Extruders

Any advise or opinion about building your own extruder / hot end assembly ?
I have designed my own hot end that I am using with a Gregs extruder, although have some trouble extruding at a high speeds.

Is the problem with the motor not having enough torque or with jams in the hot end? Also, What speed are you printing at and at what temperature?

I can only print at about 10 mms, top 15 or so, I dont know how that compares to other rep raps, but I gather it is slow.
It isnt a problem with jams or torque as far as I know.
Usally the filament chews in half and stops feeding if I go to fast or use much retraction.
I also cant use a nozzle much smaller than about .85mm, if so it just chews the filament in half.
I am using 1.75mm filament in a custom hot end that is about 7 inches long ( all ptfe with heater block at the end ) fitted on an 8 cu ft printer.
I think I solved some of my problems with new springs and bolts for the gregs extruder idler monday, but this has been an ongoing problem.

I have tried all temperatures, and several different spools of material all ABS

Something's definately off. Your motor has plenty of torque, but it's a good chance you're having jams. If the filament is melting in the ptfe, then hardening when it cools, it might cause it to jam up. Maybe too much pressure on the filament? Or could be some misalignment with the hobbed bolt. I've found the only way to find out is to disect and rebuild. Sorry, hope that helps. -Kyle

Thanks for responding,

I have tried several things to cure the issue with some success, although I still cant print at the speeds I see other rep raps working at.
The list of cures that I have tried is long , I have re-designed, rebuilt, and tweeked more than one can imagine.
I have totally scrapped one extruder ( wades ) and replaced and rediesigned heater blocks a couple times, several hobbed bolts,
different resistors, different nozzles, different software settings.....exc.
added cooling fans and even water cooling at one point.( which has been removed after a total redesign.)

It takes me a little over 1 hour to print a wades extruder drive gear ( small gear ) at .13 mm layer height, is that slow ?
I have only seen video of other printers, I have never used or seen any other printers in person other than mine, which is not a standard rep-rap design.

.13mm layer height? That's crazy! increase to .4mm layer height or more if your using a .85mm nozzle. I'm extruding with a .35mm nozzle and i can't do .13mm layer height. That might be your problem.

I tried your suggestion of increasing the layer height, I doubled it along with the speed and had limited sucess.
I was able to print at 20mms with a .25 layer height.
I think you pointed me in the right direction and with my new bolts and springs for the gregs hinge, things will work better.
Making some other major changes this weekend, so i wont be able to fully test untill next week.
( adding four MK1 pcb's to the bed, have been using other types of heat and it has not been working out )

Good luck. What size print bed are you using?

The print bed is 600mm x 600mm ( 2 foot square ).
It was designed to be an 8 cu ft print capacity printer, but
the firmware is set at 550mm on all axis, just to be on the safe side.
( I dont use Homing : )

Homing is for wussies

Still some trouble with proper extrusion, I get 10 or 15 minutes into a print and the filament chews in half/stops feeding.
It is actually random times, and seems to happen when I print something where the feeder stops feeding freqently for the printer to make a move.
I am still not using retraction, and from past experince with this machine it results in the same problem.

hmm. Still sounds like the heat is traveling up the barrel and gumming up your abs. I use stainless steel because of it's low thermal conductivity. I take a stainless steel bolt and lathe a hole through it and screw it into my heating block. I've done away with ptfe in my design and just use an aluminum heat sink and a fan on my stepper. It's a direct drive extruder that's pretty minimalistic, but effective. Could you post a picture of your extruder?

I wish I could confirm that the abs is meliting in the barrel, although I have never had to clean a jam, and have always just been able to pull out the old filament, cut it off and re-load and go.
Because of the design of the machine I am almost stuck with a long barrell, I have looked at changing the position of the extruder so I could go with one like you describe, direct drive, with a short metal barrell, ( this may still happen if I cannot save this design.)
anyway here are some pic's of the extruder.( please dont laugh too much..lol ), I threw in a pic of the heated bed also, it was in the same file.

