Need some brain power better than mine

[jjmarotz]

I am building some roller harrows to hang off the back of my S-tine cultivator that I built from a 15' 3-row tow behind model that I got from my dad after he took what he needed off of it.

Anywho..... I have the shaft, roller circles, and 1.5" angle iron I am going to use. Now my ?.... How do I figure out how to put 5 angle iron press pcs onto a 9" circle and have equal distance between the cross bars? I can easily finger out 4 bars, or 8 bars, but am thinking 5 would be the perfect fit..... I think My brain and math just don't work together so swell

Will put up pics of the entire build once I am done with this project. Was a good winter project to take up my time.

Thanks brainiacks

 

[dcyrilc]

If I'm understanding your question correctly...your looking for the proper angle? 4 bars=90 degrees... 8 bars=45 degrees... 5 bars=72 degrees.

Mark the disks as they are in your first pic, but with 72 degrees between marks.

 

[jjmarotz]

Ya in the 1st pic I marked out for 4 and 8 cross bars. But they will be too close and not allow the roller to "clean out" if dirt clods and rocks get lodged into them. I am thinking that 4 bars may not be enough to bust up the clods.

As for the degrees you state..... well..... that is where my melon shuts down I see where you are getting at but I can't wrap my brain around it

 

[dcyrilc]

How did you establish the lines for 45 & 90 degrees?

 

[Brad_Blazer]

The angular spacing is 360/5 or 72 degrees. The distance between where the leading edges hit is (9xpi)/5 or 5.655 inches. That's 5 and 21/32 inches as you wrap a tape around the arc of the outer edge.

 

[dcyrilc]

My first thought for establishing the angles would be to go to an art supply store and pick up about an 8" clear plastic protractor. Mark a line from center to an edge, lay the protractor on the line with the center on the center of the disk, and mark out 72 degrees. Draw that line and repeat.

 

[jjmarotz]

Just eyeballed things and used a framing square. Each point in pic 1 measure equal 3.5" between points on the outside edge.

 

[jjmarotz]

The angular spacing is 360/5 or 72 degrees. The distance between where the leading edges hit is (9xpi)/5 or 5.655 inches. That's 5 and 21/32 inches as you wrap a tape around the arc of the outer edge.

What the ****?? That just made me feel a tad dumber than when I started:confused2: lol
So you are saying is.... wrap the tape around the outside of the circle and mark every 5 and 21/32" inch and all 5 bars will be equally spaced???

 

[dcyrilc]

My first thought for establishing the angles would be to go to an art supply store and pick up about an 8" clear plastic protractor. Mark a line from center to an edge, lay the protractor on the line with the center on the center of the disk, and mark out 72 degrees. Draw that line and repeat.

Doing the math, you could measure along the edge from the first lin for 5-21/32" for the next line, etc. I used 3.1415 for pi with the formula pi*d for circumference. answer=28.2735" circumference around the disk (28-9/32"). Divide by 5=5.6547" (5-21/32") between marks around the edge.

Clear as mud?

 

[lostcause]

The angular spacing is 360/5 or 72 degrees. The distance between where the leading edges hit is (9xpi)/5 or 5.655 inches. That's 5 and 21/32 inches as you wrap a tape around the arc of the outer edge.

if you don't have a flexible tape handy to wrap around the circle, another option is to take one point at the outside of the circle, and measure from that point to another point along the outside that is about 5 1/4~5 5/16 away. repeat this from each new point and you should find yourself back at the start point. same result, just a different way of measuring. the math behind it is as follows:

chord length = 2*R*sin(A/2) = 2*4.5*sin(72/2) = 9*sin(36) = 5.29 inches

where:
A is the angle (360 degrees in a circle, divided into 5 equal 72 degree segments)
R is the radius (9" diameter = 4.5" radius)
chord length is the straight line distance between two points along the outside of the circle

 

[dcyrilc]

What the ****?? That just made me feel a tad dumber than when I started:confused2: lol
So you are saying is.... wrap the tape around the outside of the circle and mark every 5 and 21/32" inch and all 5 bars will be equally spaced???

Correct. Brad & I both came up with the same measurement. LOL

 

[dcyrilc]

if you don't have a flexible tape handy to wrap around the circle, another option is to take one point at the outside of the circle, and measure from that point to another point along the outside that is about 5 1/4~5 5/16 away. repeat this from each new point and you should find yourself back at the start point. same result, just a different way of measuring. the math behind it is as follows:

chord length = 2*R*sin(A/2) = 2*4.5*sin(72/2) = 9*sin(36) = 5.29 inches

where:
A is the angle (360 degrees in a circle, divided into 5 equal 72 degree segments)
R is the radius (9" diameter = 4.5" radius)
chord length is the straight line distance between two points along the outside of the circle

It's been too many years to remember that formula. I took the easy way out.:laughing:

 

[jjmarotz]

WOW!!!!!! Guess a bit more attention in math classes 20 yrs ago would have paid dividends!!!

This is where I get lost... but I think I am following what you fellas are saying. Thanks!!!!!

 

[Brad_Blazer]

Here's another option. If you inscribe a pentagon inside a 9" circle, the length of each side is 9 x sin(36) or 5.29". That's close to 5-9/32. If it was me I would abuse my digital calipers by setting them on 5.29" and using them as dividers to scribe my way around the circle.

 

[dcyrilc]

WOW!!!!!! Guess a bit more attention in math classes 20 yrs ago would have paid dividends!!!

This is where I get lost... but I think I am following what you fellas are saying. Thanks!!!!!

Brad & I gave you measurements around the outside edge, lostcause gave you the straight line distance across the disk to the same point. Try it out and see how it works.:thumbsup:

 

[Brad_Blazer]

You guys are too fast!

 

[lostcause]

It's been too many years to remember that formula. I took the easy way out.:laughing:

to quote sean connery in one of the raiders of the lost ark movies.... i wrote it down so i wouldn't have to remember. actually, i just remembered what book it was in:

american institute of steel construction - allowable stress design manual, ninth edition, 1989. pg 6-16, properties of the circle.

 

[dcyrilc]

to quote sean connery in one of the raiders of the lost ark movies.... i wrote it down so i wouldn't have to remember. actually, i just remembered what book it was in:

american institute of steel construction - allowable stress design manual, ninth edition, 1989. pg 6-16, properties of the circle.

Cheater:laughing:

 

[DJ54]

This is where an angle gauge would come in handy if you have one.

I would pick one of you marks, any one of them, and mark with an "X" so as not to loose your starting point. Set the gauge at a 90 degree angle, then close the angle 18 degrees, to 72 degrees. Set the gauge on you starting line/mark, then mark at the 72 degree angle mark. Maybe mark that one with an "X" also, so you know it is a 72 degree angle.
Leave the gauge set where it is, and move the gauge to the line you just made. Your gauge is set for the next 72 degree angle to be marked.. Just follow on around, on those new marks.
Basically, you are dividing a 360 degree circle by 5, making 5 even spaces of 72 degrees, or a pentagon.

Been there, done that... An angle gauge, and construction calculator, sure help getting through stuff like this...

 

[Brad_Blazer]

What the ****?? That just made me feel a tad dumber than when I started:confused2: lol
So you are saying is.... wrap the tape around the outside of the circle and mark every 5 and 21/32" inch and all 5 bars will be equally spaced???

That's right. With either method when you measure from the last mark to the start point if it is the same you are golden.