Hotend Grub Screws - Potential Problem?
Re the three hotend retaining grub screws - I think these may be a weak point in the design.
I've seen several posts where members have mentioned rounding off the hex sockets in these screws. I use top quality hex wrenches but even I have got one screw that is borderline messed up. I note also that a suitable allen key is not provided with the Mini tools.
Perhaps it will be better to replace the small grub screws with hex head or cap head socket screws. There is plenty of space to do so, the heatsink clears the Z axis motor by around 10mm at its closest point. So I intend to get rid of these silly little grub screws.
Does anyone have insight on what size and thread they are? By eye I am guessing they may be M2.5?
RE: Hotend Grub Screws - Potential Problem?
The three set screws in the hot end cooler is to my measurement M3 with a hex hole of 1.5 mm. Ordinary M3 screws with cone/flat tip could be used instead (not so pretty).
Have a look at my models on Printables.com 😉
RE: Hotend Grub Screws - Potential Problem?
@area51
Thank you, most useful. If that is the case I have some M3 x 6 socket cap screws which should fit fine and use a much more robust 2.5mm allen key. As you say perhaps not quite so pretty but far more functional.
RE: Hotend Grub Screws - Potential Problem?
Job done then. Confirmed the original grub screws are M3 x 4mm. I have used M3 x 6 Socket Caps here, and have ordered the correct size.
RE: Hotend Grub Screws - Potential Problem?
In the old days I just made the Set/Grub screws myself from a standard screw with a hacksaw and a file.
The smaller diameters screws gives a better grip, just don't use a to big screwdriver... 🤔
Have a look at my models on Printables.com 😉
RE: Hotend Grub Screws - Potential Problem?
@area51
It's been a while since I had to resort to making screws like that. Much more satisfying than ordering from eBay though!
RE: Hotend Grub Screws - Potential Problem?
This is a great tip, and one that I think will solve the issue of the hot end moving, as you can get a little more torque onto those socket cap screws. Probably don't need too much and definitely don't want to deform the hotend in anyway though.
RE: Hotend Grub Screws - Potential Problem?
@area51
all three of mine will not loosen and are rounded, any suggestions on how do i remove them
RE: Hotend Grub Screws - Potential Problem?
my grub screws are all solid and i cannot undo them, any ideas?
if you increase printing temp will that offset the loss of the extended hotend?
RE: Hotend Grub Screws - Potential Problem?
@andrew-p42
This is the exact problem I could foresee with the use of these small grub screws.
I believe you should try to remove them carefully using a top quality hex key. These will always fit better than the cheap give aways. If that option fails then you are looking at drilling them out or using a very small screw extractor. Either will likely be a challenge to succeed.
If all else fails you can purchase a new heatsink with screws from Prusa which is not too expensive. Needless to say if you do this I would recommend you change out the grubscrews for proper socket set screws as above.
New heatsink - https://shop.prusa3d.com/en/mini/1174-hotend-heatsink-mini.html
Good luck!
RE: Hotend Grub Screws - Potential Problem?
I unscrewed one that was super tight with iFixit 1.5 mm hex bit and had to use screwdriver extension as a lever. I am seriously considering replacing those screws with different with bigger hex or cross driver, IIRC those are M3 (3 x 0.5 mm) 4-6 mm should be enough?
RE: Hotend Grub Screws - Potential Problem?
@crawlerin
M3 x 6 will fit fine and will not interfere with anything, but the best fit is M3 x 4mm.
RE: Hotend Grub Screws - Potential Problem?
Looks like a much better solution and torx drive too. Take care to not crush the tube...
Have a look at my models on Printables.com 😉
RE: Hotend Grub Screws - Potential Problem?
Do you guys reckon phillips screws would work just as well? I don't have any hex screws on hand at the moment
RE: Hotend Grub Screws - Potential Problem?
@matteo-cristini
As long as the screw thread is M3 and the screw head is out of the way, it should work.
Or you could saw off the head with a heck-saw and make a split slot as I showed in an earlier post.
Have a look at my models on Printables.com 😉
RE: Hotend Grub Screws - Potential Problem?
@area51
Thank you, maybe I did not explain properly what I meant...
I wanted to ask if even a phillips head screw would be an improvement compared to the original hex head, and if I would be able to tighten it correctly. I know nothing about screws and I am not sure if it makes sense to replace the M3 grub screws with some M3x4mm phillips head screws, or if it would not make the situation better.
Thanks again 🙂
RE: Hotend Grub Screws - Potential Problem?
@matteo-cristini
A M3 philips head screw would be easier to tighten and remove if stuck, compared to a grub screw.
Compared to hex or torx drive, the Philip is not as good because the screw driver have to be pushed into the screw head to get a grip and the cooler must be supported to avoid bending.
Be adware that overthinking the screws could bend/dent the stainless tube it holds - that is properly why Prusa choose grub screws in the first place.
Have a look at my models on Printables.com 😉
RE: Hotend Grub Screws - Potential Problem?
@area51
Thank you! I think I'm gonna stick with the stock grub screws and use the best hex key I have around. Maybe I'll switch to torx screws as shown above once this situation is over and I can go to the hardware store again (I know I could just order them, but I don't feel like doing it right now).
I have not received my mini yet but I plan on raising the hot end right away as suggested in the other threads to avoid clogging.
Thanks again 😀
RE: Hotend Grub Screws - Potential Problem?
I had a grub screw that I could not remove. I have ordered new parts and will use standard M3X4 hex screws.
I would like to see a better hot end designed for simpler maintenance. I personally don't mind the hassle as I'm quite the maker. I'm just thinking of the target group for these printers.