How to remove threadlocked pulleys from steppers with FIRE
Posted: Wed Dec 09, 2015 10:22 pm
If you get tired of all the racket your printer makes, and you want to make it quieter, you can install Astrosyn dampers - but that means you have to move the pulleys further from the motor to account for the thickness of the dampers. Normally, the pulleys are secured to the steppers with grub screws, and these are prevented from rotating with the use of thread locker. If you try to loosen the screws later, but you don't do anything to get rid of the thread locker, you'll just cam out the grub screws.
Materials
Propane blow torch (Amazon has torch heads and propane cylinders, as does any hardware store)
Shot glass (that you don't intend to drink from ever again)
99% alcohol
Microwave
Tweezers
Toothpicks
Paper towels
Also, keep a fire extinguisher handy. You have one of those and the gauge reads fully charged, right? Keep it close by.
Removal
Do this outside, or in a place with good ventilation. I did this in my kitchen and used the stove hood's vent fan to remove all the nasty vapors. Passive hoods aren't good enough for this. The vapors are nasty, and you don't want them wafting around indoors. Do NOT allow yourself or anyone else to get near the vapors!
You need to heat the thread locking compound to a few hundred degrees Celsius to degrade it enough to free the grub screws. However, the stepper motor has magnet wire inside, and if that gets hot enough, the insulation will melt and it'll develop internal shorts that will render the motor useless. Additionally, the stepper shaft and pulley are both aluminum, and that will deform if exposed to enough heat for long enough. Therefore, we want to use as little heat as possible.
Use the adjustment knob on the torch head to reduce the gas flow to a point where you get a flame, but not an excessively large one. If you're doing this inside with some sort of fume extractor (like a fan-driven stove vent hood), hold the stepper under the hood as you do this. Hit the end of the shaft and the pulley in five-second increments. After each time you do this, take the fire away and look to see whether any whitish vapor is coming from the pulley - that's the degraded thread locking compound. You have to remove the flame to see whether it's offgassing yet. If the end of the stepper shaft or pulley starts to glow, take the fire away before anything gets warped.
Once you see the vapors, use an Allen wrench to loosen one of the grub screws a few turns, and then loosen the other one. You may have to hit the pulley with more fire if the second screw cools while you're freeing the first one. You don't have to take them all the way out while the pulley is still hot. I recommend letting the pulley cool before removing them completely because the screws are tiny and easy to lose, and having to mess with them while they're hot is tricky. The Allen wrench will soak up heat from the hot metal, so you'll want to blow across it from time to time.
Cleaning
The screws have been freed, but if you want to use more thread locker, you need to get rid of the degraded gunk that was left behind.
After the pulleys are cool and you've completely removed the grub screws, you'll see that there's some cruddy residue left in the threads of the pulleys and screws. Decant some 99% alcohol into a shot glass, enough to cover all three pulleys at once, but don't put anything into the glass yet. Heat the alcohol in a microwave for 5-7 seconds. Maintain visual contact with it the whole time it's in there, and if you see bubbles forming, stop the microwave immediately. You don't have to get the alcohol super hot - certainly not boiling. Since it's only a few tens of milliliters, it won't take more than a few seconds to get warm. Hot alcohol emits vapors, so again, be careful not to let anyone inhale them.
JUST IN CASE: I've heated alcohol in a microwave dozens of times for other purposes, and I've never had it catch fire. If for some reason you're doing this and it does catch fire, unplug the microwave and stand by with the fire extinguisher until the alcohol burns itself out. It's in a metal box, so it's not likely that the fire will escape. The autoignition point of ethanol is listed on Wikipedia as 363C/685F. I find it unlikely that a microwave would bring anything up to that temperature in seven seconds unless it was made out of metal.
If you're terrified to heat alcohol in a microwave, which would be totally reasonable, you can use room-temperature alcohol instead.
Drop the grub screws and pulleys into the alcohol. Swirl the shot glass around a little and, if using hot alcohol, let it sit for about five minutes. If using room-temperature alcohol, it'll probably take half an hour or longer. Maybe even overnight. Idunno!
Using some tweezers, remove the pulleys and grub screws, and set them on a paper towel to dry. If your tweezers are magnetic, the grub screws will jump onto them. You'll see that a lot of the gunk has dissolved, and is sitting in the bottom of the shot glass.
After the alcohol has fully evaporated, you can use toothpicks to clean the remaining gunk out of the threads. This will prepare the surfaces to receive fresh thread locking compound.
