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o.t. a little trig question

Started by Modat22, September 26, 2006, 04:18:47 PM

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Modat22

Does anyone remember how to hand draw an accurate sine wave? I used to be able to do it and I can't figure out how to make autocad do it.

Basically I need to make a couple pipe cutting templates for angled cuts and welds on my log arch.

Example. If you have a 3 inch pipe and you want to make a template for a 90 degree intersection you take the draw a line equal to the circumference of the pipe with is
9-7/16", you then have to find the amplitude of the wave which is equal to the square root of 2 * the diameter of the pipe which equals 4.2426.

offset the base line you drew 4.2426 inches both above and below the base line. Now you draw a sine wave starting with a center crossing on the start of the base line ending with the negative crossing at the end of the line. After the line is drawn you cut out the sign wave and wrap the paper around the pipe and the wave line becomes the cut path.

I can't figure out how to draw that accurate sine wave though.

If anyone wants to know how cut an angled pipe cut template you make the amplitude = the pipe diameter divided by the cosine of the angle.

Ok I know this is all wood related but I figured there might be an engineer type out there that can remember how to manually do this.
remember man that thy are dust.

amberwood

no math solution.

Use a holesaw sized to match pipe1 OD in the drill press and cut the pipe2 with that. make sure you leave sufficient stock for the guide drill to work.

DTR
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Dan_Shade

do you have excel?

it would probably be easiest to do it in there.  I have no idea how to do it in autocad.

if you do it in excel, you have to convert the degrees to radians.

edit: you could play some games stretching the thing to fit onto the paper good enough to trace it to the pipe.

Woodmizer LT40HDG25 / Stihl 066 alaskan
lots of dull bands and chains

There's a fine line between turning firewood into beautiful things and beautiful things into firewood.

Furby

I'm wanna get around all that by bending my pipe......... as soon as I figure out how. ::)

pasbuild

Bring it to your local electrical contractor and ask him ta bend it fer ya furb dats what I did ;)
If it can't be nailed or glued then screw it

bitternut

Modat22 what you need to do is download a free program called winmiter. It will draw a wrap around template for you. You input the diameter of each pipe and the angle. It also will figure in an offset. Pipes can be different size also. Here is the link.

http://home.tallships.ca/mspencer/winmiter.html

I have used it several times. Just print it out on your printer and lay it on your pipe as a template.

Modat22

Quote from: Dan_Shade on September 26, 2006, 08:03:16 PM
do you have excel?

it would probably be easiest to do it in there.  I have no idea how to do it in autocad.

if you do it in excel, you have to convert the degrees to radians.

edit: you could play some games stretching the thing to fit onto the paper good enough to trace it to the pipe.



Didn't think of that, thanks for the idea. I know about the hole saw trick, I wanted to try something different and useful for later projects.

Thanks guys
Sam
remember man that thy are dust.

Furby

Can your electrical guy do heavy wall 3" pipe?

Dan_Shade

a good exhaust shop might be able to help you bending tubing as well.

I'm not sure how good those benders that you get from northern toolhttps://forestryforum.com/board/index.php?action=position"> Note:Please read the Forestry Forum's postion on this company are.  link to northern tool Note:Please read the Forestry Forum's postion on this company pipe bender
Woodmizer LT40HDG25 / Stihl 066 alaskan
lots of dull bands and chains

There's a fine line between turning firewood into beautiful things and beautiful things into firewood.

Furby

Thought about those benders, but at those prices I might as well buy an arch.

Dan_Shade

you gotta know somebody that has one!  you may be surprised at what a good exhaust shop can do, but i'm not sure, they're stuff may not be heavy enough to bend 1/4" tubing.
Woodmizer LT40HDG25 / Stihl 066 alaskan
lots of dull bands and chains

There's a fine line between turning firewood into beautiful things and beautiful things into firewood.

jkj

Quote from: Modat22 on September 26, 2006, 04:18:47 PM
Does anyone remember how to hand draw an accurate sine wave? I used to be able to do it and I can't figure out how to make autocad do it.

In the "old" days, I would write a LISP function to create a curve in Autocad; these days I see Autocad has Visual Basic functionality, which would be easier.  (But I haven't used it, sorry.)

A brute-force but straight forward method for Autocad would be to use the Line command and enter a series of x,y coordinates, i.e., angle,value,  angle,value,  etc.  You could easily calculate the table of values with a calculator or make a list with Excel. 

