I'm getting ready to fit a barrel to an action and was wondering if I should clean up the contour before or after cutting the tenon and chambering. This is one of the roughest blanks I've seen in awhile.
Gunsmithing Barrel finishing
- Thread starter Gene Poole
- Start date
I see you sell one too. How does that work? I'm only accustomed to spinning it in the lathe (all covered up in cloth to keep the grit out) and lots of sandpaper.
As a general rule it's best to do all barrel work prior to cutting tenon and chambering. Anything that can add stress to the barrel and even remotely affect the alignment of chamber to bore.
Blank looks like someone tried to thread the entire barrel
Blank looks like someone tried to thread the entire barrel
Haven't priced Chad's barrel spinner but I assure you its the cheapest part of the equation....you will also need a good belt grinder, preferably running 2x72 belts to go along with the spinner. Bargain box belt grinders using 1x whatever or 2x48 belts just don't cut the mustard. Longer belts run cooler, last longer, and seem to cut better. Spinning barrels is the way to go but sometimes on crudely contoured barrels you need to do a bit of hand work draw filing the big chunks away. I have seen many barrels that were rippled end to end under a near mirror finish because the person finishing it was too lazy to smooth out the bumps first.
I use a "specially modified" grizzly knife grinder. The one with the super tall belt thingy.
For my purposes I cut the mast down and buy 48" belts from Enco for something less than $2.00 a piece. We start at 60 grit (only for barrels that have been boogered up really bad or for the Obermeyer's as they are always a bit rough on the outside) and work up to 320.
It's lightening quick.
One of my projects is to build a 3rd wheel for the grinder to aid with better tracking. I've not done it yet, but will get to it soon hopefully. It's a bit of a chore to blend a brake for a newby as the belt wants to walk off the thing.
It's a great investment for this kind of work. Shiraz and I have talked and the idea of offering a package deal has been kicked around. Soon as I'm able were going to zip out a big quantity of spinners here. Just a matter of getting machine time sorted out.
C.
For my purposes I cut the mast down and buy 48" belts from Enco for something less than $2.00 a piece. We start at 60 grit (only for barrels that have been boogered up really bad or for the Obermeyer's as they are always a bit rough on the outside) and work up to 320.
It's lightening quick.
One of my projects is to build a 3rd wheel for the grinder to aid with better tracking. I've not done it yet, but will get to it soon hopefully. It's a bit of a chore to blend a brake for a newby as the belt wants to walk off the thing.
It's a great investment for this kind of work. Shiraz and I have talked and the idea of offering a package deal has been kicked around. Soon as I'm able were going to zip out a big quantity of spinners here. Just a matter of getting machine time sorted out.
C.
I have found through 40 years experience as a knifemaker that buying bargain box grinding belts is false economy. I run exclusively Klingspor 2 x 72 belts...some cost as much as $12 each but they have a longer useful life than equal money in $2 belts. Its exactly like buying the best milling cutters, drill bits, chamber reamers etc. 72" belts are not that much more than 48" but typically the machine to run them is, but ususally they are better machines anyway. 72" belts also run cooler which helps in longer belt life...heat is the enemy of the belt as well as transferring to the piece you're grinding. I personally have 3 Baders -2 with DC variable motors and 1 non-variable with a larger motor strictly for rough work. I spin barrels using the variable speed models and can "tune" the speed to what spins the barrel in a more controllable manner. The gunsmith side of my life installs as many octagon barrels as round ones....those things don't spin worth a damn!
Thanks for all the replies. I'll have to get a barrel spinner and a belt grinder one of these days, but for this barrel, I just went with polishing between centers in the lathe with a sanding board and some 320 wet-or-dry and WD-40. It'll get bead blasted and cerakoted or I would have gone a few more rounds using 600.
As a general rule it's best to do all barrel work prior to cutting tenon and chambering. Anything that can add stress to the barrel and even remotely affect the alignment of chamber to bore.
Blank looks like someone tried to thread the entire barrel
Ok, were going to attempt to ejumacate the masses here. We all have our quirks. Mine is a personal crusade against spreading disinformation regarding "stress" in steel.
MACHINING DOES NOT INDUCE STRESS. Don't care who says it does, they are wrong. You RELIEVE stress when you machine. When you use a tool that removes a piece of material you are relieving stress. Period.
The analogy I use to explain this:
Make a ball of rubber bands. Snip random pieces with scissors afterwards. Do enough and ball is no longer round. Did you induce stress? No, reduced it. You just had no assurance the ball stayed round.
Now take the same ball and cook it in momma's oven at 200F for a couple hours. Now snip at it. Nothing happens OR nothing alarming happens.
Why?
The parent material has been NORMALIZED. aKa Stress Relieved.
Such is the same with barrel steel. It's normalized so that flutes, contours, etc don't turn the stuff into a banana.
Now, if you take that same ball of rubber bands, warm it up, and then pound (forge) the piss out of it till its in the shape of a box, then who knows whats going to happen when you cut on it. Why? You altered the parent material into a shape it's not normally going to form. So, STRESS has been created in the part. When "smoosh smoosh" a piece of material into a shape you ARE creating stress into that part. Forged cranks, wrenches, etc experience this. It's why they are normalized post forging and THEN machined/ground, etc. It's so that you have a reasonable expectation of the thing retaining its dimensions afterwards.
