Struggle with 1/8” dies

[Shopgeezer]

I used 1/8” drill rod for my first steam engine conrod but am having a struggle to find a die to thread it. The tables show a #5 die as “closest fractional” for 1/8” but that doesn’t seem to exist. All the sets go from 4-40 to 6-32. Mc Master Carr shows 5-40 and 5-44 dies online but none of my local suppliers have them. I am curious as to why there isn’t a 1/8” tap and die given how common the size is and I did see a 1/8” die in some of the sets but it is NPT. Why would you want a 1/8” pipe thread? Ferreting around in my plans book I saw that they called for a 5 BA thread on the 1/8” conrods. So off to Merry old England with my order (through the miracle of Ebay) and a nice little set arrived with the three taps and a die. Some experimenting suggested a #37 drill worked for the taps. The 1/8” rod takes a bit of work but it threaded ok. But the die was quite tight on the rod and I wouldn’t say that 5 BA is exactly right. I doubt that a 5-44 die would be either since the charts show that it is only close to 1/8”. So why all the hassle for 1/8”? Its a very common size, I don’t understand why there wouldn’t be a die size specifically for it.

 

[ChazzC]

5-40 used to be common for small hardware, but even my 40+ year old Craftsman Tap & Die set doesn't include them. Amazon carries them from both China and Drill America (which are sourced from all over). Little Machine Shop's Machinist Calculator gives recommended rod diameters for Numbered, UNC, UNF and Metric sizes:

5-40

5-44

Per the attached, 5BA would be 0.125"-43 (3.175mm max OD, 0.59mm pitch), so reducing the diameter of the threaded end of the rod per the LMS recommendations would ease the thread cutting operation with your 5BA die.

What scale is your engine? 1/8"Ø seems a little small for a connecting rod.

 

[krypto]

Yes, the #5-40 thread is what you use with 1/8" rod. It's easy enough to buy tap & dies from decent suppliers and you can buy the fasteners from McM and other places as well. It's handy for model work, but It's doubtful your corner hardware will carry anything as that fastener size has falling out of fashion over the years.

If you ever build a PM kit you will see they use plenty of #5-40 fasteners.

 

[danallen]

Unless you need a long thread say more than 3/8" 5-40 is an easy thread to single point in a lathe.

 

[Shopgeezer]

I am working my way through the book “Making Simple Model Steam Engines” by Stan Bray. Simple wobblers to start. The first set of engines are pretty small, which makes turning drilling and threading these wee little parts kinda hard for beginners. I think it would be easier to start with something bigger. Anyway very good learning process and excuse to buy more tools (collet blocks and collets). I found a 5-40 tap and die set on Amazon which I will order. Also getting a 7 BA tap and die set for the next engine that has 3/16” conrods. The BA sets all come with the three taps. The SAE sets don’t. I’ll have some BA taps and dies around to satisfy the ghosts of my Scottish ancestors. Don’t think I’ll go as far as getting a Whitworth set though. The ancestors have never forgiven the family for moving to Canada. Another blizzard forecast for tonight. Forty cm of snow predicted. This Spring just can’t get going.

 

[krypto]

Maybe to late, but I wouldn't recommend buying cheap taps, especially small ones. The first time you snap one off in your work you will instantly regret it.

https://www.zoro.com/widia-gtd-hand-tap-set-3-pc-hss-5-40-h2-limit-15212/i/G1723863/

 

[bluejets]

I don’t understand why there wouldn’t be a die size specifically for it.

Never heard of 1/8" whitworth...???

 

[tractor162003]

Shopgeezer, if you think that the engines are too small. Just do as I have done make it 2 times as big. If you have a part that is 1/4 inch make it 1/2 inch.​

Don't get mad at me for the bold type I could not change it.

 

[stevehuckss396]

Not sure if you solved your issue but all the threads in this set are #5-48. Studs are drill rod same as yours. I had no problems threading them. I'm wondering if your die might be of poor quality or maybe just worn out. Drill rod is some pretty tough stuff even unhardned. A dull die would have trouble climbing on to start a thread. Breaking the edge with a file might help but if it doesn't, try a new or at least a sharper die.

 

[Shopgeezer]

I struggled with threading the rod held in a vise with a hand held die holder. Gave up and ordered a tailstock die holder from India. Holding the 1/8” rod in a collet chuck and turning the chuck by hand while feeding the tailstock die holder into the work made the threading much easier. I will try polishing the end of the rod a bit to ease the 5 BA die along the rod. Overall this works great.

As for feeding the tap into the brass big end for the conrod I am super careful. I have broken many a tap in my machinery repair days. The # 37 drill and using the taps in sequence worked very well. I found a Blondie Hacks video on using a tap follower and ordered one. I tap everything in the lathe or the mill now. All turned by hand of course.

 

[awake]

I find it very hard to use a die successfully holding by hand, and the problem is greatly exacerbated by lesser quality dies.

In general, I solve this particular problem by re-designing for either #6 or M3. Very often the plans have sufficient room to accommodate the slightly larger #6, but not always. Meanwhile, it is hard to imagine a situation where M3 could not work. It is only a tiny bit smaller than the #5, and fasteners of all sorts, as well as taps and dies, are plentiful. Of course, if the goal is to match an existing part, or to achieve a level of historical accuracy, neither of these options may work.

One may also prefer not to mix metric and imperial dimensions and parts, either to avoid potential confusion, or to preserve a certain "purity" of design. FWIW, even though I started out in the world of imperial fasteners, and still tend to think more naturally in terms of inches and feet, many years of using metric particularly in the sphere of 3d printing has led me to the point that I don't seem to have any trouble with mixing metric and imperial even in the same design. I find that I routinely use whatever I have on hand or is easiest to procure, without any particular preference for one over the other. But of course, "mileage may vary"!

