My First Screw

[mikey]

As above. Another way to look at this is that it provides a run off area for your tool. You can cut until the tip of the tool enters the thread relief area, thereby avoiding gnarled ends on your thread. The depth of the relief is cut to the minimum diameter of the thread so you don't lose strength. Here is an example:

 

[RJSakowski]

Further, on Mikey's info, if you cut your threads without the relief your last cut could go a tad further than the previous cuts, possibly causing some problems. The relief gives you a larger window to withdraw. Since you are cutting manually, it is probably not an issue for you.

 

[ProfessorGuy]

This screw is about 1/4" long. I don't know the pitch, but it's about 50 TPI.

I understand the need for thread relief so the cuts don't have to end all at the exact same spot, but cutting by hand under a loupe made stopping at the "end" of the thread very easy. But cutting the thread relief before cutting the threads was not an option for me!

That's because I had absolutely no idea where the bottoms of the threads would end up, so I didn't know the final minimum diameter. I know the calculations are not difficult but I did all this work by eye! I knew I hit the correct thread depth when the flat areas disappeared from between the threads as I cut them deeper. But how deep? Didn't know, and more important, didn't really care. Since I can make my screws and holes all custom (non-interchangeable), what need have I of measurements?

 

[mikey]

Understood but it is well to keep in mind that without a thread relief you may need to take the thread very nearly to the shoulder in order to have the screw tighten deep enough. In addition, oftentimes the thread form near the end is not neat and will require some cleanup if you cannot run it off into a relief; it isn't about having them end in the same spot. You don't have to cut one but its good to know about them and how to cut them.

 

[coolidge]

That's quite nice, we need to see some action photos of these being turned.

 

[RJSakowski]

This screw is about 1/4" long. I don't know the pitch, but it's about 50 TPI.

I understand the need for thread relief so the cuts don't have to end all at the exact same spot, but cutting by hand under a loupe made stopping at the "end" of the thread very easy. But cutting the thread relief before cutting the threads was not an option for me!

That's because I had absolutely no idea where the bottoms of the threads would end up, so I didn't know the final minimum diameter. I know the calculations are not difficult but I did all this work by eye! I knew I hit the correct thread depth when the flat areas disappeared from between the threads as I cut them deeper. But how deep? Didn't know, and more important, didn't really care. Since I can make my screws and holes all custom (non-interchangeable), what need have I of measurements?

If you know the pitch and profile of the thread, you can calculate where the bottom of the thread will be. If you under-cut or over-cut the relief slightly, it won't matter much. Under-cutting will leave marks from the root of the thread, over-cutting unnecessarily weakens the screw; neither of which is likely to be a problem for you. If your depth of cut is about .8/P, you should be fairly close.

 

[RJSakowski]

but I did all this work by eye! I knew I hit the correct thread depth when the flat areas disappeared from between the threads as I cut them deeper. But how deep? Didn't know, and more important, didn't really care. Since I can make my screws and holes all custom (non-interchangeable), what need have I of measurements?

If your screws are all custom and noninterchangeable, what do you do when you lose or damage a screw? Reverse engineering something of that size would be a real problem!

 

[ProfessorGuy]

If your screws are all custom and noninterchangeable, what do you do when you lose or damage a screw? Reverse engineering something of that size would be a real problem!

My plan: just drill the hole to the major diameter and make a slightly bigger screw next time. How much bigger? About *this* much (I do them by eye).

 

[ELHEAD]

My plan: just drill the hole to the major diameter and make a slightly bigger screw next time. How much bigger? About *this* much (I do them by eye).

So do you make a matching tap for each new screw of unknown thread count?

 

[ProfessorGuy]

So do you make a matching tap for each new screw of unknown thread count?

I'll make each screw too long, cut the end into a tap (I file slots in the end), use the tap to make a perfect mating hole, cut the tap off (with its stressed and ruined threads), finish and polish the end, leaving the short screw with perfect, unused high threads. And it is perfectly mated to the hole.

All with no measurements!