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Cupping question

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Forum topic by klinkman posted 09-29-2018 01:28 PM 576 views 0 times favorited 21 replies Add to Favorites Watch
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klinkman

42 posts in 291 days


09-29-2018 01:28 PM

Topic tags/keywords: question cup twist

First post here, I’m a newbie trying to learn woodworking, and hand tool skills.

My latest project is a walnut sofa table. I’m really just milling the lumber at this point. Purchased 5 pieces of 5/4 rough sawn walnut. It’s been in warehouse for more than a year (same region/climate basically as my shop).

The material was as you would expect not straight and for the most part I’ve been able to get the irregularity out on the material for legs, aprons, bottom shelf. So now I come to the show piece, the top. The finished top is supposed to be 54×15x7/8.

I started with nice board 110×8x5/4 that I cut in half. It was straight forward to get flat, I removed the high spots with a hand plane and after a few passes through a machine planer made some more hand adjustments. After a few more passes through a planer, the two pieces were very nicely flat. I jointed one edge with a hand plane. (My planer is 13” so my idea was to take these boards to close to finished dimension before glue up.)

So at this point I have two boards, ~55 by 7 7/8 by maybe 1 1/8 or 1 1/16. I have a nice jointed edge and the “show” surface I’ve cleaned up with a hand plane, so I have a square face and edge, reference surfaces. I let them sit in the shop for maybe a day and a half. There really has been no significant weather changes in my area. Should be no big deal to take the remaining ~3/16” to get to the final 7/8” right?

This morning I check everything again and start up the planer making 1/32” passes. I only removed material from the back side. 6 or 7 passes and I’m done. Lay the pieces on the bench and these two boards are both cupped now right in the middle. The bow is towards the down side, the side I’ve been machine planing.

I’m baffled. One board is bowed about 1/16, the other (more figured one) is bowed and twisted about 1/8. How could these boards go so far out so quickly? Was my mistake just taking the material from one side? Now I’m at finished dimension I don’t want to remove too much more material. I get (now) the idea that the thinner the board becomes the more likely it will want to return to it’s natural shape.

My plan is to dowel them together and glue them up before anything else. I think I’ve got no choice but to try to and hand plane the twist out. As for longer term, can I cinch the top down with a turnbutton to remove the residual bow? Or is that asking too much from that? Would a better process have been to glue them up first at like 1” and then work to the final dimension by hand plane? Any other ideas? thanks,

-- Klinkman, hand tool enthusiast


21 replies so far

View Aj2's profile

Aj2

2321 posts in 2214 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

Lazyman

3517 posts in 1803 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 1902 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

32 posts in 2863 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

Lazyman

3517 posts in 1803 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

616 posts in 327 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

4549 posts in 1005 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

117652 posts in 3993 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

117652 posts in 3993 days


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

BTW
Welcome to Ljs

View Aj2's profile

Aj2

2321 posts in 2214 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

5313 posts in 2725 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

4549 posts in 1005 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

5313 posts in 2725 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

5313 posts in 2725 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

42 posts in 291 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

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