Some Do’s and Don’ts

Regardless of the advice, or the source, there is never a valid reason to raise the print head temperature above 120 degrees C.  Depending on the calibration of the temperature controllers, doing so may actually expose the print head to higher temperatures and cause permanent damage.  

Never touch the tip of the print head especially when it is hot as previously mentioned.  The plastic that the nozzle is made of becomes very soft at operating temperature and is vulnerable to tears and scratches.  Attempting to remove a clog or debris from the nozzle will almost assuredly damage the jet beyond recovery and cause extensive repair costs, or, total loss of print head investment. 

Do not change the print head material from build to support, or support to build without following the proper procedure.   We understand the frustration of needing a spare build jet when all you have is a spare support jet, but this generally only provides more business for BFT.  The support material is a wax based formula, whereas the build material is combination of plasticizers, resins, and dyes.  Converting a build jet to a support jet or vice versa is basically an easy task, but can only be accomplished on older PM and MMII jets without complexity. Build jets can be cleaned out by removing the heated line and purge cap and introducing VSO, or an equivalent, slowly into the print head through the top spout until it comes out the side purge.  Allow the VSO to set for a few minutes at full operating temperature. Replace the purge cap. The operating temperature will keep the build material molten and allow it to be flushed out along with the VSO through the tip of the jet. Follow up the first flush with a second one exactly like it. Now, lower the jet temperature to 60 degrees. After it has reached stability, fill another syringe with alcohol,(at least 91% pure) and slowly introduce it into the jet through the top spout. Repeat the alcohol flush one time. Now you can safely introduce the opposite material into the print head and continue on to calibration. Now for the complexity. The other print heads have a memory chip under the black cap which records such things and serial numbers, total drops fired, hours of use, etc. There is also a memory address for the type of print head that it is mounted on. When you attempt to place an incorrect print head on the carriage, whether it is of the wrong material type, or the wrong machine series, the machine will not operate and will notify you that you have an improper jet mounted. If you are familiar with the “magic jet, or mj” DOS prompt command, then you know that you can follow the above clean out process and make your opposite material jet function in either place.  

Auto bubble restoration in the SDI version print head is simply a matter of purging the print head through the side spout.  It is never necessary to inject air into an SDI version print head provided this procedure is followed.  After removing the side purge cap from the spout, allow the jet to set idle for a minute before purging.  This is ample time for all material inside the jet to siphon back to the storage tank.  Begin purging and when the flow of material is clean and steady, stop the purge and replace the purge cap.  The cap should be replaced within 5 seconds, although allowing as much time as 10 seconds will probably still be okay.  The risk is allowing too much time for the material to siphon back to the tanks and allowing air to go up the heated line.  If you allow 10 seconds or more and find that your jet is operating sporadically then re-purge and allow less time before replacing the purge cap. 

Even though it is always necessary to introduce an air bubble into the print head, a syringe is not the only reliable way to do it. The following is a simple and relatively easy method. Place a 2.75 inch length of purge tubing over the purge spout. Measure 2.5 inches from the tip of the purge spout and cut the tubing precisely at this location. Initiate a purge and stop it when the material reaches the end of the tubing. Now time it and determine how long it takes for the material to recede back to the tip of the purge spout. Write this number down and use it only for this machine. This number will change according to the condition of the tank filter and from one machine to another. Also, this number can be used to track the condition of your tank filter. If the time increases it is a sign that the filter is getting clogged and may require replacement. Now that you have the time recorded, initiate another purge but this time allow only a small amount of fluid to enter the tubing. Remove the tubing when the material disappears into the end of the purge spout and begin timing. When the same time that you have recorded has elapsed, replace the purge cap. What has happened is that the exact same amount of material has been displaced inside the print head that would be equal to a .2cc injection of air with a syringe. If .3 cc is desired, simply ad 50% more time.  This is a very easy process to perform on the go, and with some practice and a piece of Kim Wipe, can be done without the purge tubing.

It is strongly recommended that whenever print heads are being purged that purge tubing is used on the purge spout.  The exception is instruction #5 above. The build material is electrically conductive when molten.  Allowing it to flow indiscriminately all over the top of the print head is only asking for problems.  Also, when molten, it has very low viscosity and will flow into very small crevices.  This especially spells problems when it comes time to perform service on the jet.  Not only are the insides of the jet caked with material but the shear mass of it can cause temperature consistency problems.  Then there is always the risk of shorting something out on the inside such as the piezo, RTD, or the heater, thereby causing even more problems.  Ballistic Fluid Technologies generally supplies, with returned print heads, an ample quantity of short Teflon tubes to be used for purging.  Please use them and if more are required, please request them.  They are available at a very modest cost.  Also, in most cases they can be reused by applying a little heat or by dissolving the material from them using the appropriate solvent.

