Wood movement, or "The case for Trustone and Acrylics" (rant/ brainstorm) - International Association of Penturners
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Old 10-12-2009, 11:44 PM   #1 (permalink)
 
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Default Wood movement, or "The case for Trustone and Acrylics" (rant/ brainstorm)

OK, I'll try to take some pictures to show what I'm talking about, but my current camera doesn't exactly take Macro pictures very well.

AAAnyway, I'm looking over my pens for sale this morning, and a quilted maple (?) sierra I did a few weeks ago now has spider webs cracks all over the finish. It's solid, and stil 2-3 inches away you can't see them over the shine in the finish. BUT, they're there. And I swear the pen was fine on Thursday (I'm been monitoring my wood pens to see if any finish issues come up- too bad I found another one). I'm going to toss my old bottles of CA, even though I STILL don't think that's the culprit, better safe than increasingly frustrated.

Looking at the pen closer, I see the brass tube popping out from the edge of the blank! Meaning, it looks as if I didn't insert the tube all the way in, and it's no longer flush with the wood. I know it WAS flush when I installed it- it's not a huge amount, but I'd have noticed that, and I would have trimmed it long before I'd have even turned the pen. The blank is cut along the grain, so in theory there should be NO movement along the length of the tube. The bottom part of the tube is perfectly flush with the wood, so to me the only explanation is that the blank shrunk length-wise and the metal brass tube is now longer than the wood blank. The cracks in the CA finish must be buckling from the wood contracting.

I can't remember if I used CA or poly glue, but I glued up the blank some time ago. The blank was defintely dry when turned. I turned it at the same time as a lof of other blanks. I sanded to about 400 grit, then used BLO, burnishing the oil into the wood. Then, I let the blank sit for about 2 weeks, to allow the oil to dry so it wouldn't affect the adhesion of CA to the wood. Then, I finished with CA.

Where did I go wrong?

Aside from never using wood, I'm wondering what I can do to prevent this. I'll try to save the blank, but it's really frustrating to turn the CA off, resand, and build up an even thicker layer of finish. It's a nice blank, but 4 out of 5 times I end up scraping the blank and starting over....

Here's my (crazy) idea... Stabilize all blanks. Even those that probably don't need it. The biggest thing is, I've done a few trys of stabilizing some blanks, and when I've added dye to 1) dye the blanks, and also 2) see how deep the stabilizer is penetrating, it seems like it's not going in very far at all. I'm using Acetone/ plexi with vacuum, to about 20" Hg. I let it soak for at least 3-4 days. Still didn't get great results. So, here's the crazier idea- why not stabilize after I've turned the blanks down? If not to final diameter, when I've close? That way, it'll soak in almost to the depth of the tube. But if I'm using acetone, I can't use CA- I'd have to use epoxy or poly. But then again, will the acetone dissolve the glue? Can I turn the blanks without installing the tubes, and then stabilize, then glue the tubes in, then turn to the final diameter?

I'm tired of wasting time/ CA/ wood on these issues. I LOVE the look of wood, and I think people like them more than the acrylics I've gotten so far (yeah, haven't tried the really fancy custom stuff), but I'm running out of patience. I'd rather introduce 2 or 3 more steps, some additional time, and then have perfect results and longevity than do what I'm doing now and pray the blank doesn't go south.

What say you all?
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Old 10-13-2009, 12:11 AM   #2 (permalink)
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You have run into a problem that has been around since furniture has been made from trees! One thing most casual users of wood don't realize is the power of nature at the molecular level - grossly underestimated!

Not all woods move at the same amount. even within species. In woodworking theory since plywood does not move much and since laminations of 1/16 do not move, it stands to reason that wood only 1/16 to 3/32 in thick glued onto a tube will not move either, but they do. This happens more in a work shop than a heated and air conditioned room where humidity is controlled and not allowed to fluctuate considerably. In a heated and AC room that is turned off at night, then humidity fluctuates wildly in 24 hour cycles in those cases.

