A Riveting Article

A Riveting Article

(or how to set rivets without going crazy)

Written by Adam C. Madlinger

One of the more common techniques required when building models of the steam and early diesel era is riveting, or “setting” rivets. The railroads loved rivets, and for good reason: rivets are stronger than bolts in applications where high shear forces exist; that is, forces perpendicular to the shaft that tend to cut, or shear, the fastener in half. Even today, rivets are still used in industrial applications, especially in aviation.
Indeed, we are very fortunate in the hobby that rivets are still commonly used, as there are several vendors available to supply the perfect size rivets for our applications, as well as tools that make installing rivets relatively easy. Moreover, there are even products readily available that look exactly like rivets but work like nails, a great feature when trying to simulate a riveted look when it is not necessary, or perhaps not desired, to actually rivet the components together.
Rivets

The obvious place to start a riveting project is deciding what kind of rivets to buy and where to buy them. I buy mine from several sources: McMaster, www.mcmaster.com, is fast and has a decent assortment, but not the best selection and the prices are on the high side. Hanson Rivet in Pacoima, CA, www.hansonrivet.com, has every rivet imaginable at great prices, but the length of time it takes to ship from California is frustrating. My go-to rivet supplier is thus Jay-Cee Sales & Rivet in Farmington, MI, www.rivetsinstock.com. They have a large supply of rivets of many sizes and materials at good prices (if buying in bulk), and online ordering is available through their companion site www.rivetsonline.com, and shipments arrive in a few days.

There are several different head styles available, much like screws: flat, countersunk, pan, truss, universal, and round, to name but a few, with round being the most common and traditional looking choice for our application. There are also different shank styles, such as semi-tubular, blind (also known as “pop” rivets), split-shank, and traditional solid rivets. Common rivet sizes for live steam include 1/16″, 3/32″, and 1/8″, all of which refer to the diameter of the shank rather than the head of the rivet, which varies for each respective head style.
The most common for 1-1/2″ scale equipment is the 3/32″ diameter solid shank round head rivet, which I used on my locomotive (tender and cab), gondolas, flat cars, tank car, boxcar…almost everywhere that a structural rivet would have been used on the prototype.

 


Rivet lengths and proper shop head geometry. Source: Hanson Rivet.

In terms of material, the most common for live steam is either aluminum or copper, although brass, steel, stainless steel, and many other alloys are available. Aluminum is the natural choice for rolling stock that is made out of aluminum sheets, such as my gondolas. Being a softer metal, the aluminum rivets are very easy to set, but lack strength compared to the other materials, and the heads are much more susceptible to being inadvertently dinged or damaged during construction and general use of the equipment. There are several grades of aluminum rivets available, made from alloys with varying hardness. For example, Jay-Cee sells aluminum alloys 1100F (soft) and 2117T4 (hard); I prefer to use the 2117T4 (hard) whenever possible.  

Copper is a much stronger and more durable material, yet is still soft enough to set readily with hand tools; it is, by far, my preferred choice. Of course, copper is a rather difficult material to paint, but with the appropriate choice of primer, this is not a huge concern.

Perhaps the most important aspect of rivet choice is the length of the rivet, which is equal to the combined thickness of the materials being riveted together plus the “clinch allowance” (the amount that the shank sticks through the material); this “clinch allowance” varies according to the rivet shank diameter. If the rivet is too short, the back side of the rivet that is peened over, known as the “shop head,” will be too thin, and the rivet could be prone to pull out.

Conversely, if the rivet is too long, the shank will tend to bend over – like a nail bending over when it is mis-hit – rather than properly flattening and compressing. A properly set rivet should have a uniform, circular shop head with a diameter approximately equivalent to that of the head on the front side. Hanson Rivet has an excellent guide on their site that gives both the proper clinch allowances and shop head dimensions for respective rivet diameters: www.hansonrivet.com/w06.htm. For 3/32″ rivets, the clinch allowance is 3/32″, and I can concur that I have had difficulty setting rivets having a clinch allowance of 1/8″ or greater. Rivets could be individually cut down to length if you only need a few and have longer ones on hand, but I generally find it worth the price to just buy rivets of the right length from the start, rather than to have to cut a few hundred during the course of a project.

Preparing to Rivet

Not surprisingly, the first step of the actual riveting process is to drill the required holes in which to insert the rivets. The rows of rivets on prototype equipment were rarely very straight, and often look as though they were laid out and drilled free-hand. However, I just don’t think rivets look good on our models unless they are reasonably straight, and, even when laying out with a straight edge and center punch, can look too uneven when viewing long rows of rivets.

The easiest way to drill rivet holes, and get them straight in the process, is to make a drill jig. Mine is made out of a piece of 3/8″ thick by 1/2″ wide “tool steel”, about 8″ long. I used my milling machine to drill through the jig with the proper size holes for the rivets (I use a #41 drill for 3/32″ rivets) at the desired spacing, 1/2″ in my case. I then clamp the jig to the piece and drill the holes in mere moments. It’s then just a matter of moving the jig down the line and continuing to drill until the row of holes is complete.

As I move the jig down the line, I clamp the pieces of material together through the holes I just drilled using the single most important riveting tool you can have: “Cleco” clamps, or more generically “spring clamps” (an absolute must-have). Check out:www.hansonrivet.com/w77a.htm.

Clecos have a shank that is the same diameter as the rivets, and they insert through the material from either side of the rivet hole, keeping the two pieces of material perfectly aligned. Clecos have spring loaded teeth that engage on the back side once the clamp has passed through the material, preventing the clamps from pulling out of the hole and pulling the two pieces of material together. Special pliers are used that allow the clamps to be inserted and removed as needed.

