idiot newbie needs help

[Dave Lame]

OK, so i was happily sanding away with my new hand sander on two approx 24 by 36 boards. Now very nice and smooth, but WAVY!

Now what do I do?

[Willard Foster]

When you say "Wavy" do you mean the chatter marks left by the surface planer?

What type of wood are you sanding? What grit is the sandpaper?

Bill

[Stephen Cherry]

How about a handplane?

As far as "idiot" goes, you have identified a problem and are working towards a solution. Sounds pretty non-idiotic to me.

The problem with something like a sander is that it does not provide a reference to the wood to guide itself. It only has a cutting, or sanding edge. There is a whole class of tools that have been referred to as "self jigging tools" because the tool itself provides a guide for further cutting. The easiest example is a flat chisel laid flat surface down on a piece of wood. It can do nothing except cut in a flat plane because the back of the chisel guides the cut. A hand plane is an extension of this because the plane uses it's bottom to direct the cut.

A sander is different because it will continue to cut without referring to the cut surface, so it is natural that the surface is wavy. The same is true for a scraper, which can give a great surface, but will become wavy if you overdo it.

[Dave Lame]

Wood is pine.

Grit is 120

Sander is 5" random orbit.


Would I need a jointer plane or a smoothing plane?

Would a hand held power plane do the job?

Thanks

Dave

[Matt Logana]

Wood is pine.

Grit is 120

Sander is 5" random orbit.


Would I need a jointer plane or a smoothing plane?

Would a hand held power plane do the job?

Thanks

Dave

I hear those powered hand planers are only good for roughing stuff out... not at all for finish work... I would either use a Thicknesser, or try another technique... on another board... maybe you went too hard, or too soft, or both...

[Don Alexander]

sounds like you put too much pressure on the sander while sanding

next time try letting the weight of the sander be the pressure and also try using a bit finer grit sandpaper say about 220 or 280
unless you are using rough boards you should find the results more to your liking HTH

[Tom Rick]

The problem with something like a sander is that it does not provide a reference to the wood to guide itself. It only has a cutting, or sanding edge. There is a whole class of tools that have been referred to as "self jigging tools" because the tool itself provides a guide for further cutting. The easiest example is a flat chisel laid flat surface down on a piece of wood. It can do nothing except cut in a flat plane because the back of the chisel guides the cut. A hand plane is an extension of this because the plane uses it's bottom to direct the cut.

A sander is different because it will continue to cut without referring to the cut surface, so it is natural that the surface is wavy. The same is true for a scraper, which can give a great surface, but will become wavy if you overdo it.

Great answer.

[John Thompson]

If the boards were not wavy before starting the sanding.. ditto Don Alexander on too much pressure or... keep the sander moving with the grain. Don't pause during a sweep in one spot or it will dig in. As for the pressure.. let the sander do the work. For keeping the sander moving I make a light pass down.. back.. down and move to the next adjacent un-sanded swath beside it. I have discovered over the years that these new ROS's don't require spending a lot of time going over and over a surface and doing so is a waste of time and effort with the potential to burnish the surface.

Good luck...

[glenn bradley]

That is a pretty aggressive grit for pine. Also, the variations in the "hardness" of some woods will allow some areas to abrade more quickly. Once upon a time I became aware of this while trying out a ROS on some shop plywood; the surface ended up like the desert after a strong wind. A square milled block of hardwood with some 220 stuck to it may help you get back to flat.

[Jim Summers]

Pine also has a lot of wide soft wood areas and narrow harder wood areas. If it is over sanded then a little more of the softer parts are removed as compared to the slightly harder area adjacent to it.

It has happened to me several times and I then learned about it in the Bob Flexner finishing book.

HTH

[Bill HammerII]

when using a RAS I cheat and make a set of pencil marks at a angle and then another set of pencil marks that cross the first set. What it looks like is a bunch of little squares. Like lapping the sole of plane these marks allow you to remove the high spots. If you use the RAS remember that it's cutting all the time and you've got to keep it moving all the time all over the work piece. Also 120 is pretty heavy for pine I would start with a little higher grit and work my way up.

[Kent A Bathurst]

Pine also has a lot of wide soft wood areas and narrow harder wood areas. If it is over sanded then a little more of the softer parts are removed as compared to the slightly harder area adjacent to it.

Bingo. The "grain lines" are hard, the rest is soft. Zero downward pressure, let the sander do the work, very common newbie move to put on too much pressure, and oversand (meaning, keep on sanding when you are done with that grit). DAMHIKT. Pine ain't white oak, and takes very little work to sand it. Even though the pad on an ROS seems hard and flat, it ain't, and you'll create the contours in the surface. If you are using a qtr-sheet palm sander, then the pad is definitely soft, and the problem will be compounded.

If the original surface was rough, I could see a quick pass with 120 to get started, then 150-180, again no downward pressure. Don't know what you plan on for a finish, but its been a long-long time since I ever went past 220g on a flat surface. I usually stop at 180.

If you've only sanded one side of the boards, then that was the "trial" side. Flip them over and go at them again.

[Prashun Patel]

Belt sanders give flatter results than random orbitals. They are aggressive, but you can compensate for this with technique; holding the machine at a skew angle and working quickly.

I continue to get wavy surfaces with a ROS occasionally. It really shows up during finishing. The probs always come when I'm trying to remove stock. I now only use a ROS for smoothing.

If I want to remove stock, I've learned how to sharpen and use good block, smooth, and jack planes.

But don't beat yrself up; this is the way we learn!!!

[Jim Rimmer]

Belt sanders give flatter results than random orbitals. They are aggressive, but you can compensate for this with technique; holding the machine at a skew angle and working quickly.

I continue to get wavy surfaces with a ROS occasionally. It really shows up during finishing. The probs always come when I'm trying to remove stock. I now only use a ROS for smoothing.

If I want to remove stock, I've learned how to sharpen and use good block, smooth, and jack planes.

But don't beat yrself up; this is the way we learn!!!

Since you're new be aware that belt sanders can be very aggressive especially on a soft wood like pine. If you try this practice on some scrap first.

[Greg Portland]

While I agree with Prashun's idea that a belt sander would work I would instead recommend a 1/2 sheet orbital sander (NOT random orbit!) -or- use a hard pad on your current sander. The reason a belt sander works is because it has a harder backing (pad) which prevents the sander and paper from dipping into the soft grain. A 1/2 sheet orbital will do the same thing as a belt sander but it will be slower and leave a better finish when done. Having said that, see if you can get a 'hard' or 'firm' pad for your sander. I think that + proper sanding technique will solve most of your problems.