Hand-drill geared extruder

I managed to break my original BfB extruder :-(. The acrylic had flexed too many times, and the top retaining bracket broke in half. The screw thread now carefully unscrews itself rather than driving the filament down :-(

So, time to update to a modern wade-style or similar extruder, using a hobbled bolt. Of course, I could have bought the gear drives from the many RepRap shops or ebay, but that's too easy :-).
Instead, I found an old cheap hand drill, with similar sized gearing. It turned out to be on an 8mm shaft.

I added a 5mm to 8mm sleeve to a stepper motor (made from a sex bolt)  and drilled and tapped a 4mm hole for a grub screw - I could then attach the smaller gear to the stepper shaft. The larger gear I cut a small square indent to match a carriage bolt, and cut some teeth into the threads using a dremmel cutting disc. A plastic cutting board and an Ikea bracket made a mount, and three skate bearings (8mm 908) made up a channel for the filament.

It's not pretty, and it's heavier than ABS gearing, but it grips the filament like anything - I can't stop it using my full strength grip, and really forces the filament through. 

I'm currently building a heater block and nozzle to add on the bottom. Hopefully this 'RepStrapStruder' will last long enough for me to print a proper wade's extruder. 

Quick-release extruder

I pulled out my reprap at the weekend and fired it up. After levelling the bed, checking calibration, and fixing the z-flag that was loose, I started the extruder....

Nothing came out.

After some fiddling, I disassembled and reassembled the heater/nozzle - it was fill of brown/grey ABS, absolutely rock-solid, and had to be drilled out.

Since this is about the 50th time I have disassembled/reassembled my heater/nozzle assembly, I tried a modification to make it easier to change. My PEEK insulator is bolted to a penny washer with an m8 thread and two half-nuts.

From quickrelease

I cut a slot in the penny washer and I can now loosen a bolt and slide the extruder barrel/heater out to change it.

From quickrelease

This came in really handy, because as I restarted, warmed up to 225C, and fed the ABS through - it stuck fast. At least I could disassemble to find the problem.

The ABS appears to form a solid plug of the brown overheat mess as soon as it hits the heater, going solid and blocking the tube.

I think I've got a broken thermistor, or maybe the heat transfer is bad. It seems to warm up as expected, and reports the right temp (ish) staring about 16C and rising to 225C - fluctuating about 223-226C, but the ABS is definitely overheating.

I'll swop it out with another one and see if that helps.

Doorstop Heater Block

Wandering B'n'Q the other day, I checked the bargain bin and found this:

From ResistorHeater

It is a brass doorstop: Basically a 1 inch brass rod with a M6 threaded hole down the centre. It's just about the right size to make a heater block! And, it's reduced to £3!
I picked one up to play with.

Closer inspection revealed that the central threaded hole projects all the way through the block, stopping at the small indent for the O-ring.

I hacksawed through at the indent, cutting off a 20mm chunk - the m6 thread goes right through.
I drilled a couple of 6.5mm holes through for my resistors - and widened them a little, as my resistors are not straight, and added a small hole for a themistor.
Widening half the m6 thread to m8 allows me to screw in a Peek insulator.

From ResistorHeater

Here's a pic of the components:

From ResistorHeater

and assembled:

From ResistorHeater

Firing it up, I found that it reaches 220C in about 7 minutes, with no insulation. The heater seems pretty sturdy and well-attached. Starting up my (fixed) BfB extruder drive, I waited expectantly....

From ResistorHeater

Hurrah! It extruded several cm of filament - reasonably quick too!

If it starts up again later, then I might be able to build something soon!

Extrusion: 220C at motor speed of 120/255. Nozzle 0.8mm welding tip, 1.01mm filament

BitsFromBytes extruder

Reading a comment on the RepRap forums I *finally* realised that BitsFromBytes had a Forum and a separate Blog. Since I've got an older v2 kit, I hadn't checked back there for a while.

