Drilling/Tapping Frame Halves

[Dwight in Toronto]

Jim Starbuck has a topic or two in the ESU Installs section wherein he drilled and tapped N scale loco frame halves so as to screw down the right & left track feed wires for the decoder.  (Big props on that whole endeavour, by the way - super job).

The operation got me curious, so I just went to my train shop and picked up a #65 drill, a 00-90 tap, and a dozen each of 00-90 roundhead screws (3/16” long), nuts and washers.  I’ve drilled/tapped from time to time using the conventional, typical equipment, but have never attempted anything anywhere near this small and delicate. 

It’s a new modelling skill that I would like to have a go at.  Before I proceed, I was hoping that perhaps Jim and others might kindly share as many pearls of wisdom as possible.  I suppose that it goes without saying that one needs to be exceedingly careful, cautious and, above all else, take it very slow. 

Some initial questions that come to mind:
1.  Is a pin vice the recommended tool for drilling the “pilot” hole?  A Dremel?  Drilling speed on the higher or lower side?
     (I do not have a modellers drill press).
2.  What kind of oil/lubricant is best for both the initial drilling, and also for the followup tapping?
3.  Is a pin vice suitable as the tap holder?
4.  Any hints to offer regarding the tapping operation?  eg - 1/4 turn, and then clean-out?  less of a turn?  more?
5.  Any insight about the cast metal frame material used by, say, Kato vs Athearn vs Atlas vs Bachmann (ie - might one be ‘harder’, or just generally trickier to deal with in some way, than another?)

Looking forward to hearing back from folks - thanks in advance (I can feel a bead of sweat forming on my brow already!).

[Steveruger45]

Jim Starbuck has a topic or two in the ESU Installs section wherein he drilled and tapped N scale loco frame halves so as to screw down the right & left track feed wires for the decoder.  (Big props on that whole endeavour, by the way - super job).

The operation got me curious, so I just went to my train shop and picked up a #65 drill, a 00-90 tap, and a dozen each of 00-90 roundhead screws (3/16” long), nuts and washers.  I’ve drilled/tapped from time to time using the conventional, typical equipment, but have never attempted anything anywhere near this small and delicate. 

It’s a new modelling skill that I would like to have a go at.  Before I proceed, I was hoping that perhaps Jim and others might kindly share as many pearls of wisdom as possible.  I suppose that it goes without saying that one needs to be exceedingly careful, cautious and, above all else, take it very slow. 

Some initial questions that come to mind:
1.  Is a pin vice the recommended tool for drilling the “pilot” hole?  A Dremel?  Drilling speed on the higher or lower side?
     (I do not have a modellers drill press).
2.  What kind of oil/lubricant is best for both the initial drilling, and also for the followup tapping?
3.  Is a pin vice suitable as the tap holder?
4.  Any hints to offer regarding the tapping operation?  eg - 1/4 turn, and then clean-out?  less of a turn?  more?
5.  Any insight about the cast metal frame material used by, say, Kato vs Athearn vs Atlas vs Bachmann (ie - might one be ‘harder’, or just generally trickier to deal with in some way, than another?)

Looking forward to hearing back from folks - thanks in advance (I can feel a bead of sweat forming on my brow already!).

Dwight, I’ve done this on a few N scale Kato and Atlas locos.
I used only a pin vice fitted with a spinning hand rest and patience to drill and tap the holes.
I start with a punched point, done with a center point punch, in the frame to stop the drill bit wandering.
Drill appropriate sized hole for tapping with a pin vice by hand.
Tap hole using a starter tapered tap going slowly and feeling for bind the back turn a 1/4 to clear and rinse and repeat.
Tap hole with middle tapered and then the final finishing tap as above.
I didn’t use lube.
Fit screw.
BTW I screw down small pieces of PCB to the frame and solder the wire to the PCB.

Steve

[Spruslayer]

What Steve said covers what you need to know.The only thing i might add is use some kind of oil,weather it be dedacated taping oil or some other oil,WD-40/3N1 or what ever thin oil you may have and get a high speed steel tap,those carbon steel taps are just too poorly made.

[Jim Starbuck]

Thank you for the positive comments Dwight. I applaud your desire to push your skill sets by learning something you haven’t done before.

I recall drilling LifeLike, Bachmann and Kato and can’t really say they behaved much differently from one another. As Steve posted above…slow and steady. Patience is definitely the word here.
I usually use a drill press just because the frame is already in the vice for milling but it isn’t a requirement.
Start by marking the location with pin or scribed point. It only takes a small mark to keep the bit from wandering. When drilling with a pin vise it’s important to keep the bit perpendicular to the work piece. The metal chassis can be described as “sticky” when drilling and tapping and slow speed works best. Drill for a few turns then look at the tip of the bit to make sure the flutes haven’t clogged up. They usually do so use the point of a pin or hobby hobby knife to clean them out otherwise the bit isn’t cutting and will gall and break. You will get a feel for how much pressure to apply to make the bit cut but not too much that it sticks.
I wouldn’t use a Dremel but I have chucked my bit in a pin vise then chucked the pin vise in a variable speed cordless drill but it’s kind of clumsy. Again, drill very lightly for just a few seconds and check / clean the tip often. When I drill with the drill press I usually use Tap Magic cutting fluid or Labelle light oil but drilling by hand it’s probably not necessary.
A pin vise works well for holding the tap. I have one that I just leave the tap in all the time.
For tapping it works better to have a through hole if possible as opposed to tapping down a blind hole as it gives the chips somewhere to go. If it’s a blind hole try to make the hole deeper than what the threads may need to be. 1/4 turn at a time on the tap would probably be a bit much. I usually twist the cut until I feel it start to stick then back off to clear the tap. Again, you’ll get a feel for it. If you cut too far the tap can stick and it won’t want to back out either. That’s where you’ll get the feel of how far to go as opposed to specific degree of a turn.
I hope this helps.

