Making a Cross Feed Screw for a Lathe or Mill

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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.

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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.
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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!

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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.
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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.

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Finally, the finished thread.

If I forgot anything, I'll come back and add an edit to this post.

Ken
 
Came out nice, Ken! Does the follow rest on the SB9 normally bolt to the right side of the carriage? That sure makes life easier if it does.
 
Came out nice, Ken! Does the follow rest on the SB9 normally bolt to the right side of the carriage? That sure makes life easier if it does.
On the South Bend lathe, that is correct. If you notice in the pictures above, the follow rest jaw is almost on center of the cross slide. Back in the day, this was done so you used the "straight" tool holder used with the rocker tool post to thread with. Boy, has things have changed.

Something I forgot to mention in my original post, I cut all of my cross feed screws and most others here on my 9" South Bend lathe. It has very accurate lead screw with nearly no noticeable wear or lead error. I can't say that with other lathes I've had over the years. I have a piece of material bought to make a new lead-screw for my Rockwell lathe in the future. I'll probably do it on my new to me 15" Sheldon lathe. It has a unworn lead-screw on it. Still have to mount a follow rest on it. I have one that will be modified to fit that I will use to make the lead-screw. The 9" SBL just doesn't have a hole big enough thru the spindle to do a 1" OD lead-screw. Darn!

Ken
 
Hi Ken, why could you not use an Aloris style tool post for that job?
Mark
 
Hi Ken, why could you not use an Aloris style tool post for that job?
Mark
The small AXA size of the DMT model I have stuck out too far off the compound. It didn't matter if I put it to the left or the right of the center of the follower rest. You don't have this problem with most newer lathes and follow rest. And if it wasn't for the follow rest being on center of the cross slide I probably could make it work. Also there is not enough travel in the compound to get the tool bit in the right place using the Aloris style tool post.

Ken
 
Aha OK. I assume both the SB9 and the light ten would have the same issue. Good to know if'n I was to buy one
M
 
Very nice. Are you also going to turn-thread the nut, or is that a more convoluted operation?
 
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