- Joined
- Aug 16, 2013
- Messages
- 1,057
- Reaction score
- 799
We’ve been in “social isolation” for going on a month and all the interesting stores are basically closed. It’s also been unseasonably cold and we still have about a foot of snow in the yard so I needed a project.
The other day I was printing a new enclosure for my engraver and this was going to be a 4.5 hour print so I set a timer and left the printer to play by itself. When I went down to check on it 4 hours later I saw to my horror that I only had about 2 loops of filament on the spool. I’ve spliced filament a couple of times before using a short length of PTFE tube and a BBQ lighter. It works, but barely. This was when I thought there had to be a better way.
This was version 8 and fortunately most of the other versions died in CAD. The idea was simple enough just sandwich two pieces of aluminum together, drill a 1.75mm hole through at the junction, bung in a hot end heater somewhere and away you go. Then thermodynamics rears its ugly head and things start to get complicated. The heater is only 40W so the block had to be as small as possible. The heater is 6mm in diameter so 3/8” (9.5mm) base would be a minimum. A small 3/8 x 3/8 x 1” block would be ideal but would provide no support for the filament and it would just sag outside the heating block. So what I needed is a way to support the filament and keep it cool while the splice point reaches fusing temperature so a thermal break of some sort.
An air gap has to be about the best thermal break around but won’t provide any support for the filament so I had to fill it with something. Looking around the shop I fixed on the good old JB Weld. According to what I found on the internet regular JB Weld " can withstand a constant temperature of 500 °F (260 °C), and the maximum temperature threshold is approximately 600 °F (316 °C) for 10 minutes.”. This was great because I was only looking to hit between 200 and 230°C hopefully for under 2 minutes. Further reading on the internet I found that JB Weld was not recommended by the guys that over clock/hack their computers to mount heat sinks because it was only an OK thermal conductor. Excellent, good old JB Weld to the rescue ticking off all my boxes.
Water, petroleum, chemical resistant.
Resists shock, vibration, and extreme temperature fluctuations.
Can withstand a constant temperature of 500 °F (260 °C)
Can be drilled, formed, ground, tapped, machined, sanded, etc.
Not a great thermal conductor.
And best of all I had some.
Epoxied the two pieces that make up the bottom so that there was only about a 1/8” thick layer of JB Weld filling the gap and let it sit overnight.
I ran a couple of tests to see how high and fast the block would come up to temperature and it turned out that the placement of the heating cartridge was critical to performance. I got the best results with the middle on the cartridge sitting directly under the filament grove. Using an infrared thermometer the block gets up to 220 °C in about one and a half minutes. I then milled a 2mm deep groove to hold the thermistor. As you can see the JB Weld has discoloured from the repeatedly heating it but its still rock solid
It was time to see how things change with the extra mass of the cover on. So with the thermistor in its place and a k type thermocouple in the filament slot and another to read the temperature of the outer portion I was ready.
After repeated heating/cool down cycles things looked good. The addition of the top cover didn’t affect the times for the block getting up to temp. With the heater running up to 220 °C the outside never went over 30 °C so the filament is fully supported and kept cool except right on the heater block. My pyrometer also let me verify that my thermistor was reading within a couple of degrees of the thermocouple. Its time to add some hinges and see if this thing will actually work.
This was when things got a little freaky.
“J-B Weld is water-resistant, petroleum/chemical-resistant (when hardened), and acid-resistant. It also resists shock, vibration, and extreme temperature fluctuations. J-B Weld can withstand a constant temperature of 500 °F (260 °C), and the maximum temperature threshold is approximately 600 °F (316 °C) for 10 minutes.”
All good but I guess no one ever exposed it to molten PLA plastic. I wish I had a video of this one. As soon as the temperature reached around 190°C it spiked to over 300 on the OLED display. I thought something had gone south with my circuit but nope it was starting to smoke and the pyrometer was reading the same! No way that little 40w heater was capable of doing that. Pulled the plug and ran the cooling fan until things got down to a safe level. I had to pry the cover open and the JB Weld had gone soft and rubbery and partly fused to the heater.
The weather is still in the crap and were down to only about 6 inches of snow so on to version 9.
The next morning the JB Weld was back to being rock hard so I cleaned the remains off of the aluminum and started thinking of what I had on hand I could use as a DIY refractory. I could think of a lot of stuff I could use that would be perfect but like I said before “all the interesting stores are closed”. Digging around I found I had some of the furnace cement left I’d used to make my first casting furnace on the back of a shelf. It felt about half full ant I was shocked to find it wasn’t completely dried out. This stuff must be 5 years old!
Built it up the same way as the JB Weld and set it aside to air dry overnight. The instructions say to heat it to 200F, let it cool then up to 300F before putting it into service. Cycled it in the garage toaster oven (would NEVER use that thing for food) then ran it up to 500F to fully cure the cement. The problem with using that is that it gets most of its insolating properties from the air bubbles that form during curing. So even though it sands ok there is no way of getting the smooth finish that I want. I’ll want to completely redo this block when things settle down but as a temporary fix I just put a couple of strips of kapton tape on for now.
