Grinding a barrel throat.

[country gent]

When we mounted a new diamond wheel on the grinder hub we dressed and trued it by grinding a piece of softer steel. the steel would break down the bonding agent releasing the diamonds and true the wheel up. A cleaning with the white stick and it would grind carbide to a mirror finish.

With a die grinder mounted in the tool post I have ground in lathe 3 jaw chucks but this was with 3/8" shank bits and a heavy die grinder.. THe came out very good and would normally run under ,001 until some one put a pipe on them.

With a 1/8" shank mounted point in a light die grinder dressed properly extended 1"+ ahead of the collet. The play in most die grinders bearings leverage of the extended point ad slow speed of the grinder ( a 1/4" mounted point should be running in the 50000 rpm range) grinding straight true and round is going to be hard. On the lathe straight is going to depend on the machine as there is no "adjustment" for taper from the carriage travel alone. With this set up .002-.005 run out ,roundness and straight ( TIR ) would be good.

With a solid heald, parker majestic, moore or other ID grinder things will be much better. In this machine With this set up holding .001 should be no problem you have the means of adjusting for taper. a spindle thats running up to speed can dress the wheel much better and truer.You also have better control of size and depth. These machines are not always available in most machine shops let alone a hobby shop.

What might be quicker easier and more accurate for what you want to do is a small carbide boring bar in the tool post sharpened and honed to a fine edge. A 5/16" bar with extended 1" or so will be much stiffer than the 1/8" shank wheel extended. It will be easier to cut true and round. set up will be easier. less spring in the tool also. Set up a boring head in the tailstovk and you have taper adjustment thru the tail stock.

Set up is going to be critical here the barrel will need to be running dead true to center. the boring bar sharp and set to center feeds and cuts will be light. Getting thetouvh to start that far in is going to be hard measuring the size that far in harder. Here pin gauges will be a plus. When setting up the bore of the barrel will need to be indicated in with a sug pin then the chamber checked if your lucky they will both be centered if not then one will need to be "fudged in".

I would think the starting point would be a good chamber cast to see what is there for sure and certain. This will show what your working with. for the touch off of the tool a this brass ring fitted to the chamber end and a .030 wall thickness allows a touch where it can be seen and at a known point. Here once touch is made come out .025 and feed in .001 a pass until desired size is reached.

[Bent Ramrod]

If you have the lathe and grinder setup, it’s at least theoretically doable.

The late, great Rudy Kouhoupt (of Home Shop Machinist fame) set a toolpost grinder up at the proper angle and ground the irregularities out of the Morse taper in the spindle of the Atlas milling machine that he was restoring. He said it ran true afterwards. Presumably the mandrel just sat in a little deeper in the spindle socket afterwards. I’m probably going to have to do that on mine sometime, as there is a noticeable “laloop” in the cutters as they spin, with only 1/3 of the teeth actually doing the cutting.

I am not looking forward to this with relish.

If I dared to do a barrel throat, I would do a chamber cast, measure the dimensions and angles with a comparator, set the grinder in the compound at the desired angle, set the barrel in the chuck with zero runout, put tinfoil on the ways, run the lathe backwards, lock the apron down and gingerly move the stone in and out with the compound feedscrew, looking for sparks and backing out the regular feedscrew a teensy bit at a time. A dial indicator might help here. When the full surface started sparking, I would probably stop the process and examine.

I would also probably have a spare barrel handy, and be prepared to chalk the whole exercise up as a “learning experience.”

[DougGuy]

OP's barrel is CASE HARDENED. Not Melonite or Tenifer (salt bath) treated. The surface hardness of his barrel FAR exceeds the hardness of the salt bath treated barrels. I crowned his barrel in my lathe with a carbide cutter, and pressing the cutting edge against the muzzle produced a very loud squeal, and did NOTHING but shine the end of the muzzle, until it suddenly broke through the case hardening and into the softer steel underneath.

The steel under the case hardened layer is pretty soft, as in butter compared to even a standard WWII era 1911 barrel.

