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Join Date: Apr 2012
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# how to calculate the angle practically ?

07/28/2012 6:09 AM

I have to measure the angle that the knife makes with the rotating drum.
Please guide me to do so. Searched net but i think , i was not asking the right question in google.

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#1

### Re: how to calculate the angle practically ?

07/28/2012 8:03 AM

Create a template using a suitable material, such as aluminum plate or acrylic sheet.

Take a sheet of the material and draw the cross-section of the drum on it, and mark a radial line from the center of the circle. Carefully cut-out the section shaded gray and place this in contact with the drum. Then use a protractor, or whatever angle-measuring device you have that is convenient, to measure the angle between the radial line and your knife. The total angle will be this angle plus 90 degrees.

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#2

### Re: how to calculate the angle practically ?

07/28/2012 8:13 AM

draw the cross section of the drum on it and create a template ? doesnt seem right. the drum is 119" in dia.

some other method please . like water balance etc ?

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#3

### Re: how to calculate the angle practically ?

07/28/2012 9:35 AM

Just use a long straight edge, laid out as Usbport suggests and measure the angle between it and the knife.

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#4

### Re: how to calculate the angle practically ?

07/28/2012 10:58 AM

The diameter is pretty important info, and there was no indication the drum was that big. But Lyn's advice is good; use a long straight edge with a 59.5 inch radius to draw the curve of the drum. Anyone with basic carpenter's skills and tools can help you with this.

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#5

### Re: how to calculate the angle practically ?

07/28/2012 12:14 PM

Or, if this contraption already exists, just tie a string around the center shaft and stretch it tightly so that it intersects with the blade contact point and measure that angle.

Seems simple enough.

This assumes that the drum exists and you don't have any drawings of the device.

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#6

### Re: how to calculate the angle practically ?

07/28/2012 1:08 PM

Lay a straight edge on the drum so that the contact point is at the knife contact. This is a tangent to the drum, measure the angle. Measure the angle of the knife and with a little addition and subtraction you have the answer.

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#7

### Re: how to calculate the angle practically ?

07/28/2012 3:30 PM

thank you so much guys !!

next time i will try to put a autocad file ! i think cr4 must make it possible to change .dwg file to .jpeg format !!

:)

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#8

### Re: how to calculate the angle practically ?

07/28/2012 4:33 PM

You can always do a screenshot of your cad drawing, which yields a .bmp file. There are various ways to convert that to a .jpg, including Windows/Accessories/Paint.

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#9

### Re: how to calculate the angle practically ?

07/28/2012 10:51 PM

Or use Windows Snipping tool... This yields a .jpg

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#10

### Re: how to calculate the angle practically ?

07/29/2012 5:18 AM

Since you know the diameter, (119") then the drum circumference is : 119 x 3.1416 =373.85 ".

Determine the Top point of the drum using a level or other instrument, and lay a small rope from this point to the contact point of the knife, measure the rope, then finally multiply the length by 373.85 and divide by 360 you get the angle in degrees.

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#11

### Re: how to calculate the angle practically ?

07/29/2012 9:19 AM

Maybe this will work for you:

The calculation for a sector length is --> S = R x Theta (in radians)

S = sector length

Theta (in radians) = Degrees x pi/180

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#12

### Re: how to calculate the angle practically ?

07/29/2012 2:22 PM

It is hard to directly measure angles like this without special equipment. You can calculate the angle more precisely from linear measurements by using using the Law of Cosines, which in this case can be written R^2 + B^2 - 2RB(cos A) = (R + D)^2. R is the radius of the drum, B is the length of the blade, and D is the distance between the back of the blade and the nearest point on the drum. Solve for angle A. The angle you asked for is 180° - A.

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#13

### Re: how to calculate the angle practically ?

07/29/2012 9:33 PM

Mount a laser to shine a beam parallel to the blade so it reflects off the drum. If the drum is not reflective, wrap a reflective ribbon around it. The angle between the incident and reflected beams can be measured with a protractor.

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#14

### Re: how to calculate the angle practically ?

07/30/2012 10:33 PM

Modern Technology does make this to easy.

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#15

### Re: how to calculate the angle practically ?

07/31/2012 7:52 AM

Another way to do this is to extend the knife line onto the side of the drum with an appropriate marking tool, like a pencil or felt-tipped pen. This creates a 'chord'.

Using a carpenter's square find the centerpoint of this chord, and draw a line perpendicular to this chord out to the edge of the drum.

Then rotate the drum so this line and the knife edge meet.

Then draw another line extending the knife line onto the side of the drum. The angle between these two lines, A, is the angle you want. (Or, this angle plus 90 degrees, depending on how you define the angle.)

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#16

### Re: how to calculate the angle practically ?

07/31/2012 5:21 PM

i assume the trunks of wood? being cut are not pre-perfected polished surface .. cylinders (?? Ø6m or Ø3m truncks .. WTH) .. it's "easy" to calibrate* your apparattus so that from it's position you already know the "current diameter of the trunk and the angle of incident" .. now how many of you loose the job if you set up such an automated "power station" . . . i remember such stuff it's like a small dam of a small river ... where downstream is an operator pathway ramp ?? two of such side by side ??? she-boss spirit of a tree or a money or both by occasion ... (why the society has a second face hidden somewhere .. most always .. <- doesm't apply for kids (not that i remember any examples)) . . . yo, a technical question* (muh-hah)

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