Tap and die sanity check

[MRogersII]

I've mentioned in a parallel thread that I've been building a Farquharson. Thus far, in order to fit the various parts together, I've been drilling pivot points and then turning down steel pins to use for fitment. They're easier and faster to assemble and disassemble, I can just push the pins in and out with my finger. I've only just begun using a lathe. In fact, the pivot pin i made was my first lathe work. Obviously not a machinist, but trying to learn as I go.

Now I'm at a point where I need to begin making actual threaded machine screws for the final assembly and could use some guidance regarding tap and die sizing. For example, for my pivot pin... I drilled the original pivot point to .1719 with an 11/64th drill. Thus far I've been using a steel pin turned to the same. For the machine screw, I was planning to use a #16 drill, bore to .177 and tap it for 12-24. The question is what diameter do I need to lathe turn the threaded portion of my screw shank to? My chart tells me that I use a #16 drill with a 12-24 tap to tap the threaded wall of the receiver, but what diameter do I need to turn the pin I'm making in order for it to mate up properly with the 12-24 die, and ultimately thread into the 12-24 hole i tapped?

Certainly a green question, but the first pin i made took quite awhile, even without threads, and I was hoping to get this right the first time.

As always thank you all for your assistance.

Michael

 

[Keith Hansley in NC]

DM inbound

 

[MRogersII]

I re-read my original thread and thought I might should clarify my question. If I drill the receiver wall to .177, and tap 12-24 threads, then seemingly the machine thread diameter will need to be greater than .177 or there will be no contact between them. I'm guessing the diameter of the machine screw i need to make, will need to be greater than .177, but I've not found a chart to tell me how much. Hopefully that makes sense.

 

[tobnpr]

Major diameter of #12-24t is 0.216

#12 - 24 UNC : Thread Dimensions (Machining Doctor)

#12 - 24 UNC : Basic Thread Dimensions (Pitch, minor & major diameters, depth, lead), Tolerance range for all applicable classes and much more

www.machiningdoctor.com

Pick up a copy of the Machinists Handbook- everything you could ever need to know, and infinitely more.

 

[MRogersII]

Major diameter of #12-24t is 0.216

#12 - 24 UNC : Thread Dimensions (Machining Doctor)

#12 - 24 UNC : Basic Thread Dimensions (Pitch, minor & major diameters, depth, lead), Tolerance range for all applicable classes and much more

www.machiningdoctor.com

Pick up a copy of the Machinists Handbook- everything you could ever need to know, and infinitely more.

2630 pages....

 

[std7mag]

2630 pages....

They call it a "Bible" for a reason.

 

[59FLH]

The formula for nominal major diameter of a number (#) size screw is:

# size of screw x .013 + .06 =

For 00 size and smaller you subtract .013” for every additional 0 beyond the 1st 0.

Examples 00 is .047” and 000 is .034”

Hoping this info helps.

 

[MRogersII]

Thank you all for your help, and especially for the call. My translation of the data from Table 3 "Standard Series and Selected Combinations-UST" is i should turn the threaded portion of the screw to .215 (Class 2A) in order to thread it with my 12-24 die and that should mate up with my 12-24 tapped hole in the receiver wall.
Thank you all again and have a great New Year.
Michael

 

[MRogersII]

The formula for nominal major diameter of a number (#) size screw is:

# size of screw x .013 + .06 =

For 00 size and smaller you subtract .013” for every additional 0 beyond the 1st 0.

Examples 00 is .047” and 000 is .034”

Hoping this info helps.

Great tip on the formula! Thank you

 

[MRogersII]

Good evening, All. I wanted to provide a followup on the Farquharson build, and ask an additional question.

Thanks to the advice I got on making screws I have now made my first few screws, see attached. I bought a tailstock die holder and have had good success thus far. My question now is there a specific tool that guys use to cut the slot in the screw head? I thought about a hacksaw but that could make for a very wide, and possibly ugly channel. I also have some very tiny endmills that I could use to machine the slot but those seem pretty easy to break. Maybe a slitting saw but I'm not sure I have one thin enough. Thought maybe someone might know of "a better way" altogether.

As always, thank you for your help. It is very much appreciated.
Michael

 

[Walt Krafft]

Slitting saw. Buy what you need.

 

[Sniperhandle]

A slitting saw in the mill is what you need, Use a 5c Square holder or even a hex holder to hold the screw, Find center and cut your screw slot.

​

 

[WSnyder]

Maybe a slitting saw but I'm not sure I have one thin enough.

That is the way.

You can start a groove with a triangular file and finish with a jewelers saw or a fine tooth hacksaw with a modified blade. Sand the sides (the kerfs) off the side of the blade so it only cuts on the bottom. Once carefully started it will track in the groove. If you leave the screw head proud and finish it after slitting, it will give you the best chance for a nice parallel slot.

 

[Sniperhandle]

I have held a screw in the lathe chuck and used the cross slide with a sharp tool I ground to do it also, But it is slow and tedious, Hard on the lathe too. Since then I have used the slitting saw and 5c holders.

 

[Sniperhandle]

 

[DRK]

Good evening, All. I wanted to provide a followup on the Farquharson build, and ask an additional question.

Thanks to the advice I got on making screws I have now made my first few screws, see attached. I bought a tailstock die holder and have had good success thus far. My question now is there a specific tool that guys use to cut the slot in the screw head? I thought about a hacksaw but that could make for a very wide, and possibly ugly channel. I also have some very tiny endmills that I could use to machine the slot but those seem pretty easy to break. Maybe a slitting saw but I'm not sure I have one thin enough. Thought maybe someone might know of "a better way" altogether.

As always, thank you for your help. It is very much appreciated.
Michael

If you have someone locally with a wire, you might see if they will wire it for you.

 

[WSnyder]

Maybe a slitting saw but I'm not sure I have one thin enough.

FWIW Ebay generally has a good selection of NOS saw blades for far cheaper than from the tool dealers. I used to buy them from the dealers but now that they've skyrocketed in price I now search Ebay first.
Link: Ebay slitting saw blades

 

[MRogersII]

Thank you, Guys, for the guidance. Much appreciated.