Circle help

[Mason Dixon]

How do I divide the inner ring into roughly 3 foot segments with 3/8" spacing in between for joints?

 

The outer ring needs a 40' segment left in place and the rest of it deleted, how can I do that?

 

[ReMark]

These segment lengths are along the arc and not chord lengths right?

[Mason Dixon]

yes along the arc

[ReMark]

Can we get some info on the rings themselves? What are the diameters?

[Mason Dixon]

The smaller ring has a inner radius of 9'-10", the outer is 10'-8"

 

The large ring has a inner radius of 41'-2", the outer is 42'-6"

[ReMark]

An angle of 54 degrees would leave you with an arc segment of roughly 40' (480.66 inches to be exact). That's on the outermost ring.

[CarlB]

If you don't mind working with angles, just use the angle definition formula for an arc;

central Angle = arc length/radius

 

For example to get 3' length on inner circle; A=3'/9'-10" = 36/118=0.30508.

Now multiply by 180/pi to convert to degrees; 17.48 degrees

[Mason Dixon]

Thanks, that helps alot

[paulmcz]

.. and the angle for the 3/8" space in the same circle

= 2* (asin (0.1875/r))*180/pi = 2* (asin (0.1875/118 ) * 180/pi

[CarlB]

Yes if the 3/8" gap is measured straight rather than along the arc, that would be the formula. Except that "asin" (by most ? calculators) gives an answer in degrees, you wouldn't multiply the result by 180/pi.

 

So the "straight line" formula calculates the angle = 0.18208412

the arc formula gives 0.18208405,

so identical for all practical purposes. For larger angles the results will diverge.

[paulmcz]

Agreed 100%.

 

I have 2 - 20+ years old Sharp calculators and they both work in radians, if I want them to.

[Mason Dixon]

They way i've been doing it is to use the equations posted above and enter them into a polar array command but this doesn't seem to have great precision. A lot of rounding up and down on all the numbers. Can a lisp command do this in a couple of clicks? I've never used one, is there a good tutorial going over them?

[paulmcz]

Can you explain in detail what you are trying to accomplish?

 

The 3' arc on the larger inner circle has central angle 4.175 deg (0.073rad). The angle of 0.34rad makes about 14ft long arc on the same circle. So your angle of 0.34 is not for the arc of 3' and is not for the arc of 40'. Something wrong somewhere.

[paulmcz]

Yes, lisp can do this in couple of clicks. Google 'afralisp' to get you started.

 

They way i've been doing it is to use the equations posted above and enter them into a polar array command but this doesn't seem to have great precision. A lot of rounding up and down on all the numbers. Can a lisp command do this in a couple of clicks? I've never used one, is there a good tutorial going over them?

[paulmcz]

http://www.afralisp.net/

[Mason Dixon]

Thanks, I'll check out the lisp site

[eldon]

Instead of all this calculation, I would use AutoCAD's Measure and Lengthen. Saves all the finger work on calculator buttons. It would be necessary to Break the circle first.

[nukecad]

Try drawing any arc at the radius that you need and then using LENGTHEN > Total to change to the required length.

 

Quicker than working out the angles.

 

 

OOPs - I now see eldon already said that.

[JD Mather]

Measure or Divide? Make sure you have a point style you can see. Or, assuming you are going to put other components at those divisions, create a block with the component and use the Block option with measure or divide and select option to align or not as desired.

 

Can you attache a rough sketch of what you are trying to accomplish?

[eldon]

 

OOPs - I now see eldon already said that.

 

I don't mind. There is not a brownie point counter yet

 

 

Measure or Divide?

 

I would use both severally and variedly as the occasion deserved.