Total Finishing Supplies

Professional Finishing

You are not logged in. [ Login ] Why log in
(NOTE: Login is not required to post)

First Big Wall-art: it cupped...

2/16/17       
David N Member

First, I'm a CNC guy. Having put all my energy into building the machine and writing the code, I swore I'd leave finishing to the customer.

Second, this is only my second attempt at a Big Piece (40x48x8/4 cherry, varying in thickness from 3/8 to 1-1/4--it was supposed to be at least 3/4 when done, but I made the newby mistake of not buying thick enough rough lumber to start).

However, I discovered that when I tried to go to bigger glued-up pieces of expensive hardwoods, ignorance wasn't the shield I'd counted on. The wood moved, quite a bit in my wood-heated basement workroom next to the double-door to the uncontrolled garage environment.

I was shocked! when the 8/4 panel cupped, and just as shocked that so great a curve disappeared with changing humidity. (Anything I learned about RH and EMC, I learned here in the past few weeks.) I don't have a decent MC meter, but I do have three humidity gauges which give me three different readings.

After it returned to normal, I quick-like-a-bunny CNC-carved my project and sloshed on copious amounts of Danish oil to all six sides--three times. And then, I sliced off the remaining 8/4 waste to release the carving--which had dwindled to only 3/8" thick in the thinnest places.

You probably guessed that it cupped.

After spending another day reading more here, I learned about warping from internal stress, and thought what I was seeing that because it happened the instant the thick matrix was removed. However I decided to test if it was moisture content by following a tip here to place damp towels on the curved up (driest) side, and sure enough, it began flattening immediately.

Following the Conservation of Misery Principle, as one problem recedes, another waxes: how do I/can I even stabilize it with a finish so it stays "relatively flat"?

Or is there another way to hold it flat so it can be used as a wall-hanging?

Failing that, I'm going to offer it as a piece to hang in the shower, or to display on the bottom of a swimming pool.

I feel like I woke up in another universe: wood always seemed so simple. But I bet mine is not the only heart it has bruised.

Open to any advice and admonition.

Thank you.


View higher quality, full size image (2592 X 1944)


View higher quality, full size image (4128 X 2322)


View higher quality, full size image (4128 X 2322)

2/16/17       #2: First Big Wall-art: it cupped... ...
rich c.

The use of very wide flat sawn stock does not help at all. Narrow quarter sawn stock is much more stable. How reliable of supplier did you use? Was it sold as kiln dried?

2/16/17       #3: First Big Wall-art: it cupped... ...
David N Member

I used the go-to hardwood supplier, but I never asked whether it was KD. I know trim carpenters were coming in and out the entire time I was there, leading me to guess it was.

I had another supplier lined up, but drying was going to take another 30 days, and then I found this place with stock on-hand.

The truth: I wanted to run right through all of this without having to learn anything about it.

In fact, to make up my 40" width, I hoped to buy wide-enough 8/4 to have only two seams.

A fellow with experience insisted I rip them into smaller widths and make at least four, but he had to sit on me, and then babysit me to make sure I did the edge and face jointing and planing before I started gluing.

As I hinted, all this preparation removed more material than I expected, and I compounded the errors by not adjusting the project's parameters. Still, no matter that, the wood would have moved, because it moved while still in the nearly-2-inch plank stage.

I just checked again, and it's sitting nearly flat on the table. I have an idea to slip a dowel under its middle back and clamp the edges on either side, trying to give it a slight reverse bow.

But I wonder if anything can make it stay that way.

Thank you.

2/17/17       #4: First Big Wall-art: it cupped... ...
rich c.

