Reamers and Preboring

[VA_XTC_Shooter]

I have been reading through the threads about everyone's preferred reamer holder and type, etc. One thing that comes up a lot is with a pusher or floating reamer is to not influence the reamer with any tail stock misalignment. This makes sense, I understand the theory especially on an older lathe with worn bed where the alignment could changes depending on position on the Z axis.

My question is, if folks use a pusher or floating reamer holder to avoid TS misalignment, I would assume they do not prebore the chamber? If you are using a TS that is misaligned to prebore, aren't you introducing that error to the chamber and now the reamer will follow that induced error?

I would think if you have any TS misalignment, you would go the pusher/floater route and not prebore.

Am I understanding this correctly?

 

[Tucker65]

My question is, if folks use a pusher or floating reamer holder to avoid TS misalignment, I would assume they do not prebore the chamber? If you are using a TS that is misaligned to prebore, aren't you introducing that error to the chamber and now the reamer will follow that induced error?

agshooter,

When you pre-bore you use a small boring bar mounted just like a cutting tool you would use to turn the OD or ID of something. Some just bore a straight hole a little smaller than the diameter just below the shoulder. Others, and the way I have been doing it, adjust the compound to match the angle of the body of the case and bore a tapered hole. This takes a little more time because you have to feed the boring bar in by hand and also to dial in the compound to the same angle as the reamer. I've had good success with pre-boring but everyone has their own way that works for them. Most people try the different methods out there and use what works for them and their equipment.

John

 

[dnellans]

Most people that prebore do it with an undersized stub drill (less flex than jobber length), or even a dedicated drill bit per cartridge (JGS, maybe others also sell them). Like you say, at this point if the tailstock/chuck was misaligned, you have a misaligned hole and drill bits aren't particularly precision instruments so the hole might have walked, have bad surface finish, etc. You can measure the runout of your drilled I.D. to see how far off it is.

So the next step is to use a boring bar to clean up the hole, to get it perfectly co-axial to the bore. You can get fancier (like post above) if you see fit.

 

[butchlambert]

I have been reading through the threads about everyone's preferred reamer holder and type, etc. One thing that comes up a lot is with a pusher or floating reamer is to not influence the reamer with any tail stock misalignment. This makes sense, I understand the theory especially on an older lathe with worn bed where the alignment could changes depending on position on the Z axis.

My question is, if folks use a pusher or floating reamer holder to avoid TS misalignment, I would assume they do not prebore the chamber? If you are using a TS that is misaligned to prebore, aren't you introducing that error to the chamber and now the reamer will follow that induced error?

I would think if you have any TS misalignment, you would go the pusher/floater route and not prebore.

Am I understanding this correctly?

I don't think that you understand. The tail stock has nothing to do with preboring. You prebore with either the carriage or as I use the compound to taper bore. I don't care about bed wear or tail stock alignment.
If you follow good machining practices you can avoid having the issues come up that you are stating.
A worn lathe bed? Next time you set up and turn your tenon, measure the taper or run an indicator along it. I've done this on worn out lathes. Most tenons are 1" long or less. Most taper I have measured on a tenon length is .0005" That is about a tenth of the diameter of my gray hair. Your shoulder needs to be perpendicular to the bore. A worn bed does not effect this.
Hopefully this helps.

 

[VA_XTC_Shooter]

Ah, figured it was a dumb question. I was overlooking boring bar in the compound and only thinking of a drill bit in the tailstock for pre-boring.
Thanks fellas.

 

[Clark]

I drill, bore, and ream in 1/2" increments.
Lots of cleaning up each time before the reamer.

 

[JPB3]

After you indicate the barrel in, however you do it and you turn the tendon and thread or chamber first, doesn't matter... If you drill out a portion of the chamber making sure you leave enough so the pilot on the reamer can still reach to bore, THEN you put a boring bar on your tool post and bore out the drilled hole. IMO, you only have to bore 1/2'' or so, generally .005-.010'' to true up the hole. What you are doing is ensuring that the back of the chamber is running true to the throat that you indicated in.. IF you only drill the bit will follow the existing hole, the bore, and you almost certainly will have runout at the back of the chamber. By boring that you eliminate any concentricity issues..

