Bushing Neck Die for 375 cartridges

[Willbird]

The normal bushing neck dies sort of top out at 338 caliber.

C4HD and others DO make a large format bushing/die and C4HD does make some .500 OD neck bushings in the .390 range were 375 ctg fall but overall these days finding out if you are ordering an in stock item or ordering for an extended back order is a real PITA. Plus a .500 OD bushing with a .390 ID is pretty darn thin .

So I decided to make my own neck die which uses a .560 OD bushing.

I used a PTG die body, they are pretty cheap overall and it saves some time. They are 4140 steel which has no particular advantage. PTG gets $28 for them, while they do save time I'm kind of thinking next time I might just use some 12L14 for dies that will be left soft.

Here is the partially finished result.


Some of the focus here was "what can I accomplish in a spare hour" and I have a new to me laydown threading insert holder so the threads are not as mirror smooth as I would like, but it works for what we are doing. This is made from 12L14 steel.



I worked out a simple way to make some grasping grooves for the bushing retainer, overall I am not a fan of the knurling process, I like this a lot better, and the coordinates came out to nearly round numbers. To do multiples of this an indexer would make it faster but for 1 I just used the DRO. I plunged those straight down with a 1/4" endmill.





I made a test bushing out of 12L14 steel, it machines like butter, cannot easily hardened but man does it machine nice , and bar ends (leftover from cnc process that use a 12' bar) are cheap on Ebay. Serious long term bushings might be made from say O1 steel and hardened, then lapped perfectly round and to size.

[Willbird]

Here are a couple tools that make spur of the moment stuff happen easily and more efficiently.

For decades I have resisted using inserted threading tools in manual lathes. When I worked in a shop which had cnc lathes the inserts were kinda "free" and in stock. Overall carbide inserts maybe are not "optimum" for single point threading in a manual lathe for a couple of reasons.

One reason is to avoid crashing into a shoulder on the left we often run a fairly slow RPM in a manual lathe. If we are tapering out the thread often IMHO we cannot taper the same every time while not crashing into the shoulder . So it is easy to fracture the insert. And "full price" domestic mfg inserts can run $10 or more EACH which is over $3 a corner. But there are plenty of imports avail for more like $1.50-$2 per insert and that is what you see here. Cheap enough to have plenty on hand. The ones I have will not tolerate just stopping spindle while in a .01 per side cut, that will fracture the insert, we must taper out while halting the carriage motion.

But these easily will take .01 per side on a 7/8-14 thread to get the material dug out of there, then I generally take .01 on a side until it starts to look right, then .002 per side until I get close, then .001 per side followed by a spring pass (rerun without moving depth in) and check fit. If I made notes on the double depth used for different pitches (I will) I get as I do some different pitches a 5/8-18 like is on the part shown could be done real quick like. I suspect the compound degree marks on my Grizzley G4003 are not exactly correct so once I get a number dialed in the threads will look prettier.



The other tool is a "Micro 100 solid carbide boring bar". They really rock. They are not exactly "cheap", I just ordered one like the one shown but shorter so more suited to jobs like the bushing, it was $63 shipped. One cannot plow them into the bottom of a hole or drop the whole tool holder on the floor and not make them into carbide scrap . But they far out perform anything ground up by hand out of a HSS steel tool bit. They are far stiffer than a HSS boring bar. That is all about the Modulus of Elasticity .

[Willbird]

The Micro 100 solid carbide boring bars are made way down into tiny sizes like .039" minimum bore, IMHO at some size point they are not going to work out well in a manual lathe. But some prior jobs at cnc shops we extensively used the smaller ones and they worked great.

The part numbers on these go like this
BB-320750S So that is a .320 minimum bore that will bore .750 deep, the S means it is "sharp" with no corner radius. These IMHO can be hand sharpened as well so there should be some decent life to them as long as we do not drop the whole holder, or plow the tool into the bottom of a hole .

[nuclearcricket]

Willbird, you have a PM. Nice write up by the way.

[Willbird]

Willbird, you have a PM. Nice write up by the way.

TY, I just figured I'd share a few things I picked up on the project.

Bill

[redneck1]

What size is that insert? , I have some kennemetal inserts that don't fit my holder , if they will fit yours I'd be happy to send em your way .

[Willbird]

What size is that insert? , I have some kennemetal inserts that don't fit my holder , if they will fit yours I'd be happy to send em your way .

It is a 16ER AG60, might be a Mitsubishi insert that the importers have copied the shape/size ??

These inserts BTW are ER which cut to the left, an IR cuts to the right(correct for a boring bar).

The AG is the pitch range which in this case is .5-3mm pitch (comes out to like 8.7 something threads per inch).

The "16" is the inscribed circle IMHO....the size more or less, the 60 is the included angle of the thread, I do see 55's out there and we do not want those unless we are making whitworth threads . Also it looks like ACME inserts are avail too but those may take a different seat under the insert ?

Bill

[redneck1]

Dang , same inserts my cheapo China bar takes .
I'll find someone someday with a bar these things will fit .

[Willbird]

Dang , same inserts my cheapo China bar takes .
I'll find someone someday with a bar these things will fit .

They probably cost somebody a pile of $$ when purchased new .

[country gent]

We used 55* inserts for threads to be ground could get much closer to depth. saved the wheel wear, and still get a good bright thread

[Willbird]

We used 55* inserts for threads to be ground could get much closer to depth. saved the wheel wear, and still get a good bright thread

That makes perfect sense, new info .