Using the Cross Slide for Threading

ddickey

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I need to cut 1/2-20.
If I just used the cross slide what would the outcome look like?
I've read it's okay to use the cross slide on some fine threads.
Does 20tpi qualify?
 
Why would you want to use only the cross slide, if in fact you have a compound rest; the result of using only the cross slide is that the tool cuts on both sides using this plunge cut method; what happens is that the two chip streams converge at the point, interfering with each other and causing galling in the cut and a very unpleasant looking finish on the flanks of the thread. An advantage to using the compound for feeding is that you zero the cross slide on every cut and do your successive cuts by feeding the compound in, with no numbers to memorize for each new cut. Some folks like to compute the distance the compound is fed in to size the thread, or use the figures on the "fish tail" thread gage; this may work in an perfect universe and with sharp vee threads, but if you use a flat on your threading tools, it does not. Best is a thread mike, and the tables published in machinist's handbooks, but for me, a thread ring gage or a nut that has had a tap run through it is all that is necessary to insure a good thread fit for most purposes.
Lastly, I think, no, 20tpi is not fine enough to plunge in straight, and personally, I would not recommend it for any threading.
 
It will probably depend a lot on your lathe, the material you are cutting, and the tool you are using. If you are using a 2000 lb lathe with a razor sharp HSS tool to cut aluminum, you will probably get good results. If you have a 7x12 with a poorly ground HSS or the wrong kind of carbide trying to cut 4140 or 304 stainless, it will not go well.

I have gotten by just locking the compound and using the cross slide, but it tends to go better using the compound.
 
Both ways work, in my experience. I cut clean threads on my Sherline lathe for years, including 20 tpi, with a straight in feed with the cross slide (it has no compound). I can do the same with the compound on my larger lathe; I agree with Benmychree but I do know that both ways work. I use sharp, accurately ground HSS tools and cut much finer threads than 20 tpi with no real issues. You do need to take very small cuts as you progress but you'll do that anyway.

This is an M8-1.25 thread in 1144 steel cut with the cross slide on a Sherline lathe. Other than wire brushing the debris off, it is just as it comes off the lathe.

IMG_4830.jpg
 
Nice looking thread there Mike.
I use a solid tool post and don't feel like setting it back up, that is really the only reason.
If I can get threads to like that only using the cross slide I'm tempted.
 
You can make nice threads. Just take small cuts. A really good old machinist I used to know applied the top surface of his threading tools to the round,front edge of a bench grinder,making the whole top surface of his threading tools give the chips someplace to go,rather than just possibly bunching up on the threading cutter. The grind was flat all the way across the threading tool,and concave as seen from the side view.
 
Nice looking thread there Mike.
I use a solid tool post and don't feel like setting it back up, that is really the only reason.
If I can get threads to like that only using the cross slide I'm tempted.

As long as your tool is accurately ground and you can confirm that the tool is perpendicular to the work and on center then you should be fine.
 
Kieth Fenner of YOUTUBE fame has a video showing compound-only thread cutting. He uses a dial indicator to determine calculated or "look it up" thread depth. It worked very well for him and the video describes the method very well. I'll try to find it & if successful I'll post it on this thread.

Edit: Cross feed only, locked compound

I searched for about 15 min with no success. K. Fenner
 
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