I've never seen ptfe plugged directly into the hot end like that. Your performance may be limited by this. It's an impressive machine. Looks like a lot of time and effort when into it. The only thing I can think of that might help is to add a cooling fan on the aluminum bracket to blow onto the ptfe. This might help prevent thermal expansion of the ptfe, which is generally why it shouldn't come in direct contact with the heating element. You could also try making the hole through the ptfe a little bigger to account for the expansion. Generally thermal expansion means that things get bigger as they heat up, but in your case, because the rod is prevented from expanding outward by the heater block, the force is directed inward. In other words, as it gets hotter, it chokes the abs.

Interesting observation, I had not thought of the inward expansion of the ptfe causing the abs to stop moving.
The main tube ptfe you see in the pictures is lined with a 1/4" piece of ptfe that has a 2mm hole in it.
I am running 1.75mm filament....I would be willing to bet you are correct, that friction is causing the the filament to stop moving.
Since the ptfe goes deep into the heat block, I am also betting that a fan wont help much.....
I will try a little larger hole in the ptfe liner, if this does not work I am going to sling a hanger under the current set-up and go with a commercial
extruder/hotend.
Thank you.

The machine took about 145 single man hours of fab time to make it whole, plus I have spent many more hours making mods.
Video of it is searchable on you tube by typing in "rep rap 8CuP"

Awsome, I enlarged the ptfe liner to about 2.3mm and just finished up a 7 hour print , with retraction.
I hope this holds as a cure for the cruddy extrusion I was experiencing.
Thanks again Kyle, you have been most helpfull.

No problem. Happy to help out. If you ever need any 1.75 filament let me know. kyle@ohioplasticsandsafetyproducts.com

Back to the drawing board, I gave up on my design as it started doing the same thing it did before so I tried a
" commercial " direct drive extruder.
I have the same issues, filament chews in half after about 5-10 minutes of printing.
I have added an additional fan to cool the motor with not luck.
Not too sure what's going on, have tried different firmware, different stepper drivers, slow, fast, and a lot of other stuff with no luck.
Its like the ABS is too soft, I have tried a couple different rolls but still not sure.
Does abs get soft over time or is there a lot of difference in manufacturer formulas ?

Finally I have learned the lesson that all Rep Rap'ers have probably learned.
My whole problem was proper z stop calibration / first layer height and z axis level.
The nozzle was too close at points and the hot plastic had no-where to go so the back pressure caused the filament to stop moving, in turn chewing the filament in half after a couple of layers. Even causing the direct drive extruder to clunk like it had a bad motor or driver.

Strange part was sometimes I would get several good prints.......anyway all is well and lesson learned.
Printing great now.

Has anyone tried using the feed unit from a wire feed welder to feed the material to the hot side? They are very adjustable for both speed and tension on the roller(s) you might need to cut a groove or two in the roller or rollers but does it sound like something worth pursuing? I've seen non-working flux-core welders for less than scrap prices at times.

Machinery Maker: It is possible, and in theory it would work well for a Bowden style extruder.
But wire feed welders use regular dc motors, not steppers, so most of the current RepRap style electronics/software would not immediately support them without some heavy modifications.
The use of steppers makes it possible to regulate the number of movements the motor makes down to a very fine amount, where as standard dc motors cannot be controlled in the same fashion.
If one were to (re)write the firmware to support the use of a regular dc motors, along with making the electronics to support regular dc motors, then it is feasible, although it may very difficult to achieve accurate movements.
A full working RepRap style extruder can be assembled for less than 50 dollars, where a wire feed assembly itself is about the same price and you would still need a hot end to go with it.
At lest to the best of my knowledge my statements are true.

Thanks for the reply Wallmaster, I was thinking more of just using just the drive mechanism itself and adapting a stepper motor. I'm not really into re-inventing the wheel, just seeing if a well proven technology would solve what appears to be a common problem. I can machine any parts I need if the project sounds worthwhile. I am planning on building whatever I use in any event. I am completely new to 3D printers and I like to listen to the people that are more experienced than I.

Yes: If you installed a stepper into a wire feeder, it would probably work well as a Bowden style ( feeder in a remote location ) as the wire feeders are kind of bulky and would not be directly adaptable to the hot ends out right now.
Although you could easily machine hot end to fit the wire feeder I suppose.
Truthfully the direct drive extruders work pretty good aka: mk7 or qu-bd , even the gregs and wade are proven to function well.
Most problems with extruders can be traced back to calibration and set up.