The FRC way for using rivets...

[SCOTT MCMAHON]

Some teams are looking to use rivets; some are already using them.

Rivets are great fasteners, if used properly.  The first thing to know about rivets is that they’re to be used for shear forces.  This means you use rivets to hold two things that want to slide away from each other, not pull apart (keep using nuts/bolts for this).

FRC uses 5/32 rivets because they can be swapped for a #8-32 screw if needed (it is a tight fit).

Before you buy rivets, make sure you know how much you’re riveting (thickness).  Rivets are sold by the following factors:

* size

* grip range (thickness of material stack)

* rivet material (body and mandrel)

From http://www.mcmaster.com 

You’ll note that there are 4 different parts that have been ordered by the FRC team in the past (and will be in the future).  If you’re riveting a 0.09” gusset plate and some 1/16” tubing (for a total of  0.1525) you’d use the range 0.126-0.187.  Using a rivet whose grip range is too short or too long won’t work.  Do the math and order the correct parts.

Suggestions:

* Use the correct hole size for a rivet.  For example, the hole size for a 5/32 rivet is *not* 5/32.. it is 0.161

* Use aluminum rivets with steel mandrels (easier to drill out because of the aluminum dome)

* Use the pneumatic riveting tool, it provides better results and is easier and faster

* Use Cleco clamps to hold the materials together as you rivet.  Clecos are temporary spring clamps, some time called a Hole-Grip Clamp (generic name).

You’ll also want to get a set of clamp pliers… (the image below shown with a different kind of clamp [edge]).

Oh, one last thing… before you may use the pneumatic riveter, you must put 3 drops of tool oil into the air inlet.  The tool requires periodic oiling.  It isn’t unusual for FRC to put in 3 drops every 100 rivets.

Cheers,

Scott

[SCOTT MCMAHON]

I’ve noted that some students are having difficulty figuring out how big to make a hole for different purposes.

The answer is, of course, it depends.  What does it depend on?

* The screw size you want to use

* Is it for putting a screw through so it can connect to a nut on the other side, or is it to have threads cut into it so that the material becomes the nut

* The material it will go in (if you want to tape threads in the material)

* The fit if it is not for tapping

A clearance hole is a hole that a screw goes through and connects to a matching fastener on the other side (nut and bolt).  Clearance holes can have a close fit or free fit.  Close fits are intended when you want the material being fastened not to move much, if at all.  Free fits are used when you don’t really care about that.

To figure out how big a hole needs to be, and by extension the size of the drill bit used (or hole CNC’d, laser cut, etc.), you use a Drill Chart.  One easy one to use is located her (http://www.littlemachineshop.com/Reference/tapdrill.php).  I’ve included only part of this below for you to follow.  This is how to use it:

First, start with the screw size you need to use.  For example, 8-32 is screw size 8 and threads per inch 32.  In the chart below, that is the bottom line.  Therefore

* If you’re going to create threads in aluminum or plastic, you need to use a #29 drill bit to create a 0.1360 inch hole since you want to have more material in the threads for softer materials (75% column).

* If you’re going to create threads in steel, you need to use a #27 drill bit to create a 0.1440 inch hole (50% column). 

* If you’re going to cut a hole for a screw to go through and it is being CNC’d, laser cut, or you’re using the mill with edge finder and counting turns, I’d use a close fit, so that would be a #18 drill bit for a 0.1695 inch hole

* If you’re measuring, scribing, and hand-drilling the hole, you probably want to use a free fit, you need to use a #16 drill bit for an 0.1770 inch hole

Note that there are also metric versions of this, typically with SAE equivalents (we don’t have many metric drill bits around the shop since FRC is mostly SAE and FTC is largely metric with some SAE).

Make sure that you think about this stuff when you’re in Solidworks and doing your designs.

Cheers,

Scott