Threading Tools Keep Breaking

Like others have said, those are only turning tools. Being a beginner on a light lathe you're only stacking the deck against yourself using carbide. Carbide won't tolerate a lack of rigidity and it also doesn't like it when you stop the spindle before backing off the cutter. Get yourself a fishtail gauge and grind some HSS threading tools. I grind most tools freehand but my threading cutters are ground on a disc sander with a miter gauge. I use a piston type QCTP and feed with the Xslide. You might also check your setting for that thread you're cutting. That pitch looks a mile faster than a 1.5mm pitch to me.
 
I use HSS threading tools, .002-.003 cuts, flood cut with Tap Magic oil, use lower than higher speeds so I won't crash on a shoulder. Keep it as close to the chuck as possible, I use a center when I can. Proper support is very important. I make a cut and stop. back out a couple thousand (DROs) and then reverse back to the start. I never use the threading guide and instead leave the feed engaged until it's done. When I started out, I actually "taped" it engaged, so I wouldn't forget (by habit) and disengage it.
 
If you need to stop the spindle before backing the tool out, try cutting a relief groove where the thread ends. That way you can stop the spindle and the tool wont be engaged in the material. That will help stop the breakage as well. If you can't cut a groove, practice pulling the tool out at the end before shutting off the spindle. Disengage and pull out at the same time. Kinda like rubbing your head and patting your tummy, but it works!
 
A lot of good ideas here. In my mind use HSS. Just grind your own tools and save a buck or two. Until you get the hang of it stay in close to the Chuck and don't have the tools sticking out too far from the toolpost either. This is just me, but I set the compound straight in, and no more than 3 or 4 thou per side. If you're close in to the Chuck you can lose the live center too, it's just in the way. If you're into learning, there's a guy down in Phoenix called Swarfrat, he's got some nice instructional videos he puts out, and he's easy to understand. I had already learned to thread when I bought his videos but you could probably do well with at least buying the one on cutting v form threads. He'll have you setting the compound at 29.5 but that's your call. Once you've cut your first decent threads you'll say "I can do this, piece of cake".it is too, just stick with it and get your tools ground up good and you'll be counting threads in your sleep. After you've mastered the thread dial, get used to leaving the half nut engaged and backing the motor up because you'll need to know that to metric thread.
 
Not mentioned on here either . If threading up to a shoulder gives you the chills , machine an undercut to the root diameter and chamfer it 45 degrees . Turn your tool upside down and thread away from that shoulder IN REVERSE !! Nice little trick on ID threads . ;)
 
I primarily thread with a carbide insert tool from Shars (picture below). I bought inserts off eBay from a number of sellers, usually get them for about $3 each. I, like most others, set my compound to 29.5 deg. That way you are cutting on one edge and just dusting off the other. I take around 0.003 per pass and use cutting oil liberally. What the heck, bought a gallon of Rigid non-stinky oil for under $20 which will last me a lifetime of threading.

If I'm threading up to a shoulder, do an undercut to the root diameter for pucker factor. You need some relief anyhow if you need to nut or whatever you're threading into to bottom out on the shoulder. If I'm cutting metric threads, I can't disengage the half-nuts. Just shut the lathe off early and turn the chuck by hand. I've used the 3-wire method to check for depth, but find a thread micrometer to be much less cumbersome. I get at least 2 feet of threading in stainless before the tip of the insert starts to go.

I also will thread with HSS, but am getting lazy in my old age and go for the inserts in general. Pretty cheap and have worked well for me.

Bruce

upload_2016-2-25_19-57-23.png
 
Watch the video by Tubalcain. I did and cut perfect threads the first time. I used Carbide and turned as slow as machine would go. I have done 1/2 and 1 1/4 threads on both steel and aluminum. It takes me maybe a dozen or more passes but then I am such a neophyte that I am super cautious.
 
I've been using the Arthur R. Warner HSS tools. I love them. You can re-sharpen the inserts and they work great on mini lathes. The center cutting 60° tool in the 5 piece set specifically states it can be used to cut threads. While expensive compared to the import tools, they are superior. I also enjoy supporting a family owned U.S company. I get mine from LMS, but they are the same price on the A.R. Warner web store.

Just my uninformed non-real machinist opinion of course.
Roy
 
BGHansen said:
If I'm threading up to a shoulder, do an undercut to the root diameter for pucker factor. You need some relief anyhow if you need to nut or whatever you're threading into to bottom out on the shoulder. If I'm cutting metric threads, I can't disengage the half-nuts. Just shut the lathe off early and turn the chuck by hand. I've used the 3-wire method to check for depth, but find a thread micrometer to be much less cumbersome. I get at least 2 feet of threading in stainless before the tip of the insert starts to go.

Bruce

View attachment 123191
Click to expand...

Cutting metric threads without disengaging the half nuts was a lot more fun after installing a crank on the back end of the spindle. Now I do the whole job by hand, no power and no tight sphincter.
 
You must log in or register to reply here.
Back
Top