Jim

[rodsup9000]

 For best result in tapping, buy American made "gun" or "spiral point" taps. I usually tap holes with this kind of tap with out ever backing it out.  You still have to be careful when tapping blind holes.
 Here is a 00-90 tap
https://www.msdiscounttool.com/catalog/product_info.php?csv=gg&products_id=145657&gclid=Cj0KCQjwlOmLBhCHARIsAGiJg7mM-qBs4r3oyCzXDSaHRDevgxZ8gxNOkli0GFrTurj8aqSDP_pYOskaAoTtEALw_wcB
 

[Dwight in Toronto]

I’m so appreciative to have received such constructive, encouraging and expedient feedback.  The forum responses and a couple of personal emails attest to what a great group we’ve got here.

I’ll refrain from tackling this just a little bit longer, on the hopes that some equally enlightening suggestions might be still to come.  But at this point, feeling a lot more confident.  Thanks guys!

[Maletrain]

Practice on a junk frame first. I use "Tap Magic" fluid.

[garethashenden]

For best result in tapping, buy American made "gun" or "spiral point" taps. I usually tap holes with this kind of tap with out ever backing it out.  You still have to be careful when tapping blind holes.
 Here is a 00-90 tap
https://www.msdiscounttool.com/catalog/product_info.php?csv=gg&products_id=145657&gclid=Cj0KCQjwlOmLBhCHARIsAGiJg7mM-qBs4r3oyCzXDSaHRDevgxZ8gxNOkli0GFrTurj8aqSDP_pYOskaAoTtEALw_wcB

Only if you have a through hole. Spiral point taps push the chips in front of them, which is fine if there's somewhere for the chips to go. But if you have a blind hole you're far more likely to break the tap. Tapping a couple holes by hand in something gummy like Zamak is probably going to be fine, but its not best practice. 00-90 taps are hard to find generally, so this is probably a time when availability outweighs geometry.

[PJPickard]

One thing you will want is a Tapping Guide. The number one thing, especially for small taps, that winds up breaking a tap, is misalignment.  The guide will make sure you are at 90 degrees to your work piece. They are easily made if you have a drill press. All it needs to be is one hole in a piece of material that will keep your tap straight. Here is a link to a commercial one and a little bit about guides.
https://biggatortools.blog/what-is-a-tap-guide/

[Dwight in Toronto]

Tapping a couple holes by hand in something gummy like Zamak is probably going to be fine, but its not best practice.

I’m unfamiliar with the term ‘Zamak’, but I’m going to guess that this is the alloy that some/most loco frames are cast with?   If so, is this ‘gummy’ property something that needs some sort of special consideration?  Eg - does it tend to stick to the cutting threads, for instance?  Looking for some further illumination here, please & thanks.

PJPickard - I can see how a tapping guide would be beneficial, especially for the tapping DRILL operation (for guys like me who don’t have a drill press).  Gonna scrounge around and see if I might have something that might be a suitable stand-in/facsimile.

Good stuff guys; thanks. 

[MK]

Zamark is a "soft" material so when tapping or cutting it gums up the cutting surface.  It's like cutting lead, unlike hard "brittle" material like steel where the cuttings actually chip/cut clean.

[rodsup9000]

    I've never had a problem with the taps gumming up using beeswax for tapping soft metals. I've hand tapped over 500 holes in Kadee/MT freight car frames with a 00-90 gun tap. Also hand tapped over 20 blind holes in old styles Kato F units. Just got to drill the hole a little deeper for the chips. Biggest thing to remember is to keep the tap perpendicular to the hole. After 3 or 4 turns, the tap finds its way perpendicular. 

[peteski]

Dwight, Zamak ( https://en.wikipedia.org/wiki/Zamak ), also called "pot metal", is just a brand name of one of several aluminum/zinc-based soft metal alloys used for injection-molding lots of products, including model locomotive frames.

Just like "Kleeenex" brand name is used to describe any type or brand of facial tissues, or "Q-Tip" to describe any cotton swab, the word "Zamak" is sometimes used to generically describe any type of pot metal.

I have tapped plenty of holes in pot metal loco frames (or other soft metals like aluminum or brass), and I don't recall breaking any taps.  I tap by hand, without using any guides.  I place the tap in a pin vise and using gentle touch tap the hole.  If you are careful, the hole itself will guide the tap.  Here are my 00-90 taps.



The outer two are unmodified. I use  those on plastic.  You will notice that the two taps in the center have modified (squared off) shafts.  I ground the shafts square because the taps were slipping in my pin vise while tapping metal.  When I chuck them by the squared off end, they won't spin.

For blind holes I have modified one tap (3rd from the bottom). Basically I ground off the end where the tap only starts making shallow threads.  I then start tapping the blind hole using the unmodified tap, then when it bottoms out (not making full depth threads) I back it out, then I use the modified  tap to  cut the full threads which will go much closer to the bottom of the hole.  Again, gentle touch is needed not to screw tings up.  Don't forget to reverse the direction often, and also frequently back the tap out of the hole, clean the shavings, then continue tapping.



For tapping holes in any metal, lubrication is essential.  This is what I use (along with my collection of 00-90 hardware).  Very little is needed, I  bought that small can of cutting fluid about 20 years ago, and it will likely last me a lifetime.

[MK]

What is in tapping fluid anyway?  I just use whatever opened motor oil that I have lying around.

[peteski]

What is in tapping fluid anyway?  I just use whatever opened motor oil that I have lying around.

Not sure.  It is some sort of oily stuff with a funny smell. I bought it because it was not expensive, and it is designed for the task.