Rivets vs threaded fasteners

[Sperkowsky]

Our team forever has used nylocks and quarter 20 bolts. I tried to push rivets year but no one seemed to listen much and I was told that rivets can't be load bearing. We have about 150 bolts on our robot not even joking.

We have some cheap rivets and a couple of riveting guns around but can someone reccomend a good set from a place like grainger(has to have a ny state contract) we got our first 2 sponsorships ever this year so we have a little bit of spending money $1,100. We used about 900 of it on raw materials (aluminum square and rectangular tubing along with some 8020) but we have a few hundred for other stuff. Also stupid question does a new control system come every year in the kop.

[EricH]

Originally Posted by Sperkowsky

Also stupid question does a new control system come every year in the kop.

[offtopic] Nope. It used to, when we ran the IFI system--ah, the good ol' days of near-instantaneous startup and connection--but not since we made the switch to the cRIO. But you can buy the items once/year at a discount, at least that's how it's been for the last few years.[/offtopic]

Incidentally, 1197 uses a mixture--bolts for most items, rivets for light-duty stuff that will probably not be moved much, and welding for major items that we aren't planning to change.

[mrmummert]

Todd....

Come see our robot at VCU and Chesapeake...(you'll like the name) We used both rivets and 1/4-20 bolts in quantity....We've found that rivets are easiest for the students to use, especially when they want to quickly prototype systems and are not worried about how exact it is. There are pro and cons to both. Where we think rivets will work well we use them there, but there are times when there is no substitute for bolts such as arms that will be under stress as an example. (we would never ever rivet down such things as a winch or pneumatic cylinder except in some very unusual situation that might call for it.) Another thing with our students at least is that we have had to try and standardize fasteners as much as possible. very basic fasteners such as one size of rivets (in the case of Versa chassis you have to) and very few bolt and nut sizes. In earlier years we used to use a given fastener depending on its use but the students had trouble remembering all the different sizes and types let alone keeping them in inventory and stored properly.

You've seen our robot from last year. The arm used to grab and intake the ball was riveted together. During finals at VCU last year it was badly damaged, but we were able to quickly drill the rivets out and fix it between matches. But...when we went to Chesapeake we added braces in the corners and bolted them in place. What i'm basically saying is...it all depends on the application. Rivets save space and weight, but can and will be ripped out. Bolts can take a lot of stress, but placement has to be planned out better.

In last years game there was a lot of defense and more robot to robot contact so using bolts where needed was more important. This years game not so much. So what your robot does and what type of game you have would go a long way in deciding which type application you need.

[GeeTwo]

Originally Posted by Richard Wallace

We were inspired by a respected mentor's claim, posted here a few years ago, that he could remove a rivet faster than any challenger could remove a nut and bolt. We tried that speed test ourselves, and when we saw he was right, we reduced our threaded fastener use considerably.

Does that include cleanup? And did one, both, or neither of the two removers use a power tool?


We use far more threaded fasteners than rivets; the main time we use rivets is when we don't have enough room for the nut and the material is too thin to effectively tap and get the tension we need. As noted above, rivets can't be passed them through both thicknesses of channel or tubing to get resistance to torque. When it comes down to it, we don't even use many threaded fasteners that are short enough to be effectively replaced by a rivet, and many of those go in blind so that we couldn't get a rivet in or out anyway. And we still haven't figured out how to effectively re-use a rivet.

Agree with MrForbes that if we went into production making dozens of our robot, we would design for more rivets (and welds), and fewer threaded fasteners.

[pfreivald]

We standardized almost entirely to rivnuts (or hi-locks or clinch nuts or whatever they're being called these days) and 10-32 bolts, with an emphasis on lighter weight, ease of maintenance, and minimization of swarf when changing out parts.

For things that shouldn't ever need changing (radio mount, license plate holder, etc) we used standard rivets.

We're pretty happy with the results thus far.

[BrendanB]

Our team has primarily used threaded fasteners over the years. In our years of "design as you go" it required a lot of assembly and dis-assembly during the build process which didn't lend itself well to rivets. While rivets are easy to remove once you have electronics on the robot having a lot of metal chips flying around isn't ideal.

This year we made a bigger move to rivets and ordered 4000 which we've used well over half of them. Compared to last year we used less than 50 on the robot.

We do like to use bolts to keep our systems modular. While it is faster to drill out a rivet with a good drill bit it is a little messier and overtime if you accidentally drill out the hole too much you don't get a nice tight fit. You can still have a modular system with rivets it depends on user preference. For us we'd rather take off key assemblies with a wrench and allen keys.

With this being the first year we used rivets heavily I would advise you keep an eye on making sure the holes don't get drilled too big. When some of the kids catch on that you need to drill out a 3/16" hole a little more to get a rivet in which requires a .19" hole they start going a little more aggressive on opening the hole up which weakens the fit since the rivets have more play. We ordered some extra numbered drill bits which worked well for drilling out rivet holes so we can get the hole size we want without someone trying to expand the hole with a 3/16" bit.