The other day I was printing a new enclosure for my engraver and this was going to be a 4.5 hour print so I set a timer and left the printer to play by itself. When I went down to check on it 4 hours later I saw to my horror that I only had about 2 loops of filament on the spool. I’ve spliced filament a couple of times before using a short length of PTFE tube and a BBQ lighter. It works, but barely. This was when I thought there had to be a better way.
This was version 8 and fortunately most of the other versions died in CAD. The idea was simple enough just sandwich two pieces of aluminum together, drill a 1.75mm hole through at the junction, bung in a hot end heater somewhere and away you go. Then thermodynamics rears its ugly head and things start to get complicated. The heater is only 40W so the block had to be as small as possible. The heater is 6mm in diameter so 3/8” (9.5mm) base would be a minimum. A small 3/8 x 3/8 x 1” block would be ideal but would provide no support for the filament and it would just sag outside the heating block. So what I needed is a way to support the filament and keep it cool while the splice point reaches fusing temperature so a thermal break of some sort.
An air gap has to be about the best thermal break around but won’t provide any support for the filament so I had to fill it with something. Looking around the shop I fixed on the good old JB Weld. According to what I found on the internet regular JB Weld " can withstand a constant temperature of 500 °F (260 °C), and the maximum temperature threshold is approximately 600 °F (316 °C) for 10 minutes.”. This was great because I was only looking to hit between 200 and 230°C hopefully for under 2 minutes. Further reading on the internet I found that JB Weld was not recommended by the guys that over clock/hack their computers to mount heat sinks because it was only an OK thermal conductor. Excellent, good old JB Weld to the rescue ticking off all my boxes.
Water, petroleum, chemical resistant.
Resists shock, vibration, and extreme temperature fluctuations.
Can withstand a constant temperature of 500 °F (260 °C)
Can be drilled, formed, ground, tapped, machined, sanded, etc.
Not a great thermal conductor.
And best of all I had some.
Epoxied the two pieces that make up the bottom so that there was only about a 1/8” thick layer of JB Weld filling the gap and let it sit overnight.
I ran a couple of tests to see how high and fast the block would come up to temperature and it turned out that the placement of the heating cartridge was critical to performance. I got the best results with the middle on the cartridge sitting directly under the filament grove. Using an infrared thermometer the block gets up to 220 °C in about one and a half minutes. I then milled a 2mm deep groove to hold the thermistor. As you can see the JB Weld has discoloured from the repeatedly heating it but its still rock solid
It was time to see how things change with the extra mass of the cover on. So with the thermistor in its place and a k type thermocouple in the filament slot and another to read the temperature of the outer portion I was ready.
After repeated heating/cool down cycles things looked good. The addition of the top cover didn’t affect the times for the block getting up to temp. With the heater running up to 220 °C the outside never went over 30 °C so the filament is fully supported and kept cool except right on the heater block. My pyrometer also let me verify that my thermistor was reading within a couple of degrees of the thermocouple. Its time to add some hinges and see if this thing will actually work.
This was when things got a little freaky.
“J-B Weld is water-resistant, petroleum/chemical-resistant (when hardened), and acid-resistant. It also resists shock, vibration, and extreme temperature fluctuations. J-B Weld can withstand a constant temperature of 500 °F (260 °C), and the maximum temperature threshold is approximately 600 °F (316 °C) for 10 minutes.”
All good but I guess no one ever exposed it to molten PLA plastic. I wish I had a video of this one. As soon as the temperature reached around 190°C it spiked to over 300 on the OLED display. I thought something had gone south with my circuit but nope it was starting to smoke and the pyrometer was reading the same! No way that little 40w heater was capable of doing that. Pulled the plug and ran the cooling fan until things got down to a safe level. I had to pry the cover open and the JB Weld had gone soft and rubbery and partly fused to the heater.
The weather is still in the crap and were down to only about 6 inches of snow so on to version 9.
The next morning the JB Weld was back to being rock hard so I cleaned the remains off of the aluminum and started thinking of what I had on hand I could use as a DIY refractory. I could think of a lot of stuff I could use that would be perfect but like I said before “all the interesting stores are closed”. Digging around I found I had some of the furnace cement left I’d used to make my first casting furnace on the back of a shelf. It felt about half full ant I was shocked to find it wasn’t completely dried out. This stuff must be 5 years old!
Built it up the same way as the JB Weld and set it aside to air dry overnight. The instructions say to heat it to 200F, let it cool then up to 300F before putting it into service. Cycled it in the garage toaster oven (would NEVER use that thing for food) then ran it up to 500F to fully cure the cement. The problem with using that is that it gets most of its insolating properties from the air bubbles that form during curing. So even though it sands ok there is no way of getting the smooth finish that I want. I’ll want to completely redo this block when things settle down but as a temporary fix I just put a couple of strips of kapton tape on for now.
Somewhat off topic, but would you explain in detail your heater and test setup?