You cannot "shave" a case hardened piece with carbide, you have to break through the case hard layer completely. This is why I declined to attempt throating it with my $300+ carbide reamer, because once the case hard is broken through, the throat will be GROSSLY oversized, and now down into the soft metal underneath which would erode away VERY quickly under live fire. To throat it, it would cut off all the protective layer. Plus, at a cutting diameter of .359" it does not cut big enough to break through the case hard, and the cutting flutes of the reamer would be damaged in the process.

The only way this could be throated, is with a tool post grinder which would not break through the case hard layer but very slowly grind away some of the surface of it. The abrasive would need to be exceedingly fine, which would mean quite a while at the lathe, and most abrasives will change shape rapidly once applied to the work, so you'd spend more time dressing and shaping the abrasive periodically than would be practical.

Also, the abrasive would be mounted on a 1/8" diameter mandrel, or shaft, which would need to stick out of the chuck the length of the chamber plus the throat, so now you have this thin and very bendable shaft that is unsupported for that amount of length, so any pressure applied against it in a side load direction would cause it to flex a lot more than you would want. Example: Each time the abrasive encountered one of the lands, it will flex more than it would in between the lands as the resistance grows, then once it passes over the lands, it cuts deeper in between the lands than on top of the lands and you have this hexagonal shape to the freebore, it would NOT be round by any means.

This is one of those situations that just because something CAN be done, doesn't mean it should. I would strongly suggest an aftermarket barrel for the Shadow2, live with the throat as is and size to function fit, or use a different gun altogether. I realize these were meant as a competition pistol to withstand a high round count, you are just stuck with the dimensions of the throat and not much can be done about it successfully.

[M-Tecs]

If the barrel is a CZ Shadows 2 it is not case hardened. Per CZ it is nitride coated. https://cz-usa.com/product/cz-shadow-2-black-blue/

Titanium Nitride (TiN) is a very hard surface coating applied to metals in order to improve the surface properties. It is extremely thin (<0.0002"). The primary benefits are increased hardness, wear resistance, corrosion resistance, and reduced surface friction.

Vickers Hardness: 2400 – 2600 Hv (>80 Rc).

​This Vickers Hardness correlates to a hardness considerably above 80 Rc. (Rockwell C is not used above 80 Rc (1850 Hv)).
Harder than Carbide.

If it was mine I would leave as is. Due to the nitride coating your options are limited. Lapping, grinding or EDM is about it.

On a side note Ferritic nitrocarburizing or FNC, also known by the proprietary names Tenifer, Tufftride and Melonite as well as ARCOR, is a range of proprietary case hardening processes that diffuse nitrogen and carbon into ferrous metals at sub-critical temperatures during a salt bath.

Ferritic Nitrocarburizing creates a shallow surface layer of epsilon iron nitride compound that typically has a hardness ranging between 58-65 HRC.

Normally 55 HRC is considered the upper end of hardness to be machined with carbide and realistic tool life. That being said I have successfully re-chambered Melonite barrels with carbide reamers. Not barrel related but I have turned 65 HRC with carbide tooling but tool life is very limited. I've also faced carbide with Polycrystalline Diamond tooling but you need a very rigid machine to be successful.

[DougGuy]

I can cut a salt bath hardened barrel rather easily with carbide. It crowns very quickly in the lathe, and the swarf that comes off does so in separate shards, not a ribbon like softer steels. I can throat them just as easily with a carbide reamer, and the swarf comes out of the throat just like it comes off the crown, it's very similar to the dust that accumulates at a brake drum lathe. It's very easy to shave just half a thousandth, or more, when reaming the throat for freebore. It does not at all react to machining like it has a harder outer layer.

The Shadow 2 barrel, despite what CZ claims, was a BOOGER BEAR to crown in the lathe. I pressed a sharp carbide cutter against the muzzle and kept increasing the force, it shined the muzzle where it made contact, then let out a very loud squealing sound, and finally broke through into the softer metal underneath, taking a good bite of material when it did. This was my experience with the OP's barrel.

It is extremely thin (<0.0002").

Nosir, no way the hardened part of this barrel is that thin. Whatever they used on that barrel, whatever they did to it is definitely thicker than that.

