Broke my parting tool

[Ian]

Not to worry, it was a $2 Chinese brazed carbide jobbie that I had to re-profile to make work anyway.

The point is really about barrel quality. Most shooters probably have no idea how badly the bores of their rifles can be "hooked", or curved, or how much the OD can be non-concentric with the bore centerline. So I have this Savage .308 sporter barrel that was given to me, an un-fired take off barrel which clearly had a hook in the bore about 4-5" back from the muzzle and was destined to become a jack handle pending me getting a lathe to turn the end to the correct diameter. I decided to cut it down to 16.5" and thread it for practice instead. After indicating the inside of the chamber to zero in my outboard spider and a pin I turned to fit the bore indicated true in the muzzle, I checked the OD of the barrel (which looked pretty loopy from what little I could see sticking out of the chuck) at both ends. .007" TIR in front of the nut and .006" at the muzzle, not great but not terrible.

So I got my parting tool set up to lop it off at 16.6" and had a go. Interrupted cut deluxe. Anyway, it seemed prudent to stop just short of the groove diameter minus a fudge factor approximating the eccentricity of the OD and finish with a hack saw since I'd never done this before, but I underestimated the amount of hook the bore made inside the already wongo outside (the barrel OD was actually pretty straight when rolled on a sheet of glass), so my fudge factor was insufficient to keep the tool from breaking through suddenly on a groove before I reached my pre-determined whoa-up and grab the hacksaw point. Of course with the wongomatic bore the heavily-loaded tool dug in and snapped off.

Lesson well learned.

Turns out the bore at that particular spot in the barrel was .042" off center with the OD. Remember that before parting it off I had zeroed the bore at the muzzle, just 5.4" ahead of this point, but at the cut it was running about .035" off center. See why this brand-spanking new barrel was supposed to be a jack handle? Actually it might be OK now that I cut the worst part off, crowned it, and threaded it, but with the barrel being .654" there's almost no shoulder on one side of it so putting a suppressor on it would be an iffy proposition and only really possible if one put a thick washer against the shoulder and slid it over to center on the OD instead of the threads.



Before anyone busts my butt, I repeat this was a known JUNK barrel to begin with, so no I didn't put any brass pads or copper wire between the chuck jaws and barrel as I would when turning a good one.

The good news is I learned something, didn't hurt anything important, and got to trial run my outboard spider and new 4-jaw chuck which both worked like a dream. As a bonus maybe some of you will find the photo interesting.

 

[freebullet]

Uh, you lost me at parting tool but, I'm catching up.

I break stuff with the best of them. Sorry ya broke it. At least it didn't land in yer eye.

I can't believe the barrel fits in that little lathe. I would most certainly like to see more pics of how you set up for those operations.

 

[Ian]

It wasn't a "real" parting tool, just a very narrow, carbide-tipped 5/16" bar cutter that serves the purpose and fits directly into the tool post without needing the special holding fixture. Included in the 11-piece, $22 cheapo lathe cutter set I picked up for learnin'.

I'll take more pictures of the setup next time.

 

[JSH]

WOW!!
Don't look at the TC Encore rim fire barrel at the breech. That makes me shake my head.

I didn't break my parting tool, but did chip it last week.
Back to you tube for a little HSS tool grinding refresher.
I sharpened it, and finished my task. May as well practice a bit......I proceed to make more chips and it quit cutting again. Pulled it off and the dang thing chipped again!
More YouTube.
This tool hadsome what of a chip breaker ground into it. I ran across a gent that did not put a chip breaker on it and swore by it. What the heck I will try it. Ground past the old breaker and into new metal. Worked like a charm.
Saw another gent put a groove length wise in the parting bit and it just plowed off metal like who done it.

I tinkered around with some of the HSS odds and ends of bits I picked up for cheap a while back, two coffee cans full. A couple of square boring bars with the end broke off looked to be a good project. Hit the grinding stone, no sparks but the dust flew! Harder than wood pecker lips. Barely touched it. Called my buddy, must be carbide, twice as heavy as HSS.

