Rivets vs threaded fasteners

[InFlight]

It is important to have the capability to design for, and install both threaded fasteners and rivets. There are some situations like blind affixing structure to box or tube sections that are difficult without rivets. Depending on the situation - either could be used, and both would survive a season of robotic competition.

I would advocate only using Aluminum Rivets when possible. Steel rivets are a complete nightmare to remove from aluminum without a really sharp hardened bit.

We try to standardize on only a few fastener options: #6 Rivets, 10-24 & 14-20 UNC bolts. It makes it easier for the CAD team to know which clearance holes to use, and it limits the number drill bits in use (#10, #7, H) so there are less mistakes on hole sizes.

[philso]

Originally Posted by JamesCH95

We have had great luck installing PEM nuts with a machine vise, and a 1-ton arbor press can be had for <$100.

When PEM nuts have been popped out we have had good luck with holding the nut in place with pliers and re-cinching it with a light-duty cordless impact driver. It only takes a few moments, and can even be used to install the PEM nut in certain circumstances.

We are careful to use riv-nuts in truly 'blind' applications and PEM nuts in more accessible locations, where a press/clamp/pliers can get to.

Your strategy of mixing riv-nuts and cinch nuts makes perfect sense. Do you use the pliers and impact driver for cinch nuts that the arbor press cannot reach? We work at a school for the first part of the build season then move to oRyon Labs for the balance of the season. It will probably mean that the students will get more "exercise" to prepare them for moving the robot on the field.

Originally Posted by InFlight

I would advocate only using Aluminum Rivets when possible. Steel rivets are a complete nightmare to remove from aluminum without a really sharp hardened bit.

We made the mistake of using a whole bunch of 1/4 inch steel rivets on parts of our chassis. We probably could have drilled fewer lightening holes if we had used 3/16 inch aluminum rivets.

[Paul Copioli]

Since I was quoted in this thread from a post I made years ago, my challenge still stands regarding speed of rivets vs. bolts.

My challenge was only intended to be for people that claimed screws were faster.

As far as the challenge goes, it included cleanup and both "competitors" could use any power tool they wanted. However, the people using screws either had to (1) use a locking nut or (2) use loctite. I know I will bring a drill and a pneumatic riveter from Harbor Freight and will take on all challengers that think screws are faster.

Now, challenge aside, we use a combination of both depending on the job. I will never, ever use rivets in a tension (loads trying to pull "up" on the rivet) heavy applications.

When attaching sheet metal, we will only use rivets. PEM nuts (or the equivalent) are great if you know how to install them.

Again, it is really up to preference, but if you are asking for advice, then I would use rivets as the default and bolts should be reserved to where there are large pull out loading.

[FrankJ]

My issue with cinch nuts is when they go bad, they can be a difficult repair. But they do have their place. You can also buy an hand installation tool that sets them with ordinary wrenches. Highly recommended if you use them.

Paul, the reason why your challenge get quoted is because it is a good example. Although I think that you would probably give the riveters a run for their money if you were the one handling the wrenches.

[JamesCH95]

Originally Posted by philso

Your strategy of mixing riv-nuts and cinch nuts makes perfect sense. Do you use the pliers and impact driver for cinch nuts that the arbor press cannot reach? We work at a school for the first part of the build season then move to oRyon Labs for the balance of the season. It will probably mean that the students will get more "exercise" to prepare them for moving the robot on the field.

If a vise or press press can't reach we'll use a riv-nut in the original design. The pliers and impact are generally only for 'emergency' situations, or where a bit of dis-assembly would be required to re-press the PEM nut. Sometimes the pliers aren't even needed.

Originally Posted by Paul Copioli

Since I was quoted in this thread from a post I made years ago, my challenge still stands regarding speed of rivets vs. bolts.

My challenge was only intended to be for people that claimed screws were faster.

As far as the challenge goes, it included cleanup and both "competitors" could use any power tool they wanted. However, the people using screws either had to (1) use a locking nut or (2) use loctite. I know I will bring a drill and a pneumatic riveter from Harbor Freight and will take on all challengers that think screws are faster.

Now, challenge aside, we use a combination of both depending on the job. I will never, ever use rivets in a tension (loads trying to pull "up" on the rivet) heavy applications.

When attaching sheet metal, we will only use rivets. PEM nuts (or the equivalent) are great if you know how to install them.

Again, it is really up to preference, but if you are asking for advice, then I would use rivets as the default and bolts should be reserved to where there are large pull out loading.

So a friendly competition would be:

1) Start with a component, secured with whatever fastener you choose.
2) Remove the fastener.
3) Replace fastener with some form of anti-loosening feature.*
4) Bonus round(s) - repeat several times over.

Any power tools allowed.**
No assistants allowed.
No pre-loading of fasteners or tools.
Fasteners and tools may be laid out on the table.

