Ribbit Rivet...
 

Billfred & I have traded messages on the use of 1/4" rivets to assemble the kitbot frame instead of the 1/4-20 hardware. Estimated savings is a pound or three. This post to to share what we came up with, and solicit further input.

First, a riveter: Harbor Freight sells an inexpensive one here.

Then, rivets. McMaster has them (search item 97519A652 for example) but Grainger seems to be slightly more cost-effective. (Note that you'll need a variety of grip ranges)

Lastly, we thought that steel rivets with standard shear strength (1240 lbs) should be sufficient, but no testing has been done. While this is far less than the shear strength of 1/4-20 hardware, that same hardware appears to be overkill.

Upside is weight savings, downside is difficulty in dismantling the frame (never had a need to do that) and repairs if a fastener loosens. Perhaps an adhesive to reinforce the joints to further absorb shear.

Sources, ideas, thoughts, experience from teams that did it?

Don

Re: Ribbit Rivet...
 

Good news! that may not be a downside. Some teams (I think 148/217) have reported that drilling out a rivet and reriveting is faster than loosening and tightening a bolt.

Re: Ribbit Rivet...
 

I am skeptical, since tightening an accessible bolt only requires positioning the tools and making a turn or two. This could only be faster if you have a lot of nice sharp 1/4" bits around and the nut or bolt head is positioned such that it's highly difficult or impossible to reach. Rivets are definitely faster for blind assemblies.

... Upon further examination of the kitbot frame (57 has yet to use it) just about every nut on there looks difficult to reach even on first assembly with nothing in the way. So I can actually easily believe that rivets are more maintainable for the kitbot. Plus, it's not like there's not a ton of places to put in extra rivets for good measure. I'll be considering this now...

Re: Ribbit Rivet...
 

Have you tried this? My first impression is that the diameters aren't going to be right. Normally holes for .250 fasteners are not .250 in diameter, they are a standard clearance hole (in aerospace we use .286 plus or minus .005 for structure) to accomodate machining and position tolerances for parts that are drilled in detail. I don't know what they are on the kitbot - I would guess they are punched so probably even larger size and position tolerance. For rivets, the holes are usually line drilled at assembly, not in detail, close tolerance (pretty close to .250) and immediately assembled either with the actual rivet or temporary fasteners ("Cleco's") to keep all the holes aligned. This is because a rivet depends on interference with the hole when it is bucked (swaged). If the hole is too large, you will not get the shear capability, and tensile capability will be next to nothing.

Re: Ribbit Rivet...
 

From what I've seen, we practically rivet everything. We can drill out a rivet in a very short amount of time, and riveting a new one in place is almost as simple. Using steel rivets is another story. Many a broken bits from those, but we only use them in places that REALLY need them. Plus, I think it's easier to just drill in from one side instead of having to fit a wrench or something up into the inside of a possibly cramped frame. Just my opinion though.

Re: Ribbit Rivet...
 

Agreed, but remember we're talking about pop-rivets, not real rivets. I have yet to measure the holes in a kitbot, but I suspect they are only about 0.012 oversize, which is right where the rivets - er, pop-rivets, want them.
Fascinating - here I am thinking that the 600 or so lbs of shear strength of aluminum rivets versus the over 1200 lbs for steel rivets is not enough... But, reconsidering, perhaps it is plenty, especially if we use a good adhesive that will fill in any gaps in the hole (point taken, Gary) and also add to the joint strength - some kind of epoxy paste I suppose. High compressive strength, good adhesion to aliminum, can manage some shock without cracking.

Although steel is less expensive, at $13 per 100 for 'expensive' aluminum I can't see it as being much of an issue.

Don

Re: Ribbit Rivet...
 

Our team used the rivets mentioned last year on the kit bot frame. They held up well and my subjective feeling is that it was a little stiffer. We borrowed the rivet gun from a local automotive shop. However, I believe that we have about had it with the kit bot frame. We are resource strapped and need an easy frame solution. This year we are planning on using 8020 Quick frame. By using the bumpers, Poly covering, and electronic board as structural elements, the total unit should be good. I made a proto type base and have been abusing it. It's holding up very well. However, I have concerns with the corner connectors. They may not hold up for teams that go to several regionals and off season events. The should be fine for our team's one regional.