Jeff

 

[KeithB]

Ian, sorry to hear about your broken tool. Cutting off can be hard on tooling. On smaller machines using HSS might actually be better. We use an indexible carbide cut off tool with 5/32" wide inserts that have a very small bevel on the corners and a lengthwise groove down the center; the design curls the chips inward enough to make them narrower than the groove thus no binding or hanging up.

With HSS you can grind the end square or at a slight angle left or right to allow cut off w/o generating burs. HSS is also a little more resilient and forgiving when you run into something like off centered holes.

The further away you are from center the less critical it is that the tool tip be on center, but cutting off implies (at least on solid bars) cutting through the center so being on center height is critical. Too low and as you get close to center the part want to crawl up on top of the tool and if it does the stock rotation actually causes a force that tries to pull the tip off the tool (chip it) as it passes under center. Too high and the tool will stop cutting at some point and then the forces involved will make it hard to feed and will cause deflection at the tool tip (lateral forces). None of these things are good for the machine, the tooling or the part.

Good cutoff tooling is one of the things that is worth spending money on.

Glad your spider worked as intended - that's the fun part, making things so you can make more things, it's addictive. Good job!

 

[fiver]

I can see the off center by eye.
if i can see it the barrel should have never left the factory.

 

[Gary]

Ian, kinda off your topic, but do you have a QCTP?

 

[Ian]

Gary, not yet, will get one of the steel Aloris knock-offs from Littlemachineshop when the time comes. They sell one that's the perfect size for the 7"-swing lathes.

Vee-groove in the top of the parting tool, that's a good tip right there. I don't see any chip breakers on the 'tube, but do remember comments about using pliers to break off the coiled chip periodically and don't make it a game to see how big of a spool you can make.

My little setup worked pretty well until CRACK! Carbide doesn't like shock and surprise. I don't care for it much, either. If I'd been using a sharp, HSS parting tool it may have been possible to take a lighter cut and back out at the first sign of an interrupted cut into the eccentric bore, but carbide seems to either just squeak and scrape or you give it the bite it likes to take.

My next project is threading one of my Marlins for a suppressor. It isn't going to be easy at all, the barrel is .644" where the shoulder of the threads will be, and the bore at the muzzle is off-center something like .015" IIRC, which leaves just about nothing for the suppressor adapter to seat against on one side when 5/8x24 threads are cut. Looks like I'll have to go down to 9/16"x24, and that means single-pointing tiny threads inside hard steel against a very close shoulder, or going to 18 pitch and using taps that I have already, or buying two specialty taps from Brownell's. Since I can make the adapter any way I want it, it will be unique to this one rifle, and it will likely either soldered in place or put on with permanent threadlocker, I'm not worried about using the more coarse thread pitch (SAE fine).

I'm also scratching my head a little regarding how I'm going to indicate center on the chamber end without taking off the barrel....especially since I have zero confidence that the OD and ID are anywhere near concentric there. I'd turn a rod based off of a chamber cast to use as a gauge, but who knows how straight is the chamber with the bore. Might just have to eyeball it, my eyeballs are pretty good when it comes to judging runout. .007" on the barrel OD last night looked like a mile.

 

[KeithB]

Aloris type dovetail tool holders are a lot easier to set to center height and come in enough variety that you can use almost any type of tool. The starter sets with tool post and 4-5 toolholders (at least in the larger sizes) seem like a good bargain.

Since the bore is what seems to be the part that needs to align with your suppressor (and you can't really do anything about how concentric the chamber or barrel OD is to the bore anyway, right?) is there any way you could make a rod to fit the bore and indicate off of that?

We run a part that gets cut off from a 2" solid aluminum rod. The OD is polished and hard anodized before we get the material. The part is very simple, but there cannot be any scratches or dents, etc. on the OD. We can't polish out flaws. The first time we ran them we ruined a lot of parts when the chip would curl out of the slot and scratch the outside. The next time we ran them I wrote a subroutine with four simple lines of CNC code that runs the cutoff tool in .055", backs it up by .005" and then runs it back in another .055", rinse and repeat.... I just put it in a loop that calls it as many times as necessary to go from starting size to 0 in .050" increments.