I'll see about recording some trials and posting them on the YouTube. Could be fun! The Faster Fastener?

*I would argue that many bolts don't actually need this, especially when tightened with an impact gun, but as part of the competition that's fine.

**Using air tools can be really fast, but getting air tools at a competition venue can be... difficult, to say the least. I would argue that only electric or tools known to be readily accessible in the pits should be used. But, again, for a friendly competition this is fine.

[asid61]

If you say you are faster with a riveter than with a nut and bolt, what if you had practiced with a nut and bolt and were more used to it than a rivet?
What I'm trying to say is that it's the cap on speed that matters, and a 1v1 test may not be perfect depending on experience.

Mainly for less-strong stuff and stuff we don't remove we use rivets. For stuff that needs to be stiff we make sure to have a lot of 1/4" rivets.
For removable assumblies (like our elevator this year) screws offer and advantage due to better accessibility; we can't exactly rivet something out 1/2" from our bellypan! So ti saves us space.

Maybe it's just the way we put on rivets, but they don't tend to work well in tension for us, and we need many to keep ourselves stiff and not loose.

[Mr V]

Originally Posted by Loose Screw

Being a coach of an FTC team, I've had experiance with kids using both options. In our lift system, we tried using nuts and bolts. We were going to loctite all of them, but we never got the chance, and after we added more to it, it was extremely difficult to get to them to tighten them.

We decided to use pop rivets the next year so they wouldn't loosen and unscrew after competitions. However, not all of them were pressed together tightly while they were used, so as a result they were loose and eventually broke. Our problem became much bigger now that we had to redo most of our pop rivets.

As a coach I feel irritated when all of their hard work just falls apart like that, and I see how frustrated they get too. That's why I've decided that we're going to use red loctite on anything that seems like it might come undone. However, we can't access every little nook and cranny, so we'll have to use pop rivits for areas like that.

My advice: Loctite nuts and bolts for easy-access areas, and then pop rivets for areas that you can't reach one side. Just make sure they press together everything tightly for the pop rivets.

Just say no to red loctite, if you have to remove it you'll likely end up breaking, bending or stripping your Allen wrench and/or bolt. Red is supposed to be heated to be able to be removed. Blue is what I recommend for FRC use, it can be removed and usually does not cause the breakage/stripping that red does. Another option is the penetrating loctite, it is designed to be applied after the fasteners have been assembled. The one we typically keep in stock is the green version.

Nylock nuts or bolts are another good option.

[Kevin Sevcik]

Since we seem to be trading horror stories in this thread, we haven't used many riv-nuts since the year we lost a match because a cross-threaded riv-nut spun and kept us from swapping our bumpers during a tight turn between matches. That and the fact it's difficult to get things to sit flush on top of (most) riv-nuts. The PEM nut fiasco on the old IFI sheet metal wheels has made me leery of those as well.

[JamesCH95]

Originally Posted by Kevin Sevcik

Since we seem to be trading horror stories in this thread, we haven't used many riv-nuts since the year we lost a match because a cross-threaded riv-nut spun and kept us from swapping our bumpers during a tight turn between matches. That and the fact it's difficult to get things to sit flush on top of (most) riv-nuts. The PEM nut fiasco on the old IFI sheet metal wheels has made me leery of those as well.

Were you using steel or aluminum rivnuts?

[PayneTrain]

422 has evolved over the last 3 years to use 90% rivets, 10% bolts and other for fasteners. I think rivets are 1000% worth it in the long run, but you have to be proactive as a team when you design and manufacture parts you intend to assemble via rivets. I can drill out and replace rivets very quickly now because of all the time in 2013 and 2014 that was spent removing rivets on poorly thought out designs. If your parts are manufactured to the specifications of comprehensive, integrated CAD drawings, riveting is crazy easy.

Whether you use rivets or threaded fasteners, you're going to enjoy life more if you make coherent drawings and practice good machining, I just know how much I can hate life drilling out the 20th rivet on an assembly because somewhere along the way there was a screw-up. I do think the positive experiences students have had with rivets, weighed against the negatives, have helped condition better machining practices in house (The build lead and mentors 86'ing poorly done work also helps).

Todd, if you want to look past some ugly quirks of our robot when we're at VA (we sort of had to throw on some nasty looking gussets at the end to beat the snow) you can see where we use threaded and quick release fasteners and where rivets were used. Any static assemblies and subassemblies on the machine like the drive base and super structure, individual subassemblies on the lift with the shafts, grabbers, and carriages are all assembled through rivets. For the purpose of clean, universal replacements on some weird parts of the robot, we used threaded fasteners. Any point where one assembly or sub-assembly connects to another one is likely bolted on, or in the case of moving from transport to competition configuration, fitted with quick release fasteners.

[ToddF]

Thanks, everyone, for your constructive comments. You've definitely convinced me that we need to look more closely at transitioning to rivets whenever possible.