need to make more threads on a bolt

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slingshot

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Hello everybody,

I have a hardened 3/4 x 10 tpi bolt 3'' in length that i need to put in lathe and make 1/2'' more of threads on. I know how to set up and line up with the old threads the problem that i have found is that i can't advance the compound because it will get off the old thread pattern.the only way i can do this is to feed straight in with the cross slide, is there a another way? Thanks



regards
Dan
 
Line the tool up in the old threads, and then retract it using the compound.

Do the threading using compound to advance the tool.
 
Follow what Andy said, especially about using the compound to cut. You can't go wrong.

"Billy G"
 
Thanks guys so basically i need to set my dept then zero my slide and back out with my compound? when i start cutting will it no be on top of the old threads until i get back to the dept that was set? thanks
 
Your compound will be set to 29.5-30 degrees, so when you back out the compound it should follow the right hand side of the existing thread. Make sure that you account for backlash in the lead screw when setting it up or you may very well end up cutting into the existing thread. When you're cutting the threads, the compound will cut progressively on the left side, on each pass , until you reach your required depth.
 
As I have stressed for years, this is when you need a thread stop. Reminds me when a customer screwed up; (50) 5/8 x 2 feet- threaded six inches
both ends so thats 100 threadings. When finished he needs one end to be 8 inches of threads. If I didnt use a thread stop, I'd still be threading today.
You should really find or make one. It takes 100% of thinking and the backlash and time saved out of the picture. Its a positive -0- on the crosslide.

thread stop.JPG
 
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Be aware that most bolts are made with a thread rolling, or forming method. This means that the area with threads started out much smaller than the proper major diameter of the thread. At the end of the threads, there will be a short portion between the old and new threads where this will be evident, because in the forming process, the dies are just short of where the blank necks back up to full diameter.

At times, depending on what particular bolt you need, you can search for a "tap bolt" which is threaded to the head. They are not available, to my knowledge, in any grades other than low carbon, grade 2. Not a hardened alloy. If high strength is needed, I would suggest getting B-7 stud and welding a nut to it for a head. *disclaimer: B-7 is 4140 HT, so welding is a little more difficult to get right without loosing material properties.*
 
So that's what that is,a thread stop. One came with my Atlas. Now I know!!!


Master of unfinished projects
 
To GK1918. I don't know how to on my mobile but. Here's a big THANKS!


Master of unfinished projects
 
GK1918 said:
As I have stressed for years, this is when you need a thread stop. Reminds me when a customer screwed up; (50) 5/8 x 2 feet- threaded six inches
both ends so thats 100 threadings. When finished he needs one end to be 8 inches of threads. If I didnt use a thread stop, I'd still be threading today.
You should really find or make one. It takes 100% of thinking and the backlash and time saved out of the picture. Its a positive -0- on the crosslide.
Click to expand...
Can I assume that the brass is clamped to the dovetail, and the slot-head screw slips through it and into a threaded hole in the cross-slide?
Ken
 
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