Help with rotary

[Steve Busey]

Using an Epilog Helix 35W.

I've been trying to do some graphics on a pen barrel, but the graphics keep getting compressed.

I've set the vertical size of my CDR layout to the circumference of the barrel (.54" dia x pi = 1.696"), the horizontal to my barrel length, but when I do the burn, things get flattened, when viewing side to side (barrel end to end). I'm trying to wrap my head around this whole rotary thing. What am I missing?

Here I created a test barrel with square grid (at 0.1" spacings) and a circle to try and illustrate what's happening. Oddly, the grid printed all the way around the barrel, so I don't believe the laser thinks the form height is wrong. But viewing the grid, it's clearly compressed when viewed end to end. It appears a larger diameter barrel using the same grid would fix the spacing, but how do I calculate the layout size for the barrel I have (in this case, .54")? How would you approach the job of doing graphics on barrel?

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Thanks in advance!

[Glen Monaghan]

The squares and circle in your first photo appear very narrow for their height. However, in your second photo, taken more nearly perpendicular to the side of the barrel, the squares appear very nearly square, although ever so slightly narrower in the "around barrel" (more-or-less up-and-down in this photo) direction than in the end-to-end (left-to-right) direction. And the "circle" covers the same number of squares in each direction. So, the question is, are we simply seeing distortion due to the curvature of the barrel, ie, the curvature is making the "around barrel" direction look compressed versus the "along barrel" direction?

Use a piece of paper wrapped around the barrel to measure the length of 10 or 15 squares around the barrel and compare to the length of the same number of squares along the barrel. If they are the same, then it's a perceptual issue due to the curvature; if different, then there's still a problem to solve...

-Glen

[Phil Horne]

I have had all kinds of problems with the Epilog Helix 60 watt I have been using.. Sometimes it prints fine sometimes its compressed sometimes only half of the image is compressed.. I have tossed a bunch of work because I cant sell the stuff Im engraving for my customers sometimes.. I have been able to find no rime or reason to why the darn thing craps the bed..

The last run I did of 300 tubes It was a really simple file that basically said "Property of VaperMate" on them. Fortunately I own the company so I decided I would still use them but only 1 in 10 of the tubes came out correctly. I have tried using both Corel Draw X5 and Illustrator CS5 with the same result. I have no idea what might be causing this and it is very frustrating to say the least.

This same thing happens on two different rotary attachments on 3 different lasers...

Phil

[Steven Cox]

From the pics I think Glen is right on the money we're simply seeing distortion due to the curvature of the barrel.

[Braden Todd]

Try multiplying your image by pi as well. It will look distorted but as the piece spins it will correct the image.

What type of a rotary are you using?

Hope this helps!

[Steve Busey]

Using the Epilog rotary jig for the Helix, barrel mounted on a pen turning mandrel.

I measured one test circle with the calipers - .38" end to end, .34" around the barrel - more than just a visual perception issue - a 11% distortion. Tonight I'll try either stretching the image 10-15% vertically, or telling the system that my barrel is 10-15% smaller.

The actual graphic I want to print is a trail of cat paws winding around the barrel, but they come out noticeably "squished" and distorted, far more than barrel distortion. I'll try the paper wrap, too. (I'm running out of reject wood barrels to test with!)

[Martin Boekers]

From the pics I think Glen is right on the money we're simply seeing distortion due to the curvature of the barrel.


I have had issues with mine to different on two pieces that are alike. If it is perceptual there must be a formula for it.

[Martin Boekers]

Try multiplying your image by pi as well. It will look distorted but as the piece spins it will correct the image.

What type of a rotary are you using?

Hope this helps!


Could you expand on this? Say I have a graphic that is 3"wide x 4" tall. How would you do this?

[Phil Horne]

For me I dont think its distortion caused by the curvature of the barrel, otherwise it would be consistent across all work pieces, but like I said the amount of distortion is random and sometimes it comes out just fine, other times half of the image will be just fine and the other half will be compressed. Its very frustrating. I guess maybe Ill call epilog and see if they have any input. Of course this is all going to be a moot point later this week since Ill have my own G.Weiki laser in house and wont have to use another companies lasers any more.

