Quality Control for Picture Frames
A lot depends on the desired finish of the frame. If all the frames are to be paint grade, then species is less important. If some will be stain grade, you need to work with the appropriate wood. In my opinion, the actual species used is less important than the way the parts are treated and made. All wood will move. Some more than others, but it all moves.
Start with wood at the proper moisture content. Joint, plane and prep your wood in the normal fashion, but leave it oversized by 1/16" to 1/8". Sticker and stack it for a few days and let it relax. Removing material as you initially prep the stock changes the balance of stresses in the remaining material. Allowing the stock to relax after the initial prep will reestablish the balance and stabilize the final product.
After sitting for a few days, re-mill the stock as if it were rough lumber (face joint, plane, edge joint, rip, etc.). You will be surprised as you re-mill the stock how much it has moved. It should remain stable after re-milling since you removed very little material.
This is the process I use when making furniture. I have a game table I built some years back. The stock was prepped and parts cut in New Hampshire. The piece was actually assembled in the US Virgin Islands after I moved there. The piece now resides in my home in Tennessee since we have moved back to the mainland. All the joints of this piece are strong and the moving parts still operate correctly. Proper prep of the parts is the key.
From Professor Gene Wengert, forum technical advisor:
Contributor R has some good points. Let me clarify that wood will move only if the moisture content changes. So, if you make a frame with a miter joint (the most sensitive joint to movement), the incoming lumber must be with 1/2% MC of the correct value (measure the MC to 0.1% resolution), the shop must be at the same EMC value, once made the frame must be stored in a plastic bag to prevent MC changes in shipment and storage. The correct MC is the value that the frame will achieve in the final product. Modern, good art museums will have a control RH condition... for example, 50% RH which is 9.0% EMC. So, your target is 9.0% MC throughout manufacturing and storage.
A miter can be best made using a special jig and spline. I would suggest that you consider using a hot melt, PUR adhesive (special hot melt, not the hobbits type).
Many woods are fairly stable (teak is quite stable) and some move quite a bit (like oak). You can get info on all major species in the Wood Handbook. See Table 13-5 in the 2010 edition or Table 12-5 in the 2002 edition which is posted here at WOODWEB in the archives.
From the original questioner:
Thanks for the responses. Contributor R, what you are saying about milling the stock twice makes good sense, and I'll probably do that.
Gene, your comments on controlling the moisture content bear on what is probably the most troublesome part of a project such as this. The wood must, of necessity, go from a non-air conditioned environment into an air conditioned environment. I'm in the Dallas, TX area, and my shop is not air conditioned. Over the last few weeks shop temps have been 105 to 110 degrees, and I have no idea what the RH has been. I have only a very small air conditioned room in the shop, hardly large enough to condition the wood before machining and store it afterward. The profiled stock will be delivered to another location, where I'll have a non-air conditioned work area in which to measure, miter, assemble and finish the frames before we attach them to the paintings and deliver them to who knows where.
I think that what I really need to work on is keeping the stock in a controlled environment as much as possible, and minimizing the time spent in the uncontrolled shop floor environment. I'm learning there is a huge difference between this kind of quality craftsmanship (that I aspire to) versus the high volume furniture factory work that I done too much of over the years.
From Professor Gene Wengert, forum technical advisor:
You can make a small plastic walled room and put in a dehumidifier from Home Depot. You can also get an old trailer, paint it a dark color, and use it to keep the wood, as it will run about 7% EMC average. Vent to the outside if it too dry inside. If it averages 7% MC, or 35% RH, you can store wood forever.
You can get an RH instrument from Radio Shack for under $30 that will give you accurate enough readings for this. At least you will know when things are okay or are troublesome.
You indeed are learning that some customers and some uses have extremely high quality demands. Moisture is often a key factor to achieving and maintaining quality.
From contributor N:
If you consider painting the frame, I would use moulding grade MDF. You buy it in fixed lengths - 8, 10 or 12' are standard - so the cost is known. Prime it with an automotive primer to seal the pores.
From contributor C:
I do not know if it is the best wood in your condition or not, but I generally use basswood for making softwood frames. But if you want to make hardwood frames, you can use oak and maple wood.
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