Dimensioning wood for benchtop lamination - how flat is flat?

[Marko Milisavljevic]

I'm looking at a couple of 8ft boards of soft maple that have a fair bit of bow that would take almost 1/4" of material removal on ends and another 1/4" on opposite middle to straighten out, plus a bit of twist. As I'm selecting material for 4in thick benchtop lamination, I'm wondering how far do I have to go with jointing in all dimensions, and how much can I rely on lamination to "even things out"? I'm thinking surface that is bench top would be fairly important, the rest can cancel itself out with judicious placement of components, for as long as sides are flat enough to allow them to fully clamp together and get glued. Any advice appreciated.

[Brian Holcombe]

Marko,

4" thick boards are going to be a bit of a bear to manipulate with pressure. So I would get them perfectly straight before the glueup. You'll still need to flatten it after, but just not as much.

[Adam Cruea]

I wouldn't worry about a bow from one end to another, but what I would worry about more is cupping and severe twisting.

[Kurt Cady]

Sounds like hes using 4" wide boards, not 4" thick. 1/4" bow over 8' can easily be clamped out

[Marko Milisavljevic]

Sounds like hes using 4" wide boards, not 4" thick. 1/4" bow over 8' can easily be clamped out

Correct... I should've been more clear, I am using 8/4 stock, and am getting either ~5 or about ~9-10" wide boards to be ripped before dimensioning to ~2 x4" for lamination. Without a proper 7.5ft long solid reference surface it is pretty hard to tell how flat my jointing is... If a #8 gives me a continuous shaving, I'll assume it is good enough.

[Jim Koepke]

If a #8 gives me a continuous shaving, I'll assume it is good enough.

That may not be a safe bet. Two sticks and a piece of string can be used to make a poor man's straight edge.

jtk

[Brian Holcombe]

Does use a precision machined straight edge and feeler gauges? Fwiw I think that you can still have a bow in a table and produce a continuous shaving.

[bridger berdel]

if you can clamp the boards together without glue so no gap is visible you can laminate them. if there are a lot of boards that are pretty straight and one that is bowed the straight ones will discipline the bowed one. if you oppose the bows you can get away with more than one bowed board, but its best if most of them are pretty straight to begin with.

[Winton Applegate]

How flat is flat
Well when it comes to my woodworking and my bench tops and glue joints in say a dining table top at the butt joints for the long planks I go for a gap to start with that I can not put a .0015 inch feeler gauge under a 48 inch Starrett straight edge any where along it's length. The feeler may start but jam just as it goes into the gap.

From that starting point I refine the joint.;)
I sight with a bright white styrofoam sheet on one side with a bright light shining on it and then I look through from the opposite side. Where ever I see light I mark and plane to close the gap. My last test before glue up is I retest with the feeler gauge to be sure I haven't got out of whack some where and I also look all along the joint with the parts stacked vertically to be sure the joint looks perfect.
Over kill ? You betcha. But I get stellar results that make me smile.
A lot of the stuff I have done this with is too thick and too stout to use a "spring joint" to get it to close up. I have had zero problem with a joint splitting and opening up on the end.
I enjoy a joint that actually does not depend on the clamps to close the gap but simply to apply enough force to meet the spec for clamping pressure for the particular glue I am using. For hide glue that means no clamps. Fun, fun, fun.

NOW BACK TO YOUR BENCH AND YOUR REAL QUESTION (S)

I am not sure exactly what you are asking . . . sounds like two questions :
1. how flat should the planks be to put them together ?
and
2. how flat should my bench be ?


My first real FLAT planing surface was made up from two by fours that I didn't even glue together. I didn't even flatten their wide surfaces . . . I just put them together.
how can this be you may ask.
well
I through bolted them with no glue. Crazy huh ? Seemed like a fun thing to do at the time. See photos of Japanese planing beam (s) (I made three of these). I still use them in various situations. Vary versatile things to have around.


