LumberJocks

All Replies on Cupping question

  • Advertise with us
View klinkman's profile

Cupping question

by klinkman
posted 09-29-2018 01:28 PM


21 replies so far

View Aj2's profile

Aj2

2280 posts in 2192 days


#1 posted 09-29-2018 03:10 PM

To me it sounds like you just didn’t read the grain and picked a board that has maybe a cathedral grain that runs out and ends in the middle of the board. Or maybe a board that’s particularly flat sawn and rift that runs out midway.
The ideal boards that I pick for top have a small cathedral in the middle with rift on both sides.
Not only do they behave well it looks good for a table top. Very harmonious
My best guess from a thousand miles away.

-- Aj

View Lazyman's profile (online now)

Lazyman

3431 posts in 1782 days


#2 posted 09-29-2018 03:32 PM

Pictures would help verify Aj’s theory (a good one) but it fairly common for boards to move after planing and jointing (which is why it is recommended to mill oversized, wait several days and mill to final dimensions) so it stands to reason that with an unmilled side, you could be creating (more) uneven stresses that could exaggerate the movement relative to that side, especially if the grain orientation might cause some of that anyway. Note that if the endgrain at both ends doesn’t look similar to each other, indicating that the grain does not run straight from end to end, you are more likely to have problems with warping and twisting in particular. The other reason to plane the other side, beside the potential for the twisting you are seeing, is to make sure that it is parallel to the first side. This will make construction easier as it will be hard to attach anything (legs, aprons) to one side and have the other side level to the floor.

EDIT: One other thought…If you have a moisture meter, make sure that the moisture content is not really high, especially if it was not kiln dried wood. If you don’t have one, you can get one cheap from Amazon that will give you a reasonable indication whether you are in the ballpark.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

View TheFridge's profile

TheFridge

10858 posts in 1880 days


#3 posted 09-29-2018 03:37 PM

i never lay panels or pieces to be be panels flat after milling. Always on their side. If you lay them flat then one side will readily absorb more or less moisture than the other. If it does happen I’ll stand it up and it’ll usually equalize and straighten out enough so I can glue it up or use the aprons to pull it flat. Sometimes I’ll put a fan blowing at side with the belly.

I try to skim the faces and let sit stickered for a week or so before dimensioning for important stuff. Works for me.

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

View crippledcarpenter's profile

crippledcarpenter

30 posts in 2841 days


#4 posted 09-29-2018 03:42 PM

where these boards kiln dried or air dried when you bought them? if they where air dried, where they sticker stacked or just in a pile on top of each other. that they cupped towards the side that you had freshly planed the day before would lean towards that the boards were not dried enough. removing the rough cut side exposed the face of the board would cause it to dry faster than the unplaned side.

-- haste makes firewood.

View Lazyman's profile (online now)

Lazyman

3431 posts in 1782 days


#5 posted 09-29-2018 03:42 PM

I just realized we didn’t respond to your question about gluing them together before you proceed, I think that is a bad idea. It will be hard to fix any problems after that and you are likely to wind up with a wavy board. You need to start with flat, straight boards before you glue them into a panel.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

View WoodenDreams's profile

WoodenDreams

605 posts in 305 days


#6 posted 09-29-2018 04:41 PM

How was the grain direction, Sounds like too much moisture in the board still. I usually the boards in my shop for at least one week before use, sometimes I’ll preplan and get the boards a month in advance. 6” or wider boards I normally rip them to a minimum width of 3” or 4”, joint and glue up to my desired width. More work, but I like the results. If I’m doing small boxes then 6” width max is ok for me. The planer rollers push down on the wood, so if you don’t take out high spots first you’ll get the high spot back. One time I bought a 4/4×6”x8’ piece of mahogany to build some small boxes, it started to rain taking it to my shop, the once flat board was now a really twisted board, it never came back to shape, after 6 months I cut it to 6” lengths and made some smaller boxes out of it.

View Rich's profile

Rich

4493 posts in 984 days


#7 posted 09-29-2018 04:42 PM

The amount of distortion you’re talking about is minimal. On a table top that size you will be able to pull it flat assuming you build a solid frame to attach it to. You mention cupping in the title of the thread and bowing in the text. I assume you meant cupping.

I suggest gluing them up. Contrary to popular misconceptions, don’t alternate the cupping. Instead, glue them so that the top has one single bend. If it will leave you with a grain pattern you’re happy with, the best option will be to attach the top to the base with the crown up in the middle. It’ll be easiest to pull it flat. If you really love the other side, that’s fine, it’ll still work.

Go ahead and attach the top to the base. Allow for movement. I like Z-clips. They’ll work well in this case since you can cut the slots in the aprons a little further from the edge to ensure you can get a good pull when you screw them to the top.

