Hotend crashed into PEI and burnt a hole through it  

Re: Hotend crashed into PEI and burnt a hole through it

So what, if any, is the tip for possibly avoiding this issue? My kit is on its way, will arrive Friday, this is my first Prusa but my second 3D printer.
Since this has happened to more than a few people I'm guessing there must be some common thread as to when/how it happens?
Such as maybe something that should be explicitly explained in the build instructions or calibration instructions? Such as "do NOT do step X before you first complete step Y" or something like that? Any ideas?

The Mangled Bed Club is a club I would prefer to not have a membership in if I can avoid it! 🙂

At this stage I don't think there is one thing that can be advised to avoid it happening 🙁 The main thing is when you build it take your time, do lots of checking of measurements and things, and follow the instructions closely. Before doing anything else make sure the firmware is up to date.

There is no reason that this should happen if everything is put together correctly, it didn't happen to me and we all have the same parts afters all!

Good luck, not that you'll need it I'm sure and hope it all goes well! Happy Printing!

Re: Hotend crashed into PEI and burnt a hole through it

At this stage I don't think there is one thing that can be advised to avoid it happening

It's a tough sort of thing to avoid (I'm waiting on my mk2 kit right now, but have dealt with similar systems previously). I actually keep a thin piece of metal handy for when I'm fiddling with such things. I slip it in the second it seems like something is going wrong. Even then though, you can still miss the boat.

I thought maybe I'd share that idea though (of using a thin piece of metal to trigger the probe in-case of emergency), for those that might be concerned. Especially if you've got a kit and are building it, or getting it tuned in.

Re: Hotend crashed into PEI and burnt a hole through it

So what, if any, is the tip for possibly avoiding this issue? My kit is on its way, will arrive Friday, this is my first Prusa but my second 3D printer.
Since this has happened to more than a few people I'm guessing there must be some common thread as to when/how it happens?
Such as maybe something that should be explicitly explained in the build instructions or calibration instructions? Such as "do NOT do step X before you first complete step Y" or something like that? Any ideas?

The Mangled Bed Club is a club I would prefer to not have a membership in if I can avoid it! 🙂

Make sure your running the latest firmware, follow the initinal start directions to a "T" The build and first start directions are really good, and Josef is improving them constantly based on feedback.

The first start guide specifically says to do the first calibration while the hotend is cold, to insure that if something like that does happen it just hits the bed and not burns it, (and gives you a chance to fix your build mistake 😀 )

Ive built two mk2's one from scratch, one as an upgrade, and have not had the bed crashing issue, I gouged one bed (but that was totally on me, as i was using a razer blade to remove a print LOL)

Dont worry two much if you just dent or scratch the PEI surface its not hard to replace, and its fairly cheap (like $10 a sheet i think)

EDIT: as a side note to the orirginal poster. There is no need to auto-home before a print as you said in your first sentance, as this is the first thing the printer does when you start a new print. 🙂

Re: Hotend crashed into PEI and burnt a hole through it

Thanks very much for the comments! @ erron.w, 3Delight, and Joshua

Yes, since this is my first kit build of a Prusa I intend on going slowly and precisely on everything. I'm not at all saying the people who have had the issue did not go slow and precise though!
I have not even received the kit yet but I have read thru the assembly instructions twice because I want to already be familiar with the parts, steps, etc before I even start.
@Joshua - the thin sheet of metal is a great idea, I had mentioned in an earlier post in this thread that maybe before doing the calibration for the first time to put a 2mm sheet of Lexan or something just in case. 🙂
Unfortunately I do not get my kit until Friday and then I will be out of town Sunday thru Saturday. So it will be Sept 25 before I can even start the build. 🙁

Re: Hotend crashed into PEI and burnt a hole through it

You must be very strong willed. I have no idea how you will be able to resist not building it, luckily you will be out of town.
It was killing me that I had to wait till I got home to build mine 😈

With the new software release's that Prusa have released they combated most of the bed hitting. The main problems happened early on in the 3.0.3, a few at 3.0.7.

Its the preventative measures that would be really nice to have.
I know Prusa at some stage included a spare PEI sheet which was a nice touch. It gave that peace of mind just in case it did, you then did not have to wait to get a new bed or PEI sheet.

Re: Hotend crashed into PEI and burnt a hole through it

My nozzle gouge was not that bad, but I'll relay my story so you can prevent it.

I did build the kit very carefully and got everything square, but I installed the probe a bit too high. The installation manual provides a good picture, but then you have to visually compare rather than use a measurement, and even fractions of a millimeter make a difference.

For the first X/Y calibration routine, it prompts you to raise the Z all the way up. Then it moves down towards the bed, but it leaves a fairly safe gap, and it starts looking for a calibration point at the front center of the bed. It does this by sweeping back and forth and slowly lowering the nozzle. Because my probe was too high, the nozzle hit before the probe sensed the calibration point. The nozzle started dragging back and forth on the PEI sheet, and it left a mark. Fortunately, it was mostly outside of the print area.

