Piloted Finish Reamers: prebore or not?

Rprecision

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I am fine tuning my chambering process. I have been learning of some different methods I want to try.

One method involves drilling then boring the chamber to within .020-.040" of finish diameter and short of length. The theory being it takes less load and wear to run the finish reamer.

The heart of my question: I use PTG reamers with precise fitting nose bushings. Since the bushing will not be following the bore for a majority of the prebore, then engaging the bore after the body is engaged, does this create a problem?

Does anyone use this method?

I have never tried it and want to get some advice.

Thanks
 
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Messmaker

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I have been curious of this as well. Looking forward to responses of people that pre-bore.
 
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Wannashootit

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I don't pre-bore... reamer wear isn't a big concern with a flush system and I don't see how it would save any significant time.
With that caveat, I don't see the benefit of a piloted reamer insofar as alignment; a chamber reamer is a form tool and it's going to follow the pre-bored hole. I don't see a potential "problem" as the pilot will (or should, assuming the bore was correctly dialed in concentric to the spindle axis) simply engage wherever it does. Possibly, the pilot may reduce opportunity for chatter (?).
 
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Mordamer

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I pre drill just far enough so that the pilot enters the bore for about 1/4" before the shoulder of the reamer starts to cut. This usually allows me to pre drill about 1" of material out. I generally use a drill that is about .050" under the diameter of the shoulder on my reamer.
 

LongRifles Inc.

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It largely depends on your setup and your tool as to how successful boring ends up being. I don't do it simply because of what happens to the tool.

Grab a 6x6 square piece of steel. Now go to work on it with a torch. The corners heat up at a higher rate than the "meat" of it right?

Now, think of the friction present with any cutting tool. The transition from the shoulder to the case body is one of the highest torsional loads placed on the cutting tool. Lots of tool pressure being exerted right in that spot. Pressure means friction and friction means heat. It does not take much of anything to get too heavy-handed and nuke that corner. Do it and fail to catch it and you are going to kill the tool and the barrel.

That's part 1.

Part 2 is your using the outer edge of the tool and the rest of it for the last little bit of work. That's promoting uneven tool wear.

I am of the opinion that if you're going to do this, then get a rougher that you can hog shit with, then chase it with a finisher to qualify the size and finish. The idea being the loads applied are applied progressively and evenly across the bulk of the cutting surfaces.

Prolly didn't help for shit, but that's my take on this.

C.
 
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Terry Cross

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I don't pre-bore... reamer wear isn't a big concern with a flush system .....
I disagree.
If you are running HSS dreamers, you will get tool wear regardless of your flush system or coolant type.

You may still get decent looking surface finishes but you may eventually get caught with your pants down due to a dimensional variation from tool wear. Even the throater area of your reamer can wear and suddenly cause pulled bullets and other issues....

Have your finishers checked and if needed, cleaned up often depending on how many chambers you cut.

Going to quality carbide tooling would minimize all the above.

./

edited for spelling..
 
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Rprecision

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It largely depends on your setup and your tool as to how successful boring ends up being. I don't do it simply because of what happens to the tool.

Grab a 6x6 square piece of steel. Now go to work on it with a torch. The corners heat up at a higher rate than the "meat" of it right?

Now, think of the friction present with any cutting tool. The transition from the shoulder to the case body is one of the highest torsional loads placed on the cutting tool. Lots of tool pressure being exerted right in that spot. Pressure means friction and friction means heat. It does not take much of anything to get too heavy-handed and nuke that corner. Do it and fail to catch it and you are going to kill the tool and the barrel.

That's part 1.

Part 2 is your using the outer edge of the tool and the rest of it for the last little bit of work. That's promoting uneven tool wear.

I am of the opinion that if you're going to do this, then get a rougher that you can hog shit with, then chase it with a finisher to qualify the size and finish. The idea being the loads applied are applied progressively and evenly across the bulk of the cutting surfaces.

Prolly didn't help for shit, but that's my take on this.

