People often ask me why the edges of their laser cuts are not square. The laser beam is being focused at an angle to a spot, so no cut can be perfectly square, but there are things that can make it worse. Note: All of the images are exaggerated to show the affects.
You first need to understand how the lens works. Laser cutters use a collimating lens. This means it takes parallel rays from the beam and focuses them to a single spot. For a couple of complicated physics reasons, it can never do this perfectly, but it should do it close enough not to be a factor in this discussion. Below is a picture of a collimating lens. A typical beam width is usually about 5mm-8mm and a typical lens is about 20mm-25mm wide.
You can see that the beam forms an hour glass shape. This can cause a little angle. With a 6mm wide lens and a 50mm focal length, this angle is typically 3-4 degrees.
To get the least affect on your part, you might want to center the focus in the middle of your material.
If you are getting a bigger angle than a few degrees, it is more likely because the beam is not in the center of the lens. The lens will still focus to that same point, but the hour glass is at quite an angle to your work piece.
This type of angle is offset in one direction, so you may see it more in certain directions of travel. If the beam is moving from right to left in the above image, you might not notice the problem at all.
Does a longer focal length help? It can, but due to the complicated physics issues I referred to earlier, a longer focal length creates a larger spot size, which reduces power density. See this calculator.
3D Systems recently acquired Geomagic. Several years ago they acquired Alibre. Alibre is a parametric CAD program. It appears that they are simply re-branding the existing version of Alibre as Geomagic, but will incorporate feature of the Geomagic product line over time. Here is the basic product line.
I have used Alibre and Cubify Invent and find them to be quite capable. Some day I may loose my easy check out access to Pro/Engineer and these products are on the radar as possible solutions. I found the even Cubify invent could do a few little tricks that are a pain in Pro/E.
In a couple weeks we are going to do a CNC V Carving night at Pumping Station One. We hope to fabricate a number of designs on the CNC router. This blog post will serve as a basic introduction to the concept and will help people get artwork ready.
What Can V Carving Do?
V Carving uses a V shaped bit to to “carve” a design into the material. Because the bit has a v shape, you can cut narrow shapes with the tip or wider shapes near the bottom.
You can even cut shapes wider than the widest part of the bit by doing multiple passes of the bit. The depth of the cut is proportional to width of the cut, so you need to make sure your material is thick enough. If you have very wide areas, you can set a depth limit and you can make that area have a flat bottom with a second flat bit.
Normally routers cannot cut square inside corners because you are cutting with a round bit. V Carving can get around this limitation because the bit can rise up into the corners until it gets to the zero radius tip.
V Carvings can look great simply cut in the natural material, but they can really pop when you put a contrasting finish in the carved areas. This is a time consuming process and can be difficult to do well.
You can often shortcut this process by using masking materials. You start by applying a background finish to the work piece. This is then masked with tape or specialized masking material. The router then cuts through that as it is cutting the design. Now, only the cut area is exposed and you can simply spray paint the exposed area. If the design has multiple colors you can cut one color, paint, remask and repeat the process.
The files should in in DXf, DWG, AI, EPS or PDF format. Many programs like InkScape and CorelDRAW can output these formats. If you have hi resolution bitmap, some of these programs can convert to a vector format. Feel free to try that, but help with that will be beyond the scope of the session.
The quality of the masking material comes into play with very fine details. If your design will leave tiny isolated dots of masking, some materials may not stick well enough and break free during cutting. If that happens, you can manually touch up those areas later. I like to use Avery Paint Mask, but plain masking tape, adhesive shelving paper and materials for vinyl cutters also work.
What is good artwork to start with
Avoid very thin lines lines. The material needs to be needs to be perfectly flat and consistently thick for this.
Very large areas to cut will take a long time, so avoid them for this session.
Multiple colors. Multiple colors is OK, be each color needs to be separated from the other color so there is masked uncut area between them.
This logo would work. The red would be the base material and all other colors would be cut and colored.
This one would be very hard to do because of the adjacent colors.
How to bring the artwork to the session.
To save time, the artwork should be as ready to import as possible. Problem artworks will be pushed to the back of the queue and might not get cut.
The artwork needs to be in a digital, vector format. By digital I mean you can sent the file electronically. Vector files are created with actual geometry. Lines are lines and not a string of pixels. Scans and photographs are not usable. If you zoom in and the image gets pixelated, it is not ready to use. The shapes also need to be closed. If you have a square, for example, all the corners need to meet or the software cannot determine inside from outside. Tiny gaps can be closed in the CAM software, but if you can see them, close them.
Try not to be too complex or have large cut areas. These will take a long time and will limit how many people we can accommodate in one session. We can still create G-Code, but you many need to cut it at a later date.
If there is time I my cut small PS:One snowflakes for the people who did not bring any artwork.
The idea material is a smooth, pre-finished piece of wood. It needs to be as least as deep as 1/2 the width of your widest feature if you are not planning a flat bottom. The material should be as flat and consistently thick as possible or the results can be distorted, because the depth of the cut is so critical. Avoid oily or wet finishes because the mask material may not stick well. Plywood does not look well and often interior layers have voids.
