Posts made by mendenmh

@Manuel207 Are the parts really rectangular, or parallelograms? They would have the right size in x & y if there is skew, but the right angles will be very slightly off right. It is most noticeable on circles, since slight bumps on the corners of rectangular pieces make it really hard to measure the angle between the flat faces. What I did was printed a large, thin circular plate and then measured it carefully, and adjusted the skew until it was round. I now have a really well-calibrated printer.

@Manuel207 Are the oval's axes aligned along x & y, or at 45 degrees to x & y? If the axes are aligned along x & y, it's not the skew compensation, but a scale issue between the axes, or backlash in the belts. If it's at 45 degrees, the skew compensation would fix it.

(update... oops. I forgot this is core-xy, so the syndrome would be different. since the belts already pull at 45 degrees, both belt slip and skew should make an error at 45 degrees. This still leaves the question as to which axis the error is on.)

Have you tried kapton tape (which is extremely heat resistant), or the off-brand Koptan that comes from China (and is MUCH cheaper). They are an absolutely marvelous print surface. The only trick is the initial application of the tape, to get it smooth an bubble-free. Once you have a nice layer, it lasts a very long time. The silicone adhesive on it sticks nicely to aluminum, and works fine up to beyond 300C. I bought a roll of 9" wide tape (the Koptan from China), I think a pound of it, a few years ago for maybe $40. It is a lifetime supply.

@zapta Make sure when you do the boiling water 100C point, that you look up the local barometric pressure, and then use a conversion table to get the correct boiling point. It varies quite bit, especially if you are at altitude. This is why an old explorers trick in the mountains was to keep a thermometer, and put it in boiling water to measure the altitude.

@zapta A class A RTD is probably the most reliable, affordable temperature measurement device you can use to cover a moderately wide range with no special calibration. A thermocouple of appropriate type can be used without any calibration, and fairly good accuracy, over a very wide range, but the resolution isn't so good. If you want to go first-class, an SPRT (standard platinum resistance thermometer) is ideal, but costs. These are RTDs manufactured to extremely precise specification (loosely wound, special platinum wire, so thermal stresses don't change it, etc.).

@deckingman @zapta The difference between using an NTC and either a Pt RTD or thermocouple is that tiny variations in beta on an NTC correspond to large variations when applied over a wide temperature range. RTDs and thermocouples have low sensitivity (resolution), but tend to be more accurate without secondary calibration over a very wide range. The problem with NTCs is that commercial uncalibrated ones are trimmed to give the right answer at 25C, typically, and without secondary calibration to determine specific values of beta and c (etc.), one is using faith-based thermometry.

Note: I make my living on experiments that require precision (<0.01C) thermometry. For narrow range work, calibrated NTCs are unbeatable. I have one calibrated to 0.01C accuracy from -30C to 70C. The cost of the unit and calibration by Fluke was $1800. To go outside that range, though, really is hard with that type of sensor.

This is a much harder task than you are expecting. The temperature measured by a surface probe will depend critically on the thermal contact made between the probe and the surface. The temperature of the surface may also not be terribly close to whatever temperature you really care about on the hot end (the melt chamber? the nozzle tip? what?). The probe itself, of course, may not be accurately calibrated in the first place.

The closest we probably get to good measurement of hot end temperature probably comes from either a Pt RTD (Pt100 or Pt1000), or a thermocouple. Either one must be seated deeply in a well in the heater block. At this point, you probably know the temperature of the core of the heater block to a degree or so. The actual nozzle temperature is probably much lower, and that may be critical for the melt characteristics. Of course, the difference between the heater block and the nozzle tip will depend strongly on the fan speed and filament flow rate.

So, what are you really trying to accomplish?

@hpiz @infiniteloop A convenient number to remember about the AWG scale is that a 3 gauge number decrease almost exactly doubles the area of the wire. (See https://en.wikipedia.org/wiki/American_wire_gauge). This is an ancient bit of lore, but it is pretty easy to remember, and useful for scaling wire sizes. The statement that CAT6 wire is inappropriate for running steppers is absolutely correct. Get thicker wires.