Now the chips come off in very small curls, don't jam up in the cut, and rarely scratch the workpiece OD. It is kind of like peck drilling, where you drill in a little, pull back to clear out the chips, and then drill a little deeper. There is a macro command for peck drilling in CNC code, but there is no peck cutting off macro, so I wrote my own. (If anyone wants to see the sample code let me know, I'm not going to post it here.)

Maybe not a bad idea to consider backing off a cutoff tool often enough to break up the chips; sort of like reversing direction when hand tapping.

 

[freebullet]

I realize you were practicing on that barrel. But, am I all wet in thinking a guy could just zip off the end with a chop saw then true it with the lathe? Seems faster but....

About the shoulder issues.

Couldn't a fella do a quick stitch weld, cool, stitch...ect. Then turn the profile back down to an appealing taper from the new improved shoulder?

Few years back I had to weld a part I didn't want warped. I wound up using a putty that blocks heat transfer around the welded area. It worked like a champ. I'd think with the putty & a proper penetrating stitch it could be done. Am I off the reservation in those thoughts?

 

[Ian]

Since the bore is what seems to be the part that needs to align with your suppressor (and you can't really do anything about how concentric the chamber or barrel OD is to the bore anyway, right?) is there any way you could make a rod to fit the bore and indicate off of that?

Yes Sir, that's exactly what I did. Unfortunately, the bore inside the barrel made an arc that threw it off center .021", or .042" TIR, just a few inches back from the muzzle (where the bore was running true via turned pin and test indicator). I knew it was off some, so I calculated to stop the parting cut about .015" short of where it would begin cutting the groove at the diameter point I was parting, but the bore arced more than that and as I was creeping up on my stop point, pop goes the tool.

a guy could just zip off the end with a chop saw then true it with the lathe? Seems faster but....

I can assure you that any future barrels I shorten will be cut on the Milwaukee 12" chop saw with a water mist, or with a hack saw. Easy enough to face them off on the lathe afterward and re-crown.

Couldn't a fella do a quick stitch weld, cool, stitch...ect. Then turn the profile back down to an appealing taper from the new improved shoulder?

I've done this with my tube barrel extensions on two ARs. There is no way I have figured out to spot weld, chain weld, etc. even with a MiG, and not warp the tube. The people who weld things all the way around barrels with the TiG process in a welding lathe amaze me, such as Liberty chopping an AR barrel and welding on their integral Leonidas core.

What might work would be to turn the barrel back another 3/8" or so past the "shoulder" when cutting the thread major diameter, and make a snug bushing for it. Actually, make the bushing ahead of time . Then sweat the bushing on with high-temp solder and face off the shoulder after cutting the thread relief, and then thread the muzzle. Ideas?

 

[Ian]

Hooboy. Here's the other Marlin challenge: How to indicate the chamber end. Here's what I have right now with a mock-up trial run just using tape to protect the barrel. The last few seconds of the video finally sort of capture the chamber runout, sorry for the shaky camera work there but I was trying to hold a light and get the camera to focus on the chamber at the same time. I don't know how much it's off but I'd guess at least ten to 15 thousandths.

While the video was uploading, I had a sandwich and sketched this out.



The red rod would poke inside the chamber and have a polished bulb tip of some sort to ride against one side of the chamber wall while the other end would be held securely on center somehow, like pointed and stuck in a small hole in a solid mount so the opposite end in the chamber could wiggle around some. The yellow squiggle would be a spring keeping tension on the rod, and the green part would be some sort of support to keep the rod positioned at the bottom of the chamber and not let it ride up the side. The rod would not rotate, it would just act as a lever tracing the chamber runout. The other thing that might work would be to cut a fired case in half, fill the neck end with JB Weld, put it in the 4-jaw indicated true and centered, face it, drill a pilot hole in it, and then put it inside the chamber and use a pointed rod like a dead center in similar fashion to the drawing.

 

[Brad]

I broke a parting tool once. Scared the crap out of me.



When these let go it is a noisy event.

