Author: chad

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Christmas Gifts

Samantha and I are very deliberate with our budget; it allowed us to pay off our debt including our house. You can only be so strict before it wears you out, though. So part of our budget is “blow money”. We each get money to spend on whatever we wish, no questions asked. (though legal and ethical limitations probably still apply)

We also try to be deliberate with gifts and avoid blatant consumerism. We both became annoyed at family gatherings that just seemed to be an exchange of gift cards. Generosity is also supposed to be part of our ethos, so that along with our frugality lead us to find a replacement. We’ve settled to trying to substitute the plastic stuff and gift cards with quality time (a nice dinner together) or homemade gifts (but ones that take effort, skill and time).

Enter my new laser. Samantha didn’t really get it. I saved up several months of my blow money to purchase it, so she didn’t care that I bought it. She did, however, ask what it was for and why I wanted it. That, of course, is the dumbest question in the world… to which I had no concise answer. Finally, it came time to think about Christmas and the answer manifested itself.

For all the women in the family, I made wooden earrings. Complete with a backing card made from scrap reclaimed corrugated cardboard. For the important women (mothers), I made honeycomb earring holders. (also pictured with the holders is the vanilla extract we’ve made for several years that is now a gift expected by a few)

They were well-liked, and more importantly to me, Samantha thinks I’m a little less crazy for wanting the laser.
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K40 Wiring Diagram

The power supply that came with my K40 was a bit different than the typical one that I have seen in the various builds. In the end the only difference is the placement and labels on the output pins. I received a question about how to hook it up, so I dusted off and completed a wiring diagram I had started for when I get around to making a comprehensive page of my build (minus all the trial and error).

It seems people are stumbling upon this blog now; I should really think about completing the design of the website… Just another project on the list.

Here is the diagram for those who might find it useful.

k40-ramps-diagram.pdf
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New Air Assist Nozzle

I mentioned in my previous post that, after installing the z-table, the air assist nozzle proved to be too long and ran into the frame of the table. Though, there was already a problem with the length; the gap between the tip and the work surface was too small. The close proximity allowed loose bits that popped out (which also happened more with the air blasting out so close to the cut) to be pinched, which would stall the gantry. So, with two good reasons to remake it I pulled a piece of aluminum out of the scrap bin and put it in the chuck of my lathe.

The last nozzle I made to have the tip about a 1/4″ above the focal length; the new one is about an inch. The airflowis less concentrated on the piece, but after a few test cuts it does seem to still be quite sufficient.
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Installing LightObject Z Table

The Z table arrived a few days ago and I got a chance to install it thanks to the Holiday. It was pretty straight forward, but I do need to remake the air assist because the frame interferes and the gantry can not reach the home position.

I just put some countersunk through holes in  some 2″ x 1/8″ aluminum flat bar I had and tapped a matching holes on the frames of the Z table and and laser bed.
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I Purchased a Z Table

The bed on the K40 is terrible. There is a spring clamp (which is not very accommodating to begin with) in the center to hold a work piece, but it’s only a fraction of the travel area of the head. After spending a good deal of time trying to align the mirrors to be able to cut consistently across the entire area, I realized that since the bed was connected to the bottom of the case with standoffs rather than joined to the frame of the linear rails, the height on one side of the table varied by .8cm depending on which direction the diaphragm of the sheet metal on the bottom was popped.  So, all of it came out.

On a forum that I spend a good deal of time looking at there is a regular that has a quote in his signature: “I used to spend my time to save money but now I’m willing to spend my money to save time”. As I began to think about designing and building a motorized Z table, that quote came to mind. Rather than reinvent the wheel and spend more hours designing, purchasing parts, and building my own.

LightObject.com has a bed made for the K40. The hours I worked to earn the $155 it costs is fewer than what I would spend designing and building my own. Plus, it will be here in a matter of days. Another A4988 driver on the RAMPS board and a few settings for the motor should all I need to get it operational. I will need to figure out how to mount it properly to avoid the issues of the case not being ridged, but that should be rather simple.