Re: Ribbit Rivet...
 

I'll ask, since nobody else has; what kind of rivets were you using in the frame?

I shopped around Grainger (since there's a warehouse here in town) and found a few potential options:

5LE49 - 1270 shear/830 tensile, $8.86/25. (Aluminum w/ aluminum mandrel)
5LE56 - 2400 shear/1850 tensile, $10.40/10. (stainless/stainless)
5LE53 - 2400 shear/1850 tensile, $7.45/25. (steel/steel)
4AR31 - 1270 shear/1550 tensile, $7.01/100. (steel/steel)

The hitch with 4AR31 is that the material thickness only goes up to 0.250". While that's on the money for the kit frame (in theory, since you're joining two 1/8" pieces of metal next to each other), it would seem like going to ones with 3/8" grip range (which all the rest are) would give us a bit of breathing room.

No small part of my motivation to try rivets stems from what Kevin noted: it's a pain in the butt to get to some of those nuts, particularly once you've got the rest of a robot on board. It became the job of one of the kids at each event to check each nut and bolt and tighten as necessary, and Ron Karpinski still handed me a fistful of nuts and bolts at BE.

Greg Needel was talking with me the other night on the subject, and he was a little wary of going all rivets. He threw in the idea of leaving one bolt in on each end of the connections to soak up some of the shear loads. While I'd still take zero bolts over non-zero bolts if it does the job, checking 12 or so bolts sure seems a lot easier than checking the (if I counted right) 72 on a standard kitbot.

1618 is getting the riveter Don linked to, though the team is currently on a Thanksgiving hiatus until the 28th. I'm hoping we can get some knowledge before the holidays, or at least before Kickoff.

Re: Ribbit Rivet...
 

Correct me if I'm mistaken, but going all rivets on the kitbot like this isn't a permanent solution even for a season, is it? Just bring the screws and nuts along, and barring a catastrophic failure in a match, you can always drill them out and put bolts back in fairly easily within a match or two, correct?

If you can't replace the rivets in an hour or two.... well isn't that the point?

Re: Ribbit Rivet...
 

We used rivets from Mcmaster-carr. Part # 97519A653. I would caution riveting right from the beginning. If you make a mistake and need to drill out the rivets, it's a pain. We put the frame together with bolts and riveted after we were sure of the dimensions. There are higher strength rivets available, but they are very very difficult to remove. For the last couple years we have used the kit frame and riveted 1 x 1/8" 6061 angle on to the KOP base. It has been very effective. Our team lis low on skills, money and machining ability. It worked for us. Last year it took the students forever to build the frame. This year we are going to use the 8020 quick frame. It realy is quick to build a frame.

Re: Ribbit Rivet...
 

One more detail on the 1/4" rivets. We did not use back up washers. It is a real pain to get them on inside the frame. If they are not held perfectly flat against the inner wall you will have a bad rivet joint. On the 1" angle 1/8" rivets we always use backup washers. They are critical to a good lasting riveted joint. We have not had a steel backup riveted joint fail in 4 years of using rivets. However, a couple joints were accidentally done with AL rivets and those joints did loosen up.

Re: Ribbit Rivet...
 

Alright, a bit of an update on the matter.

We tried the Harbor Freight riveter. It failed; the riveter could not reliably hold onto the mandrel when we needed it to and release when we needed it to. After struggling through two riveters' worth of jams and stripped threads and frustrations, we switched to the Marson Big Daddy Riveter (the name of which has already become a running joke within the team) today, and knocked it out in about a half-hour. It's so smooth and easy to work with, it made me genuinely giddy. That riveter runs about $100, but it's some of the best money the team has spent all season. The Grainger part number is 4Y128; on McMaster-Carr, it's 90239A510.

We started with steel rivets, but a bit of consultation with some folks (along with worries as to whether it was the rivets that were causing our riveter issues with the Harbor Freight unit) led us to switch to Grainger part 4Y031, aluminum rivets with an aluminum mandrel and grip range right up to .250". With all the rivets in place, the frame feels fine--maybe even better than last year's with the absence of all the little wiggling that happens with bolts.

