## 12892Re: [PPLetterpress] Laser Engraved Photopolymer Plates

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• Oct 26, 2011
I have been working with CNC routers and that logic will be similar. Technically such machines move a tool (router or laser for example) in a 2-dimensional XY surface from one X1Y1point to another point X2Y2. Every straight vector in the software file will mean one such move (a circle will be many very small straight moves after each other).

One stepper motor takes care of the X-movement and at the same time another stepper motor takes care of the Y-movement. Technically the software can say for example to move with a straight line from (X1= 0.123 mm, Y1= 0.234 mm) to (X2= 0.548 mm; Y2= 0.965 mm) but often the machine cannot move with such a 0.001 mm accuracy and tolerance.

Stepper motors move in steps and "one step" can translate on a specific machine to for example a move of 0.040 mm/step in the X-axe or Y-axe and then they will claim that machine has an accuracy of 0.040 mm/step what then translates as 625 of these steps are needed to move the tool 1 inch in the X- or Y-direction.

If you would for example use such a machine to make only horizontal lines along the Y-direction then you could in theory make 625 of those lines per inch in the X-direction. First line at X= 0mm, second line at X= 0.040mm, third line at X= 0.080mm, etc...

Most routers & lasers however do not move with only horizontal lines (like an inkjet printer does) so you can't compare this with traditional screen or printer logic.

Best regards,
Erik

When you say LPI do you mean DPI? LPI refers to the screen resolution of a halftone. http://desktoppub.about.com/cs/intermediate/a/measure_lpi.htm

As Gerald mentioned earlier, most plates are made from films output at 2400 or 2540 DPI.

Harold

On Tue, Oct 25, 2011 at 10:10 PM, Joe Lanich <ppp@...> wrote:

Thank you for the compliment, you are very kind.

"Scanning precision" or "scan gap" on a laser is the amount the laser head indexes in the Y axis per pass on the X axis. The lower the scan gap the more passes the engraving will be divided into. More passes equal more time. We run our laser at a scan gap of .04mm (0.0016") and the manufacturer refers to this 600DPI. If you do the math, 1" / 0.0016" = 625LPI. With laser beam diameter being around .003"-.005" I don't see any great benefit going above 625LPI for most work. At a scan gap of 1000LPI your plate engraving time would be 60% longer than 600LPI and you might not even be able to see the difference.  I am still experimenting though, so I am open to other opinions.

We use Illustrator to create all of our files and import them into the laser control program which then creates the code the laser needs to operate.

CorelDraw? No hipster letterpress printer would be caught dead using CorelDraw! I kid! I'm sure it is a great program.

-Joe

On Tue, Oct 25, 2011 at 2:05 PM, Scott Rubel  wrote:

This is informative. You do some fun work.

I looked at the link and it seems like a wonderful machine, except for the "scanning precision" of 50-1000. I'm not sure what that means. Is that the same as maximum resolution? If so, I wonder why they would not want to take full advantage of what a laser is capable of.

In the compatible software category, it does not include Illustrator or InDesign. You said it likes vector files best, so do you make everything in CorelDraw (which I didn't even know was sill around)?

--Scot

On Oct 25, 2011, at 5:46 AM, Joe Lanich wrote:

Scott,

You will have to excuse my adjectives. I try to remain humble because I know I am still young and I still have much to learn. I don't want to oversell anything on a mailing list created by a man that prints pieces such as this: http://www.flickr.com/photos/bielerpress/5288736711/

For the work we do (invites, coasters, greeting cards, etc) I would say this direct engrave polymer is excellent. You can find photos of our work here: http://www.laughingowlpress.com/work/. The photos on that page are not all inclusive to this direct engrave material. Some of the work was with conventional photopolymer, laser engravings of MDF and delrin, and type. Now we use the direct engrave polymer exclusively. Using the direct engrave process allows us to go from computer to plate in one step with minimal equipment investment. It has shortened our lead times and lowered our cost compared to when we had plates made offsite.

The laser engraver we have is a 40watt Rabbit 6040. You can find it here: http://www.rabbitlaserusa.com/laser_RL6040.asp . You can use any engraver you wish. For this direct engrave polymer we run ours at 28% power, so you could even have a lower wattage of laser and still have success. In the end the machine you buy will affect both your quality of engraving and ease of use. My biggest gripe is the import control software for our laser is clunky, but it works. It likes vector files the most.

The engraving does leave a slope on the engraving, you can see a picture of it on the briarpress.org thread about this material.

Thank you for your questions. They greatly help with understanding the material. I look forward to more.

-Joe

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Boxcar Press
501 W. Fayette St. #222
Syracuse, NY  13204
www.boxcarpress.com

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