Another threading thread!

Well, I tried cutting my thread and it was a disaster. The thread was really rough and ragged. It looked like it was torn more than cut. I even tried using another 1/2" piece cut at 13 TPI and I got the same results. Both pieces were 6061 Aluminum. Is that the issue? I have a piece of 12L14 steel I can try.
 
devils4ever said:
Well, I tried cutting my thread and it was a disaster. The thread was really rough and ragged. It looked like it was torn more than cut. I even tried using another 1/2" piece cut at 13 TPI and I got the same results. Both pieces were 6061 Aluminum. Is that the issue? I have a piece of 12L14 steel I can try.
Click to expand...
Are you are advancing the tool with the compound? If so, is the compound angle set at 29-30 degrees from perpendicular to the work piece? Or another way to look at it is 60-61 degrees from parallel to the work piece. Can you post a pic of your setup? Aluminum shouldn't be an issue.

Tom
 
Yes, I'm using the compound to advance the tool. I have it set to 29.5 degrees.297921


297922

297923
 
29-30° from perpendicular to the spindle, not 29-30° from parallel.
 
This is one of the best examples of the ever-recurring problem of setting the compound incorrectly, the photography is really perfect.

Other than a bit more stick-out on the part than is absolutely necessary, your setup looks ok. Except you are actually cutting a 120 degree thread instead of a 60 degree thread. The angle of the compound is way too shallow -- it needs to swing another 30 degrees to get on where you need it. More like 11 and 5 on a clock face instead of 10 and 4.

Are there graduations on the opposite side of the dial to allow you to set that properly? This happens soooo frequently with new folks setting up for the first time.

-frank
 
Ah. Of course. I feel really dumb. The markings on the compound slide reads 0 when parallel to the lathe axis. It should read 90. There is no markings on the back side. I used my machinist's protractor to set it to the correct angle.

I did a test cut and it was much better. I don't think I cut it deep enough since a nut wouldn't go on. I thought it wasn't going on because the major diameter was raised from the thread cutting. So, I switched to a regular cut to smooth it out. Nut still didn't go on. I see a thread mic in my future!
 
No need to feel dumb, it's called learning for a reason. There's lots of things to be aware of and try to keep track of when trying something for the first time. Invariably one or two will get away! Next time you won't make that mistake (a different one, perhaps ;) )

As for the raised burr, I typically run a file over the tops rather than a full cut, but your choice.

-frank
 
I should have used a file like you mentioned. Then, I could have continued cutting the thread deeper. I guess the 0.75/TPI calculation is only a guideline. Learning.....
 
Well, I've successfully cut my first thread! It is a 1/2"-13 external thread. I think I made every mistake in the book.

I've learned to not reverse the lathe direction to move the cross slide back into the starting position unless you retract the cross-slide (backlash bad!).

Also, check the feed direction! I tried and tried to get a nut onto the thread to no avail. I bought a set of thread gauge wires (a little tricky to use) to measure the pitch diameter and found my pitch diameter well within spec. I couldn't understand why the nut wouldn't go on. Finally, I realized that I cut a left hand thread! Argh!

In any case, I've learned a lot and thanks to all here.
 
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