I dislike parting off, it is always a bit scary. Keith is right about tool height. Too low and the part will eventually want to ride on top of the blade. Too high and it is harder to cut and it tends to dig in. Getting it exactly square is important too. You know it you aren't because the groove gets wider and wider and one end of the groove is a bevel.

 

[KeithB]

Does the end of the suppressor have to butt up against a shoulder? Could you leave a shoulder inside to butt up against the end face of the barrel?

 

[Ian]

Keith, why yes, yes I could, now that you reminded me.... DOH!

I remember now it has been done both ways for suppressors and muzzle devices. The M1A, for example, uses a floating, captured nut to essentially just clamp the front sight block/flash hider assembly snug against the flat face of the muzzle. The commercial suppressor for my .45 ACP 1911 also shoulders on the muzzle because the groove dimension and bushing ID don't allow enough material for a shoulder behind the threads. I think that from a universal fit and production standpoint it is much easier to seat muzzle brakes or direct-mount suppressors against a barrel shoulder than the muzzle, but since this is a one-off and I can control the fit of all the parts involved, using the muzzle face for alignment might be the simplest solution, I'll give that some serious thought.

Speaking of simple solutions, I played with the chamber end alignment some more and was able to eyeball it to what I'd put money on being under .001", meaning I cannot by eye at any speed detect any bore runout at the throat. The back end of the crooked chamber is another story, though

I tell ya, this is like owning a bore scope. Don't put your barrel in a lathe and run a bunch of test indicators on it unless you REALLY want to know how bad it is. Sometimes ignorance IS bliss. At least I know this barrel will put ten cast bullets in 5/8" at 100 yards, sometimes less, if I'm on my "A" game at both benches.

 

[Ian]

I broke a parting tool once. Scared the crap out of me.

View attachment 3748

When these let go it is a noisy event.

I dislike parting off, it is always a bit scary. Keith is right about tool height. Too low and the part will eventually want to ride on top of the blade. Too high and it is harder to cut and it tends to dig in. Getting it exactly square is important too. You know it you aren't because the groove gets wider and wider and one end of the groove is a bevel.

Yikes. One of those "real" parting tools might break my lathe if I got stupid with one. Did you review Joe Piezenski's parting tool video? He has a whole checklist of things that have to all be correct for the tool to work, and when I get a QCTP and parting tool holder I intend to copy his list into my personal lathe operating notebook. He also talks about tip angles, tip walking, and how sometimes you want an angle for production work so you can choose which piece retains the nib.

 

[smokeywolf]

Nobody likes parting. One thing I didn't see mentioned is "step-parting". The method is to feed your parting tool in approx. one to two times its width, draw it back out, move it over (toward the side that you're not keeping) by about 70% of its width, feed in double the depth of your first plunge. Withdraw the tool, move back over to your first position (on Z axis) and feed in past your second plunge again and keep moving back and forth and going deeper until you get separation.
I will sometimes leave .020-.030" to face off with a turning/facing tool.

If I have to do one plunge all the way thru with the parting tool, I grind a chip breaker into the top or front and if at all possible run flood coolant.

 

[fiver]

one of my most accurate rifles has a muzzle brake that butts up against the muzzle and then clamps around the barrel.
it wouldn't be too hard to center that up with a rod cut to rifling thickness and an 0-ring out on the other end of the can to assure center.

 

[fiver]

double

 

[Ian]

After sleeping on it I decided to order a muzzle brake with M14x1 LH threads. That will give me something like a .563" major and ~.042" worth of barrel shoulder all the way around, minus the .0125" OD TIR, which only knocks the thin side down to .036" shoulder to bear on. Should be a good compromise between making the barrel threaded portion too weak and not having a rear shoulder.

As an experiment, last night I ground a boring bar and successfully bored the tapered end shoulder (drill bit taper, I assume) square on an A2 flash hider. If I were to bore the inside shoulder on a commercial 5/8x24 brake square to match the face of my muzzle, I would install the brake in the suppressor, mount the suppressor between chuck and steady-rest, and align-bore it to avoid any issues with not being able to indicate the brake alone at more than one place lengthwise in the chuck. I also ordered some spare 5/8x24 brakes in case I change my mind and decide to try the internal pilot and 5/8" threads.