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Internal Threading
- Thread starter m.batz2
- Start date
It's difficult to see the tool and things happen very quickly. Hi Tony,
I read these comments about cutting thread. I am curious and I wander if it could be a mistake in the cutting speed by one zero to many? 600 rpm is 10 revs per second. It is possible that I missed something like that CNC is in use here? 500-600 rpm is rather fast and difficult to control?
Regards
Juliusz
Mike, let me add my two cents to the subject of threading internally or external.
1. As Tony points out 1018 is tough to get a good finish on but it can be done. Start with good lube, Moly-Dee is my benchmark but some of the high sulfur lubes are very good. You may find these in the "pipe threading section" of your local store.
2. I always use the compound to advance the tool, cutting on one very good edge is much easier than trying to deal with cutting on two edges, especially on our hobbyist machines. I use an angle of 30 degrees which means that when threading internally you must change the position of the compound slide. As an aside as you add top rake to the tool you will decrease the included angle of the resulting thread. This is usually not an issue but if you are after precision it has an effect.
3. I use carbide (MT-3-TR/L) and HSS with similar results. If you use HSS make sure it is sharp before you begin and do not forget to put the proper radius on the end. The lack of a radius can cause the tip to break if threading without a landing area. I have a variable speed motor on my lathe and thread at a slower speed depending on the thread pitch 60-120 RPM.
4. As mentioned in earlier posts the feed rate has to be slow, especially for internal threading. I usually start at 0.004 and then work down to one or two thousands for the last few passes with the final pass being straight in on the cross slide usually less than one thousand. A rub pass also helps.
5. To remove burrs that stand above the outer/inner diameter of the the thread I use Scotch brite pads, they do a decent job of removing extraneous peaces of metal.
6. Since I do both metric and Imperial threading but have an Imperial lead screw I use a tool retractor and never disengage the half nuts. This is a minor point but it does make threading an easier process with fewer things to go wrong.
Having the know how and skill to turn threads on a lathe greatly expands your flexibility in how to construct projects. I personally prefer the appearance and performance of turned threads. For internal threading you reach a point where the tap is your only choice, usually around 0.500 or so. Many good threads are finished off by running a die over them after the last pass in the lathe. Being confident about being able to thread on the lathe is one of those thresholds that you pass through on the climb up the competence ladder.
Jim
1. As Tony points out 1018 is tough to get a good finish on but it can be done. Start with good lube, Moly-Dee is my benchmark but some of the high sulfur lubes are very good. You may find these in the "pipe threading section" of your local store.
2. I always use the compound to advance the tool, cutting on one very good edge is much easier than trying to deal with cutting on two edges, especially on our hobbyist machines. I use an angle of 30 degrees which means that when threading internally you must change the position of the compound slide. As an aside as you add top rake to the tool you will decrease the included angle of the resulting thread. This is usually not an issue but if you are after precision it has an effect.
3. I use carbide (MT-3-TR/L) and HSS with similar results. If you use HSS make sure it is sharp before you begin and do not forget to put the proper radius on the end. The lack of a radius can cause the tip to break if threading without a landing area. I have a variable speed motor on my lathe and thread at a slower speed depending on the thread pitch 60-120 RPM.
4. As mentioned in earlier posts the feed rate has to be slow, especially for internal threading. I usually start at 0.004 and then work down to one or two thousands for the last few passes with the final pass being straight in on the cross slide usually less than one thousand. A rub pass also helps.
5. To remove burrs that stand above the outer/inner diameter of the the thread I use Scotch brite pads, they do a decent job of removing extraneous peaces of metal.
6. Since I do both metric and Imperial threading but have an Imperial lead screw I use a tool retractor and never disengage the half nuts. This is a minor point but it does make threading an easier process with fewer things to go wrong.
Having the know how and skill to turn threads on a lathe greatly expands your flexibility in how to construct projects. I personally prefer the appearance and performance of turned threads. For internal threading you reach a point where the tap is your only choice, usually around 0.500 or so. Many good threads are finished off by running a die over them after the last pass in the lathe. Being confident about being able to thread on the lathe is one of those thresholds that you pass through on the climb up the competence ladder.
Jim
No, that's manual. It's just that it's 16 TPI. A good rhythm and it's not too difficult to do. CNC would be much faster than that. If this is a blind thread, without a relief, I would probably run it more like 3-400 RPM, but that's the best way to get a smooth finish on such a soft material.
Some of it may just be the stock itself. At work, depending on where the stock comes from, at times you can get clean threads and the next time, using the same settings and the same tools, the threads will all be fuzzy. A lot of times I will set up a piece to use just to get my settings adjusted and then toss that piece in my toolbox for later setup practice runs.