Hornady Concentricity Gauge

[autoxforfun]

I've had this Hornady Gauge sitting on the self for several years and never use it anymore.  With the work on the Magnum cartridge, I am now neck turning and find that using an ball micrometer for measuring neck thickness a bit of a pain.  So I was looking at this gauge and thought I may be able to make this work for measuring neck thickness.  

First step was to replace the piece which held the nose of the bullet with something that could be used to index against the inside of the neck.  I was thinking that the pressure of the dial indicator would hold the neck against the pilot and then as I rotated the case, it would read the neck thickness.  It could be moved in or out to reference a different spot on the neck.  IF this works, then I'll upgrade to a better dial indicator to get finer resolution.

Here is the old piece from the gauge (top) with the new piece with the pilot (bottom).




Here is the finished product measuring a case.




I will need to run some cases thru it and compare the data to the micrometer and see if it work reliably.

[bikemutt]

I agree with you about ball micrometers; they are well-intentioned tools but for necks they require a good degree of consistent axial position in the neck; the shoulder and the mouth areas are quite often not representative of the mainstem of the neck.

It's been a while since I donated my dust-gathering Hornady concentricity gage to the range reloading room, where it continues to gather more dust, I don't recall exactly how it works. That said, from your picture it looks as if the brass body is either being held, or is resting in a holder of sorts, the neck appears to be resting on a mandrel of sorts. My concern is any shortage in body-neck coaxiality is going to be reflected in your indicator readings.

[gman47564]

Cool.. did you make the pilot bob?

[autoxforfun]

Cool.. did you make the pilot bob?

I did....having a lathe to make stuff like this is sooooo great.

[autoxforfun]

I agree with you about ball micrometers; they are well-intentioned tools but for necks they require a good degree of consistent axial position in the neck; the shoulder and the mouth areas are quite often not representative of the mainstem of the neck.

It's been a while since I donated my dust-gathering Hornady concentricity gage to the range reloading room, where it continues to gather more dust, I don't recall exactly how it works. That said, from your picture it looks as if the brass body is either being held, or is resting in a holder of sorts, the neck appears to be resting on a mandrel of sorts. My concern is any shortage in body-neck coaxiality is going to be reflected in your indicator readings.

Chris, I agree with your concern.  The stock Hornady base holder is a cone shaped recess....I guess they figured it would self center and could accepts different size base diameters.  I was considering turning it around and machining a more precise relief for the base that I'm using.  Currently, I have just one magnum cartridge that I'm neck turning so this could be done with a simple machining operation.  If I needed to accommodate more case diameter, I could create a stepped relief for each one.

The other option would be to see if I could machine it to accepts standard shell holders.....more complicated.

[bikemutt]

I've never looked for one but, a tube-style micrometer with a ball at the end of each anvil, instead of one being flat, would be nice  .

Another method for conventional neck turning would be to add an indicator mount to the handheld, or machine held assembly, in the same radial axis as the cutter. Then, zero the indicator on the mandrel, retract it off the mandrel and hold it there, turn the neck, then drop the indicator on the turned neck, the difference should be the wall thickness to a precise degree.

Hey, it's OK to dream here no 

[autoxforfun]

Hey, it's OK to dream here no 

Always !!

[DHuffman]

I've got two Hornady neck turning tools that are made on the same frame. I've always wanted to find another use for them since I got Mr Century 21 gear.

[bikemutt]

Bob,

This spindle ball tip may be worth a look: Starrett Micrometer Balll Spindle/Anvil Tip

I found that while dual spherical tip micrometers are available, the anvil side of the tips are too large to fit inside the necks of all but 45/70 or .500 cases.

So, I got to thinking, why not start with a standard tube micrometer which most of us reloaders already have, then find either a replacement spherical-tip spindle, or find a snap-on spherical spindle tip.

The advantage to using a spherical-tip spindle is it can be calibrated to give direct readings; snap-on tips on the other hand, require subtracting the added length of the tip from the readings.

I ordered the eBay one in the link above, for $20 it's worth it to see if the concept works.

Tube mic plus spherical spindle tip image:

[autoxforfun]

What I was going to try next was to get a turning insert that will allow me to put a 'ball' profile on the pilot that I have....like on the picture of your micrometer.  This should improve the reference point and give me a narrower measurement point to use.  Also will ensure that I don't have any error due to a donut forming or a ridge at the mouth.  Doing that and improving how the base is secured hopefully will make this a useful tool.

[bikemutt]

You've inspired my crazy gene Bob 

I thought about something like the staged picture below, attaching a spherical-tipped mandrel to a Dial Test Indicator (DTI) so that the DTI stylus is active and zeroed on the mandrel. The mandrel would be placed inside the bore, the DTI stylus outside the bore, or vice-versa, for a direct, sensitive and accurate reading of wall thickness.

I just can't figure out how to do it, yet  .

I'm curious to see what you come up with for turning a ball end.

[jvw2008]

It doesn't need to be a ball. It could be a sharp ^ shape.

[bikemutt]

It doesn't need to be a ball. It could be a sharp ^ shape.

I'd be concerned about scratching the necks.

[jvw2008]

LOL I don't think it has to be THAT sharp.

A point tip might be easiest to make on a mill. The ball is probably better using a lathe. Simply my guess based on very limited experience.

[bikemutt]

LOL I don't think it has to be THAT sharp.

A point tip might be easiest to make on a mill. The ball is probably better using a lathe. Simply my guess based on very limited experience.

You're onto something Jerry, when turning a point on the lathe, it doesn't have to end in a point, it could be a 1mm or so flat. Then finish it up with sandpaper so any sharp edges are removed. I like it  .