Drilling and Tapping Styrene

[Benjamin Maggi]

Not sure if this post belongs here or under the "scratchbuilding" forum, but I am bodymounting Kadee #1 scale couplers on a USA Trains 44 Tonner and will need to build up a styrene pad and then drill and tap it. I have ordered 4-40 stainless steel screws, a 4-40 drill, and a 4-40 tap. Is there anything I should know about the procedure, or any tips?

Thanks.

[Anonymous]

basic principle with all tapping is drill hole deeper than needed or  all the way thro. use tap slowly - half turn forwards quarter turn back to clear chips

suggest removing at half final depth to  clear hole out. when finished and inserting securing screw try a spot of liquid cement on threads to act as a thread lock

[Anonymous]

It seems unlikely to me that the material (polystyrene) will be strong enough to hold a tapped screw under even the lightest conditions?

Ian

[devils]

As long as you use styrene of a reasonable thickness, 1.5 -2 mm sheet, you should have no problems. I would double it up to give 3-4mm thickness where the screw is to give plenty of material to tap into. As long as you don't tap too near the edge styrene is suprisingly strong. I tapped screws into the plastic tender of my 2-8-0 to body mount the coupler and it's been fine pulling very heavy accucraft stock, before I sorted the wheels to get free running.

Follow the instructions for turning back to clear waste from the hole, it's unlikely to break in styrene but it's the most common reason for a broken tap in metal and it's a good habit to get into.

Good luck

Paul

[John Busby]

Not sure if this post belongs here or under the "scratchbuilding" forum, but I am bodymounting Kadee #1 scale couplers on a USA Trains 44 Tonner and will need to build up a styrene pad and then drill and tap it. I have ordered 4-40 stainless steel screws, a 4-40 drill, and a 4-40 tap. Is there anything I should know about the procedure, or any tips?

Thanks.

Hi scoobster

Probably should really be in scratch building, but right now you need advice rather than told to put it somewhere else.

Mission Control we have a problem

If I read your post correctly you have a tap and a tapping drill that are both the same size it isn't going to work, as you will have no styrene to cut the thread into!! the tap will just fall through the hole.

You need to consult a chart to find out what the correct tapping drill size is, it will be smaller than the tap.

Also you will have to carefully drill the hole using a hand drill.

Power drills have the nasty habit of melting plastics.

These drills are obviously quite small so have plenty on hand, as you will break the drill precisely 5 minutes after the shop has closed and you will not be able to get another one till Monday if you don't have a few on hand.

regards John

[Anonymous]

well pointed out - refer to this table http://www.boltdepot.com/fastener-information/US-Tap-Drill-Size.aspx

 

gives you all drill sizes

[Benjamin Maggi]

So, if I am reading it correctly, if I plan on using 4-40 screws (1/2" long, metal), I should drill the hole using a 3/32" bit and then tap it with a 4-40 tap? For the record, I plan to sink the screw into about 7/16 of a styrene pad that will be built out of laminated 0/125 stryene layers cemented together. I plan then to epoxy this pad into the shell of the 44 tonner. Thus, the strength will be the result of a 1/2" screw (minus the amount of the coupler box itself) into a stryene pad that has been epoxied. I only plan to pull a couple of cars with it. If properly done, it should be strong enough, right?

Also, I don't mind this being moved into the scratchbuilding category. I did not put it there because I was asking a technical question about taps, not specifically about scratchbuilding. Anyways...

Thanks for all your help guys!

 

[FJ and G]

Dumb follow up question.

Why tap styrene. Can't you just use a drill bit smaller than the bolt, then simply thread the bolt in?

[devils]

You can if you use self tapping screws, but it puts more stress on the styrene as it forces its way in and is more prone to cracking it. That's why commercial stuff has a moulded boss to drive them into as the circle is stronger. Tapping the hole would be better for a stress situation like a coupler box in G scale or any little crack will soon cause it fail and your coupler and its box will part company with the loco.

Paul

[Anonymous]

I am yet to be convinced this the best or even a worthwhile material for this application.

Ian

[Anonymous]

Not sure if this post belongs here or under the "scratchbuilding" forum, but I am bodymounting Kadee #1 scale couplers on a USA Trains 44 Tonner and will need to build up a styrene pad and then drill and tap it. I have ordered 4-40 stainless steel screws, a 4-40 drill, and a 4-40 tap. Is there anything I should know about the procedure, or any tips?

Thanks.

Hi scoobster

Probably should really be in scratch building, but right now you need advice rather than told to put it somewhere else.

Mission Control we have a problem

If I read your post correctly you have a tap and a tapping drill that are both the same size it isn't going to work, as you will have no styrene to cut the thread into!! the tap will just fall through the hole.

You need to consult a chart to find out what the correct tapping drill size is, it will be smaller than the tap.

Also you will have to carefully drill the hole using a hand drill.

Power drills have the nasty habit of melting plastics.

These drills are obviously quite small so have plenty on hand, as you will break the drill precisely 5 minutes after the shop has closed and you will not be able to get another one till Monday if you don't have a few on hand.

regards John

John,

Man your right about that because I broke off plastic several times not thinking and I was not a happy camper. I need the light bar for a job the next day (Sunday) so I had to use some JB on it.

William

[John Busby]

Hi scoobster28

If the job is done properly it should pull more than just a couple of cars.

That is correct a 3/32 drill followed by the tap

Hi Ian

The material is OK for what is intended as long as it is thick enough and has enough body around the holes to support the bolts.

Its like our trains enough thickness and body around the self tappers that hold most of our trains together (they would be better with threaded holes and bolted)

regards John

[Benjamin Maggi]

Thanks guys, this will be my Saturday project. I have two engines to do, and each one has a different pilot arrangement for a total of 4 customized pilots/plows, etc. After doing it in HO scale, it just seems like it will be easier (and a heck of a lot more fun) in this Scale. My eyes will like it better too... and I am only 24.

[CandCRR]

How about putting (gluing) a thin brass or sheet metal layer in the middle of the styrene?  It may add more holding power for the tapped screw holes.

Jaime

[Benjamin Maggi]

Actually, one option I thought of was epoxying a piece of brass angle in the space, such that when the engine was on the rails the "L" shape would be attached to the pilot and jut inward from the lower end. Then, I could just put a 4-40 nut on the other side (epoxied in place) and screw the coupler into that. Unfortunately, I think that I would not be able to fit anything except a 1/4" angle in there, and that probably would not be strong enough. But your idea is interesting.

[Anonymous]

How about putting (gluing) a thin brass or sheet metal layer in the middle of the styrene?  It may add more holding power for the tapped screw holes.

Jaime

I like your idea Jamie, gives it way more support and can use the styrene as only spacers and to hold it.

William

[markn]

If you have the space-how about gluing in a small threaded metal or nylon post-check a hobby shop that carries building supplies for r/c aircraft-they make several bits for making "hard points" in balsa and other soft woods.