Roughing reamer or pre-boring?

B

Brodie

Guest
I have been reading many articles on the different ways of chambering a barrel and was curious if many people use roughing reamers? The majority of the posts I have come across on the net favour pre-boring the chamber.
Is there an advantage to one method over the other or is it simple a matter of cost (I would imagine it could get pricey quick if buying two reamers per calibre?)
Would a piloted roughing reamer be the simplest set-up? Or is pre-drilling still needed?
 
Brodie said:
I have been reading many articles on the different ways of chambering a barrel and was curious if many people use roughing reamers? The majority of the posts I have come across on the net favour pre-boring the chamber.
Is there an advantage to one method over the other or is it simple a matter of cost (I would imagine it could get pricey quick if buying two reamers per calibre?)
Would a piloted roughing reamer be the simplest set-up? Or is pre-drilling still needed?
Click to expand...


Here is a problem with semantics the noun "roughing reamer" a lot of reamer makers prefer the noun "re sizer reamer". Why? Because they are used to make sizing dies for resizing your fired brass. And can be used to cut and under sized chamber, before you would use a finish reamer.


The best way to think about this, there is more than one way to skin a cat.
 
Butch...I just couldn't stand it...here goes...why pre-bore or rough ream a hole and then stick a piloted finish reamer in that hole when you know the pilot isn't going to guide anything until the chamber body and neck are nearly finished...and what if (heaven forbid) the bore (lands/grooves) makes a slight change in direction just in front of the bored hole...will the reamer pilot have to hit that at an angle then correct itself under a the stress of a hole bored to the centerline of the barrel blank...I have always understood that pre- boring or rough reaming was to reduce wear of the finish reamer, which I can understand...but if we are dealing with a bore that does not run straight then I personally want my pilot in the lands and grooves from start to end of reaming a chamber...or maybe the pilot is should not be on the reamer so it can follow the pre-bored hole without influence of the bore...:rolleyes:

OK...I have just put on my fire suit...I am ready..."Flame On"...:p
 
All a roughing reamer will do is take some of the work off the finish reamer and make it last longer. It will follow what ever path a just finish-only reamer path would take. Whereas preboring will true up any runout the barrel may have because of curvature between the desired neck area and the original breech end hole. (Did I say that right??)

Anyway, preboring will show you how good your alignment job was because what you want for a benchrest chamber is for the neck/freebore/leade to blend perfectly concentric to the barrel bore at that point. This allows the bullet to be presented to the bore and negates any in-bore yaw of the bullet.

Some will suggest preboring at a taper equal to the chamber body and some will say just a 2-3 cut straight prebore will work. Actually they will get the same end result if good machining practice is followed.
 
Repeat from another thread...

...get rid of the pilot
I haven't used a pilot since I can remember. I indicate throat, rough drill, angle bore then finish ream. If you have indicated the throat and forward of that (where the pilot rides rides) is out, as most of them are, all of the other work is a wasted effort. The reamer is going to follow the pilot to some degree even with single point bored hole. Bore scope the throat when you are done. We are reaming the throat @ about 1.5 degrees and normally about .0003 (that's only .00015 per side) over bore size, any misalignment will stick out like a sore thumb. We are spilting the atom with these kind of measurements. If your setup is correct what is the pilot for? This is the business end of reaming for accuracy.
Regards...Herb Coates
 
Thanks for all the replys.
I have a couple old barrels sitting around, I think I'll do some practicing on these before I make an attempt on an expensive custom.
 
Bob,
my next thread will be about barrel break in or proper cleaning techniques. Care to elighten me now?:p:)
 
Brodie...why ask a question about chambering if you haven't chambered a barrel..???
The best thing to do is put that barrel in the lathe..set it up and get after it...then you will have an understanding of all of the info that is being sent your way...
Its like driving a car..you won't learn by reading a book or watching it on a movie...
I have yet to put a barrel in the lathe that I don't run into something that I haven't experienced before...
The most fun is learning to single point thread at 220-400 rpm...:eek:

Remember "it is better to do than to have"
 
HCP said:
...get rid of the pilot
I We are spilting the atom with these kind of measurements. If your setup is correct what is the pilot for? This is the business end of reaming for accuracy.
Regards...Herb Coates
Click to expand...
Try it both ways then closely inspect the leade and freebore area with a borescope. I've yet to have an out of center leade using a snug fitting pilot. I have had at least 2 cones that were out of center using a reamer with the pilot bushing removed.

In the process that Remington did use (don't know about now) to chamber barrels their reamers did not even have a pilot, period, fixed or removable. I have come across several chambers in their varmint class barrels that had rifling on one side of the chamber neck.
 
JerrySharrett said:
In the process that Remington did use (don't know about now) to chamber barrels their reamers did not even have a pilot, period, fixed or removable. I have come across several chambers in their varmint class barrels that had rifling on one side of the chamber neck.
Click to expand...

A few hours with a borescope and a collection of factory rifles is an eye opening experience. I recently had the use of a borescope for two weeks, looked in all my rifles and most of my friends rifles - that experience certainly adjusted my expectations about what to expect from a factory rifle.

FWIW: In those I looked at, the best factory bores were in CZ 527s.

Fitch
 
Brodie

For the new guy, it is not hard to bore a little to far in or a bit
to large with a small boring bar. If the reamer doesn't clean this up,
just shorten the barrel and start over. Now when you prebore, thereby
opening the chamber to where a dial can get to the throat area, you may
need to reindicate. If using a rougher, you may find the same thing.When
I use a rougher, it is only about 2/3 depth so any re correction has the
uncut length to pick up a difference. Since the neck is completely untouched.
It also has no throat. Wether you prebore ,predrill or use a rougher, checking
your final destination and adjusting to it is an insurance policy.
The rougher I use is a 3 flute carbide with chip breakers. A great tool
by dave Kiff. Being 3 flute, it does not load up very fast. But don't drop it.
Some very good guns have been made using non piloted reamers. Every
set up no matter how well made is flawed in some way. The pilot is just
more insurance. It is a common misconception that a drill or reamer will
follow a hole. I have seen hundreds of countersunk and counterboreed
holes done without piloted tools that were way off. Which ever way you choose, you will succeed, if you recheck every step of the way. Assume
nothing.
 
Brodie said:
I have been reading many articles on the different ways of chambering a barrel and was curious if many people use roughing reamers? The majority of the posts I have come across on the net favour pre-boring the chamber.
Is there an advantage to one method over the other or is it simple a matter of cost (I would imagine it could get pricey quick if buying two reamers per calibre?)
Would a piloted roughing reamer be the simplest set-up? Or is pre-drilling still needed?
Click to expand...

Nobody really adressed your question I see. Here's my 2 cents worth after chambering a few dozen barrels.

First, Boring and drilling are different operations.

I do not use a roughing reamer because I see no advantage to it over using a finish reamer only.

Also, if you've run the rougher and then indicate the throat.... and it is out, what do you do now? Get the parting tool out?

The advantage of the drilled hole is that you can indicate the throat after drilling and adjust the workpiece to get the throat running true again. Then Bore it back so the roughed chamber is running true, then ream.

Ben
 
You must log in or register to reply here.
Back
Top