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Mayo Pardo
03-13-2017, 3:21 AM
I recently tried cutting some acrylic that appears to glow at the edge when normal room light hits it. My usual cutting grid is a rectangular acrylic ceiling light baffle.
I had no masking on the underside or top surface of the glow acrylic.
It cut real nice however when looking through it, there was a couple places that looked fogged or as if there was oil or liquid on the underside surface. I tried cleaning this off with denatured alcohol and within a minute or two, the edges started to craze/crack. Especially at corners or changes of direction along the edge. Maybe I should have masked both sides or at least the underside...

I assume this oily look happened for two reasons - the acrylic ceiling light baffle doesn't allow smoke and fumes to travel through one square to the next and the fumes may have redeposited on the acrylic. Or it may be the acrylic grid itself that is doing it when it gets cut by the laser.

This brings me to the idea of making a pin table which has been mentioned recently.
So I thought if I could use the laser as a drill and make holes in 1/2 inch MDO plywood, I could just insert finishing nails into the holes, and I'm good to go. Well, not so much with my 30 watt laser.

Making several test holes, I discovered several things.

1. Although tedious, it would be more efficient and the holes will be more uniformly vertical if I did it on a drill press instead. I could mark the hole locations on the board using the laser though.

2. The smallest hole I can get my laser to "cut" rather than engrave, is 0.002.
Smaller and nothing happens.

3. Too slow at too much power and kiss the hole diameter good bye.

4. 40 copies of holes placed on top of each other, and duplicated every 1/2 inch along the X direction does not get processed in such a way that all 40 copies of the first hole get done, then the next hole gets all 40 copies done, etc. Instead, job control does one copy in the first hole, moves to the second hole and does one copy, then to the third, etc. Then it goes back to hole 1 for the second copy. I did not try the "vector sorting" function to see if that would be more efficient.

5. For some reason I could not get job control to cut the holes unless I had black set to engrave even though there was no black being processed. When I had black set to ignore, the red cut holes would not run. I had blue set for positioning, so I could maintain positioning while testing one hole at a time, and later 5 holes at a time.

6. The vector holes will process lots faster than engraved holes.

It was an interesting experiment and I plan to keep at it just to see what else might happen with other variables. It seemed the best holes I got were by doing only 10 to 15 copies at a time all in the same hole. More than that at one time tends to burn out the diameter unpredictably in plywood.

Another observation that was not an observation -
The movement of the laser for a 0.002 diameter cut vector hole is not really even noticeable!

Doug Griffith
03-13-2017, 10:07 AM
It looks like you have a Shopbot. That's a much better tool for the job.

Instead of trying to cut holes through 1/2" ply, why not cut through multiple pieces of much thinner stock and laminate together. The nails will help index the parts together. Just a thought.

Gary Hair
03-13-2017, 11:29 AM
FYI - in Job Control you can set the number of passes, much easier than creating multiple copies of the artwork. It's in the material database.

Lee DeRaud
03-13-2017, 12:21 PM
Instead of trying to cut holes through 1/2" ply, why not cut through multiple pieces of much thinner stock and laminate together. The nails will help index the parts together. Just a thought.What he said: that's how I make cribbage boards. For this application, I'd use 1/4" MDF from Home Depot, about $6 for 2'x4'.

Lee DeRaud
03-13-2017, 12:35 PM
This brings me to the idea of making a pin table which has been mentioned recently.
So I thought if I could use the laser as a drill and make holes in 1/2 inch MDO plywood, I could just insert finishing nails into the holes, and I'm good to go. Well, not so much with my 30 watt laser.
...
2. The smallest hole I can get my laser to "cut" rather than engrave, is 0.002.
Smaller and nothing happens.
That hole size sounds too small, like by a factor of 20, for anything I'd be inclined to call "finishing nails". 23ga pins are in the 0.025" range, 18ga brads about 0.045".

Glen Monaghan
03-13-2017, 10:46 PM
1. Although tedious, it would be more efficient and the holes will be more uniformly vertical if I did it on a drill press instead. I could mark the hole locations on the board using the laser though.


I did exactly this a few years ago, only with a melamine coated shelf board, and I used 18 ga nailgun nails for the pins that raised substrates 1" above the board. I cut several sheets of 3mm baltic birch on the pin table, running a bit on the slow side to ensure that all the piece cut through (I hate trying to cut intricate pieces loose with an exacto knife when the cut is incomplete). So, despite the inch of standoff, there was enough laser beam intensity on the melamine board that both the melamine and the mdf under it badly charred, smoked, and made a huge mess, especially when small pieces cut loose from the bb happened to fall onto the black mess. Also, if I happened to get pins where the beam just nicked them, the pins would stick to the underside of the bb and pull out when lifting the cut sheet away, and then (per the perversity law of nature) fall loose and land in the most inopportune and/or inconvenient of locations, or simply disappear.

Kev Williams
03-13-2017, 11:51 PM
Sounds like you were cutting extruded acrylic, which is infamous for crazing when alcohol come in contact with a laser cut edge. It's also the source of your 'oily' stuff, and I suspect your edges were probably sticky-

After many failed clean-up attempts and do-overs when cutting acrylics of any kind (but Rowmark in particular) I've found that my time and money is better spent on transfer taping both sides of acrylic before cutting the stuff with a laser. And while a pin table would be nice, as I've noted in other threads I just use #6 lockwashers on my solid tables. I just pour them out and space them out as necessary. Anyone who's cut Rowmark with their masking or no masking is familiar with the mushroomed cut edge. Cutting thru transfer tape, nearly eliminates the mushroom, and prevents flashback on the bottom even when cutting right on the table. Nice thing about transfer tape, a little bath in warm water breaks down the adhesive bond, so it pretty much just falls off.

Just did a little test, I'm cutting 'TEST' twice thru white Rowmark, right on the table, not raised, one cutting thru Ttape on both sides, the other cut with no tape.
I didn't do any cleaning, other than to remove the tape after the 2nd pic-

It's easy to tell which is which ;)
356012356013356014356015356016356017

If I'd raised this off the table, the bottom side would be much better than it already is...

Jerome Stanek
03-14-2017, 7:58 AM
I agree with Doug the Shopbot will punch those holes out in no time. I did this and used the peck drill routine. I made a file in Aspire using the array functionand used a .125 end mill then used .125 pop rivets. I went to a ceiling company and bought the rivets from them they were a lot cheaper when you need hundreds of them

Dave Sheldrake
03-14-2017, 8:30 PM
0.002 inches is only just under 5x the wavelength of a CO2, that's going to need laser drilling kit