So we have a guinea pig good friend testing out the idea of selling our smaller mill design as a kit. Below you can see all 77 parts all laid out prior to packaging. Since this was being shipped to Australia we really wanted to make sure we did not miss anything!
Or as I prefer to see it, the kit version of the mill all packaged up and ready for shipping!
Cassius V1.0 in Kit form, ready for shipping
We got the shop a hand tapping station. Since we started doing a lot of hand tapping it was beginning to be a bottle neck in moving from prototyping to production. Eventually tired hands won out and we gambled buying an import tapping station. I have to say I was on the fence about and it has totally changed how we tap holes. Before we used to drill a hole in the work piece, then change out the drill bit for a tap and use the drill to ensure the hole was tapped accurately. With the hand tapper though we can drill all work pieces and then tap them all with less hassle and re-fixturing of parts.
Our new tapping station
I had never used one of these stations – so I may write up a tutorial later once I have logged more time with it. These type of stations allow the vise to move in two axis. The goal is to let tapping will align the work piece. If you fixture a round part with just a slight amount of play the part will align itself so the tap is true to the bore as you tap it. Brilliant. I highly recommend getting one if you do a lot of tapping, well worth it for for like 60-80. Also since the tool relies on a bit of slop this may be one time where an import quality (once you clean it up properly) does not significantly impact performance.
As far as we could tell it looks like someone put together an initial minimum design for using the Allegro 3967, and all subsequent versions have been small revisions of that design. The problem is that looking at the data sheet for the A3967 and the schematic for the EasyDriver there were a lot of places I could not figure out what the original engineer was thinking. We looked at making our own board around the A3967 – but instead chose to directly drive the stepper motors with darlington transistors and control the phase timing from a microcontroller.
Cassius V1.0 PCB
We spent about a month having problems with Sparkfun’s version of the Easy Driver boards before deciding to make our own driver board. When they worked – which was most of the time – they were awesome. We started off concerned, becuase disconnecting a motor while the board is powered can fry the chip responsible for microstepping the attached motor, the Allegro A3967. Now this is a problem because it means if a motor fails it also is likely to take the electronics with it. We still decided to try the Easy Driver bord out because we had heard good things about it.
Once we started hammering on them we found it was also possible to fry boards so they would only drive the motors in one direction. The plans are open so we could look over the datasheets and review the design. That made us go from concerned about using the Easy Driver to flat out running in the opposite direction.
[Update: So after talking to Brian Schmalz, the developer of the EasyDrivers he was unable to reproduce our error after hammering on a number of boards and motors. It looks like we were either having a problem with our stepper motors or - what I think to be the more likely case at this point - I just made a mistake in how I wired up the motors. My best guess is the trick I used to wire up a unipolar stepper motor so it could be driven by a bipolar stepper motor driver was at fault. Only problem is I cant figure out why it worked at all if that was the problem. The important update though is that you should be fine using the EasyDrivers with bipolar stepper motors. ]
So up until now we have been using a heavily modified Taig lathe for all our lathe related prototyping. We use it to make shaft couplers, bearing inserts, and to machine the ends of the threaded drive rods.
Taig set up for shaft coupler run
Today we got a new Lathe! Well, new in this case is actually circa sometime in between the late 30s and early 50s, but hey it is still new to us!
Atlas 10F being brought to its new home
In addition to 5 more inches of swing, the Atlas is 20 times heavier and 3 times at big as the Taig. The plan is to migrate over machining to the Atlas while we CNC the taig. Then start using the taig as our main production lathe again.
Atlas 10in, ready to start making things round and round things have a smaller diameter
Stalk the wild streets of Seattle around the university district – and if you are lucky you may just run across one of Purple Crayon’s prototypes in the wild. Our intrepid photographer had to wait for hours to sneak up on the mill to get this rare picture. The pictured mill is one of the early software development prototypes being used in someone’s home to cut graham crackers as a test of using the mill to make parts for crazy custom gingerbread houses.
Cassius V1.0 software development station
This is probably how a large number of our units will get used by customers. The mill was designed to be in self contained boxes (the cover is off the mill in this picture) specifically so they could be used by customers who dont have access to a work space anywhere but in the home. In this case cracker crumps are prevented from flying everywhere and caught in the box for later cleaning – allowing the unit to be used next to someones main workstation in side the home.
The early prototypes are color coded, red, blue etc. There are no planes to offer one in fire engine red like the one pictured.
Since the initial tests of castings of individual parts went so well we decided to try casting assemblies of parts as a single piece. Right now there are a few assemblies of parts we are gluing together and we wanted to test casting them as a single piece. The process was the same as described before – only this time the molds were more complex.
Below you can see the mold for the Y carriage. Aluminum and wood pins were placed in the mold to provide removable mold pieces. To cast parts from the resulting mold the pins are inserted into the mold, which is then prepared and cast as described in the earlier post. When the cast material has hardened the pins are removed to remove the work piece. Wood pins provided aligned holes for screws, and channels in the finished parts for screwdrivers and other assembly tools to pass, and the Aluminum pins were machined where precise holes were required such as bearing or motor mount points. After it dries there is some slight flexing of the mold material so using solid shafts helps keep the holes aligned in the mold.
