All Replies on How do I know when my wood is flat? - Hand plane.

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View AESamuel's profile

How do I know when my wood is flat? - Hand plane.

by AESamuel
posted 02-26-2015 07:42 PM

18 replies so far

View Mykos's profile


103 posts in 2036 days

#1 posted 02-26-2015 07:56 PM

First thing, is your combination square blade perfectly straight ? Check it against a table saw top or a granite counter top and see if you can still see light. You need to have a reference surface that is guaranteed straight/flat to start from.

A piece of aluminum angle extrusion stock is usually very straight as well.

How flat you get your wood depends on your own personal preference for exactness and the nature of the project. If it’s a garden planter then it doesn’t need to be dead flat. If you’re cutting joinery on the piece and you want it to be crisp with no gaps then those light showing low spots will be visible in the final piece. A tenon shoulder or dovetail baseline with a low spot on the face of the board will show as a gap.

View Smitty_Cabinetshop's profile


15831 posts in 2860 days

#2 posted 02-26-2015 08:03 PM

Can I offer “if it feels flat, it is flat.”

That means, of course, if you’re happy with the feel (and fit), it doesn’t really matter what the straight edge says…

-- Don't anthropomorphize your handplanes. They hate it when you do that. -- OldTools Archive --

View Rick  Dennington's profile

Rick Dennington

6351 posts in 3436 days

#3 posted 02-26-2015 08:08 PM

Run it through a jointer and planer….it’ll be flat enough…

-- " At my age, happy hour is a crap and a nap".....!!

View bandit571's profile


22035 posts in 2925 days

#4 posted 02-26-2015 08:25 PM

One: A #4 is too short to make a table top “flat”

Two: Need a much longer plane. It will take down the “high ” spots, while skipping ove the low ones. When you can get a shaving full a full pass of that longer plane, stop, and move a little to the next high points. When all points can produce a full shaving the length of the pass, top is flat.

Three: Wood will move over time, so what is flat now, may not stay that way over the years. Nature of the wood. Get it as close as YOU feel is flat enough, and call it good.

-- A Planer? I'M the planer, this is what I use

View JayT's profile


6018 posts in 2453 days

#5 posted 02-26-2015 08:30 PM

Can I offer “if it feels flat, it is flat.”

That means, of course, if you re happy with the feel (and fit), it doesn t really matter what the straight edge says…

- Smitty_Cabinetshop


You are making a project from wood. Even if it were possible to get it dead flat, as soon as temperature or humidity changes, it’ll be slightly out. Get the piece to where you are happy with how it looks to the eye and feels to hand and call it good.

-- In theory, there is no difference between theory and practice. In practice, there is.

View Ripthorn's profile


1459 posts in 3227 days

#6 posted 02-26-2015 08:58 PM

Flat is dependent on the project. You will never get wood “truly flat” and have it stay that way; it moves and always will. If you are going to build something like a box, getting the faces flat may be somewhat less critical than other projects. Also, checking for light is a good technique, but only if you know how much light should come through. The human eye can see light through an opening of less than a thousandth of an inch, which is way more than wood needs. A set of feeler gauges comes in handy, because then you can quantify how out of flat you are. If you are 2 thousandths out of flat, I would say that is more than good enough. If you are 10 or 15, then your application may require further flattening.

One final note on the light thing, if you are using a hardware stole metal ruler, it may not be perfectly straight.

-- Brian T. - Exact science is not an exact science

View bonesbr549's profile


1579 posts in 3309 days

#7 posted 02-27-2015 01:19 PM

I’d reccommend Rob Cosmons rough to ready.

His technique where he would take the cut piece and rub it down on a known flat surface. I used my TS top. Lift up the piece and the high spots will be burnished and easily visible. Worked great. For Twist, I use winding sticks.

A Good square will tell you a lot for a specific point but not the entire surface.

-- Sooner or later Liberals run out of other people's money.

View JohnChung's profile


416 posts in 2316 days

#8 posted 02-27-2015 02:28 PM

Rule of thumb. Place the wood on a level surface. Try to rock it on the sides. If no rocking it is generally good enough. If the surface is expected to as precise as a machine…........ The poor plane will suffer.

1-3 thou is good enough in all conditions I can think of. Just remember that wood moves too.

View AESamuel's profile


88 posts in 1464 days

#9 posted 03-06-2015 07:34 PM

Thanks for all the replies!

I took a piece of oak that I flattened and put a small piece of printer paper underneath the ruler from my combination square, apart from a 0.5” strip along one side, I couldn’t pull the paper out from underneath the edge of the ruler. Is this flat enough? (I’m mainly making candle holders but I’m starting a foray into dovetails boxes!)

View AESamuel's profile


88 posts in 1464 days

#10 posted 03-06-2015 07:35 PM

Double post.

