Concave flats: Normal?

[rich pierce]

Just draw file the barrel and move on.  It's what we do.
David

100%. Way better than some corncob looking barrels from days gone by.

[2 shots]

 dealing with the same thing on my Kibler fowler,  rice makes the barrels for that one i believe. just part of the game.

[Bob Roller]

Has this condition been reported on other makers barrel ? As I said earlier,the planer I used to help Bill Large cut straight across and no concave radius ever occurred.I have no idea how many times I came into Bill's shop and the planer was running and had finished the cut and I would shut it off and index the barrel and start the next cut.
Bob Roller

[Jim Kibler]

Since our product was brought up, I will speak for it.  If there is any concavity to the flats it is VERY small.  We produce flats by side cutting with carbide endmills so it's hard to envision how this occurs.  With this said, I have seen a TINY amount on barrels we have produced.  I would guess this is no more than .001" and probably less than .0005".

Another big thing to consider...  Is your file flat and straight.  Very few are.  I would suggest sighting down your file to determine the curve and using the convex side on the barrel.  Believe me, it makes a considerable difference.

Finally files can bow when drawfiling.  This can influence results. 

I can honestly say, our barrels have a FANTASTIC finish and any small deviations are insignificant.  Watch my videos on drawfiling.  Learn to do it well and get after it.  I can have the top five flats filed in around 20 minutes.  I hear of some taking hours and hours to draw file a barrel and it's hard to imagine. 

[HSmithTX]

I would rather have .002-.003" of concave in the flats with straight off the mill finish vs some of the other barrels out there that get a 40 grit belt sander to take the machine marks out.  The one or two flats that remain kinda straight after the belt sander aren't bad but the others that wander off axis are a real bugger to get back on axis.  The straight but concave flats come in pretty fast if you are using a good sharp file. Use a file that is aggressive enough that it doesn't fill and stop cutting,  it needs deep enough gullets to pass the chips and continue to cut.  Once it's flat you can use finer files to clean the last marks out. 

[45-110]

Yes I have complained about the belt sander finish also for many yrs. I particularly don't like the wash board or waves it can create. Hrs. of draw filing is not pleasant work. Side milling can and does leave a much better finish and leaves a flat surface.

[davec2]

Just to give some specifics to what Jim K has said, here is a section from and old post of mine ( https://americanlongrifles.org/forum/index.php?topic=57140.0 ).  This is about a Rice barrel.....

I had an hour today and thought I would try and get the barrel draw filed.  Now right out of the crate, the barrel had the expected tool marks full length along all of the flats....not really deep but significant enough that I thought I might not be able to get all the draw filing done in the hour I had.  In addition, there was some discontinuity in the surfaces near the waist where the barrel was moved in the machine to complete the milling of each flat.  Again, no criticism here, I just thought it would take a little more time in those areas to get the surface discrepancy filed out.

Just for fun, I took out my phone and opened the stop watch function.  I hit the button on the stop watch and started in on one flat.  It went really well and when I finished I reached over and hit the "stop" button.....5 minutes and 35 seconds.  I timed each of the next four flats.....all less than 6 minutes.  All five primary flats draw filed in less than 30 minutes.  It went so quickly and well, I had time to finish up all eight flats...just for kicks. 

One last point of interest....as I was sweeping up the steel filings on the bench and floor I looked over and saw a gram scale on my bench that I use for making detonators for explosive charges.  I weighed the steel filings to see how much metal I had removed......9.8 grams.  So just in case anyone else out there was wondering how much metal you are taking off draw filing a barrel, there is is......right about 1.1 grams for each flat on a 43" barrel.

I did convert the 1.1 grams of steel removed per flat to a thickness.  Assuming an average flat width of 0.4", a barrel length of 43", and a density for mild steel of 0.2904 lbs / in^3, the 1.1 grams of steel removed per flat to clean up the surface equates to 0.00053" in thickness.  So, on average, the removal of a half a thousandth of an inch of material results in a smooth file finish with no remaining tool marks.

[kutter]

I'd rather have to go after the slight concave in the middle of a length of a flat than trying to straighten out a bbl length of up and down & side-to-side waves from a belt grinder or other set up.

But if the bbl is advertised as perfectly finished, or normally shipped as that, I would let the mfg'r know of the issue.
I wouldn't demand a replacement, or think anything more of it.
Stuff happens when making things. Good mfg'rs make adjustments and make things right again to stay in biz.
They like to keep customers happy.

In other words,,Not a big deal in my way of thinking

[Scota4570]

That is about how long it takes me too.  Maybe some folks are making a bigger job out of it than it actually is. 

I use a 14"single cut mill file.  For browning prep I do not mess around with finer files or sand paper.  The browning action obliterates the filing marks.  I do a quick blend of whatever marks are left from the file with maroon scochbrite.

 Lately I have  been using a bronze suede brush for carding.  Some fine rust texture does build in the surface but I think I like the look of it that way.  I used to bring it to at least #400 grit then blend and finish.  That is fine for a rust blue but for browning not so much.  It ends up looking to smooth and reflective for what I want now. 

On my last build my son and I did it together.  His natural inclination was to be very fussy.  Once I showed him how to get after it with the big file and how to draw file properly it went smoother.  I showed him how to use a marker to make sure he was staying level and how to make the stroke with his whole body rather than his arms.   

I find that the larger file does not pin and therefore saves time  because I do not get the gouges in the file texture from the pins stuck in the file teeth.   

[45-110]

Well I can tell you that if you want a fine rust blue or brown finish on a higher class rifle, you don't want to have to mess with scallops, waves, concave flats ect. There will be enough hours in metal prep to get the file marks out and polished up.

[2 shots]

dealing with the same thing on my Kibler fowler,  rice makes the barrels for that one i believe. just part of the game.

please note: this is in no way a complaint about Kibler kits, i was just saying i ran into the same situation as the o/p. i love both of my Kiblers.

[Canute Rex]

As a capper to this discussion, today I decided to just put my head down and file. File, card, file, card. There are still a couple of depressions around the breech I have to finesse, but I have a pile of filings and a smooth barrel. More material removal than I expected, but not a functionally disqualifying amount.

I'm trying to decide whether to put some fine sandpaper over a steel block and refine it, but that's a whole new discussion.

Thanks for all the input.

CR

[flatsguide]

Mostly a product of geometry from using the end of the end of an endmill making the cut instead of side milling. Try to envision a milling cutter taking a long pass on a round bbl blank. If there is no taper the cut will be flat’ but if the machine is a CNC machine and the head or table is going up and down ( to produce a swamped profile) the flat portion of the endmill is no longer parallel to the desired shape and this will leave a concave cut. The steeper the profile the more concave the cut will be.
Cheers Richard

[bob in the woods]

I have seen that to some degree on almost every barrel I've used. There were a few Colerain barrels which were pretty much concave to the same degree as yours.
I have always thought that it was a result of the fixtures utilized in the machining process.  Adds a few minutes to the draw filing work, but not a real problem.
Barrels that were hand forged and hammered octagonal would take a lot longer to file