No such thing as working with wood and not "having to learn something". I've been doing it for over 40 years, still learning.
Kiln dried stock can have many reasons for moving. Improperly dried so the core is still wet. Expose that from one side and the wood moves. It can be case hardened from drying too fast and this causes stress in the wood and it moves as the stress is relieved from only one side. You moved the wood from some environment at the store into your shop with a much different environment. You need to rest the wood with all surfaces exposed to air and let it rest for days to acclimate. Letting it sit on the floor or on a bench limits the air movement on one side and it moves. WATCO oil does not stabilize the wood nor does it slow wood movement from environmental changes as well as a film finish. Letting it sit on a surface while finishing will also let it move. You need to keep air circulating all around it when you know the wood is trying to acclimate. If you try to limit movement by adding cleats to the back, it must have long slots for screws and not be glued. This wood will move every season forever. Just curious, how did you sand out all the machining marks before finishing, or was the picture after a roughing cut?

2/17/17       #5: First Big Wall-art: it cupped... ...
Leo G

I've had things change shape during the finishing process where one side was covered and the other was waiting for it's finish.

One of the few ways you will stabilize that is to put a film finish on it that will slow the exchange of moisture. Wax is the best, the rest will let moisture in slowly and out the same.

I've straightened pcs out by placing them on a sawhorse and a heater below. When it's nearly there remove the heat and put the finish on and hope it's sealed good.

2/17/17       #6: First Big Wall-art: it cupped... ...
Jim Conklin  Member

Website: http://www.jhconklin.net

I am not going to add anything about the warping beyond that the side with the longest continuous grain is going to be the longest.

Beyond that. Is that a 3D topographical map you rendered onto cherry? Really cool. Really. I hope you get the bowing stress thing worked out (relieve the back?) so you can showcase the thing. It is fascinating.

2/19/17       #7: First Big Wall-art: it cupped... ...
Bart

I cut my teeth with one of the top carvers in the country. Lots massive carved doors and entries etc.....big stuff. Usually starting with 10/4 and milling ourselves. One thing I learned is take your time, like weeks. Rough size it, joint one side let it sit to adjust and do this with all remaining steps then finally glue it up for carving. One thing he did do which is time consuming for some doors to avoid bread boards on the back of doors we would pre drill the planks for all thread across the doors top and bottom to stop cupping.
Nothing of consequence was ever rushed out the door. Raw lumber usually sat in the shop for a least week or two before anything happened.

good luck

2/20/17       #8: First Big Wall-art: it cupped... ...
Gerry

If you could mount it on battens across the grain fastened tight in the middle and with sliding hold downs on the outside you might be able to get it to stay flat. Don't know if your situation would allow for that but I think the piece will continue to move as RH changes.

2/21/17       #9: First Big Wall-art: it cupped... ...
Bill  Member

Website: canadianacabinets.com

I wonder if, once flat you can carve out some of the back to relieve tension. Just a thought.

2/21/17       #10: First Big Wall-art: it cupped... ...
Bart

I had thought over the weekend. Since this is wall art you could possibly integrate 2-3 clean looking stainless steel cables on the back that would act as a tensioner to take the cup out and something to hang the piece by. You'd have to be careful when tensioning it you wouldn't want to crack it.

my2cts

2/21/17       #11: First Big Wall-art: it cupped... ...
Bart

One more idea. You could put in the sun cup up for awhile and see if it'll warp back straight. If it does batten real quick.

2/23/17       #12: First Big Wall-art: it cupped... ...
David R Sochar Member

Here are a few things:

The wood was probably dried poorly. The thicker the wood, the more likely it is not dried correctly. Sounds like you went to a hobby shop. Professional lumber vendors will dry thick wood correctly and it can stand being cut into and not warp. As rich dais, the center was wet and as it dried, it shrunk, cupping your work.

It is not to be assumed that all wood will warp. Things can and should be done to not cause it yourself - stable comfortable temps and humidity, deep cuts made slowly, and plan to hold it flat, since once it is out of your hands, it may cup.

Frame and panel was developed to help control large panels of solid wood. It has worked pretty well for over 500 years. It accommodates wood movement.

The TWO RULES are : All wood moves, and all woodworkers disagree as to how much, why, when etc. But it is a science and as such, is predictable.

Wood will move and nothing you or I do will stop it. So-called primitive people cut stone by drilling a line of shallow holes in the stone and placing wedges of hardwood that were desert dried into the holes, then wetting them. The wedges swelled with the water, and exerted pressure along the line, eventually cracking the stone. Pyramids could then be built, with water and wood.

