Archive for September, 2011

Laser Cutting Sandply

Sunday, September 25th, 2011

burnt sandply

So I went to Home Depot several months ago to pick up some plywood for cutting on the laser decided to try out some sandply. It's cheaper than birch or oak, lighter, and seems to be less prone to warping, which is pretty important when laser cutting. Given that sandply is less dense than the bitch I had been cutting, I expected the laser to cut through it without issue. When I tried it out on the same settings I had been using for birch and I was not impressed.

Above you can see that some parts continued to burn after the laser cut through the wood (air asset doesn't seem to have an effect on this charring) and below you can see that the laser just barely failed to go all the way trough several parts at the same laser settings used for birch. I haven't tried to see if I can elevate the issues I was seeing, but I'd say that sandply is probably not a go to material for laser cutting functional wood parts.

Sandply that's not cut all the way through

Making Stamps with Lasers

Saturday, September 17th, 2011

The above image shows the first mounted stamp I made up with my laser cutter, which was created as a stand in for CCCKC's official hackerspace stamp for hackerspace passports (I can't wait to get mine own soon)!  It should be no surprise that I love to use laser cutters for making all kinds of stuff.  I thought I'd start posting some of the myriad of ways you can make stuff with a laser cutter/engraver and today I'm going to cover making stamps like this.

First off, you'll need access to a laser cutter that supports raster etching.  Almost all commercially available laser cutters will support this, and most will support a special stamp mode.  I'll be covering how to do stamps with Epilog Laser drivers, but Universal Laser and GCC laser cutter (I've seen them sold under the LaserPro and Pinnacle brand names) drivers also have stamp modes, I'm just not familiar with how they implement their stamp modes.  Unfortunately laser setups that have to be driven directly by G-code like the Lasersaur and some of the A4 size laser cutters out there probably won't be able to make stamps with the methods I'm outlining here.

First off, you'll need a few supplies.  First and foremost is laserable rubber, which is specifically designed with laser based stamp production in mind.  It's available from a number of sources online and comes in a couple varieties , one of which is low odor rubber which is what I've been using.  Next you'll need the other components of the specific type of stamp you'll be making, called the mount.  If you just want a simple, easy to mount and use stamp, you'll probably want to pick up a self inking stamp.  These come in several sizes, are pre-inked in most cases, and simply have an adhesive strip you place your cut out engraved rubber on and you're done.  Most also have an indexing strip you can stamp and insert after mounting your rubber. Here's an example I made up:

The second option for mounting stamps are "artistic" stamp mounts, like the kind used for crafts that you find at local hobby stores.  These consist of a wood block (or an acrylic block), a foam rubber cushion that forms a bond between the block and the rubber (or some foam rubber with a sticky coating or simply a sticky film if you're using an acrylic block), and the rubber stamp itself.  If you've got some wood scraps or acrylic to use, all you really need is some cushion, making this style the cheapest stamp mount you can make.  It also gives you the most freedom since you can make them almost any size or shape and the results can still look very professional.  Hand stamps are similar in construction to wood block artistic stamps but have a handle and often an index strip on the side, or you could just print the mount if you have or know someone with a 3D printer using this design.  Here's a picture of the 2"x2" blocks I used for the CCCKC stamp above:

Artiscic stamp blocksI coated one with polyurethane because I planned on etching it with the laser later and the polyurethane coating protects the wood from the byproducts of the etching without masking.  Here's a small scrap of cushion as well:

stamp cushion

The cushion has adhesive coating on both sides and is used to mount the stamp to the block and distribute pressure when stamping.  I picked up all my sample stamp supplies from JMP because they had all the supplies I wanted in one place, but they're not the cheapest source out there.

