View Full Version : Mystery Boring Bar

11-15-2013, 03:59 PM
I picked up a boring bar for $5 at a used tool store. It's in reasonable condition, and has one insert in the bar. I've tried to find information on the bar using google, but I can't seem to come up with a manufacturer that uses a naming scheme that matches the codes on the bar. The bar is 3/4" in diameter with 4 flats, about 10" long

It says S-STFOR-12-3 made in usa 08094 .

The insert is triangular, with a fairly large radius on the corners, a center hole with a screw, and a clamp. It is set perfectly perpendicular to the long axis of the bar, has about a 7 degree clearance angle, and appears to be mounted with a slight positive rake. The insert is perfectly flat on the top.

I can find a couple of references to S-STF0R 10-2 with a zero rather than an O, that are Kennametal bars, but the locking mechanism and insert mounting do not match my bar.

The S which indicates steel is probably right, as there is a little bit of surface rust.

Using the ANSI nomenclature on the center 5 characters suggests
S = Screw lock only
T = Triangle
F = 0 end cutting
O = other(not a zero in this case)
R = Right hand

If the 12 were referring to the diameter, that would make sense even though it is not in the proper place, as it is a 3/4" bar.

If the 3 were referring to the size of a triangular insert, this would be a 3/8" circle, which would result in the length of the side of the triangle of .6495, and the insert is clearly larger than that.

Can anybody help me with what I have? Or what insert should be used? For the latter, I suppose I could take the insert out and try to measure it up.

11-15-2013, 05:13 PM
Does the pocket have tapered walls or straight? If straight it uses something like a TNG, if tapered, it uses a TPG. Straight with a screw or stud, something like a tnmg. If you take then bar down to a machine tool supply shop they can figure out what goes in there.

11-15-2013, 06:20 PM
Sounds like the "O" or "0" is a "mistake", could it be a mis-stamped "C" ?

The general description sounds an awful lot like a STFC-R or STFCR boring bar, the "12" is a 3/4" bar but some makers make them as "-2" which use a 21.51 insert, other makers make them as "-3" which use the larger 32.52, generally a "TCxT" insert. Dorian for one makes a bar with those designations. My very limited experience has been not all of those hold down screws are the same size, so if you can figure out who the maker really is, you may save yourself a bit of hassle.

Edit: Kennametal, or at least one listing I found, does show an STFD but lists no corresponding insert (that column is there but blank), not in your size, still...

11-15-2013, 11:19 PM
It's pretty clearly a full circle. Here's the stamping on the bar:


And here's the insert pocket:


The clamp screw uses a .125" allen wrench, and the screw that retains the insert uses a .0625" allen wrench. The insert is about .125" thick.
The pocket that holds the insert is tapered to match the insert. I removed the insert and the clearance angle seems to be 10 degrees, as best as I can measure it.
I don't have any way of measuring the radius on the insert, and one of the tips seems to have been "touched up", but the distance across the factory corners of the insert is .601"

So, building on what others have said:

T-Triangular, that one is easy!!
P-11 degree clearance angle- I measured 10 degrees, but I could easily be off a degree
()-Tolerance Letter
B-The hold down screw is clearly a 90 degree head, and there is no chip breaker

3-I stood drill bits on the insert, and the inscribed circle is about 3/8"
2- Measured .125 thick
2 or 3- Can't measure the radius, but it's in the .030 to .047 area.

TPMB-322- Googling this comes up with a lot of references to the Warner HSS inserts, but they talk about an 82 degree countersink angle on the mounting hole. I don't think it's a HSS insert, as it is only weakly magnetic.

Found a number of TPGB-32x on Ebay, but the countersinks don't look right on some of them.

I guess I'll follow macona's advice and go down to a local supplier. I'll invest the money for a full price insert to find out exactly what I have...

11-15-2013, 11:45 PM
Looks like some parts are missing, I think there should be a round stud shat screwed into the hole in the center and then there is a clamp that holds the insert down. These are pretty much consumables so you should be able to get them when you get the inserts.

Probably not a TPMB, Probably just uses generic TPG-32x, *x is radius. That kinda looks like a carbide seat and not an insert. Radius is selected for the finish and what you are doing. Sharp inserts cut easier but leave lines at higher feed rated. They also allow you to cut into a corner better but are also more fragile. The more radius you use the more power is required for the cut but they have a smoother finish and are more durable.

11-16-2013, 02:32 AM
Confused, yes...to me, strictly speaking in my own mind, that bar is not a screw down or solely screw down which, again to me, is one of the "S". But why let confusion ruin a good opportunity to search.

There is a company called "spe-d-cut" http://www.spe-d-cut.com/PDFS/catalog/spe_d_cut_catalog_lkd.pdf that is a pdf file and sometimes those don't link well for me, anyway, they do list a series of boring bars STFOR/L. Some of those bars, including I think the one you have, use an insert screw, a bridge clamp, a clamp screw and a clamp clip. They list inserts as TP TPG, TPGB. [That pdf link seems to work, their listing of inserts also confuses me as "TP" does not seem complete and they did not designate blanks or "x" as position holders so...TP then TPG, then TPGB]

Also found a "STFOR" listed as a #302 insert holder for Narex/MTE Universal Boring Head and in that case the "0" referred to 10 degree clearance angle (the only other reference I could find was an "O" for other). For that holder they list a TCMT 110202 as the insert. Oh, and that listing it was strictly a screw hold down, no clamping and illustration was too small to see if a seat was used.

11-16-2013, 07:09 AM
You have to bear in mind that the insert that came with it may or may not be a correct one. That assumption has lead me astray before when acquiring used tooling.


11-16-2013, 11:52 AM
Sorry about the confusing pictures, there is a small 90 degree taper flathead hold down screw, and a clamp that goes on top of that.
I hadn't thought of the fact that the insert might be the wrong one!!! I don't think that the triangular piece shown is a seat, as the clamp sits 1/8" above the insert before you start screwing it in place. Also, the top of the insert seems to be on the centerline of the bar.

RussZHC, I think you nailed it. That Spe-E-Cut catalog is something. The STFOR bar is on page 214. The Diagram and description (0 End Cutting, Steel Shanks, Positive Rake, 11 Relief Angle Screw Down Inserts) match. The 3/8 Inscribed circle and 1/8 thickness listed in the chart match the insert I have. The picture of the "bridge clamp" and "clamp clip" match as well. The only oddity is that they don't list an R bar in that size.

I'm considering the mystery solved!! Thanks to everyone for the help. What did we do before the internet??

11-16-2013, 04:02 PM
If it helps, 08094 is the ZIP code for Williamstown, NJ.

11-16-2013, 06:46 PM
If it helps, 08094 is the NSN supplier code for Boston Gear.