We'll be building our drivetrain over the next week (maybe this Saturday if the AndyMark order gets in, which we're doubting); we'll know more about how they hold up as build season rolls on.

Re: Ribbit Rivet...
 

Ahhh, my favorite subject: Rivets.

We use rivets (pop rivets) on every joint on our robot that connects to sheet metal. Even items that need to be disassembled quickly are held together with rivets. I swear by them. We use 5/32" and 3/16" aluminum rivets with aluminum mandrels. We also use 3/16" alimunim rivets with steel mandrels in certain high load areas. We have used a total of 20 of these "high load" rivets in the last 3 years (2005, 2006, and 2007). We are not using any steel rivets this year. We have approximately 2,500 rivets on our robot this year.

I challenge anyone using a nut and bolt to disassemble and reassemble your bolted joint to beat my students in a timed race with us using rivets. We use a pneumatic rivet gun from Harbor freight. They are a whopping $24 each. They last about 3 seasons and then you have to get new ones.

Attached is our gun in action on a previous robot.

I do not think you need steel rivets, but I have no test data to back that up. I can tell you this: we have never failed even one rivet on our 2005, 2006, or 2007 robots.

Re: Ribbit Rivet...
 

We're going with rivets on the kit frame as well and wherever I can convince students it's simpler. Oddly, we're using the harbor freight riveter and we aren't having any issues aside from and operator error tonight. I think it's important to make sure you're using the right tip and that the internal spacing is correct since that affects the jaws clamping, releasing, etc.

Our frame feels pretty good, but I was a little concerned in a few places. We've drilled a few extra holes to fill with rivets to add a little strength. I'm mostly concerned with the lack of precision in the kit frame. There's a distressing amount of slop in all the joints, such that only two out of the three sides of joint are being properly clamped. The third side ends up with about a 1/16th gap that the rivet won't clamp up, so rivets on the side aren't going to do much against shear loads. Or much of anything, really.

Also, to Paul, do y'all use the rivet gun in the Pits? If so, are you bring in a compressor/etc. or do you have some other solution?

Re: Ribbit Rivet...
 

We use the riveter in the pits. We bring a pancake style compresor that is sold at Home Depot or Lowes. It is the same compressor finish carpenters use for their finish nailers.

Re: Ribbit Rivet...
 

Glad you guys are having good luck with the rivets. They have been a very successful method for our team since 2002. One more tip. When drilling for the 1/8" rivets we use double end short drill bits that are typically used by sheet metal duct fabricator. They drill aluminum well and when the bit dulls just flip it. Once again we have never had a riveted joint fail. About 4 joints over all those years loosened a little.

Re: Ribbit Rivet...
 

Billfred, we also had similar issues with the Harbor Freight riveter - it wouldn't let go of the mandrel after popping the rivet.

We fixed it with a liberal application of grease to the gripping jaws. After removing the outer tube, we also unscrewed the inner tube. Some grease on the jaw outsides and they were reinserted, along with the spring, and tightened. Then we added a healthy dollop of grease to the inside of outer tube (and got it all the way in to the bottom, maybe 1/2" deep, around the screw in nose-piece) and screwed it all together - now it works like a charm.

You definitely get what you pay for.

Don

Re: Ribbit Rivet...
 

I add a little twist to that old phrase:

You usually don't get what you don't pay for.


Anyways, thanks for the rivet gun lube instructions, that is something I never though of and sounds very helpful!

We've had lots of small rivets fail, but we use them where we shouldn't, and we also use them as sort of a safety valve....the little rivets break off instead of letting the mechanism get bent up.

Re: Ribbit Rivet...
 

Lubrication could well be an issue with the HF riveters, now that I think about it--over the multiple times I disassembled it, it appeared that there was only just enough lubrication to get your hands messy.

Of course, to fix that would involve getting the kids away from the Big Daddy Riveter. That might be a task. ;)

Re: Ribbit Rivet...
 

I challenge any team to build their robot with 95%+ rivets :D
Team 1501's Scorpion had 1900+ rivets :ahh:
In the three years that we have been around we have probably used almost 5000 rivets.
Beat that, if you can :D

Re: Ribbit Rivet...
 