I met programmer and maker, Joe Walnes, through a few local Chicago maker groups. He showed me a really cool web based G-code viewer he wrote to preview his 3D printer G-code. It used WebGL for super smooth motion of the model. It also allowed you to drag and drop your own files right into the page. It worked great, but really only worked with 3D printer G-code. He posted the code on GitHub.
I have a couple programming projects in the works that need a G-code viewer, so I decided to update his program to handle more types of programs. Joe had a really nice UI and design pattern for the code, so I left that alone. He also helped me out with a few issues as I worked.
A parser is a bit of code that breaks down text into tokens, or the basic grammer of the G-code. He was working with very well formatted G-code so his parser was pretty simple.
G1 X5 Y5 Z6 E0.124
I was dealing with really Fugly lines of G-Code like this, so I needed to totally rewrite the parser.
Reprap 3D printers basically use G1 (straight moves) for everything. I needed to add the code to handle G2 and G3 (arc moves). This was a little tricky because there are no arcs in WebGL. I had to break them into small line segments. Joe also treated each Z level as a separate layer. That is nice for printers, but not for general G-code. I changed that and the way the color of the lines worked.
A Work in Progress.
It works on all my CAM generated 3D printer and CNC router G-code, but I want to add code to deal with more advanced features that are often hand coded like incremental moves, machine offsets, parameters, math functions and subroutines.
I will post the source code soon.
You need a WebGL capable browser like Chrome, Opera or Firefox. I hard to turn on WebGL in my Firefox. I got it to run on my Android phone in Opera, but could not spin/zoom the model with the screen controls.
To view your own files, just drag and drop the G-code into the browser. It will use the zoom settings for the previous model, so if you drop something that is a different size or offset to the side you may need to zoom around to find it.
The subject of skateboards came up about 2 weeks ago at meeting of local makers. One of the PS:One Hackerspace guys confessed he wanted to buy a longboard for getting around town. Longboards are more about basic transportation and carving smooth turns than doing tricks. The large size also encourages design and graphical creativity. I thought it was the perfect opportunity to get the creative juices flowing. It was a fun project that cost less than $50 to complete.
Once I get these ideas in my head I am totally obsessed with them. The only way to clear my brain is to actually build the thing whether I need it or not. I finally got some time between 2.x Lasers and ORD Bots orders on the CNC router last Sunday night.
3/4″ baltic birch deck.
Logo inlay on top near the front in a contrasting wood type.
The inly would be 1/4″ thick so minor dings and chips would not wreck the inlay.
Pockets cuts on the back to look cool, reduce the weight and give the board a little flex.
Miter the edges of the pockets for a cool look, make it more comfortable to carry and make it less prone to chipping.
Round the perimeter edges.
I really like the drop style truck mounting, but I would stick with a conventional bottom mount to start with.
Drop through mounting – Image from Moose
I found a whole bunch of longboard PDF templates here at Silverfish Longboarding. I started with the ST11 version. I felt the exposed wheels would allow more wheel, truck and mounting options without the wheels “biting” the board. The outline had a few sharp corners that I smoothed out. I didn’t want the line that is produced when you round the edge with the sharp corner. I imported an SVG of the snowflake logo from the PS:One wiki and sketched in some pockets on the back that looked cool, but still preserved the strength off the board with hope for a little flex.
I bought a truck and wheel kit off eBay for about $35 (free shipping). I only did basic research into what made a good choice. I just bought something that fit the basic requirements and looked cool (wide, reverse kingpost, big red wheels).
The basic deck is 3/4″ thick Baltic birch plywood.. The local high end lumber yard, Owl Hardwood, had some really nice 13 ply material. The top side is perfect. The back side is really good with only a few small blemishes and all the inner layers are high quality with no voids. Most plywood has knots and voids on the inner layers. The exposed edge and the pockets would show the inner layers so I wanted them to look good.
Cut the inlay piece out of 1/4″ thick oak.
Mount the Baltic birch on the router and check for Z flatness in the inlay area. I mounted it on a sacrificial particle board. This board was clamped by itself, so unclamping the plywood would not affect the position of the sacrificial board.
Cut the pocket for the inlay slightly under sized. I then continued to profile the edges larger until it fit tightly.
Glued the inlay in place.
Cut the bolt holes for the trucks.
Cut the deck outline. I purposely cut extra deep into my sacrificial base so that I would have a clear outline of the board. This would allow me to flip it squarely to do the back side.
Cut the back pockets 1/4″ deep.
At the last minute I decided to add the the PS:One logo to the back as a 1/8″ deep pocket. It turned out to be my favorite detail.
Used a 1/2″ 90 Deg V bit to miter the edges of the pockets. I did a profile pass on the pocket lines set inside the line 0.02″ to make sure the tip was always inside the edge for a clean cut. The depth was set to leave 1/16″ of the original pocket wall.
