MakerBot Replicator 2x: More Air Prints, custom heat sink

I am increasingly frustrated with the MakerBot Replicator 2x we have at the office. It seems you need to spend twice the amount of time working on it as you get viable prints. After a streak of good luck and reliability, as of late it refuses to complete any kind of medium or large size print job. It'll get part of the way complete, and then stop feeding filament- a classic air print.

I am guessing the problem is because the aluminum block that holds the stainless steel feed throat for the hot ends in place isn't cooled sufficiently. If it gets too warm, the stainless steel feed throat will get too warm, and the filament will soften before it gets to the hot end nozzle and jam. I thought I would attack this problem by creating an improved heat sink and attempt to move more heat away from the aluminum block, and thus attempt to keep the stainless steel feed throat cooler. I also attempted to improve the insulation between the hot ends and the aluminum block.

First, I constructed a heat sink using 1/8" thick copper sheet purchased from Mcmastercarr. I thought the copper would create a improved heat flow path from the aluminum block to both of the fan-cooled heat sinks, as well as increase the total mass of the heat sink. It should also allow improved heat flow from the aluminum block near extruder #1 to extruder #2's heat sink.

Heat sink cut, drilled, and ready to go

Trial fit of stock heat sinks checking for hole alignment

Test fit on drive block

Test fit on drive block

 Next, I wanted to reduce the convective & radiant heat transfer from the hot ends to the drive block by adding some 1/32" thick silicone rubber, also sourced from www.mcmastercarr.com.

Covering all air gaps on the top of the extruder platform

Sheet of self-adhesive rubber cut to fit the bottom of the aluminum hot end block

Adhered to the bottom of the aluminum block

Extruder #2 Re-attached

During this assembly and dissemble, the thermistor / thermocouple for hot end #1 failed. The stock cables are very thin and fragile, so it wasn't much of a surprise. Makerbot actually sent a replacement thermocouple free of charge. The new thermocouple wire is much thicker and appears more durable than the stock cable.

New Makerbot Replicator 2x thermocouple on the left, original on the right. The stock cable used much smaller gage cable. 

Since this is not the first time I've completely disassembled extruder #1's hot end, the stock ceramic / polyimide / insulation hot end insulation was cracked and looking pretty sad. Rather than tape it back together with some kapton tape I ordered a replacement insulation set off of amazon.com from VIRA design.

Mini-Review of the Vira Design Makerbot Replicator 2x upgrade kit, AKA: Upgrade Kit for the Hot End Insulation on Makerbot Replicator 2x-extruder-reprap

• Shipping: Slow-  took about two weeks- it appears as though they paid for shipping, then make the parts, then shipped them out. 
• Packaging: Poor- all the parts were tossed in a much-too large box- although since nothing it breakable it didn't matter
• Instructions: Poor- zero instructions included with the kit, although if you are capable of installing it you'll be able to figure it out
• Part quality: Good- cast silicone parts are serviceable, but required x-acto knife cleanup of all thru-holes
• Value: Good - you'll have a hard time producing these parts yourself for much less, let alone the time required to design, create molds, and make the parts. If you need replacement insulation for your hot ends these are a good option. Plus they are completely non-fragile, unlike the stock ceramic insulation. 

Vira Design upgrade kit for Hot End Insulation on Makerbot Replicator 2x Mini-instructions:

1) Use an X-acto knife to clean out all of the thru-holes in the silicone insulation parts.

New rubber insulation on the right., prior to trim

 2) Cut the white insulation to size for the flat end of the aluminum hot end block.

Using aluminum hot end block as pattern to cut white insulation

 3) Cut kapton / polyimide tape to hold the white insulation to the aluminum block

Cut tape using X-acto

 4) Stick white insulation patch to kapton tape

Ready to go

 5) Attach insulation patch to aluminum hot-end block

Attach tape / insulation patch to aluminum hot end block

Insulation in place

 6) Insert hot-end assembly into silicone insulation

Ready to go!

 Next up, loading new thermocouple into hot end block. I put a dab of thermal heat sink compound onto the threads to improve heat conduction and also to prevent the thermocouple threads from seizing in the aluminum block. When I threaded it in I rotated the aluminum block rather than the thermocouple to minimize any stress on the thermocouple wire. I also only tightened it finger tight- no tools used.

Thermal heat sink compound on thermocouple threads

Hot End #1 installed. 

Next up, finish installation and fire it up.

Thermal compound on the interface between the new copper heat sink and the aluminum hot end block

Thermal compound on the back of the aluminum fan cooled heat sinks

Up and running!

So, after all this, you'd expect it runs perfectly..... And the answer is... NO! Very frustrating. It might work slightly better but I'm still getting air prints. So far I've only been trying authentic MakerBot brand natural ABS filament. I'll try using some generic colored ABS filament- I believe it has a higher melt temp, which might help.