This is an addendum to Loctite testing (was: 1678 Robot Reveal 2022), which has been closed. One of my goals of testing was to determine how long after Loctite comes in contact with PC does hazing/cracking start to form.
At MTTD this past weekend, our Alpha bot needed a belt tensioner. Found some parts to use and made a quick and dirty pit fix.
The tensioner was assembled and the bolt was inserted thru the hole drilled into the PC. ONLY THEN was “stick” style blue Loctite applied to the last few threads.
Sigh, I decided the bolt was too short and pulled the bolt out of the hole and smeared a tiny bit of Loctite onto the PC as the bolt backed out of the hole. I was a little lazy and didn’t bother to remove the smeared Loctite (despite knowing better -after all, it was only a tiny bit); sigh again.
Loctite and polycarbonate are definitely not friends, as a team we have learned the hard way that mixing both element results in the worst outcome possible for polycarbonate plates.
Truly find surprising the state of the PC on the photo, since in our expirience Loctite tends to act quickly in a pretty destructive manner, breaking PC right away after it comes in contact.
Image attached is from a plate we had at our 2023 offseason robot which similar to your story came in contact with it on a small amout and completely broke off the PC.
A hard lesson we learned this year is that simple green seems to be worse. Whatever you do do not use it as a lubricant to slide silicone sleeving onto a polycarb tube(it was the only type of soap that we had handy).
For those looking for Loctite 425, this is one of those instances where McMaster seems to have the best price. Amazon: $33. McMaster: $26. Still a little bit of sticker shock for 0.7 oz.
Watch out for Loctite around AM compliant wheels as well.
True Story:
2018 in queue going on to the field our partners were putting on a AM green compliant wheel on to the intake claw. They lathered the bolt up in Loctite, tightened it down. I warned them that is a bad idea as that will eat the wheel up like acid. They said “nah it will be fine”. in about 90 seconds that wheel came off that robot, through the cube portal in the alliance station wall, into my hands. As I hold the wheel I tell them this is why you don’t use Loctite around the wheel. Funny moment of instant learning. Moral of the story don’t use it around wheel hubs.
Please see the link to the original testing at the top of this thread. Loctite 425 was one of the thread lockers tested and per my test, it was NOT safe on polycarbonate.
All the test samples showed crazing. All the test samples showed tearing after being bent. The control samples did not show any crazing or tearing.
Again, my goal was to try and determine when Loctite might adversely affected PC. My first test of 425 was at 24 hours. If you need to thread lock something on PC, and your time table to use is less than 24hrs. It might be ok.
425 does not specifically state that it is PC safe. The only product I could find that says it is safe for use when in contact with PC is Vibra-Tite’s VC-6. However, I didn’t test it because it’s ~$100 for a 1 oz (?) bottle!
Ah yes, loctite and polycarbonate, name a better duo. My team’s big mishap with loctite was when we were assembling our final shooter for Crescendo. One of the members was not paying attention and sure enough within a week the plate was useless.
We plan to invest in some select sizes of these bolts that have a nylon patch applied to them that helps prevent loosening from vibration (might not be as effective as a chemical thread locker but better than nothing). These should be fully safe to use around polycarbonate and have the benefit of not needing any cure time. Also far cheaper than the upfront cost of the Vibra-Tite VC-6 which I’m sure would go missing before we used all of it.
Definitely a few for the special fastners box, they are useful (e.g. need to go through a polycarbonate plate into a blind hole in AL or into a nut strip), although these are effectively single use items before the patch loses its properties, at least to my knowledge, (there are probably a few types that hold up better).
Low profile nylocks are my go to for most applications, but you can not always make this work (and they can be a pain to install in tight spaces when you should just tap the hole instead of a clearence & nut on the other side)