 

[tobnpr]

I take a slightly different tack in that I do a very minimal pre-bore.
I don't even pre-drill, I still prefer the reamer to do most of the cutting. I use dark oil in a flush system and I'm not overly concerned about reamer wear, labor and not allocated cost of the reamer due to wear is the major expense in chambering.
I have a small Micro-100 boring bar that'll fit right into the bore. I bore out just shy of the neck diameter, only about 1/4" or so deep. Just enough so that the neck of the reamer hits the concentric hole when it makes contact with the barrel.

As said, everyone finds what works best for them in terms of time and results. Don't be afraid to experiment a bit.

 

[WayneShaw]

I recently ran my 6PPC reamer into a 30 caliber barrel to make a 30PPC. I drilled, reached in to the grooves/lands, indicated, bored the hole true straight with the carriage .010 under shoulder, then reamed. I checked the chamber body for runout in relation to the groove diameter, and I couldn't ask for it to have been better. No pilot.

 

[HillbillyLongRifle]

I drill and bore my chambers and use most reamers without a bushing at all. If a bushing is used it better be real undersized!

 

[swd]

I drill, bore, and ream in 1/2" increments.
Lots of cleaning up each time before the reamer.

That’s taking the long way home..

 

[Dusty Stevens]

Just start making chips and try different methods. You need to know all the tricks incase you get a curve ball. Dont lock yourself into one method just becase other folks do it. Sometimes your equipment and barrel dictates how youll chamber it.

 

[DaveTooley]

About the only absolute is to get a concentric chamber you have to start out with a concentric hole.

 

[hothead]

I don't think that you understand. The tail stock has nothing to do with preboring. You prebore with either the carriage or as I use the compound to taper bore. I don't care about bed wear or tail stock alignment.
If you follow good machining practices you can avoid having the issues come up that you are stating.
A worn lathe bed? Next time you set up and turn your tenon, measure the taper or run an indicator along it. I've done this on worn out lathes. Most tenons are 1" long or less. Most taper I have measured on a tenon length is .0005" That is about a tenth of the diameter of my gray hair. Your shoulder needs to be perpendicular to the bore. A worn bed does not effect this.
Hopefully this helps.

How do you setup compound to taper bore? most of the chambers I do are improved type cases. 284, Br ,
like that . The taper is so small it would be easy to make a mistake and over bore. I've been boring for a long time , most times I step bore. if a long reamer it might have 3 steps.
So, how do you setup to taper bore??

 

[butchlambert]

How do you setup compound to taper bore? most of the chambers I do are improved type cases. 284, Br ,
like that . The taper is so small it would be easy to make a mistake and over bore. I've been boring for a long time , most times I step bore. if a long reamer it might have 3 steps.
So, how do you setup to taper bore??

Indicate the flute on your reamer while adjusting your compound. Before you ask, your tailstock needs to run true.

 

[Norton's Bench]

About the only absolute is to get a concentric chamber you have to start out with a concentric hole.

Best answer.

 

[hothead]

Indicate the flute on your reamer while adjusting your compound. Before you ask, your tailstock needs to run true.

Thanks Butch, my tailstock does run true, i'd be willing to bet, it would pass your inspection.
How close do you taper bore compared to finish dementions?

 

[dskogman]

I use a piloted core drill from PTG in a floating reamer holder to hog it out then run a clean up pass with a boring bar. The core drill cuts a very accurate hole so the clean up pass is really not needed.

 

[jackieschmidt]

I drill, then single point bore the chamber with the compound set on the same taper as the case.

Before I do this, I indicate the area where the grout will form.

I won’t get into exactly how I chamber barrels and how I set a barrel up. That is a entire different discussion.

 

[swd]

I drill, then single point bore the chamber with the compound set on the same taper as the case.

Before I do this, I indicate the area where the grout will form.

I won’t get into exactly how I chamber barrels and how I set a barrel up. That is a entire different discussion.

Jackie is your whole article on chambering still on bencherestdot.com? That's a great article for the guys who haven't read it. I highly recommend reading it.