View bannerpond1's profile


397 posts in 2140 days

#11 posted 03-06-2015 09:12 PM

You need a jointer and a planer. Any amount out of flat is going to translate the error to the rest of the project. You’ll just frustrate yourself and waste wood until you do it right.

-- --Dale Page

View AESamuel's profile


88 posts in 1464 days

#12 posted 03-06-2015 09:38 PM

You need a jointer and a planer. Any amount out of flat is going to translate the error to the rest of the project. You ll just frustrate yourself and waste wood until you do it right.

- bannerpond1

That’s not possible for me – I do woodworking in my living room. I also want to use hand tools as much as I can – people managed for hundreds of years without a jointer and a planer so I’m sure I can too.

View Mykos's profile


103 posts in 2036 days

#13 posted 03-07-2015 02:37 AM

The paper test sounds like you’ve got it flat enough.

View woodenwarrior's profile


238 posts in 2436 days

#14 posted 03-07-2015 03:23 AM

AESamuel, you bring up a very good point. People have done it by hand for thousands of years…I think we sometimes get wrapped around the axel about using machines to reach perfection when it’s completely within our grasp to accomplish the same by hand. In my opinion, slight imperfections are a sign of hand workmanship and should be embraced over sterile machining. Machines make the process easier not necessarily better.

-- Do or do not...there is no try - Master Yoda

View BurlyBob's profile


6034 posts in 2507 days

#15 posted 03-07-2015 03:29 AM

I moved up to a 4 1/2 and will begin using a 5 1/2 as soon as I get in on line. My projects have been slightly smaller 10”-20” If I was going much bigger I’d pull out my 7. I picked up a woodpecker tri square last month and using it like you for light gaps. Sounds like you right on the money. I’m tackling half blind dovetails with a Leigh jig. Having a bit of trouble getting the joint snug. The wood flatness is not the issue for me, it’s the adjustments.

I have to agree with Warrior. You can get to wrapped up looking for perfection.

View daddywoofdawg's profile


1028 posts in 1817 days

#16 posted 03-07-2015 05:32 AM

remember sanding will take the surface down too.You can mark with a pencil the start of where you see light to the end of the same,everywhere under you edge,then turn it do the same.and you have mapped out your high spots which are any where you don’t see light,i.e the light is coming from the low spots,hard to raise the low spots so bring the high down to the low you’ll know when little or know light shows.

View DocBailey's profile


584 posts in 2601 days

#17 posted 03-07-2015 06:00 AM

I concur with those above who advocate a jointer as a pre-cursor to a smooth plane,

It’s an old analogy, but bears repeating—the jointer (22-24” sole) bridges the low spots like an ocean liner in rough waters; the shorter (8-9” sole) smoother rides up and down the hills and valleys like a row boat in those same rough waters.

That short plane will never get you to “flat”—what you’ll end up with is a board with smoother hills and valleys.

View rwe2156's profile


3239 posts in 1722 days

#18 posted 03-07-2015 12:56 PM

I respect your philosophy re: hand work. You do not need a jointer or planer. And I submit you can actually achieve superior results flattening a board with hand tools. At the very least, I know you will achieve a superior surface with no sanding required.

I’m curious as to what you’re work surface is.

There are lots of videos on YouTube regarding milling and flattening stock by hand. I like Cosman’s (although he’s a little anal about things at times) and Rennaisance Woodworker.

A #4 plane is not going to do the job for flattening. It is too short and too narrow and will follow the hills and valleys already in the board. In fact, you can end up accentuating them. You will need to invest in at least one more plane. I would suggest a #6. It will do an adequate job for most any face planing task. It will even do a decent job as a jointer. Since purchasing their #6 I’m a huge fan of the WoodRiver planes. They’re a great value for the money. If working from the rough, you will need a scrub plane.

To achieve the goal of a board that has no twist, cup or warp, you need winding sticks. Using a rule as you are doing will not detect twist, and twist is the big killer.

There a couple ways to check for twist:

1. Place the winding sticks at each end and eyeballing their top edges for parallel.

2. Use a dead flat surface to check for rocking.

The procedure is basically to make one side sit down flat with no rocking on a flat planing surface (perferably a dead flat workbench). Remove material from the corners to achieve this goal. If the board is warped or cupped put the concave side down.

Then place this side down, and use your winding sticks and straight edge. Remove material until you achieve a flat surface. Planing crossgrain or diagonally is an effective way to begin. Then scribe a thickness line all around the board referencing off the finished surface, and remove material to achieve a uniform thickness.

As far as how flat, you don’t need to take it to the extreme. Don’t forget you are working with a material that is consistently inconsistent. I’ve flattened many a board only to return the next morning and find my efforts have been in vain. This is usually because of changing humidity or unstable wood, but it can just happen!

Good luck.

-- Everything is a prototype thats why its one of a kind!!

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