]

I want to flatten a table top... don't have a 45" wide belt sander. My thought was, use a straight edge and run it along the top, with some type of marking material on the bottom of the straight edge...the low spots would show no markings...

Then, plane down the high spots till the entire top is evenly marked when passed over the top. Is there a good marking material for this? Or an easier method? It's relatively flat, so it only needs a little work...

[John Schreiber]

That's a neat idea, but I don't have any suggestions. The usual way is to put a raking light behind the straightedge and look for where there it touches the surface and mark it with a pencil. The other thing to keep in mind is that a long plane like a jointer does roughly the same thing except rather than mark the high points, it cuts them off.

[Mike Cutler]

I just do as John suggested. Find the high spots and mark them with chalk.

I also have a top to right now.

[lowell holmes]

The procedure outlined from various sources is to scribble pencil marks back and forth across the width of the piece for the entire length. Then as you plane, the marks will disappear from the high spots and stay in the low spots. I think Rob Cosman describes it in his video "Rough to Square". The same procedure is used to flatten water stones.

[Stephen Shepherd]

White chalk works for dark woods but I wouldn't recommend using a graphite pencil as graphite is also a lubricant and can interfer with finish or glue. I use soot (from a candle) on a metal straight edge to transfer marks to the high spots.

Works well for the bedding when planemaking and for inlaying or fitting metal into wood.

Stephen

[Jim Dunn]

Machinist's use a product called Dykem blue. I would not recommend it unless you can get it for free. Also it stains EVERYTHING it comes into contact with.

[Will Blick]

Well, I did consider the scribble with pencil technique.... but my guess is, for a large top, you end up planing a lot of flat areas....

I thought about jointing a board flat, glue 80 grit sand paper to the bottom, to create visible scratch marks.... should be interesting...

I agree a jointer plane "sort of" does this task. Of course, if the piece is up to 2x the length of the jointer plane, the plane alone would suffice....but as the piece becomes waaay longer, in this case 44" x 65", the plane by itself is bit less effective.....hence why i wanted to quickly identify the high spots, then attack them. Unfortunately a jointer plane will cut not just high spots, but flat spots as well.

Nothing like a wide belt sander.... the only cabinet shop in town who had one, went under, otherwise, a handful of passes and it would be flat...

[David Keller NC]

"I thought about jointing a board flat, glue 80 grit sand paper to the bottom, to create visible scratch marks.... should be interesting..."

Will - You can do this without the necessity of gluing 80 grit sandpaper to the bottom. If you use a reasonably hard wood to make your test-plank, just putting firm pressure on it as you rub it back and forth on the top will burnish the high spots, which will be quite visible in raking light.

[Paul Atkins]

Haven't tried this, but what about a long flat board with carbon paper? I've used chalk on walnut to match curved mouldings - worked great.

[george wilson]

Dykem blue is like artist's oilpaint in tubes. It is for metal only. Don't get it anywhere near your table. Carbon paper will get into the wood,too. Stick to light squiggly pencil lines. Too much graphite is not wanted,either. If you use something wrong,you could ruin the table for good.

[Randy Klein]

I wouldn't worry about getting it demonstrably flat. If it's flat enough that your eye can't tell, then you're done. It's not like you are going to referencing off the top for any joinery, which is when you need to be concerned about flat.

It it looks flat, feels flat, then it's flat. If it doesn't, plane away only those spots that are upsetting the visual, then recheck.

[Richard Magbanua]

I understand yer plan but wouldn't you want to mark all areas, high and low? Once you take a shaving from a high spot that is marked you would lose your guide. Since a straightedge/sandpaper would only tell you which spots were the highest, those marks would be gone after the first swipes of the plane. If I understand correctly, the surface would be flat (relative to your hand plane) once all of the markings disappear. This is how I flattened my 8 foot workbench with my #5 and it worked surprisingly well.

[Will Blick]

Rich, there is something compelling about what you wrote... hmmm... Before I can hit the low spots, I have to first get through the high spots, which is the way a jointer plane works......

After removing the high spot markings, and trying to get to the low spots, I will keep trimming down the high spots by default, even though there is no markings remain on the high spots. ..... not sure how this evaded me from the start... the older you get, the more this happens :-)

This is pretty much the same as the pencil scribble technique mentioned by Lowell.....which I use when flattening my stones... But when you flatten a stone, the flattening piece is bigger than the stone, so its a no brainer...

I should have the top in a few days... unless something better comes up, I will try this method first... thanks...

[Ed Hazel]

In the body shop we would use this http://www.eastwoodco.com/jump.jsp?itemID=17609&itemType=PRODUCT no idea on its effect on wood finishes. Its a fine powder that you apply to the panel and as you block sand the the powder is removed from the high spots and you keep blocking until the powder gone.

[bridger berdel]

using transfer color to measure flatness like you are describing is a time honored method. the straight edge technique isn't bad, but be aware that you'll still need to check frequently with winding sticks...

I sometimes use lumber crayon dissolved in paint thinner for transfer color. be aware that it can get soaked/ smeared into the wood pores where it won't be coming out easily. for the really high spots that are being removed by the plane, a little color in the pores is no big deal, but as you approach your final surface you'll want to switch to something less fluid.

[Tony Bilello]

Chalk on dark wood and pencil on light wood.
When you are finished, wipe off the chalk with thinner so as not to get the 'dust' into the wood when final sanding. As for the pencil, just sand it and dont worry. I have done that for years and never had a problem. I spray lacquer and if anything at all would react to the graphite or oily substance, lacquer would.
When you find your high spots, dont make it an exact science. Just draw scribble lines and go for it. Stop every few minutes and check with your hands. Just run your hands across the surface. Its amazing how accurate your sense of touch really is. When it feels good, check it again with a straight edge. Like someone already said.....if it looks and feels flat - it is.
I always used a very large and heavy Porter Cable 4 X 24 belt sander instead of a plane. This particular sander wants to stay flat and not dig in.
After all, you are only catching the high spots.

[Tom Henderson2]

White chalk works for dark woods but I wouldn't recommend using a graphite pencil as graphite is also a lubricant and can interfer with finish or glue.
Stephen

Hi Stephen-

I think the technique being discussed is to just draw a matrix of lines across the wood, not covering the surface with lead powder.

Since the pencil lines are all removed by subsequent planing, how will it damage the finish?

-TH

[Jim Koepke]

Pencil and chalk get my vote.

Dykem blue is for marking metal and can leave a nasty stain on wood depending on whether you use the liquid or the oil paint.

I have also heard that you do not want to plane after sanding as some of the abrasive left behind can be nasty to a plane.

Lamp black (or soot from a candle) on a straight edge sounds OK, but after the soot is rubbed off the straight edge, following high spots would go unmarked.

What I do, is look and feel. If you can not feel high and low spots nor see them, then no one else will either.

If you have a stone rolling pin to roll around on it after planing, you will feel any imperfections transmitted through one of those.

jim