http://i801.photobucket.com/albums/yy298/noydb1/YeOld2x4benchplaningbeam_zps86006a1f.jpg (http://s801.photobucket.com/user/noydb1/media/YeOld2x4benchplaningbeam_zps86006a1f.jpg.html)


http://i801.photobucket.com/albums/yy298/noydb1/Undersidedetails_zpse9f45d76.jpg (http://s801.photobucket.com/user/noydb1/media/Undersidedetails_zpse9f45d76.jpg.html)


http://i801.photobucket.com/albums/yy298/noydb1/Thisisbetterthanthat_zps7279432f.jpg (http://s801.photobucket.com/user/noydb1/media/Thisisbetterthanthat_zps7279432f.jpg.html)


now to your second question
The beams are extremely flat.
My woodworking bench is extremely flat.
I verified it with a 48 inch Starrett straight edge and I think this is IMPORTANT especially when planing thinner planks that can flex under the force of planing.
now
my work bench has super flat and close tolerance glue joints as I describe at the start of this post.
was this necessary ?
NO
but I had fun making them that way and every time I look down at the near invisible glue joints it makes me all swell headed and dizzy which I particularly enjoy.


http://i801.photobucket.com/albums/yy298/noydb1/IMG_0045.jpg (http://s801.photobucket.com/user/noydb1/media/IMG_0045.jpg.html)


So glue joints don't have to be so good on such a thick bench (as long as you can stand looking at them)
The top should be pretty darned flat if you plan on using it as a hand planing bench and a reference for flat when you build your projects on it.

[Mel Fulks]

Sometimes on old benches with thick tops you will see joints that look slightly open but are still holding . To avoid that compression ring set damage just avoid wiping bench with damp cloths. I've used sprung joints on thick wood if there are not too many pieces being glued at one time. On the relatively narrow pieces usually used on bench tops they are not needed. But the wood can't be allowed to slide around because of a bowed piece . I put clamps on the ends vertically to keep them from moving while clamping .

[Sam Babbage]

A flat bench is nice, but there is flat and there is flat enough. I've worked with several old school master craftsmen who would give George Wilson a run for his money; none of their benches were what internet woodworkers would call flat. My current employer started his trade just after WW2 in Venice and makes me look like a rank amateur, his bench at work is older than I am (33) and has never been flattened since it was made. It is so far from "internet" flat it isn't funny. Build your bench, get it pretty flat, shim things in the rarish cases that you need super flat. Super-flat benches and hyper-sharp tools only waste your time and stop you from focusing on the skills that will truly improve your work. I am an hobbiest that had a very early mid life crisis and did a traditional apprenticeship. When I first started I was shocked at the lack of flatness/sharpness of things, but over a decade have come to realise that these things are crutches.

[Jim Matthews]

I'm with Sam - if your chisels don't roll off the top, it's probably flat enough.

For dead-flat assembly, you can easily fabricate a torsion box that can span sawhorses
or slip over the bench you're building now.

Unless you're using this for laser optics, what you've described is adequate.
If you must get it dead flat, a router on a sled will do the job.

http://theschoolofthetransferofenergy.com/2011/01/29/jig-for-flattening-slabs/

I've seen it done, and it makes a huge mess.

[Winton Applegate]

Without a proper 7.5ft long solid reference surface it is pretty hard to tell how flat my jointing is...

errr . . . Marko,

Note the length of the CHEEP and easily made planing beam I posted in my photo. Eight foot ceiling. The two beams I made to make my 'REAL' work bench are each eight feet long there abouts. So that takes care of your 7.5 ft reference.

Buy the straight edge, you will need it to check your four thousand dollar power jointer tables when you go pro anyway.

Oh and for the neigh sayers hee, hee, hee once the bench is flat just flip the long planks over and eye them against the bench top for straight. Teeters it is convex and shows where exactly and if it does not teeter then look at the gap, and guess how much, if you like, rather than use a feeler gauge, Bob forbid, to judge the concavity.

But

a flat bench is just a waste of time.
Keep chanting that . . .
in time you may even be able to believe it.
"Good luck
I'm pulling for you
we are all in this together"
(quote by Red Green)

[Winton Applegate]

Buy the straight edge
I like this one

http://www.amazon.com/Starrett-380-48-48-Inch-Steel-Straight/dp/B0006J4H36/ref=sr_1_5?ie=UTF8&qid=1384588070&sr=8-5&keywords=starrett+straight+edge

longer may be too heavy to use safely, shorter is well . . . shorter
and cheeper brands (I have a few of those) are not straight enough. How do I know ?
I HAVE USED THE BLOODY THINGS.

