Engineering to Save $5000

Upon receiving our pre-owned 3D Printer we discovered the machine was having a few issues.  However, we expected a bit of work to flush out the bugs.  When the print head was removed to troubleshoot a clogged extrusion nozzle, we discovered a much larger problem …

The material extrusion nozzle and heating tube appeared to have sprung a leak during the previous ownership.  There is quite a large amount of material now extremely hard and carbonized (plasticizers all cooked out).  Left unchecked, the material would continue leaking eventually rendering the head unusable and unrepairable.

Without knowing how the print head is constructed, the only option was to disassemble the entire head.  We were able to put the partially disassembled head back into the machine to heat the nozzles back up (seen in the picture above).  The material was slowly and carefully pulled away from the nozzle while soft.  Once the material was pulled from the heat tube, it solidified into a rock-hard substance within a minute.

We pulled out the heating tube causing the problem, removed the foil and fiberglass over-wrap.  Most of the leaked material residue came off with the foil exposing a clean heat tube and heating element.  It wasn’t until now that we identified the source of the problem.

In the picture above, notice the inlet buffer (tanish brown plastic looking disk) is broken leaving a small piece left in the center of the heating tube.  Also, note the material residue on the face of the inlet buffer.  The material had been leaking between the fractured inlet buffer.  This was most likely caused by a clogged extrusion nozzle in combination with a stress fracture in the inlet buffer from the heating and cooling cycle.

How do we fix this?  First, let’s call Stratasys and see if they have a replacement ….

PRINT HEAD, FDM2000, WATERWORKS ABSi …………………… $5000

Ouch!  Now, we’re totally dedicated to getting this machine functional as we have a decent bit of money already into its purchase price.  However, if we invest another $5k, we’re probably better off buying their new machine for $15k.  Now it could be suggested that this is Stratasys’ planned obsolescence.  Maybe, maybe not.  The head is so complicated and designed for low production (expensive to manufacture parts) that it actually does cost that much to rebuild every part in quantities of less than say 5 at a time.  You’ll get a glimpse of this in a second.

Now what?

The part we need is very simple and something we could make in about an hour or less with the right equipment.  Pull out the calipers and let’s get this done…

Done.

Only one question… What type of plastic can hold the tolerances we need (+/- 0.001″) throughout the temperature range of the heating tube (room temperature to 290 degrees C) ?  Phenolic? No.  ABS?  Not a chance.  Engineering plastics ?  Absolutely now which one?

Cut to the chase… Polyimide is typically sold in very thin sheets or adhesive tape for insulating electrical circuits but is also solid in bars at about $71 per inch.  We can’t just chuck up just one inch in the lathe and what if we need another one?  Wow… the hits keep coming.  We found a surplus 5″ bar for about $150 and got it done …

One minor improvement was made where the small boss meets the large disk.  We added a radius to reduce the stress caused from the coefficient of thermal expansion differences between aluminum and Polyimide.  A chamfer had to be added to the heat tube to clear the new radius.

Heating tube reinstalled into print head (on right).

Because the head was taken apart, the tip offset between the model and support tips must be adjusted.

Back in action…

After replacing the clogged nozzle that started all of this, the machine has worked quite well for us.  We’ve had some minor hiccups and a lot of calibrating to do but all is well now.

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