C.
I didn't consider some of those points. Makes sense.

I questioned the method from the idea on maintaining concentricity. Assuming bore is perfect, prebore is perfect the reamer has to follow the prebore perfect for everything to find its place.

If there's only .0005 off there in the wrong spot the nose could hit the bore better the .002" off in a heartbeat. Snap goes the reamer....

I think I have decided not to try this after all.
 

Rprecision

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I pre drill just far enough so that the pilot enters the bore for about 1/4" before the shoulder of the reamer starts to cut. This usually allows me to pre drill about 1" of material out. I generally use a drill that is about .050" under the diameter of the shoulder on my reamer.
If I do anything I will try your method. Although, I'm not comfortable trusting a drill bit to run true enough to follow with a reamer.
 

Supersubes

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If I do anything I will try your method. Although, I'm not comfortable trusting a drill bit to run true enough to follow with a reamer.
I do it exactly like mordamer does. It’s pretty simple really, you must keep it shallow enough that the pilot will engage the bore though. For most reamers thats 1”-1.2” deep tops. I don’t have a flush system, and find that this method is much faster. I use a center drill to start the hole, then a short twist drill bit after that.
 

81STFACP

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After dialing the bore, drill, indicate the area ahead of the neck, dial in the groove if adjustment is needed. Using a small carbide boring bar, I taper bore short of the shoulder in length and diameter. Run the finish reamer longer than headspace. Adjust tenon shoulder to headspace, thread and finish tenon.

Quality check the entrance to the chamber, the body, the neck and throat.

Here is typical.
Chamber entrance:

Chamber body

Neck

Leade

I am not a machinist nor a gunsmith, just a retiree trying to learn new things.
 

Wannashootit

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I disagree.
If you are running HSS dreamers, you will get tool wear regardless of your flush system or coolant type.

You may still get decent looking surface finishes but you may eventually get caught with your pants down due to a dimensional variation from tool wear. Even the throater area of your reamer can wear and suddenly cause pulled bullets and other issues....

Have your finishers checked and if needed, cleaned up often depending on how many chambers you cut.

Going to quality carbide tooling would minimize all the above.

./

edited for spelling..

Absolutely, I shouldn't have said reamer wear "isn't a concern" - it obviously is...
What i meant to say was that I do not believe a short pre-bore would lessen reamer wear to any significant extent. Thanks.
 

MachoMan

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I have done it both ways and the chamber seems to have better (Less) run out when I pre bore- I check the throat area and the back of the Grooves before I start and insure I'm inline though the barrel to the throat area or in front of , once this is assured I have my bore thru bore aligned I drill to remove the material with a carbide drill. then I place a small boring bar in and remove .002-.003 per pass and insure I have clean up of my drilled hole. Now the reamer will follow what I bored all the way in and to depth that I pre determine from the reamer. you can take the reamer bushings off and through in the garbage.) (Although I don't) I usually allow .0002 on my bushing to bore as you don't want the bushing to bind up and scar the lands on the end of the chamber as well ) the reamer will follow the bore and I re inspect after depth with indicator all the way into the lands and check run out and then in the throat area and then in the middle of the chamber then at the back. when I didn't pre bore every .075 to .100 into the chamber I feed I would pull out and clean up everything and re oil and go another.075 to 100. now I can work fast and feed more per rev as I have room for the metal shavings to not block up. I do not have a flush system or a CNC lathe. chambers from lands to end .0002 and under and when I used to feed the whole reamer you would see more run out in the back of the chamber. To much feed makes the reamer want to wallo in the bore and can cut it oversized as well when u don't have a good flush system and steady machine held feed.
6 Creed more on a manual 14x40 Machine ( Last night )

IMG_4461.jpg
 

Edds

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Some Gunsmiths think a barrel should be dialed in in three locations. The way they accomplish this is to dial it in in two places then pre-bore the chamber to make it run true to the other two spots.
 

wadebrown

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If I do anything I will try your method. Although, I'm not comfortable trusting a drill bit to run true enough to follow with a reamer.
You follow the drill bit with a boring bar then the prebored hole is concentric with whatever point you indicated off of.
 