[john.k]

Should be easily set up to run true to a few 10th,or even 1/10 is possible .however ,I suspect the overhang in the grinding spindle would result in chatter the moment the wheel touched the metal.........Anyone whos done any grinding at all will tell you that soft metals are the problematic ones ,harder the metal ,easier it is to grind.....Id give it a go if it was mine,however a customers job ,then I would hone it ......diamond dust cuts quite quickly on a properly prepared hone...........please note,stirring abrasive slurry is not honing.

[dverna]

Decades ago my mentor took my S&W M52 barrel and stubbed a Douglas barrel into it.

If there is enough meat to do that, it will allow you to cut a new chamber and the leade/throat you want. That would be an option to save the barrel if you try grinding or lapping it and it does not work out.

[Flailguy]

Thank you all for the responses! I am by no means a machinist, but I believe I will attempt this on a cheaper ar barrel prior to the cz barrel and if it goes well I will attempt it on the cz. I also need to buy some pin gauges and other measuring tools before I try it. if anyone has any other ideas/suggestions please share!

[Flailguy]

I will also attempt to source some quality 1/4" shank diamond bits for the added rigidity.

[Texas Gun]

Die grinders guns worst nightmare and guys willing to use them on guns the machinist worst nightmare

[DougGuy]

if anyone has any other ideas/suggestions please share!

You will need at minimum a lathe with a 4 jaw chuck, and a GOOD dial indicator on a mag base. You will need to fit a very snug gage pin into the bore, and index off this gage pin right behind the barrel hood. If you can't get it within .0001" here keep trying until you do.

I once had (before it self destructed) a really cool Cratex air driven high torque rotary tool that I mounted in a boring bar tool holder on my toolpost and made a toolpost grinder out of it, I did a few DW forcing cones with it while it lasted, it MIGHT have throated a 9mm barrel but I doubt it due to the length of the shaft sticking forward of the chuck. I have since seen some China mandrels with 1/8" and 1/4" chucks that would do what I need in an internal toolpost grinder but I haven't seen enough call for one yet, they are roughly $200 or so.

DW forcing cone ground on 5 degrees with 320 grit mounted stone then polished out with fine scotchbrite:

Attachment 269443

Note: the DW barrel is just about as hard as the Shadow2 barrel, pressure against the carbide to break through the hardening and crown the muzzle was very close in nature to what it took to crown the Shadow2 muzzle.

[M-Tecs]

. if anyone has any other ideas/suggestions please share!

I would start with a quality chamber cast or pound cast to see how it compares to a SAAMI chamber and what actually needs to be done. That can be found on page 27 https://saami.wpengine.com/wp-conten...sting-Copy.pdf

The biggest challenge will be blind touching off on the 2 degree leade angle. You can go a little larger than .358" but if you go too large you lose headspace. If I was doing this with this method I would turn a steel chamber insert with a .360" ID so you have a diameter touch off reference point. Set your tool so flex cuts smaller not larger. Example would be boring bar slightly above center. Same for grinder rotation. You will also need a travel dial indicator or digital readout for the carriage. You will also need a good understanding of the compound backlash or a travel indicator for the compound.

If you go too deep that is not much of a problem if it is a problem at all. If you go too large in diameter and lose the headspace shoulder the barrel is junk.

[edp2k]

My sense is that the OP is not a highly experienced machinist.
This will not end well.

A quality aftermarket barrel is the way I would go.
I also sense that a quality aftermarket barrel is the way the OP will end up going after damaging his factory CZ barrel.

Not being negative, just trying to be realistic, and actually trying to help.

On the bright side, the OP will damage his barrel much cheaper by doing it himself
versus paying someone to damage his barrel.

Not really kidding.

[GARD72977]

I bet the OP is sorry he started this thread.

I would not worry about indicating the barrel from the bore. I'm willing to bet it was chambered by indicating from the OD.

A 3 jaw chuck will work fine. Put the BBL in and indicate it while tapping it with a brass mallet.

You should be able to "touch off" by sound or visual. Go slow and I bet you will be fine. It's not rocket science.