For example, using Excel, create a column of angle values in column A from zero degrees through 360 degrees with the desired precision, e.g., 0,10,20,30, etc.  (A1=0, A2=10, ... A37=360). If you are familiar with Excel, you can create this table by entering just two numbers and dragging to complete the column.   In column B, create a table of sine values.  Since the sin() function in Excel is in radians, the formula in B1 would convert from degrees, i.e.,  =SIN(A1*PI()/180)

Since the sine values will range from 0 to 1, to make the wave more manageable you can build in a scaling factor.  For example, in some cell, say D1, put some numeric value.  Then the formula in B1 would be =SIN(A1*PI()/180)*$D$1, B2 would be =SIN(A2*PI()/180)*$D$1, etc.  This would make it easy to scale the function to fit the task - just change the number in D1.  To test your table, select both columns and insert an XY scatter chart to display the sine wave.

Then enter the coordinate pairs in Autocad and you will have a sine wave.  Note that you only need to create the first quadrant - the others can be added by copying, flipping, rotating, and aligning.

(Caveat: my expertise with Autocad is many years old so there may be some built-in functions these days that I'm not aware of.  I do this sort of thing all the time using 3DS Max so I wrote software to quickly import tables of values I create with Excel or by other means - perhaps that is easy to do with Autocad.  However, the brute-force method described above works well - I tried it just now to make sure and made a beautiful sine wave.)

JKJ
LT-15 for farm and fun

Modat22

Thanks for the link Bitternut, My XP pro doesn't like the program and crashes when I try to print for some reason. I'll test it on my laptop tonight at home.

JKJ Thanks for the hints, I'm sure I can draw this in CAD if I have the coords list. I'm actually surprised that Cad doesn't have the native ability for sine waves built in but it doesn't. I've been using Cad myself since version 10, the new guys coming into the field are starting to confuse me the way they draw things.

I'll play with excel and see if I can figure it out then transfer these to Cad. These templates would be very useful IMO.

Thanks
Sam
remember man that thy are dust.

KGNC

Modat:
Back in the old days when I was on the drafting board this is what I would do to draw a sine wave.
Draw an x and y axis
At 0,0 draw a circle with a diameter that matches your wave height.
Mark off the circle in equal increments, say 15 degs.
Mark off the x axis in the same # of increments.
At each increment just translate the y coordinate from the circle to the proper x position.
Use your trusty french curve to connect the points.
If you like I can draw you up a sample in acad.

Modat22

Quote from: KGNC on September 27, 2006, 10:22:56 AM
Modat:
Back in the old days when I was on the drafting board this is what I would do to draw a sine wave.
Draw an x and y axis
At 0,0 draw a circle with a diameter that matches your wave height.
Mark off the circle in equal increments, say 15 degs.
Mark off the x axis in the same # of increments.
At each increment just translate the y coordinate from the circle to the proper x position.
Use your trusty french curve to connect the points.
If you like I can draw you up a sample in acad.


Ahh thats the answer to my original question, I used to do this on the board prior to cad and couldn't remember how to do it. Thanks, I'll duplicate your instruction on CAD and see how it turns out.

Thanks
Sam
remember man that thy are dust.

firecord


Timburr

Modat, expanding on KGNC's comment.

If you require a pipe joint with a different angle or a 'swept' bend with a series of joints, then mark off the incremented circle. Draw in a side elevation of pipe showing the angle required, divided by half, below the circle. Transpose y co-ordinates from circle to angle and tranfer x coords. accross to your sine wave. This will result in a much flatter wave form.

We used to use this method for forming grain drying ducting out of sheet metal (no sharp bends allowed). Makes a stronger bend too
Sense is not common

highpockets

Firecord, that metalgeek page is nice. I need to saddle a piece of 6" for my friends wood heater chimney.

Any of yall making charcoal?  What about homemede refractory? 
Louisiana Country boy
homemade mill, 20 h.p. Honda & 4 h.p. for hydraulics.  8 hydraulic circuits, loads, clamps, rotates, etc.

Modat22

I made homemade refractory before but I'll never do so again. Its cheaper for me to buy a 50 pound bag of kiln liner.

I've used high temp chimney cement and vermiculite glass mixed  1 part cement to 3 parts vermiculite.

I have made a bunch of charcoal from creek willows (its really clean burning)
remember man that thy are dust.

Quartlow

You guys are making my head hurt  ???  ??? Maybe this will help too

http://harderwoods.com/pipe.html
Breezewood 24 inch mill
Have a wooderful day!!

SPIKER

I think you should be able to draw a circle in autocad, 1/2 the wave lenght you want, draw a bysecting line through/over it and cut on the line then move 1/2 of it over and attach end of right lalf to the left half wala sign wave form I think it should be 100% as true sign wave is 360 degrees start to finish correct?

mark M
I'm looking for help all the shrinks have given up on me :o

Modat22

Not a true sine wave that way, KNG's method words great in autocad though.
remember man that thy are dust.

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