 

[DLanum]

A useful calculation for the "Major diameter" or bolt size or like you have 1/8" diameter rod stock.
The first thread number is the diameter.
To determine the OD size,
Multiply the first number times 13 and add 60.
So for your 5-40 threads,
5 x 13 = 65 add 60 = 125 or 0.125 diameter.
For 6-32 threads
6 x 13 = 78 add 60 = 138 or 0.138
For 0-80 threads
0 x 13 = 0 add 60 = 60 or 0.060
Hope this helps explain thread sizes.

 

[krypto]

Yes, you want to use fixtures to keep you taps and dies straight. A have a few for the lathe, but for the smaller sizes like #5-40 I use this holder:

The die is held in the front and the fixture slides on a hollow shaft held in the tailstock. For power threading, you just hold the piece with the knurling and run the die up the rod. If you let go, the die just spins with the work so it's very easy to do a precise job. Reverse the lathe to remove the die. You can also hold taps and larger dies with the different heads.

I made this holder based on a design by Neil Butterfield who used to sell them. I believe the Chinese are selling them on Ebay now.

The same holder with handles installed for manual threading. The handles were made to fit the lathe.

For tap holding, sometimes I use the fixture above, a standard drill chuck or a ER-32 collet holder that fits in the tailstock. For small work, I generally use this spring-loaded tap follower.

This holder is handy as it's MT2 so it fits directly in the tailstock. It's also quite a bit bigger than the Fisher tap guide it was based from so it has greater travel. I made this as well.

 

[Steamchick]

Krypto: Taps will beak very easily when a bending moment is applied... Apprentices learned (by having a token payment deducted when beaking taps) that holding taps true to the hole, with holes of the RIGHT size, and not vaving the tap holder around but simply rotating it carefluuly ensured "no broken taps". Now I am not perfect, but I rarely break a tap. - Maybe 2 or 3 in the last 30 years? - And it was always my fault from "bending" the tap - as seen by the angled break....
Sharp taps and dies are good to use, blunt ones should be MELTED DOWN!
K2

 

[Rockingdodge]

If the book is uk based then the 1/8" tap is most likely 1/8" x 26tpi BSF, that's british standard fine but there's nothing to stop you using sizes of drill rod and taps & dies local to your area, just check the knock-on effect on other components.
I will often convert US fixings specified to metric, BA, BSF, ME or whatever is the closest fit.
Roger

 

[PeterDRG]

For holding a tap perpendicular I find one of these useful. It is based on a commercial design. I have a STEP file if anyone is interested.

 

[Steamchick]

In y collection of old taps and dies I have 1/8BSW, so I suggest you check tables for that. I am away just now so cannot look in my Machineries handbook or other tables, but I am sure you'lls find them on line?
K2

 

[Richard Carlstedt]

another trick to prevent breakage of small taps is to do it upside down.
It uses gravity to clear chips , you can stop and the natural position of the tap wrench
shows you where it should be, so you can tweek your way into the part using your thumb and forefinger.. Picture shows a 1.2 mm tap
Rich

 

[Steamchick]

I am working my way through the book “Making Simple Model Steam Engines” by Stan Bray. Simple wobblers to start. The first set of engines are pretty small, which makes turning drilling and threading these wee little parts kinda hard for beginners. I think it would be easier to start with something bigger. Anyway very good learning process and excuse to buy more tools (collet blocks and collets). I found a 5-40 tap and die set on Amazon which I will order. Also getting a 7 BA tap and die set for the next engine that has 3/16” conrods. The BA sets all come with the three taps. The SAE sets don’t. I’ll have some BA taps....... etc.

Hi Shopgeezer, I find for most modelling work that BA sizes are good (not excellent), Whitworth too coarse and look crude, BSF and Cycle (26 tpi) limited to sizes of around 1/4in and above, so use a lot of 32tpi ME and when necessary 40tpi ME. BA threads were designed for small sizes so very practical for most non-scale models, but 32tpi ME and 40 time were designed to "Look best" on models. The problem being the smaller the thread pitch, the better - more precise - you need to be at making the threads.
Standard metric threads are designed - like Whitworth and BSF to be practical and strong.
The Americans decided that they would standardise not on the Whitworth 55 degree thread (an Engineering and mathematical optimum) but a 60 degree thread for UNC and UNF - and modern metric went that route as well.
But in different global zones not everything is equal. There are 12 Imperial inches to the foot, but Korean inches are 1/10th of a foot.... making inch sizes different from Korea. Japanese metric threads are JIS thread shape and tolerance which jus different from European metric thread shape and tolerance...
And that doesn't consider pipe threads, gas threads, etc. In INCH or Metric sizes.... and tapered pipe threads get more complex.
Enjoy,
K2

 

[peterl95124]

I made 28 #5-40 engine block studs, for my V12 engine, from 1/8" steel rod. to get the die to start you need a 45-deg chamfer on the end of the rod, you need to use your lathe tail-stock to supply pressure on the die to get it started (and to get it started square to the rod). there's no way I could have made any of these by just trying to force the die onto the rod by hand, even if I could have gotten the thread started there's no way it would have been concentric/coaxial with the rod. Your frustrating experience is exactly what I'd expect from not doing the threading on the lathe and trying to do it by hand, but you had the presence of mind to ask, hopefully at least one of these many replies has helped, we look forward to seeing some of your progress.

in USA Albany Fasteners does carry odd numbered (#3 and #5) screws, nuts, and bolts, that few others do, so they get a lot of my business.