Turning a barrel blank

[cdhknives]

Just thinking aloud here... With respect to #6, you aren't going to drill and bore between centers, so now you are dialing in a steady rest to hold the chamber end while you drill and bore. I don't know about the rest of the forum but I am lucky to get within 3 thou on my steady rest. The chamber reamer floats one method or another so that isn't critical to hold the bore exactly on centerline...if the reamer pilot is guiding it start to finish. If the taper bore is off, it sounds like that will drive the reamer to a crooked chamber. As to how tight the tolerance of the boring operation is, I leave that answer to the experienced hands. I am very wary of such with my skill level and hardware. I may end up buying a roughing reamer after all...that takes the whole drill/boring operation out of the equation.

For debate on profiling before or anfter chambering, some go so far as to recommend final lapping and air gauging after profiling due to stresses being relieved changing the bore. Wallowing out a chamber is that X10. I plan to chamber after profiling for that reason alone...it just seems to make more sense. Besides, I think the profiling is the hardest part for me, so I'll do that first. If I ruin it, it is less hours down the drain!

 

[seasicksteve]

There are a bunch of different ways to do this It comes down to finding a method that youre comfortable with and best suits your equipment. As long as you realize whats important and map a strategy to get there it doesnt matter what way you do it. Most important to me is the chamber needs to be concentric with the bore and the chamber needs to be cut on size. If you are doing it for profit there are other considerations but I assume like me this is a hobby

 

[mickri]

I have found that if I have turned something between centers and then need to place a steady rest if I put the steady rest in place before removing the tailstock center I don't lose concentricity. I can then drill the end of the work. With a barrel the bore is already there. With step drilling using small increments the drill will follow the bore. At least that has been my experience. Even with that I am leaning towards not pre drilling/boring and just using the reamer to cut the chamber. It takes longer but time doesn't matter because this is just a hobby for me.

 

[Tozguy]

For a steady rest to work it has to ride on section of barrel where the OD is concentric to the bore.

 

[Tozguy]

The bore is visually fine but I didn't cast it before tapping in my center pins. It should be okay for starting the reamer unless it is way out, right?

Some new barrel blanks will be marked on the end if the end needs to be cut off. Both ends of a lapped barrel will have a slight deviation in bore size so standard procedure is to cut an inch or so off each end. No bore measurements required. It is done as a precaution.

I am lucky to get within 3 thou on my steady rest

When chambering between centres the steady rest does not have to be dialed in precisely. Please read Rod's procedure in post 11 again. But chambering with the barrel through the headstock does require a very precise ''dial in''.

 

[cdhknives]

We are bouncing all over now...sorry. Dialing in the steady was in regards to trying to drill and bore to save reamer wear, and it looked to me like that would require the same level of precision as chambering through the headstock. If the drill and bore is not parallel to the barrel bore the reamer is going to follow it and not the pilot resulting in a crooked chamber, right?

 

[Bamban]

if the reamer pilot is guiding it start to finish. If the taper bore is off, it sounds like that will drive the reamer to a crooked chamber

If you drill, then single point taper bore, just run the finish reamer without the bushing. This is how I did the last 40 barrels I did. I am not in the business, I have only chambered 170 barrels the last 5 years. I could not tell the difference in the runout between with and no bushing.

This is just one example of a barrel finished reamed without a bushing. There are more in YouTube channel.

Watch "12 Aug 2020 Chamber Runout To The Neck" on YouTube

If the drill and bore is not parallel to the barrel bore the reamer is going to follow it and not the pilot resulting in a crooked chamber, right?

If the bushing were to follow the off center, assuming workholding integrity is not compromised, you will have an oversized backend of the chamber, but not crooked.

If you want to use a floating reamer holder, I can loan you a Dave Manson one. Your pusher type approach should work as well. I went through expense to see which one works the best for me, I settled on my own design and that $75 one sold on eBay.

Here is checking the dialed in throat, the swing back CW shows the groove. If you notice the chambers were cut before the tenon threads. It is just one way I am comfortable with. In addition I leave the tenon about 0.020 larger, and shorter than headspace length. When I run the finish reamer I go in 0.010 longer than calculated headspace. To set the final headspace I creep up on the length and diameter and turn towards the tailstock till I attain headspace, then thread, and finish breech. For me it is easier to cut 0.0005 on the shoulder than trying to go in 0.0005 with the tailstock.

Watch "My Grendel Barrel" on YouTube

With my limited skills I find easier to attain repeatable results with my process.

There are so many ways to skin the proverbial feline, whichever one you are comfortable with within the limits of your machine and getting repeatable quality resultals is the proper way for you.

 

[Tozguy]

The drill and bore is definitely to guide the body of the reamer as already explained.

The key operation when chambering between centres is to cut a concentric surface for the steady to ride on. This is done with the barrel between centres and you single point a light cut next to where the threaded tenon will be cut. This guarantees the parallelism you are aiming for.
Then you set the steady up on that freshly cut surface. The steady has to be snug on the barrel and well lubed. The TS centre can be withdrawn now. If you have a dti then check the bore for run out and reassurance.
I recommend that you practice this common procedure on a piece of round before tackling a barrel so that you fully understand the machining principles and build your confidence.

 

[mickri]

I have a 1.25" round bar about 18" long that I intend to practice on.

 

[Earl]

Offering this up for comment and constructive criticism...no old guys around that I know to mentor me and I have read all I can, time to give it a try! Please be gentle! LOL

I may be biting off more than I can chew but here goes. I bought a Green Mountain blank on special, only 21", Stainless Steel, 6mm, 1:9 twist, to build a handy (hoping to get a 20" working barrel but 18" would be ok) 243Win rifle on an old Rem 700 action I have been working with. I have a couple of takeoff barrels thanks to another member here and have swapped them a couple of times, so I have a good working vise and action wrench.

First step, turning to shape. I want a slightly heavy barrel, basically minimum taper forward of the chamber...somewhat because I like the look and somewhat because I don't want to mess with turning a taper. I have a 3/4" spindle bore so I want to turn the forward 3/4 of the abrrel to about that diameter, then flip to turn the chamber end. I will blend the transitions in later. I have to work between centers due to the small spindle bore. That leaves me either losing a lot of barrel to chop off the section under the dog or resetting it to turn the other end. Good or bad? Pic of setup below.


Second question, the blank was off center when I started. I took an hour thinking my pins were bad but in the end I think the blank was really a good 8-10 thou off at one end. Is that common? Pic of center pins below.


My order of operations, let me know if I am missing anything:

1) Rough turn 3/4 of barrel length including muzzle end between centers
2) Flip and rough turn chamber end and taper (steps and grind to shape later in step 4?) transition. Cut and thread receiver tenon.
3) Switch to 4-jaw, use spider on left end of spindle and 4 jaw to align, then cut face for Rem 700, rough chamber (I have Forster reamer and gauges)
4) Go back to centers, use belt grinder to finish sand to final surface (protect lathe from grit!)
5) Return to 4 jaw, final finish chamber by hand
6) Crown
7) Final install on receiver, final verify headspace, reassemble and test fire...

I do see an issue with your order of operations. #2. Cut and thread tenon. You need to get your 4 jaw on and indicate off the bore, then cut your tenon and thread. I do lots of barrels (benchrest shooting addict) Very few (almost none) of the barrel blanks have the bore true to the outside diameter. Most are off enough that you don't need a dial indicator to see the runout when the lathe is turning. Most barrels are also banana shaped. I did one Friday that when I got the chamber area running true, the muzzle end was running out 80 or 90 thou. I took it to the range on Saturday and it turned out to be competitive. Good luck with your project.