Gunsmithing How do you guys cut a chamber?

[OnyxSkyDV]

Question for you guys. I'm getting ready to cut my first chamber, and wanted to get your guys input.

Do you use a normal twist drill bit to clear out about half of the desired size of the chamber, use a small boring bar to clean it up and get about 90% to size, and finish it off with a reamer, or do you just have at with the reamer from the get go?

If it's of value, I'm doing this in a 12x36 bench lathe, and I know it's not nearly as rigid as some of your multi ton CNC machines.

Onyx

 

[300sniper]

Re: How do you guys cut a chamber?

I bore the chamber about .010" under the reamer shoulder major diameter to a depth that still allows .075"-.100" of the pilot into the bore.

 

[Ritten]

Re: How do you guys cut a chamber?

I "just have at it" with the reamer. I just take my time, go slow, use plenty of oil, clean it often and it should last for more chambers than I will cut with it in a few years. At that point I'll either resharpen or dedicate it as a rougher.

 

[OnyxSkyDV]

Re: How do you guys cut a chamber?

This makes me ask another question I wondered about. If you resharpen the reamer, is it undersized at that point and used for a roughing only reamer, or do you sharpen it somehow on the flanks so that the diameter isn't decreased, just the thickness of the flutes?

(I assume the latter, but figured I would ask)

Thanks for the input 300 and Ritten!

Onyx

 

[selfbowhunter]

Re: How do you guys cut a chamber?

i always prebore as 300 does. by doing this the reamer does very little work and you are assured of very little runout with the bored hole from what i understand.

chuck

 

[OnyxSkyDV]

Re: How do you guys cut a chamber?

Does anyone chamber the barrel before cutting the tenon and fitting to the action, or is chambering always done after the barrel is fitted?

Thanks again guys!


Onyx

 

[wnroscoe]

Re: How do you guys cut a chamber?

Drill
Pre bore
Connect Muzzle Flush system
Carbide roughing reamer .200" short
Finish Reamer to Final HS.

 

[Ratbert]

Re: How do you guys cut a chamber?

What tool do you use for pre-boring the hole? I assume you single-point it to maintain concentricity but my smallest boring bar isn't small enough or long enough for such an operation.

 

[LRI]

Re: How do you guys cut a chamber?

Thread your tennon first. Set the breech, then chamber.

Sharpening a reamer makes the tool shorter in overall length. Doesn't mean it'll cut small/short, just that the tool gets shorter. "Set back" is prolly a more applicable term.

The cxs series insert boring bars from sandvik do a great job. If you get a 1" depth hole/bore its sufficient for the reamer to track on center. They will go to a .212 hole sits nice for almost every caliber.

 

[GasLight]

Re: How do you guys cut a chamber?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Ratbert</div><div class="ubbcode-body">What tool do you use for pre-boring the hole? I assume you single-point it to maintain concentricity but my smallest boring bar isn't small enough or long enough for such an operation. </div></div>

I use one pretty close to this:

http://www.ebay.com/itm/Micro-100-BB-200...=item2c6585d1eb

For the speeds I am turning, I am sure something similar in HSS would be better suited, but this is just paving the way for the reamer.

 

[Ratbert]

Re: How do you guys cut a chamber?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Onyx</div><div class="ubbcode-body">Does anyone chamber the barrel before cutting the tenon and fitting to the action, or is chambering always done after the barrel is fitted?
</div></div>

I always cut the tenon first because I haven't figured out a way to time the barrel the way I want with a pre-chambered barrel.

 

[OnyxSkyDV]

Re: How do you guys cut a chamber?

You can get pretty small on the boring bar.

http://www.jtsmach.com/jtswebshop/Workholding/WH253.asp

Some 1/8" shank bars there, and a good price.

Onyx

 

[Ratbert]

Re: How do you guys cut a chamber?

So once you've pre-bored a hole, do you use a pilot bushing at all, or just remove it and let the pre-bored hole guide everything?

 

[Ratbert]

Re: How do you guys cut a chamber?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: GasLight</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Ratbert</div><div class="ubbcode-body">What tool do you use for pre-boring the hole? I assume you single-point it to maintain concentricity but my smallest boring bar isn't small enough or long enough for such an operation. </div></div>

I use one pretty close to this:

http://www.ebay.com/itm/Micro-100-BB-200...=item2c6585d1eb

For the speeds I am turning, I am sure something similar in HSS would be better suited, but this is just paving the way for the reamer.</div></div>

For some reason I seem to have a mental block against remembering that the entire world does not revolve around insert tooling.

