Thin Sheets of Wood - 3mm

[DavidJHolmes]

I've been trying to make some boxes, puzzle boxes to be precise. I have a set of plans I purchased off the net a while back and having a couple of sheets of 3mm walnut I had a go at making it. The stuff I had was the sheets the model shops sell usually in 100mm wide and 450mm long. I picked it up from a craft fair and got some nice pieces, however I was a bit short because of the larger pieces of the box, so I had a browse on the net and found some similar but in 150mm wide. This came and after removing from the packaging I left it in the workshop until I had time to come back to it. I've picked it up today and its cupped, bowed, twisted and not much use for making a box. In fact I've tried and its not good. I'm pretty miffed as it wasn't particularly cheap.

Now I don't think there's much point me ordering more as the same could happen. So I started thinking could I cut my own (I don't have a band saw yet, but could get access to one), but my thicknesser only planes down to 5mm (it's the Titan one from Screwfix). Is 3mm a bit silly, would the thinner wood be prone to warping more? I only chose 3mm as the plans scale to any wood thickness but the 3mm makes a nice 100mm cube.

What would be the correct procedure if I was to cut my own with regards to drying out the wood? i.e. can I cut it from the timber yard straight away or do I leave it in my shop for a period of time and then machine it to dimension?

Thanks

 

[custard]

Hello David, you've set yourself a tough challenge, once you take timber thickness below about 12mm the movement problems start to increase exponentially, and by the time you get to 3mm it's definitely becoming the exception rather than the rule to have a piece of timber that behaves itself. You can plane down to 3mm even with your planer by using a sled or clamping a piece of melamine covered MDF to the planer's base, you'll need freshly sharpened knives to prevent the workpiece self destructing under the pressure rollers but really that isn't the main problem, the main problem is the wood itself.

When I need timber that thin (as I often do for lamination work) I recognise I'll have to pull out all the stops to be successful. Most importantly that starts with selecting a straight grained and quarter sawn board as your "donor" piece, ensuring its been given plenty of time to reach moisture equilibrium in your workshop, bandsawing off a pack of well oversize 3mm veneers and then taping the pack back together and leaving it once again to settle, personally I then pass it through a drum sander to get to final thickness but as I said before there are work arounds for planing it. Even with this painstaking approach I'll expect to lose a fair percentage of lamination pieces.

I'd be interested to hear how the luthiers on this forum deal with thin workpieces, I guess they're using 3mm stock all the time for guitar bodies and such like.

Good luck!

 

[profchris]

For ukuleles, 1.8 mm or thinner!

My experience of the boards from model making shops is that they are pretty stable. BUT, humidity changes will make any piece of wood that thin move quite a lot.

I think David's first step should be to bring the wood indoors to see if it flattens. I suspect it was cut at something like 50% humidity, and that it's been near 100% in the W Mids recently.

If so, the main thing is to glue up the box at around the humidity it's expected to live at. Higher and it will crack, lower it swells. Use as near as possible vertical grain pieces for the largest widths, narrower parts can go further off the vertical. A simple humidity meter is two strips of thin veneer glued together with the grain at 90 degrees, noting how much it bends as humidity changes.

Luthiers cope by assembling the body at low humidity (50% in the UK, often 40% in the US) and designing it so that it has scope to expand when humidity rises.

I was playing in a nearby pub last night and everyone except the cornet p!ayer complained when their instruments went out of tune as the rains arrived outside.

 

[DavidJHolmes]

Thanks for the replies guys. I don't know why but I thought the stuff from the modelshops would be quite stable and flat. Maybe because the models are quite small and any movement would be pretty bad for the model. My workshop is quite warm. Its very well insulated and very easy to raise the temperature to too warm, but I am careful at what point I glue up. I've only really used MDF but I want to start using hardwoods, I thought this would be a good start, maybe a bit of a complicated start! Ive left the last two pieces laying flat to see if they move anymore either for the better or worse.

I thought of using a sled through the planar, i was going to have a gander on youtube to see if it was possible.

 

[ED65]

...after removing from the packaging I left it in the workshop until I had time to come back to it. I've picked it up today and its cupped, bowed, twisted and not much use for making a box. In fact I've tried and its not good. I'm pretty miffed as it wasn't particularly cheap.

Did you lay it flat on your bench after it arrived? That could have been a lot of the problem if so since the top face could dry out, or get wetter, much more easily than the underside in contact with the benchtop.