[Kevin Sevcik]

Originally Posted by GeeTwo

Does that include cleanup? And did one, both, or neither of the two removers use a power tool?

I'm guessing power drill and hand rivet tool, and probably ratchet and hand wrench for the threaded. But a power tool for the threaded will probably only get things down to even, so rivets still win on weight.

Originally Posted by GeeTwo

As noted above, rivets can't be passed them through both thicknesses of channel or tubing to get resistance to torque.

Teams that design primarily with gusseting+riveting in mind would probably tell you that you're designing your joint wrong if you have to run a fastener through both walls of the tube.

Originally Posted by GeeTwo

When it comes down to it, we don't even use many threaded fasteners that are short enough to be effectively replaced by a rivet, and many of those go in blind so that we couldn't get a rivet in or out anyway.

Okay, so this has me the most confused. We exclusively use blind rivets on our robot. It's right there in the name that they're meant for blind holes. They're just about the only way to attach something in the middle of a tube, short of drilling+tapping or bolting through the whole tube. Are you talking about blind holes into solid material? That's the only kind of blind hole I can think of that (most) blind rivets won't work in.

Anyways, we move to using lots of rivets on our robots. As others have mentions, we're only using threaded fasteners for things we're planning on removing occasionally and joints that are too awkward for a riveted solution.

We're pretty standardized on all aluminum 5/32" (thanks to Vex) and 3/16" structural rivets. When we're not using the premade Vex gusset plates, we typically use 1/16" for gussets on lightly loaded joints and 3/32" for heavier loaded joints. We've mostly been reserving the 3/16" rivets for the heavy duty joints. I'm afraid we're not super-scientific on the spacing and amount of rivets. The students and other mentors tend to throw a lot of rivets at a joint because they're light and easy to install.

The only time I see problems with riveted joints that I wouldn't with threaded fasteners is when there's poor fit up. Threaded fasteners will obviously let you pull together two sides of a joint that aren't already clamped together. Rivets (especially standard pop rivets) aren't nearly so good at pulling together two sides of a joint. If you have poor fit up, you'll see gaps between your gusset plate and the tube you're riveting to. That gives rooms for thing to shift and loosen and almost always results in wobbly joints after a short while.

We use rivets because they're typically lighter and faster than threaded fasteners. Yes, a threaded fastener of exactly the right length into a threaded hole is about the same weight. It's just a lot more tedious. Installing a rivet is as fast as drilling a hole (in place if necessary) and popping in a rivet. Your other options are drilling a hole, lining up a nut and bolt on either side, then tightening. Or drilling two different size holes, tapping one, and tightening down the bolt.

Other rivet advantages are they can't be cross-threaded and it's stupidly easy to add a few more to a joint if you need to for some reason.

If you're worried about getting the right hole sizes, holes wobbling out, strength, picking the right grip range, etc. then go with the 3/16" high grip range structual rivets. Also, no matter what rivets you need, buy them from Rivets Online. They're cheaper than McMaster for pretty much all your riveting needs.

[FrankJ]

This is starting to sound like a what is the best oil for your car debate.

We have gone from all bolts to a mix bolts & rivets. Since we switched to rectangular tube for out chassis, it is almost completely riveted. As Kevin mentions it avoids a difficult to design bolted joint in the tube.

While rivets might when a disassemble - assemble race under controlled circumstances, I think the general case goes to bolts. For an example try talking a formula one team into riveting their wheels on.

For less than ideal fit up & tension applications, the superior clamping force of a bolt gives it the advatage. For pure shear applications, a properly done rivet design is hard to beat. Every rivet has a recommended hole size. Google is your friend.

[JamesCH95]

We have used rivets in the past, but I don't really like them for four (engineering) reasons:

-There is a reliance on the human factor to install them, which requires training. They can't be 're-set' like a riv-nut can be.
-Holes cannot be opened up as much to allow for mis-alignments or tolerance stack-up when using rivets.
-They are (as pointed out) sometimes tricky to use with soft materials or materials susceptible to creep.
- Drilling rivets out takes a power tool, a drill bit, and can introduce metal swarf into a robot. Not an ideal situation for several reasons.

Rivets can, and are, used quite successfully in FRC. I prefer the advantages of threaded fasteners and blind threads to those of rivets though.

We use PEM (cinch) nuts and Riv-Nuts frequently on our robot. We love blind fasteners because assembly is faster than a fastener+nut and we can put mounting points in locations traditionally unavailable to faster+nut combos. We can put blind threads into thin material and thick materials with ease. Everything can be quickly disassembled. And, unlike tapping material directly, damaged threads can easily and quickly be replaced. At least as quickly as rivets.

Also, I would posit that I could uninstall and then install a blind-threaded fastener faster than a rivet of similar strength could be removed and installed. Cordless impact drivers are *awesome*.