Print Head Versions (see pictures on Products & Prices page)
There are some noticeable differences between the versions of print heads.  The oldest version is the 6 Pro print head.  There are basically three types of 6 pro heads representing all of the developed stages of the print head technology.   The first is the type with the removable hexagonal shaped cap.  This the oldest technology and the most difficult to repair and maintain.  It is also the least reliable and was only used in the 6 Pro line of model makers.  The next design that is used in the  6 Pro head is basically the MMII, Patternmaster, T66/T612 internal works mounted on a 6 Pro shoe.  This is an improvement in reliability in that it no longer has the hexagonal cap.  It has a dip tube on the inside of the print head that allows for longer duration printing without re-establishing a bubble (a bubble is required inside the print head to provide inertial dampening to counteract the movement of the print head). The major faults with this design are that the bubble has to be injected manually. There is also an occasional freeze problem at the top of the build jet where the heated line is attached.  This jet is typically not easily repairable since the parts that go together to make this jet are interference press fit together and don’t come apart readily.  Special tooling is required to repair these print heads.  These jets are also limited in their frequency response and are not capable of running reliably at resonance without additional modification.

The third version available for the 6 Pro is the SDI version used in their RTM and 20/20 and BigFoot series model makers.  This version possesses the following advantages.  First, there is no need to inject an air bubble.  Although one is still required, it gets established automatically each time the jet is purged with the proper procedure.  Secondly, at the top of the print head there is an extension where the heated line mounts.  This extension supplies heat from the print head further up inside the heated line.  This prevents freeze offs at that location.  Thirdly, the general design of the print head is one of a modular concept.  This modularity allows the print head to be easily repaired.  Although it still requires significant technical skill, repair is performed with relative ease.  Fourthly, there is the increased frequency response.  The SDI version print head is capable of operating reliably at resonant frequencies.  The fifth difference has the orifice plane slightly recessed to offer more protection from lateral damage and better heat delivery to the orifice.  Finally, the piezo is better protected internally against thermal damage.   The latest SDI print heads can tolerate temperatures in excess of 160 degrees C without cracking the piezo.  Unfortunately, the potting compound cannot.  So if the jet is exposed to elevated temperatures, it is the potting compound that suffers permanent damage.  Potting compounds are developed specific to the application and any requiring this technology to operate at higher or lower temperatures can be accomplished by developing alternative potting materials.

The only cross over applications between 6 Pro, MMII and RTM came from Sanders Design International, Inc.  For several years, SDI provided RTM print head technology for 6 Pro and MMII applications.  With the introduction of the T66 and the T612 into the market, SDI’s RTM  jet technology has not yet found its way into these applications.  Along with the introduction of the 3Z series machines came some of the RTM features. However, there are still some not being used.

Ballistic fluid technologies is currently positioned to service all of these products with the latest technology plus new innovations.

Welcome to our technology Page

Some Background- (Well educated consumers make the best customers)
In general, your model maker print head is an electro-mechanical device that delivers small droplets of phase change hot melt materials.  The heart of the device is a small potted assembly of a piezo tube, an aluminum housing, a high temperature plastic nozzle, a couple of wires and some potting compound.  The remainder of the device deals with maintaining temperature, providing a consistent filtered supply of material to the nozzle, and a cable for delivering power and drive signals.

All in all it sounds quite simple.  In fact, the precision that is required throughout the manufacturing process is so sensitive that a few percent deviation from the process renders a non functioning component.  The orifice diameter for example is held to within .0002 in.  If it were not, the droplet size could not be regulated and the corresponding stream of droplet dynamics could not be controlled sufficiently to produce accurate models. Beyond this, the device is increasingly sensitive. 

The major vulnerable areas are: the delicate orifice, the sensitivity to over heating, and the fragility of the piezo.  The nozzle is made of a high temperature plastic that is very soft and delicate when it is at operating temperature.  Touching it at this time can easily damage it.  Even in light of this apparent drawback, it will provide service for years if not physically damaged.  It is extremely resistant to fluid abrasion.  It is strongly advised not to touch it directly or risk permanent damage doing so. 

Then there is the sensitivity to thermal damage.  The potting material has a glass transition temperature (Tg) slightly above the normal recommended operating temperature of the build jet.  When the print head temperature is raised above this Tg, the associated increase in the co-efficient of thermal expansion risks cracking the piezo. 

There is an additional risk to overheating the piezo; the loss of poling.  Poling is the phenomenon that gives the piezo its ability to molecularly shift and apply energy to the fluid.  When the temperature gets too high, the piezo can lose its poling and thereafter lose its ability to shift.  When this happens, the jet will no longer function. 

All of the above problems will render a print head useless.  The only one that is correctable is the last one, poling.  As a matter of course, all piezos are re-poled when returned for service.  Print head owners can be reassured that long term storage of spare print heads has no major effect on the piezo poling.  Print heads can be stored at room temperature for years without suffering any significant losses.  Storing print heads at temperatures lower than room temperature will do practically nothing in preserving print head functionality.  The cost of re-poling is built into the type of service requested, or can be provided separately.