Keep in mind that there are 2-56 sheet-metal 'self-tapping' and plastic 'self-tapping' screws out there; what he'd need for this is not the latter, but a thread-cutting screw -- some of these have one cutting 'flute' and edge made with a divot cut out of the end of the screw; somoe of them have one or more broached cut in the threading at the end of the screw, with a little taper on the end couple of threads to allow gentle starting of the cut thread.
These screws do not have nearly the 'flute' chip-clearance capacity of real taps, or twist-drill bits, so you need to be careful with backing them more frequently, and backing them out to clear broken chips from the relief cuts, too. This may be on the order of 1/8 turn or so, not the 'couple of turns' you could use with a fluted or relieved tap. In some materials, carrying the cut material along as you thread the screw a long way can result in progressive messing up of the formed threading.
With care you can use these as thread chases to clean up messed-up threading, but be careful not to use force until you're sure the screw is properly engaged in the actual 'right' threading path. It will happily cut cross-threads (right up until it jams or the shank twists off ) and the resulting hole will take a screw, all right, but may not hold it...
I don't remember if the hole is supposed ot be pre-tapped or not - perhaps you got one where that step was missed. I have built quite a few Branchline kits, both Yardmaster and Blueprint, and none of them had issues with the truck screws fitting. If it's supposed to be a self tapping screw, make sure it really is, and there is not a burr ont he screw itself preventing it from fitting properly. What helps for self tapping screws is the same thing as using a tap - after a few turns, back it out and clear out the chips, rather than trying to run it in in a single go.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
If you don't have any taps, this Kadee 2-56 drill and tap set is handy to have on hand for when you need it.
#246 Tap 2-56 and Drills #50 and #43 [246] - $8.99 : Kadee, The Coupler People
Paul
Modeling HO with a transition era UP bent
Hey all, thanks for the tips. Turns out I was able to find some spare screws that did the job. However, this isn't the first time I've had this problem and it won't be the last, so I'll give those suggestions a spin if and when the issue comes up again. Thank you all!
Do you have a 1/16" (0.0625") drill bit handy? If so, place it into the hole Does it fit? If it does with a little room left over it's most likely a 2-56 (0.07") tapping hole and the correct size. If the 1/16" drill bit does not fit - the hole is too small. If the latter is the case, drill out the hole with the slightly smaller 1/16" drill bit then use a screwdriver to cut the threads inside the hole with a 2-56 screw.
If you end up tapping the hole with a 2-56 tap, I wouldn't bother with lubricant. You really don't need it with most plastics. Just make sure you rotate the tap back 'n forth a few times every 1/4 turn. That will break up any chips in the hole and help to clear them via the flutes of the tap.
Tom
https://tstage9.wixsite.com/nyc-modeling
Time...It marches on...without ever turning around to see if anyone is even keeping in step.
If the plastic is hard, it may also have become brittle. So if tapping, use a lubricant, go slowly, and reverse the tap to disengage the cuttings more often. There will be people here who know the best lubricant choices for this.
If the hole hogs out, just clearance-drill it, turn down a plug of styrene sprue (filing it chucked in a drill if necessary) and glue it in the hole, and use a 2-56 tap drill and tap to cut new threads.
You could also use a thread replacer like a Keensert (without perhaps driving kees -- simple adhesive should hold) which would put permanent metal threads in the hole forever, but the tools and insert cost might not justify the expense, especially at this bitty size. Threading brass tube and gluing it in would give much the same effect...
2-56 screws are the common truck attachment size for most HO kits. I would have to go pull out a Branchline kit and take a look. The screws should self tap into the plastic, but sometimes the plastic is a little hard. Pre tapping the hole with a 2-56 tap should fix the problem and allow the screws to go in.
Sheldon
I'm trying to assemble a Branchline Trains Yardmaster series boxcar kit, and I'm just about done-except for installing the trucks. And so I've hit an obstacle.
The screw holes for attaching the trucks seem too small to accommodate the 2-56 screws that were included in the box. I tried forcing one in (which worked on a McKean models kit), but it didn't catch as deep as I got it (maybe like 1/3rd of the week) and I didn't want to push it any further for fear of hollowing out the screw hole. I'm stuck, and I'd like to wrap this up so I can move on to other kits.
So my questions are:
1) Should I still be able to use 2-56 screws to attach the trucks? Or will I have to get smaller screws?
2) If the former, what am I doing wrong? Have I just not gone deep enough? Do I need to use a drill?
3) If the latter, why include the wrong-size screws in the first place? What size screws would I need instead?
Any tips/help would be appreciated. Thank you!