Construction with gussets and bolts

[Joseph Smith]

I've been investigating some new design and construction methods that my team hasn't explored in the past, and I really want to try assembling the frame and important structures with machined gussets and bolts. I have a few questions for teams who have used this construction method. In this scenario, I'd be using two gussets, top and bottom, to create a 90 degree joint between two lengths of rectangular aluminum tubing, all 1/8" wall thickness.
1. Is it better to put a long bolt all the way through and use a nut on the other side, or to tap the gusset and tubing and use shorter bolts?
2. If a bolt all the way through is used, are large washers needed to spread the load to prevent the tube from being crushed?
3. If the parts are tapped and a short bolt is used, would it be preferable to tap both the gusset and the tubing or to drill clearance on the gusset and only tap the tubing?
4. Is locktite a necessity with the tapping method?
5. What has been your overall experience with this method of construction? Pros/Cons?
Thanks!

I should clarify, with the pretapped method, we would be using machine screws or something of the sort.

Clarification #2: We have used a lot of rivets in the past, and do like them for certain applications; however, I'm specifically interested in trying out bolts on the critical parts of the frame- primarily drivetrain- where it can see a lot of stress due to collisions or hard driving. These would be parts that we shouldn't ever have to disassemble or replace between matches (fingers crossed) so I'm not really concerned about the speed of installing/removing them.

[notmattlythgoe]

Originally Posted by Joseph Smith

I've been investigating some new design and construction methods that my team hasn't explored in the past, and I really want to try assembling the frame and important structures with machined gussets and bolts. I have a few questions for teams who have used this construction method. In this scenario, I'd be using two gussets, top and bottom, to create a 90 degree joint between two lengths of rectangular aluminum tubing, all 1/8" wall thickness.
1. Is it better to put a long bolt all the way through and use a nut on the other side, or to tap the gusset and tubing and use shorter bolts?
2. If a bolt all the way through is used, are large washers needed to spread the load to prevent the tube from being crushed?
3. If the parts are tapped and a short bolt is used, would it be preferable to tap both the gusset and the tubing or to drill clearance on the gusset and only tap the tubing?
4. Is locktite a necessity with the tapping method?
5. What has been your overall experience with this method of construction? Pros/Cons?
Thanks!

Are you set on using bolts? The VersaFrame line has been designed to use rivets and many teams have been very successful with it so far.

[Joseph Smith]

Originally Posted by notmattlythgoe

Are you set on using bolts? The VersaFrame line has been designed to use rivets and many teams have been very successful with it so far.

We've used versaframe extensively, especially this last season. I'm looking into construction methods that don't rely on rivets as the primary means of fastening, and that utilizes our machining resources rather than the cash in our pockets. We have a laser-cutting sponsor, so designing gussets rather than buying them would make sense for our team.

[Dale]

I'd second the idea of using rivets. Rivets have a huge weight advantage over bolts and don't vibrate loose. Most teams use 1/16" wall tubing for most things only going to 1/8" where needed. We use 3/16" rivets which come in a million different styles with different sheer strengths. McMaster Carr has most everything.

We use the wide range rivets so we don't have to stock a bunch of different lengths. The high strength rivets with steel shanks have higher strength for demanding applications but they are a pain to drill out.

[Nyle]

I'm going to second the rivets option. We've been using gussets and rivets for a while to build our robots and it's worked quite well for us. They're very fast to install, just as fast (if not faster) to remove, and pretty much always just as strong.

We have occasionally used bolts to hold things together during construction, or to allow assembly/dis-assembly in situations where a drill/rivet gun may not be available; when we do this we usually have the bolts go all the way through to the other side of the tube and use a nylock nut to hold it all in place. If you do want to have a bolt to allow quick dis-assembly, be sure to either buy bolts at just the right length or be ready to cut down bolts to size—it'll make assembly/dis-assembly significantly faster.

[notmattlythgoe]

Originally Posted by Joseph Smith

We've used versaframe extensively, especially this last season. I'm looking into construction methods that don't rely on rivets as the primary means of fastening, and that utilizes our machining resources rather than the cash in our pockets. We have a laser-cutting sponsor, so designing gussets rather than buying them would make sense for our team.

My comment about VersaFrame was more to make the point that rivets have been used very successfully. Make your own gussets and attach with rivets. Plus, rivets are much cheaper than bolts.

