View Full Version : Thread cutting
10-14-2001, 12:03 AM
Anyone have some good tips for threading 1018 CRS? This crap just about drives me crazy tying to get clean threads. I'm using insert tooling in a lathe.(No coolant pump)
10-14-2001, 02:17 AM
Set your crosslide at 29* or 29.5* to the right for RH (internal threads is oposite). Align your sharp-V tool with a thread cutting gauge to the work. Calculate your infeeds - you should need to do about 9 or 10 passes with no in feed on the last 2 passes to remove slop. ONLY INFEED WITH YOUR COMPOUND. At the end of the cut retract the cross slide to clear the work and go back to the start of the cut. Return the crosslide to previous position. Adjust the compound for the next pass. Pick the thread up with the thread chasing dial and engage halfnuts for next pass. A little cutting fluid is advised for each pass.
This method will produce glass smooth threads in Stainless Steel. For Stainless each pass should be incremented at least .003-.004 as it has a tendency to work harden.
If you do the cuts dead on (90* feed) each successive cut removes much more material than the last (v shaped chip). When you set the compound to 29* the infeed of compound shaves one side and cuts on the other side of the tool - producing a nice vee-groove.
CNC lathes feed 90* but jog the tool right and left in the groove on alternate cuts to even out wear on the tool.
I hope this helps - threading can be a real pain at times. Practice is the best teacher.
[This message has been edited by Thrud (edited 10-14-2001).]
10-14-2001, 03:53 AM
Insert tooling, carbide I presume. Carbide is wonderful stuff but it needs to be ran hard and fast to get good surface finishes.
Carbide insert tooling would be great in a Cnc machine, at slower manual machine threading rates I use high speed tools, grind my own.
1018 just doesn't thread very pretty, but there are things you can do. Use a sharp honed tool and lots of lubricant.
Have always used black oil in the past, sulpherized cutting oil, but as of late I have been using something new? New to me, actually one of the oldest cutting lubricants there is, and it seems to work very well indeed. Lard oil, plain old rendered out pig fat saved from a pork roast, some use bacon grease, they say it smells good.
Thrud says how many passes,9 or 10. He's working stainless, mean stuff but it threads pretty. I don't use as many free passes on 1018, after a couple I don't even get a fuzz.
Sharp tool and lots of lubricant.
Have fun, watch that dial.
1018 cold-rolled is not great stuff to work with. It's kind of "gummy" to cut. Thrud's description is the classic way to cut threads on a lathe. Use those guidelines.
I agree with Halfnut -- you'll probably do better with a sharp, honed, HSS toolbit. Because carbide is so brittle, it has to have very small relief angles so the cutting edge stays supported. You can put a keener edge on HSS that will cut better and require less power.
I cut threads at around 60 rpm -- slowest back gear -- which reduces the amount of heart failure as the carriage gallops along towards the headstock. Slather on some cutting oil of one kind or another with a small brush. I used lard oil for a while and found it worked very well. It does tend to grow stuff if you leave it sitting around open, but it's an exellent lubricant for cutting threads in steel. These days I usually use sulphurized thread-cutting oil from a plumbing supply place.
[This message has been edited by SGW (edited 10-14-2001).]
10-15-2001, 10:48 PM
You're right about 1018 being crap. It's a pain in the ass to do anything with. I have good luck with TiN coated carbide inserts for turning. I use a disposable carbide tool for threading and get amazingly good results on 1018. Divide .742 by your threads per inch to get total depth of cut; take .005 per pass max.; every .015 (3rd pass) make a pass without advancing compound; every .020 (4th pass) crank cross slide in .001 for one pass; and finally, make 2 or 3 passes at your final depth. Works every time, even on 1018.
[This message has been edited by bdarin (edited 10-15-2001).]
10-15-2001, 11:12 PM
Thanks to all who replied. I've got some good ideas here I think. I'll definitely go back to the 30 deg. on the cross slide which is the way I originally learned to do it. Ditto on the steel tools. Grind and squint time.
Lard oil? Um, I think not. :-) I'll stick with the black stuff although it's not the best in the world. Finally got the coolant pump working so that should help some.
My slowest speed is 40 and that's what I seem to end up using most of the time. At 6 tpi things happen pretty quick.
Thanks to bdarin for the formula. Hadn't heard of that one. I think most of the problem with this 1018 is build up on the tool. It'll go along cutting fine (more or less) for a while and then dig in and really gouge out a thread or two, even tearing a thread off. Usually on about the last pass it seems. :-( Oh well, I'll figure it out eventually.
[This message has been edited by snorman (edited 10-16-2001).]
10-16-2001, 09:42 AM
Snorman..... the .742 figure is for a 29* compound setting. For 30* use .75
10-19-2001, 01:57 PM
You guys have heard this from me before about carbide and some argue but I still believe. You have to generate the proper surface footage to make carbide work correctly, these speeds coupled with the speed in which the carrage is traveling with 6tpi thread make things difficult on the HSM. Use very sharp HSS and lots of oil. In feed using compound slide at 29-30 degs as stated earlier and don't crowd the tool take light cuts .005 works well for me. If you can, dump the 1018 and get some 12L14 it has almost same composition and strength qualities as 1018 and will take the most beautiful thread you have ever seen.
Yep, leaded steel (Ledloy or whatever) is amazing to work with. My only complaint is that it tends to rust very easily.
I've also found LaSalle "Fatigue-Proof" steel to machine beautifully. You can't go as fast as with Ledloy, but the surface finish one gets is incredible.
10-20-2001, 11:14 PM
Our shop does a lot of oil field work and we use a lot of "Stress Proof" steel. Is that the same as "Fatigue Proof"? It cuts and threads like a dream, so I try to sneak it in on anything requiring threading. The bossman is cheap, so can't always do that. :-)
Stressproof is similar to Fatigueproof, but not quite the same. I think the basic alloy is the same, but the drawing/rolling/whatever is different to give somewhat different qualities. If you do an Internet search, you can find descriptions of both. I did that a while ago, but don't remember the details.
I expect for home shop work, the differeneces are largely irrelevant. Judging by Snorman's report, they are both nice to work with.