I shot a Shadow 2 when they first came out. I ended up using a Lee 38SW powder through die to expand the case. This kept the case from swaging the bullet. This allowed a .357 coated bullet to shoot through the CZ bbl.

Good luck with your project

[DougGuy]

^^^^ Only an beats on a lathe chuck with a hammer! If OP follows your advice he'd be just as well off with a Craftsman 3/8" drill and a 3/8" chinese made drill bit.

[country gent]

Some issues will be not so muvh the dia of the points shank but the length when extended to the length of chamber and throat there isnt much let for the collet usually. A 1/4" shank point isnt going to have much wheel on it either. .340-.250 = .090 /2 is .034 use able wheel on each side of shank. SInce a softer stone is used or harder materials and harder for softer materials. Wheel break down my become an issue.

Cuts are going to be small and light .001 at the most and then spark out before the next is made. this will be impossible to see and hard to heat with an air powered grinder. Even an electric will be tough.

The nicest of these home made grinder attachments was one made to it aloris tool blocks. It did address the spindle speed issue alkso. the 1/4" die grinder was mounted aboce the block and a 3/4" shaft was machined for Double angle collets used in a moore jig grinder.In the mounts were 2 ball bearings and the shaft was driven by the die grinders with pulleys and an o ring for a belt. He had several pulleys made for this for different sized wheels. He had even fit a muffler to the rear exhaust die grinder. It was a sweet set up and did a very good job. Now this is from memory. It was made from a block of 2" X 4" X 4" ( probably a left over from a job). 2 clamps for the grinder mount were bolted on top with a desatco clamp to ovk the air grinder on but a oring rolled forwatd and back will work. The front end of block was bored for the bearings thru and a step to locate them left inside the thru bore was close to the same as it inner dia of the outer race. The space between the bearing held the oil to lubricate cool the bearings. Bearings were sealede ine side with that to the outside on each end.Pulleys were threaded 5/8 18 with a small set screw to lock. and the spindle threaded the same. Pulleys for the grinder were on a 1/4" shaft to fit in the collet of the grinder. An oil cup was in the ipen area of the spindle with a gole and set screw to drain and one for a "full sight", fill thru oil cup till oil just rundd out front set screw. A bonus to the oil cup was it released pressure when it warmed up and didnt damage seals. A small guard was made for the belt and pulleys. A center in the back and the front collet mount on the shaft made set up was easy a center in the head stock and tail stock aligned it straight and on center line.

[GARD72977]

^^^^ Only an beats on a lathe chuck with a hammer! If OP follows your advice he'd be just as well off with a Craftsman 3/8" drill and a 3/8" chinese made drill bit.

I turn bronze bushing like this at work. You have to turn them around and turn what was in the jaws. With a little practice and a light hand it's not hard to indicate to within .001

You may not like it but it works.

[W.R.Buchanan]

After reading this entire thread, my solution would be,,, to throw that barrel away, or maybe drive it into a Wall Stud and hang your coat on it,,, and then buy a different one that you could machine to your liking.

You've already spent way too much time on this and have no solution that will work. Who Case Hardens Barrels?

Just get a Stainless Barrel that you can have Doug Re Chamber and throat the way you want it. NO reason why it can't be single point bored on a lathe. NO need to mess with the lead as you are only going to open the throat .001-2. which is .0005-.001 per side, and nothing that goes thru there is going to know the difference.

It's a 9MM Pistol Barrel,,, Not a Sniper Rifle.

I'd just Chuck it in a Collet on my Hardinge Chucker and bore it,,, literally a 20 minute job.

My .02 Randy

[DougGuy]

Bar Sto barrels for the Shadow 2: https://barsto.com/product-category/...dow-2-barrels/

[Flailguy]

For the record I am not sorry I started this thread.
Also I already stated I am not a machinist.

I started this thread asking for information and I have received a good amount.
I have some work to do to prepare but at the end of the day if i ruin a barrel so what!
At least I gave it a shot and I will likely gain some valuable experience in machining.

Thanks to all that gave me useful information and not criticism for trying something out of the ordinary.