 

[wnroscoe]

Re: How do you guys cut a chamber?

All of my reamers have bushings, roughers and finishers. I use bushings with them all.

I use the .250" diameter carbide boring bar from MSC and it's worth it's weight in gold.

 

[turbo54]

Re: How do you guys cut a chamber?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Ratbert</div><div class="ubbcode-body">So once you've pre-bored a hole, do you use a pilot bushing at all, or just remove it and let the pre-bored hole guide everything?


</div></div>

Use a live-pilot bushing on the reamer.

 

[300sniper]

Re: How do you guys cut a chamber?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Ratbert</div><div class="ubbcode-body">So once you've pre-bored a hole, do you use a pilot bushing at all, or just remove it and let the pre-bored hole guide everything?


</div></div>

right now i am still using the pilot since i am using a floating holder. i'm using a floating holder because i know the limitations of my tailstock. once i have a machine that will maintain dead nuts reamer alignment throughout the required travel, i will use a rigid setup and no bushing. i have total confidence in my setup and method right now but with a rigid holder, no bushing and a flush system, chip evacuation should be about as good as it gets. it also eliminates any potential damage to the lands by shoving a steel bushing in to the bore. i haven't seen any damage from the bushing but it still doesn't make me feel good about it.

 

[LRI]

Re: How do you guys cut a chamber?

General rules for drilling/reaming a hole.

Once you have roughly 2-1/2 times the diameter of the tool engaged/supported in the part, the path of the tool is pretty much set in stone.

Where this gets a little fuzzy is when using a form tool like a chamber reamer. Relying on the pilot, freebore, and throat to align the tool doesn't really work. The shoulder/case body has a lot more circumference and this means the ability to influence things.

So, still using the 2.5 X diameter rule just figure it at the shoulder/body junction. If its around .4 (like a 308) figure you need an inch of qualified/bored hole to start. Once the shoulder of the tool is at the 1" depth it'll track really well.

Something you may discover is the sudden increase in chip load as the tool begins to cut on all of its surfaces. This is where you really want/need to pay attention as its a great way to shank a tool (break it). Just be diligent and even/fluid with your feed and you'll be fine.

 

[Beef_Supreme]

Re: How do you guys cut a chamber?

Anyone ever used a tapered core drill ground to dimensions slightly smaller than a roughing reamer?

 

[hero's machine]

Re: How do you guys cut a chamber?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Beef_Supreme</div><div class="ubbcode-body">Anyone ever used a tapered core drill ground to dimensions slightly smaller than a roughing reamer? </div></div>

How much do they cost? You would still have to single point after drilling, but if the price was right....it could be a winner.

 

[skog]

Re: How do you guys cut a chamber?

Isn't that called a roughing reamer?

 

[tullius]

Re: How do you guys cut a chamber?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: GasLight</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Ratbert</div><div class="ubbcode-body">What tool do you use for pre-boring the hole? I assume you single-point it to maintain concentricity but my smallest boring bar isn't small enough or long enough for such an operation. </div></div>

I use one pretty close to this:

http://www.ebay.com/itm/Micro-100-BB-200...=item2c6585d1eb

For the speeds I am turning, I am sure something similar in HSS would be better suited, but this is just paving the way for the reamer.</div></div>

If you're turning HSS speeds, you could just make a boring tool on the lathe. Kinda like this threading tool ..

 

[Rprecision]

Re: How do you guys cut a chamber?

I have always used the finish reamer all the way through. I take .025" at a time, remove, clean, and so on.

I guess in my mind I would like to believe that following the bore as a guide is more precise then haveing the reamer follow a bored hole. I maintain less then .0005 runout to the bore with the PTG bushings I have. I then drive with floating reamer holder. My fear it that the reamer would get off center in the bored hole, then when the pilot reaches the lands have .001-003 or worse runout. Would this cause a problem, possibly break a reamer.

When I buy a reamer I expect it to last 4 barrels. I have yet to wear one out

I have done as many chambers as some of the pro's and other folks here do in a day (4), so I am always up for learning

I know a well know smith in the varmint/benchrest crowd, Gordy Gritters, has a video about this very thing. I just havent had the time or money to buy/ watch it.

http://www.gordysgunsmithshop.com/gunsmithingvideosdvds.html

I think it's important to remeber we are all working with differant machines with various levels of accuracy. What one method works for some may not always be the best for all.