How NOT to validate your chambering job

[INTJ]

Yesterday I chambered a 33XC. Had to use the 5.5" stylus on the Interapid, which as we all know is a pain. I finally did get it dialed in.

After I had finished the chamber I decided to check the runout. I put the indicator just inside the breech and it showed .002" runout. I thought "no way."

I then checked further forward in the chamber. Zero runout. I then checked the throat, the shoulder and a couple more places in the chamber. All zero. I went back to the breech end and had .002". That didn't make any sense.

I pulled the barrel from the lathe, and discovered a small piece of cellophane tape was at the back of the breech.

I had wrapped the go gauge with tape to make it less wiggly. I put too much on and it messed up the tape when I inserted the gauge. I pulled a layer off, but didn't see that a little bit was left in the chamber.

Go figure. Lesson learned.......

 

[Dusty Stevens]

You gotta pull the barrel and re-indicate it in the throat and ahead of the throat then check runout. If you check in the same setup you cut a part in youre just checking lathe bearings. An indicator rod is an easy way to set up an already chambered barrel to check chamber runout although its not perfect at all

 

[FireMedic]

You gotta pull the barrel and re-indicate it in the throat and ahead of the throat then check runout. If you check in the same setup you cut a part in youre just checking lathe bearings. An indicator rod is an easy way to set up an already chambered barrel to check chamber runout although its not perfect at all

I’m confused. Why would pulling the barrel be any different? He obviously already indicated these areas before chambering. And should be able to do a quick confirmation that it hasn’t moved…then check runout of the chambering job.

Depending on how you hold the reamer, I’d be more concerned about a chamber that is cut oversize then a couple tenths runout.

I want my chambers to have no runout and cut to size, concentric with the bore and on the same plane as the bore at the chamber end.

 

[Dusty Stevens]

I’m confused. Why would pulling the barrel be any different? He obviously already indicated these areas before chambering. And should be able to do a quick confirmation that it hasn’t moved…then check runout of the chambering job.

Depending on how you hold the reamer, I’d be more concerned about a chamber that is cut oversize then a couple tenths runout.

I want my chambers to have no runout and cut to size, concentric with the bore and on the same plane as the bore at the chamber end.

Theres going to be no runout if its in the same setup unless the bearings show some. Lets say you put a bar in a chuck .025 off center, turn it down .075 and stick an indicator on it. What are you proving with that?

 

[rijndael]

Theres going to be no runout if its in the same setup unless the bearings show some. Lets say you put a bar in a chuck .025 off center, turn it down .075 and stick an indicator on it. What are you proving with that?

Thanks for that, I now get it.

 

[Dusty Stevens]

Thanks for that, I now get it.

Its just for simplicity, figuratively speaking. You can loosen the barrel and spin it 180deg and do the same thing

 

[xr650rRider]

What's accomplished is proving nothing moved during chambering. If you dial it in to 0, cut chamber, measure and get 0, then your still in same position where you initially dialed in the barrel. If you initially dial in with .002" runout, cut chamber, measure your going to get 0 if nothing moved but your still .002" out.

 

[Tucker65]

I get what Dusty is saying but what I would check is the lands and grooves just in front of the chamber. If they are still running true then I would say your chamber is true to the bore.

 

[urbanrifleman]

I would go shoot it.

 

[GenePoole]

@INTJ , I'm not sure I'm understanding. Was it the tape that just gave the erroneous reading, or did it somehow deflect the cutting of the reamer and resulted in a OOR chamber?

 

[Ksracer]

If you check in the same setup you cut a part in youre just checking lathe bearings.

I fully agree with you for single point tools.

But I've had a new reamer that cut off center before. The flutes on the body wouldn't cut freely. So as I'm feeding the reamer, it's binding up on the body and becoming hard to keep from spinning. All of a sudden 1 flute started to cut and took a .002 thick chip from the shoulder all the way to the breech. Except after about 180* of rotation, the pressure was relieved and it stopped cutting again. After pulling the reamer and seeing what happened, I tried feeding it another .100, but it started binding again and the back of the reamer was walking in a circle.

I was able to save the chamber by taper boring out the bad section and finishing it with a different reamer. Thankfully it was a .260 Remington with a heavy body taper and not a Creedmoor or I might not have cleaned up.

 

[INTJ]

@INTJ , I'm not sure I'm understanding. Was it the tape that just gave the erroneous reading, or did it somehow deflect the cutting of the reamer and resulted in a OOR chamber?

The tape gave the erroneous reading. Had any tape been in the chamber when chambering, the reamer would have just cut thorough it.

 

[Machinist John]

Experience is the sum of many mistakes. I have had my share.

Glad you found the culprit!

 

[tobnpr]

Had to use the 5.5" stylus on the Interapid, which as we all know is a pain. I finally did get it dialed in.

Specifically, you indicated which two points?

I'll never use a 5.5" contact point. Full one thou resolution. I know we're not measuring, but that's half the resolution of the standard tip. I'll stick with the Grizzly rod that far up the barrel.

 

[Dusty Stevens]

Specifically, you indicated which two points?

I'll never use a 5.5" contact point. Full one thou resolution. I know we're not measuring, but that's half the resolution of the standard tip. I'll stick with the Grizzly rod that far up the barrel.

You can probably resolve down to 1/8 of a div pretty easily on an interapid so the .001/div can become .0002 without looking real close. Zero is zero hes not looking to hit an actual number just any runout. The grizzly rod bushing has more runout than that

 

[ridgeway]

There can still very well be run out in a chamber in same setup and nothing move from original dial in process...

 

[Tucker65]

There can still very well be run out in a chamber in same setup and nothing move from original dial in process...

Now if you have that, then I'd say there is a problem.

 

[ridgeway]

Now if you have that, then I'd say there is a problem.

Not necessarily.

 

[INTJ]

Specifically, you indicated which two points?

I'll never use a 5.5" contact point. Full one thou resolution. I know we're not measuring, but that's half the resolution of the standard tip. I'll stick with the Grizzly rod that far up the barrel.

I agree with @Dusty Stevens.

My experience, when I first made the jump to all direct reading, I got a barrel dialed in to about .0002. I then checked it with a Grizzly Rod and tight bushing using a Mitituyo 10ths test indicator--it showed zero.

With a Grizzly rod there is probably .0002" of clearance between the bushing and the rod, then another .002" between the rod and bore. Maybe it's only .0003" total, maybe it's .0005" total. Regardless, there is a lot of potential tolerance error, and that is probably why Gordy himself says to make it final check with a direct reading indicator.

Anyway, that is why I learned how to direct read off an Interapid. While I'd rather not have to fuss with the 5.5" stylus, it is still miles ahead of the Grizzly Rods for me. It is such a high quality indicator that it's easy to see even the smallest movement.....that is when I finally figured out how to use it. There is a learning curve......

 

[INTJ]

Theres going to be no runout if its in the same setup unless the bearings show some. Lets say you put a bar in a chuck .025 off center, turn it down .075 and stick an indicator on it. What are you proving with that?

So that makes sense with a rigid setup like real machinists use or with preboring. Those methods always true the part to the spindle.

However, I used a JGS floating reamer holder and didn't prebore. I indicated just in front of throat and the breech. Since the floating reamer holder follows the bore, what ever straightness I achieve is with my dial in.

With a floating reamer holder, if I had dialed to .0002" runout, I would still have .0002" runout after chambering, at least as I understand it, since the reamer is simply following the bore.

Right?