Re: CAUTION: Loctite cracks acrylic - New replacement parts
I only wanted to build my Rapman 3.1 once, so along with following the instructions to the letter (hand-tight plus half turn) I added a dab of Loctite 243 threadlocker to the bolts before I threaded the nuts on.
Less than a week has passed and now EVERYWHERE where the loctite came into contact with the acrylic, the acrylic has fractured and in some places cracked right through. The acrylic on the bolt head end is totally fine.
My advice is to construct your Rapman WITHOUT loctite, and only later on when a nut falls off repeatedly, apply the tiniest amount of loctite and only in such a way that it will not come into contact with the acrylic.
To be fair, the label on the loctite does say "may attack some plastics".
Now I'm in a race to print replacement parts for my rapman before it totally falls apart; it's a miracle it's still standing! (Pictures of my newly-designed replacement parts later in the thread)
thanks Nordom, yes there are 3 corners (front right both top and bottom, and the z motor corner) that require urgent replacing, and then a further 4 less-urgent parts before i can even think of printing what i actually bought the printer for!! however the newly-designed parts should be a lot stronger and i look forward to contributing them to the wiki.
Hello chylld,
I am really sorry to hear this story. I can imagine the care you were putting in assembling your Rapman, adding that finishing touch of making sure everything stays together with some drops of Loctite. Just to see days later that it falls apart.
Thank you for warning us for Loctite and in case you can't print everything before a fatale crack let us know and we can jump in and print the remaining parts for you.
I used loctite on the acrylic without any problems to seal up some cracks and it worked like a charm ?!?!? Now, there is a number of loctite products, I cannot say with 100% certainty which one I used, but I know it is either "loctite super bond power gel" (30% chance) or "loctite super bond liquid" (70% chance) ..
IIRC 243 is for "thread locking" - so it is meant to be used on metal only..
unfold: thanks for the kind offer. i hope it won't come to that, but if it does i will be asking for help very quickly!
bogdan: i really must blame my own ignorance of the label. "MAY ATTACK SOME PLASTICS" should have been warning enough but my eagerness got the better of me. there are a few places I've just found where the loctite didn't touch the acrylic, and there are no cracks there. but overall, out of about 50-60 places i know i used loctite, 90% have cracks where loctite was applied (the nut end) and 0% have cracks on the bolt head end. and every crack has a blue tinge (the colour of the loctite) :/
Chylld, that’s a bummer, sorry to hear it. My distributor told me not to use it as he also experienced and showed me exactly what you describe. On the bright side now that you are forced to replace the corners you will have a much better machine. It is something you probably would have done in the log run anyway. Another thing my distributor had plenty of spare parts on hand, so might yours if you need them. You could get a sheet of 5mm acrylic (cheap stuff) or scrap from the kit and fashion temp parts if necessary or use super glue (it is safe to use) and glue a doubler over the affected area. Before you do that I suggest getting some scrap acrylic affected with the loctite to test how it reacts and performs. I'd print parts for you if I still lived in Syd and not Czech.
I just paid my distributor a visit this afternoon and informed him of my predicament. I'd also lost the grub screw from one of my Y pulleys which explained why my Y accuracy was sloppy at best! Ironically I lost it because I didn't use loctite there.
Thankfully my distributor keeps one kit open for random salvaging; so I got a replacement pulley from there and in the future could probably also get acrylic parts. However I'm determined to print some new parts myself. The challenge with the new corner blocks is that I need to replace them without taking the rest of the machine apart - I'm confident it will fall to pieces if I do that. Hence my new corners need to be fitted in-place. The prototype is half built as I type this, will take a photo when it's done :)
I just paid my distributor a visit this afternoon and informed him of my predicament. I'd also lost the grub screw from one of my Y pulleys which explained why my Y accuracy was sloppy at best! Ironically I lost it because I didn't use loctite there.
