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kaucukovnik.vi
(@kaucukovnik-vi)
Active Member
Horrible quality control

The printer is a wonderful machine when it works.

My first print head had busted grub screws, now I'm discovering the replacement has the exact same issue. One would think you'd take extra care not to repeat the SAME problem. Even the documentation says they are not supposed to be overtightened! Can't you even follow YOUR OWN GOD DAMN INSTRUCTIONS?

Your support is nice and helpful, but at this point it's just damage control. This is not the reputation I came to Prusa for. Keep your gummy bears and deliver a working product instead.

This topic was modified 11 months ago by kaucukovnik.vi
Posted : 29/06/2021 11:01 pm
kaucukovnik.vi
(@kaucukovnik-vi)
Active Member
Topic starter answered:
Update

The first tech guy I chatted with denied ever having heard of such an issue, let alone twice with the same customer. The next one told me they replaced the screws and now this defect should be virtually impossible (why replace screws that have never been an issue, eh?) The second replacement arrived, the grub screws are somewhat different, yet busted again (this time I tried one right away).

TWO replacement hotends within 1 year of operation, same defect every time. Outside of warranty this means almost half the entire machine's price. The printer also managed to nick the buildplate, so we're talking the equivalent of one entire new machine in two years. Whatever that price is, this isn't what I'd call a quality product. At this point I'm done with Prusa. When this hotend clogs up for good, that's it. I got quite a few prints out of the thing so it's not a total loss, but still a disappointment.

I'm sure this is all nice and dandy if the printer itself is your toy and the prints are just a nice bonus on top of having fun tuning and modifying the thing in your mechanized workshop, but if you want a dependable tool, this ain't it.

Posted : 21/07/2021 3:42 pm
BogdanH
(@bogdanh)
Honorable Member
grub screw

My Mini is still working normally, but it doesn't have that many hours of printing behind -so I'll keep finger crossed 🙂.

May I ask you what "grub screw" you're talking about? (link to photo would be nice). I'm asking to avoid any unnecessary damage.
Thank you.

[Mini+] [MK3S+BEAR]

Posted : 21/07/2021 5:49 pm
abacabie
(@abacabie)
Active Member
More grub screws

it’s the 3 grub screws that keep the heatbreak in place, I have heard of that happening before, I received my mini three weeks ago and before I even turned it on I replaced the grub screws with 3mm M3 ALLEN BOLT SOCKET CAP SCREWS , they were just over £1 from e-bay for a pack of 5.

Posted : 22/07/2021 1:19 am
BogdanH
(@bogdanh)
Honorable Member
heatbreak screws

Thank you for clarifying.
Yes, I've read about that at the time of my purchase and so I was prepared to be careful enough. That's also pointed out in assembly manual, but is kinda hard to know how much torque is just right.

[Mini+] [MK3S+BEAR]

Posted : 22/07/2021 8:10 am
AndrewTerry
(@andrewterry)
Eminent Member
Posted by: @abacabie

it’s the 3 grub screws that keep the heatbreak in place, I have heard of that happening before, I received my mini three weeks ago and before I even turned it on I replaced the grub screws with 3mm M3 ALLEN BOLT SOCKET CAP SCREWS , they were just over £1 from e-bay for a pack of 5.

Do the screws prevent overtightening because of their cap, or does it make them easier to get to/maintain?

 

Posted : 22/07/2021 8:33 am
DRKMSTR
(@drkmstr)
Trusted Member
Grub Screw Tip

How was the Grub-screw overtightened? Was the screw stripped or the screw head stripped?

The grub screw works better for me with an imperial-sized hex/allen wrench than a metric one (I use a 1/16" wrench). The screws they use have a bit of an oversized socket / they become oversized when torqueing on them.

Hope this helps!

Posted : 22/07/2021 11:26 am
abacabie
(@abacabie)
Active Member
Grub screw thingy's.

 

Posted by: @andrewterry
Posted by: @abacabie

it’s the 3 grub screws that keep the heatbreak in place, I have heard of that happening before, I received my mini three weeks ago and before I even turned it on I replaced the grub screws with 3mm M3 ALLEN BOLT SOCKET CAP SCREWS , they were just over £1 from e-bay for a pack of 5.

Do the screws prevent overtightening because of their cap, or does it make them easier to get to/maintain?

 

Easier to maintain, the grub screws provided may be fine, i just seen a few posts of them been stripped and for the sake of £1 i thought it best to change them.

Posted : 22/07/2021 8:51 pm
mark
 mark
(@mark-3)
Estimable Member
Grub Screw Tools

I used a Torx screwdriver from this set on the grub screws:

https://www.amazon.com/gp/product/B001KBEO1O

They are tapered, so they fit well and don't strip them out.

