Internal Threading Bar

[4GSR]

Tool-Flo in Houston has them in their API catalog, and will grind just about anything not in the catalog. I have a few from the "old days" lol. That's why I made that bar. I already had an OD holder, and had a pile of internal inserts.

My brother worked at a shop back in the early 1980's that used vee notch tooling. Triangle Grinding developed it from what I remember. Sandvik sucked them up! Anyways, they would use one end of the insert but would not use the other end. Complained it affected their measurements when cutting threads. So he would bring a few home for my dads shop every once in a while. Dad did just like you did, made his own holders. Never ran out of threading inserts. I don't remember what happen to the tools when we closed down the shop. I know we had nearly 10 lbs of inserts for those holders laying around.

 

[epanzella]

The problem with such threading tools is that there is no front relief to allow for the thread helix, unless you build a lathe fixture to cut the 60° disc at an angle, and then you have to know the projected apex of that angle to properly grind the top, and then as you sharpen it, that apex "rolls" around until you end up with zero or even negative front relief. I know lots of people use them, but they are technically at a disadvantage.

I mill the cutter to a few thou under half diameter. I sharpen it on a flat stone at the top. The natural taper of the 60 degree cut seems to give me all the relief I need. I've cut from 13 to 40 tpi without a problem. Maybe with coarser threads I would need an angle to the helix. The threading tools I used to buy never seemed to have a certain helix angle. I build smokeless powder muzzle loaders and my most common cut is 16 to 20 tpi internal threads

 

[Tony Wells]

Well, when they give you only a few minutes to cut a tool joint, like the old days, yeah, I guess it could effect the tip to tip dimension so if their holder used a stop on the opposite end, they would have to comp for it, either with an offset in NC/CNC or not hitting gage at the zero point on the dial..... lazy rascals.

 

[4GSR]

Here's a boring tool that was carved out of a piece of 1" square HSS. I bet it took a couple of days to grind that all down.

 

[Tony Wells]

Espanzella, rest assured, the front is rubbing. Maybe not much, but there is an allowance for thread helix angle either on the inserts, or built into the holder on factory tools. On finer threads, you're getting away with it, but you're right....the coarser the thread, the more pronounced the helix effect is, and also the smaller the diameter it is, the more important it is.

 

[Tony Wells]

LOL Ken, I can't believe that's the only piece of HSS there was. I bet it was a broken something else first.

 

[4GSR]

LOL Ken, I can't believe that's the only piece of HSS there was. I bet it was a broken something else first.

Yeah, It looks like it was a larger size boring tool of some sort before becoming a very small boring bar. This was in a lot of about a dozen tools that were ground as boring tools and mostly for threading that I bought off of eBay.