[Martin Boekers]

For me I dont think its distortion caused by the curvature of the barrel, otherwise it would be consistent across all work pieces, but like I said the amount of distortion is random and sometimes it comes out just fine, other times half of the image will be just fine and the other half will be compressed. Its very frustrating. I guess maybe Ill call epilog and see if they have any input. Of course this is all going to be a moot point later this week since Ill have my own G.Weiki laser in house and wont have to use another companies lasers any more.


I used to wonder if it was a conversion thing, maybe compressing the spaces between lines, but I to have had it randomly. I have 2 Epilogs and 2 rotaries
both have issues from time too time. If it's important I'll stretch the graphic, but that takes testing and wasting a piece.

[Michael Doyle]

You have to consider the dia of the driven piece, not the engraved piece. If your pen is not the same dia as your mandrel, you will have to change the aspect ratio of your image.

[Steve Busey]

You have to consider the dia of the driven piece, not the engraved piece. If your pen is not the same dia as your mandrel, you will have to change the aspect ratio of your image.

Michael, do you have any rules o' thumb to go with that concept? I have the MT2 end of the mandrel over the drive wheels. Should I base my vertical form height based on the MT2 diameter where it sits on the wheel? (Seems I tried that at one point in my tests, but the results apparently didn't work for me...)

Edit:
Or should I create a mandrel/dowel to correspond to the size of the barrel? From a glance at your site, looks like you've conquered the issue - appreciate your input!

[Michael Doyle]

I think I went with the ratio of mandrel to pen dia when doing it originally, but can't find my early notes. Since then Its just been guestimates based on experience.
The easiest thing to do is to turn a couple of scraps and do a matrix of sizes to satisfy yourself as to what is needed.
For thinner pens, I stretch the design on the vertical only

[David Fairfield]

If you look up Epilog rotary on this forum, you will find all sorts of woes. For some things (big, heavy and untapered) the design is smart and works well. For most of the things I'd want to engrave (small, light and tapered such as glasses and pens) it stinks. Objects are prone to wobble and slip on it. Slipping will result in a compressed graphic, as the object you are engraving turns slower than the correct rate of feed. I no longer accept commercial jobs for the rotary, though I do use it for personal use.

That said, and even when functioning properly with no slip, I found that graphics usually need adjustment to look normal on the face of a curved surface. You need to compensate for perceptive distortion, and that can be done by eyeballing and trial and error. If the ellipse looks too narrow on the pen, widen it in the graphic, and see what you get. There's probably a reliable mathmatical formula for this, but that would be well over my head.

Dave

[Braden Todd]

I have both types of rotary from Epilog, the standard roller one and the 3 jaw chuck rotary. When I got the 3 jaw rotary I was reading that pieces with a diameter of .050"-.50" had to have the vertical height of the pattern multiplied by pi. This would stretch the image and allow it to be wrapped properly when engraved.Ex. If artwork is 4" long and .5" tall, the calculation would be .5 x 3.1416=1.5708I am not sure if this is only true for that specific rotary, but it works great for me. I never would've tried a small/light piece with the other rotary and now it's no issue at all.Hope this helps

[Glen Monaghan]

I have both types of rotary from Epilog, the standard roller one and the 3 jaw chuck rotary.

3 jaw chuck rotary from Epilog??? Maybe _for_ Epilog but surely it was from someone else...

-Glen

[Braden Todd]

This is the unit I have and love! I never have to worry about light weight items slipping!!234271

[Glen Monaghan]

Ahh, my brain slipped a gear there. Yes, now Epilog does have a 3 jaw chuck, but they are specifically for their fibermark lasers and cost around $2500! I thought it was not compatible with their CO2 line but, as I was investigating just now, I found that they have some literature talking about how to use it with Legends and Minis...

-Glen

[Real Mercier]

Here is a method I use when doing pen blanks on my Epilog rotary.

