Threading Tools Keep Breaking

[BGHansen]

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

Good point on supporting a U.S. company. I work at the GM plant in Lansing, MI; Lansing Grand River where Cadillac CTS, ATS and Chevy Camaros are built. We would appreciate the rest of the country considering our products when they are new car shopping. It is a global economy; our transmissions come from France, wire harnesses from South America, many other parts from Mexico, Canada, China and Korea. Regardless, about 1500 Americans putting them all together.

Bruce

 

[aliva]

This is one type of insert you need. there are other design's, check out Carbide Depot.com

 

[BGHansen]

View attachment 123211This is one type of insert you need. there are other design's, check out Carbide Depot.com

Secret decoder ring required for threading inserts. The one in aliva's post is probably a 16 ER AG60. The first two numbers are the insert size. 06 is 5/32", 08 is 3/16", 11 is 1/4", 16 is 3/8", 22 is 1/2" and 27 is 5/8". The first letter will be E for external threading or I for internal threading.

The next letter is R for right hand threads, L for left hand. The ending numbers are for the threads per inch/range of tpi. A60 is 16-48 tpi. AG60 is 8-48 tpi. G60 is 8-14, N60 is 5-7. If they end in "UN", the number ahead is the tpi (one thread size, no range). For example, 16 ER14 UN is a 3/8" insert, external right hand thread at 14 tpi. Metric inserts are similar; number followed by GM. A 22 IR3.50 GM is a 1/2" insert, internal right hand thread at 3.5 mm pitch.

I mention it because I bought a set of ten 16 IR 14 UN's off eBay for around $22. Got them and noticed the threading "V" was not as pronounced as the 16 IR AG60's I already had. Many places sell them, best prices I've found are on eBay though you'll likely be getting them from China.

Bruce

 

[Silverbullet]

This is one area where a turret lathe is superior , the die heads are adjustable and collapsible taps will out perform single point threading. Another problem with cutting threads is the pressure put on the tool and holder and cross slide makes them flex which is what will cause the chipping your getting. My Logan lathe hates single point threading I've done it and have watched the compound slide bend and flex at the beginning and ending of the cuts.

 

[planeflyer21]

Secret decoder ring required for threading inserts. The one in aliva's post is probably a 16 ER AG60. The first two numbers are the insert size. 06 is 5/32", 08 is 3/16", 11 is 1/4", 16 is 3/8", 22 is 1/2" and 27 is 5/8". The first letter will be E for external threading or I for internal threading.

The next letter is R for right hand threads, L for left hand. The ending numbers are for the threads per inch/range of tpi. A60 is 16-48 tpi. AG60 is 8-48 tpi. G60 is 8-14, N60 is 5-7. If they end in "UN", the number ahead is the tpi (one thread size, no range). For example, 16 ER14 UN is a 3/8" insert, external right hand thread at 14 tpi. Metric inserts are similar; number followed by GM. A 22 IR3.50 GM is a 1/2" insert, internal right hand thread at 3.5 mm pitch.

I mention it because I bought a set of ten 16 IR 14 UN's off eBay for around $22. Got them and noticed the threading "V" was not as pronounced as the 16 IR AG60's I already had. Many places sell them, best prices I've found are on eBay though you'll likely be getting them from China.

Bruce

I learn something on here very often but the vexing question of how inserts are titled has bugged me for years!

Thanks Bruce!

 

[Chris Hamel]

I have done fine with the brazed on carbide bits. A couple of things. One - I grind a lot more relief on the bit from the way it comes from the factory. I use a green silicon carbide wheel.. Second thing I have found is that when I get near the end of the operation, I will often repeat a pass without advancing the compound it will still take off some metal (guess my old South bend has that much flex in it). Keep in mind that when you get near the end, you are only advancing a few thousandths

 

[Tozguy]

Rigidity, deflection, and tool life/cost are reasons why I thread by feeding with the compound set at 29.5 deg. and this, even for fine pitched threads. It also gives me only one side of the tool to sharpen .
A narrow deep cut works better on my hobby lathe. A wide but shallow cut (as in plunge cutting) is an invitation to chatter. I don't like it when a clean up pass has a lot to clean up.

It is important when sneaking up on final thread dimensions that I can rely on getting what was dialled in. I am a fan of smooth and close fitting threads which doesn't happen when there is stuff going on that I don't control. So the lathe is set accordingly and worked well short of its cutting limits.

 

[kennycrawford]

I am a relative newbie to machining too. I own the G4000 lathe and have threaded on it. On the small diameter you stated, 8mm, the fact that the larger bits you were using probably rubbed on the thread while it was cutting. It is because for threading you are cutting a spiral and you need to have clearance for the thread to pass safely as the tool moves down. I ran into this with the insert tooling bought with my lathe. I ruined a bunch of stuff before finding forums like this and Youtube to help me along. I hope I explained this clearly, I am guessing one of the other previous posts already mentioned this but I have no background in the machining trade and the terminology can still be foggy for me sometimes.

The G4000 lathe in itself is a project. Between the Pitkin donut , 4 bolt clamps, gib straightening, headstock aligning, extending the cross slide and putting bearings in the compound and crossslides, I have been busy learning how the machine operates. I can tell you that what is in my garage now works so much better than when I purchased it nearly 2 years ago it might as well be a different tool. Just my observation.

 

[benmychree]

Looks to me that you have too much flex in your tool post/tool holder. Typically things start out fine but as you get towards the last pass, the tool will grab and go under center, causing a chipped cutter. I can tell you if you are using a QCTP, a wedge type has a big advantage over a piston type.

I have had both wedge and piston type tool holders, and there is really no difference in ridgidity between the two; I have accidently forgotten to lock the holder in, and even parted off that way with no chatter. According to Aloris, the only reason for the wedge type is that it is more positionally accurate. As to threading tools, I very much agree with the posters on this thread; use HSS, learn to grind them from scratch, or use the Aloris threading tool, which is form ground and only needs sharpening on the top. For internal threading there is the HSS boring type tools with integral shanks or threaded on tips made by Bokum; they are also form relieved and sharpen on top, preserving the thread angle for the life of the tool; I have found many of them on E Bay, and they also make lead style and flat bottom boring tools that are a pleasure to use. I take issue with the tiny cuts recommended in the posts; perhaps they are necessary for tiny machines, but they will tend to dull cutting tools more rapidly that deeper cuts, especially the first cuts can be deep, then ease up. Also I see no mention of lubricants, which are quite necessary for threading steel; I use Tapfree for most all lathe work.

 

[armytbone]

What a wealth of info. Thanks everyone for the replies! Just digesting all of the tips is a task unto itself. At first, the thought of angling a tool with a 60 degree tip made no sense. If I turned it 29.5 degrees, it would end up as a flat cutting surface parallel to the workpiece. That, in turn, wouldn't make any grooves! But then it clicked. As everyone stated, I didn't have the correct cutting tools. A correct tool that can be fed on the 29.5 degree angle set on the compound would allow the tool to cut on one side only, rather than feeding at 90 degrees and causing immense stress on the tip and both sides of the tip. It's no wonder that I broke a few! Alas, I will be ordering the correct tooling.

Which brings me to another concern -- the tool post. That four position turret tool post holds 1/2 inch bits a tiny bit low of center. I have a handful of feeler gauge fingers to be able to shim, but is there a good QCTP for the G4000 that would make for a good upgrade? Thanks for ideas.