How to avoid cupping?

[ByronBlack]

I wonder if someone can help me with a wee problem.

I'm making some pine packing boxes for a friend who sells olive oil and olive related gift items, so these boxes are used as a presentation box.

It's a regular normal box the size of a shoebox, and has a sliding lid. My problem is that when the box is brought in from the workshop, the lid cups excessively within a few days, and fails to slide properly, the rest of the box is fine. The wood is planned 10mm panels cut from 2x4 timber on the bandsaw.

The lid is made of two thin panels edge jointed with opposing grain - but cupping still occurs. Can anyone recommend a method or work-flow that will stop these sliding lids from cupping.

He's asked me to make a further 10 for him, but I need to find a way to sort this problem by the end of the week! eep!

 

[orangetlh]

pine panels are renowned for cupping. The only tip i can offer is after you have planed them, make sure u stand the panel up verticaly or lean it against something making sure there is plenty of room for the air to circulate around them. we buy laminated panels in that are shrink wraped, you can store them flat like this but as soon as you take the wrapping off and store them flat they cup very badly

 

[Steve Maskery]

Hi BB
Nature of the beast, I'm afraid. Do you stick your blanks after resawing them from the 4x2? It might help if you bandsaw them, bring them indoors for a couple of ddays, plane them a bit, stack them a bit, then plane them a bit more.

Two other options are:
1 Use only quartersawn pine - not easy to do as the trees are not that big to start with, or

2 Laminate the lid from bandsawn pine veneers - a lot of work for what you are trying to achieve.

HTH
Cheers
Steve

 

[ByronBlack]

Thanks for the tips fella's, I was a bit worried that someone would say something along the lines of 'no can do amigo'.

So, steve, if i'm following you right, I should cut the panels from the main stock, bring them indoors and lay them on sticks for a few days, plane them ( i assume a little bit on each side) then store them again for a further few days, and then plane a bit more, glue up to the final width, and plane to finished size?

Quatersawn might not be an option, as i'm cutting the blanks from builders timber so I don't get to choose - the boxes have to be made on a budget. As for laminating - I did think about this, but for larger numbers it could be quite a long process.

Would coating the pine in linseed oil or danish oil help to avoid cupping as the oil would fill the grain and stop moisture movement?

Failing all that, is it possible to get pine veneered ply or hardboad around 10mm thick?

One last idea - not sure if my thinking is right here or not. At the moment the lid is comprised of two edge jointed panels to make up the width - would it be better to make the lid out of three thin panels with differering grain direction - maybe the two outer panels will stop the central one from cupping?

 

[orangetlh]

I normally cut and plane timber to about 3 or 4mm oversize, stick it, let it settle and then re-plane, normally find that stops the majority of movement. You dont want to take too much off either side as you said as the timber will dry at different rates and move. Main thing is to get good circulation to all sides of the boards, which i find with pine is best to stand up. I dont think sealing the timber would make too much difference, but its worth a try.

You can get pine veneered MDF and ply which is normally around 9mm thick, differs between the two types of board though. The only problem with that is you will have MDF of ply showing around the edges.

As with any timber the more laminates you put in the more stable it will be and the extra laminate would even the movement out.

 

[ByronBlack]

cheers for the quick reply orangeth - much appreciated. I wish now that I came up with a different idea for a lid! But i'm getting paid to make these, so I can't complain.

How long should I stick the panels for before re-planing? And should I glue up the panels before sticking them?

Sorry for all the questions, I just need to get it clear in my head to work out a flow..

 

[orangetlh]

No problem, happy to help. some people say two weeks under sticks. I think that is a bit too long. To be honest most of the movement will pretty much happen overnight. give it 3-4 days just to be sure. Personally i would cut the timber. Face side and edge it, thickness the width and leave the thickness. Glue them up using your face side as your guide, stick them for a few days and then finish them to size, that will get the movement out but also make it quicker to finish as it will flatten your joints too.

 

[tombo]

does the lid have to be wood?, we got some wine in a box like you describe but the lid was perspex

Tom

 

[Steve Maskery]

BB
You got me right.
I agree with the rest of the ideas too.
Linseed oil will not solve your problem, I am sure,
Like I say, nature of the beast.
Cheers
Steve

 

[Gill]

Tom's idea of using perspex gets my vote, especially for display boxes .

I can understand that clear plastic might be a problem if the olive oil is being sold in clear bottles, but tinted perspex is available and it will inhibit UV bleaching.

Gill

 

[ByronBlack]

Guy's, you have some excellent idea's here! Orange - i've done as you suggested, the panels are now in sticks in the workshop, i'll check them in a number of days and re-plane, and assess the situation..

I love the idea of perspex, but how cheap is this? I'm making the boxes for £4 each (in batches of 10) and the wood i'm using is very cheap builders 2x4 which makes a lot of panels..

I do like the idea alot though

 

[orangetlh]

Acrylic sheet isnt too expensive as long as they arnt too thick. I have seen some in screwfix but the trouble is you have to buy quite a lot of it and I dont know how many you are planning to make.
here is the link

http://www.screwfix.com/app/sfd/sea/sea ... =1&x=0&y=0

 

[ByronBlack]

Thanks for the link orange, unfortunatly it's a bit too expensive, the first batch is for only 10 boxes at £40, i'm hoping with the sticking and drying I can avoid it, otherwise I think pine veneered ply may be a better option

 

[Gill]

I'm sure perspex is available much more cheaply in branches of B&Q. I think the last sheet I bought there cost me around a tenner.

Gill

 

[ByronBlack]

Gill

Can you remember how big that piece was for £10? If I could get ten lids out of it, it would then be a definite solution.

 

[frank]

bb what about using 3ply and glue the thin pine onto it the ply could be the runner for the lid i dont think it will cup .

frank

 

[Gill]

Hi Byron

I can't remember . Pop in to your local branch and have a look - I'm sure there must be a branch somewhere near you.

Alternatively, it might be worth picking up a sheet of perspex from C&A Building Plastics, if that company's near by.

Gill

 

[ByronBlack]

Thanks for the link gill - their prices are quite good, i'll give them a call.

Frank - I don't know why I didn't think of that, that could be the answer.. thanks!

 

[Losos]

BB _ Have you considered popping in to your nearest sign maker :?: They use Perspex & Acrilic sheets and usually have lots of off cuts which they want to get rid of. I used to be able to get several one foot square or rectangular bits for a quid. I've had them in different colours & tints as well.

 

[ByronBlack]

Losos - thats an excellent recomendation, and something I will do, however, the box making may turn into something with high quantities, so i'm really after a cheap easy to get material in small-ish quantities on a regular basis - i'm starting to come over to the idea of a little ply laminted, either way, you guy's have given me plenty of options to think about - thanks!