While catching up on the blog, I found a really useful post by Tony (copied below):
MK2 extruder
I was able to get some very nice results from the original GM3 powered BFB extruder, all the same principles apply, keep the melt zone short and support the PTFE close to the heater. Stability of the motor speed and the quality of the motors were the only slight issues. I ran both single and twin motor versions for many months without a problem. I still believe this original extruder design is very good and it certainly proved itself reliable over that time.
For those who had problems getting them to work I strongly suggest you blueprint the design exactly as it should be, by all means sharpen the thread and undercut it with a hack saw if you must but this should be the limit of the mods. The most common error I have heard about is the omission of the small reaction washer behind the main feed screw. Miss this out and you will never grip the filament tight enough. Build the extruder exactly as the instructions and it works, mess with the PTFE add custom heaters and coach bolts for the drive screw(what!), and you are in unknown territory. Run it how it should be first, get some experience in printing, you will then start to see where modifications would pay dividends, the original one works very well and starts reliably from cold.

Coach bolts? Who would do such a thing! :-)

Time to re-check. If it's only me and one or two others having problems with the BfB drive, then it's probably either my setup or incorrect assembly.

Re-state the problem.
Initial problem: heater/motor control worked fine, but extruding at 250C and any speed only resulted in 2-3mm/minute, almost too slow to see. Tried various temps and speeds, same result.
Removing heater, I was able to manually pull the filament through (screw thread not biting).

Tightened all the bolts - still no change to extrusion. Tightened to the point the acrylic started to crack (on the 2mm plate holding the bolt/filament roller). No change. Springs fully compressed. (reaction washer in place)
Disassembled, sharpened bolt thread with die. Better grip, but no better extrusion.

Examining the heater and drive separately, found that the heater required a reasonable force, but extruded OK, but the drive system still wasn't strong enough - although it seemed more than strong enough during testing, it still wouldn't extrude.

I then experimented with some different nozzles and drive systems. I found some nozzle designs needed less force, but needed careful machining to be reliable.
Replacing the m8 thread with a coach bolt , which had a much larger, sharper thread really gripped the filament very well - but still didn't extrude. WTF?

I think the problem is the thread is very grippy - but the pitch is about 4 times larger than the m8 thread. The coach bolt drive is very strong, but drives faster than the m8 thread - a few mm per revolution. I think pushing too fast chokes the extruder, stalling the filament, and stripping the filament (confirmed by examination). It might work very well, but needs to be geared slower (or driven by a stepper).

OK, so after reading the BfB forum and posts, I stripped down my extruder to have a closer look.
A careful inspection of the extruder parts revealed this:

From BfBExtruder

The heater bolts are *slightly* too large for the channels in the extruder drive, causing a gap between the plates. This meant when I removed the heater to check the drive system, it closes up - and the drive works properly. When I screwed in the heater to check the extrusion and bolt to the reprap, the bolts screw in - the gap opens - and the pressure is taken off the screw thread. The screw doesn't bite the filament, and doesn't pull it through.
Bugger.

I'll file the channels out, reassemble to the original BfB extruder, and try again. I think it *might* just work this time (famous last words...)

As we say in computing, PICNIC (Problem in chair, not in computer)....or should that be PIANID (Problem in Assembler, Not In Design)...

More Extruder Experiments

Time to write up the past few weeks of experimenting in making extruders:

From Renoir6_Extruder

This is a quick extruder made from a short section of 5mm brass tube, 8mm PTFE rod with a central 3.2mm hole for the filament and an experimental PTFE nozzle.
The PTFE is drilled about 8mm in to 5mm diameter, and the tube is push-fit into the PTFE.
The nozzle is made from 10mm PTFE rod, drilled almost to the end with a 5mm diameter. Part of the outside is shaped down to 8mm (to fit a large washer for support) and tapered a bit. The final breakthrough was done with a .35mm hand drill where the PTFE is about 2mm thick.

The heater is made from a couple of layers of kraken tape and some (partly) insulated nichrome wire reclaimed from a previous nozzle.

Warming this barrel up, the tape didn't appear to be affected, so I fed some ABS down. it seems to melt fine, filling the 5mm brass easily, but I hadn't bolted it down properly to hold the PTFE together, and I pushed the nozzle off before it came out the 0.35 hole.