Ha! We've used over 10,000 rivets....:D

...all in the very same hole.:ahh: Darn it, Eric, learn how to set those rivets already!

(Er, just kidding. We're up to maybe 50 or 60):p


Don

Re: Ribbit Rivet...
 

We're probably near 100 rivets between the wheel tread and the frame, and I am enjoying it. Our superstructure is still in a state of flux because of other things, but someone will have to make a good case for us not to use 'em.

Re: Ribbit Rivet...
 

Who uses rivets instead of bolts on pretty much everything? we've been using 1/8" rivets for minor construction things but not a whole lot. Our we underestimating the rivet?

Re: Ribbit Rivet...
 

Andy,

You are grossly underestimating the rivet. We use them for almost every mechanical joint. The only structural place we don't use them is on the end of our wheel shafts to retain the wheel as the shaft is not very conducive to taking rivets. We use bolts to temporarily hold things together until we rivet them.

-Paul

Re: Ribbit Rivet...
 

We've been using a lot of rivets this year, and designing the robot to be able to use them in many places. The ball manipulator stuff is mostly thinwall aluminum tubing held together with sheet aluminum brackets riveted on, the chassis is fiberglass channel and sheet aluminum riveted together. The framework that hold the ball manipulator stuff is aluminum angle, which we are bolting together, but we might replace some of the bolts with rivets. We are again using a modular design, so there are 4 easy to reach bolts holding the ball manipulating assembly to the chassis, for quick full access to the drivetrain/electronics for repair.

Re: Ribbit Rivet...
 

A 1/8 rivet will not fit into a 1/8" hole. You need to use a #30 drill bit. You also need to use Clecos and Cleco pliers (to install and remove Clecos)

Re: Ribbit Rivet...
 

Well, now that ship has come and gone, I can more fully take stock of how it turned out.

We wound up riveting our entire frame using 1/4" rivets; the only places we took them out were places where we wanted to mount other things with bolts. (I'm starting to believe Paul and his speed claims after making those changes.)

The result held itself together well through weeks of inexperienced students working around them and some bumperless bumping around the hallways of Columbia High. We didn't have a chance to see how the frame holds up to competition-grade whacks, but I remain pretty optimistic. I'll wait on the Chesapeake postmortem before declaring it a success, though.

The best picture I have of our handiwork is seen at http://www.flickr.com/photos/billfred/2283099106/ that photo is from about a week before ship day.

Re: Ribbit Rivet...
 

I removed the semicolon that snuck into your link

Seems that rivets work better when you use several of them, smaller sized, and on joints that are designed for them. In other words, you kind of have to design the robot around the assembly method...and the kit frame is designed to bolt together. It should hold up ok, but you might want to look at some other riveted robots for ideas for next year.

Re: Ribbit Rivet...
 

We riveted most of the Kitbot connections, and left bolts in some others. I don't have a good photo - wait until later this weekend, after NJ - but IIRC we riveted all the places where there were 2 'bolts' holding something, and bolted the 'single bolt' places, with the notable exception of all the ones where they might stick out into the bumper space.

We were really unhappy with the Harbor Freight riveter, but didn't have the funds to get a better one. We did have to keep it leberally greased just to function - the problem was that it would not release the manderl after the 'pop'. One of these days, I'll try to figure out why that is so.

I like the idea of a pneumatic riveter. Almost as cool as a hand-operated hydraulic hole punch (which I first saw at Palmetto)

Don

Re: Ribbit Rivet...
 

Rivets are quite godly indeed...

we use rivets wherever possible. Usually, we use the 3/16 variety for mid-high stress and then 1/8 for low stress applications. It saves quite a bit of weight compared to bolts.

We also got a very nice pneumatic riveter this year, which handles rivets VERY well, much better and faster than our old manual ones.

Personally, I find using rivets more convenient. Even if you need to remove them, it's usually not hard (just get a slightly undersize drill bit and pop it out). However, when the end of the rivet shaft dosent pop out right, then it's tricky to drill out without damaging the hole/piece.

Overall, though, I love rivets, and they're very likely why we're able to stay at weight. =D

Re: Ribbit Rivet...
 

