- Joined
- Apr 24, 2021
- Messages
- 462
What about hss blanks I grind? I gave up because I thought it couldn’t be done that route?
-
Welcome back Guest! Did you know you can mentor other members here at H-M? If not, please check out our Relaunch of Hobby Machinist Mentoring Program!
How to thread stainless
- Thread starter FTlatheworks
- Start date
- Joined
- Apr 24, 2021
- Messages
- 462
- Joined
- Mar 26, 2018
- Messages
- 2,724
Yeah it can be higher, I just wouldn't do your roughing with these inserts as they will wear faster than the blunt inserts that give a crappy finish. The other benefit is that these inserts have a very small minimum depth of cut so you can actually skim tenths off of a part. You can't do that with general purpose inserts.
I rough within 10 or 20 thou of finish size and take a few passes with these to hit the dimension accurately and with good finish.
- Joined
- Apr 24, 2021
- Messages
- 462
Makes sense. Before I knew these were for non ferrous, or softer metals, I tried to rough with them on mild steel. I liked the stick out they had which is why I was attracted to them. Needless to say, I destroyed them in probably 2 mins.
- Joined
- Mar 26, 2018
- Messages
- 2,724
Yeah with these you need to be gentle. As an example, I ran a prototype product job in 316 stainless with these. Very small depth of cut (maybe 3-5 thou) in many passes (CNC) due to poor workholding conditions. I would get 1-2 hours of cutting per insert corner before the finish would get crappy and I would index.
Granted the CNC can control the feedrate better than I can, but still a data point. At $0.50 per edge from import suppliers, it was pretty economical.
Here is the finish right off the machine in 4140 from those inserts on my 12x36.
- Joined
- Apr 14, 2014
- Messages
- 3,152
I'm as old school as you, maybe even older school. rather than 303 for the wine industry my experience is with 316 in the food industry. Almost every operation including turning, facing grooving, and threading was done with user ground HSS blanks. It was my first experience working in a machine shop (no apprenticing just on the job learning) so I had no idea 316 was more difficult to work with than any other material.
I was taught the "proper" methods to turn, thread, etc., etc. by a couple of old Krauts that worked for the Fuhrer in the Fatherland. They watched like a hawk and made sure you understood the proper feeds, speeds, and angles, and could grind the tool properly. If you should be so unfortunate as to make a mistake they could unleash an ungodly rampage in German. I didn't know exactly what they were saying, but between the attitude and a hand across the back of the head it was obvious they weren't pleased.
It took a while to learn to do exactly as instructed, but when you did finally figure it out it was worth the trouble. After a while it all seemed second nature. I still do a lot of 316 with 303 and 304 thrown occasionally. When I'm working and concentrating I can still feel them breathing down my neck, and offering hints as how to do it "properly". All in all it was a great learning experience, I'm just sorry I started (34 yrs old) so late in my working career. I would have loved to have started 15 years sooner so I could have learned more.
- Joined
- Apr 24, 2021
- Messages
- 462
4140 is a tool steel and much easier to machine, right? Can you get comparable in 300 series?
- Joined
- Mar 26, 2018
- Messages
- 2,724
- Joined
- Dec 26, 2015
- Messages
- 2,079
I do a lot of 304 work and use indexable tooling exclusively. @mksj has made excellent suggestions.
Single-point threading 304 requires best practices and quality tooling to be successful. The old-school idea of plunging in at 29-30 degrees using the compound to advance DOC is IMO just that - old school, based on HSS usage, and completely unnecessary. On 304 specifically, that technique puts all the cutting activity on one side of the V-shaped tool, while the other side of the tool is consistently rubbing and work-hardening the 304. Far better to plunge into the thread perpendicular to the spindle axis. Material removal rates are also important with 304, the the tendency is run too slow and take shallow cuts which will also work-harden 304. If you're serious about wanting to master 304 threading and willing to invest in decent indexable tools, DM me, and I'll share some of my techniques and tool suggestions.
- Joined
- Dec 20, 2012
- Messages
- 9,422
I've cut and single point threaded a LOT of austenitic stainless steel over the years but would still defer to John, Mark and David given their production experience. I did want to add a few things, though.
My sense is that you're a novice hobby machinist. No offense, just trying to get a feel for your level of experience. The reason I raise this is because while stainless is not that difficult to work with (it isn't all that hard), it does require you to know how to cut it and experience counts. Every lathe is different, even lathes of the same model, and every user is different. The feeds and speeds listed in tables and charts are intended for industrial lathes and may or may not apply to YOUR lathe.
You also need to know what you're cutting. 303 has sulfur in it so it machines easier and work hardens less. 304 is much harder to cut without work hardening and this is especially true with carbide inserts; 316 is even worse. Work hardening happens with SS because unlike most materials that eject the heat from a cutting operation in the chip, SS tends to retain the heat in the remaining material AND the tool. Temperatures at the point of cut can get into the red heat range on a heavy roughing cut, especially with carbide tools, so work hardening is a real thing. If you can, use 303.
