View Full Version : Riddle me this

David Hafnorske
11-21-2002, 07:54 PM
Any machinist worth his salt knows that most common threads are 60 degree. So therefore why do supply companies sell square, thread restoring files. Seems like someone missed the boat on this one. Maybe me, please explain. And no, it doesn't say anything about being for square threads.

11-21-2002, 08:16 PM
On each side of the square are little teeth that match the pitch and thread form. I have a starrett thread restoring file, it has 8 different pitches (TPI's) on it. Works great!!!!

11-21-2002, 08:44 PM
As spope said, the square shape only serves to provide four different 'faces' on each end of the tool. It is a face that has the working formed file for a particular pitch . . . the corners of the square are not used to restore threads. There is also a universal 60* thread restoring file that looks more like a knife and works the way you were thinking.


Rich Kuzmack

Pi = 355/113 . . . to
<85 parts per billion

11-22-2002, 12:09 AM
You can buy single row files for thread restoration.

All threads are not 60* - id est BA & BS threads. I have even seen a thread restoration file in Princess Auto here in Edmonton for the british threads - I phreaked! http://bbs.homeshopmachinist.net//biggrin.gif

David Hafnorske
11-23-2002, 11:50 AM
What do you do use this file sideways? I think that would be very cumbersome. A plain old triangle file seams like it would work as good and thread pitch doesn't matter. I still don't see the advantage. and yes I know there are umpteen billion thread types. I could invent my own if I wanted to. Good luck finding a file for that!

John Stevenson
11-23-2002, 12:13 PM
Very common use of one of these files is when you are screwcutting.
When you have finished the thread you select the face of the file that has the correct pitch on it to match your thread from the 8 you have on offer. Once you have selected this then the other 7 are nothing more than a file handle!
You run at low speed and present the selected face to your work and run along the thread. This will remove all burrs and round off the creast radii to give you a smooth thread.
I have about 6 or so with various pitches that I have collected over a period of time. Some are special and must be unobtainable nowdays. I have one that has all the pipe threads on it. I also have british and metric pitch files.
As I operate a jobbing shop I wouldn't be without these.

John S.

11-23-2002, 06:29 PM

The single cut file for threads is just a 60* vee - all other sides (like an on edge pillar file) are "safe" or non-cutting.

Wow, neat idea - now I have a use for mine! Thanks, eh. http://bbs.homeshopmachinist.net//biggrin.gif

George Hodge
11-23-2002, 08:54 PM
I've always figured the thread files were for restoreing damaged screw threads,and I've used mine a bunch of times for just that. You place the first couple of vees in the good threads and use the file just like you would a regular flat file,working your way across the damaged threads. I found that even if you don't have the exact same number thread on the file,just pick one that is divisable by the one you want to repair. ( Boy that sounds like Greek)!!!! If you have 12 tpi. you can use the 3 tpi.side of the file. etc. I've used them on threaded shafts up to 4 in. in diameter,that had a flat milled on one side,which made it impossible to use other thread restorers. Had one that Thrud is refering to,but prefer the square section files.

David Hafnorske
11-24-2002, 07:22 PM
A friend told me that they are like three triangle files lined up side by side. Now that makes sense. It's just the same as a triangle file times three.


Peter S
11-24-2002, 09:17 PM
I have found that a triangular needle file is great for fixing thread damage.

Thread restoring files (the square ones, with selection of TPI or pitch) are considered pretty useless and not found in the toolboxes of us snobs! http://bbs.homeshopmachinist.net//smile.gif

John Stevenson
11-25-2002, 07:41 PM
Possibly there is some confusion as it sounds as if some people haven't actualy seen a thread file.
I've posted a pic at:-
There are three in this shot. Far left is a pipe thread file which has all the popular pitches used on pipes. Centre is a standard metric file and far right is a awhitworth 55 degree form file that also gas an internal chaser part at the end of the file.
Very handy for cleaning up internal threads in the lathe.
I think the pics with the posts above are quite self explanitary.

John S.

11-25-2002, 11:13 PM
Yeah, those are the square ones I know and never thought of chasing threads with mine! The single "V" file looks similar to a pillar file on edge (V on the bottom edge. safe cuts (non-cutting) on the remaining three surfaces.

11-26-2002, 09:27 AM
The square thread restoring files are better than the triangular in that they will straighten a rolled thread, leaving a full thread rather than remove the damaged portion as a file will.
As John S. points out, they are also good for finishing threads in the lathe as they will clean up and burnish the thread.
The tool snobs are missing a good bet here. Too bad.