Extruder Mk5 questions/ideas
Posted by robotgoldfish
|
Re: Extruder Mk5 questions/ideas January 12, 2011 11:50AM |
robotgoldfish Wrote:
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> I am building my extruder based on the makerbot
> store mk5 extruder parts. and am going to use a
> replacement extech type K thermocouple probe.
>
> The best idea I can come up with is to put the
> bead into the threaded hole on the side of the
> resister block and hold it in place with kapton
> tape. Does anyone have a better idea?
Yes, use a thermistor
Thermocouples have stiff wires that you have to run all the way back to where the chip is. I doubt Kapton tape will hold it. If the heater block is insulated from ground then you can just trap the thermocouple in it by drilling a close fitting hole and than crimping it with a punch.
If the heater is grounded then I would insulate the contact point with Kapton and clamp it with a PTFE clamp and a couple of small screws. That is what I do on my heated beds. Or glue it in a hole with high temperature thermally conductive glue. Makergear sell some.
>
> I am going to start with direct drive and later
> convert to a Bowden style
> but I am still not decided between a stepper or a
> dc motor. The stepper will let me control the
> filament position better. But the dc motor will
> let me limit the torque and the pressure at the
> tip. Any one have any thoughts on the matter?
The pressure at the tip is not the same as the torque on the motor. A lot of the force needed to extrude is moving the viscous plug at the start of the melt zone. Unless you nozzle is very small that force dominates. If there is constant pressure at the nozzle you will get constant flow but constant force on the feed does not give constant flow, in fact it is chaotic due to positive feedback. I.e. the force flow rate curve has a negative slope region.
>
> I was also considering using a torque limiter
> that would let me run a stepper or motor at full
> power without the risk of stripping the filament.
To limit the torque of a stepper just reduce the current. I don't see the point of running it with more current and then limiting the torque in some other way.
I must admit I always set the current so the filament strips before the motor stalls. I think that gives the most reliable system. It only strips if there is some other fault, such as the heater fails or the filament gets tangled. The filament stripping means it fails safe.
>
> Oh and thanks to everyone for the helpful and
> welcoming atmosphere of this Wiki and Forum.
[www.hydraraptor.blogspot.com]
-------------------------------------------------------
> I am building my extruder based on the makerbot
> store mk5 extruder parts. and am going to use a
> replacement extech type K thermocouple probe.
>
> The best idea I can come up with is to put the
> bead into the threaded hole on the side of the
> resister block and hold it in place with kapton
> tape. Does anyone have a better idea?
Yes, use a thermistor
Thermocouples have stiff wires that you have to run all the way back to where the chip is. I doubt Kapton tape will hold it. If the heater block is insulated from ground then you can just trap the thermocouple in it by drilling a close fitting hole and than crimping it with a punch.
If the heater is grounded then I would insulate the contact point with Kapton and clamp it with a PTFE clamp and a couple of small screws. That is what I do on my heated beds. Or glue it in a hole with high temperature thermally conductive glue. Makergear sell some.
>
> I am going to start with direct drive and later
> convert to a Bowden style
> but I am still not decided between a stepper or a
> dc motor. The stepper will let me control the
> filament position better. But the dc motor will
> let me limit the torque and the pressure at the
> tip. Any one have any thoughts on the matter?
The pressure at the tip is not the same as the torque on the motor. A lot of the force needed to extrude is moving the viscous plug at the start of the melt zone. Unless you nozzle is very small that force dominates. If there is constant pressure at the nozzle you will get constant flow but constant force on the feed does not give constant flow, in fact it is chaotic due to positive feedback. I.e. the force flow rate curve has a negative slope region.
>
> I was also considering using a torque limiter
> that would let me run a stepper or motor at full
> power without the risk of stripping the filament.
To limit the torque of a stepper just reduce the current. I don't see the point of running it with more current and then limiting the torque in some other way.
I must admit I always set the current so the filament strips before the motor stalls. I think that gives the most reliable system. It only strips if there is some other fault, such as the heater fails or the filament gets tangled. The filament stripping means it fails safe.
>
> Oh and thanks to everyone for the helpful and
> welcoming atmosphere of this Wiki and Forum.
[www.hydraraptor.blogspot.com]
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