We did something similar with our robot this year. We used rivets (McMaster-Carr #97526A434) and I splurged and got a decent rivet gun (McMaster-Carr #90239A510). We wanted to paint the frame red and then throw on yellow rivets, but we ran out of time.

The gun worked great. The rivets held when our robot dropped off the 3 foot table we were working on. Rivets are very forgiving. We had no experience with them and all but 2 of the rivets were tight on the first application. The two that were loose were easily drilled and replaced. Those little guys saved us about 1 lbs over the bolts. We shall see how they do in competition, but right now, i'm sold.

Re: Ribbit Rivet...
 

We used 1/4 this year a step up from 3/16 and 1/8" rivets. We seemed to cut the amount of rivets we used in half this year by just switching to 1/4" They are gods (small g) among meer mortals in the fastener kingdom. But there are a few criterion that I like to follow when using them.

First, the ultimate importante is to have a pneumatic riveter, its much nicer/cleaner if you do and your kids don't end up walking around like popeye with one massive fore arm. Make sure you buy the right size riveter, and you get what you pay for. This year we used harbor freight riveter ran us around $95 but we had some issues, worked out the kinks and got it going pretty well. Don't waste your time with the HF hand riveter, it literally broke on the second rivet we popped.

For 1/4" aluminum is good, don't really need steel, we popped a few in the highest stress parts of our bot, but ehh it was probably overkill.

If you use 1/4" make sure you have plenty available, they are somewhat hard to find at a local hardware stores, we tried somewhere in the neighborhood of 6-10 stores before we tracked them down. Order them with the other parts, its cheaper and easier. ( I just happend to mis count )

When drilling out rivets be careful, this is kind of why I cringed when Paul said the challenge. Its true, rivets can stack up speed wise with most of FIRST style bolt construction, but hopefully you really won't have to drill out most rivets. Often times when drilling them out, you can open the hole a bit more, if you do this overtime the rivets aren't as snug... I know its like a few thousandths thing each time but if you come in at an angle I just hope your safety factors are high. Which with rivets, they usually are higher than you even know.

Use them everywhere and anywhere, sheet metal construction is one of the strongest available options if you want to put the engineering into it. One of the greatest parts is its amazingly cheap, to cut out entire robots worth of sheet on a water jet it can be a couple hundred dollars worth of labor. When all you have to do is place shafts and pop some rivets, its an amazing building experience.

If you don't for some reason think the rivets are strong enough, there is also the rivet/apoxy route. Adding structural apoxy like loctite E-20NS or the E-20HP which IF YOU NEVER WANT TO TAKE IT APART is amazingly strong.

So what have I learned with rivets over the last two years,

strong as heck, easy to use, have a good pneumatic riveter, apoxies are awesome if you don't want to take it apart, rivet where possible, don't drill them out too often, marvel at how cool they look and how light they are. Play count the rivet games with other teams that come by.

Happy Riveting.

Re: Ribbit Rivet...
 

Don,

When some of the students and mentors had this difficulty with our HF riveter, it was often due to using the wrong mandrel on the front and improperly setting the length of the jaw assembly. The 1/4" mandrel is, in fact, big and sloppy on a 1/4" rivet. The smaller mandrel is for 3/16" rivets and it allows the jaws to push too far forward, preventing the popped rivet mandrel from releasing. Similarly, the jaw assembly can be screwed in and out to set the unclenched grip of the jaws. The closer this assembly is to the body of the riveter, the stronger the grip when pooping and the stronger the grip when unclenched. Moving the assembly out from the body loosens the grip.

As mentioned, you get what you pay for. We paid $50-ish for our HF rivet gun. So we've acquired a dirt cheap rivet gun to get comfortable with, at the cost of it needing some TLC.

Re: Ribbit Rivet...
 

We use as many rivets as possible every year and have riveted the KitBot for the last three years with ZERO problems. We, of course, riveted it again this year. For the KitBot we have always used ¼” aluminum rivets with aluminum mandrels specifically either:
MSC #04045431 ($7.42/100 - Marson Brand)
McMaster #97447A651($12.75/100 - POP Brand).

