Advice on a reliable method for making starter holes in diecast hopper frames

I'm starting on a large project to convert  approximately 40 Atlas hopper and other freight cars to Kadee couplers. I have my shiny new MicroMark tap press sitting on the desk; have a small Ryobi drill press ready to work, but I have not been able to devise a practical method for accurately making starter holes for the drill bit to drill the new screw locations. Can't just whack it with a hammer and punch, because the force needed to make a good dimple would be enough to wreck the plastic superstructure. I tried drilling without a starter hole; epic fail; the small bit wanders all over the place. I figure somebody MUST know a trick for this...

Any and all thoughts and/or ideas  will be greatly appreciated.


Original Post

Make and use a drill jig. Take a small piece of brass or steel, and mark and center punch your hole centers.

Drill with the same size drill as you are going to use for the hopper project. Locate the drill jig on the hopper, and the drill will follow the jig and put the holes in the right place.



Cheeseburgers at 120 MPH.

 I use the holes that are there and make the Kadee's fit by slightly enlargeling the mounting holes on the Kadee. They will walk their way on by alternately tightening the screws. They are away from the body and probably not totally per prototype.

Pauls got the right idea. Build a jig seeing you have so many similar cars to do.

 If you want the couplers to sit tight against the carbody. I would make up a jig from a piece of steel. You can buy strips at Home Depot. Go for a piece around 1/8 thick by about 1/2 inch wide.  Drill two holes that line up with the factory tapped mounting holes. This will allow you to screw the plate to the body. Now put the Kadee box where it needs to be and mark where the mounting holes are needed. You should end up with 4 holes directly in line. If not. Just start over and make another.  Two holes will have a loose fit so the stock 2mm screws can slide through snugly and tighten it to the carbody. The other 2 should be drilled slightly bigger by a number or 2 than the bit you will be using prior to tapping. When done you should be able to transfer the jig from car to car.  Just line up the jigs hole with the bit in your press and you should be good to go. Drill slowly and change out the bit if the drilling gets harder to drill and requires more pressure. Use a good quality tap and some cutting fluid.


Or Google    " Center Drill Countersink Drill Bit"

Will still need to keep the car from moving.   I remove the frame and clamp them down.

The die cast metal does a number on drill bits.  A little cutting oil may help them last longer. 

Use the center bits to make a starter dimple.  The smaller the center bit the faster it breaks drilling too deep in die cast.

Carbide bits are good.   Get several in the sizes you need.   Wax your taps.   Important to use the right size drill for your pilot hole.   Breaking a tap in die cast is not a good thing to do.

All good ideas.  You do know you do not have to whack it like you were driving a nail?  Try "taptaptap". Or get one of those good "General" spring-loaded center punches, back the cap all the way off, and hold it in place with your finger for a very small dimple.  A #56 drill does not need much of a dimple.

Also use cutting fluid, once you get the drill started.  If you use a jig, start out with cutting fluid.

Just use a kadee coupler box as a jig. Use a pin vise with a drill that just fits the holes in the coupler box. Spin a pin vise a half dozen turns or so just enough to dimple the die cast. Then replace the drill with the proper thread tap size. #50 if you plan to use 2-56 screws.

BTW the problem with die cast is not that its hard, zamac is mostly aluminum. The problem is its actually a bit soft and can catch the drill and break it. Oil is a good idea. Carbide bits are a bad idea because they are very brittle and can break easily. Rarely are they as sharp as high speed steel drills. HSS will tolerate slight off axis drilling without breaking, not a lot but much more than carbide.



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