Tapered Craftsman Porch Columns

      A long discussion of the materials and joinery needed to reproduce this traditional architectural element. February 5, 2007

Question
I need to build a couple of craftsman style tapered columns for a front porch. I was planning on using solid wood until I talked to a contractor that said he has cut them from MDO plywood. The porch has overhang but the columns will get wet. Whatever material I end up using, my plan is for polyurethane glue and splines or biscuits at the joints. They will be painted, of course. Anyone think MDO is tough enough for this application if the paint is kept up?

Forum Responses
(Architectural Woodworking Forum)
From contributor F:
Don't think you can go wrong with MDO.



From contributor D:
I have used MDO for many years and trust it far more than the alleged "water resistant" MDF that is now available. I have used MDO in columns as you describe, and tons of signs. It is also useful for the box type planters that are popular (though tin liners should always be used).

The resorcinol glued plies and resin impregnated faces (I like the two faced material) make for a great paint surface and a long lasting product. We have used loose splines running the full length for corner alignment at assembly and reinforcement of the mitered assemblies.



From contributor C:
Ditto to all the positives... It's a very dense fir cored exterior ply with a very weather resistant coating that sands and paints well.


From the original questioner:
Thanks for the replies. It will be much more economical to use the MDO. I couldn't find wide enough boards to nest the tapered parts for good yield.

Anyone know where there is a calculation program for the lengths, angles and bevels for four sided tapered hollow columns? I know I've see programs where you can enter the knowns, such as overall height and the width at the top and bottom of the columns, and then the unknowns, like length of the blanks and bevel angles, will display.

Also, the simple way to build these would be to use butt joints. Not sure if I could get the ply edges to paint the same as the paper faces and I am also unsure if the edges could take the weather like the paper faces.



From contributor J:
I have use MDO in the past with good results. You might want to consider Azek sheet goods as an alternative as well. Their glue kind of welds miters and butt joints together and it is solid all the way through, so you'd be able to use butt joints rather than miters.


From contributor L:
You will definitely want to miter these, otherwise the exposed edge will show over time. One trick I used to make the parts before I had a sliding table saw was to make a square edged pattern representing the long point dimensions of the column sides, and then use a large bearing guided chamfer bit to cut the actual pieces. You can rough out the pieces within 1/8" on a table saw and then use the chamfer bit like a pattern bit to true them to the pattern. This also gives you consistently perfect burn-free 45's.


From the original questioner:
That sounds like a good method for 45 degree cuts. Problem here is, even though the columns are square in the plan view, the sides are at a raking angle (tapered) so the bevels will not be exactly 45 degrees. Some serious trigonometry is required to determine the angle of the bevels and the sides' overall length.


From contributor P:
You might consider butt joints; miters tend to open up in exterior use. Also, Extira is another option on the material.

Spreadsheet Calculation Program



From contributor A:
I have made three sided taper columns and used my lockmiter on the shaper. Even though they taper, it is still a 90 degree box. At least it has worked for me in the past. Just a thought. The problem I have with miters, aside from the reasons mentioned, is they take longer to assemble. Lockmiters go together so darn fast, I use them for everything I can.


From contributor W:
Gary Katz has an article on his website on building these columns.

Related article: Tapered Columns



From Gary Katz, forum technical advisor:
I'd use Exira, too, and you don't have to use lock miters. But never miter them. I've done them with butt joints many times. I actually prefer seeing the faint line of the butt joint telegraphing through the paint - so much nicer than seeing a miter open. I use a sled on my table saw and it's fast, easy, and enjoyable work.


From the original questioner:
Yes, Gary, I can understand how you would rather see the telegraphing of a butt joint instead of a seriously open miter. What I wonder is, can the open miter problem be strictly attributed to solid wood that is joined with miters and used in an outdoor situation, or are stable materials such as MDO and Extira also vulnerable?


From Gary Katz, forum technical advisor:
I'm not sure about MDO, but I know that the installation instructions for Extira (and all composite exterior trim products) recommend that you don't use miters. Many of those products move in both directions, as there's no real grain, and miters are prone to failure. I know everyone thinks that miters are the only way to work, and it used to be that you could miter anything and it would hold up - old growth material was like that. But... the telegraphing is minimal. No more than showing where the butt joint is. It's just a sign that the material is swelling and shrinking a little.


From the original questioner:
I am not really concerned about the line between the back of a face and the edge of a side. I am more concerned that the whole thickness of the material's edge will paint and look different that the wide faces.


From contributor P:
As I recall, Extira is uniform throughout. Even if it were like MDF, this is not an issue.


From Gary Katz, forum technical advisor:
That's right, the "end grain" is uniform and paints out smoothly. Just prime it well - the whole thing, front and back, and top and bottom edges, before installing. Three coats. Patience = Durability.


From contributor E:
Extira over MDO.

On the subject of joinery, I'm a "celebrate the seam" type. I'd be more inclined to butt joint the boxes with fronts and backs. (Instead of a "pinwheel" type glue up.) And V-groove the seams so they look intentional.



From the original questioner:
Gary, curious about how priming the insides of the columns affects your joint gluing. Are you masking to leave a pure surface in the glue joint area when Extira is used?


From contributor E:
Not sure if you figured out the miters. This free software should do the trick. I use it often and every calculation is right on.

At WOODWEB's Software Connection, click on "ShopMath."



From contributor E:
Polycut is another good compound miter calculator.


From the original questioner:
Thank you all for your thoughtful replies! Interestingly, for the taper on my columns, (approx 3" for an 83" height), the miter was 44.9 degrees or so, or almost 45 degrees. I guess mine are more of an elephant's trunk than an elephant's leg.


From Gary Katz, forum technical advisor:
Boy, that compound miter idea had me spinning. I'm so math challenged. I figured I'd better not open my mouth with any objection, not understanding the idea at all. I've used my lock-miter bit on several of those tapered columns and even started wondering how or why it worked! "Maybe it didn't," I thought. Thanks for running your 3 inch taper through the calculator! I feel a lot better now, knowing that it did/does work. And now I understand why.

Bill Shaw - talking about coped crown corners - has told me several times that if a corner is out of square 2 degrees, it means several inches over ten feet. I see how that applies to these columns, too.



From the original questioner:
I am fairly good with geometry, but I am challenged a great deal by the trigonometry required to calculate the bevel degrees for compound angles too. But yes, even when a four sided column is square in section, the more pronounced the tapering of the sides, the further from 45 degrees the bevel cuts will be.


From contributor P:
For the math challenged, we usually just cut the shape (pyramids) of the pieces we want at a 90 deg bevel. We then place the bottom of the 2 pieces against a framing square and bring the top together. We then just eyeball the bevel cut, and usually within a couple of tries we are right there. We use the slider or you could use an overshoot board.

This was an interesting discussion about compound miters:
Bevel Cuts for Slope-Side Boxes



From the original questioner:
Thanks for that. Sounds like a good old horse sense method to me.

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