Thankfully my distributor keeps one kit open for random salvaging; so I got a replacement pulley from there and in the future could probably also get acrylic parts. However I'm determined to print some new parts myself. The challenge with the new corner blocks is that I need to replace them without taking the rest of the machine apart - I'm confident it will fall to pieces if I do that. Hence my new corners need to be fitted in-place. The prototype is half built as I type this, will take a photo when it's done :)
Funny, on one of our 3.0 machines one of the z grubs was lost and I only found out after a few perfect prints... I can't see any errors because of the missing grub screw, maybe the Z carriage is very rigid and can perfectly be driven by one belt only. Makes me wonder why your prints where sloppy.
I never had problems with my Z... only my Y. Because of the missing grub screw, the Y motor was only turning one of the two belts resulting in very sloppy Y accuracy.
I just finished replacing one of my corner blocks with a custom-designed one. Here is the extent of the damage (keep in mind, I didn't over-tighten anything... I did finger tight + 1/2 turn)
Here is the new corner in place. It's one piece, prints in 2 hours on standard Axon settings (compared to 6 hours for the Wiki version) and with 3 bolts from the original corner block, holds very tight and snug on all 3 rods.
Edit: added STLs. cnrv6bfl_bbr is for bottom front left and bottom back right, while cnrv6bfr is for bottom front right.
| Attachment | Size |
|---|---|
| cnrv6bfl_bbr.stl | 272.31 KB |
| cnrv6bfr.stl | 272.15 KB |
Lovely... exquisite design and simplicity! Nods head (I would design in gussets and two fasteners to increase clamping area, spread load distribution and as a back up should one come undone) Now I’m interested in your invention… what you got up your sleeve haha ;D? The most important thing I have found is to understand the capability and limitations of the machine so I can design for it. In the Aerospace industry where I did my training most parts are designed based on the capability of machines in some cases new machines are designed to make parts. Our 3D printers just about make anything possible at home! Don't ya just love it :-)
That looks VERY nice! :)
niiiiiiiice ... please share :)
thanks guys, just need to alter the model a bit before i release it. in the meantime, here's another pic:
and in 3d view:
That is REALLY elegant.
thanks forrest! it did take 4 iterations to get to this point, the previous ones were too complex. tonight i will be designing a new Z motor corner since that is the one with the next biggest cracks... and i will try to incorporate an easier method of adjusting Z belt tension since the current method requires about 3 hands which i don't have.
i will try to incorporate an easier method of adjusting Z belt tension since the current method requires about 3 hands which i don't have.
That would be a real blessing.
I just hope this is strong enough to keep the whole rapman stiff .. this acrylic crosses by themselves are not stiff enough .. if corners also get wobbly you can kiss precision goodbye ... anyhow, the print looks great to so great work, really :) .. when you are done, please upload the stl's with pics on the wiki
I just hope this is strong enough to keep the whole rapman stiff .. this acrylic crosses by themselves are not stiff enough .. if corners also get wobbly you can kiss precision goodbye
I will find out when I replace an adjacent corner :) When I installed this one, I found it was quite easy to move the bars around enough to slide my new corner in. The current acrylic design is really lacking alot but that has been said many times already.
Now that I have the old corner pieces out, I can take some precise measurements and adjust the model and also increase the 608 hole to 22.5mm (22mm in the design = 21.5mm printed). I'll incorporate these changes into the next corner and if they work well I'll redesign this one and upload all STLs.
So far it seems that 3.0 = 3.1 wrt basic structure geometry...
Now that I have the old corner pieces out, I can take some precise measurements a
No need to waste time measuring (as I already spent it) so here ya go
No need to waste time measuring (as I already spent it) so here ya go
Thanks, that will be a big help. However I still need to know the positions of the horizontal bars. Your diagram suggests that the bar that runs left-right is half-way between the 2 Z bars - should I also assume the same for the bar running up-down?