So here are my tips for preventing this:

1) The goal of aligning the probe is that it is almost level with the nozzle, but slightly above the nozzle. Keep that in mind. If in doubt, it is safer to have it too low at first, then raise it a little and re-run the calibration routine as needed.

2) The manual that comes in the box mentions putting a piece of paper under the nozzle for the first 4 points of the X/Y calibration routine. I didn't do this, because I didn't read the warning until after the damage had been done. I recommend you follow the warning, and keep your hand on the power button. As soon as you feel the nozzle is actually dragging the paper around, quickly turn off the printer...then you will want to lower the probe. (Note that the nozzle may touch the paper, and there's still space between the paper and the bed. That's OK. You should be able to tell if there is no more space between the paper and the bed.)

3) To change the height of the probe, you can loosen the bottom nut a fair amount so you can access the top nut. Then count how much you turn the top nut, and be aware of the direction you turn it and what effect it will have on the probe height.

It sounds like the more damaging situation is when the printer is unaware of the correct Z height, and it moves a hot nozzle into the middle of bed. I'll let others continue the discussion on that since it hasn't happened to me yet. I am going to avoid using the "home" function for now and just move Z manually (using the Move Z setting) when needed. That has worked for me so far.

Re: Hotend crashed into PEI and burnt a hole through it

I do wonder if Prusa could come up with a printed part that you push up against the mount and then adjust the pinda into that printed part.

I was just writing the above and figured I would have a go. I came up with this. I am sure there is lots of other better designs or even more accuracy. Just an idea for a few less heartbreaks especially if Prusa is able to come up with a set distance from bed.
I have no idea how licenses work so I just click what makes sense 😕

Thingiverse file. This is only set to 17mm so needs more. Would be interesting to know what the average is down from the mount to the tip of the pinda so I can adjust?

Thingiverse
http://www.thingiverse.com/thing:1771044

[attachment=0]IMG_20160914_201644[1].jpg[/attachment]
[attachment=1]IMG_20160914_201625[1].jpg[/attachment]

Re: Hotend crashed into PEI and burnt a hole through it

Hi,

a lot of thing have been told, I wonder if a simple counter-measure could be implemented in the firmware:

Every time the printer is switched on, the firmware would ask to level the X axis to the top Z-level, in the same way as in the XYZ calibration.

That way the X axis will always start from a flat situation, with both Z threads aligned to the top
That way the printer will have a security margin, in case of a bug in very specific situation (In case this happen, pure hypothesis) so that a wrong Z value wont make the nozzle dig in the heatbed.

Would that makes sense ?

Re: Hotend crashed into PEI and burnt a hole through it

Is that sort of thing not already implemented yet in the new firmware but still causes a few problems now and then?
I guess there is more then a few problems with the bed crashing issue so with a set height and some firmware updates at least half might be sorted? 😉

Re: Hotend crashed into PEI and burnt a hole through it

Every time the printer is switched on, the firmware would ask to level the X axis to the top Z-level, in the same way as in the XYZ calibration
I don't see any reason why to annoy hundreds of happy MK2 users by such irritating process. 😕

Re: Hotend crashed into PEI and burnt a hole through it

"If in doubt, it is safer to have it too low at first, then raise it a little and re-run the calibration routine as needed."

This, this right here. I think when you're dealing with probes like that, always set it a little low, especially for your first time, then carefully adjust. Also, test it, test it by using a piece of metal to trigger it, to test that the probe is working, before the hotend ever even reaches the bed.

No matter how careful you are, it's easy to miss a step, forget something, or there may just be a defect. Carefully following the instructions is important, of course, but when you get to turning it on, it's best to try and keep a few things in mind, and keep your finger on the power switch in case anything goes wrong.

I do this with any 3d printer I've had.

I like the idea of the spacer block. I was thinking a simple stair step that'd help measure the offset of the nozzle from the probe. That'd be especially useful for the cases where you might make adjustments to the hotend(or get a new hotend) and would need an easy way to align the heights.

I've been thinking a little bit about a few tools that might help with the assembly. It'd be easy to design some guides/jigs, but you know that'd not be so helpful to those that this is their first printer, so printing the guides/jigs wouldn't be so easy. :p

Re: Hotend crashed into PEI and burnt a hole through it

I question the PRO support here. They are promoted from the ranks of commentators. What perks do they get. I know one that had inside information before the MK2 was launched after I bought my MK1 a week or two before the launch.

Other companies provide 3D printing kits and give great in-house support. I own one, my first kit built 3D printer. In October 2014.

PJR says he is trying hard to support Josef....Why ? What does he owe him. What perks do PROS get ?

Its time Prusa Research stepped up and contributed to real support.

Re: Hotend crashed into PEI and burnt a hole through it

Isn't it curious that everything on this list is essentially an implementation issue?

