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Gregg Vaughn
05-11-2009, 9:16 PM
My scrap pile is about the size of the hair pile that I pulled out trying to figure out the formual for engraving objects with different diameter ends on the Epilog rotorary attachment. If there is a logical answer to how to
set this up in Corel to get the engraving to be the same scale on the object being engraved, it completely escapes me.

I tried using the diameter of big end, small end and middle as the vertical measurement on Corel .... nothing worked.

Has anyone found the magic formula?

Doug Griffith
05-11-2009, 9:44 PM
Hi Gregg,
Here is a calculator I found online. It may help you out.

http://www.unikatissima.de/e/?p=2117

Cheers,
Doug

Frank Corker
05-12-2009, 4:39 AM
I found this to be one of the hardest things to achieve, distorted images, but not so long back someone on this site did come up with a convoluted method. I also heard about making some type of jig where you attach temp disks to either end of the workpiece in order for the whole lot to rotate evenly on the rotary. I just found it easier to buy stuff that was a boring up and down shape. If anyone should be able to work this out it would have been Doug, with his oversized mathematical brain I thought he would already have had a machine to do just that!

Dan Hintz
05-12-2009, 9:06 AM
This question has come up a lot lately, so I'll post my solution again.

If the object is a simple cone in shape (i.e., different diameters at each end but non-curving sides), take the ratio of one diameter to the other and shrink one end of the image to match. For example, say a vase has a 5" diameter top and a 4" diameter bottom and you're trying to put a 3" wide image on it. The top of the image stays at 3" wide, but the bottom of the image needs to be shrunk by 4/5, or down to 2.4" (3 * 4/5). The sides of the image (in your drawing program) will now look like this:


\ /
\ /
\ /
\ /
If the object has a complex shape, the easiest way is to scan the outline of the object and use that to modify the image to fit into the outline. This will usually require polylines and curve fitting, something not every graphics program handles correctly. Even so, you can often cheat and get it close enough.

Mark Winlund
05-12-2009, 11:21 AM
Dan has it right. Distort the image in Corel. Easy to do.


Mark

Doug Griffith
05-12-2009, 3:16 PM
You're killing me Frank!!!

Dan's formula is correct. In Illustrator take that percentage and apply the opposite to the smaller dimension under Effects:Arc. Then expand the appearance to make it useable on a laser. There must be a similar function in Corel Draw. There's also a plugin called Squizz that does similar even with more organic shapes.

Cheers,
Doug

David Fairfield
05-12-2009, 3:18 PM
I use simple trial and error and distort the image accordingly. Where the engraving is too wide on the finished product, narrow it in the drawing, where its too narrow, widen the drawing. One glass will be sacrificed during this phase, you can cover it with tape if your test images start to overlap. No math involved.

Dave

Real Mercier
05-12-2009, 10:02 PM
I've been lurking here for a while and have gotten a lot of help here reading the posts. I have a rotary attachment for my Epilog Laser. I wrote a quick Excel sheet to figure out the ratio of the different diameters. I hope it helps.

Frank Corker
05-13-2009, 4:57 AM
Real, as a lurker you have just leaped out of the bushes like a flasher! Nice little combination, I am not mathematically minded, but even I can work that xls file. I do see one little problem, sometimes the top of the vase shape has a different circumference to the bottom of the vase shape as well as having that centre circumference being bigger than both ends. (Have to watch I don't trip on my tongue here). When it is on the rotary the top fits on one set of wheels and the bottom sits on another.... okay it's official I'm back to being in the mist again.

Michael Doyle
05-13-2009, 9:04 AM
This is an interesting topic. The items that I engrave have all been thinner than the drive point, so I have to stretch the design. For tapered cylinders the design actually is an isosceles trapezoidal shape, with the wide end corresponding to the thin end of the cylinder.

It took a while for the light bulb to come on when I first started doing this. I played around with a circle on some scrap pieces, changing the aspect ratio until I could make it look round on the tapered pieces.

Tom Bull
05-13-2009, 9:06 AM
There is a pretty good free spread sheet program in the Open Office software. Little slow to open, but powerful, free, and not MS. Just Google for Open Office for more info, or www.openoffice.org (http://www.openoffice.org) to get download.

Frank Corker
05-13-2009, 9:55 AM
......actually is an isosceles trapezoidal shape...

exactly!

Doug Griffith
05-13-2009, 11:45 AM
I use simple trial and error and distort the image accordingly. Where the engraving is too wide on the finished product, narrow it in the drawing, where its too narrow, widen the drawing. One glass will be sacrificed during this phase, you can cover it with tape if your test images start to overlap. No math involved.

Dave

Another "no math" method is to apply a piece of film over the item and draw the live area with a pen. Then remove the film, apply to something flat, and scan it. Place this in your graphics and use as a template.

David Fairfield
05-13-2009, 12:36 PM
Thats a really good idea, Doug.

By the way, I use "envelope distort--> make with warp---> arc" in AI to correct the image. A couple of tweaks with that, and scaling the image a little wider is all it usually takes, unless the workpiece has some wierd hourglass thing going on.

Dave

Doug Griffith
05-13-2009, 1:00 PM
Thats a really good idea, Doug.

By the way, I use "envelope distort--> make with warp---> arc" in AI to correct the image. A couple of tweaks with that, and scaling the image a little wider is all it usually takes, unless the workpiece has some wierd hourglass thing going on.

Dave

Darn, I thought you found a better method. I just checked and your method is exactly the same as mine with different mouse clicks.

Don't you miss the days of KPT Vector Effects? I emulate OS9 just to play with it. Also, try Squizz if you can. It has some pretty powerful mesh warping features. I've used it for predistorting images that index to vacuum formed parts.

Gary and Jessica Houghton
05-13-2009, 2:18 PM
Setting up cylindrical objects
with a balloon or tapered shapes:
1) Measure the circumference of the object at the point of
rotation.
2) Measure the circumference at the point of engraving.
3) Divide Circumference #1 by Circumference #2 (above).
4) Stretch or compress the text as required by using the values
in the Property Bar.
Examples:
A. Tapered Shape
4 at lip of the glass (driver motor point)
3 at engraving point
4 / 3 = 1.33 Stretch the text to 133% of its original
size to maintain the aspect Ratio.
B. Balloon Shapes
3 at lip (driver motor point)
4 at engraving point
3/4 - .75; compress the text to 75% of its original size
to maintain the aspect ratio.

Hope this helps.

Real Mercier
05-13-2009, 10:56 PM
Actually, Gary and Jessica have it dead on. Those are the only 2 diameters you need. The other end can be any size. The important thing is the engraving area be parallel to the laser. That is why the free end of the rotary attachment is height adjustable. With the tapered glass, you raise/lower the free end until the topmost surface (length of the glass closest to the laser) is parallel to the laser. And it does not matter which end is on the drive wheels. What does matter is the circumference of the end on the drive wheels. This sets the page height in CorelDraw. The page height is what tells the laser what one full revolution of the object is.
Same goes for the baloon object. You want the center of the etch area to as parallel to the laser as possible. If you do not level the object, the laser focus will be in only where you focused it. Above and below the focus would be out. That is all my spreadsheet does. Hope this helps.

Frank, me a flasher leaping out of the bushes!! Not a pretty sight, trust me.

Gregg Vaughn
05-14-2009, 9:49 AM
Thanks everyone! The Excel SS from Real is great and will probably cover most of the shapes I work with. I hope my hair grows back now ...