- Joined
- Jan 22, 2011
- Messages
- 8,031
Benny,
of course there are many other elements to a thread, but the P.D. (Pitch Diameter) is the one most people focus on, and that is really the only element that wires will help you measure. If the flank angle is accurate, at 60°(in the case of common U.N. threads), then the measured P.D. resultant from an over-the-wire measurement is quite valid. Other than that, you should also confirm that the major diameter is within standard limits (or certainly as close to, but no larger than the spindle thread you are emulating. The minor diameter of a working external thread is a function of the actual P.D. and the root radius or root flat, whichever you have. On a thread gage, however, it is standard to have actually a very narrow groove in the root rather than either a radius or flat. This to ensure that the part being checked doesn't have an undersized minor diameter in the case of an internal thread, or an oversized major diameter in the case of an external thread. That could interfere with the function of the gage, either ring or plug. The working gage is designed only to contact the part on or close to the Pitch Line. To make "soft gages" for shop use, I try to use as sharp a tool as I can, as far as the nose radius goes. This usually means I have to switch to a fresh edge on the finish passes to make sure the sharp tip is preserved. I don't go so far as cutting a groove in the root.
If you are hand grinding your threading tool, it pays to be especially fussy on the angles, and keeping the tool on centerline while cutting. Any errors there will compound into less than accurate P.D. measurements. It's pretty common for people to cut threads to a set depth per-side, and if you have a sample in your spindle thread, you should be safe using it to get close and avoid having to use the wires too many times. They are a bit of trouble. Some people use a pair of rubber bands to hold them in place. Some people use a dab of grease. Others use styrofoam, as mentioned earlier. Any cheat goes. But save yourself some aggravation: Put a shop towel under where you have the wires. They're tough to find in the chip pan.
Edit to add: If for some reason you don't have the 0.092 wire, do not substitute smaller wires without making sure that the over wire measurement will not fall below the proposed major diameter. If you do that, you will be measuring the major, not the wires, and the wires will be loose and fall out easily. I have software to calculate for other wire size should you need it, but be aware that the 0.092 wire is selected to contact the flank as close to the Pitch Line as possible.
of course there are many other elements to a thread, but the P.D. (Pitch Diameter) is the one most people focus on, and that is really the only element that wires will help you measure. If the flank angle is accurate, at 60°(in the case of common U.N. threads), then the measured P.D. resultant from an over-the-wire measurement is quite valid. Other than that, you should also confirm that the major diameter is within standard limits (or certainly as close to, but no larger than the spindle thread you are emulating. The minor diameter of a working external thread is a function of the actual P.D. and the root radius or root flat, whichever you have. On a thread gage, however, it is standard to have actually a very narrow groove in the root rather than either a radius or flat. This to ensure that the part being checked doesn't have an undersized minor diameter in the case of an internal thread, or an oversized major diameter in the case of an external thread. That could interfere with the function of the gage, either ring or plug. The working gage is designed only to contact the part on or close to the Pitch Line. To make "soft gages" for shop use, I try to use as sharp a tool as I can, as far as the nose radius goes. This usually means I have to switch to a fresh edge on the finish passes to make sure the sharp tip is preserved. I don't go so far as cutting a groove in the root.
If you are hand grinding your threading tool, it pays to be especially fussy on the angles, and keeping the tool on centerline while cutting. Any errors there will compound into less than accurate P.D. measurements. It's pretty common for people to cut threads to a set depth per-side, and if you have a sample in your spindle thread, you should be safe using it to get close and avoid having to use the wires too many times. They are a bit of trouble. Some people use a pair of rubber bands to hold them in place. Some people use a dab of grease. Others use styrofoam, as mentioned earlier. Any cheat goes. But save yourself some aggravation: Put a shop towel under where you have the wires. They're tough to find in the chip pan.
Edit to add: If for some reason you don't have the 0.092 wire, do not substitute smaller wires without making sure that the over wire measurement will not fall below the proposed major diameter. If you do that, you will be measuring the major, not the wires, and the wires will be loose and fall out easily. I have software to calculate for other wire size should you need it, but be aware that the 0.092 wire is selected to contact the flank as close to the Pitch Line as possible.