We have all been humbled by wood. You have a nice piece of work, call it a learning experience and enjoy it from that added perspective.

2/24/17       #13: First Big Wall-art: it cupped... ...
David N

What day is this? The 24th? Gak. I apologize, but you'd be proud of me: I was readin.

Based on the recommendations all over WoodWeb, I ordered Bruce Hoadley's _Understanding Wood_ from the library and it arrived today. However, I continued hunting information on the web, which UW now corroborates.

My Biggest Mistake was letting the air in the work area get too hot (the Forest Products Lab Wood Handbook FPLGTR113 recommends storing wood in cooler temps and under a plastic covering after manufacturing).

My second biggest was believing that the Watco Danish oil sealed the wood by virtue of being absorbed. I understood that the product was a mixture of varnish and oil and I assumed that with each new coat, the varnish was built up, leading to a sealing coat.

First @Bart, I had that very idea: I made a "spine" out of a 3/4" dowel with a flat side for the center back and stretched cables side-to-side across it. I found stainless steel "mirror hangers" in the hardware store, about an inch wide and in a squared-off J profile, and bought a very scary circular saw for the dremel tool to mill slots in the edges. That bit was dicey because the edge is only 1/4" in places.

I put the hangers in the slots, and attaching a turnbuckle to one side with an S-hook, and the stretched 18-ga galv. wire between the turnbuckle and an S-hook in the hanger on the other side. I was very surprised that there was still enough travel in the buckle to tension it up, even with my clumsy construction.

The wires pluck like a banjo. I've got 8 of them space roughly 4-1/2 inches apart.

I don't know if steel wire is going to be strong enough for cherry... :^) I'll rig some other way to hang it.

@rich c
The picture was of what I deem the finish cut. I don't have a good way to sand it, but I scrub every inch of it with stiff brushes. The back side was cut first with a "bowl-cutter" bit, which I discovered doesn't quite have a flat bottom, so it left an interesting pattern of concentric Vs. However, as it was mostly flat, and face-down, it participated less in moisture loss than the face-up side.

I had let the piece rest on the machine's table for several days, but not, as you guessed, raised to allow air movement across the bottom. There had been some cupping even in the pre-cut 8/4 stage.

@Leo G
(middle name Leo here) That's a nice trick to know. I did what you said in a different way. After I got it to lay down again by laying damp towels on the over-dried side (took 5-hours), I put a dowel under it's back and clamped the edges which had earlier cupped flat to the table. I let it dry that way for several days.

As soon as I unclamped it, I was ready with "spar varnish". 2 coats. "If it's good for ships," I assumed, "the only thing more robust would be what they put on submarines." Wrong again. Firstly, FPLGTR113 indicates that a minimum of THREE coats (and 6 or more for real ocean applications) are required to get good finish, but secondly, it recommends 2-part polyurethanes above clear varnish.

Even after unclamping, a cup of perhaps an inch remained. However, I was able to take that out with my "wire braces."

@Gerry
Before I hit on the idea of slots and wires, I was considering over-wide plywood battens (I was calling them strongbacks) with "fingers" to wrap around the edges with enough clearance to allow the panel to grow/shrink. However they would have been visible. The piece is really too thin to trust screwing into--and of course, I'm using a method which is trusting that 1/16" of wood is enough to keep a hanger from tearing out.

@David R Sochar
I blame my poor excuse for a workshop. It would've been my garage but my son insisted in moving the CNC machine, at least, into the basement which is only slightly better.

I got it at a hardwood supply warehouse. I only assumed it was kiln-dried. (Unfortunately, I haven't been back to the place to show the piece and pick the owner's brain.) Just as you say, learning experience. For all the heartache, I wouldn't trade the experience.