The keys to turning SS is to use a sharp tool, coolant and you must keep the tool cutting - do not dwell or the tool will rub and build heat and you'll work harden in an instant in 304/316; feeds matter, especially with SS. The aforementioned CCMT and CCGT inserts will work and David will set you straight on inserts but I would reinforce that you need a positive rake insert on a small lathe when working SS. With that said, I much prefer a good HSS-cobalt tool for stainless steel because I can get it sharper than any carbide insert and I can grind it to reduce cutting forces so that the tool cuts easier without building a lot of heat. While I normally would turn SS on my Emco lathe, I have cut a lot of 303 and 304 on a little Sherline lathe with HSS tools so I know that these tools work. Cobalt will also hold an edge at high temps so the tools stay sharp longer, even with heavy cuts. The problem is that you have to know how to grind these tools.
Coolant matters, especially when using inserts. For me anyway, coolant is used to reduce temperatures at the point of cut as well as for providing lubricity so use some kind of cutting oil or coolant. Sulfur-bearing oils with EP additives work well, as does the water-based AnchorLube. A coolant stream is ideal but dripping coolant or cutting oil at the point of cut works well enough. Regardless of which way you go, use a LOT to try and keep temps down.
For threading, I own the aforementioned Carmex inserts and they work, especially for smaller threads where the helix angle is less of an issue. However, I actually prefer to use a good HSS-cobalt threading tool with 15 degree relief angles for SS because it cuts cleaner at lower speeds so I don't have to deal with work hardening a thread. I cut straight in with my Sherline and set the compound at 29.5 degrees on my Emco lathe and both methods work well.
Another tooling option would be to consider the threading tools from AR Warner; they sell both stand up and lay down style inserts that are sharp T-15 HSS inserts and should work well in SS. Their HSS CCMW turning inserts and SCLCR tool holders are also an alternative to carbide turning tools; they are sharp when new and are easily sharpened by flattening their tops on a fine or extra-fine diamond stone so you might look into them.
Whichever tooling system you choose, practice. These tools don't just magically make you capable just by owning them. You need to learn which speeds, feeds and depths of cut work on the machine you have and the only way to learn this is to cut.
My sense is that you're a novice hobby machinist. No offense, just trying to get a feel for your level of experience. The reason I raise this is because while stainless is not that difficult to work with (it isn't all that hard), it does require you to know how to cut it and experience counts. Every lathe is different, even lathes of the same model, and every user is different. The feeds and speeds listed in tables and charts are intended for industrial lathes and may or may not apply to YOUR lathe.
You also need to know what you're cutting. 303 has sulfur in it so it machines easier and work hardens less. 304 is much harder to cut without work hardening and this is especially true with carbide inserts; 316 is even worse. Work hardening happens with SS because unlike most materials that eject the heat from a cutting operation in the chip, SS tends to retain the heat in the remaining material AND the tool. Temperatures at the point of cut can get into the red heat range on a heavy roughing cut, especially with carbide tools, so work hardening is a real thing. If you can, use 303.
The keys to turning SS is to use a sharp tool, coolant and you must keep the tool cutting - do not dwell or the tool will rub and build heat and you'll work harden in an instant in 304/316; feeds matter, especially with SS. The aforementioned CCMT and CCGT inserts will work and David will set you straight on inserts but I would reinforce that you need a positive rake insert on a small lathe when working SS. With that said, I much prefer a good HSS-cobalt tool for stainless steel because I can get it sharper than any carbide insert and I can grind it to reduce cutting forces so that the tool cuts easier without building a lot of heat. While I normally would turn SS on my Emco lathe, I have cut a lot of 303 and 304 on a little Sherline lathe with HSS tools so I know that these tools work. Cobalt will also hold an edge at high temps so the tools stay sharp longer, even with heavy cuts. The problem is that you have to know how to grind these tools.
Coolant matters, especially when using inserts. For me anyway, coolant is used to reduce temperatures at the point of cut as well as for providing lubricity so use some kind of cutting oil or coolant. Sulfur-bearing oils with EP additives work well, as does the water-based AnchorLube. A coolant stream is ideal but dripping coolant or cutting oil at the point of cut works well enough. Regardless of which way you go, use a LOT to try and keep temps down.
For threading, I own the aforementioned Carmex inserts and they work, especially for smaller threads where the helix angle is less of an issue. However, I actually prefer to use a good HSS-cobalt threading tool with 15 degree relief angles for SS because it cuts cleaner at lower speeds so I don't have to deal with work hardening a thread. I cut straight in with my Sherline and set the compound at 29.5 degrees on my Emco lathe and both methods work well.
Another tooling option would be to consider the threading tools from AR Warner; they sell both stand up and lay down style inserts that are sharp T-15 HSS inserts and should work well in SS. Their HSS CCMW turning inserts and SCLCR tool holders are also an alternative to carbide turning tools; they are sharp when new and are easily sharpened by flattening their tops on a fine or extra-fine diamond stone so you might look into them.
Whichever tooling system you choose, practice. These tools don't just magically make you capable just by owning them. You need to learn which speeds, feeds and depths of cut work on the machine you have and the only way to learn this is to cut.
Last edited: