Draw cross-section for tapered leg

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Littlebranch farm
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Draw cross-section for tapered leg

Post by Littlebranch farm »

I am trying to cut a 30 in long leg that would taper from 2 in at the top to 1 inch at the bottom.
I am starting with a 2.5 square blank.
My issue is drawing my cross-section for the 2-rail sweep. I manage to get a tapered leg, but it is not 2 in at the top and 1 in at the bottom.
How do I calculate the height of my cross-section? Do I have to divide my variables by Pi?
If I were working on a flat surface, I would have 1 leg measuring 1in for the top and the
screen grab.png
other 0.5 at the bottom, correct?

4DThinker
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Re: Draw cross-section for tapered leg

Post by 4DThinker »

If you start with a 2.5 square block, then round it to a 2.5 cylinder, you need to tell the toolpath that you want the start depth to be .25" to end up with a 2" top diameter. I prefer to use the moulding toolpath to make tapered legs. Much simpler than dealing with model creation and 3D cuts.
30in tapered leg 4D.jpg
30in tapered leg 4D.crv
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30in tapered leg 4D.crv3d
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4D

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adze_cnc
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Re: Draw cross-section for tapered leg

Post by adze_cnc »

Littlebranch: Do note that your material might be 2.5 inches but your settings tell the program that it is only 2 inches in diameter. If you try to cut the material down by 1/4" (which will get doubled---one for each "side") to get the 2.5 down to 2 inches you're going to end up with something that tapers from 1.5" diameter to perhaps 1/2" diameter as far as the program is concerned.

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SteveNelson46
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Re: Draw cross-section for tapered leg

Post by SteveNelson46 »

Adze is absolutely correct. In order to get a taper from 2.5" to 1" over a distance of 30 inches your profile line needs to have a slope or angle of approximately 1.43 degrees.
Steve

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Re: Draw cross-section for tapered leg

Post by sobfu »

I dont know if this will help but I started making a few tapers for walking sticks and used a flat rectangle from clipart greater than my design area, clipped the model to the design area which takes away the rounded edges. Then I used the fade function of the model which will fade up to 100% of Model thickness. I used the model because it allowed me to add some clipart to the taper stick whereas the moulding toolpath does not.
Capture.JPG
The image shown is unwrapped.

Dave

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SteveNelson46
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Re: Draw cross-section for tapered leg

Post by SteveNelson46 »

To be exact, the actual formula for calculating the angle of the profile or slope is:
angle of line formula.png
The rise = .5"
The run = 30"
so the inverse tangent of .01666 = .9548
Calculated for a 30" length by 2" to 1" diameter taper
4dthinker's vector view is probably easier to understand.
Steve

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Re: Draw cross-section for tapered leg

Post by 4DThinker »

Nice to see some math here Steve.
I learned drafting while in high school, and have used that since then to solve challenges like this. A previous department head was sure I was using calculous to create the complex joinery challenges my furniture design students presented. I didn't have the heart to tell her that all I used was drafting techniques I learned in high school.
4D ;)

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SteveNelson46
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Re: Draw cross-section for tapered leg

Post by SteveNelson46 »

It really wasn't all that difficult. After calculating the slope by dividing the rise by the distance I just used the windows calculator in scientific mode to calculate the inverse tangent.
Steve

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Re: Draw cross-section for tapered leg

Post by rscrawford »

Start with Z0 at the centre of rotation, and X0Y0 at the one end of blank (spindle set up above X0Y0). Turn spindle on, set feedrates, etc. Use a 1/2" ballnose.


G1 Z1
G1 Y30 Z0.5 A172800

This will give one continuous spiral down your blank, cutting 0.0625" per pass, from a 2" diameter down to a 1" diameter at the end of your 30".
Russell Crawford
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