Preparing to make a complex mold
Below you can see one of the prototype Y and Z carriages using cast pieces. As before the white parts were cast plastic, and the black pieces were cut from ABS sheet plastic.
Cassius - Early prototype carriage using cast parts
Here is a slightly better view of the cast parts. The picture parts were from early attempts and there were a few visible casting defects, but the part functions fine.
Cassius - Close up of early prototype Y-Z carriages using cast parts
As part of prototyping production methods for our mills we tried playing with castible molds and plastic to provide a solution for the rapid production of multiple copies of a part. The results were fairly promising and the company may offer cast kits at some point.
Smoothon.com offers multiple lines of castable plastic resins with lines of compatible mold materials, and release agents. Smoothon.com also supplies tutorials for all their products – but the casting process is fairly simple and we will show what we tried here.
Start by gluing an original part to be copied down to a water proof sheet of flat material, and build a mold box around the parts. When casting multiple parts add small pieces of material connecting the parts. This will leave a channel in the cast mold through which the liquid plastic can flow, allowing the entire mold to be poured from a small number of points. Next add one or more pieces of material that will stick up out of the mold to provide pour points. Also add other pieces of material should also stick up out of the mold to allow places for the air to escape. The air vents can be very small – tooth picks work well.
Pieces mounted in mold box
Once the parts have been glued into the mold box hot glue the mold box to the underlying water proof sheet. This prevents the liquid mold material from leaking out of the box. If using a wooden mold box it is also a good idea to hot glue the interior corners of the mold box to make it liquid tight and able to hold the molding material. Pictured above is a mold ready for casting, and the same mold once cast is pictured below. You can see small pieces of wood used as risers for air and pouring points. Once the mold has hardened, you break down the mold, remove the original pieces and pull out the risers that were added for pour points and air venting.
Mold box filled and drying
To cast parts you just re-assemble the mold treating the inside with a release agent. You want to glue the box down to the underlying sheet again, this time to prevent any liquid plastic from escaping. When casting large pieces you should also put something heavy on top of the mold to prevent the mold material from floating up when you pour in the liquid casting material. At this point you just mix and pour your liquid plastic and fill the mold.
Make sure to have some place to pour off any excess material in case you mix too much plastic. Be sure to carefully read the directions on how the material used should be mixed and handled to avoid air bubbles in the finished casting. Stirring either to vigorously or not enough can both cause defects to result in most cast materials.
Once the plastic hardens break down the mold box and remove the pieces. A sample mold with cast pieces is pictured below.
Pieces in mold
Then just peal the parts out of the mold and cut off the flashing.
Removing pieces from the mold to clean up the flashing
Below are pictured some white sample cast parts next to their black ABS plastic pattern originals. The “wavy-ness” you see on the cast surfaces is because I used aluminum foil as a casting surface. They foil was not perfectly flat and this ended up being reflected in the cast surface.
Cast pieces next to the originals
So in summary casting parts turned out to be very easy and fast once you had an original. We anticipate that our customers who want a large number of a particular part will probably end up making molds or casting off parts made by one of our products.
For custom confection design one of the things our products will be able to make are custom molds. This is most likely how people would make custom shaped chocolate pieces – not carving them. However, we realized that cheap chocolate bars with a high wax content are available everywhere. So we looked into using cheap chocolate as a substitute for machinable wax. While expensive, since machinable wax is reusable and easy to get a hold of. We are even going to ship a small quantity of machinable wax with our mills. In a pinch though, from our initial testing it defiantly looks like chocolate will work as a substitute.
The picture shows the letters S&T stippled into the surface of the chocolate and a swirl pattern carved most of the way into the bar.
At 10:30pm on December 26th 2008, Konrad and Aaron brought the company’s “Bluebox” prototype online successfully demonstrating 3-axis positioning. We were both fairly excited. Bluebox is the third generation of a design that we have been working on and tweaking for months. Testing showed mechanical things are finally starting to get dialed in, and everything was working better then we hoped.
We forgot to take a picture with both of us in the frame. Hence the duplicate pictures.
An old school garage style startup, Purple Crayon is a new company dedicated to developing and selling consumer personal fabrication technologies. At its core the idea of personal fabrication is to provide anyone the ability to “make stuff” regardless of skills or knowledge. The idea is similar to modern desktop printers, which make it possible for anyone to produce high quality printed material with absolutely no idea how the printer works. Personal fabrication technologies will have an impact on the same scale of the industrial revolution – enabling anyone with a vision to build it, or share with others to build or modify a version of their own.
The first step on the road to consumer personal fabrication devices is making 3D scanners, printers, and milling machines cheap, popular, and easy to use; so that’s what we’re going to do. Purple Crayon’s first products will be a combination computer controlled milling machines and scanner, designed for use in the home. Keep checking this web site for information on buying one of these units, which will go on sale in April or May of 2009 for under $1,000. We will be using this blog to track our progress and post links of interest on personal fabrication technology – so check back often.