-- Knowledge is not skill. Knowledge plus ten thousand times is skill. -- Shinichi Suzuki

View a1Jim's profile

a1Jim

117627 posts in 3972 days


#8 posted 09-29-2018 04:57 PM

As others have pointed out planning wood on one side changes how much moisture enters your wood on each side after planning more moisture enters that side caused by the Capillary action. Another point that has been made is how the wood is milled as an impact on how much wood movement you will have, the most desirable milling being quarter sawn. Again others have pointed out how you store even overnight, wood should not be laid flat, either place it on stickers or on edge for equal air contact, the point of rough cutting wood and letting it acclimate is also important. lastly, I’m not sure if anyone mentioned checking the moisture content before you buy wood, but that’s also an important thing to do.
Given that your only talking about a 1/16th” you may be able just to mist the convex side of the wood with a spray bottle of water and see if that brings things back to flat.

View a1Jim's profile

a1Jim

117627 posts in 3972 days


#9 posted 09-29-2018 05:11 PM

BTW
Welcome to Ljs

View Aj2's profile

Aj2

2280 posts in 2192 days


#10 posted 09-29-2018 05:11 PM

I new you guys would fill in the many other reasons why boards warp twist or bow. I admit I was feeling lazy and didn’t want to keep writing. Thanks :))

-- Aj

View AlaskaGuy's profile

AlaskaGuy

5284 posts in 2704 days


#11 posted 09-29-2018 05:34 PM

As a newbie you might find this short article helpful on expressing written lumber sizes.

https://chestofbooks.com/home-improvement/woodworking/Community-Shop-Projects/Reading-And-Writing-Dimensions-Of-Lumber.html

-- Alaskan's for Global warming!

View Rich's profile

Rich

4493 posts in 984 days


#12 posted 09-29-2018 05:43 PM


As a newbie you might find this short article helpful on expressing written lumber sizes.

- AlaskaGuy

Interesting. I’d never heard that before. Sadly, I’ll probably forget the rule before I need it next.

-- Knowledge is not skill. Knowledge plus ten thousand times is skill. -- Shinichi Suzuki

View AlaskaGuy's profile

AlaskaGuy

5284 posts in 2704 days


#13 posted 09-29-2018 05:46 PM

General rules of stock preparation. Cut project piece about 1’’ over final lenght, remove the same amount of stock form each side, and NEVER lay freshly jointed/planed sock flat on a table or any manner the stops air circulating from reaching both sides of the stock. I like to sit them on edge.

-- Alaskan's for Global warming!

View AlaskaGuy's profile

AlaskaGuy

5284 posts in 2704 days


#14 posted 09-29-2018 05:59 PM


As a newbie you might find this short article helpful on expressing written lumber sizes.

- AlaskaGuy

Interesting. I d never heard that before. Sadly, I ll probably forget the rule before I need it next.

- Rich


Learned that many years ago with I first started visiting lumber yards. I told the guy behind the counter I need some 8 foot 2 by 4’s. He said what you want is some 2 by 4’s 8 foot long. 2×4x8’.

Go online to a lumber supplier and see how they list their lumber or find a cut list on a set of plans. They will be thickness x with x lenght.

-- Alaskan's for Global warming!

View klinkman's profile

klinkman

41 posts in 270 days


#15 posted 09-29-2018 06:10 PM

Thanks all, really appreciate the input and the experience here. To answer some of the questions:

The unmilled lumber was acclimated in my shop for more than two weeks before I started working it. After initial dimensioning, the boards were stood against the wall so all 4 sides where evenly exposed, for like I say a day and a half or so. Our humidity this morning is 57% and the boards measure a bit over 9% MC.

Using the cathedral pattern to guide selection is an interesting idea. However, a) There was not a big selection, an b) this material was rough sawn with both ends heavily painted. So it was nearly impossible to tell the grain pattern of what I was buying. Do you guys bring a hand saw and/or plane into your supplier so you can look at the grain? Is that acceptable to them? (There aren’t a lot of suppliers in my area.)

@Rich. Thank you, your comments were very helpful, along the lines of what I what I was thinking. I used the term incorrectly, I’ve experienced primarily bowing. I’ve worked with the boards this morning and I think you’re right, glue them up as one bend. I’m going to go in this direction, your comments give me some confidence I can get the deflection out in assembly. I don’t think it will take that much pressure and I can adjust the heights of wooden turnbuttons to get the right force.

Thanks all for your comments. I’m sure I’ll be back with more questions. – EC

-- Klinkman, hand tool enthusiast

View Rich's profile

Rich

4493 posts in 984 days


#16 posted 09-29-2018 06:27 PM


@Rich. Thank you, your comments were very helpful, along the lines of what I what I was thinking. I used the term incorrectly, I ve experienced primarily bowing. I ve worked with the boards this morning and I think you re right, glue them up as one bend. I m going to go in this direction, your comments give me some confidence I can get the deflection out in assembly. I don t think it will take that much pressure and I can adjust the heights of wooden turnbuttons to get the right force.

