Question for one of you math wizzards.

[SAA3840]

How can I calculate what the radius of a piece is?

I want to replace all the wood on a 'Buggy Seat' bench. I've attached a picture of it. How can I calculate what the radius of the cut-out that the spring sits in? I haven't a clue.

[Deolman]

To me it looks like it is elliptical. I would take it apart, trace it, cut it close with a band saw and finish it out with a sander. If you really want to try it with the CW, I would trace it onto graph paper first. Then using the grid in designer, try to duplicate it. No matter what, it looks like you have your work cut out for you.

[Router-Jim]

I would measure with a tape:

A. The width of the base where the springs meet the base.

B. The height of the base where the springs meet the base.

C. The height in the middle of the base (narrowest point).


Then I would set Designer so I could view a grid line.

I would make a rectangle who's sides equaled A & B and center it just for reference.

I would choose the arc tool and go from the top left of my rectangle to the top right. The using the grid I would pull the center of the arc down to equal C. At this point I believe Designer will give you the radius of your arc.

HTH

Jim

[brdad]

If it is a consistent radius, there are several online calculators like the one here (http://www.saltire.com/applets/advanced_geometry/three_circle/three_circle.htm).

If you want to verify the consistency, calculate the radius, then cut an arc at the calculated radius out of cardboard, and hold it up against your existing piece.

[AskBud]

I would measure with a tape:

A. The width of the base where the springs meet the base.

B. The height of the base where the springs meet the base.

C. The height in the middle of the base (narrowest point).


Then I would set Designer so I could view a grid line.

I would make a rectangle who's sides equaled A & B and center it just for reference.

I would choose the arc tool and go from the top left of my rectangle to the top right. The using the grid I would pull the center of the arc down to equal C. At this point I believe Designer will give you the radius of your arc.

HTH

Jim
I used something just a bit different:
Design the board the true size.
Measure the length of the ARC.
Lay a ruler across the top of the arc and measure the center depth.
Place a "Temporary" arc on the design to fit those measurements.
Now, draw a Circle that overlays the Temporary Arc
(you will probably need to move the Circle up the design, in order to have the lower part of the circle sit in the temporary arc).
Once you have the circle correctly designed, you may activate the "CUT" command.
Last, delete the Temporary arc, if you wish.
AskBud

[Jeff_Birt]

You could get pretty close with a couple of T-squares. You can find the center of a circle by laying out two chords (line from one point on the circle to another) as far apart as possible, then you bisect the chords and drop perpendiculars from the bisection points. Where the perpendiculars meet is the center point. Measure from the center point to the original piece and you have the radius.

So, layout two T-Squares on opposite sides of your hoop. Our 'perpendicular' lines will be the inside of the vertical parts of the T-Square. The distance from our perpendicular line should be the same distance to each spot where the top of the T-Square contact the hoop. Where the two (inside) perpendicular line cross is the center-point.

I'm sure that was clear as mud so here is an easy way:
Trace 1/2 of the hoop onto a piece of paper. Scan it in to your computer. Make a closed shape PNG out of it. Import it into Designer, re-size it until it is 1/2 the size of the original. Copy it and flip the copy 180 degrees and but them up against each other. Trace the hoop shape with the lines/curve tools in Designer.

[Dyna Rider]

How can I calculate what the radius of a piece is?

.

Hi Mike
if you have Machinery’s Handbook look up Circular Segment. If not just go here www.engineersedge.com/area_properties/circlular_segment.htm . Myself I like Deolmans reply. Also If the legs are thicker then 1” don’t think the machine will cut it all the way through. Secondly if it’s not a circle there’s no constant radii

Bill

[Digitalwoodshop]

Like others have said. Take a ruler and lay it over the top of the wood. Measure the width of the gap and the depth. On my board sample I made the basic cut with 2 lines left and right and then a Arc Tool line. Remembering to connect the lines with the connect tool and seeing the nodes light red.

AL

[SAA3840]

Well I've certainly got a couple of ways to do it. Once I get it all sorted out and made, I'll post a picture or two of the new wood attached to the old bench hardware.

Thanks to all of you.

[acruser]

Lay a straight edge across the arc and measure the depth of the curve or sag (s). Measure the distance on the straight edge where it contacts the arc (d). d/2 = (len). The radius (r) can then be calculated with
r = (s^2 + len^2)/2s. The ^2 means to square the number.

[ChrisAlb]

I agree with Router Jim on this one. The "easiest" way is to use a straight edge and measure the length and depth of the arc.

Set up the grid in Designer to match the nearest fraction on the depth. i.e., if the depth is 2-1/4, set the grid to 1/4".

Attach the ends of an arc to the horizontal center line at zero. Attach each end of the arc half the total length to the vertical centerline and pull the center to the depth. That will get you there.

This can be done for all the arcs on the bench. For the springs, I'd leave the spring in there so you can measure the depth to the bottom of the spring. That notch in the base for the cross strut could make measuring the "wood" a bit tough.