Which sander to flatten a slab?

[Mark Gibney]

I need to sand the top of a large slab even, in my own shop using a hand-held tool.

I have used a belt sander before, but it's slow going. I got to thinking about a floor edger (first photo), or the Festool Rotex.

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It's been a long time since I used a floor edger but I think I remember them being fairly controllable. I haven't used a Festool Rotex.
The slab was surfaced way back, but since then it has twisted a little. I don't want to use a router and sled - this wood is very brittle and chips out so much with a router - it's Blackheart Sassafras with the grain running at maybe 20* across on the edge. Nice looking wood but I'm not real used to working with tropical lumber.

I'd love to hear for any of you with more wisdom on this than me, which really opens up the field, which way you'd go on this.

thank you, Mark

[Hoang N Nguyen]

Honestly, IMO if you want to go the sander route, a drum sander would be a better bet. I use it to flatten table tops and glue up panels all the time.

I have no experience with floor sanders so no input from me there.

The Rotex is a great sander and might work if you buy the hard pad for it. The rotex mode should eat away at the high spots fairly quickly.

[John LoDico]

Or you could forego using a sander at all and use a router with a sled-type jig. See this article:

http://www.finewoodworking.com/2011/09/29/level-big-slabs-in-no-time-flat

[Dan Hulbert]

Plane and cabinet scraper?

[John TenEyck]

What John said. A router sled will flatten any size slab and leave it smooth enough that all you need from there is a ROS. The router sled is stupid simple to build and use with about zero chance of failure - perfect in my world.

John

[Hoang N Nguyen]

He said he didn't want to use router and sled.


I don't want to use a router and sled - this wood is very brittle and chips out so much with a router

thank you, Mark

[John LoDico]

Oops, my bad for not reading carefully.

[William M Johnson]

I have used the RO 150 extensively for just what you are wanting to do. It works great, and I also own a 24" drum sander. Latest project was mesquite.

Get the hard pad and use in "Rotex Mode". Start with course paper and work up. There is a learning curve, keep pressure on that pad. I also recommend getting the auxiliary handle costs a little more but helps a lot.

This is the most used sander I own. I just color sanded and polished a car I painted. The variety of pads, spacers etc is extraordinary. I actually polished the mesquite desk to 1500 grit. You could see yourself in the reflection without any finish.

Practice on something else first because the rotex mode is aggressive. Watch a video on YouTube

Bill

[John C Cox]

I think I would get some 40 grit and 60 grit and try the floor sander first. Its made for hogging off deeper cuts.

But - the random orbital would probably do well if thats what you have.

The trouble with either is that you will have to use winding sticks or some such to verify you arent just sanding along the curve.

[Sam Murdoch]

The cool thing about the RO 150 is that you can take it all the way from rough to finish. Though I do prefer a finish sander - the ETS150/3 for example - for the 2 or 3 grits of final finish - the RO will do it too if you have learned to control it. Control gets much easier as you process from rough to smooth.

[Brice Rogers]

First, I am a person that likes to do most things myself and am kind of a McGeiver. But I would probably call around to find a cabinet or furniture building shop that has a large drum/belt sander. I'm guessing that they would not charge a lot to run your slab through a few times.

The reason why I suggest this (even though it is out of character for me) is that when sanding surfaces with smaller devices, the softer wood gets removed more quickly than the harder wood. So with the smaller sanders, they will leave low areas and the surface will never really be flat. With a commercial belt sander you have the best chance for a pretty flat surface. Maybe they could sand up to something like 220 grit and leave you to do additional sanding should you desire.

[John TenEyck]

He said he didn't want to use router and sled.

IMHO it won't chip out if you use a climb cut, and that's perfectly safe to do with the router sled. In fact, that's how I use it all the time. 1/2" straight bit, climb cut, shallow cuts about half the bit width.

John

[Ole Anderson]

You could do the trick the Shipwright did, carefully tune an electric plane so it only removes a few thousandths and go at it. Episode 26, about 8 minutes in. An earlier episode tells how the tunes the plane for flatness. https://www.youtube.com/watch?v=iGjFQjss5bE&t=304s

[Prashun Patel]

If you are flattening for a table and perfectiOn is not necessary just use a belt sander. It is actually quite good at finding highs and lows. Just don't tip or dig in. Keep it moving.

[Bill Dufour]

you can rent a floor sander get either the rectangular pad type or the multiple ros in a frame. How big is this slab.
Bil lD.

[Mark Gibney]

Prashun, yes a belt sander is a great tool for this most times, but it can be slow going. I remember being amazed by the floor edger years back, the speed it cuts at.
Ole - great link. That guy is so good at explaining what he's doing. Don't think I want to risk using an electric planer, not just yet. But I might binge watch that boat building this weekend.
Brice - my vote would be to pay to have it go thru a wide belt sander, but it can be difficult to find someplace. The shop I used to go to upped and moved to Alabama.

Thanks everyone for your input, much appreciated.

[Wayne Lomman]

As a side note, where is your black heart sassafras from? For me it is a local Tasmanian timber which is not tropical at all but a cold rainforest species. Cheers

[Mike Cutler]

Mark

-How big is this slab? If a floor sander would work, it must be fairly large
- How much do you need to take off?

If a belt sander is too slow for you, I would have second thoughts that you'd be happy with any type of a pad sander. A belt sander with the right grit, can remove material fast.
Hand power planer can mess up some wood really, really fast, if you're not careful, and you'll still end up with a sander in your hand.

I know you don't like the router sled, but if you look at the geometry of a router, "bowl bit", there is no hard edge to catch. Used on a light climb cut, it may be a possibility for you. Any sanding solution, other than a machine powered sanding option, is going to be slow and tedious.

[Prashun Patel]

In my experience, there's no fast way to flatten a slab unless you have a super wide jointer and planer.

Even a router sled requires considerable set up and patience.

If you are too far out of flat to want to deal with a belt sander, consider a power hand planer.

[Larry Edgerton]

I use a strait line air board with 40 grit. First I mist the top with spray can lacquer lightly so it does not sink in, then work down the high spots with the straight line. The pads are very hard and will not conform to odd shapes. Next, when I am seeing very little black I move to a random orbit air board with a hard pad starting with 60 grit and moving to 80/100/120 as it gets closer to perfect, then switch to a 6" RO to get to a finishable surface.

The RO air boards are expensive, but a cheap air straight line sander will do the job about as good as an expensive one. Wear gloves, they vibrate a lot. You can go just a bit farther with the straight line and skip the RO airboard.

If it is more than an 1/8-3/16 out I would use a router sled to get it closer.

That will be 2 cents please.

[Mark Gibney]

Wayne, I got the sassafras from a friend who had it for years. Thanks for the info that it is not tropical, I'll read up more about it.

Is it a popular wood to work with in Tasmania?

[lowell holmes]

You might consider hand planing diagonally to flatten the slab and then go from there. Ease the corners of the plane iron to avoid tracks.

After the slab is close to flat, you might finish with a belt and then pad sander.

[Wayne Lomman]

Black heart sassafras is quite popular in Tasmania but not necessarily common. Sassafras is common but black heart only occurs if a particular natural wood fungus is present.

For what it is worth, I would go with the router sled too unless you can find someone with a widebelt sander. Cheers

[John T Barker]

Flatten? As in make flat?

[Tom Bender]

It may be a reasonable task for hand sanding. Make a big sanding block, maybe 4 x 10 and glue the paper to it. A broken sander belt should provide good paper. Give it big handles like a hand plane