Unclamp the deck.
I used a 3/8″ 1/4 round bit with guide bearing on the router table to round the edges.
Stained using Minwax Golden Oak stain. It is a light colored stain that varies quite a bit with the wood type.
Sealed. Minwax Satin Poly Urethane.
Design, research, ordering parts…about 1 hour.
Total time on the router…about 1 hour.
Sanding and Finishing…about 1.5 hours.
$10 worth of baltic birch
$5 1/4″ x 8″ oak for inlay
$35 trucks and wheels.
Already had all bits, stain and varnish
I want to laser cut a bunch of little PS:One snowflakes out of grip tape and sprinkle them on the deck.
I am not super happy with the way the baltic birch stained. Woods like that can look blotchy due to varying wood density. I might have done better pre treating with a wood conditioner the birch or going without stain.
The tool is attached to a hand held frame. Actuators within the frame can move the tool to compensate for errors you would make when trying to cut a complex shape.
A high contrast pattern is placed on the work piece. They are the horizontal bands of shapes in the image above. The tool creates an internal map of the work piece using a camera. It can then accurately determine it’s location anywhere on the work piece without the drift that might occur using incremental positioning sensors. The outline of the cut to be made is shown on the screen. The location of the tool center is also shown on the screen. You only need to follow the line within the correction limits of the tool. The tool digitally corrects to produce remarkably good results.
This same idea could be applied to a lot of different 2D fabrication tools. There is a very comprehensive paper here showing all the details.
Thermal friction drilling very cool (hot actually) drilling technique that is especially useful for creating tapped holes in thin wall materials. The pressure and friction of a specially designed conical bit heats the material to a plastic state and forms it into a hole that has 3-4 times the depth of the wall thickness. It looks like it is best for hollow tubing because the back side of the hole is a little rough. The bit forms the top of the hole into a flat bushing which is perfect for fastening to round tube.
The bit is made from carbide and is held in a special holder/collet assembly that isolates the heat generated on the tool from getting to the machine. Lubrication is required to prevent the material from welding to the bit. Any machine that meet the speed and power requirments, including drill presses can use this technique. According to the web site a 6mm hole would require about 2500-31100 RPM at 1.2kW (1.6 hp).
Most of the thermal drilling companies recommend thread forming taps. These taps form the threads by displacing the metal rather than cutting it. The resulting threads are smoother and stronger than cut threads. I have used them on conventionally drilled holes. The pilot hole needs to be slightly larger than a standard pilot hole. The taps are a lot stronger because they do not have flutes. The can be run faster and don’t bind up with chips. It looks like the combination of thermal drilling and thread form taps creates a very clean operation.
Inventables announced a filament extruder competition the GE Garage at Maker Faire on 5/19/2012. The contest is to design a machine to extrude ABS or PLA filament from pellets to 1.75mm using less than $250 worth of materials. The extruder must be able to add the colorant as well. The first person to upload a solution wins. Inventables plans make pellets and colorant available to people to play with.
Inventables is now taking pre-orders for Hadron ORD Bots. I will not be shipping anymore kits and Inventables is now the official, authorized distributor of the kits. Go here to get on the list for one of the units. The Inventables kits will also have the following improvements.
Bright Dipped Finish
The previous version looked great, but the matt finish quickly gets dirty and scuffs often looked like sceatches. Bright dipping is a chemical polishing that is done before the anodizing process. The goal is to get the finish quality of a Mag Light.
Open Ended Wiring Holes.
A well wired ORD Bot is a thing of beauty, but once wired some of the parts are trapped by the wiring.
By adding open ended wiring holes, the wires can escape out the sides. This will allow you to completely side off thing like the gantry without removing any connectors.
Wider Extruder Platform.
Deep extruders like some of the Wade’s family of extruders previously had to overhang the front a bit. This adds more depth and an extra hole pattern to give you more options.
With loop belts you will not have to measure and cut from open ended stock. They will be a lot easier to install and will have twice the grab in the belt clamps.
Build Platform Changes.
Added holes for the ORD Bot heated build platform.
Increased spacing between the wheels. This improves rigidity, reduces the sensitivity and cleans up the busy center area where the clamp and switches. fit.
Electronics Plate Changes
The Electronics plate will now have hole patterns for the RAMPS, ORDuino and Azteez controllers.
There has been a lot of interest in an ORD Bot with a bigger build area. This is the Quantum’s larger brother. This uses the MK1/MK2 heated built platform which is about 214mm x 214mm. You can go larger, but you are on your own.
The name is not yet determined. I wanted something similar to Quantum that conveyed a larger volume. A search of units of volume reminded of one of my favorite units “The Firkin”. Not only does Firkin sound cool, it is part of the FFF (Furlong/Firkin/Fortnight) unit system and it is a measure of beer. The other suggestions was Hadron, which is very similar to Quantum but larger and means thick or stout in greek. Firkin is cool, but Hadron is more family friendly.
They share all parts except the MakerSlide length, the handle and the build platform.