Although many frown on this it is often possible to salvage warped stock, for example by dampening and then clamping flat (or slightly bent to the opposite side, to allow for spring-back), or with cupping dampening one side and putting the board outside in the sun on the lawn. This works with much thicker boards than 3mm where there's much more strength in the wood so it wouldn't take much with thinner stuff. It sounds like you've already cut it up, and the smaller the pieces the easier this sort of flattening can go.

...but my thicknesser only planes down to 5mm (it's the Titan one from Screwfix).

With pieces of the very modest sizes you're dealing with here this screams hand tool to me. You can plane down a couple of mill of thickness on smaller pieces of hardwood in no time at all, and you'll end up with a much better surface besides, at best requiring no sanding at all.

What would be the correct procedure if I was to cut my own with regards to drying out the wood? i.e. can I cut it from the timber yard straight away or do I leave it in my shop for a period of time and then machine it to dimension?

Regardless of when and how you get the wood down to final thikcness I think with very thin stock it's worth storing it with much greater care than normal, if necessary stickering it in a small stack off to one side, with a weight on top.

If you've only just re-sawn the wood and you intend to use it a few hours later or the following day some will store it inside a bin bag and apparently this can also greatly help in preventing warping from unequal drying out.

 

[DavidJHolmes]

...after removing from the packaging I left it in the workshop until I had time to come back to it. I've picked it up today and its cupped, bowed, twisted and not much use for making a box. In fact I've tried and its not good. I'm pretty miffed as it wasn't particularly cheap.

Did you lay it flat on your bench after it arrived? That could have been a lot of the problem if so since the top face could dry out, or get wetter, much more easily than the underside in contact with the benchtop.

Although many frown on this it is often possible to salvage warped stock, for example by dampening and then clamping flat (or slightly bent to the opposite side, to allow for spring-back), or with cupping dampening one side and putting the board outside in the sun on the lawn. This works with much thicker boards than 3mm where there's much more strength in the wood so it wouldn't take much with thinner stuff. It sounds like you've already cut it up, and the smaller the pieces the easier this sort of flattening can go.

...but my thicknesser only planes down to 5mm (it's the Titan one from Screwfix).

With pieces of the very modest sizes you're dealing with here this screams hand tool to me. You can plane downloaded n a couple of mill of thickness on smaller pieces of hardwood in no time at all, and you'll end up with a much better surface besides, at best requiring no sanding at all.

What would be the correct procedure if I was to cut my own with regards to drying out the wood? i.e. can I cut it from the timber yard straight away or do I leave it in my shop for a period of time and then machine it to dimension?

Regardless of when and how you get the wood down to final thikcness I think with very thin stock it's worth storing it with much greater care than normal, if necessary stickering it in a small stack off to one side, with a weight on top.

If you've only just re-sawn the wood and you intend to use it a few hours later or the following day some will store it inside a bin bag and apparently this can also greatly help in preventing warping from unequal drying out.

Thanks for the reply. I opened the pack and left them stacked on the bench so perhaps this wasn't good. I'll try dampening them slightly, I have two left and they're not much use at the moment so may as well experiment.

I might try some thicker wood to practice and then work to the thinner sheets. I can't really decide how to tackle it.

 

[profchris]

Thanks for the replies guys. I don't know why but I thought the stuff from the modelshops would be quite stable and flat. Maybe because the models are quite small and any movement would be pretty bad for the model. My workshop is quite warm. Its very well insulated and very easy to raise the temperature to too warm, but I am careful at what point I glue up. I've only really used MDF but I want to start using hardwoods, I thought this would be a good start, maybe a bit of a complicated start! Ive left the last two pieces laying flat to see if they move anymore either for the better or worse.

I thought of using a sled through the planar, i was going to have a gander on youtube to see if it was possible.

Don't confuse "warm" with low humidity. Today it was around 20C here and at least 80% humidity.

I've found that thin plates tend not to distort permanently, but return to their former shape once humidity is back to their "natural" level. If we ever get a run of dry days you might find they're flat again.

But flat sawn boards (non-vertical grain) will always be problematic as the wood will try to curl even when made into a box. How big are these boxes? Small is less risky.

 

[NazNomad]

I'd be interested to hear how the luthiers on this forum deal with thin workpieces...

... with copious amounts of reinforcement. :-D