I’m a huge fan of what REV has created with their 040 MAXTube. It’s lightweight and strong. The Thrifty 2 stage elevator I built using it weighs less than 20 pounds with gearboxes and motors, which is really pretty incredible.
However, I’ve seen my students on 5010 and other examples of people just absolutely crushing it (quite literally.) Because the material is thin (like 1/16 wall tubing as well), it’s really easy to overtighten thru bolts and bow your tube walls -
These spacers have .003" of clearance around the material edge and that seems to print well on Markforged or Prusa printers & inserts with a small amount of resistance into 040 MAXTube. Using these with thru bolts should prevent squishing your tubes -
However, it seemed silly to not get a free feature here when there’s one available. Using this McMaster part will let you turn these into light duty mount points, or simply insert a 10 bolt to make sure the spacer doesn’t fall out when you remove the thru bolts. Printing them on their flat face without supports seems to work just fine -
I’d love to see what other teams are coming up with to prevent this from happening as well! I should also mention REV has metal tube plugs available that are very nice and will prevent this issue too. Kudos to them for making a really nice product that my team is excited to use.
In general, does everyone use through bolts, or do some use rivets or separate shorter bolts for top and bottom (I.e. should also avoid crushing the tube)?
I’m pretty sure we are, we don’t plan to run our drive base this thin next season but it was a fun experiment and with these spacers I’m sure any other applications we have for it will be fine.
This was “bought some light max tube to try on a practice chassis with no superstructure” levels of construction. We’ll be running something else (probably normal grid maxtube when @Greg_Needel gets that back in stock) for in-season.
My biggest worries I have with rivnuts in such an application is bolts loosening over time. With a through bolt, I can tell a student to just slap a nyloc on there and never have to think about it again. The rivnuts would mean ensuring either a nylon patch bolt or loctite is applied, and that’s just an extra headache IMO.
Would love to hear easy solutions though to that if other have any
Anti-crush has been a standard element of tube structure on my team’s robots for many years. We typically use a material called “wood” for that purpose. Wood can be fabricated into many useful parts.
Most of the time, we end up doing a larger clearance hole for the bolt head on one side - you don’t need to worry about crushing it when the bolt head is inside the tube!
My team is currently running Mk4is, and what we plan on doing for season is creating a bottom gusset with through holes and rivet holes to mount to each corner of the chassis, and then secure the modules to the top of the 2x1, using the through holes to access the inside of the tube. Not sure if that made sense, I can attatch a screenshot of my CAD when I’m at home.
Also, that may not be a recommended way that @PatrickW intended these to be mounted, so i’d wait to see what he thinks about that. But it’s worked great for us in the past.
It’s called thread locker, and I’ve found the Vibra-TITE to be far superior to loctite brand or any other brand I’ve used in the past.
And for everyone saying rivnuts, those are not rivnuts in that 3d printed block. They are threaded inserts and I wouldn’t trust them to hold anything important, you can easily strip out the 3d printed block tightening the bolt. Rivnuts hold great as long as they are properly installed, there in lies the problem a lot of people have with them
Edit: sorry if I came off sounding like an a$$ that was not my intent
You definitely could, but those aren’t rivnuts inserted into the plastic part, they’re a screw to expand threaded insert. My comment on rivnuts was if you were installing said rivnuts directly into the tube, as like Ryan said in his initial post, the plastic inserts are to prevent crushing, but aren’t exactly intended for high load situations (if you thread/bolt into the threaded part instead of using a throughbolt).
Thank you for explaining to us all that threadlocker exists. If you read 2 sentences further in my post there, you’d see I explicitly said that I view that as a headache. With the screw to expand inserts being in plastic, you’d also need to ensure one is using the correct type of threadlocker, so as not to accidently destroy the plastic block if any loctite (sorry, threadlocker) touched the plastic.
I’ll also add that I’m very aware that Ryan linked threaded inserts in his post, and my above comments were indeed about rivnuts as that’s what Chrisrin mentioned in his comment I replied to.
I was suggesting rivets or two short bolts with probably Nylock nuts (top and bottom) to replace each through bolt. With the latter, it’s a little tricky but doable to get each one treaded, but then you can really torque them down tight.
If the insert is placed opposite where the faster enters so you pull the insert into the printed part as you tighten they are much less likely to fail. We also increase our number of walls on our prints to give the insert some more material to hold onto.
@Ryan_Dognaux , those blocks look great. We’ve done similar with 1/16 wall in high stress areas for years. We are excited to play with our new shipment of Rev tubing.