@deckingman @samlogan87 Actually, if you want, you can regenerate calcium chloride in your oven. However, the energy cost probably makes it a dumb idea. It is very cheap in the first place, and the brine is fairly environmentally harmless, so putting it down the drain isn't a problem. Note that CaCl2 doesn't get to as low humidity as silica gel, but it is plenty low for filament drying. It can absorb a HUGE amount of water compared to silica gel, which is nice for keeping a big box of filament dry. As long as there is any solid CaCl2 left in the brine, it is keeping the RH somewhere in the 10% range near room temperature.

@kuon run multiple 12mm belts side by side?

Try moving the sensor to a different input. It is possible you have a bad ADC channel.

Do you have adaptive layer heights turned on in your slicer? If there is a transition 25 layers up in the design, the printing characteristics may change there, due to speed and layer height changes.

It would be interesting to put a small load (10k resistor, e.g.) across the fan, and re-measure that voltage. Maybe the board has a leaky FET.

Also, it is possible that the fan draws very little current at low voltage. That may be low enough that nothing is biased on until the voltage is much higher. In that case, you may just be charging some tiny input capacitance, and a small current might create a significant voltage. The load resistor would tell more about this.

@gnydick yeek! There is something funny with your meter.

I agree, it shows an mV label when on that range, but I have no idea what it is doing. Have you tried putting it on an appropriate manual range and seeing if it still does this?

I do have one idea. Is the "H" at the top 'Hold" mode. I have seen meters sometimes in hold that hold the number, but not the range info. Could it have captured that number in the mV range, and then switched to a volts range while still holding the display?

@gnydick Is it possible your meter had autoranged to a millivolt range, and you were reading 3987 mV, or about 4 volts, due to leakage currents?

@dc42 A quick solution would be to at least sort the leads into sets, so any one package has all identical leads. That way you can continue to buy the bulk leads, but any single user doesn't have to deal with the variation.

@jay_s_uk You and I said the same thing, about the negative temperature coefficient. I said resistance is higher at lower temperatures; you corrected to lower at higher temperatures.

However, your statement about the value for a thermistor being specified at zero degrees is wrong. Most thermistors are standardized at 25C. Pt100/Pt1000 are, indeed, standardized at 0C. But it is still correct that the 100000 is the right number to have put in the file.

@foesi
"but I have put 84000 there which is the resistance I measured at around 18°C"

That's a really unlikely resistance for a 100k thermistor at 18C. It should be well above 100k, close to 150k, at that temperature. These thermistors are specified at 25C, and have a negative temperature coefficient, which means the resistance is higher at lower temperatures.

Is it possible you used your fingers to hold the meter leads on the thermistor, and got a reduced reading due to leakage through your skin?

Anyways, use the nominal 100k value in your calibration. It is probably very close to correct.

Although an IR sensor may make a useful remote diagnostic for general conditions, I doubt it will work too well for the hot end control. IR sensors are very sensitive to surface conditions. A clean, shiny nozzle will have a low emissivity, and read cold. As soon as it gets a little dirty, the emissivity will rise, and it will read hotter.
I see a lot of people on numerous forums who have tried to 'calibrate' their thermistor (or other readout) temperature against an IR thermometer, and somehow, the assumption is made that the IR thermometer is the correct value. This is almost certainly wrong, in most cases. There are way too many optical factors that go into these to make them really useful. Expensive, commercial, multi-band sensors can be good, because they can make a reasonable assumption about the emissivity, but basic single band ones are only useful for general surveys of temperature differences across a uniform surface.
On the other hand, as a general diagnostic, it might be interesting to watch how the surface of the sample cools at different fan speeds, print speeds, etc., and use this to develop better printing conditions. Let us know what you learn.

@fcwilt OK, good to know you found both. The 5.18 is the much simpler (and cheaper) one. I have seen exact ones, like the 5.00, but they are more expensive. I think it requires a couple of stages to get 5 exactly, or a lot of teeth on the gears.