LumberJocks

Lap Desk - Roasted Maple Brittleness issue

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Project by linjay posted 01-29-2016 10:36 PM 736 views 0 times favorited 4 comments Add to Favorites Watch

The dark wood in this item is roasted maple. The light wood is curly Maple.
I made a jewelry box (http://lumberjocks.com/projects/181466 ) with similar materials. In the write-up I mentioned that after maple is roasted it isn’t really maple anymore. The roasting process makes it quite brittle and can also initiate internal shrinkage cracks. One of the roasted maple strips in this lap desk actually fractured about 3 weeks after it was finished. The fundamental driving force was probably uneven expansion between the two materials. But regular maple would normally tolerate these stress levels.
A contributing factor could be that this strip had a very small cross section—about 3/16’ X 1/4”. The 2nd picture shows this fracture in more detail. It goes right across the piece from one glue line diagonally across to the other. The cause of the fracture also could be due to an initial fault in the material which propagated—bad luck. So far the jewelry box top has not had any fractures. The cross section in it is about 3/16×3/8”.

-- It's easy when you know how - but that's the hard part. Ontario, Canada





4 comments so far

View bushmaster's profile

bushmaster

1365 posts in 1747 days


#1 posted 01-29-2016 10:55 PM

Very nice box even if part of it was roasted. Interesting concept. Someone else posted a project made of popular that was roasted or baked, Instead of white it was black. Would be interesting to learn how they do it and try it.

-- Brian - Hazelton, British Columbia

View bearkatwood's profile

bearkatwood

1205 posts in 476 days


#2 posted 01-30-2016 02:06 AM

We made a desk last year that had smoked/or roasted bamboo, so I completely understand the brittleness issue. Doesn’t look like it gave you too many troubles, the lap desk turned out great. Very pretty.
We made two of them. Roasting the bamboo made it turn into just a grassy material that was very frail and brittle.
Here is the desk we did.

-- Brian Noel

View drobertson's profile

drobertson

57 posts in 2581 days


#3 posted 01-31-2016 04:49 AM

Hey, good to see other people roasting wood. I have enjoyed some of the effects I manage to get with the process.

One interesting thing about the wood is that after cooking it many of the compounds in the wood responsible for warping are gone. It is actually more dimensionally stable than before cooking it. The downside is the process also makes the wood more brittle, which it sounds like you discovered. The other issue I have had is the process of cooking should be done low and slow or the heat will warp/crack the wood you are working on.

My approach is to take the rough parts I intend to heat treat and wrap each one in several layers of aluminum foil. I then make sure my wife will let me use the oven for a day or so (important step). I set the oven on 160 and slow roast the parts for at least 12 hours. This temp doesn’t actually do much to the wood except dry it out. I then slowly step up the temp by 20 degrees every 15 mins or so until I hit my target temp, normally about 360-400. The parts then roast for roughly 2 hours at that temp.

Note – this is all vodoo so you need to do lots of tests on different types of wood. I have had everything from great results to just tossing the wood after. Take notes as you do different woods, it will help you a lot later.

Here is a trick that I use on some pieces that I am worried about. The wood I bake are somewhat small pieces, so I am not sure how this would work on a table or something like that. While the wood is finishing baking I prepare a mix of 2 part 1 hour epoxy mixed with about 30% – 50% (by volume) acetone. I take the wood out and let it sit long enough for me to be able to hold it. When I can handle it I immerse the rough parts in the epoxy/acetone solution. If the parts are super hot expect some bubbling, but this normally isn’t a big problem.

The thinned epoxy will go right through the wood and the rapid cooling seems to suck it in faster. After 20-30 minutes in the solution I take the parts out and wipe them off and set them out for drying. The epoxy won’t set until the acetone is died out and this can take a day or two. A fan helps.

Bubbles of acetone and epoxy will come out in places, so I use this on rough cut parts. Once the epoxy has dried the wood is extremely solid and tough. At this point it seems to have great dimensional stability. Even soaking in water doesn’t do much. The wood still works very well, but is harder and heavier than before, mainly due to the epoxy hardened in the wood. This pretty much fixes the brittleness issue and in my opinion helps to give the wood some depth.

A few things to note. Epoxy resin loses some of its strength when you add that much Acetone, but I am doing this to fill the wood, not to attach it to anything, so that doesn’t bother me. You can keep the acetone resin mix for a week or two and it will still work, but the longer it sits the more the epoxy is breaking down. Eventually it turns cloudy and just doesn’t seem to work anymore.

View drobertson's profile

drobertson

57 posts in 2581 days


#4 posted 01-31-2016 05:04 AM

I got too excited about someone else using baked wood to mention this before. Great work, it really came out nice. As I browsed through your other posts I was very impressed with your skills.

Please keep sharing.

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