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Noob- Interesting observations using a range rod

ShelbyG

Plastic
Joined
Feb 9, 2019
I'm completely new to using a lathe and had some questions from some things I observed when trying to co-axially align a barrel.

I'm using a Viper truing jig and an unchambered .264 dia barrel. I roughed the barrel into the jig using a PTG range rod and .001" accuracy dial indicators.

1. Once I roughed in the rod and switched over to a test indicator with .0001" accuracy, I was able to adjust the barrel so that I could traverse the length of the rod with zero deflection. However, when I rotated the lathe, I showed deflection at the barrel end and the end of the range rod. When I adjusted the barrel so that I had alignment at the barrel (except as noted below in item 2) and alignment at the end of the range rod, I showed .0002 - 0003" of displacement when I traverse the length of the rod. Is this normal?

2. I think my range rod has a flat spot. When I was adjusting the barrel end of the range rod, I consistently showed a low spot at one point on the rod as I rotated it. I marked the low spot on the rod and then using the jaws as a reference point, I found that as I rotated the chuck 3 out of 4 of the jaws showed zero deflection to each other, but when I rotated to the jaw that I aligned with the mark on the range rod, I had about .0004" low point. I then removed the rod and aligned it with a different jaw on the chuck. Rotated the chuck and found the low point moved with the rod. I interpret these results as being a flat spot in the rod vs an alignment issue with the barrel. Is this a good assumption?

Thanks in advance.
 
(a)You worry too much,(b) All barrels are bent.(c) Some are more or less straight on the OD ,but the bore wanders about (d) refer a.......Therefore ,dial in the muzzle end ,and forget about it,then dial in the chamber end to the nearest 001,which is good enough IMHO.....Then rough out the chamber .Having roughed out the chamber better than 80% of material removal,then set up with your rod.This will ensure the throat is concentric,which is what is important.
 
I do similar to John, but I use a long stem indicator and measure on the surface of the bore instead of using a rod. A Mitutoyo 513-512 pocket type dial test indicator works well.

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I make my own rods from drill rod or brass, depending. How do you plan on chambering? If you dial it in one gazzilionth, it only matters if the reamer hold8ng method is correct. Welcome to the fun!
 
I've gotten rods that weren't straight, but never a flat spot. Check it by itself between centers. Cut a fresh center in your headstock and even if your tailstock center is off somewhat, it should still show no out of round at any point along the rod if it is straight and true. If your rod has no center cuts, then it was done on a centerless grinder and will be useless as an indicating rod. You would think that even the most novice machinist would know that it needs to be ground on centers to be useful but believe it or not, I got 3 of these from a gunsmith tool manufacturer that had no center cuts and were up to 0.004 out-of-round. I finally talked with the manufacturer and they sent one that was ground between centers.
 
I do similar to John, but I use a long stem indicator and measure on the surface of the bore instead of using a rod. A Mitutoyo 513-512 pocket type dial test indicator works well.

Sent from my Pixel 2 using Tapatalk

Ordered a similar model from Brown and Sharpe yesterday. I'll see what I get using this to help align the bore.

Thanks
 
I make my own rods from drill rod or brass, depending. How do you plan on chambering? If you dial it in one gazzilionth, it only matters if the reamer hold8ng method is correct. Welcome to the fun!

I haven't gotten to the point that I've finalized this plan. Right now I'm thinking live finish reamer with a floating holder (most likely the one from Bald Eagle). For now, I was just trying to see if I could successfully align the barrel in the lathe.
 
I've gotten rods that weren't straight, but never a flat spot. Check it by itself between centers. Cut a fresh center in your headstock and even if your tailstock center is off somewhat, it should still show no out of round at any point along the rod if it is straight and true. If your rod has no center cuts, then it was done on a centerless grinder and will be useless as an indicating rod. You would think that even the most novice machinist would know that it needs to be ground on centers to be useful but believe it or not, I got 3 of these from a gunsmith tool manufacturer that had no center cuts and were up to 0.004 out-of-round. I finally talked with the manufacturer and they sent one that was ground between centers.

Thanks for the info. I'm getting another rod for comparison purposes. It just seems odd that there is essentially no deflection in the rod showing on the test indicator until I get to the exact spot that I marked on the rod and for about 1/2" in length. If I traverse the rod length away from this point, I can get to where I have essentially no deflection showing on the test indicator as I spin the chuck.
 
Best to use two DTIs with a range rod.

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Best to use two DTIs with a range rod.

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This is essentially what I'm doing. What I'm observing is the ability to get next to zero run out at both indicators, but if I traverse the range rod by moving the saddle away from the chuck, I show deflection as the test indicator moves along the rod from the chamber end of the barrel to the end of the range rod. My second issue was the presumed flat spot I mentioned.
 
Range rods are slightly tapered, so you will see the needle move if as you run it up and down the rod.

Ahhhhh, that's right. Funny how I "knew" (from reading the description) they were tapered, but forgot how that would influence the test indicator as I moved along the rod.
 
I like Genes 2 indicator method to take another variable out of indicating(way twist). Also, flat tips are a big help in indicating rods.
 
OP,
I know you know this, but please be safe! Lathes are VERY unforgiving. When in doubt, hit the red stop button and reevaluate. We’ve all been new at one point and launched chuck keys across the room or turned on the lathe in gear while threading ..... and didn’t double check the speed ....
 








 
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