Warped frames

[jdbondy]

After visiting a modeler friend recently, I returned to my current project with excitement, only to find that some frames that I had cut out from boxwood sheets several months earlier now show severe warping:

The grain of the wood is of course oriented vertically on these frames. Other frames were cut out with the grain running horizontally, and as you might expect, they warped in a manner perpendicular to these. These frame shapes were cut from a 1/8" boxwood sheet, and they were sanded to a thickness of 3/32".  The model is going to be of an 83 foot schooner done at 3/16" scale. The 3/32" thickness of the pieces shown above corresponds to the thickness of the frames on the builder's plans.

So it appears that in order to avoid warping, I will have to laminate 2 layers of 1/8" boxwood together, then rough out the frame shape, then thickness sand the shape equally on each side so that I have fibers of wood running in perpendicular directions surrounding a central core of glue. But I am worried about how much wasted wood that will involve. Plus, when the frames are brought to their proper molded dimensions (on the order of 3/32-5/32"), I am worried that they will still warp because of their very fine dimensions. I really don't want to have to mimic how the frames were built in reality because that would be so much more work. 

Let me know of any ideas you have! I was hoping that the boxwood would be better behaved than this.

 

[Captain Poison]

You Could try to moisten the pieces and press them between two woods, you could leave for 48 hours to ensure that they are completely dry and see the result, If unfortunately you notice the same problem after the process, the solution would be to remake the Parts.

[vossiewulf]

How were those frames stored? Fully seasoned or kiln dried castello boxwood shouldn't do that unless stressed.

[druxey]

How disappointing! My first suspicion would be that the wood was improperly dried or poorly seasoned. Either that, and/or the log the wood was not quarter cut. In my own experience, wood will move where it wants to. You could try the remedy suggested above, but this may prove to only be a temporary solution.

 

In 'real' boats, wood grain more or less follows the contour of the frame which is built in sections. There are no cross-grained areas. This gives maximum strength, as well as minimizes the problem of warpage. Perhaps you might want to rethink how you are going to construct your model.

[Mark P]

Good Evening JD;

 

Boxwood is wonderful stuff! I love its tight grain and smooth surfaces. But it does have its limits, and I would suggest that your chosen method of construction exceeds them, unfortunately.

 

Natural wood, even when kiln-dried, will distort over time if the moisture content in the atmosphere is different to that in which it was previously stored, or to the percentage to which it was dried. 

 

To be honest, cutting whole frames from a single sheet is inadvisable, as it is going to include a variety of short-length grain patterns which will have an inherent instability. The only way to counteract this tendency, and assuming the timber is dried/seasoned to start with, is to assemble the frames and keel quickly and use fairly stout stringers or filler blocks between each frame.

 

Depending upon how much of your frames will be seen, you would probably do better to use plywood up to deck level, and rebate short lengths of boxwood frame into the top of these to form the bulwark timbers. 

 

All the best,

 

Mark P

[Gregory]

( Can't resist.. )

 

Where did you get that boxwood, that you can afford to use where it will never be seen ?

[Nirvana]

Question, was the patterns left on each frame while being stored?
That could be one of the reasons they have warped by moisture.

[vaddoc]

Soak the wood and then compress between two flat surfaces with a significant weight on top as it will be distributed across a large area. It will flatten a bit but not all the way.

 

I ve found that for such purposes, it is better to laminate the sheets that the frames will be cut from. Lamination gives very strong, very flat sheets that resist movement. It is impossible to find flat plywood in the thicknesses we use. If I need a 3.5 mm sheet, I laminate 2 sheets of 1.5 mm each using finishing epoxy resin.

 

I have a whole box of 2 mm maple sheets that I received dead flat and a year later are horribly twisted. I suspect improperly seasoned/kiln dried wood.

 

Regards

Vaddoc

[jdbondy]

Thanks for all the feedback. I am in north Texas, and the humidity does fluctuate between 30% and 100% with passing weather fronts. So that doesn't help. 

 

Since the original post, I took two layers of 1/8" castello boxwood and glued them to each other with wood glue. This was left overnight. I then cut out two frame shapes that approximate my warped frames shown above, then used the thickness sander to bring the shapes to about 3/32" thickness. This was done symmetrically, so the glue joint is in the center of the thickness of each shape. Within hours, these frame shapes had developed significant twist. So laminating two layers is not a solution either, it seems. 