Results
I did this yesterday. I was afraid that I might damage the magnet wire, but it turned out alright. My printer is SO QUIET! I ran dc42's Duet calibration, and the printer is running fine now.
Materials
Propane blow torch (Amazon has torch heads and propane cylinders, as does any hardware store)
Shot glass (that you don't intend to drink from ever again)
99% alcohol
Microwave
Tweezers
Toothpicks
Paper towels
Also, keep a fire extinguisher handy. You have one of those and the gauge reads fully charged, right? Keep it close by.
Removal
Do this outside, or in a place with good ventilation. I did this in my kitchen and used the stove hood's vent fan to remove all the nasty vapors. Passive hoods aren't good enough for this. The vapors are nasty, and you don't want them wafting around indoors. Do NOT allow yourself or anyone else to get near the vapors!
You need to heat the thread locking compound to a few hundred degrees Celsius to degrade it enough to free the grub screws. However, the stepper motor has magnet wire inside, and if that gets hot enough, the insulation will melt and it'll develop internal shorts that will render the motor useless. Additionally, the stepper shaft and pulley are both aluminum, and that will deform if exposed to enough heat for long enough. Therefore, we want to use as little heat as possible.
Use the adjustment knob on the torch head to reduce the gas flow to a point where you get a flame, but not an excessively large one. If you're doing this inside with some sort of fume extractor (like a fan-driven stove vent hood), hold the stepper under the hood as you do this. Hit the end of the shaft and the pulley in five-second increments. After each time you do this, take the fire away and look to see whether any whitish vapor is coming from the pulley - that's the degraded thread locking compound. You have to remove the flame to see whether it's offgassing yet. If the end of the stepper shaft or pulley starts to glow, take the fire away before anything gets warped.
Once you see the vapors, use an Allen wrench to loosen one of the grub screws a few turns, and then loosen the other one. You may have to hit the pulley with more fire if the second screw cools while you're freeing the first one. You don't have to take them all the way out while the pulley is still hot. I recommend letting the pulley cool before removing them completely because the screws are tiny and easy to lose, and having to mess with them while they're hot is tricky. The Allen wrench will soak up heat from the hot metal, so you'll want to blow across it from time to time.
Cleaning
The screws have been freed, but if you want to use more thread locker, you need to get rid of the degraded gunk that was left behind.
After the pulleys are cool and you've completely removed the grub screws, you'll see that there's some cruddy residue left in the threads of the pulleys and screws. Decant some 99% alcohol into a shot glass, enough to cover all three pulleys at once, but don't put anything into the glass yet. Heat the alcohol in a microwave for 5-7 seconds. Maintain visual contact with it the whole time it's in there, and if you see bubbles forming, stop the microwave immediately. You don't have to get the alcohol super hot - certainly not boiling. Since it's only a few tens of milliliters, it won't take more than a few seconds to get warm. Hot alcohol emits vapors, so again, be careful not to let anyone inhale them.
JUST IN CASE: I've heated alcohol in a microwave dozens of times for other purposes, and I've never had it catch fire. If for some reason you're doing this and it does catch fire, unplug the microwave and stand by with the fire extinguisher until the alcohol burns itself out. It's in a metal box, so it's not likely that the fire will escape. The autoignition point of ethanol is listed on Wikipedia as 363C/685F. I find it unlikely that a microwave would bring anything up to that temperature in seven seconds unless it was made out of metal.
If you're terrified to heat alcohol in a microwave, which would be totally reasonable, you can use room-temperature alcohol instead.
Drop the grub screws and pulleys into the alcohol. Swirl the shot glass around a little and, if using hot alcohol, let it sit for about five minutes. If using room-temperature alcohol, it'll probably take half an hour or longer. Maybe even overnight. Idunno!
Using some tweezers, remove the pulleys and grub screws, and set them on a paper towel to dry. If your tweezers are magnetic, the grub screws will jump onto them. You'll see that a lot of the gunk has dissolved, and is sitting in the bottom of the shot glass.
After the alcohol has fully evaporated, you can use toothpicks to clean the remaining gunk out of the threads. This will prepare the surfaces to receive fresh thread locking compound.
Results
I did this yesterday. I was afraid that I might damage the magnet wire, but it turned out alright. My printer is SO QUIET! I ran dc42's Duet calibration, and the printer is running fine now.