As far as our experience with manual ¼” rivet tools here is what I can tell you:

It 2005 we purchased a “NuLine” ¼” rivet tool from MSC (#74327552 - $99.62). It has worked well for us but after 4 build seasons we have literally worn it out. It is made in China (or Taiwan?) and it shows. The main problem is the insert for the ¼” size rivet partially cracked and broke last year and then completely broke this year. The arms are linked by tiny E-clips that have continued to fall off since the beginning. After one too may times of crawling around on the floor looking for the E-clip that fell off we just replaced the pin with a 10-32 bolt this year. We have managed to keep it working but it is time for a new one. After our various modification and fixes the spent mandrels now come shooting out the back of the tool at a rather unsafe velocity. The handles are also very bent and battered from repeated use. Bottom line: I would rate it 3 of 5 stars. It has been a good friend but I think we pushed it a season or two past its useful life. If you are looking to invest is a quality tool that will last a lifetime this is NOT it your tool. It works for a while (~2-3 build seasons) but then literally starts falling apart.

As a replacement I decided to give the Harbor Freight 41291 ($13.99) rivet tool a try. I had a couple of $10 HF gift cards so it was free and good thing because if I had paid $1.00 for it it would have been a waste of money. It will grip and set the rivet fine but then you have to disassemble the thing to get the spent mandrel out before you can set another rivet. After reading through this thread I see that we aren’t the only ones with this problem and others have fixed it with liberal amounts of lubrication. I may give that a try but after the frustration that thing has given I really dread even messing with it any more!

Yesterday I broke down and ordered us a Marson “Big Daddy” rivet tool from McMaster (#90239A510 - $96.92) in preparation for competition. It should be here tomorrow and I am expecting great things after the reviews I have read of the “Big Daddy”. I was a bit hesitant because the McMaster image looks suspiciously like the piece of junk Harbor Freight 41291 but hopefully the HF 41291 is a cheap and poorly executed imitation of the superior Marson “Big Daddy”. The Marson “Big Daddy” from McMaster was the least expensive and best quality (from what I have read online) I could find. An added bonus is that replacement parts for the Marson “Big Daddy” are readily available from McMaster which is NOT the case for the import tools from HF and MSC. I will update this post with my review of the “Big Daddy” after we have received it and had a chance to break it in and see if it lives up to my expectations.

Re: Ribbit Rivet...
 

Another problem when drilling them out is that they can spin. IF you're drilling one out and the bit all of the sudden does not seem to be cutting, STOP! Spin the rivet for a minute with the drill bit and it'll be too hot to touch. Do that in plastic and it will have already melted.

Thanks Kevin & Chuck, for the good info. Next year we'll put a real riveter in the budget.

As for the HF hand riveter, I agree it's not worth a dollar, but with some careful work we did manage to get it to work OK. Indeed, mandrels do not come out until you lube the tips of the jaws liberally. I'm not going to waste anyone's time explaining how to fix that (PM me if you need it), my advice is buy something else.

Don

Re: Ribbit Rivet...
 

correct i find it faster scene we always have some kind of drill bit in the drill but we didn't use rivets

Re: Ribbit Rivet...
 

Agreed if the heads off already and the bottoms showing we usually just hammer out the rest with a 1/4" transfer punch :-)

Re: Ribbit Rivet...
 

Alright, time for a bit of hard data from us:

Perfection.

We ran eight rounds at Chesapeake, ignoring practice. For the most part, these were pure lapping, but we made our fair share of hard hits along the way. (The zip ties on the lane divider feared us, and we had our fun with low gear as well in a few matches, perhaps most notably the Great Pileup of Q56.) Through it all, the riveter stayed in the bottom of our tool cart.

Granted, all of this was with bumpers on our front and sides; we left them out of the corners and the back for various reasons. It would be nice to give this robot a few more events before declaring it a total success, but I'm quite satisfied right now.

Re: Ribbit Rivet...
 

2106's gun stayed in the bottom of the chest as well. not a single loose rivet. Now if we could find a way of riveting chains to the sprockets...

Re: Ribbit Rivet...
 

We got to use our rivet gun...something about trying out new treads, and then we finally got around to reinforcing an arm bracket that had needed it for a while. But we didn't have any failed riveted joints.