From Renoir6_Extruder

It had been at 220C for a half-hour or so, so I deconstructed it to see if the kraken tape was damaged:

From Renoir6_Extruder

It seems to be unaffected. The covering you can see on the nichrome is the original insulation: it seems to decompose and can easily be scraped off with fingers, but even where the nichrome is just bare wire the kraken tape is unaffected. This isn't a long term test, but it's promising.

From Renoir6_Extruder

This extruder uses a brass tube, and a PTFE nozzle and insulator as above, but uses a different heater. Two wirewound resistors are placed inside M8 coupling nuts. The nuts are then held together in a vice and a 5mm hole is drilled between them.
The two coupling nuts can be placed around the brass tube (or even a welding tip) and held together with tape. you can also pop a thermistor between the tape and the nuts for temp monitoring.

To provide pressure to the PTFE tube joints, a large m8 washer is placed over the nozzle (10mm PTFE rod turned town to 8mm) and bolted to the existing BfB extruder drive (using the enhanced coach bolt drive).

From Renoir6_Extruder

This warms up fine to 220C and extrudes with some force. This PTFE nozzle has a 0.6mm hole, about 0.5mm thick PTFE (thin enough to see light through) but is still able to contain reasonably high hand forces. It extrudes, slowly, but immediately expands to a much larger extrusion.

From Renoir6_Extruder

Eventually I decided to re-build a more traditional extruder. A couple of taps with a hammer broke up the fire cement and allowed me to reclaim the nichrome, m6 BfB barrel and nozzle.

From Renoir6_Extruder

Using a combination of learning from my experiments, I've built yet another version:

From Renoir6_Extruder

3ohm nichrome heater directly around the nozzle, and 4ohm above. PTFE screwed to nozzle and also secured using bolts and washer. Washer heat isolated using a turned PTFE washer - also holds the m6 barrel nicely in the m8 washer. kraken tape insulating the heater. Coach bolt hack on a BfB lasercut extruder drive, standard GM3 DC motor/gearbox. Standard BfB aluminium nozzle.

I'll see how this one performs soon... :-)

One step forward, one step back

My jerry-built extruder is blocked.
The coach built drive is still working fine, providing quite a bit of force to the filament - enough to dear big chunks out of it.
The extruder nozzle is blocked.

This happened before, during hand testing. I've restarted and stopped the nozzle several times, and only twice had a jam. Last time, clearing the 0.6mm nozzle hole with a pin did not restart the flow, so it isn't a nozzle blockage. Providing *excessive* force suddenly cleared the blockage and restarted the flow, where it went back to normal.

There is one factor that was the same between blockages.

Both times, immediately before, the filament had been left in the nozzle, and the nozzle had been left hot for several minutes, while testing other stuff. Then the nozzle was turned off and cooled down (end of testing).
The next day, the nozzle was blocked.
On other tests, either the filament was withdrawn while hot, removing the bulk of the plastic, or after extrusion the heater was switched off immediately. Restarting the next day was fine.

I *think* what happens is that the heat travels up the filament, softening and widening it. Over a couple of minutes or so (if it cools immediately) this isn't a problem. If the heat is applied for several minutes, the filament softens further and further up, pressing against the sides of the channel, causing more and more friction. Because my insulator isn't uniform (there is a .3 mm step near the top, and a hole across (see screwdriver drive) this gives plenty of friction - blocking the filament channel. This is why clearing the nozzle doesn't help.

I'd suggest that if you're not using the extruder, or between days, turn the heat off - or better, withdraw the filament an inch or two while hot. My fully assembled extruder worked well, but last time I was testing the axes and trying the sort out a software bug, and I left the extruder hot for 20mins or so while doing so. The next time, it's solidly blocked - no extra force is shifting it. I'll either have to leave it hot for a half-hour or so to see if it softens enough to shift, or disassemble and drill out the stuck filament.

I went out yesterday and bought a small vice (£4.50) and a reamer like Nophead's (£3.00). I'm planning to use the Afghan Lathe technique to make a new extruder insulator with a larger melt chamber (4-5mm?) and a tapered entrance to see if this helps.