Clecos are available from the rivet suppliers and, in bulk, cost less than $0.50 each; at that price, it’s prudent to have several dozen for large jobs. I use ones that can clamp up to ½” deep, so that I can also use them to hold the drill jig in place. If you do not have Clecos available, 2-56 nuts and bolts can be used instead; conveniently, a 2-56 screw is just the right diameter to fit through a 3/32” rivet hole.

It is a good idea to disassemble the pieces after drilling and deburr and clean the front and back side of the rivet hole on each piece to remove any cutting oil and chips that inevitably accumulate between the two pieces of material. Deburring will provide a very slight countersink that will allow the head of the rivet to sit flush with the face of the material, as there is often a very slight radius between the underside of the head and the shank of the rivet. On the other end of the rivet, this will also allow the shop head to clinch the material evenly and, if set properly, I’m told that the rivet itself will be water tight.

Here is Jack Bodenmann’s Tender for his Berkshire. The Clecos hold the panels in place while holes are located and riveting begins.

Setting the Rivets

The easiest part of the job may actually be setting the rivet in place. The concept is very simple: the head of the rivet is held in place with a die that conforms to the geometry of the head, so as not to deform the head as the force is applied to peen over the back of the rivet. The process of setting rivets can be accomplished either by using a head die with a regular hammer or pneumatic air gun, or using a rivet squeezer. Unless using a rivet squeezer, it is much easier to perform this operation with two people.

If using a hammer or air gun, the rivet head is held in place by either resting the part upside down on the die that is, in turn, supported on a sturdy table, or by having a second person firmly hold the die against the rivet head; the back of the rivet is then peened over with the hammer or air gun to set the rivet. Rivet bucks or regular pin punches can be used to help peen over rivets in tight spaces.

Dies are available from the rivet vendors, and should be held in a large block of steel. The more mass holding the rivet head in place, and the more firmly the die is held against the rivet head, the better and easier the rivet can be peened.

While air hammers (available from Home Depot, Harbor Freight, McMaster, etc) are quick and require much less effort, care must be taken not to over-peen the rivets. I turn the pressure down to about 25 psig on my air gun and – again – hold the die very firmly against the head. Most of the time, and especially for more delicate parts and softer materials, I prefer to use the traditional old ball peen hammer rather than the air gun.

The better alternative to set rivets is to use a rivet squeezer, again available from all of the rivet vendors. Although a squeezer costs a few hundred dollars, please trust me that the price is well worth it. A rivet squeezer is essentially a deep-throat C-clamp with an arbor press at the tip (instead of the screw clamp that a C-clamp has). The arbor press action brings two dies together at the tip with several thousand pounds of force. The rivet is literally squeezed, between a rounded die conforming to the head and a flat die on the back side that forms the shop head, in one smooth motion that requires only one hand to operate.

I personally purchased my squeezer from Hanson Rivet, part number HS-60: http://www.hansonrivet.com/w82b.htm. This model has the deepest reach available, 6”, and can squeeze rivets up to 1” long. This is the only real limitation of rivet squeezers: if the rivet is deeper than 6” into the material or is longer than 1”, you will have to resort to the old fashioned method described above.

The operative term “smooth” used above cannot be understated. During the course of setting thousands of rivets on a car or locomotive, fatigue and injury can set in, from the repetitive stress imparted on your body both from the hammering approach as well as with the squeezer. Take plenty of breaks while setting rivets, and switch jobs back and forth every so often, if working with another person.

Removing Rivets

Inevitably, you will probably have at least one rivet that just doesn’t work out. Removing rivets is easiest if the back side is accessible. I use a sharp chisel to remove as much of the shop head as possible, and then use a pin punch of the same or slightly smaller diameter to knock out the rivet. If unsuccessful, I drill out the rivet with a slightly smaller drill than the original hole, so as not to enlarge the hole in the process.

If only the front side is accessible, I either: 1) chisel off the head, being careful not to mar the surface of the part, or 2) file a flat on the head, center punch the rivet, and drill the rivet out using the same size drill as the original hole.

Alternatives to Riveting

Drive screw. Note the helical flutes on the shank. Source: Hanson Rivet.

Occasionally, it is not necessary or not desired to actually rivet pieces together; often rivets on our models do not fasten together any parts, but are merely for show to simulate the rivets on the prototype. Such is the case on many flat cars, or rivet lines around the smokebox on steam locomotives, or the rivet lines on my tank car (which is, in actuality, a single, continuous piece of PVC pipe).

In such instances, I would recommend you consider “drive screws,” available from McMaster and all of the rivet suppliers. Drive screws have the same head profile as rivets, but can be installed just like nails. The pilot hole is drilled undersize, and the shank of the screw has helical flutes that dig into the material as they are hammered in.

Drive screws are measured by “nominal size,” and what the industry calls a “#2 drive screw” corresponds approximately to a 3/32” rivet, although the drive screw head is ever so slightly smaller in diameter. More information can be found at: http://www.hansonrivet.com/w58.htm. I primarily use McMaster part number 91654A077 (and others of varying length, as required) and set them with my pneumatic air gun at 25 psig using a bit with a rounded dimple that matches the radius of the screw head.

Finally, there are some instances where you want to be able to remove or disassemble components in the future, but retain a riveted look; such is often the case with cab sides and firebox wrappers on a steam locomotive. In those applications, I recommend using a combination of either 1) #2 drive screws, or 2) rivets countersunk and filed flush on the back side for the majority of the rivet row. Then, use a few 2-56 slotted round head screws – which have an identical head size – intermixed in the row to actually fasten the components together. Once assembled and painted, the slotted screws will disappear to the eye amongst all of the screw or rivet heads, even if viewing from only inches away.

 

Can you find the slotted screws in this picture of Jack Bodenmann’s 1-1/2” Scale Berkshire (right)? Source: J. Bodenmann, www.jbodenmann.com