General Discussion (Model Railroader)

I am currently working on converting all my cars to body mounted couplers, and I just bought a bunch of Kadee coupler boxes, but I totally forgot the whole part of how I need to attach them to the car when I bought them.  What size screw is the best screw for the boxes?  I will be drilling a hole and need a screw that will self-tap itself too.  Where is a good place to get them?  Thanks for the help.  -Michael

You will need 2/56 screws in various lengths as well as appropriate drills and taps. Self-tapping screws are too course to allow correct tension on the box but not so tight as to jam the coupler swing.

The center hole in the KD box is for a 2-56 screw.  You're best bet is to buy the KD package that contains the the 2-56 tap and proper drill bits for the screw hole and clearance hole.  Get a pin vise for the bits and the tap.  Instead of using a self tapping screw, drill the hole, tap it and use a regular 2-56 screw.  You're have more success getting everything to work right.

By the way, I'f glue the top of the box (The big piece) to the car, and let the scrww focus on holding it closed. Athearn has a set of screws that are wonderful for this purpose, don't recallt the length, but I also only remember seeing one type of bag of screws from Athearn.

As has been said 2-56 screws of various lengths are the most common. The drill & tap set by Kadee gives all the tools needed. Be sure to lubricate the tap when threading through metal.

I glue the top of the box to the car then drill and tap for 2-56 then assemble the coupler. The bottom of the box is held by the screw.

Many cars such as those by Athearn and Accurail have a coupler box bottom that is held by friction. I drill and tap the box cover and use a 2-56 screw to hold the box together.

rockymidlandrr:

I am currently working on converting all my cars to body mounted couplers, and I just bought a bunch of Kadee coupler boxes, but I totally forgot the whole part of how I need to attach them to the car when I bought them.  What size screw is the best screw for the boxes?  I will be drilling a hole and need a screw that will self-tap itself too.  Where is a good place to get them?  Thanks for the help.  -Michael

 

2-56 is the right size for the center hole in the Kadee coupler boxes.  Get pan head screws about twice as long as the coupler box is thick.  Say 3/8" long.  You want a #50 drill.  Ordinary machine screws will self tap into plastic, and give a firm fit.  If you tap the hole in the plastic you will find the screw will be loose.  Only in metal (say a locomotive) needs the hole tapped.  

  If you glue the coupler box lids on you will curse yourself when the coupler needs repair.  Secure the lid with a screw and the coupler will never fail. 

   You are also gonna want a coupler height gauge.  Kadee sells them, or you can make your own from a block of wood, with a coupler screwed to it on the end of your test track.  If you do-it-yourself, use the NMRA gauge to get the guage coupler at the right height.  You will find that many cars will have the coupler too low.  In which case a #6 flat washer under the trucks will bring the coupler up to height.

 

dstarr:

If you tap the hole in the plastic you will find the screw will be loose.  Only in metal (say a locomotive) needs the hole tapped.  

The part about loose screws is true, but some cars, like the RivaossiRPO, need to be tapped, or the screw will just sit there and spin for hours and hours with no real discernable results. (Just did it last weekend) Drill it with a #48 or #49 instead of the above #50, so the screw can finish the job, but can also make it though the car painlessly. Dremels make the job a snap, but you need to be able to line it up with the screw hole in the coupler box while the bit is spinning, and be careful not to destroy the screw guide on the coupler box in the process. The battery dremels are slower, and will punch the hole while giving you a split second more before they chew up the screw guide on the box. And for FRED's sake, be sure to do it in LOW GEAR and not let the flipper slip into soething higher. It is possible to flip a couplerbox out of it's melded plastic bonds and fling it halfway across the garage...  

dstarr:

If you glue the coupler box lids on you will curse yourself when the coupler needs repair.  Secure the lid with a screw and the coupler will never fail. 

We were just glueing half the box to the car, and screw on to secure.

Flashwave:

dstarr:

If you tap the hole in the plastic you will find the screw will be loose.  Only in metal (say a locomotive) needs the hole tapped.  

The part about loose screws is true, but some cars, like the RivaossiRPO, need to be tapped, or the screw will just sit there and spin for hours and hours with no real discernable results. (Just did it last weekend) Drill it with a #48 or #49 instead of the above #50, so the screw can finish the job, but can also make it though the car painlessly. Dremels make the job a snap, but you need to be able to line it up with the screw hole in the coupler box while the bit is spinning, and be careful not to destroy the screw guide on the coupler box in the process. The battery dremels are slower, and will punch the hole while giving you a split second more before they chew up the screw guide on the box. And for FRED's sake, be sure to do it in LOW GEAR and not let the flipper slip into soething higher. It is possible to flip a couplerbox out of it's melded plastic bonds and fling it halfway across the garage...  

dstarr:

If you glue the coupler box lids on you will curse yourself when the coupler needs repair.  Secure the lid with a screw and the coupler will never fail. 

We were just glueing half the box to the car, and screw on to secure.

 

I have never had good luck drilling with a Dremel.  They just turn too fast.  I use a pin vise most of the time.  For really thick metal like an Athearn diesel chassis I use my wood shop drill press on the slowest speed.  

"lid" and "box" are a bit confusing.  Most cars have a coupler box cast into the car that accepts Kadee couplers and a thin flat lid to hold the coupler in place inside the box.  So I tend to think of "lid" as the bottom removable part of a coupler box .

When you are installing the genuine Kadee boxes, the thin flat looks-like-a-lid part glues onto the car bottom and the thicker looks-like-a-box part goes on the bottom  and is/should be secured with a screw.I tend to call the thicker bottom part a "lid" cause it's on the bottom and comes off.  I clearly have unresolved nomenclature issues here. Sorry about that.

   Anyhow, yes, you glue the thin flat part to the bottom of the car.  Back when I was younger and stupider I  glued the thicker bottom part to the flat part, and regretted it later.  I use a screw now. 

 

 

If you're talking about tapping a 2-56 hole, you'll need two different size tap drills for plastic or metal. The tap drill sizes for a 2-56 tap is a #50 for metal and a #51 for plastic. Using a slightly smaller drill for plastic will give you a deeper thread in plastic and a better hold than trying to make a machine screw work like a tap. In plastic, I use the drill in a pin vise and hand drill it. For metal, I use my drill press, which can run MUCH slower than a Dremel. The tap is always in a pin vise or hand drilling handle. As stated above, when drilling or tapping metal ALWAYS use cutting oil. For ease of use, I have one of the A-West needle point bottles with cutting oil in it just for this job.