Finish threading aluminum by ending with a few shallow cuts, that will cleanup the finish. Some lubrication (oil, IPA, WD40, soap water, etc) will also improve the finish of the thread. Check your cutting tip for cold "welded" aluminum, that will ruin the finish.
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Single point threading speed for aluminum
- Thread starter o0norton0o
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That's good for the compound angle.
Can you show us a close up of your cutter? It's in the dark and not quite in focus.
As @Huub Buis said, you need lubrication for threading, especially aluminum.
Can you show us a close up of your cutter? It's in the dark and not quite in focus.
As @Huub Buis said, you need lubrication for threading, especially aluminum.
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Use the backgear for threading. Blame the cutting tool for poor finish
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How does your chuck attach to the spindle of the lathe ? You have to check it's not a screw on chuck as some one mentioned, otherwise it will unscrew if your making chips with it running in reverse.
Stu
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I made a "draw bar" styled chuck lock for turning things in reverse...
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New Guy with an Atlas 10200 metric lathe
Hi all, I bought this lathe this summer to do some turning down and threading for a project. It was aluminum material, so I got it done, but the quality could have been better. So after doing multiple turning and threading operations, I was finding the limitations of the machine and it's...
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I just threaded this piece this morning. I believe it is 6061, although I wonder, as it gave me some issues turning down the initial diameter. You can see the OD is not very nice. This piece gave me trouble a while back and I through it in the scrap bin. For this piece, I used it.
It is a 3/4"-13 thread, up against a shoulder. (19.05mm / 1.954mm pitch) I used about 90 RPM, as that is a slow as I can run my lathe and used a HSS cutter. (Aloris AXA-8 with a P10 HSS blade.) Threaded towards the chuck. Used about 1.5 thread widths for the gutter. Messed up a little by not having enough gutter depth, so I cleaned it up some. The threads seem to be clean - they'd be cleaner if I blasted it with compressed air, or used a pipe cleaner on the threads. No ragged edges in the threads. There's a little trash right by the gutter, but that will clean up easily.
Why 13 TPI? Because I messed up, it should have been 14 TPI. I found out about the screw-up when I looked up the pitch diameter. Yes, a non standard thread for the size. Oops. But, it doesn't matter in this case, because I will be making a matching female piece. I found an online thread pitch calculator that told me the nominal pitch diameter for a 3/4-13 thread is 0.70004. My pitch mic tells me it is 0.7000, so good enough.
So it is possible to make decent threads in aluminum at low speed. I will drill a hole and single point the internal thread to 1/2"-20 this afternoon. I will probably do that in reverse, since you can't see what's going on for internal threading, especially for small bores. I found a left handed carbide micro100 threading tool for pretty cheap, so I will use that. Makes the setup easier, in my opinion, for internal small bore threading.
It is a 3/4"-13 thread, up against a shoulder. (19.05mm / 1.954mm pitch) I used about 90 RPM, as that is a slow as I can run my lathe and used a HSS cutter. (Aloris AXA-8 with a P10 HSS blade.) Threaded towards the chuck. Used about 1.5 thread widths for the gutter. Messed up a little by not having enough gutter depth, so I cleaned it up some. The threads seem to be clean - they'd be cleaner if I blasted it with compressed air, or used a pipe cleaner on the threads. No ragged edges in the threads. There's a little trash right by the gutter, but that will clean up easily.
Why 13 TPI? Because I messed up, it should have been 14 TPI. I found out about the screw-up when I looked up the pitch diameter. Yes, a non standard thread for the size. Oops. But, it doesn't matter in this case, because I will be making a matching female piece. I found an online thread pitch calculator that told me the nominal pitch diameter for a 3/4-13 thread is 0.70004. My pitch mic tells me it is 0.7000, so good enough.
So it is possible to make decent threads in aluminum at low speed. I will drill a hole and single point the internal thread to 1/2"-20 this afternoon. I will probably do that in reverse, since you can't see what's going on for internal threading, especially for small bores. I found a left handed carbide micro100 threading tool for pretty cheap, so I will use that. Makes the setup easier, in my opinion, for internal small bore threading.
The thread looks OK but the turning finish is a bit rough. My first thought is that the turning tool is a HSS tool that has not nose radius at all. If it is an insert, check the tip is not chipped. It could also be that the turning tip has some cold welded aluminum on it.
For turning aluminum I use the ground and polished G type inserts (DCGT, CCGT, etc). These give a good finish on almost all turning conditions.
For small internal threads, for which I don't have a tap, I use a small self made 5 mm HSS threading tool. For larger diameters, the IR11 type inserts.
For turning aluminum I use the ground and polished G type inserts (DCGT, CCGT, etc). These give a good finish on almost all turning conditions.
For small internal threads, for which I don't have a tap, I use a small self made 5 mm HSS threading tool. For larger diameters, the IR11 type inserts.
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I agree that the turning finish is not good in the picture. Used a TCGT insert, which usually gives a very nice finish. I think it is because I was trying not to reduce the diameter by much and it was bouncing/deflecting. I'll clean that up later with a deeper cut. I reduced the diameter to 3/4" for the threaded section, and the finish was great - same insert. Nonetheless, I will check it under magnification - it doesn't take much to mess up a cutting tip.
The inner thread will be single pointed because I want to ensure it is concentric to the outer threads. I don't know how to do that with a tap. This is an adapter for an airgun moderator, so the concentricity of the threads matters a lot. For other threads, that don't matter much, I use a tap.
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So, I messed around with some scrap still using the upside down cutter/ reverse spinning chuck/ cutting away from the headstock and I got the same horrible result. It seems as though the cutter isn't tracking the the first pass. I'm working on a theory why it's happening and have ordered some new HSS 60 degree cutters, some blue dye, and other stuff so I can work it out.
One interesting note is that I made these before and while the result was a rough thread which I could have improved with better operator skills, the resulting thread was correct from the gear set that I installed. The different element on this run is the way I use the half nuts. Last time I actually left the half nuts engaged and just turned the lathe backwards to get to the thread start position. This time I have been using the half nut lever to engage and disengage the lead screw. It's pretty obvious that I need to chuck some scrap and try both techniques and see if I get the same result from both. I have checked the gear math 3 times, even taking the small gears off and counting the teeth, and since I had previously made a diagram of the gears with their tooth numbers on my first batch and the threading worked, so I know the gears are correct to cut my threads...
I'm working through this issue, and I'll report my mistake/s once I work them out... I'm going to make samples by using the half nut lever and leaving the half nut engaged and just backing up.... If one works and the other doesn't I should be able to figure out why...
One interesting note is that I made these before and while the result was a rough thread which I could have improved with better operator skills, the resulting thread was correct from the gear set that I installed. The different element on this run is the way I use the half nuts. Last time I actually left the half nuts engaged and just turned the lathe backwards to get to the thread start position. This time I have been using the half nut lever to engage and disengage the lead screw. It's pretty obvious that I need to chuck some scrap and try both techniques and see if I get the same result from both. I have checked the gear math 3 times, even taking the small gears off and counting the teeth, and since I had previously made a diagram of the gears with their tooth numbers on my first batch and the threading worked, so I know the gears are correct to cut my threads...
I'm working through this issue, and I'll report my mistake/s once I work them out... I'm going to make samples by using the half nut lever and leaving the half nut engaged and just backing up.... If one works and the other doesn't I should be able to figure out why...
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