To understand this (maybe) - for those that have used wooden handled hammers for decades, think of the handles that come loose. The reason that they come loose is that over the course of two years or so, the humidity changes causes the wood to swell microscopically and shrink microscopically. When it swells, the cell walls in the outer layers are crushed and those cells do not respond to its original shape and size when humidity is decreased, creating space - i.e. loose handle. All because of humidity changes. Very few people think of the power of expansion and contraction on such small items like hammers or pens for that matter, but it happens.

Adding this in later: There are two thoughts that are on my mind about this problem:
1. that your burnishing the wood with BLO caused more of a moisture to build up more than expected. High heating that comes from burnishing and the subsequent cooling will pull moisture in. This will take the temperature range from probably 120 (burnishing) down to a 40? low. That is an 80 temp range with humidity involved. With a cool dry night in the fall in Minnesota, I can imaging that the humidity will drop down below 30%.

2. IF you had a freezing night and the blank was exposed to that, then a combination of all would be my guess.

Stabilizing is the best bet. Don't forget that even kiln dried wood when exposed to high levels of humidity will increase its moisture content over a few days to weeks.
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Old 10-13-2009, 07:16 PM   #3 (permalink)
 
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Default Shrinkage - not just a problem after swimming

Figured/burled/quilted wood WILL move around after it's turned. "Wet" wood is of course worse than seaoned.

Wood will also shrink longitudinally when it dries. I think you maybe had high(er) moisture content when you turned this pen and it dried out and shrank on you.

I once made a couple of pens that had to be ready on short notice without really enough drying time on the blanks. I drilled them and glued the tubes, then baked the blanks for a couple of hours at 170 degrees before trimming the ends. Worked just fine, and these were highly figured/burled beechwood (beech is very prone to shrinkage).
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Old 10-13-2009, 07:50 PM   #4 (permalink)
 
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The idea that wood does not shrink along it's grain is not correct. Wood shrinks and expands in width thickness and length. but non of them by the same amount.
My answer to the problem you are having is to use only stabilized woods for my pens. Stabilizing is the closest thing I have seen to taking out woods movement. Otherwise wood is going to move no matter what you do. Having a top notch glue job where the brass tube is concerned is also a big help but not a sure fire prevention. I gave up on raw wood pens when i had a whole bunch of them develop cracks, gaps or other problems just as yours have here.
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Old 10-13-2009, 07:55 PM   #5 (permalink)
 
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If you go the route of stabilizing all woods, you will miss out on a number of beautiful timbers, including most rosewoods, lignum vitae, snakewood, thuya and many more. Of course, 99% of all pen sales are plastic, so eliminating the problem areas might be your best bet. Tough call.
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Old 10-13-2009, 11:42 PM   #6 (permalink)
 
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Old 10-14-2009, 09:31 AM   #7 (permalink)
 
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Wood shrinkage along the grain is almost nil for wood that has reached EMC. One big exception might be wood near the pith, burls, or reaction wood that has not reached EMC. Most of the cracking appears during drying process and before you turn.

I have seen brass while turning and sanding a blank on the lathe. Really thought those blanks had reached EMC. Could be just a lousy blank too. That is another reason for buying extra tubes.

If wood is cracking after completion (finish applied & assembly) can only assume wood had not reached EMC, or moisture exchange penetrating wood. Finish not slowing down moisture exchange.

I have cracked blanks during assembly process had nothing to do with EMC of the blank. I have also had spalted blanks crack and chip off while turning. Know what did wrong!
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Old 10-14-2009, 09:53 AM   #8 (permalink)
 
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I can give you a solution to the length. When squaring the ends, don't make them flat. I make the ends slightly concave. Doing it prevents exactly what you are experiencing, as well as reducing the effect of trimming the brass on length specific kits.
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Old 10-17-2009, 12:51 PM   #9 (permalink)
 
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Quote:
Originally Posted by Russianwolf View Post
I can give you a solution to the length. When squaring the ends, don't make them flat. I make the ends slightly concave. Doing it prevents exactly what you are experiencing, as well as reducing the effect of trimming the brass on length specific kits.
I can definitely do that. However, the main issue for me is the finish. It looks good from any decent length, but there are a bunch of cracks do to the contraction...
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