[BrendanB]

Originally Posted by Joseph Smith

I've been investigating some new design and construction methods that my team hasn't explored in the past, and I really want to try assembling the frame and important structures with machined gussets and bolts. I have a few questions for teams who have used this construction method. In this scenario, I'd be using two gussets, top and bottom, to create a 90 degree joint between two lengths of rectangular aluminum tubing, all 1/8" wall thickness.
1. Is it better to put a long bolt all the way through and use a nut on the other side, or to tap the gusset and tubing and use shorter bolts?
2. If a bolt all the way through is used, are large washers needed to spread the load to prevent the tube from being crushed?
3. If the parts are tapped and a short bolt is used, would it be preferable to tap both the gusset and the tubing or to drill clearance on the gusset and only tap the tubing?
4. Is locktite a necessity with the tapping method?
5. What has been your overall experience with this method of construction? Pros/Cons?
Thanks!

1. Whenever we have bolted a gusset/tube we have gone all the way through with a bolt. We try to keep tapped parts to standoffs and to a minimum. If its a part you may have to remove and install several times you start increasing the risk someone who is rushing won't make sure the threads are lined up and damage the threads. Our first year using tapped parts was in 2013 and by mid season a few standoffs were replaced because the threads were gone.

2. To prevent the tubing from being crushed you need to work on training teammates (and sometimes adults too) how to properly use tools. There is a difference between making sure you have a snug fit and turning the wrench to extremes to get a tight fit which typically ends in bending the tube.

A downside to using bolts extensively is they are much heavier than other alternatives such as aluminum rivets. The more parts you have in your assemblies the more weight you need to consider that is getting used holding it together.

This past build season we relied mostly on gussets from Vexpro or homemade versions held together with 3/16 aluminum rivets. We did use bolted connections in a few key areas we knew could be removed frequently and didn't want to rely on drilling out rivets over and over.

[Ed Law]

Originally Posted by Joseph Smith

I've been investigating some new design and construction methods that my team hasn't explored in the past, and I really want to try assembling the frame and important structures with machined gussets and bolts. I have a few questions for teams who have used this construction method. In this scenario, I'd be using two gussets, top and bottom, to create a 90 degree joint between two lengths of rectangular aluminum tubing, all 1/8" wall thickness.
1. Is it better to put a long bolt all the way through and use a nut on the other side, or to tap the gusset and tubing and use shorter bolts?
2. If a bolt all the way through is used, are large washers needed to spread the load to prevent the tube from being crushed?
3. If the parts are tapped and a short bolt is used, would it be preferable to tap both the gusset and the tubing or to drill clearance on the gusset and only tap the tubing?
4. Is locktite a necessity with the tapping method?
5. What has been your overall experience with this method of construction? Pros/Cons?
Thanks!

I should clarify, with the pretapped method, we would be using machine screws or something of the sort.

Rivets are the way to go. There are different choices of rivets that will give you different strengths.
Bolts are heavy and time consuming to take out during quick repair in the pit. If it is a critical joint with a very high load, use bolts. I would get it all the way through and put a spacer in between if you have access. A washer will help reduce the chance of collapsing the section but if a student wants to use a drill to tighten a bolt and not paying attention, you can still collapse it. We always use lock nuts so no locktite is needed.
To save weight, I would use 1/16" high strength aluminum alloy for the two gussets.
We usually use rivets everywhere and more rivets in area with anticipated higher loads. If any rivets failed during matches, we just replace them. If it is in an area we do not want it to fail again, we would replace with bolt and nut. If you don't have access to use nut, then use self drilling screws for repair. They work really well.

[AdamHeard]

Rivets are awesome.

Blind Rivet Supply has great prices.

http://www.blindrivetsupply.com/Butt...Alum_Alum.html

[mrmummert]

We mainly use rivets with the Versa chassis...but in some areas we add
bolts as insurance incase of rivet failure if we have the weight and space
for them. We don't tap the Versa chassis for them. The only time we tap
any structural part for bolts is if we use 80/20 as part of the frame.
We've been able use both in the same robot. The past two years we've made
the basic frame from Versa chassis and added other structural parts using
80/20 by bolting them to the Versa chassis.

