1" - 10 internal thread

[wa5cab]

Subtract the pitch from the major diameter to give you your minor diameter. Example 1/4-20. Pitch is 1/20 = .050" so .250 minus your pitch (.050"). Minor diameter is .200". The important thing is to be able to hit the right pitch diameter for the clas of thread. The Pitch diameter is an imaginary diameter where the v of the threads have the same distance across the thread and the v where it is bisected. Think of a triangle. Two imaginary lines form the cylinder and this is your pitch diameter.

Sorry, but this isn't quite correct. It is difficult to give the MOLO page numbers that apply because there were 10 versions printed over the decades and pagination varied. And due to potential copyright violations, we haven't allowed the scans of several of the versions that are floating around the Internet to be uploaded to Downloads. However, I stretched a point and put Chapter 7 - Threading from Versions 1 and 9 in Downloads. If you look on (printed, not file) page 104 of Version 1, near the top of the page it says that the minor diameter is the major diameter minus the double depth of thread. The single depth of thread for the almost never made exact (sharp at both major and minor diameters) 60 degree V-thread is 0.866 (Cosine of half of the 60 degree included angle) times the pitch. On page 135 is Table V, Depth and Double Depth of National Form Threads. The line for 20 TPI shows that the number to subtract from the major diameter to get the minor diameter is .0650" or .0758", depending upon which cutter shape you are using.

 

[MarkM]

Take a look at drill and tap charts then do the math. Your kidding right? What does a 1/4-20 call for regarding a tap drill?
Yes a go no go guage would be used to measure internal pitch diameter. Usually a set and a range

 

[mattthemuppet2]

When I made a back plate for my 618 (1x10tpi spindle like yours) I made a spindle thread copy to match the spindle, then used that as a Go gauge for making the back plate. Came out just fine, better than the one that came on my 3 jaw even.

 

[wa5cab]

Take a look at drill and tap charts then do the math. Your kidding right? What does a 1/4-20 call for regarding a tap drill?

No, I'm not kidding in the least. On my Atlas wall chart, 1/4"-20 UNC calls for a #7 drill, which is 0.201" diameter. 1/4"-20 was probably a poor size for an example in this case as I have never seen an ID threading tool small enough to go into and make a 1/4" diameter tapped hole. Your method is probably a good shorthand method to roughly calculate the tap drill size for UNC and UNF tapped holes. But if you look at tap drill charts, most of the time they will say what percentage of the thread will actually be made. The tap drill chart sold many years ago by Atlas-Clausing says for approximately 75% threads. A tap can't make 100% threads except in thin material, and even then, the tap drill recommended for the hole will only make maybe 85% thread. Internal threads made on a lathe take several passes and are normally 100% if V-Form and around 98+% if Unified National made with a V-form threading tool.

 

[MarkM]

The original poster is fairly new at machining and asking a simple question regarding a simple unc 2b thread. A common thread. Were not discussing thread depth tool geometry or any special type of thread. Why add this confusion to a newbie? This formual is used in industry for simple threading applications for international use. Where does a 100% thread come into play here? Do you even understand the relationship of pitch diameter thread depth and internal diameter?

 

[mikey]

I wanted to just step in and give a practical solution to the original question and then I'll get out of the way.

Minsk, have a look at the attached chart. Scroll down to find the data for a 1"-10 thread. Since it is difficult to directly measure thread pitch of an internal thread, the best option is to make a plug gauge with a class 2a thread that is made to the quoted thread pitch tolerances in the chart. Bore your hole to 0.892" ID and thread it until the plug gauge fits with no significant play and you're there.

To be sure I'm clear, make the plug gauge to a Dmaj of 0.9982" OD and cut an external thread so your thread wires or thread mic reads between 0.9853" and 0.9332". Then cut the internal threads until this gauge fits snugly in the thread and then stop.

Okay, back to our regularly scheduled programming ...

 

[minsk]

newbie is bit of a stretch..i am more in utero. seriously though...thanx to everyone who chimed in.....what a great forum and community ..knowledge is power. i have learned so much just cruising around this forum. unfortunately i cannot use a threading tool on my new old Atlas lathe. my lathe did not come with change gears for threading. i ordered a 1" - 10 tap from flea bay. ill keep you guys posted. and again thank you so much for input

 

[David S]

What type of tap did you order? If you make the spindle protector like I did then you will be tapping in a bore that doesn't go all the way through. You will need close to a bottoming tap.

Since this is only a protector and doesn't require any real structural strength, you could just thread 3 or 4 threads in the opening and all should be good.

David

 

[minsk]

right hand 1" -10 .

 

[wa5cab]

minsk, David meant is the tap that you ordered a Starter, Plug or Bottoming Tap? A Starter tap will have a diameter at the loose end of a few thousandths smaller than the thread minor diameter (or of the tap drill diameter) so that it will pilot or guide itself into the drilled hole. The first 3/4 to 1 rotation of the tap (or often more) will not cut if the hole was drilled with the recommended tap drill. The thread starts cutting in the second rotation and the cut diameter slowly increases until it is between 1/2 and 3/4 of the length of the threaded part of the tap. So the last 1/4 or more of the tap doesn't or shouldn't be doing any cutting. The bottoming tap cuts to the Major diameter with all but the first thread. The Plug tap is in between the two extremes.

Spindle nose thread protectors normally have an ID on the visible end smaller than the thread minor diameter for the last 1/8" of length. The diameter of this hole is in between the thread minor diameter and the big end diameter of the spindle nose. This protects the end of the spindle from damage and stops the protector from screwing on when it hits the end of the spindle. Normally, the ID within about 1/8" to 3/16" of the bottom of the hole is bored out to slightly more than the female thread's major diameter. This gives a space in which to get the threading tool stopped before it runs into the bottom of the hole. It also gives the bottoming tap clearance so that it can cut through the bottom of the thread, so that the protector will screw all of the way onto the spindle. You can make your thread protector with a tap instead of with an ID threading tool, but you are going to need the the Plug and Bottoming tap, and you are going to need a boring tool to cut the thread relief area. If you are going to use taps due to lack of threading gears, use the chart that mikey uploaded. It is more complete than most. I already had it so it is probably in the Charts folder in Downloads as well.

MarkM, to answer your last question first, yes. I've been doing this sort of thing for over half a century. If he is going to use taps to cut the thread, then there is no reason not to use the recommended tap drill size for most of the hole. As I said earlier, that will produce about a 75% thread which is fine for a thread protector. Also, 1"-10 is UNS, not UNC.