@dc42, I'll have a look into that thank you. For now just insulating the entire thermocouple seems to have done the trick.

JamesM: You were right all it took was some insulation in the end, i covered them with Kapton and away we go. Thank you very much Jean-Marc for the Kapton suggestion.

DC42, I checked and there is indeed continuity between the thermocouple and the steel case. Is there a way around it? I would really like to be able to use these thermocouples.

Good call, I have not. I'll have a look tomorrow.

What is the pitch of you lead screws?

Can you show us a copy of your config where you setup your steps/mm for the Z-axis.

I'm using the standard daughter board supplied by Duet with the latest MAX31856 chip on it. I saw the line in the documentation where it refers to the electrical insulation however that is only if using a bare tip thermocouple which neither of these are.

I've tried grounding the shielding as well and that does not make a difference.

Hi All,

I've got an interesting challenge. When I use glass shielded k-type thermocouple wire I get a accurate temperature reading, as soon as I switch to k-type thermocouples with steel braiding I get a 0.0°C temp reading. This has happened with three different types of thermo couples now.

Glass shielded thermocouple wire.

Steel braided thermo couple wire.

I've tested them by using a multimeter which has a temperature reading function and they all work fine, each one of them gives the same reading as the next including the glass shielded thermocouple.

Has anyone else come across this before? If so did you manage to rectify the problem?

Any help would be greatly appreciated.

Regards,

Andre

@littlehobbyshop is right on the money. I would suggest you go over your z-axis assembly again. I've had this exact same problem and it was due to the Z-axis screws translating movement into the platform.

Things to check:

• All bolts on z-axis are tight
• Stepper motor alignment needs to be spot on to ensure you are not enduing bend into your screws.
• Remove bearing constraints from your screws. You can add a captive constraint which is well over size just to stop the screws from wobbling around too much.
• If all your bearing cars are hard mounted to the platform then I would think you are over constrained.

I hope this helps.

I'm not using a name brand servo unfortunately.

My M569 parameters are T2.5:2.5:0:0

As mentioned earlier though I'm just suspect that the low F value I'm requesting is not supported, it seems that only from F40 onwards it works as predicted.

I can also send it a command through the console and it executes it perfectly, however when I run a gcode file it runs 3 times faster than predicted.

Hi,

I'm currently experiencing two very strange problems while trying to extrude using an external servo drive plugged into a "Duet Expansion Stepper Breakout Board".

First Problem
When I input "G1 E10 F10" I expect it to feed 10mm of material in one minute, however it does it in 20 seconds, 3 x faster than expected.

When I input "G1 E10 F100 I expect it to feed 10mm of material in 6 seconds, and it does it in 6 seconds.

This prompted me to do a test to see where the extrusion starts correcting inself and this is what I found:

G1 E10 F10 - 20 seconds
G1 E10 F20 - 20 seconds
G1 E10 F30 - 20 seconds
G1 E10 F40 - 15 seconds
G1 E10 F50 - 12 seconds
G1 E10 F60 - 10 seconds

and so forth. I guess what I'm asking is, is there a minimum extrusion speed when using a external drive?

Second Problem
When I send a command via the gcode console the servo reacts exactly as I want it. For instance if I send G1 E100 F500 I expect the servo to be running at 1500rpm.

Now when I use a gcode file prepared by slicer asking for the same speed the servo runs 3 times faster.

Does this somehow tie into my first problem where for some reason the servo was rotating 3 times slower than the requested speed?

If anybody could shed some light on this I would really appreciate it.

Regards,

Andre