Thin copper

[Linda Mehlenbacher]

I cut and engrave mostly wood with my engraver. I have an Epilog 35 watt mini. One of my regular customers wants to know if I can cut him watch hands out of .016" (0.41 mm) copper - being so thin, would I be able to do that? I'm thinking I can only mark it but I'm not sure.
Thank you for any replies.

[Bert Kemp]

I don't think your going to cut copper with a 35 watt.

[Rich Harman]

No. Some high power lasers even use copper for mirrors, it is both reflective and an excellent conductor of heat, which means that the heat needed to cut it is rapidly moved away from where you need it to be.

[Keith Colson]

I have tried this, the thickest metals I can do on 60watts is 0.05mm to 0.1mm and it comes out pretty cooked and warped.

What you can do is paint both sides, remove the paint with the laser in raster mode (both sides). Then you can etch it with ferric chloride or ammonia persulfate You need to make sure you use some really good paint as it has to last through the etch cycle. Bees wax I have heard is a good resist to use. When I get my hands on some I will try bees wax. I make quite a few PCB's on my laser so I have had some good practice with "very thin" copper.

Good luck
Keith

[Dave Sheldrake]

At 6.5kW (6,500 watts) I can just about cut 5mm copper at 1/2m a minute feed rate using 400 psi of gas assist. Above 6.5kW yields no real benefits, the stuff is a nightmare to cut with the CO2 wavelength as the absorption rate is just under 0.55% Vs the 10,6000 beam. In effect at 6,500 watts only 350 watts or so is actually getting *into* the material. Like Rich said, the stuff gets used for laser mirrors on CO2 lasers so there is also the possibility of damaging your optics trying to cut copper :(

YAG and Fiber at 1064nw wavelength still only get to about 28 - 30% absorption

the stuff is the bane of my life :(

cheers

Dave

[Richard Rumancik]

Linda, your customer probably meant to say brass, not copper, as I can't imagine any copper stiff enough to make clock hands. But regardless you will have the same issues as copper in that it will not cut with the laser.

Normally this kind of part would probably be made using photofabrication if the hand has any kind of complexity. This is done with a sensitized material and a photograpic negative or positive of the part. Keith's idea is to avoid the photographic image, and image it directly with the laser.

To be honest it is quite a bit of work and a lot of steps to go this route. Also, I question whether you can get the required edge quality. I have made gobos from .010" brass using electrolytic methods but the edge quality was not great - good enough for my purpose but I have some doubts about clock hands. When photo-etching, the professional fabricators will often etch from both sides to improve the edge quality but this is more difficult to do with a laser. Circuit boards are often only about 1-ounce copper which means the copper layer is about .0014" thick. Your part is more than 10 times as thick so it is a little more challenging to find a suitable resist (paint) and etch correctly. It could be done, but it won't be a simple task to get good results and you should expect a lot of R&D.

[Bill George]

Rowmark makes brass or other types of metal looking plastic tag material. Sure its not "real" but it looks darn nice.

[Chuck Stone]

To be honest it is quite a bit of work and a lot of steps to go this route. Also, I question whether you can get the required edge quality. I have made gobos from .010" brass using electrolytic methods but the edge quality was not great - good enough for my purpose but I have some doubts about clock hands. When photo-etching, the professional fabricators will often etch from both sides to improve the edge quality but this is more difficult to do with a laser. Circuit boards are often only about 1-ounce copper which means the copper layer is about .0014" thick. Your part is more than 10 times as thick so it is a little more challenging to find a suitable resist (paint) and etch correctly. It could be done, but it won't be a simple task to get good results and you should expect a lot of R&D.

I've used adhesive polyester (bumper sticker!) as a mask and lase from both sides, but
registration is a bear. But if you get it etched and positioned well, hot ferric chloride
will do it. And you're right.. it's a bit of work.

[Richard Rumancik]

If you used Flexicolor/Flexibrass it is .022" thick, just a bit thicker than the .016" the customer asked for. It is not as stiff as brass so flexing might be a problem. You also need to figure out how it would lock on the clock shaft. Or is the customer okay with just a simple hole? Normally clock hands have a tight fitting "ferrule" (tube) that will grip on the clock shaft and keep it parallel to the clock face. Maybe you could bond a cheap (straight) hand to the back of Flexibrass to supply the attachment means - this could also stiffen the hand. Depends on the customer's budget as well.

[AL Ursich]

For the paint and laser then acid dip method.... I wonder if just vector cutting the outline exposing the copper of the clock hand would be the trick and the hands will drop out as they etch through. Some use a plexi tank the shape of a book on end and add a fish tank air pump to the rig bubbling the fluid for faster etch. I remember some youtube videos on it.

AL