# Pantograph problems



## Alchymist (Jan 2, 2011)

Looking to build a pantograph driven router when the weather warms up, so I started with a wood mock up of the pantograph, and it's proving maddening. 

Nowhere on the internet can I find a good description of the arm ratios, so I winged it. i came close to the ratios I wanted on the first or second try, but no matter what ratios I use, a straight line on the tracing results in a curved line on the work table. 

I then copied the dimensions from a supposedly working unit found on the internet, seen here:

http://www.ies-math.com/math/java/geo/panta/panta.html

Guess what - curved line on the pen trace. Anyone with any ideas? I was assuming that with, say, a 3" line on the pattern, and a 2:1 ratio, I should get a straight line 6" long. Am I making an ass out of Um and me?


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## woodnthings (Jan 24, 2009)

*that thing just doesn't look right*

The pivots seem to be in the wrong places...pivot point, drawing point etc...
Take a look at this Video. The guy is annoying, but the mechanism works:

https://www.youtube.com/watch?v=6ph5VPuhO9s

Probably better:
https://www.youtube.com/watch?v=4S2VqNgnYSg


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## epicfail48 (Mar 27, 2014)

http://woodgears.ca/pantograph/index.html
http://woodgears.ca/pantorouter/index.html

Dunno about the ratios, but either of those should help give an idea of construction


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## Alchymist (Jan 2, 2011)

[/QUOTE]



epicfail48 said:


> http://woodgears.ca/pantograph/index.html
> http://woodgears.ca/pantorouter/index.html
> 
> Dunno about the ratios, but either of those should help give an idea of construction


Construction at this point is secondary, need to get the straight line problem figured out. I have watched the videos from woodgears, but that app isn't really what I'm looking at.



woodnthings said:


> The pivots seem to be in the wrong places...pivot point, drawing point etc...
> Take a look at this Video. The guy is annoying, but the mechanism works:


His pivots are reversed because he's reducing, not enlarging. Construction of both look alike except for dimensions ( see pic).

Anyway, thanks all, and i will duplicate the one in the last video and see if it works in a straight line, probably tomorrow.


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## Alchymist (Jan 2, 2011)

Did one with the dimensions in the above video - straight lines! Woohoo! Now to scale it up 1.5 times to get the size I need, and try it again. Only thing I can think of with the other one is the ratio of the sides is wrong.


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## Alchymist (Jan 2, 2011)

OK, brainstorming a little. I measured the distance from the pivot point at the apex of the two long arms to each short arm, and came up with the following:

Ratio Distance Xfactor
1:1--------6" & 6"-------2:1
2:1--------8" & 4"-------3:1
3:1--------9" & 3"-------4:1
4.2:1-----10: 2.4"----5:1 

Wondering why the last line wasn't 10:2.5 for a 4:1 ratio?


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## Alchymist (Jan 2, 2011)

Doubled the dimensions to scale up to what I thought I would need for the machine build.Wound up with acceptable bed size:
X2 = 13X17, X3 = 14X16, X4 = 13X20, and X 5 = 12X20.

The pattern area is a little small at 2.5X4" for the X5, but it's large enough to fit my monogram patterns.

The X2 bed area may have to be cut down, as for some reason the pattern area and the bed area overlap (outlined in red in the pics).


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## Alchymist (Jan 2, 2011)

OK, base bolted together, and 1st 4 parts finished. I'll let you all guess what they are. :laughing: Just know they were a pain to fixture and machine. :thumbdown:


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## Alchymist (Jan 2, 2011)

Base finished. Next item - 1/2" X 36" rods cut & fitted, with 1/4-20 threads in each end. The the real challenge - bearings for the 1/2" rods.


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