Now you'll need some artwork. Ideally you'll want a nice crisp high resolution black and white raster image or some vector artwork to work with.  The easiest way to get a nice crisp black and white image from raster artwork that's well defined (already high contrast) but a little blurry around the edges and/or not quite black and white is to:

  • Desaturate the image (either by converting its color space to grayscale or using the desaturate operation in your image editor of choice) to remove color.
  • Adjust the brightness/contrast of the image and turn the contrast all the way up.  This will eliminate any intermediate shades and leave you with just a black and white image.  You may need to adjust the brightness to get the desired effect.

Gimp can handle both of these operations easily.  Here's a quick example showing what I did to clean up the original artwork for this stamp and how adjusting the brightness effects the final output:

Steps to prepare raster artwork for making stamps
When done, remember to save in a non-lossy format like PNG of GIF to prevent the re-introduction of compression artifacts.

If your raster artwork is too low resolution you can try the bitmap tracing operations in your favorite vector graphics suite (both Inkscape and CorelDRAW have this functionality) and clean up the results a bit manually.  There are plenty of resources online if you need additional help cleaning up or creating artwork.

Once you've got artwork and your supplies you'll need to follow the recommendations of your particular laser manufacturer to set up your artwork and configure the laser. You can find Epilog's tutorial here. You only need a single outline for a single stamp to define the "fence", but if you're making multiple stamps the fence needs to encompass all the stamps (if you don't do this it looks like only the first stamp is rastered).  The entire area inside the fence will be rastered so don't spread stamps out too much or you might waist material.  Here's my artwork prepped for cutting in CorelDRAW:

CCCKC logo in CorelDRAW

On my 35 watt Epilog Mini-18 I used raster settings of 10% speed and 100% power for the CCCKC stamp.  Under advanced options, select "Stamp" for raster type, and I checked the mirror option under the stamp settings because I didn't mirror my artwork beforehand (see above pic).  I stuck with the recommended settings for the shoulder and widening options.

The driver is doing a few interesting things for you in the background:

  • Creating a negative of the raster image within the defined vector outline (which is why it's important to define one even if you're just going to cut it out manually)
  • Flipping the image horizontally (if you checked the mirror option)
  • Expanding the area that will be raised 0n the final stamp based on your widening selection
  • Ramping up and down laser power at the edges of the raised sections based on the shoulder profile you selected

All these operations can be easily done in photo editing software if you're laser cutter supports raster mode but doesn't have a stamp mode for some reason, but I've yet to encounter a cutter where this is the case.

Once the raster etching is done, take a look at the result but don't touch anything yet.  If you feel the etching is too light, just tweak the settings and run the job again.  The second pass will etch even deeper into the material, but will only work if you haven't moved the stamp material around.  The stamp will be coated in dust that you'll have to clean up later before placing your stamp (and you'll likely want to clean up the laser cutter a bit too after making some stamps).

Once you've reached a depth you find appropriate you'll need to cut out the stamp.  You can simply do this manually or do a vector cut with the laser.  This was my first stamp, so I opted to cut it out by hand and play with vector cutting settings later.   Recommended settings for vector cutting imply that you don't want to cut it at full power (this may indicate that higher power settings char the material). With my 35 Watt Epilog, a speed setting of 5%, power setting of 20%, and a frequency setting of 500Hz cut about 2/3 of the way through the sheet after a single pass of raster etching but cut all the way through after I did 2 raster passes on later stamps.  Higher power settings cut a bit deeper but did induce a little charring, so it looks like I'll have to try a few more settings combinations to dial it in.  Here's the CCCKC stamp before cutting it out from the sheet:

Stamp before being cut from sheet of rubber

Once you've cut out the rubber you need to cut out the cushion.  I just used an X-Acto knife but it cuts easily with scissors as well.  The description on the cushion order page indicated that PVC was used in the cushion that I ordered, so it would be a bad idea to cut on the laser because of its chlorine content.  There are a number of other options for cushion, but it's likely that they have similarly incompatible chemistry (the acrylic stamp mounting films I looked at seemed to contain vinyl, which is another no-no).  Since you won't likely be cutting the cushion out on the laser, you'll probably want to cut the stamp and cushion out at the same time (you may even want to adhere the stamp to the cushion before you start cutting).