MachoMan

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You follow the drill bit with a boring bar then the prebored hole is concentric with whatever point you indicated off of.
Yes. You do not want to just drill! You have bore it to clean up and true the hole all still under size to the smallest OD on the reamer body.
 

Wannashootit

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Some Gunsmiths think a barrel should be dialed in in three locations. The way they accomplish this is to dial it in in two places then pre-bore the chamber to make it run true to the other two spots.
Ya lost me...(?)
My brain tells me it's impossible to establish more than two points being in axial alignment without bending the barrel.
 

ugsly308

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I dial in the barrel at the end and up at the throat area then prebore about half way and use reamer to cut the rest. It has worked well for me so I will keep doing it.

Casey
 
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Rprecision

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I wanted to leave some feed back for others on my experience with this topic.

I decided to try preboring a practice chamber before my next barrel.

I used many of the techniques suggested by Gordy Gritters in his latest book.

I drilled to about .200" shy of finished length. I bored it true leaving around .030" left to ream.

With prebore I ended up with a chamber that had .0002" runrout at the start of the chamber and a unpreceviable runout (less then .0001") at the throat. For a old worn out lathe I was thrilled! I will probably continue to use this going forward.

I am still learning and just want20200305_163630.jpg20200305_170611.jpg20200305_170614.jpg20200317_220624.jpg20200317_151734.jpg20200317_221215.jpged to leave some feedback for others.
 

dustingaunder

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Thanks, I forgot to mention this was the first time I tried using the copper wire as a interface with the barrel and spider. Seemed to work very well and limited the stress input.
I love my copper rings. Probably a dozen of them on my headstock. I land them in the groove on the jaws so they’re nice and square in the same place on every jaw. Probably doesn’t matter but you might like it.
 
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Vodak

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I like the copper ring idea, I've always used copper pads doing this sort of stuff. I'll have to try that out.
 

Supersubes

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I wanted to leave some feed back for others on my experience with this topic.

I decided to try preboring a practice chamber before my next barrel.

I used many of the techniques suggested by Gordy Gritters in his latest book.

I drilled to about .200" shy of finished length. I bored it true leaving around .030" left to ream.

With prebore I ended up with a chamber that had .0002" runrout at the start of the chamber and a unpreceviable runout (less then .0001") at the throat. For a old worn out lathe I was thrilled! I will probably continue to use this going forward.

I am still learning and just wantView attachment 7280571View attachment 7280572View attachment 7280573View attachment 7280574View attachment 7280575View attachment 7280576ed to leave some feedback for others.
Depending on the tip angle of your drill bit, no need to stop .2 short. That’s a country mile imo. If you’re going through the effort, stop .050 short.
 

hengehold

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I am fine tuning my chambering process. I have been learning of some different methods I want to try.

One method involves drilling then boring the chamber to within .020-.040" of finish diameter and short of length. The theory being it takes less load and wear to run the finish reamer.

The heart of my question: I use PTG reamers with precise fitting nose bushings. Since the bushing will not be following the bore for a majority of the prebore, then engaging the bore after the body is engaged, does this create a problem?

Does anyone use this method?

I have never tried it and want to get some advice.

Thanks
I asked PTG how many chambers I can cut with a finish reamer and if I recall correctly he told me about 100. Do you think you will cut half that many in one lifetime with the same reamer?

if not, I say go with the easy route and stay with the 100% finish reamer approach.
-TH

PS- I stayed at a Holiday Inn last night.
 

Rprecision

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I asked PTG how many chambers I can cut with a finish reamer and if I recall correctly he told me about 100. Do you think you will cut half that many in one lifetime with the same reamer?

if not, I say go with the easy route and stay with the 100% finish reamer approach.
-TH

PS- I stayed at a Holiday Inn last night.
I appreciate the advice. My approach has been on producing the most accurate chamber. Like anything, that's specific to my equipment, tooling and skill.

Tool wear is not a factor for me at this point.

Having done it both ways, I found prebore to produce better results, that is for me!
 
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