@Bill
Your suggestion had occurred to me, and in fact, I found a youtube video where I watched a fellow use a circ saw to make, very crude, relief cuts in ugly twisted lumber pieces, to get it to lay flat, and planed it and finally glued some strips into dados perpendicular to the cuts to put some strength back. My biggest problem with the approach is not being able to lay the piece flat again after I cut off the holding wood.

I actually thought, "Hey, I have the model in the computer: I could cut its negative out of the back and have a model that was a uniformly thick shell." (But then I laid down until that went away.)

@Jim Conklin
Where do you live?? My son has been urging me to keep the faith with this effort, at least until I meet my fan. :^)

Thank you for the encouragement. Today, I confess to investigating "wood alternatives".

@rich c again:
Prior to today's weakness however I had had the thought that if I started with quartersawn stock I'd give myself a head start. I have made friends with a reputable miller about 50 miles away, but I'm going to take this result to him and get his advice.

A carpenter I showed it to suggested treating the entire piece as the (large) panel in a ficticious door and routing stiles and rails to make a stout floating frame for it.

Thank you all and each. I have some residual questions but will try to remember them for a separate post.

2/24/17       #14: First Big Wall-art: it cupped... ...
David N

Sorry to leave you hanging. Here's a picture of the status. (I expect to hear "pings" in the middle of some night when the wires start letting go. :^) )

@Bart
I ran right by your first post. Got it. Slow down some. Thank you. Given the time I've had to spend on investigating fixes, I can obviously afford time for better preparation.

Thanks again all.


View higher quality, full size image (4128 X 2322)


Post a Response
  • Notify me of responses to this thread
  • Subscribe to email updates on this Forum
  • To receive email notification of additions to this forum thread,
    enter your name and email address, and then click the
    "Keep Me Posted" button below.

    Please Note: If you have posted a message or response,
    do not submit this request ... you are already signed up
    to receive notification!

    Your Name:
    E-Mail Address:
    Enter the correct numbers into the field below:
     

    Date of your Birth:



    Return to top of page

    Buy & Sell Exchanges | Forums | Galleries | Site Map

    FORUM GUIDELINES: Please review the guidelines below before posting at WOODWEB's Interactive Message Boards (return to top)

  • WOODWEB is a professional industrial woodworking site. Hobbyist and homeowner woodworking questions are inappropriate.
  • Messages should be kept reasonably short and on topic, relating to the focus of the forum. Responses should relate to the original question.
  • A valid email return address must be included with each message.
  • Advertising is inappropriate. The only exceptions are the Classified Ads Exchange, Machinery Exchange, Lumber Exchange, and Job Opportunities and Services Exchange. When posting listings in these areas, review the posting instructions carefully.
  • Subject lines may be edited for length and clarity.
  • "Cross posting" is not permitted. Choose the best forum for your question, and post your question at one forum only.
  • Messages requesting private responses will be removed - Forums are designed to provide information and assistance for all of our visitors. Private response requests are appropriate at WOODWEB's Exchanges and Job Opportunities and Services.
  • Messages that accuse businesses or individuals of alleged negative actions or behavior are inappropriate since WOODWEB is unable to verify or substantiate the claims.
  • Posts with the intent of soliciting answers to surveys are not appropriate. Contact WOODWEB for more information on initiating a survey.
  • Excessive forum participation by an individual upsets the balance of a healthy forum atmosphere. Individuals who excessively post responses containing marginal content will be considered repeat forum abusers.
  • Responses that initiate or support inappropriate and off-topic discussion of general politics detract from the professional woodworking focus of WOODWEB, and will be removed.
  • Participants are encouraged to use their real name when posting. Intentionally using another persons name is prohibited, and posts of this nature will be removed at WOODWEB's discretion.
  • Comments, questions, or criticisms regarding Forum policies should be directed to WOODWEB's Systems Administrator
    (return to top).

    Carefully review your message before clicking on the "Send Message" button - you will not be able to revise the message once it has been sent.

    You will be notified of responses to the message(s) you posted via email. Be sure to enter your email address correctly.

    WOODWEB's forums are a highly regarded resource for professional woodworkers. Messages and responses that are crafted in a professional and civil manner strengthen this resource. Messages that do not reflect a professional tone reduce the value of our forums.

