- Joined
- Jun 22, 2016
- Messages
- 280
I'm new to metal machining. Been trying to do an internal thread about 5/8" diameter (OD of shaft threads is 0.743) 16tpi. Material is 4130. Carbide insert (new). Using a 4 jaw chuck, dial indicator centered (0.0005+-, 0.001 OA), 60rpm, cutting oil. I get some tearing but it seems like the metal also wants to flow up as I cut. I bore to the proper finished size, make multiple passes until the thread looks fully formed. By then the ID has decreased to the point where the thread will not fit on the shaft. The top of the threads has become sharp. I've tried using a boring bar to just take the tops off but then they tend to mush over, making it a no go.
Each time I take the part off the lathe to try a test fit I find it difficult to get it back on the lathe to where the treads will cut in the same groove again.
What is the proper way to do this? How do you measure an internal thread accurately. I can do that on an external using wires. I think it is time to make an external threaded test piece to match the part so I can test the fit on the lathe. Of course that introduces another variable.
Each time I take the part off the lathe to try a test fit I find it difficult to get it back on the lathe to where the treads will cut in the same groove again.
What is the proper way to do this? How do you measure an internal thread accurately. I can do that on an external using wires. I think it is time to make an external threaded test piece to match the part so I can test the fit on the lathe. Of course that introduces another variable.