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[Carl Morris]

I have a Pennyhedron that used to be too loose, so I wrapped it in rubber bands and microwaved it 30 seconds or so, and it tightened up.  Now it's too tight.  Well, it's great for developing finger strength, but not much fun for people who don't know how to grab it.  Any suggestions for how to loosen it up?

    -- Carl

[Eric Fuller]

I'd just leave it alone...chances are it will loosen back up on its own for a perfect fit.

[Robert Yarger]

I agree, leave it alone and it should fix itself. If you are in a hurry, put it in the freezer.  That would shrink the wood, and a freezer also removes moisture which would make it even smaller.  However, most likely the puzzle will eventually go back into being too loose again once it matches the temperature and humidity of its original environment.

[Carl Morris]

Hey, you guys were right!  I checked it today and it's fine.  So what happened, does microwaving the pieces make them temporarily swell up a little?

    -- Carl

[Scott Peterson]

Hard to know exactly what happened in your case.  Sometimes I use the microwave trick when gluing.  The microwave excites the glue a little when it is not yet cured, and under the pressure from all around applied by the rubber bands - all the pieces find their home.  I think the microwave helps the glue cure up too.   

  What I'm not exactly sure of is the effect of the microwave on already cured glue.  Does it soften the glue enough to let the pieces move a little closer under the pressure applied from the rubber bands?

If I have a puzzle that assembles a little too tight, I take it to work with me and leave it in the A/C.  I also bring a ziploc bag too.  I check it a few times throughout the day to see if the fit has improved - and when it does, I zip the puzzle up in the bag.  Sometimes this works, and sometimes not...

  One other thought - if you microwave a loose puzzle again, maybe try slipping in little scraps of wax paper between the sliding joints to prevent the fit from becoming too tight during microwaving.

[Robert Yarger]

I think you have to treat a microwave puzzle like you do when you microwave hollendaise sause.  You have to check it every 5 seconds, but even then the effects are temporary.

I don't think that regular wood glue is effected at all by the microwave.  However, if anyone ever finds a solvent for cured wood glue, let us all know.  I'm sure it will come in handy in repair work.

I think that aside from the simple concept of hot things expanding, wooden puzzles in the oven or mircorwave are effected by the heating up of moisture in the wood which makes it swell even after it is cooled.  Also, there is a slight warping component, and wood that is unevenly heated or exposed unevenly to humidity will curl in the direction of that source, but later relaxes.  STill, I am just taking guesses here.

[Canuck]

Cured glue will most definitely be affected by the 'Microwave', I've done it many times in fact.  I wouldn't recomend it, unless you're sure you can live with the potential disaster of it completely coming apart

[Robert Yarger]

I have never put an item into the microwave, but I would assume that it would be the same as putting it in the oven, which I do to cure finishes all the time and never have 0had a problem. 

Do you think the amount of time or degree of heat is a factor, or perhaps just the microwaves affect glue differently than oven heat?  If indeed the microwave dissolved wood glue than that would be handy to know.  I will play around with it for a bit.

[Canuck]

I think the big difference between the microwave and the oven is the 'waves' will 'excite'(as Scott says) the glue, where I don't think that'll happen in the oven.  It's really important to remember that you need to keep the time  in the microwave short(no more than say 10 seconds, of course that's with mine, you may need to decrease/increase the time based on your own microwave)it's quite easy to really heat up the wood, especially anywhere adjacent to a glue joint.

[RKB]

I must run some tests with Titebond, but I know one thing for sure and that is that European (white) glues can be affected with heat AND moisture.

I had some succes in taking antique chairs apart (for repairs) by putting wet towels in the microwave and draping these over the glue joints.

Smaller pieces can be placed in the microwave with a few drops of water over the glue joints. That's definitely better than steaming the whole thing.

[Eric Fuller]

microwaving absolutely softens glue joints, and quite nicely I might add.  It makes them somewhat pliable and with the right design can give you a great fit.

[Carl Morris]

Starting on page 194 of Geometric Puzzle Design, Stuart Coffin writes:

"One very useful appliance in my workshop that I discovered late in the game, but wish I had earlier, is a microwave oven.  It reduces the setting time of glue joints dramatically, especially with dense tropical woods like rosewood.  The individual blocks can be preheated, or placed in the oven after gluing, with or without the jig.  Ten seconds is usually enough -- too long and the joint will be weakened.  Equally useful is the ability to take apart pieces already glued, which typically takes about 30 seconds in my small microwave."

I used a little more than 20 seconds in a small microwave to adjust my Pennyhedron.

    -- Carl

[Robert Yarger]

You guys are brilliant.  Heating up glue definately softens it enough to pull apart.  I thought I was going to have to remachine 20 pieces that I glued in error, but tossed them in the microwave instead.  Worked like a charm and saved me 2 hours worth of work.  Thanks for the tip.