[Jon Stratis]

While we mostly use rivets, we have, on occasion, used bolts as well. Rivets are extremely easy and quick to do, using a small drill bit and a pop rivet gun. Bolts, on the other hand, require larger holes, wrench and Allen wrench, and may not be as quick or easy, depending of familiarity and the exact situation.

For your specific questions, when we use bolts:

1. Most of the time we use long bolts with nuts, although we also utilize rivet nuts quite a bit - they're great, and provide a much better mount than tapping some relatively thin sheet metal.

2. We usually don't need washers- the long bolts are going through gusset plates on both sides, which act, more or less, as large washers themselves. Of course, you want to make sure you aren't over tightening things!. If we are worried about tubing being crushed, we use some plastic/nylon stock, machine it to fit inside the tube, then drill through the whole mess. It gives you support where you really need it, and is fairly light weight!,

3. We always only tap one piece and use clearance for all others. Otherwise, you create the possibility of binding issues and other difficulties putting two tapped pieces together.

4. Unlocks or locktite on everything... These robots move around and rattle so much, anything not properly secured will work it's way loose over the course of competition. And of course, fall apart at exactly the wrong moment!

5. As stated, overall we usually use pop rivets, not bolts. The exceptions being places where we want some added strength (anticipating loads the pop rivets wouldn't be able to handle, in either size or direction) or want a piece to be easily removable/swappable.

[philso]

We used 2 x 1 inch tubing with 1/8 inch walls for our chassis and lift tower and 1/16 inch wall 2 x 1 and 1 x 1 tubing for the other structures. Most of it was riveted using 3/16 inch rivets and 1/8 inch thick gusset plates that we made. Some joints, like the lift tower to chassis were done using 1/4-20 bolts to allow the lift tower to be removed for shipping. This construction was adequately strong for this years game and would probably be good enough for last year's game. Last year's robot was made from aluminum channel held together with eight 10-32 screws in the corners. There were fewer than the rivets we used this year and it held up fine with the abuse it was subjected to.

I would strongly suggest using washers under the heads of any socket cap bolts (see link below). They bearing surface area of the socket cap bolts is smaller than the bearing surface area of hex head bolts. I have seen quite a few instances where the head of the socket cap bolts have "crushed" the aluminum sheet due to the high concentration of force. Some joints have gotten loose because of the deformation of the aluminum. This is different from crushing a tube.

http://www.andymark.com/product-p/am-1207.htm


Do be careful where you use the 1/8 inch wall tubing. We ended up overweight and had to replace quite a few pieces of our structure with 1/16 inch wall tube to get the weight down.

[GeeTwo]

Tapping 1/8" aluminum for machine screws is an exercise in futility - for any thing heftier than holding an encoder in place, they're almost certain to be stripped out, or rattle loose, or both. Always end in steel, or 1/4"+ aluminum. Self-tapping or sheet metal screws in 1/8" aluminum are not too bad, but can still be stripped out more easily than I'm comfortable with for the FRC team.

When we've used bolts and gussets with tubing or c-channel, we've usually gone all the way through, and used gussets on both sides to help distribute the load (minimize deformation of the tubing). Never use a single hex nut for any joint under load or vibration. Either get nylon locking nuts, or jam two nuts together to lock them in place. Sprocket-type lock nuts work when they're new, and being pushed against steel (they often mangle aluminum rather than grip). They don't work as well after they've been flattened - and how many teens will notice the difference?

[Bennett548]

If you are sure you won't be taking it apart, look into structural adhesives. The area between a gusset plate and tube is pretty big and thin, so an epoxy or CA glue can add a lot of strength. We love Black Max (Loctite 380) because it doesn't get brittle so it can survive impacts and shock loads. Be prepared, it is extremely messy.

I would suggest self-drilling, self tapping screws to hold everything together while the glue or epoxy cures, and to add a little strength.

[sanddrag]

Originally Posted by GeeTwo

Tapping 1/8" aluminum for machine screws is an exercise in futility - for any thing heftier than holding an encoder in place, they're almost certain to be stripped out, or rattle loose, or both. Always end in steel, or 1/4"+ aluminum.

I have to respectfully disagree. I've tapped 1/8 aluminum quite successfully in every thread from #4-40 up to 1/4-20 and it works just fine if you're careful about it.