Too expensive ? ? ? ?
it is the price of a small hand plane ! ! !
Build a box for it, take care of it . . .
or perish in the deep dark realm of hope and guess work.

PS: and no body please start in with the "old time woodworkers didn't have such tools". The Japanese had straight edges nearly as accurate, made from wood, for many hundreds of years; if the others didn't then they were working harder than they needed to.

Wood changes ? They tuned them. I have an ebony straight edge I made and here in Colorado it does not change significantly, really . . . I test it and it stays the same.
I test it on a Starrett surface plate. No rocky no gappy . . . just flat.

PS: I didn't buy the surface plate and the straight edges to use on wood I bought them for metal work and machine tools.

Why wouldn't I use them on the woodwork and to set up my woodworking tools ?
I am not THAT Neander.

[bridger berdel]

I've done it, and made that huge mess. I've also done it with planes, and unless the amount of wood to remove is huge, like an inch or something, the planes (at least in my hands) are more accurate and almost as fast, considering setup and cleanup.




.
If you must get it dead flat, a router on a sled will do the job.

http://theschoolofthetransferofenergy.com/2011/01/29/jig-for-flattening-slabs/

I've seen it done, and it makes a huge mess.

[Kees Heiden]

If I "need" a long straightedge, I go to the homecentre and buy one of these melanine covered particle board bookshelves. They have them up to 3 meters long. And the sides are remarkably straight. Straighter then I will ever need in a woodworking project that long.

[Noah Wagener]

One way that you could get a "solid 7.5 foot reference" was described by Stu Tierney somewhere on here. Join two boards face to face with a couple of dowels (he actually used some type of dovetail key which i don't think i could elucidate) and plane the edges together. Any deviance from straight will be doubled when you pull them apart and put together edge to edge. Keep planing until the edges mate nicely. Planing separately you could get two boards to mate nicely but one may have a hill while the other has a valley. This is also explained in Scott Wynn's Woodworker's Guide to Handplanes. Handplane gets spell checked on my computer. I don't now how long 2 eight boards would stay straight but i think long enough to get a bench built and you could easily keep rechecking and adjusting.

But i think you question was actually can you just clamp out any gaps. That i have no idea. I hope Bridger is right and i also wish i would have read this thread before i glued my top together as i lost 2 inches in width on a 16 inch wide top.

bon chance

[Bobby O'Neal]

When building my Roubo recently, my standard for my top laminations was zero cup, zero twist and any bow over 9' didn't concern me. And when I say zero cup and twist, there is some fudge in there, I'm sure. I doubt I doubt I have the skills and tools to confirm zero cup or twist over 9' but before adding glue I did a dry run in the clamps for each stage (I think I did it in three). I did put a slight block planed hollow in the centers to tighten up the mating corners.

As for flat, I got pretty close by hand and got bored/tired of it and built a router sled, ala The Wood Whisperer and it worked very well. About two hours of work including building the jig and routing with a 1" bit.

All the best with yours.

[Marko Milisavljevic]

any bow over 9' didn't concern me

How long is your bench? :eek:

[Prashun Patel]

Clamps will remove a little bit of bow, but only if you clamp up boards a few at a time. Trying to clamp out bow through a stack of laminations is difficult.

Also, know that an occasional minor gap or visible glue line will not affect the functionality of the bench; there will be more than enough force keeping the whole shebang together and poundable. I know this only because my two benches have minor gaps in a couple places and they work fine. They're not fine furniture, but they're fine functionature.

[Bobby O'Neal]

How long is your bench? :eek:

i should've said 9.5' because the finished length is 9' and they were 9.5' when milled and glued. I trimmed the slab to 9' afterwards.

[Bobby O'Neal]

Also, I think Prashun makes a better point than I did. I shouldn't say ANY bow didn't concern me because I did not encounter any extreme bow. I'd say of the 26 boards that made up my bench top, only 6-8 had any bow and that wasn't more than 1/4" over the 9'+ so it wasn't a problem to clamp out when they were sandwiched by good straight boards and vicious Besseys.