Heater 2.1: Approaching 20 DPI in sugar for $20

Thursday, January 03 2008 @ 03:44 PM PDT

Contributed by Windell

In going from the original coarse air heater that we used in the first version of the CandyFab 4000 to the vastly improved Heater 2.0, we were able to take the effective fabbed pixel size from about 1/5" to about 1/16".
The basic idea of Heater 2.0 is that we take a ceramic heating element from a soldering iron and wrap fine refrigeration tubing around it. One of the shortcomings of that design is that the thermal transfer between the ceramic and the air was very inefficient, due to several different factors. The net result is that the heater ran unpleasantly hot while the air was not hot as we would like. The natural way of compensating for lower temperature is to turn up the airflow, of course, which does lead to degradation in resolution.
Here are the first results with Heater 2.1, an improvement on same basic design. Instead of a ceramic heater, it is now based on a low cost and highly robust cartridge heater, which can be obtained new for as little as $15. We have used this design to print some high-resolution objects, such as the trefoil knot shown above, finally approaching a true 20 DPI resolution, and easily the cleanest output yet achieved with the CandyFab.

Here is the basic construction of heater 2.1. We start with a 55W, 120V cartridge heater. This particular one is a from Watlow, and I picked it up surplus. This is a very common type of heater, with a stainless steel case, and is typically rated for fairly high temperature. If building your own heater with this design, consider part number 3618K351 from McMaster-Carr (3/8" dia, 1" long), available as a 100 W or 150 W heater for 120 V or 240 V for $19.01. Another good source of low-cost cartridge heaters is Gaumer Process. (There are quite literally dozens of other manufacturers to choose from.)
As before, 1/8" OD copper refrigerator tubing is wound, tight, around the exterior of the cartridge heater, now providing a large metal-to-metal contact area. The cold air enters from the top so that it can warm up before it approaches the hottest part of the cartridge heater, and finally exits from a simple nozzle at the bottom. A single "preheat" turn is added around the middle, perhaps unnecessarily.

The cartridge heater inside the copper tubing coil. A cartridge heater has a fairly high thermal mass, which leads to a fairly stable temperature. Because it is designed to operate without forced air cooling, we can operate this system with vanishingly small air velocity. This enables very even heating, even melting, and minimum displacement of melted and unmelted sugar, allowing us to achieve vastly improved resolution.

Here is what the heater and coil looks like when you view it from the business end.
One note on construction: The last turn, with the nozzle, is bent inward somewhat, providing a stop to index the heater inside the coil. You could employ a similar technique on the other end to fully trap the cartridge heater.

Finally, the heater and copper tubing are wrapped up in foil-backed ceramic insulation. By trapping heat, we significantly reduce the total amount of power that we need to dump into the heater and at the same time make the outside relatively safe to touch. (I wouldn't want to hold my fingers against it, but you probably won't have lasting damage from momentary contact.)

With the insulation in place, we can mount it to the CandyFab and try it out. Here, we're fabbing a new chain.

We fabbed this chain with the exact same model that we used for our original chain (please compare and contrast), just at a much smaller scale befitting the improved resolution that we get with this heater design. We may have gone a little too small, however, because a weak point in one of the links led to us only getting this partial chain of fragile links out.
As you can see, the beam width is as small about 3/8" (1 cm) in most places and slightly smaller yet in some areas. At this tiny scale, minor nonuniformities in the build can lead to weak areas that break easily. It is also worth noting that the consistency is very much like that of a sugar cube; a bit more porous than we have been used to with our earlier heater designs. That probably indicates that we need to turn up the temperature of the melts a bit more. On the other hand, we have been able to achieve much better color uniformity with this heater design than with any that we previously used. Also, when we work a little harder, it appears that our true 3D resolution is approaching an effective 20 DPI.

And the knot? It's just delicious.

Comments (4)

The CandyFab Project
http://www.candyfab.org/article.php/heater21



Here is the basic construction of heater 2.1. We start with a 55W, 120V cartridge heater. This particular one is a from Watlow, and I picked it up surplus. This is a very common type of heater, with a stainless steel case, and is typically rated for fairly high temperature. If building your own heater with this design, consider part number 3618K351 from McMaster-Carr (3/8" dia, 1" long), available as a 100 W or 150 W heater for 120 V or 240 V for $19.01. Another good source of low-cost cartridge heaters is Gaumer Process. (There are quite literally dozens of other manufacturers to choose from.) As before, 1/8" OD copper refrigerator tubing is wound, tight, around the exterior of the cartridge heater, now providing a large metal-to-metal contact area. The cold air enters from the top so that it can warm up before it approaches the hottest part of the cartridge heater, and finally exits from a simple nozzle at the bottom. A single "preheat" turn is added around the middle, perhaps unnecessarily. The cartridge heater inside the copper tubing coil. A cartridge heater has a fairly high thermal mass, which leads to a fairly stable temperature. Because it is designed to operate without forced air cooling, we can operate this system with vanishingly small air velocity. This enables very even heating, even melting, and minimum displacement of melted and unmelted sugar, allowing us to achieve vastly improved resolution.
	Here is what the heater and coil looks like when you view it from the business end. One note on construction: The last turn, with the nozzle, is bent inward somewhat, providing a stop to index the heater inside the coil. You could employ a similar technique on the other end to fully trap the cartridge heater.
Finally, the heater and copper tubing are wrapped up in foil-backed ceramic insulation. By trapping heat, we significantly reduce the total amount of power that we need to dump into the heater and at the same time make the outside relatively safe to touch. (I wouldn't want to hold my fingers against it, but you probably won't have lasting damage from momentary contact.) With the insulation in place, we can mount it to the CandyFab and try it out. Here, we're fabbing a new chain.

We fabbed this chain with the exact same model that we used for our original chain (please compare and contrast), just at a much smaller scale befitting the improved resolution that we get with this heater design. We may have gone a little too small, however, because a weak point in one of the links led to us only getting this partial chain of fragile links out. As you can see, the beam width is as small about 3/8" (1 cm) in most places and slightly smaller yet in some areas. At this tiny scale, minor nonuniformities in the build can lead to weak areas that break easily. It is also worth noting that the consistency is very much like that of a sugar cube; a bit more porous than we have been used to with our earlier heater designs. That probably indicates that we need to turn up the temperature of the melts a bit more. On the other hand, we have been able to achieve much better color uniformity with this heater design than with any that we previously used. Also, when we work a little harder, it appears that our true 3D resolution is approaching an effective 20 DPI. And the knot? It's just delicious.