Tapered column - How To


PeteJr

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I'm looking to make this tapered 8 sided column for a table I'm building.

Anyone know how to calculate the taper and miter angle based on the overall length of the column?

I've read that a bird’s-mouth joint can be used as an alternative to a mitered joint for columns however I'm not sure this works on a tapered column.

 

Pedestal Table (1).jpg

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Draw 2 'donuts' on a sheet of paper, scaled (or full size) to represent the ends of the column. Divide the concentric circles into 8 equal parts. Draw cord line between each point where the 8 radial lines cross the circles. Measure the length of a cord on the outer circle of each donut. These dimensions represents the face width at each end of the boards that make up the column. Center the dimensions on each end of the board, and draw a connecting line down each side to show the face taper. To get the edge taper, divide a 360* circle by the number of segments, then divide by 2, because half the taper is cut from each adjoining board. So, 360/8=45, 45/2=22.5. Set the tilt of your saw blade to 22.5*, then cut along the face angle line you drew.

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He has the layout method right ! I will add one step.  Make a template or better yet make a sled to cut the tapers. I use those auto adjust toggle clamps to hold the board in place. I switch the clamps from jig to jig by using round head screws in every hole. You would need to have a stop for the first cut and then after cutting all the boards a second stop to position them for the final cut. 

Cut a spare piece just in case.

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1 hour ago, wtnhighlander said:

Draw 2 'donuts' on a sheet of paper, scaled (or full size) to represent the ends of the column. Divide the concentric circles into 8 equal parts. Draw cord line between each point where the 8 radial lines cross the circles. Measure the length of a cord on the outer circle of each donut. These dimensions represents the face width at each end of the boards that make up the column. Center the dimensions on each end of the board, and draw a connecting line down each side to show the face taper. To get the edge taper, divide a 360* circle by the number of segments, then divide by 2, because half the taper is cut from each adjoining board. So, 360/8=45, 45/2=22.5. Set the tilt of your saw blade to 22.5*, then cut along the face angle line you drew.

If I'm understanding this properly the face taper is a function of the diameter of the column at each end and the edge taper is always 22.5* for an 8 sided column.

Now if I want to overall column length to be 24" I have to account for the face taper angle.  It's probably not much in this case because the face taper is a low angle.

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4 hours ago, wdwerker said:

He has the layout method right ! I will add one step.  Make a template or better yet make a sled to cut the tapers. I use those auto adjust toggle clamps to hold the board in place. I switch the clamps from jig to jig by using round head screws in every hole. You would need to have a stop for the first cut and then after cutting all the boards a second stop to position them for the final cut. 

Cut a spare piece just in case.

Oh I'll be cutting lots of extra pieces - perhaps I'll make a prototype out of poplar and refine the jig and my technique.

3 hours ago, highdesertdreams said:

As someone who attended extra (non credit) graduate courses in mathematics for fun this is perfect!

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The math here is simplified if you separate the two characteristics. All the angles will be the same angle no matter the taper. So just build a tapering jig to handle large pieces of wood to the top and bottom widths as needed. Then tilt the blade accordingly. If the angle is right the pieces will fit.

Sent from my MotoE2(4G-LTE) using Tapatalk

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On 4/2/2016 at 3:04 PM, PeteJr said:

Oh I'll be cutting lots of extra pieces - perhaps I'll make a prototype out of poplar and refine the jig and my technique.

I prototype most everything, being still fairly new to this craft.  But I believe that those trees have not died in vain. At least some of them.

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