Need Tool For Internal Threading

[4GSR]

Hare's a few "home brew" threading tools I've collected over the years.

 

[epanzella]

You can make your own as small as you want using your lathe and some O-1 tool steel. I used 5/8 inch O-1 square stock that fit in my BXA toolpost. Turn the 60 degree threading profile with a 60 degree carbide or HSS cutter. Mill or grind off what you don't need and you're left with a perfect 60 degree threading tool. You need to cut it a little below center to get your relief in the hole. If you grind it go slow and keep it from getting red hot. If you mill it just stick it in the tool holder (what I did) and adjust the height by eye. If you don't have a better way to hold an end than just sticking it in a 3 jaw, don't forget to wrap it in some tape or paper so you don't have hard on hard. Heat the last inch of the cutter with acetylene, map or propane until it's red and no longer magnetic (1450-1500DegF) and quench in oil. Good to go. I tried tempering but it stays sharper longer when I use it in it's hardest state. By treating only the last inch of a 2 inch shank the untreated part seem to provide the needed "give" to avoid shattering. The last picture is the treated threading tool and the boring bar needed to make the hole. I needed to work inside of .460".
Ed P

 

[rwm]

Thanks guys. Great info.
It might be fun to make my own out of O-1 although I have never turned or machined it. I was also thinking about brazing on a piece of carbide on a shank.
Then again, those brazed tools are so cheap at Shars.....
R

 

[bosephus]

0-1 drill rod is nice stuff to work with i have been using a lot of it recently to make die's .
if you watch enco for 25% off and free shipping deals you can buy it slightly cheaper then plain old mild steel from most online sources

 

[bbutcher]

This will be my first adventure into internal threading. I need to purchase a tool for internal threads 3/4 x 16. I would like to be able to do as small as 1/2" . I prefer indexable carbide. My lathe (Asian 9 x 20) accepts 1/2' tooling. The toolpost will fit 0.750" but that would put me above center at the tool tip.
I was looking at something like this:

http://www.use-enco.com/CGI/INSRIT?PARTPG=INLMKD&PMPXNO=7908975&PMAKA=422-3038

The shank looks to be too large and would put my tool above center? I do not see any with 1/2" shanks? How are these tools typically held in the tool post? Any advice would be helpful.

Another thought. Should I just take a piece of 1/2" CRS and machine my own holder to fit that insert?
R

Carbide threading inserts are a possibility. They are available in a variety of shapes including the ones you found at Enco. Yes, you could make your own tool holder, but it depends on whether you have more time or more money. The carbide insert must be angled correctly to get the required rake angle, so the tool holder can take some time to fabricate.

Some single point carbide threading inserts are specified for one thread only (e.g. 16 TPI) and they will cut not only the vee sides of the thread, but also cut the inside diameter making a nice thread, but you need a different insert for each different pitch. Note they also make IR (internal) and ER (external) series inserts. Note that if you need a left hand thread, you may need a different insert, or perhaps use an ER series and rotate the part in reverse, cutting on the back-side of the bored hole for an inside thread. Many of the indexable ones have three cutting points and can be rotated when you wear out or damage one surface. There is also a series of inserts that will work for a range of pitches that do not cut the inside diameter of the hole, more like a vee thread; more versatile, but not quite as precise. It can be tricky getting the tool holder and insert to fit inside smaller diameter bores, so 1/2 inch diameter indexable insert may be pushing the limit. Multi-point threading inserts are also available. For smaller diameters, you probably are better off with a single point boring bar type tool. Little Machine Shop has a good selection, also check E-bay.

If you Google "inside threading lathe tools" and images, you will see a variety of shapes and styles.

The tool can be held in a boring bar holder for a QCTP or if square in a standard holder, just adjust the height to be on or very slightly above centerline of the part. Remember for inside cutting above centerline is good, for outside, a tiny bit below is good, since in both cases if the tool digs in and flexes, it pulls away from the surface rather than digging in deeper.

 

[Rick Leslie]

For common threads, I always try a tap first. Like has been stated; if your hole is true, the tap should follow it. The problem with hand taps is they are usually cut a little large on the thread OD and make for loose tolerance threads. I suppose this is to accommodate the millions of import bolts and screws on the market. If you want tight threads, you may have to single point the ID.

Compounding your problem is the small ID requested. Getting a boring bar into a .500" hole is tough. Getting one with a threading insert to work is really an execise in patience. I would practice on a few scraps with different cutters/methods before trying it out on the real thing.

One final thought: When I thread internally, I try to thread on the back side of the work with the cutter upside down. This puts the cut on the back wall of the hole which makes it easier to see, plus you use the same motion for your 'turn-out' at the end of a cut as you would on external threads. It works much better than it sounds.

 

[barrels]

go to enco get a tru-flow .5 threading bar uses n2 inserts

 

[benmychree]

Another alternative is the form relieved HSS threading tools sold by Bokum Tool Co., they are made in many different sizes from tiny to quite large; they also make boring and grooving tools in HSS and carbide; some have integral shanks, and others screw onto threaded boring bars. They are sharpened by simply grinding on the top of the form, which can be done easily by hand, or with a fixture if you have a surface or tool and cutter grinder. I avoid insert threading tools due to the cost of the inserts and the fact that they are easily chipped, also I believe the Bokum tools are less bulky, thus fit into smaller holes and make chip flow better. I have been using their tools since about 1970 and really like them.