If you normalized it afterwards by heating it back up and allowing it to relax, then again, when you machine on it, it should stay reasonably close to its parent form.
To the OP:
Spin/contour your barrel and be fearless of ruining your barrel. You'll be fine.
A spinner is nothing more than a pair of bearing cassettes fitted with plastic (sometimes brass) dead centers. It's mounted on a 1x1 steel box tube rod. You rub it up against a belt sander and polish the inclusions out of the barrel surface. It takes less than 5 minutes to bring a barrel up to a nice even finish.
Advantages:
1. NO abrasive media anywhere near your lathe.
2. Very fast
3. Superior finish (with practice)
4. For a shop with multiple people using one piece of equipment it moves an operation somewhere else so the machine stays productive
5. Safer. No worries about fingers getting in the chuck or a belt wrapping itself around the barrel and pulling your hand in.
Disadvantages:
1. Takes some practice to get the hang of it.
2. #1
3. If you DON'T know what your doing you can give yourself a really nice broken nose AND ruin the barrel.
4. Requires purchasing an additional piece of equipment you may not already have. (belt sander)
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3. If you DON'T know what your doing you can give yourself a really nice broken nose AND ruin the barrel.
i dont think i broke mine but it was awful bloody for a while,,,,
there is no need to see how fast the barrel will spin when your 12 yrs old,,,,
i dont think i broke mine but it was awful bloody for a while,,,,
there is no need to see how fast the barrel will spin when your 12 yrs old,,,,
I assume that among your other skills you have a post graduate degree in metallurgy?
What you say is about "90% correct". When forging/casting operations are performed the metal is usually normalized (held at 50 C over the metal's upper critical temperature for 1-1/12 hours per 25mm of thickness and then air cooled). Yes, this is done on rifle barrel steel prior to it's being drilled and reamed. Sometimes even after these operations for some premium blanks.
Where you and the metallurgists depart is that while a small amount of machining will not add stress, removing large amounts of metal CAN and does. An example of this in rifle barrel manufacture is the contouring pocess were as much as 50% of the barrel blank can be removed by turning. Metal is being pulled by the tool until it reaches it's elastic limit and then separates from the other crystalline structure of the surrounding metal. The slower the material is removed, and with proper lube/coolant, the less stress is returned to that normalized blank.
Here's an excerpt from a paper written by a metallurgist:
This is probably the #1 reason that not all rifle barrels perform well as they warm up and those barrels that have the least amount of material removed from the blank do best (ie: Bench Rest Barrels in "Heavy" or "unlimited" class). They do better because as they warm the stresses don't affect the bore axis, not just because they're stiffer.
FWIW, I used to work in an R&D shop where we made ultra precision parts for military projects. Tolerances were so close that after every machining operation most parts were sent off for "normalizing" in the Heat Treat Shop. The last operations performed were precision grinds on mating surfaces using pre-warmed parts and heated coolant/lube and removing so little material in a pass that it might take a day or two to finish the part. All to prevent stress from returning to the workpiece.
Noted and I appreciate the correction. As it pertains to this post/thread: Is anything I stated going to ruin this guys project? The inclusions he's shown in photos look to be around .02" in depth at the most. Would you consider this invasive or heavy?
C.
Damn good information. However at what point in precision gunsmithing does this get into diminishing returns. I have no doubt that you are absolutely correct, but how much is truly applicable to the subject at hand? I know that the goal it the most precise machining possible but...
It's all going to depend on how far up you dial your "Precision Meter"
I know some shooters that only use barrels that are normalized twice, hand lapped twice, and are chambered using a chuck that not only can be dialed in at the bore, but also has a secondary "ball mount" on the chuck that allows for adjusting out all "wobble". Runout where the range rod enters the bore is adjusted with the jaws and the runout at the extreme outer end is then dialed out using the "ball mount". All this rather than just letting the pilot on the reamer keep it all "straight" and perfectly aligned with the true axis of the bore rather than just the mouth. Let's face it, precision is somewhat of a "sliding scale". It moves up or down according to what the customer wants to pay. As an example, I recently paid just over $800 to have a Remington SS Action with PTG bolt trued and a new barrel installed. Not an "off the shelf barrel" but one built specifically for this rifle. All I took to the shop was the old barreled action and what I got back was a a product that wasn't the result of "good enough". The results show at the range too.
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Deadshot2, I hear what you are saying about the sliding scale and I agree. I guess I was referring to taking so much care in not inducing "stress back into the steel" that an operation would take a day or two to complete.
$800 for an action true and barrel install to include the cost of the new barrel is a pretty good deal...
$800 for an action true and barrel install to include the cost of the new barrel is a pretty good deal...
Considering what these parts were going to do and who was paying for them it was the appropriate amount of care.
$800 for an action true and barrel install to include the cost of the new barrel is a pretty good deal...[/QUOTE]
Just remember that the PTG bolt was already "trued" and the didn't have any trigger work to do. I agree that it was a pretty good deal for what I got. Also helped tha the barrel maker is just a short 15-20 minute drive from my house. No shipping hassles and it's fun to be able to see how your barrel is going to be made and subsequently finished.