[shewejff]

We switched almost exclusively to rivets many years ago, and I can't imagine going back. We use primarily 3/16" and some 1/8" for non-structural areas. The only times that we really use bolts is if we have a pre-existing threaded hole (e.g., mounting a gearbox), we can't fit more than a couple rivets in a critical connection so we need the strength, or if the area is so tight that we can't get the rivet gun head in there to be able to pop it.

As some have said, drilling out rivets can be done very quickly, especially if you have a drill with a 3/16" bit at the ready. The big disadvantage is the shavings. Whenever we need to drill out a rivet, we have to cover up the electronics and be careful to take the coverings off nicely. This is a minor nuisance.

People complain about rivets loosening up, but we tended to have the opposite issue. Students almost never tighten bolts enough. We would always have to make bolts "mentor tight". One of the mentors (usually me) would come over and give the wrench another quarter to half turn after the student was done. Otherwise bolts would slowly loosen over the competitions. We very rarely have any issues with rivets loosening. Plus, if the rivet is popped, you know that it's the right pretension. I don't have to go over and tighten it a little more.

There are some other advantages. Rivet heads are pretty small compared to a typical socket head (and even compared to a button or low-profile head). Rivets can be put in blind. I don't have to worry about how to get the wrench on the back side. That's huge when planning your design.

The only real disadvantage to the rivets that we have come across is the difficulty of popping the 3/16" rivets. We have a lot of younger students and girls on the team. It can be difficult with a standard rivet gun. We have a huge massive rivet gun and a pneumatic rivet gun which both make it a lot easier, but the heads are a little bigger so it's hard to get in tight spaces.

[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.

[philso]

Originally Posted by FrankJ

This is starting to sound like a what is the best oil for your car debate.

Originally Posted by shewejff

The only real disadvantage to the rivets that we have come across is the difficulty of popping the 3/16" rivets. We have a lot of younger students and girls on the team. It can be difficult with a standard rivet gun. We have a huge massive rivet gun and a pneumatic rivet gun which both make it a lot easier, but the heads are a little bigger so it's hard to get in tight spaces.

There are good and bad applications for both bolts and rivets.

We have some students who love to use the socket cap 1/4 screws and will stop building when they run out rather than the hex head ones. I guess they think they are cool, or something like that. Unfortunately, they tend to not put a washer under the heads and over-torque them causing the screw heads to "crush" the aluminum. One student over-torqued the screws holding the motor in one of the new clamping gearboxes and pulled the head completely through the plastic.

We also have team members who have trouble crimping a lug onto a 12AWG wire with a ratcheting crimper. Those same team members probably also have trouble tightening a bolt/nut properly. It is a never-ending struggle to teach the team members how to properly do what they need to do.

Originally Posted by JamesCH95

We use PEM (cinch) nuts and Riv-Nuts frequently on our robot. We love blind fasteners because assembly is faster than a fastener+nut and we can put mounting points in locations traditionally unavailable to faster+nut combos. We can put blind threads into thin material and thick materials with ease. Everything can be quickly disassembled. And, unlike tapping material directly, damaged threads can easily and quickly be replaced. At least as quickly as rivets.

I would like to get our CAD guys to design using these. The difficulty is with installing them properly without the proper equipment (like what we have at work). The best may be to find a sheet metal sponsor who can install them properly. The downside with the cinch nuts is that a ham-fisted team members can inadvertently "punch one out" leading to a hard-to-fix situation since they can be installed in inaccessible locations.

[JamesCH95]

Originally Posted by Loose Screw

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.

Are you sure this is a wise course of action? Red loctite can be (a) totally useless if the threads are cleaned a de-greased first and (b) the worst of both rivets and threaded fasteners (unservicable and difficult to drill out). I would suggest FRESH nylok nuts

Originally Posted by philso

I would like to get our CAD guys to design using these. The difficulty is with installing them properly without the proper equipment (like what we have at work). The best may be to find a sheet metal sponsor who can install them properly. The downside with the cinch nuts is that a ham-fisted team members can inadvertently "punch one out" leading to a hard-to-fix situation since they can be installed in inaccessible locations.

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.

[JDGallagher]

The general thought behind our wide use of rivets is that theyre faster, lighter, and less likely to come undone during competition. They may not be stronger that a bolt of equal weight, but we've found that 1/4 rivets are light enough and probably overkill in strength for our applications.

[Jon Stratis]

We use a mix of rivets and threaded fasteners. Most often rivets are used for gusset plates on structural members - a couple of rivets can do a great job holding things together when all the stress is sheer. Threaded fasteners are used for situations where things need to come apart by design (for example, the top half of our robot this year detached for transport in the trailer), or when they are holding something in tension, or when we simply can't afford the height of a bolt head.

We're also big proponents of rivet nuts (or whatever else people call them). They are ideal when you need to bolt something to some tubing but don't want to go all the way through the tubing, or when access to a nut is going to be difficult. It just takes a little practice to get used to installing them!

Removing a pop rivet is quick and easy with a drill, and inserting one with a rivet gun is even easier. I can't count the number of times something has been riveted together, then later had to be taken apart and put back together for some reason. It happens all the time!