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Sunday, July 23, 2017

Using Attach Canvas in Fusion 360 to Find an Unknown Measurement

For the last few weeks, on my spare time, I've been creating models from scanned prints in Fusion 360.

Most of these prints are produced in the 1940s, and they border on artwork.  When an drafter nearly
80 years ago could accomplish with pen and paper was impressive.  They were certainly masters of their
craft!  You can see a sample of a similar drawing here

How can you find the missing dimension? 
But a challenge I encountered was one that even modern users of 2D drawings encounter.  Missing

In some cases, the missing dimension was a result of a drafting error, in most cases, the dimension
was referenced on a different drawing that was unavailable to me.

But it doesn't matter how the dimensions ended up missing, if they can't be found or derived.  Without the missing dimension, creating a model from the drawing becomes much more challenging.

Fortunately Fusion 360 has a nice tool that makes finding this dimensions pretty simple, as long as
you have a single dimension, and the drawing is consistently scaled. 

How do you do it?  Here's how I was able to figure out what that phantom dimension.

Convert your drawing into an image file, a *.png, *.jpg, *.jpeg, and *.tif are all formats you can

Now this image can be imported using the "Attached Canvas". icon.

Fusion 360 will want to know which plane you want to place the image on, and will also want you to browse for the image you want to insert.

Once an image and a plane are selected, you'll have an opportunity to scale the image, using either the handles or in the dialog box.  You can scale it here, but there's a step coming up where it'll be easier to scale the image accurately.  In my case, I used this yet to be seen step.

The Attached Canvas Preview
The drawing will import onto the Fusion 360 canvas, but it's not calibrated.  It's up to us to make sure the scale of the drawing  is 1:1. . 

I recommend re-positioning the attached image easier to measure.  Once that's done, locate the "Canvases" folder in the browser.  Right click on it, and choose "Calibrate".

This step gives you the opportunity to measure a known value on the Attached Canvas.

Choosing the calibrate option will allow you
size the imported image. 
Returning back to the situation I found myself in, The drawing I was reproducing had edges I with dimensions I could use, so I just picked an edge with a dimension, and chose the extents of the dimension for scale.

In the case of my drawing, the dimension I chose was 5 inches.  Naturally, the calibration the dimension on my canvas, but trust me!  It's 5 inches!

Calibrating the image using a known edge.
The image will resize according to that known dimension, and if the drawing with a consistent scale, measurements can be taken from any part of the drawing and a reasonably accurate measurement can be made. 

A measurement taken to obtain the part thickness
By using this method, the dimensions of the part can be obtained from the drawing, and the drawing turned into a 3D model.  

But of course, it's not all a walk in the park. There are some things to be aware of going in.

You've already seen me use the phrase "consistently scaled".  In other words, the drawing has to be created to some sort of accurate scale.  If it's sketched to different scales in the X and Y axis, it will be difficult, possibly impossible, to get good dimensions.

I've also used the phrase "reasonably accurate".  That means you can't quite get to the last decimal point of your measurement.  But you can get close enough to determine many measurements.

For example, if you measure .193 on a part that can be expected to be a standard thickness, then you might be looking at a thickness of .1875 inches.

But even if not perfect, this method can get you exactly what you need when no other methods work.

So give it a try!

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