 

I was hoping to build my model in plank-on-frame style, but I am afraid that this means that I will revert to a plank-on-bulkhead method and use basswood for the interior structure, saving the boxwood for planking. It's a little disappointing, because I have builders plans for the model and wanted to take full advantage of that. But Mark P, I think you are right that it was a pipe dream to hope that cutting frames from a sheet would yield flat frames.

 

Nirvana, the patterns were applied with rubber cement. I thought that the patterns could have had an effect but I don't think that removing the patterns would have prevented the warpage.

[mtaylor]

I suggest that if you're going to want frames, use the Hahn method of two layers.   Each layer is made up of 3 or 4 pieces with the joins in the middle of the first piece.   I hope this makes sense...  

 

The closest I can show is these two pics... first the pile of blank parts and then pile of blanks.  The last pic shows how these are overlaid.  I hope this helps.   

 

Edit: These are the frames I used for me Licorne build and there was a long stretch of time between cutting the frames, building them and installing them.  I used cherry for my frames as I needed a lot of wood and at the time, boxwood was twice the price of cherry.

 

    

 

 

 

[druxey]

Laminated wood need an odd number of layers (3, 5, 7, etc.), each layer with grain at right angles to the next. Or - well, you've already discovered the result!  A simplified frame structure such as shown above will work. It's a bit wasteful of wood, though.

 

Do you have any way of modifying and controlling the humidity in the home? Where I live we need a humidifier in winter and A/C in the summer.

[mtaylor]

Indeed the Hahn method wastes a lot of wood.  

[jdbondy]

Mark, how thick were the blanks you used to build up the frames? What frame thickness were you working toward?

[mtaylor]

JD

The blanks were 1/8" and thus the frames ended up at 1/4 inch.   For a look at how I did it, see my Licorne build.   Some others do all the frames first then glue to the keel.  I just glued them as I made them. 

[jdbondy]

Mark, I will be sure to look at your Licorne build. In fact I may have perused it before. My frame thickness would ideally end up at 3/32", so less than half the thickness of your frames. That's a big part of the problem I am struggling with. 

 

But it is fun to experiment with the different possible solutions to the problem: two layers vs three, wood glue vs epoxy, etc. I expect to learn some important lessons by the time I find a solution.

[mtaylor]

JD,

Definitely nose around a bit in the Scratch area.  You can also "fudge" a bit and say go to 1/8" on the frames (1/16" per layer) unless you're leaving some frames exposed and going for historical accuracy.  The "catch" with Hahn is that his framing is his own not historically accurate.  So there's a Catch-22 there.

[jdbondy]

For better or for worse, I have solved my warped frame problem. I created one example frame to test the idea of using 3 layers of 1/32" boxwood. Mark, the 3 layers were composed in the same way as you assembled the patterns for your frames:

While still wet, these were put between pieces of 1/4" basswood sheets, which were then clamped:

A very flat frame was the end product:

A close-up shows the 3 layers laminated together:

So like I said, for better or for worse, looks like I have a solution. And this example is really strong. Do I really want to pursue this route? I don't know...

Thanks for all the guidance!

[Jaager]

JD,

If you pursue this method,  you may find that a frame press a useful tool.

 

I made one from a HF bench top pipe vise - sold by them long ago - and 3/4" plywood  12" x 12".

 

This one is from Amazon and is smaller than the HF model.   I have large dowels at all 4 corners in an attempt to keep the clamping surfaces parallel.  It sits in the middle . The tool looks like a wine press ot 1st generation printing press.

 

Something similar can be made using a pipe clamp.

 

These are sized for 1/2" or 3/4"  central pipes.

[jdbondy]

Here's my next-generation framing press:

It is made of all those books I haven't looked at since medical school and residency! Beneath them, the frame is compressed between two 1/8" sheets.

[jdbondy]

My wife points out that my frame press is way more expensive than the one from Harbor Freight...

[cog]

She may be right, but it looks like there won't be much of a health hazzard ...

[Altduck]

Well, if  you made a career in medicine, you can tell her "Yes, but they paid for themselves many time over"