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4GSR
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I am posting pictures of the setup I use to cut a thread on a rod or bar to use for a feed screw for a lathe or mill. Fairly straight forward.
Make sure you have enough material sticking out of the chuck as shown, even if you have to start out with a longer piece of material. Oh, Make sure the chuck you are using has a good firm grip on the screw. It slipped on me and cause havoc before I could get the lathe stopped. The threading insert shattered into several pieces. I destroyed two inserts doing this job. Most of the blame was me, not the machine! Running the spindle at about 125 RPM! And missing my number on the thread dial! I was trying to keep from going into back gear, which I managed not to. I did get it threaded okay.
Notice I have the tool bit just behind the follow rest jaw for cutting a left handed lead thread. Also notice I have the compound set at 90 degrees or parallel to the screw being cut. The reason for doing this, is to allow "side stepping" the threading tool once you get to the depth you need for the thread being cut. Example, I'm cutting a 10-pitch Acme thread, the basic depth is 0.060" deep. You add 0.010" to the depth for root clearance for a total of 0.070" deep.
One more thing, I generally try to use a piece of 1144 T, G, & P Stressproof for making screws. I have used drill rod for screws too. Try to stay away from 1018, 1215, 12L14,(reason being, they are too soft) or other unknown steels. Some steels can turn your project into your worst nightmare, too.
The tool block I'm using is one my dad made many years ago, I guess in his shop class at school. We modified it a time or two to fit the tooling we had on hand at the time when it was used. It's the only tool post arrangement I can use properly with the follow rest. The Aloris style tool post just will not work for this application on the 9" SBL.
Leave the live center loose in the tailstock so it will allow the follow rest to self align with itself while cutting. Again, make sure you have running clearance of the cutting tool and tailstock so you don't crash. Oh, as always, use your favorite cutting oil/ fluid for cutting the thread. I did not use the one's shown in the picture. I used a combination of Mobilmet 766 and Trim cutting oil. Don't be afraid to use lots of cutting oil!
L
Start out taking about three passes taking a .010" depth of cut per pass. Back off to 0.005" per pass until about 0.050" depth is obtained. On a smaller lathe such as 9" SBL, this is about as deep as you can get without it taking more power than the lathe can put out. Got to remember South Bend didn't put anything larger than a 1/4 HP motor on the 9" workshop lathes! And that is what I have. So, this is where you side step the threading tool side to side by about 0.005" in both directions. This should get you enough room to get the threading tool to depth. Once the depth is reached, again, start side stepping the threading tool to get a nice clean thread.
Check the pitch diameter of the thread using thread wires, not the nut. More than likely, the thread will still be slightly over sized on the pitch diameter. Continue side stepping the threading tool until you get the pitch diameter in spec. DO NOT GO DEEPER WITH THE THREADING TOOL! The reason for not doing this, is the standard threading inserts off the shelf are ground to the nominal root width of the internal thread, not the external thread. FOR an external thread, the root width varies with the Outside Diameter of the thread and class of fit for the thread. For example, this thread I'm cutting calls for a root width of 0.0332" for the external thread. Internal thread root width is 0.0319". The other thing I didn't mentioned earlier, I usually run a insert width one thread pitch smaller, not always, but most of the time. As on this thread, an 12-pitch insert. Just means having to side step the threading tool a bit more in the threading process.
Polish the thread flanks with some 180 grit emery cloth by taking several passes until the thread starts getting very shiny as I did on my cross feed screw.
F
Finally, the finished thread.
If I forgot anything, I'll come back and add an edit to this post.
Ken
Make sure you have enough material sticking out of the chuck as shown, even if you have to start out with a longer piece of material. Oh, Make sure the chuck you are using has a good firm grip on the screw. It slipped on me and cause havoc before I could get the lathe stopped. The threading insert shattered into several pieces. I destroyed two inserts doing this job. Most of the blame was me, not the machine! Running the spindle at about 125 RPM! And missing my number on the thread dial! I was trying to keep from going into back gear, which I managed not to. I did get it threaded okay.
Notice I have the tool bit just behind the follow rest jaw for cutting a left handed lead thread. Also notice I have the compound set at 90 degrees or parallel to the screw being cut. The reason for doing this, is to allow "side stepping" the threading tool once you get to the depth you need for the thread being cut. Example, I'm cutting a 10-pitch Acme thread, the basic depth is 0.060" deep. You add 0.010" to the depth for root clearance for a total of 0.070" deep.
One more thing, I generally try to use a piece of 1144 T, G, & P Stressproof for making screws. I have used drill rod for screws too. Try to stay away from 1018, 1215, 12L14,(reason being, they are too soft) or other unknown steels. Some steels can turn your project into your worst nightmare, too.
The tool block I'm using is one my dad made many years ago, I guess in his shop class at school. We modified it a time or two to fit the tooling we had on hand at the time when it was used. It's the only tool post arrangement I can use properly with the follow rest. The Aloris style tool post just will not work for this application on the 9" SBL.
Leave the live center loose in the tailstock so it will allow the follow rest to self align with itself while cutting. Again, make sure you have running clearance of the cutting tool and tailstock so you don't crash. Oh, as always, use your favorite cutting oil/ fluid for cutting the thread. I did not use the one's shown in the picture. I used a combination of Mobilmet 766 and Trim cutting oil. Don't be afraid to use lots of cutting oil!
L
Start out taking about three passes taking a .010" depth of cut per pass. Back off to 0.005" per pass until about 0.050" depth is obtained. On a smaller lathe such as 9" SBL, this is about as deep as you can get without it taking more power than the lathe can put out. Got to remember South Bend didn't put anything larger than a 1/4 HP motor on the 9" workshop lathes! And that is what I have. So, this is where you side step the threading tool side to side by about 0.005" in both directions. This should get you enough room to get the threading tool to depth. Once the depth is reached, again, start side stepping the threading tool to get a nice clean thread.
Check the pitch diameter of the thread using thread wires, not the nut. More than likely, the thread will still be slightly over sized on the pitch diameter. Continue side stepping the threading tool until you get the pitch diameter in spec. DO NOT GO DEEPER WITH THE THREADING TOOL! The reason for not doing this, is the standard threading inserts off the shelf are ground to the nominal root width of the internal thread, not the external thread. FOR an external thread, the root width varies with the Outside Diameter of the thread and class of fit for the thread. For example, this thread I'm cutting calls for a root width of 0.0332" for the external thread. Internal thread root width is 0.0319". The other thing I didn't mentioned earlier, I usually run a insert width one thread pitch smaller, not always, but most of the time. As on this thread, an 12-pitch insert. Just means having to side step the threading tool a bit more in the threading process.
Polish the thread flanks with some 180 grit emery cloth by taking several passes until the thread starts getting very shiny as I did on my cross feed screw.
F
Finally, the finished thread.
If I forgot anything, I'll come back and add an edit to this post.
Ken