Spider!!!

[cdhknives]

No, not that kind...

This should allow me to dial in rifle barrels for muzzle threading. I've got 2 AR's that could use this treatment, and a couple of other rifles that might want to wear a can eventually.

The 4 set screws will be removed normally, to allow free feeding of long stock and my drawbar. This replaced the normal spindle bearing preload collar. 1.25"x20TPI. Yes, that is not a typo. The first step was to cut a thread gauge that matched the spindle threads so I would know when the interior threads were complete. Then take a piece of DOM tubing of appropriate size and start turning. My second set of interior threads...lots easier now.

 

[Franko]

How far does your spindle stick out, CD? It looks like you've attached your spider to it with set screws, so I assume it sticks out enough to do that.

 

[wa5cab]

Franko,

It is a standard Atlas spindle. The bare threaded length is approximately twice the thickness of the standard threaded collar. The bare thread length with the standard collar in place is marginal for attaching anything like a spider or lever operated collet closer without removing the collar. All of the lever type collet closers are set up to replace the collar. So should any spiders.

 

[Franko]

thanks, Robert. I waiting to see how the spindle bore on my PM1228 is. A spider looks like a very handy gizmo.

 

[cdhknives]

Do you think 1/4-20 set screws are too light? I got that comment on another site...???

Material is A513 steel tubing.

A513 (alloy 1020-1026) Steel
This alloy is generally used for DOM tubing. Its higher carbon content means higher strength, but lower weldability and machinability.



ASTM A513 alloys 1020 - 1026 Mild (low-carbon) steel
Minimum Properties Ultimate Tensile Strength, psi 87,000
Yield Strength, psi 72,000
Elongation 10.0%
Rockwell Hardness B89
Chemistry Iron (Fe) 99.08 - 99.53%
Carbon (C) 0.18 - 0.23%
Manganese (Mn) 0.3 - 0.6%
Phosphorus (P) 0.04% max
Sulfur (S) 0.05% max

 

[cdhknives]

How far does your spindle stick out, CD? It looks like you've attached your spider to it with set screws, so I assume it sticks out enough to do that.

There is a good 1/2" or more of threads with the collar removed. The one set screw is to lock the and prevent unscrewing in use, not to actually physically hold the collar in place. I single pointed interior threads to match the spindle...still a challenge at my experience level!

 

[chevydyl]

did you retain the plastic piece in the stock collar that seats against the thread under the set screw? or did you cut the threads into the set screw itself?
the 1/4-20 is just fine, max stock size is 3/4 anyway and its the stupid end, theres not an awful lot of load on that end.

 

[cdhknives]

I put a 3-4 pieces of #9 lead shot under the set screw to protect the spindle threads.

 

[wa5cab]

knives,

1/4"-20 set screws should be adequate. However, you would have a more stable spider if you had bored the unthreaded end only out to about 13/16" or 7/8". The set screws wouldn't be prone to rock as much. You only have about one diameter of thread engagement. Plus for adequate strength against strip-out in alloy steel, minimum recommended is usually 1-1/2 diameters. With aluminum a bit more. And this is that rare application where if some is good, more is better.

 

[mksj]

I prefer to use fine thread pitch screws for the spider. My outboard spider is a bit larger (1- 9/16 bore) I use 3/8" x 24 spider screws and 5/16" x 24 set screws with dimples to secure it (there are no spindle threads). The fine pitch screws are available with brass tips in a set screw and cap screw version, but I am making my own variations. Will also make a set with ball bearing tips that will apply pressure to bronze fingers (allow distributed load as opposed to point contact, example of another persons work for fingers below).