7/8" 9tpi...what insert ???

[Brian H]

I am looking in my little black book and trying to decipher which threading insert I need to do a 7/8" 9tpi thread. I have a 60 deg tool I'm trying but it is not looking right. I only have an 11ER insert tool and its too small for the threads.

I measured the 60 deg tool with my guage and its spot on but its not cutting nicely so I want to go to an insert tool

 

[PeterT]

This calculator might help you size an insert or grind a cutter. Coincidentally I was just looking at this when generating helical threads in cad, the root flat starts getting larger on the bigger threads (0.014-0.020" in this example). Sharp vee's start looking a little odd. There is a formula that determines root & crest as a function of thread depth. I'm assuming inserts take this into consideration over a bracketed thread span but I don't have any myself.

UN imperial screw thread calculator

theoreticalmachinist.com

 

[Susquatch]

I am new at this too so take my advice with a grain of salt.

In days gone by, I would have ground a nice 60 degree form in a HSS tool and then put a nose on it per @PeterT 's chart info above.

If I were to guess, I'd suggest your nose is too pointy. Even a sharp square nose is better than one that is too pointy.

If it were me today, I might get a ER9UN insert and try it.

The problem is getting just one insert. 10 is easy peasy.

Accusize sells an assortment if you want to try that and get some other sizes too.

Threading Inserts, Carbide, Tin Coating, Replacement of 12-Pc-UN-Threading Set

The Accusize Inserts for UN External Threading tool holder Set is commonly used as the following tools (and solutions): Inserts for UN External Threading tool holder Set, etc.

accusizetools.com

They are out of stock right now though.

Also, the set has 8 and 12 but no 9. But I'd bet good money that the 8 would work if you cut till the nut fits using the OD from Peter's info. But again, I'm new to insert threading too. So no guarantees. It's just what I would try to do.

 

[MrWhoopee]

16ER-AG60 will cut 8-48 tpi. Since they cut such a broad range, the tip will be sharper than necessary for a 9 tpi.

If you have the time, here's where I get my threaders,

https://www.aliexpress.us/item/3256805517605965.htm

and inserts,

https://www.aliexpress.us/item/3256805935771680.htm

 

[RobinHood]

16ER-AG60 will cut 8-48 tpi. Since they cut such a broad range, the tip will be sharper than necessary for a 9 tpi.

If you have the time, here's where I get my threaders,

https://www.aliexpress.us/item/3256805517605965.htm

and inserts,

https://www.aliexpress.us/item/3256805935771680.htm

That insert will work just fine if you set the compound inline with the z-axis and plunge in to depth of a 9TPI thread. Then just use the compound to widen the thread to proper dimensions. The root radius will be a bit off, but should not matter. The crest radius can be massaged with a file.