Never is the problem ever with the design. Ever. For instance, if the printer was badly assembled, it's never the fact that the design of the printer is (unnecessarily) difficult to assemble. It's just that you assembled it wrong. Or the staff assembled it wrong. Or it's a defective part this or a damaged part that or missing whatever. Or maybe it’s UPS’s fault.

It's never a problem with the design itself.

While overall it's decent, I looked at the assembly and was like, "Oh Hell no, you assemble it. That way you can't blame me when it comes out wrong." I can tell you, being able to say, "PR assembled my printer" and deflect the pot shots that you guys like to take at other users has been worth every penny.

That said, it’s also not really that useful to complain about support. Support is as it always has been, and always will be. Better to just focus on the details and get the actual problem fixed.

Back to the sensor:

You shouldn't need an external jig to set its height. The jig should be built into the mount itself. How this is achieved depends on the sensor you select.

Either the threads end at a specified location, or the housing has a cap at the end where you can't push it any further. It's not complicated.

This is a prototype for another printer. The threads were *printed* for this probe, and I was shooting for the threads to end exactly where the probe bottoms out. I missed a little bit (kind of hard to measure where threads “end”), but it otherwise works. Bottom it out or make sure it clears the lip, then lock it at the top with a nut. Done. Easy to install, easy to adjust, easy to validate. No Loctite necessary either.

PR instead wants you to validate the probe location by eyeballing the top of the sensor housing against the cable retainer or something, which should immediately remind you guys of another post I made:

Re: Hotend crashed into PEI and burnt a hole through it

@gz1 lol. Yes lets get jiggy with the PINDA probe, integrated Callibration parts and jigs will help the kit build for sure.

Re: Hotend crashed into PEI and burnt a hole through it

gz1. thats a good design. Much better then mine. It can simply slide over it.
Can you add to my post here
http://shop.prusa3d.com/forum/improvements-f14/mk2-pinda-height-template-idea-only-t1753.html

Hopefully we can get some sort of "standard" height.

Re: Hotend crashed into PEI and burnt a hole through it

...
That would be excellent solution if all probes triggered at the same and well known height. But, obviously, they don't.
After some experiments this process worked for me perfectly:
1. Set the probe low enough (lower than nozzle).
2. Run calibration and wait for result (triggering height).
3. Readjust the probe to get the nozzle as low as possible without touching the bed, to achieve maximum clearance, adjustment is based on information gathered in previous step.
4. Rerun calibration, set fine Z adjust, happy printing.

Re: Hotend crashed into PEI and burnt a hole through it

I guess I can join the club of having the hotend crash into the PEI. One of the belts wasn't tight enough and it crashed into the bed. No doubt that's my fault but the PINDA sensor didn't stop it from happening.

I saw the steps to replace the PEI and I'm dreading that day when I have to do that. Has anyone used the thicker PEI from Amazon and got it to work?

Re: Hotend crashed into PEI and burnt a hole through it

The probe is only triggered as an endstop when it is over one of the nine calibration points and no where else on the heatbed. Thus if the z-axis brings the extruder down anywhere else over the heatbed it will not know it has hit the bed. With the printer correctly built this should never happen. This is why it is so important to check everything multiple times before using it for the first time! These are the risks you take with a home built kit printer.

If the Y or X endstops are not set right or not working or not triggered the printer won't know the exact position of the Probe so problems will occur.

The tip of the PINDA probe needs to be about 1mm higher than the tip of the nozzle to calibrate and function correctly, when I put mine together I first lined it up with the mark shown in the manual, but it was not low enough so I instead went for the 1mm option and that works perfectly.

This is not a €2,000 factory built printer, it is a kit for enthusiasts, if the user can't assemble it correctly then they made a judgement of error in buying this particular printer. However, the design of the printer works for the vast majority of users so you can't blame that if it is assembled wrong! This holds true for both end users and staff. The last I heard Josef runs a very tight ship and if a member of staff makes a mistake that costs money it is docked from their wages!

Taking gz1's idea and running with it, maybe Prusa Research could make the PINDA Protection Hat double as a settings guide? If it is extended vertically until it is flush with the Probe mount when fitted correctly? The lower nut could even fit into the end of the hat so you screw it on using the hat and maybe the combination of the nut and the hats own thread would keep it in place without needing any loctite? This would I should think work for users who just stick to the printer as it is and don't mod it at all. I will add to the list of things to ask Josef when he's back in the office, OK?

The green lines indicate the etension I'm sugesting, and the dotted the recess in the end for the nut:

Re: Hotend crashed into PEI and burnt a hole through it

Yep that would work 😉

Re: Hotend crashed into PEI and burnt a hole through it

As I said, this will work if (and only if) all probes trigger at exactly the same height. Do they? I'm not quite sure. Too many factors in effect - probes differ, heatbeds differ, even printed extruder parts differ.