Regards,

Mark

Posted : 22/07/2021 11:04 pm
Richard D
(@richard-d)
Eminent Member
RE: Horrible quality control

I swapped my grub screws for three cap-headed set screws.  Not only are they MUCH less likely to strip than a grub screw, I can now use the same hex key on them that I use for pretty much all of the other screws on the machine.  Probably the cheapest but one of the easiest and most effective mods you can make 🙂

 

 

Posted : 07/01/2022 12:20 pm
Distinctly Average
(@distinctly-average)
Eminent Member
RE: Horrible quality control

I would be interested to hear how they broke? Had you stripped the thread or rounded the Allen head? Either way it should be fixable without the cost of a hot end.

Posted : 24/01/2022 12:14 am
Distinctly Average
(@distinctly-average)
Eminent Member
RE: Horrible quality control

Just checked the heat sink, the bit that the three screws mount in, is a spare part available for €16.99 so no need to replace the whole hot end assy in the worst case scenario. I found on Amazon some grub screw remover tools for that size costing just €2.89.

Posted by: @distinctly-average

I would be interested to hear how they broke? Had you stripped the thread or rounded the Allen head? Either way it should be fixable without the cost of a hot end.

 

Posted : 26/01/2022 8:28 pm
mark
 mark
(@mark-3)
Estimable Member
RE:

 

Posted by: @distinctly-average

Just checked the heat sink, the bit that the three screws mount in, is a spare part available for €16.99 so no need to replace the whole hot end assy in the worst case scenario. I found on Amazon some grub screw remover tools for that size costing just €2.89.

Posted by: @distinctly-average

I would be interested to hear how they broke? Had you stripped the thread or rounded the Allen head? Either way it should be fixable without the cost of a hot end.

 

Take it apart first before you order parts. The heater and thermistor were seized in the heatsink and I had to replace them too.

At least to the US, shipping is a significant cost for these small parts. You don't want to pay to ship multiple orders if you can combine into one.

The grub screws came out with a tapered Torx driver.

Regards,

Mark

 

Posted : 26/01/2022 8:54 pm
Distinctly Average
(@distinctly-average)
Eminent Member
RE: Horrible quality control

I don’t have a problem with mine. I was more wondering how they had broken their grub screws. I was not sure if they had rounded them, hence the suggestion of an extractor, or they had stripped the threads in either the heat sink or just the thread on the grub screw. All have ways of recovery though. Parts above was worst case scenario.

As for your jammed parts problem, did you try and remove them hot or cold? In things like this there are options. Also, when re-fitting you can use thermal compounds that also contain a grease designed specifically for this type of thing. We use to use it on fuser units in very high speed (roll based, 300 feet per minute) hot fusion laser printers. You had to replace the compound every couple of years on those but, the parts that used it always released well.

Posted : 26/01/2022 9:52 pm
Richard D
(@richard-d)
Eminent Member
RE: Horrible quality control

Not done it myself, but grub screws are relatively easy to strip - especially if you over-tighten them while trying to secure the heatbreak within the heatsink.  50p worth of cap screws and it solved two problems - first, the risk of stripping the grub screw was eliminated; and second, I can now use the same Allen key as Prusa suplpy and which is used for everything else when disassembling the hot-end. 

Posted : 27/01/2022 1:08 pm
mark
 mark
(@mark-3)
Estimable Member
RE: Horrible quality control
Posted by: @distinctly-average

I don’t have a problem with mine. I was more wondering how they had broken their grub screws. I was not sure if they had rounded them, hence the suggestion of an extractor, or they had stripped the threads in either the heat sink or just the thread on the grub screw. All have ways of recovery though. Parts above was worst case scenario.

As for your jammed parts problem, did you try and remove them hot or cold? In things like this there are options. Also, when re-fitting you can use thermal compounds that also contain a grease designed specifically for this type of thing. We use to use it on fuser units in very high speed (roll based, 300 feet per minute) hot fusion laser printers. You had to replace the compound every couple of years on those but, the parts that used it always released well.

The threads don't strip. The heads round off, but a deep tapered torx driver can grab them and get them out. I did use a little of the thermal grease supplied by Prusa when reassembling the heater and thermistor. My original heatblock, heater and thermistor were covered in cooked filament that glued them together. That is why I added a silicone sock. I am using the one that specifically fits the Mini.

Regards,

Mark

Posted : 27/01/2022 1:46 pm
Distinctly Average
(@distinctly-average)
Eminent Member
RE:

Cool stuff, well quite hot actually…. I am lucky to own a set of screw extractors so in the event of it happening to me I should be fine. Having said that I had plenty of suitable torx bolts so used them on mine.

On the sock front, I am awaiting delivery of one. It is a pain to get anything at speed in these very odd times.

My comments were really pointed at the OP. Most times a head is damaged it is user error. Excess torque, incorrect or cheap tools, or just general cack handedness. Not convinced in this case it was a quality control problem. Even if it was there are almost certainly ways of recovering without having to replace a full hotend assy and the cost of that.

This post was modified 4 months ago by Distinctly Average
Posted : 27/01/2022 6:13 pm
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