Thanks all for your comments. I m sure I ll be back with more questions. – EC

- klinkman

If you’re talking about bowing (down the length of the board) that’s a different story. I assumed you meant cupping across the board.

You can still glue it up as one bend and pull it flat when you mount it to the base, but there’s some value in gluing it up with the bowed faces opposite one another. Doing that can help one to offset the other resulting in a flatter final board. You have to be sure to use cauls and do a really clean glue-up though, otherwise you just wind up with a really crappy glue joint that you’ll have to repair.

Just so we’re on the same page:

-- Knowledge is not skill. Knowledge plus ten thousand times is skill. -- Shinichi Suzuki

View AlaskaGuy's profile

AlaskaGuy

5284 posts in 2704 days


#17 posted 09-29-2018 06:33 PM


@Rich. Thank you, your comments were very helpful, along the lines of what I what I was thinking. I used the term incorrectly, I ve experienced primarily bowing. I ve worked with the boards this morning and I think you re right, glue them up as one bend. I m going to go in this direction, your comments give me some confidence I can get the deflection out in assembly. I don t think it will take that much pressure and I can adjust the heights of wooden turnbuttons to get the right force.

Thanks all for your comments. I m sure I ll be back with more questions. – EC

- klinkman

If you re talking about bowing (down the length of the board) that s a different story. I assumed you meant cupping across the board.

You can still glue it up as one bend and pull it flat when you mount it to the base, but there s some value in gluing it up with the bowed faces opposite one another. Doing that can help one to offset the other resulting in a flatter final board. You have to be sure to use cauls and do a really clean glue-up though, otherwise you just wind up with a really crappy glue joint that you ll have to repair.

Just so we re on the same page:

- Rich


Good illustration, I’ve known seasoned woodworker who miss quote the proper term causing much confusion.

-- Alaskan's for Global warming!

View Lazyman's profile (online now)

Lazyman

3431 posts in 1782 days


#18 posted 09-29-2018 11:21 PM

I am not as experienced as the other guys who have responded but personally, I would take one more pass at correcting the problems before glue up. I’ve always been afraid to glue up panels that aren’t flat, especially if they have different problems (you mentioned bowing, cupping and twisting). You also need to make sure that the 2 surfaces are parallel to each other. If you never ran the non-show side through the planer, that could be part of the problem.

My thought is that since you are trying to make what sounds like a nice piece, you don’t want to find out you did something that will bother you every time you look at it. At a minimum, practice your clamping, including cauls, completely before you start the actual glue up. If you cannot pull everything into alignment before, I would worry that it won’t be any easier after the glue up. If nothing else you need to find out if you need more clamps. (The answer is always always yes BTW.)

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

View Rich's profile

Rich

4493 posts in 984 days


#19 posted 09-30-2018 05:26 AM

Well, everyone’s got an opinion. I do have a lot of experience doing things right, and learning from doing them horribly wrong. I didn’t just make that up about flipping the boards so one is bowed up and the other down.

Since some folks doubt me, how about we listen to one of our more esteemed LJs, Mr. Charles Neil. Skip about two minutes into this video and see what he has to say about bowed boards.

Here’s the video link: https://www.youtube.com/watch?v=S2vT666VWLo

It’s part of his Build a Pie Safe series. I’ve recommended this many times because, even if you have no desire to build a pie safe, he covers so many fundamental concepts about cabinetmaking. Almost everyone can learn at least one new thing from watching. I’ve learned a lot from Charles.

-- Knowledge is not skill. Knowledge plus ten thousand times is skill. -- Shinichi Suzuki

View AlaskaGuy's profile

AlaskaGuy

5284 posts in 2704 days


#20 posted 09-30-2018 06:19 AM

I believe you. I’ve done it before myself especially on longer stock like for a table and such.

The problem is if you have matched your grain and color and then start flipping them it can mess with appearance. You can do the with laminating to pieces of bowed plywood. Anyway you don’t have to convince me. It does works. Something I forget to mention earlier. I often time on the first milling leave the stock over size and sit 24 hours and then take one final pass on the jointer and a pass through the planer to final thicken just before glue up.

-- Alaskan's for Global warming!

View Lazyman's profile (online now)

Lazyman

3431 posts in 1782 days


#21 posted 09-30-2018 12:43 PM

And I certainly wasn’t arguing with either of you either. I was simply saying that not having as much experience as you guys, and Klinkman being a self described newbie, I would not want to learn the hard way what can go wrong on a project that you want to look nice.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

Have your say...

You must be signed in to reply.

DISCLAIMER: Any posts on LJ are posted by individuals acting in their own right and do not necessarily reflect the views of LJ. LJ will not be held liable for the actions of any user.

Latest Projects | Latest Blog Entries | Latest Forum Topics

HomeRefurbers.com