I love my MendelMax 1.5 3D printer, but the one thing I kept having problems with was the QUBD extruder. My filament would keep jamming! After doing some research, I realized the barrel was getting too hot, causing the filament to melt inside the barrel to he point where it would make it impossible to extrude. I machined a new barrel for my extruder, and in this post I’ll show you how you can create your own.
What I didn’t realize, was that most people who’ve purchased these extruders all have the same problem. THEY JAM. The prints typically start out fine, but then eventually the extruder gear loses traction on the filament because of increased friction within the barrel. The gear then chews up the filament as it continues to try to extrude.
QU-BD Custom Barrel
The reason why the filament is jamming is because it is getting too hot inside the barrel. The solution for this is to make a barrel that has a PTFE liner. PTFE, also known as Teflon, is a very high temperature plastic. It’s the same stuff you find on your non-stick pots and pans. It has a melting point of 260°C, so it is safe to use this mod when printing PLA and ABS. You can purchase PTFE as tubing, which is what we’ll do here. The PTFE tube will act as an insulator between the stainless steel barrel and the filament, keeping the filament cool enough so it won’t jam the barrel.
I got this idea from REDington on the Buildlog forum, but I made some modifications that improve the assembly of the barrel.
People have tried a number of different solutions to the problem. I highly recommend these mods in addition to the new PTFE lined barrel:
- Replacing the filament idler – The stock feed mechanism doesn’t do a good job of gripping the filament and feeding it through the barrel. When it hits resistance it will sometimes skip or stop feeding altogether. I highly recommend replacing your feed machanism with this spring-lever assembly. (Yes, I realize the irony of asking you to print something out in order to get your 3D printer to work properly… Maybe you have a friend that can print it for you?)
- Replacing the Drive Gear – Using a better drive gear will provide a better grip on the filament. This will help the extruder feed the filament more consistently and reduce the chance of jamming. Replace it with something like this.
I’ll link to some more great QU-BD extruder resources at the bottom of this post.
Machining your new Barrel
I’m not a machinist. I didn’t do this mod at my buddy’s machine shop. That said, you do need to have a little basic knowledge of tools, and be safe. If this is at all beyond your skill level or you don’t understand any of the steps, proceed at your own risk. All I used was my drill press, some drill bits, files, and that’s about it. Now, I didn’t want to modify my existing barrel because I didn’t want to screw it up if I made a mistake. So I decided to make mine using an stainless steel bolt that I would drill out and modify. Here’s what you’ll need:
- Drill Press
- Cut-off tool
- Metal File
- 5/64″ drill bit
- 5/32″ drill bit (sacrificial, we will be grinding the tip down)
- 5/32″ OD PTFE tubing
- 1 25mm long M6 Stainless Steel bolt (availible at any hardware store) -OR- purchase a stainless steel stud and avoid having to cut the length.
- Measure length, then cut the head off of the bolt. – We only need the threaded portion of the bolt, so we need to cut off the bolt head. You want to have a finished barrel length of 26.5mm (~1-1/32″) if you’re trying to match the existing barrel. (The one I made was about 3/4″ long; TOO SHORT. It still works, but I wouldn’t go less than 1″.) Make sure you cut it a little longer than you need, because you will use a file to finish each end so they are perfectly flat and smooth. You can use a bandsaw, cut-off wheel, or hack saw. Just try to cut as straight as possible, because you will need to file that end flat to clean up the cut surface. It’s best to put the bolt in a vise while you cut it.
You could avoid this step by purchasing a 25mm M6 stud. But I’m not sure how readily available they are at your local hardware store.
- File BOTH ends of the bolt – It’s absolutely critical that the end mating up to the nozzle is perfectly flat. Once the barrel is installed, it needs to make a complete seal against the nozzle. You’ll want the other end flat too so it’s easier to feed the filament into the barrel.
To file the ends, chuck the barrel into your drill press gently. Turn on the drill press. Place your file on the drill press table and lower the spinning barrel onto the file with gentle pressure. You may want to slide the file back and forth while your putting pressure so it doesn’t wear in one spot. Flatten one end, then re-chuck the barrel in the drill press, mark and measure the length of the barrel, and finish grinding down the barrel to your mark.
- Drill out the barrel with 5/64″ drill bit This is the most critical part. You need to center the drill bit with the bolt as best you can. To do this, chuck the barrel into the drill press again (lightly), then clamp your aluminum block on your drill press table. Align the block so it is centered with the barrel. the barrel should be able to screw right into the block if you have it aligned right.
Once everything is aligned, take the barrel out of the drill press and thread it into the block, using a nut to lock it in place. Next, chuck your 5/64″ drill bit and drill all the way through the bolt. Take your time, make sure you’re centered, and dab a little oil in the hole as you go along to cool the barrel.
- Bore out 3/4″ deep with 5/32″ bit Now that we have the barrel diameter correct for the filament, we need to bore out the shaft for the PTFE tubing. We DON’T want to go all the way through with this step because we need something to keep the tubing from coming out of the tube. The end we bore out is the end that will be touching the nozzle. So pick the flattest, smoothest, most centered hole and that will be the end we drill into next. (If the other end is a little off centered it won’t matter as much.) Using the 5/32″ drill bit, drill into the shaft 3/4″ as shown below.
- End mill the liner seat to 15/16″ deep The drill bit you just used had a taper on it. That taper is bad for the PTFE tubing because it will cause the end of the tube to squeeze against the filament as it’s being fed through. So what we have to do next is grind the end of our drill bit flat, so we can create a nice, flat seat for the tubing to sit against. Continue to drill down to 15/16″ from the top of the barrel.
- Bevel and countersink On the feed end, use a 3/8″ drill bit to countersink the hole slightly. This will make it easier to feed the filament into because you’ll have a wider hole. Also, feel free to bevel the edges slightly to get rid of any burrs. Just use a hand file while spinning the barrel in your drill press. Remember not to tighten the chuck too much, the walls of the barrel are very thin now.
- Insert liner You’re barrel is pretty much completed! Now, insert an 1-1/2″ length of the 5/32″ PTFE tubing into the barrel. Again, make sure the end is cut squarely so it sits against the barrel seat flat. Push it as far as it can go, then cut off the tip very carefully with a razor knife. You want to cut it off a little bit longer, then use a file to square it down flat with the metal.
If you’re anything like me, you’ve already disassembled your extruder about 10 times by now trying to fix it, so this part should be pretty quick for you.
To get a proper seat on the nozzle, hand tighten the nozzle first. Then, unscrew it a half turn. Thread your barrel in until it bottoms out on the nozzle. Finally, tighten the nozzle so it fully engages the barrel seat and the aluminum hot end block. This is really important or else you will have filament leaking in between the nozzle and barrel.
A couple other quick tips for you would be to use thermal grease when you’re reassembling everything. Use it on the following parts:
- Nozzle threads into the hot end block
- Barrel threads into the black aluminum cold end block
- On the black aluminum block where it meets to the heat sink
This will help conductivity on the hot end to keep the nozzle hot, and it will also help keep the barrel cool by making a better path to the heat sink.
Ever since I replaced my barrel, I haven’t had one jam. I’m finally able to create reliable prints from my printer.
For more great information about these mods and other ideas to tweak the QU-BD extruder, check out these links:
Also, if this is your first time visiting MasterSketchup.com, check out some of my tutorials to get you started with Sketchup Make. Sketchup Make is a great tool for creating models for your 3D printer. Once you get your extruder printing properly, it will be time for you to get back to printing 🙂 Thanks!