Anyone use aluminum bolts?

We had some significant weight issues this year with our robot, and we realized the bulk of our weight was hardware-related. We had standardized with 1/4"-20 socket cap bolts, but are thinking of switching to either:

  1. 10-32 bolts
  2. Aluminum 1/4"-20 bolts

I’m worried the aluminum bolts will not be as durable, but they are 1/3 the weight of steel bolts. Thoughts?

Step down to 10-32 bolts, 1/4-20 is overkill for most FRC applications. Look up some of 973’s work, they use a bolt pattern that allows for use of either a 10-32 Bolt or a 3/16" Rivet. Not a bad way to save weight.

I’d recommend staying away from Aluminum Bolts whenever possible. I’ve seen a few over-eager students give them a turn too many with a wrench and snap the heads right off.

We have used them in the past, but yes only put the in the hands of people that are unlikely to over-torque and sheer them. Our current stock is often used to replace at steel fastener that was used previously and swapping to a rivet isn’t practical.

The one real nice thing about stainless steel bolts, is the need to never replace them (in a properly designed usage). Aluminum simply isn’t as durable, and as already said, it’s pretty easy for a student to over tighten and pop the head off. All of our bolts are stainless steel.

That said, the key to any good design is using the right part in the right application. Some things on a robot (like the frame that provides the structure for the entire robot and takes the brunt of the impacts) should be done with 14/20’s. Others can be done with 10-32’s. Still other applications can use smaller sizes.

We have a standardized set of bolts for use with our robot, everything from 1/4-20’s to 4-40’s. by using a constant thread count for each size, we can match up bolts or taps very easy - there are no 10-24’s in our shop, so we have no 10-24 nuts and no 10-24 taps. All we have is the equipment for 10-32’s.

We also use pop rivets for a lot of applications. By a lot, I mean most applications that aren’t structural. A couple of pop rivets can, in the correct application, easily replace a heavier bolt.

Do you use stainless nuts also? If so, what do you do to avoid galling?

Aren’t the KOP frame bolts aluminum? They seem to be much lighter than a hex head counterpart. We use them extensively without issue.

According to AM they’re just Zinc Plated Steel:

Maybe it’s because they’re SHCS?

Welds don’t weigh much. Rivets don’t weigh much. Smaller screws (10-32) don’t weigh much.

I’d be concerned about how fragile aluminum bolts are…

If you can replace a steel fastener with an aluminum one, then the steel fastener is too big for the job. Just use a smaller fastener, or reconsider your design to eliminate the need for so many fasteners.

You can use rivets without any problems for structural applications; the key to success is to design the structure in a way that both uses many rivets to spread the load out and has the rivet locations in areas where they will primarily see compression or shear loads (tensile loads will pull the rivet out).

If there are expected tensile loads, this too can be overcome by the use of a bracket that rivets in two planes 90 degrees apart so that one is always the shear load joint.

Once you use rivets (especially with a pneumatic riveter), you’ll never want to use bolts again.

I’ll second that rivets can and should be used structurally to save weight. We have used them with no problems. If you really need a bolt, I would recommend a 10-32 over an aluminium bolt.

Keep in mind, all these fasteners can be appropriate, just in different situations.

Truer words have never been spoken.


Amen! But, you still have to be able to get on the rivets squarely – that doesn’t change. But, boy, does it make driving those 3/16th guys a lot less painful! :slight_smile:

We have used aluminum bolts to replace steel in the past. The lazy susan turret we had in 2009 and this year both had holes designed for 1/4-20 iirc, so there we used AL.

Off topic: I’d personally use 10-24 bolts over 10-32. coarser threads in my experience are stronger (the weight difference is negligible).

I agree that rivets rock… just keep in mind that if you ever need to remove/replace the part, you will have to drill out the rivets and rivet it again. In this application, I suggest NC (national Coarse) bolts and locknuts…

+1 to rivets.

We have used aluminum nuts a few times when a large bolt was used in shear.
No complaints so far.

Also of note: aluminum 1/4-20 screws cost about five times as much as steel 10-32 screws.

I prefer 10-32 primarily because the tap is stronger, also most COTS parts with 10 are 32TPI, and also you can finesse the tightening more. I’ve never stripped out a 10-32 thread in aluminum. 10-24 is much more common in hardware stores though.

Anyhow, you have to really decide what’s best for the application. 10-32 button head is my bolt of choice, but occasionally we’ll go to flat head in areas that need it, socket head if button head isn’t available for the length. In any bolt, I prefer the black-oxide alloy steel as it is stronger than stainless by nearly double. Some sizes from McMaster are only available in stainless though, and stainless is often cheaper.

Occasionally, we’ll even go to other sizes even all the way to 3/8-16, for mounting the superstructure for example, or 6-32 nylon socket heads for mounting Victor speed controls, or 1/4-20 nylon socket heads for mounting the power distribution panel.

We use 3/16’ aluminum rivets for most fastening applications. We also have a selection of 1/4"-20 bolts in both steel and aluminum, depending on the application. When you need to save weight aluminum is much lighter, obviously, and an aluminum rivet is lighter still. On the other hand if you need strenght, go with steel.

We have had the occasional superman come along a twist off the head or cross-thread the bolt. That’s just a learning opportunity:rolleyes: They generally don’t do it again.

this year my team (1056) used primarily rivets to hold our chassis together and we weighted an astonishing 99.1 pounds at full construction. and unlike what one of our mentors thought the rivets held our frame together through all of our collisions. so i would highly encourage the use of rivets/aluminium bolts.

To shave off some weight in Seattle so that we could increase (double, it turns out) shooting performance, we swapped the bolts provided with the AM C-Base Chassis with equivalent hardware in 2024-T6 aluminum.

The swap was expensive – we used about $40 worth of hardware – but it has performed well.

I wouldn’t use them everywhere, but with the structural additions we made to the standard frame in the design of our drive pods, I suspect that we have far more bolts holding the frame together than we really need anyway, so the swap was safe.