Measure the diameter of the pen blank where you want to engrave. Multiply by pi (3.1416), this gives you the circumference of the blank and is your page height in Corel. The length of the blank is your page width. I usually draw a box with these dimensions on a page. Place your graphics where you want them.

Next, you need the diameter of the mandrel where it sits on the drive wheels (mine is .625" diameter), multiply this by pi. This corresponds to one full turn of the mandrel (360°). This is the page size you want. Next I will select all and stretch (or shrink) my box and graphics in the Y direction to match the 1.963 mandrel page height (.625 x 3.1416).

This works for me everytime.

Hope this helps.

Real Mercier

[Phil Horne]

Here is a method I use when doing pen blanks on my Epilog rotary.

Measure the diameter of the pen blank where you want to engrave. Multiply by pi (3.1416), this gives you the circumference of the blank and is your page height in Corel. The length of the blank is your page width. I usually draw a box with these dimensions on a page. Place your graphics where you want them.

Next, you need the diameter of the mandrel where it sits on the drive wheels (mine is .625" diameter), multiply this by pi. This corresponds to one full turn of the mandrel (360°). This is the page size you want. Next I will select all and stretch (or shrink) my box and graphics in the Y direction to match the 1.963 mandrel page height (.625 x 3.1416).

This works for me everytime.

Hope this helps.

Real Mercier

Would it be possible for you to take a pic of it all setup. I just want to make sure Im wrapping my head around this correctly.

Thanks
Phil

[Real Mercier]

See if this helps. I saved it in version 9.0

[Phil Horne]

See if this helps. I saved it in version 9.0

Actually I meant of the rotary setup with the work piece.. I just want to make sure..

Thanks though I really appreciate the cdr file.. I think that will help too.

I cant wait to get my GW 1290 this week and start playing with it!!!

[Steve Busey]

I think I went with the ratio of mandrel to pen dia when doing it originally, but can't find my early notes.

Your explanations helped put things in the right perspective, Michael.

I took another old scrap pen barrel, epoxyed a dowel into it and after it dried, center-drilled a 1/4" hole in the dowel and placed the mandrel rod in that. So I ended up with the same diameter on the rotary roller as my work piece. No image stretching was needed, and the graphic printed proportionally correct. (although, this was for the top of a Euro style pen kit, and there was a visible change in the graphic size as it rolled over the top shoulder)

I'll try and post a picture later of my modified mandrel for others to see.

[Phil Horne]

Your explanations helped put things in the right perspective, Michael.

I took another old scrap pen barrel, epoxyed a dowel into it and after it dried, center-drilled a 1/4" hole in the dowel and placed the mandrel rod in that. So I ended up with the same diameter on the rotary roller as my work piece. No image stretching was needed, and the graphic printed proportionally correct. (although, this was for the top of a Euro style pen kit, and there was a visible change in the graphic size as it rolled over the top shoulder)

I'll try and post a picture later of my modified mandrel for others to see.

That would be great!!

[Real Mercier]

There is no trick here. I place the mandrel directly on the rotary. For the Epilog, I set the home position to the center of the pen barrel with the red dot pointer and set the driver to Center-Center engraving.

The key thing to remember is that the drivers assume the page height to be one full circumference (360°). You want to set the page height to the circumference of piece on the drive wheels. You stretch or shrink your graphic to adjust for the difference in diameters.

Real Mercier

[Steve Busey]

I'll try and post a picture later of my modified mandrel for others to see.

A picture of my quick & dirty mandrel setup. I replaced the metal Morse Taper 2 end of the mandrel with a scrap pen barrel (filled with a dowel and center drilled to the size of the mandrel rod). An astute observer will note that the scrap barrel in this pic is actually smaller than the workpiece, but it was closer than the original MT2 end (seen in the 2nd pic). I plan to turn a couple dowels down on the lathe made for a couple of the common pen kit sizes I work with, but I needed to hurry and get this one out the door, so it was fast and dirty.

Thanks for everyone's input. (I even got an unsolicited phone call from Epilog tech support - they do maintain a presence around here!)

Moral of the story: the end of the mandrel that rides on the drive wheels (left) should closely match the diameter of the workpiece.
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