    Messages are inappropriate when their content: is deemed libelous in nature or is based on rumor, fails to meet basic standards of decorum, contains blatant advertising or inappropriate emphasis on self promotion (return to top).

    Libel:   Posts which defame an individual or organization, or employ a tone which can be viewed as malicious in nature. Words, pictures, or cartoons which expose a person or organization to public hatred, shame, disgrace, or ridicule, or induce an ill opinion of a person or organization, are libelous.

    Improper Decorum:   Posts which are profane, inciting, disrespectful or uncivil in tone, or maliciously worded. This also includes the venting of unsubstantiated opinions. Such messages do little to illuminate a given topic, and often have the opposite effect. Constructive criticism is acceptable (return to top).

    Advertising:   The purpose of WOODWEB Forums is to provide answers, not an advertising venue. Companies participating in a Forum discussion should provide specific answers to posted questions. WOODWEB suggests that businesses include an appropriately crafted signature in order to identify their company. A well meaning post that seems to be on-topic but contains a product reference may do your business more harm than good in the Forum environment. Forum users may perceive your references to specific products as unsolicited advertising (spam) and consciously avoid your web site or services. A well-crafted signature is an appropriate way to advertise your services that will not offend potential customers. Signatures should be limited to 4-6 lines, and may contain information that identifies the type of business you're in, your URL and email address (return to top).

    Repeated Forum Abuse: Forum participants who repeatedly fail to follow WOODWEB's Forum Guidelines may encounter difficulty when attempting to post messages.

    There are often situations when the original message asks for opinions: "What is the best widget for my type of shop?". To a certain extent, the person posting the message is responsible for including specific questions within the message. An open ended question (like the one above) invites responses that may read as sales pitches. WOODWEB suggests that companies responding to such a question provide detailed and substantive replies rather than responses that read as a one-sided product promotion. It has been WOODWEB's experience that substantive responses are held in higher regard by our readers (return to top).

    The staff of WOODWEB assume no responsibility for the accuracy, content, or outcome of any posting transmitted at WOODWEB's Message Boards. Participants should undertake the use of machinery, materials and methods discussed at WOODWEB's Message Boards after considerate evaluation, and at their own risk. WOODWEB reserves the right to delete any messages it deems inappropriate. (return to top)


  • Forum Posting Help
    Your Name The name you enter in this field will be the name that appears with your post or response (return to form).
    Your Website Personal or business website links must point to the author's website. Inappropriate links will be removed without notice, and at WOODWEB's sole discretion. WOODWEB reserves the right to delete any messages with links it deems inappropriate. (return to form)
    E-Mail Address Your e-mail address will not be publicly viewable. Forum participants will be able to contact you using a contact link (included with your post) that is substituted for your actual address. You must include a valid email address in this field. (return to form)
    Subject Subject may be edited for length and clarity. Subject lines should provide an indication of the content of your post. (return to form)
    Thread Related Link and Image Guidelines Thread Related Links posted at WOODWEB's Forums and Exchanges should point to locations that provide supporting information for the topic being discussed in the current message thread. The purpose of WOODWEB Forums is to provide answers, not to serve as an advertising venue. A Thread Related Link that directs visitors to an area with inappropriate content will be removed. WOODWEB reserves the right to delete any messages with links or images it deems inappropriate. (return to form)
    Thread Related File Uploads Thread Related Files posted at WOODWEB's Forums and Exchanges should provide supporting information for the topic being discussed in the current message thread. Video Files: acceptable video formats are: .MOV .AVI .WMV .MPEG .MPG .MP4 (Image Upload Tips)   If you encounter any difficulty when uploading video files, E-mail WOODWEB for assistance. The purpose of WOODWEB Forums is to provide answers, not to serve as an advertising venue. A Thread Related File that contains inappropriate content will be removed, and uploaded files that are not directly related to the message thread will be removed. WOODWEB reserves the right to delete any messages with links, files, or images it deems inappropriate. (return to form)