• This Forum is for adults 18 years of age or over. By continuing to use this Forum you are confirming that you are 18 or older. No content shall be viewed by any person under 18 in California.

Prebore and floating reamer holder

I often wonder about 0.0001 precision and accuracy measurements in the garage or shop environment.

I retired from the semiconductor industry, I still remember how our calibration/metrology labs demand strict requirement for vibration, temp and humidity requirement to guarantee measurements at that level. Maybe they just like to waste money.

How good of a spindle TIR and environmental conditions in the shop is required to get to that level of measurement?

I am not a gunsmith nor a machinist, just a hobbyist trying to learn.
My shop isn't a balmy 60°, climate controlled, space. But if a .0001" indicator isn't registering, I'm okay with what runout might be there. It's more about guaranteed repetition than anything, not leaving anything to the will of the gods. As measurement .0001" is useless in my shop, but an indication it's useful.
 
My wording is probably wrong but an absolute measurement like I.D. or O.D. is more susceptible to environmental error than a relative measurement like runout.

As long as your test indicator is working properly and your lathe spindle has less than 0.00005" runout, it's pretty easy to trust a 0.0001" TIR measurement even if it's not from a temperature controlled metrology lab.
 
WOW! 29 replies on a discussion of whether to prebore or not.

Butch's computer has to be broken.:)

Jim

Been out of town. An old high school buddy retired as State District Judge and a huge party was held at a Wichita Falls pub-way too many folks. The next night we were at his home for our class's high school reunion.
We had a wonderful time.
 
I pre-bore because I lack patience... I don't have a muzzle flush system and pulling a reamer every .100" or even .050" is excruciatingly slow....mind numbing even. I drill and bore the hole large enough in steps so the reamer enters far enough for the pilot to enter the bore (that is dialed in on the throat) and also contacts at the back end. For alignment, that give you two points of contact as far apart as possible that initially will guide that reamer straight TO WHERE YOU HAVE IT DIALED IN. If you didn't dial in properly, it'll not work out for you and a tighter pilot will try and move you back on course. If you ever have a longer chamber reamer get tight towards the end, that's the pilot binding on an off center bore trying to straighten that mis-alignment.

I have chambered the same as Stan also and the rifles shot just as well. It works and I would likely use that method if I didn't have to pull a reamer, clean chamber, clean reamer, re-oil, and start cutting again. When doing so I tend to push things too far trying to get another .100" or so and risk picking up a chip and putting a nice ring around the danged thing that may or may not clean up depending on how far I have to go.

This should not always delve into a p****ng contest. It all works well when done properly, it's just that some methods work better for others depending on their setup AND comfort zone.
 
I dial in where the throat will be and dial in the muzzle end. Drill .015 smaller than the body shoulder junction to a depth of .100 shy of that depth. at that point all check the throat area again with the indicator to make sure it’s still good. Then go in with a boring bar to get the hole straight and also get the reamer started in so the body of the reamer has support as to help with any chatter. I run a loose bushing on the reamer also. Ive tried May different ways and they have all worked just fine.
 
I pre-bore because I lack patience... I don't have a muzzle flush system and pulling a reamer every .100" or even .050" is excruciatingly slow....mind numbing even. I drill and bore the hole large enough in steps so the reamer enters far enough for the pilot to enter the bore (that is dialed in on the throat) and also contacts at the back end. For alignment, that give you two points of contact as far apart as possible that initially will guide that reamer straight TO WHERE YOU HAVE IT DIALED IN. If you didn't dial in properly, it'll not work out for you and a tighter pilot will try and move you back on course. If you ever have a longer chamber reamer get tight towards the end, that's the pilot binding on an off center bore trying to straighten that mis-alignment.

I have chambered the same as Stan also and the rifles shot just as well. It works and I would likely use that method if I didn't have to pull a reamer, clean chamber, clean reamer, re-oil, and start cutting again. When doing so I tend to push things too far trying to get another .100" or so and risk picking up a chip and putting a nice ring around the danged thing that may or may not clean up depending on how far I have to go.

This should not always delve into a p****ng contest. It all works well when done properly, it's just that some methods work better for others depending on their setup AND comfort zone.
We'll said sir.
 
All things are relative. Most of the bench rest guys do something like this regardless of the method of indicating (throat and muzzle vs Gritters method.) If it doesn't sound beneficial to you, maybe it isn't. I chambered quite a few barrels for hunting rifles before I started pre-boring and they all shot very well by hunting rifle standards.
 
Do any of you use a bore mandrel inserted into the bore to dial in the barrel before chambering? Can't imagine any other way to do it.
 

Upgrades & Donations

This Forum's expenses are primarily paid by member contributions. You can upgrade your Forum membership in seconds. Gold and Silver members get unlimited FREE classifieds for one year. Gold members can upload custom avatars.


Click Upgrade Membership Button ABOVE to get Gold or Silver Status.

You can also donate any amount, large or small, with the button below. Include your Forum Name in the PayPal Notes field.


To DONATE by CHECK, or make a recurring donation, CLICK HERE to learn how.

Forum statistics

Threads
165,560
Messages
2,198,216
Members
78,961
Latest member
Nicklm
Back
Top