Help with "fuzzy" threads . . . .

[rcsimpson]

I am learning single point threading and assume that this will most likely be RPM related but I'm spinning as slowly as possible right now (70 rpm) so I don't screw up anything.

Threading 1/2 x 28 back to a 90 deg. shoulder, although I have a slight relief cut at the shoulder so I can quit easily.

Using partial profile thread triangle insert. I have fairly good luck if I make 3-4 passes and finish with a die. If I try to make the final passes the threads are "fuzzy". I know with partial profile I'll have to do some kind of finishing or just chase with a die.

Material is chrome moly gun barrels. Although I can do the same on aluminum and it shares the same "fuzzy" look.

[mc-motorsports]

I would go up in RPM and use uncoated inserts. You don't want to use TiN coated inserts on aluminum, titanium or materials containing chrome, including chrome moly or SS. If your using coated inserts, it could be galling, otherwise more than likely just need more RPM. Lots of coolant and check your % levels or use a tapping oil.

[rcsimpson]

I'm not sure how I'll ever pull this off. If I have a Grade BXC coated partial profile insert the Carmex site is telling me 130-300 sfpm for alloy steels. For a 0.5" diameter this would be 993 rpm on the low end of 130sfpm. There is no way I'm going to stop at the shoulder with that fast of an RPM.

[lerman]

Cut in the opposite direction. Away from the shoulder.

Ken

[rcsimpson]

So I'd have to get "left handed" tooling? SCRATCH THIS
Looks like I can use RH tooling but change out to a negative anvil on toolholder. Based on other comments I probably will switch out to a full profile insert that is non coated as well.

[mc-motorsports]

If you can flip the tool over, you can cut the opposite direction. Other than that, 300rpm and an uncoated insert should do the trick.

[rcsimpson]

Thanks for the all great info. mc-motorsports you've been very helpful. I looked all over "heck and back" today trying to find an uncoated lay down thread insert. Seems like everybody makes them coated with something or other. Any good recommendations?

This is the holder and tooling I got from Enco.
422-3701 16 ER A60 BXC PARTIAL PROF THD INSERT 3 $14.68 N $44.04
422-3041 SER 0500 F16 1/2 SHANK EXTERNAL THD TOOL HOLDER

It's just 3/8 in. lay down triangle inserts. I also have some two point Kenemetal stuff but it's coated too. And it seems to break REALLY easily for some reason.


I think this InterState one may work out. Not sure:

Lay Down Threading - Indexable Inserts ANSI Number: 16ER28UN Material: Carbide
Industry Grade: TCN55 Thread Type: UN Thread Style: External Pitch (TPI): 28
ANSI Number: 16ER28UN
Material: Carbide
Industry Grade: TCN55
Inscribed Circle (Inch): 3/8
Thread Type: UN
Thread Style: External
Pitch (TPI): 28
Rotation: Right Hand
Insert Style: 16ER

[mc-motorsports]

The enco insets you are using are TIN coated...

http://www.jtsmach.com/jtswebshop/Ca...ling/CN747.asp
grade C5 is what I use, and what you need. Uncoated tungsten carbide, made for lower speed threading for steel alloys. Not sure if these inserts will work with your tool holders, but I buy everything from JTS, they are local for me.

MC

[mc-motorsports]

Oh, and the problem your having is most likely what we call "tearing". More speed, lots of coolant.

[CarbideBob]

A: Use cutting oil
B: More Speed, as much as you can stand. (yea I know stopping in time gets scary, I put a dial indicator on my carriage so I can tell when I'm coming up on my stop point.)
D: up sharp (non-honed) insets (PVD coatings only, CVD is always honed)
c: More positive rake (top face) tooling

Don't know why you can't finish this thread with a partial profile insert.

Not sure what you definition of chrome moly steel is.
If this is 4130,4140 or 6150 type steel then this is what Tin coating was invented for.

This is one case where "cheating" the tool above C/L may help (gives a more positive cutting action).
Bob

[mc-motorsports]

Not sure what you definition of chrome moly steel is.
If this is 4130,4140 or 6150 type steel then this is what Tin coating was invented for.

Chrome-moly was given it's name by the chromium content of the material, obviously. TiN is a Titanium based coating which forms oxides and are not reccomended for aluminum because aluminum forms oxides which in the case of rubbing the two together creates gulling.

You can argue that the chromium content of Chrome-Moly is minimal, yet manufactuing parts for Swagelock, Parker, Whitey and Cajon, experience in CNC lathes where less than 20 micro finish, no rips or tears is critical to where they will regect the complete order if they find 1 part in 100, you don't use coated inserts. Will the insert last longer? Sure! I love TIN endmills for 4140, but not for turning. TIN endmills and inserts are great, I can't say they out weigh uncoated inserts as much as the manufacture says they will, but they are worth the additional cost when you divide cost per part as I used to do.

His definition of "fuzzy threads" is more than likely "tearing" which I've heard a lot about doing production lathe work and making precision fittings for the companies mentioned above. It's a simple fix, more RPM, uncoated inserts and good coolant.

[mc-motorsports]

Whoops, forgot to add that Chromium or chrome is another material that forms oxides as we know that will create what we know as gulling when rubbed against another material that form oxides such as titanium or aluminum. How ever minimal in certain situations...