Feeler Gauge

[pjr]

Hi

I noticed a post where PenskeGuy mentioned using feeler gauges to set the initial head gap.

I have been doing likewise, setting to 0.1mm when cold, but when warm the nozzle hits the bed when moved to 0,0,0 at the start of the print.

I guess the size of the gap when cold is dependant on the hardware and printing temperatures and the the cold gap should be set so that the hot gap is precisely zero. Would that be correct, or am I missing something here?

Any advice gratefully received.

Thanks in advance

Peter

[plexus]

Hi
I noticed a post where PenskeGuy mentioned using feeler gauges to set the initial head gap.
I have been doing likewise, setting to 0.1mm when cold, but when warm the nozzle hits the bed when moved to 0,0,0 at the start of the print.
I guess the size of the gap when cold is dependant on the hardware and printing temperatures and the the cold gap should be set so that the hot gap is precisely zero. Would that be correct, or am I missing something here?
Any advice gratefully received.
Thanks in advance
Peter

Metal expands when it's hot. this is why the gap closed on you. I set the gap to be as small as possible at operating temperatures. I set the bed to the hotest I will use 120C and the hot end to ABS temps 230C. I use a 0.001" feeler gauge and set it so that it requires some force to remove the gauge. I want the gap to be as small as possible. It is largely printer dependent however - I can get away with this on my current set up. when I first got the printer however using the stock bed and hot end, I needed to do this with a 0.013" gauge because the non-uniformities were getting in the way of a reliable print. the current printer is much more rigid, I use a machined-flat aluminum heat bed and more accurate hot end. now I can get away with the 0.001" gauge.

I think the idea is to get the gap as small as possible for what will work. so for your printer it will be something you have to determine by trial and error.

When the printer starts, it will move the hot end to the start position while it raises up the Z axis to position the nozzle at the layer thickness you specify. if you set the initial gap at a place where it is different than where the printer starts, the Z gap will be different and may be too close or too high for a reliable first layer. Unless, you have a uniform bed-to-nozzle distance it will be hard to figure out. also setting the gap at around the middle of the print bed is good too.

So. Uniform bed, rigid printer, levelled across the entire print area with respect to the nozzle and set the tightest initial gap as possible at the middle of the bed. test print a first layer and adjust your approach depending what you get.

[pjr]

Hi Plexus

Thank you for your extremely helpful advice.

My printer has an aluminium bed bed and initially was about 0.5mm lower in the centre than the edges. I turned it over and it is now flat to within a few microns.

The instructions I have read elsewhere are to use one (or two) sheets of paper, but this is rather imprecise. Your 25 microns at operating temps is what I will aim for.

I don't think I need to be as accurate as you, so I will heat everything up, adjust for 30 microns (metric feelers), let everything cool and then measure the cold gap for future use.

FYI, after zeroing the head and before the print, I have copied the Cura GCode into KS to raise the head and extrude 3mm of filament before moving to the start print position. This prevents any possible dragging of the head over the blue tape.

Many thanks again.

Peter

[Dreide]

I guess the size of the gap when cold is dependant on the hardware and printing temperatures and the the cold gap should be set so that the hot gap is precisely zero. Would that be correct, or am I missing something here?

Yes, and if getting it precisely to zero is not possible (or recommendable) for practical reasons, there is always the option of compensating the gap with a Z coordinate offset. This can be done in several ways, e.g., by setting the EEPROM parameter (something like "Z home pos") accordingly or by using the KISSlicer parameter "Z Offset" (in the Printer / Hardware tab).

[inventabuild]

Does anyone know of any accurate non-metal feeler gauges? I am concerned about repeated rubbing between a metal feeler gauge and the tip of the hot end resulting in a change in the shape / dimensions of the hot end.

[PenskeGuy]

Actually, I just use a sheet of paper. For the tolerances and resolutions that we're dealing with, it's more than sufficient.

[Davide Ardizzoia]

25 MICRONS ?!?!?

Just checking clearance at cold extruder / plate will GREATLY differ from heated situation, easily giving you double that values.
And most of printers (if not all of them) have a flex/play surely above 25microns.
KS has RAFT if you need to deal with such extreme precision requirements.
I surely use raft 98% of the time, regardless of layer thickness.

Moreover, IF the first layer is that thin you will need VERY PRECISE flow settings...not to mention to the risks of delamination.

IMHO, f'corz.
Brgds
Davide Ardizzoia

[pjr]

Hi Guys

@PenskeGuy - In a post on 5th Jan, you implied that you advocate the use of feelers: "Yep. Feeler gauge is the way to go."

@Davide - Maximum 25 micron gap when everything is hot and the Z axis is homed. The first layer will then not have any additional gap to cope with and so will stick better.

You are correct in that most printers will have a Z-axis play of more than 25 microns, but fortunately gravity helps us with this and as long as the slides are relatively free-moving, then that play will not affect the print to any degree.

As for rafts, I haven't used them much in KS as when I have, I have found them impossible to remove. I haven't spent any time with different raft settings as yet though. I have found that when printing PLA on tape with the bed at 35 degrees, I don't need rafts.

Peter

[plexus]

Use paper if you dont have a feeler gauge. and, if your printer is not that rigid. i initally was using paper but I did a number of upgrades to my printer that resulted in more rigidity and mechanical accuracy. i found that using paper was placing the nozzle too high over the print bed. That's when I switched to a feeler gauge and settled on 0.001" for my printer. anything higher than 0.002" and I wont get a good first layer.

Getting a good well adhered smooth flat uniform first layer is really important. so whatever you need to do to get it. a feeler gauge isn't essential. you can use regular paper and if you find that it looks like the nozzle is too far off the heat bed when printing the first layer, then you need something thinner and that might be where a feeler gauge comes in.

I get right in there when its printing, being careful not to get hurt by the movingness of it (new word). and I look to see how the layer is going down. you can tell if the nozzle is too close or far. it should be laying it down while it flattens off the top of the otherwise round extrusion. there is a fair amount of variability here if the bed is flat. i would guesstimate that as long as you are in the middle 1/3 of the height of the extruded filament bead that's good. closer will get you better layer adhesion. in fact I control how much layer adhesion I get by adjusting the nozzle height within that variance. I can see it by eye and adjust my Z height using an integrated micrometer. so I can dial in pretty accurately. my machine is quite rigid so it works down to about 25µm resolution. ok maybe 50µm. it allows me to ability to have this kind of control over the first layer. I will also manually raise or lower Z to get the layer the print as I want. I do this in real time while its printing by turning the Z couplers. ant turning them as close together as possible as there are 1 on each side. i don't worry about a little inaccuracy as its never appeared to be a problem. then, i make note of if I went up or down to get the first layer to print right and then I adjust the Z an guesstimate up or down to set a new Z. so in effect I am setting Z by determining the qualities of the first layer in real time relative to the current clearance.

[PenskeGuy]

@PenskeGuy - In a post on 5th Jan, you implied that you advocate the use of feelers: "Yep. Feeler gauge is the way to go."

Well, was essentially citing the concept, not necessarily the tool used to perform a go/no-go test; or the thickness thereof. Any material of any arbitrary size can be used as a feeler gauge, depending upon the task at hand. Therefore, considering the accuracy and resolution of the hardware we are currently dealing with, a sheet of bond paper is more than sufficient to get a bed parallel to the transport. It has a nice tooth that provides a reliable feel, without endangering the nozzles.