Actually this is not that important; the horizontal bars can be anywhere really. The critical measurements are the distance from the corner Z bar to the bearing... using calipers around the Z bars and their threaded rods, I measured 43.1mm and 43.5mm for the stock corners and 43.2 for my custom one. Your diagram suggests it should be 43.36 so it's close enough.
also increase the 608 hole to 22.5mm (22mm in the design = 21.5mm printed)
my advice - don't
make the hole in your design 22.0mm as this is how big hole you want / how big the 608 bearing is. Then tweak the machine / slicer so that your hole gets really 22.0mm. Don't tweak STL to the machine as for e.g. if I print it I will get hole for bearing 23mm and it will be useless.. Also, if tomorrow you use slicer that slices stl correctly you will also get holes to be "too big"...
In order to get holes to be "proper" size when slicing using skeinforge, there's "stretch" plugin that do wonders :)
The critical measurements are the distance from the corner Z bar to the bearing...
Yes, the critical measurement is "Z slider bar" to "Z threaded rod" .. and they are 25mm center to center in X and Y plane or sqrt(25*25+25*25) directly center to center (35.3553mm) - that is center to center, if you add 8mm as a thickness of the rod you get to your 43.35 measurement of outside to outside of the rod.
They are spaced 5mm in Z axes (this is important to get correctly if you replace one corner at the time).
spacing between centers of the screw holes around rod is 11mm (Center to center) and holes are 17mm from edge (center to edge)
my advice - don't
make the hole in your design 22.0mm as this is how big hole you want / how big the 608 bearing is. Then tweak the machine / slicer so that your hole gets really 22.0mm. Don't tweak STL to the machine
You make a good point... however my X and Y are only smaller when making circles in the XY plane. I noticed this after printing the corner block in the wiki; the horizontal holes were close enough to 8mm in diameter but the Z bar hole was barely 7mm.
I want my STL to be as accessable as possible, i.e. printable using Axon on default settings. So I think what I will do is have 1.5mm depth at 22.5mm diameter, tapering gently to 22.0mm over the next 1.0mm, and then a 45 degree taper to 16.0mm to hold the bearing while providing clearance for the M8 nut. I think this will be the best compromise.
stretch only affect XY plane :D .. look at http://www.bitsfrombytes.com/wiki/index.php?title=Skeinforge_Stretch ... it has pretty good explanation also "why" the holes are smaller
They are spaced 5mm in Z axes (this is important to get correctly if you replace one corner at the time).
spacing between centers of the screw holes around rod is 11mm (Center to center) and holes are 17mm from edge (center to edge)
Yes... I didn't measure but I assumed 5mm Z distance between horizontal bars. Then again the acrylic may have been so poor it was compressed to 4mm! :)
11mm distance between M3 holes I admit is quite interesting. This implies that an 8mm rod will be held snugly between its M3 bolts, but I've found this is not the case. Moot point however as I am doing away with that design limitation.
11mm center to center ... if you take 3mm out of it (1.5 on both sides) you get 9mm so 0.5mm on both sides of the rod - this coincides with how my acrylic pieces used to sit ...
11mm center to center ... if you take 3mm out of it (1.5 on both sides) you get 9mm
11 - 3 = 8 :)
I think the M3 bolts themselves may be slightly smaller than 3mm diameter, say 2.8. Given that I was observing play at the other end of the rod about 40cm away, this could be the explanation.
:D :D :D :D that's why I should be asleap at 03:40 and not on forum :D :D :D
btw, holes are with 1.45mm radius so they are bit larger then 3mm allowing bolts some free movement ... anyhow I don't think this is crucial for the build, the distance between lead and drive rods are what is incredibly important (that's what I messed up the first time)
:D :D :D :D that's why I should be asleap at 03:40 and not on forum :D :D :D
btw, holes are with 1.45mm radius so they are bit larger then 3mm
You should really get some sleep :) 1.45 x 2 = 2.9mm.
[me=Bogdan Kecman]off to bed [/me]
this 30h days are not good for my mental health :(
Hi chylld,
i'm sorry to hear that! But thank you for your warning! I also thought about using Loctite!
I hope you can print all necessary replacement parts before the cracked parts break totally appart!
Regards
Nordom