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View Full Version : Epilog Rotorary Attachment Quandry



Gregg Vaughn
08-19-2008, 7:51 PM
While I'm picking everyone's brains this evening, another challenge is evading me, this one for the Epilog rotorary attachment users ....

When engraving vases on the rotorary attachment I have never quite found the formula for keeping the image at the same scale as the Corel drawing when the vase if not a constant diameter. For example, if the bottom of the vase is 10.5" in circumference and the top is 6" in circumference, how do you determine the height of the Corel sheet so the rotation of the vase causes the original 4" by 4" Corel Drawing to actually be 4" by 4" on the vase?

There must be a way to figure this. I can come close, but I've never hit the bulls eye ....

Frank Corker
08-20-2008, 5:59 AM
I'm with you on this one. If there is a way to get it 100% I'd like to know

Dan Hintz
08-20-2008, 8:30 AM
How much math do you want to do? ;) What I'm about to write assumes that I understand what you're truly asking, and I make no guarantees that assumption is correct.

If the vase's profile is V-shaped (not curved), the math is simple... it's simply a ratio of top circumference to bottom circumference. For example, let's say the top is 6" in diameter and the bottom is 4". that's a ratio of 1.5:1, so the top of the pic needs to be 50% larger than the bottom. Select the entire image and stretch the top (or squeeze the bottom) by 50%. Output that to the laser.

Now, if the vase has a curved profile, you'll need to estimate the change in circumference (unless you intend to do mathematical curve fitting). For example, let's say the top is again larger than the bottom but with a curved profile. Your pic modification will be done in the same manner, but instead of the pic being stretched linearly as you go from top to bottom, the stretch will need to be curved (like a mirror image of the vase's profile). In fact, if you're careful, you may get some great results by taking a picture of the vase's profile and using that as the basis for your stretching outline.

Needless to say, stretching for a V-shaped vase is much easier :p

David Fairfield
08-20-2008, 9:28 AM
Can't help with Corel, and Dan already laid out the math. I'd only add that it helps to measure the glass circumference at the cross section where it meets the rotary tool's drive wheels. In Adobe I use the warp envelope to distort the drawing into an sort of arch configuration which compensates for taper and or bulge. I skip most of the math, I use a sacrificial glass for a trial and error process until the illustration looks square and right to the eye. Its like making an illustration look right when its held up to a fun house mirror, a nice trick on a wine glass if you have the time.

Dave

Frank Corker
08-20-2008, 12:02 PM
Okay, I get it, have someone else do it for you.

Chris J Drew
08-20-2008, 12:20 PM
Check out the "interactive envelope tool" - Corel's help file tells you how to use it.

You don't need to change the height of the Corel page, only the shape of the artwork itself.

The "interactive envelope tool" lets you squash/stretch your image/text, by moving nodes.

As Dan says, this is much easier for a workpiece with a straight taper.

Measure the circumference of the workpiece where the top of the artwork will be.
Measure the circumference of the workpiece where the bottom of the artwork will be.
Divide one by the other to get the ratio by which you need to scale the top or bottom of the artwork.

Put a guideline through the centre of your artwork.
Place some guidelines either side of this to snap your envelope's nodes to.

If your workpiece has a curved profile you'll need more measurements.
For simple curves you'd probably only need one more measurement, tweak the envelope node's bezier "handles" to match the curve.
Dan's suggestion of using a side-view of your workpiece as a guide is spot on!
A bit of trial & error / experimentation will get the look you're after - what measures right doesn't always look right!

You can make envelopes for each shape of vase/glass/whatever that you're engraving & save them to apply to future jobs on the same shaped piece.

- hey, this is my first post! I've been lurking for a while... hello everyone! nice forum!

Scott Erwin
08-20-2008, 1:59 PM
That is a good idea...use the envelope tool....didnt think of that one and I use Corel a lot ... Brain (exhaust gas from rear) on my part....

I have tried different ideas but this one is so simple...couldnt see the forest through the trees I guess on this one... DUH...

Gregg Vaughn
08-20-2008, 2:55 PM
Thanks everyone! I'm off to give it all a try ....

Stephen Beckham
08-21-2008, 10:04 AM
Honestly - I gave up on the hard math since Epilog put out their Center-Center printing. It doesn't care how wide/long the vase is or how big the corel image is. It only cares how big the image is - then it divides by two to keep it centered. So - I use the standard deck size for corel layout and just worry about my 2X2 image. I'll also draw a square around that - run it in vector mode to see what kind of shape I'm going to get on the vase.

If you go with the Center/Center method - then go back to Dan's answer. Practice with changing a square into a polygon on the screen to make it look like a square on the vase... Then you'll likely go back to Frank's answer... :D

Chris J Drew
08-21-2008, 2:31 PM
Yeah, centre-centre engraving is a given for this kind of thing.
( Sorry I forgot to mention that in my post! )
1 simple calculation tells you how to shape the envelope.