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Air Assist

An air assist is a needed accessory for a laser cutter that my K40 did not include. An air assist does a few things. It helps blow away bits of carbon out of the way so the laser is more effective at cutting through the material and it keeps a flame from forming which makes black smoke that fouls up the lens, blocks the laser from cutting the material, and instead heats the lens– eventually damaging it.

The few things I have cut usually resulted in me lifting up the lid to blow on the laser point because when the carriage was traveling in a certain direction the flame would ride right up against the plastic bearings. Also, the lens needed to be removed and cleaned with nearly every use or it would block the beam to the point it was not effective.

The first thing I needed was an air supply. It doesn’t take a lot of air and I didn’t want to deal with the noise of a compressor, so I went with a large aquarium aerator. The Active Aqua AAPA70L supplies plenty of air and the sound is hardly noticeable along with the water pump and steppers.

To deliver the air people have either put a bent piece of tubing to the side aimed at the general location or created a nozzle that fits over the lens and directs the air straight down into the piece. The later has the benefit that the lens being sounded by positive pressure so it’s pretty much impossible for the smoke to come into contact with it.

There were some plans on Thingiverse, but I don’t have a 3D printer. Prints of a couple of those were being sold on eBay, but the quality looked terrible– which is why I do not have a 3D printer.

Then I found plans from Bart Dring (of MakerSlide fame) as well as a blog of another who turned a metal one on a lathe.

I have a Mini Lathe. I could make my own.

 

The Problem
Nozzle made by Bart Dring

I did some measuring on the carriage and realized the one from Bart Dring would fit the laser lens (it was designed for the same one) but it would interfere with the rails the bearings were mounted too.

I didn’t have a piece of material suitable so I ordered some 6061 1-1/4″ round bar. I also ordered some better tools for the lathe that I already indented to have– An OXA quick-change tool post, 3/8″ indexable insert cutters, and a boring bar set.

The ability to position the calipers in the laser was limited so I was not very confident in the precision of my measurements. I made a piece to check. I chucked up an old aluminum “cupcake” ingot that’s been aging in my basement for a few years

I finalized the dimensions and it was time for the real thing.
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Coolant Circulating System

Distilled water is cheap (especially when you make it), but having to change the water frequently is a pain. Up until now the coolant for the laser has consisted of a bit of distilled water in an open aquarium. Bacteria and algae grew fast and changing the water was needed every couple of days to keep it from getting slimy.

Ideally, at some point in the future, I will change the coolant to Dowfrost. Or maybe I’ll be convinced that RV antifreeze is okay to use, but I can’t say for sure what is in whatever brand they have at the hardware store, or even what concentration of propylene glycol. If it is mixed too weak you won’t be dehydrating the micro organisms anymore and the glycol will just bee a food source.

I found a couple people using a low power inline UV sterilizer and straight distilled water with good results. I’m not sure it will work indefinitely, but if can keep growth down and allow me to do water changes after a month or two I think I’ll call it a success.

I opted for a 3 watt UV-C sterilizer from JBJ Lighting, the Nanozapp JB7356. It should be sufficient for the five gallon reservoir and 800L/hr flow of the pump that came with the laser.

I purchased an 8 gallon plastic tote from Lowe’s that seemed like it would be structurally sound when filled with liquid. Holes where drilled for the power cables and tubing. The plugs of the UV sterilizer and pump needed to be cut off and replaced to feed through the grommets.

The silicone tubing is clear, so to help cut down on light and growth I ran it through some 1/2″ black polyethylene tubing I had. I put some tubing connectors for the black tubing on the reservoir and made a nut/spacing washer with PVC conduit female adapter to fit the pipe thread.

It runs. We’ll see if it works.

