As an HO junkyard specialist, I have seen my share of less-than-desirable modeling practices. Most of this knowledge has come from acquiring locos and rolling stock from train shows, eBay sellers and individuals.
Many older HO train items were assembled with #2-56 machine screws (where #2 indicates the fastener diameter and 56 indicates the threads per inch). Many Japanese brass locos were assembled with M1.4 (that is, 1/4 millimeter diameter) or M2.0 diameter metric screws. The valve gear typically utilized M1.0 fasteners. On the other hand, many Korean locos were assembled with a variety of metric fasteners of different diameters. Rivarossi locos were also assembled with a variety of metric fastener of different diameters as well as with what I generally call small diameter sheet metal screws. For example, M2.5 diameter fasteners are commonly used on Rivarossi locos. Athearn and Varney products were assembled with #2-56 machine screws as with small diameter sheet metal screws. For example, the trucks on Varney rolling stock were attached with sheet metal screws.
Some modelers are neither machinists nor engineers. These modelers may have little or no knowledge of small diameter taps and dies or small diameter drill bits (or specialized drill bits utilized for working on printed circuit boards). They probably have little or no knowledge of how to measure a fastener using a caliper (Venier-type, dial-type or digital-type). I consider these types of tools to be almost mandatory for any decent modeling effort.
It is disappointing when modelers sort through their junk box and install any old fastener in a loco or piece of rolling stock. For example, a modeler tries to install a sheet metal screw in a threaded hole which has been drilled / tapped for a #2-56 machine screw.
I often see threaded holes which have been stripped out due to the installation of a fastener which was not designed for a particular threaded fastener. When this occurs, it is desirable to re-tap threaded hole with an over-size tap and install an over-size fastener. Of course, this takes some work. The mating feature (perhaps a driver retainer plate which goes on the bottom of a loco) may also require drilling with a larger diameter drill bit to provide clearance for a larger diameter fastener.
Another alternative to re-tapping a stripped-out threaded hole and installing a larger fastener is to squeeze to last 1/8-inch to 3/16-inch long section the of threads on the fastener between the jaws of a bench vise. The thread spacing will remain about the same. However, the cross-section of the fastener will become thinner is one dimension and thicker in the dimension at 90-degrees to the first dimension (that is, the fastener cross-section will become oval).
I often see fasteners which have been cut off with a pair of diagonal (cutter) pliers. This leaves a burr on the end of the threads. This kind of fastener is difficult to install, and it ruins the internal tapped threads on a mating part. There are a couple of practices which can help. One approach is to file the burr off with a jeweler's file so that the end of the fastener is flat. Proving a slight radius or chamfer on the perimeter at the end of the threaded fastener is very helpful. Alternately, a hex nut of the proper size may be installed o the machine screw prior to cutting. After cutting to the desired length, the threads on the fastener may be filed as previously discussed. Finally, the nut can be removed from the fastener which tends to clean up and recondition the threads at the end of the fastener.
Rivarossi, Mantua (cabs) and AHM locos have plastic posts which are designed to be assembled with sheet metal type screws. If an over-size fastener is installed instead of the correct-size sheet metal screw, it may cause the post to crack / split. There is a simple fix for a cracked / split plastic post. Measure the diameter of the post and make a bushing (split band) from 0.010-inch thick tin can stock.
The length of the bushing / band may be about 3/16-ilnch long. Determine the circumference of the bushing / band using the formula: C= (Pi)(D) - 3.14 D. Cut out a rectangle with dimensions of 3/16 inch x 3.14 D. The cutting of the tin can stock may be accomplished with an older pair of scissors. Then roll up the rectangle into a bushing using a pair of Kadee coupler pliers with tapered jaws or a pair of needle nose pliers. A mandrel such as the shank on a screwdriver may also be used to help shape the bushing.
(Note: On Mantua cabs it is a good idea to make the rectangle 3/16-inch long and about (3/4) C. This is because the plastic post on the cab is partially attached to the front of the cab.)
Slip the bushing over the outside of the plastic post and attach with super glue or your favorite adhesive. It may be necessary to squeeze the perimeter of the bushing so that the crack / split in the plastic post closes while the glue cures.
Many HO steamers have shoulder screws which perform two functions. The screws hold the retainer plate snuggly against the bottom of the loco chassis. The screw also allows the pilot and trailing trucks to swivel freely. A shoulder screw can be recognized because there or three different diameters on the screw (that is, the thread / shank diameter, the shoulder diameter and the head diameter). The shoulder portion of the fastener may vary from about 1/16 inch to 3/16 inch high depending on the thickness of the attachment area on the pilot or trailing truck. If a shoulder screw is not used, then the driver retaining plate will come loose or the threaded machine screw may fall out and get lost. The shoulder screw can be tightened up against the shoulder and the fastener will stay put.
I have seen my share of broken crank pin screws. Please avoid using any kind of adhesive to attach a crank pin screw. It makes removal for maintenance or replacement a real headache. If done carefully, a "light" squeeze with a pair of pliers on the threaded end of
the crack pin screw can create a slight oval cross-section shape which may hold the crank pin screw in place. Don't get carried away with too much of a squeeze or it will ruin the crank pin screw threads or be impossible to install.
If a crank pin breaks off, cut a slot across the crank pin location with an X-acto saw blade and turn the broken crank pin piece out with a jeweler's screwdriver.
Rivarossi locos are a special case. There must be a small diameter washer next to the plastic driver center. The Rivarossi crank pins are a shoulder machine screw. The shoulder fits against the washer, the washer presses on the driver center and the hex-head brass bushing on the inside of the driver pulls up against the plastic driver center. If a washer is not utilized, then the crank pin will work its way loose from the brass hex nut.
Rivarossi and Mantua locos utilize small diameter bushings. The Mantua 2-8-2's and 4-6-2's utilize a brass step bushing (small outer diameter outside / larger outside diameter in the middle / small outside diameter on the inside). A home-made substitute can be made from three separate bushings (stacked-up) on the crank pin screw. The small diameter bushings may be made as previously discussed.
Small diameter jeweler's screwdriver shanks may be used for rolling up thin wall bushings (0.005-inch thick to 0.010-inch thick) from either brass or tin can stock. After cutting out the appropriate-size metal rectangle, a pair of Kadee coupler pliers or needle nose pliers may be used to form a u-shaped piece. The u-shaped piece may then be shaped in its final form using the screwdriver mandrel.
I got interested in in small diameter metric fasteners as well as small diameter taps and dies very late in my modeling career. I ended up purchasing bags of small diameter fasteners as well as small-diameter metric taps and dies very late in my modeling career. The products came from China.
I am going to post this now because I don't want to lose all my typing. I apologize for any typos.