Rubber stamp and cushionAll you have to do now is mark your block and assemble it.  I engraved the stamp into the wood block rather than making a sticker (as most commercial stamps I've see do) or stamping the top, which is kinda difficult to do at that point.  Here's a pick of the stamp totally assembled after stamping:

Mounted stamp

Next time around I think I'll make the etching of the stamp and the block a bit deeper, but the results of my first stamp making attempt seem to be pretty functional.  Maybe I'll experiment with some acrylic mounts next...

Building Boxes and Enclosures with Laser Cut ABS

Wednesday, September 7th, 2011

Above is a picture of a recent project I did for a client that wanted a custom enclosure for some experiments with mice. It's constructed from laser cut ABS sheets and held together with screws, but it doesn't use the now somewhat ubiquitous T-slot construction used in many laser cut enclosures.  Because ABS isn't extremely brittle like acrylic and doesn't have a grain or laminate layers like wood, you can simply screw it together without significantly effecting structural integrity if you do it right.

(Safety Note: This should go without saying, but if you're cutting ABS, properly handle the fumes! You need a properly sized carbon filter on your exhaust and you need to have adequate air flow. Additionally the parts should be left to outgas in a well ventilated area for at least 24 hours after cutting!)

I first used the method I'll be outlining here to construct a "dark box" add on for a piece of lab equipment.  It had to fit very snugly inside an existing box, not let light through, and not provide climbing holds for the mice under test.  I didn't want to end up gluing everything together (I'm glad I didn't, I had to modify the setup for an additional experiment later), and T-slot and bracket based attachment methods were not ideal.

First off, in my enclosure design I've added tabs to ease alignment of all the connecting parts.  If done correctly, tabs will prevent you from assembling your enclosure incorrectly and allow you to quickly align edges of parts you're screwing together.  Tabs also allow you to insert screws into both of the parts you're joining perpendicularly, which a regular butt joint wouldn't allow you to do.  I use 1/2 inch #4 flat head sheet metal screws for 1/4" ABS.  I drill a 3/32" pilot hole is drilled into the parts that will be joined.  Pilot holes are a must, as you can drive a screw in to ABS with a little work, but you'll see stress lines and bulging, if not outright splitting of the plastic if you don't use an appropriately sized pilot hole. I place the pilot holes at design time and cut them into the part so I have a nice guide when it comes time to drill.  Here's an example of a part with tabs and pilot holes in place:

To make sure I hit the correct depth, I add some tape to the bit to let me know I've drilled far enough into the piece.

I use right angle clamps to hold the parts I'm joining in place while drilling.

Here's a close up of the tabs and pilot holes after they've been drilled:

Next I countersink the holes and install the #4 screws:

You can prep and screw a side together relatively quickly with a little practice.  Once you've got a few sides on your enclosure, you can rely less on clamping parts together and simply hold down the panel you're installing with  one hand while drilling with the other (assuming you've added tabs to your parts so they align properly and stay in place).

Here's some pics of the finished product:

I've also used black oxide coated screws with this method to make the final enclosure look a little cleaner as well.  Overall I like the look of this method over T-slot construction for some projects since you don't have to oversize some parts to accommodate the tabs and screw holes and the joints seem a little sturdier as well.

KC Fabricators and CCCKC members in print

Thursday, September 1st, 2011

3D Printing Gang

Up on the MakerBot blog you can see the article running in 3D Artist magazine:

It features a picture of the KC Fabricators local 3D printer operators group (I'm second in from the left) meeting at CCCKC. The pic was originally taken as an entry for one of MBI's challenges to see how many bot's (and their owners) we could get together for a meet up. Don't know who this David Neff guy that seems to be claiming copyright on our photo is though...