Update: 2019-12-01

Water is still clear, I haven not had to change it yet.
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Cutting Vent to Extend Work Area

The ventilation duct on the machine protrudes into the work area quite a bit. The sheet metal is spot welded in a number of inaccessible areas– otherwise I would remove the entire duct. So I just lopped it off with a Dremel (actually a Rotozip). Not perfect, but much straighter and cleaner than the cut made by the factor in the aluminum channel next to it.
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Mounting the LCD Display

The control panel on the lid was the obvious place to mount the LCD. I had already removed the potentiometer for laser intensity and the momentary switch for test firing the laser– both of those functions were present in the Arduino controller. I had thought about keeping the ammeter and the laser power switch, but they were in the way and really didn’t provide anything too useful. So they’re gone now, leaving only the power switch.

The only other issue was the distance from the panel to the Arduino at the bottom of the case. So I found som

The control panel on the lid was the obvious place to mount the LCD. I had already removed the potentiometer for laser intensity and the momentary switch for test firing the laser– both of those functions were present in the Arduino controller. I had thought about keeping the ammeter and the laser power switch, but they were in the way and really didn’t provide anything too useful. So they’re gone now, leaving only the power switch.

e 70cm IDC cables on eBay.

In Inkscape I drew a mounting panel as well as some spacer washers that would hold the LCD and cover all of the holes left by the abandoned controls, starting with GLDC controler.GTO from the schematics file of the RepRapDiscount Full Graphic Smart Controller page. I opened it in Gerbv and exported it as an SVG. The size of the LCD screen was way off of the outline in the file, but everything else seemed correct so I made an outline slightly smaller to overlap the metal frame around the LCD and centered it on the PCB as the LCD seemed to be.

I experimented with some scrap hardboard I had and decided to cut it at 300mm/sec at 50% power. I renamed the Inkscape layer to 50[feed=300] and exported it with Turnkey Laser Exporter plugin.  After starting I had to stop and go back to Inkscape to reorder the paths to cut from the inside out for the nested parts. It worked great other than there being a bit more flame than I would like, but an air assist which is already in my plans should help with that.

As amusing as the instructions on the panel in broken English are, I didn’t really want them there. After tearing off the sticker on the panel there was some chipped paint and a bit of adhesive that just didn’t want to come all the way off, so I just flipped it over. I placed the mounting panel were I wanted it traced the location of the LCD and marked the holes with a transfer punch.

Everything bolted together nicely and looks pretty clean. The SD card is also quite easy to access on the open lid which saved a bit of effort of trying to line that up with a hole and requiring the LCD to protrude from the case more.

 
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Wire Cleanup & Blown Fuse

I cleaned up the rat nest of wiring I had from testing. I got some series 2500 wafer connectors and pins from Tayda to replace the headers on the RAMPS so I couldn’t accidentally hook something up backward in the future, as I tend to do that while quickly messing around in my moments of free time.

I still need to properly mount the boards and screen. I’m still debating where I want to mount the screen. I’m leaning toward mounting on the lid, but I would need some much longer IDC cables to be able to easily open the lid. To keep things clean and avoid wire nuts and splices, I also ordered some series 2400 pins to utilize in the wafer connector on the power supply for the 5v(red) and active low laser pin(green). I scavenged some XH series JST connectors (from an old IDE Raid array module) to use for the laser PWM(blue).

After reconnecting I fired it up and ran a program. I realized I had left the laser switch off. I clicked it on while the program was running and after a couple of seconds the motors stopped, the laser turned off and the LCD faded to black… shit. I could hear the pump and water running which was my first fear (a flow switch is on my list because I will forget to turn it on at some point) and I checked the tube and didn’t see a problem. I didn’t have a light on the power switch but I had 120v on the female end of the power cable.

After taking a closer look at the male connector I see a built-in fuse holder.

I think it says 4A on the fuse. First I checked that there were no direct shorts, and there were not. 40W at 120V would be about 3A. Plus maybe a couple of hundred mA from the motors. Some more current from a spike from pushing the switch and of course some inefficiency in converting to higher and lower voltages. 4A seems reasonable to get to, so hopefully, it is that and not a failure somewhere. I’ll find out after I get some replacement fuses… I think there is still one Radioshack left in town. 

Perhaps I should dial back the laser output as well.