How To Chuck Up This Bolt

[Ronno6]

I am trying to come up with a way to chuck this Crosman 760 bolt up in my lathe in order to turn an O-ring groove:

https://www.jgairguns.biz/760-c-78_89_173/crs760044-brass-bolt-p-10932.html

The magnet end steps down from .1865 to .1665.
The groove will need to be in the major OD near where it tapers down.
I have the groove figured out, I just need to find a way to hold the bolt.

Near as I can figure I will make a sleeve to make the OD big enough to grab with a 3 or 4 jaw chuck.
Then the short leg can be between jaws.
Either slot the sleeve or put a set screw or 2 to grab the bolt.

Or.........?

[sb327]

Sounds like you have it figured out, that’s the way I would go about it. Then you have a jig to do as many as you want.

Dave

[Ronno6]

I wonder how well a 3/16" straight compression copper tubing fitting would hold it......

[sb327]

Not sure how well that would work…

Dave

[Ronno6]

As long as the probe is a close fit in the sleeve, the leg of the probe will function as a lathe dog by contacting the chuck jaw.
Interesting.....

[OTmachine]

 Bored to fit aluminum soft jaws on a 3 jaw chuck.  I make the ones for my 6” 3-jaw out of 2.5” diameter x 1” thick aluminum.  Drill and counter-bore 1 hole for 1 socket head cap screw on center of diameter to attach to master jaws.  Works Great!
You would have to add some clearance on the rounds for your smaller diameter.  Number them and use a similar diameter to reattach and align them next time.  Takes minimal clean up to bring them true using a spider.

[JPSAXNC]

I make a slotted sleeve to hold the part and hold it in a collet or chuck. It's accurate and easy.

[KWK]

I am trying to come up with a way to chuck this Crosman 760 bolt up in my lathe in order to turn an O-ring groove:

https://www.jgairguns.biz/760-c-78_89_173/crs760044-brass-bolt-p-10932.html

The magnet end steps down from .1865 to .1665.
The groove will need to be in the major OD near where it tapers down.
I have the groove figured out, I just need to find a way to hold the bolt.

Near as I can figure I will make a sleeve to make the OD big enough to grab with a 3 or 4 jaw chuck.

Then the short leg can be between jaws.
Either slot the sleeve or put a set screw or 2 to grab the bolt.

Or.........?

I like this idea if you slot the sleeve. Mark it before you remove it from the 3 jaw and you can return it to concentricity after you cut the slot.
 If the probe end needs support you can chuck a short brass round in the tailstock then drill it from the headstock to steady the part for the grooving operation. A #19 number drill .166 should get you a pretty close bushing. It will probably drill a tad oversize and give a perfect fit. If the bolt has any runout when sleeved and chucked this will force it to run true where the groove goes.
If the #19 number drilled hole is too snug a simple steel "D" reamer (or D-bit reamer) can remove a few tenths easily in brass.
Yes, let a chuck jaw drive the bolt handle

[Ronno6]

Great ideas, Mr. Karl!

As I may pare down the OD of the tip, I could make the centering support any diameter I choose...

[KWK]

To me these are the situations that make machine work interesting and challenging. Ever since I was 14 years old tinkering and learning in my father's home shop. We didn't have extensive tooling. I had to find a way. And still do.

[KWK]

My immediate thought was of a Jacobs Armature chuck to steady the end but perhaps the bolt diameter is too small. I have one but never used it! Yet.

[Ronno6]

Here are some pictures of my setup

I started with a .725" OD piece of aluminum, probably 2021 that I had in the junk pile.
Thru drilled 3/16"
Cut the slot with a hacksaw by hand, then de-burred the cut inside with a round file.
The first step down from the major diameter was intended to allow installation of a 5/8" shaft collar for stiffness, but proved to be unnecessary.
The smallest step was to provide clearance for my tool holder...it is a left-hand so needed some room.
I purchased a RH holder, but it is a 1/2" shank, and, although it would mount in the QC holder, I was not able to drop the holder sufficiently for the bit to hit the C/L.

I was able to get the bolt chucked up and managed a .001" TIR by playing with things a bit.

Bottom line....it worked....

I did not reduce the diameter of the tip, as it would not have pushed a pellet in past the TP had I done so..

The 2.7mm OD O-ring is a better fit than the plain brass, but could have been a smidge tighter...

[DIAMOND]

Looks like a winner!

[Ronno6]

Looks like a winner!

Well, it was NOT.

I knew that the Crosman magnets were larger in diameter than the Daisy's....
But i didn't think it would extend back so far.
The O-ring groove was right at the end of the magnet, and cur the tip of the probe off......
So, I gotta ger a new bolt.

Good idea, but..........

[Ronno6]

Actually, it should be simple enough to turn a new tip for the end of the probe.
I can make the magnet shallower and put the O-ring groove right where I want it to go.
(Headslap)

[Back_Roads]

Actually, it should be simple enough to turn a new tip for the end of the probe.
I can make the magnet shallower and put the O-ring groove right where I want it to go.
(Headslap)

X2

[Ronno6]

Well, here 'tis.
I replaced the last .750" of the probe, used a Daisy magnet pressed in and ground flush at the tip.
I joined the probe parts together with a 6-32 set screw.

Now, let's see if it fits....

[Ronno6]

Yes !!
It fits and zero blowback detected by a tissue over the loading port when firing a pellet on 6 pumps.

Nice little "crack" as well.....a definite improvement.