Indicating & reaming throat under jaws/spider

[Carl S]

You don't have to pull down on your spider pins much at all to make them hold.very little really.your holding inboard and outboard on your barrel.the whole design-idea of the spider requires very little torque on the pins to make them hold.

 

[Dusty Stevens]

You don't have to pull down on your spider pins much at all to make them hold.very little really.your holding inboard and outboard on your barrel.the whole design-idea of the spider requires very little torque on the pins to make them hold.

Its tightening them down to get that last few thou thatll get you

 

[DaveTooley]

Just very lightly snug up the screws to get the barrel dialed in then rotate and tighten screws. Not much more than a good one handed twist on a t-handle.

My screws protrude about 1/2" so. I go finger tight on the OD, finger tight on the muzzle w/gage pin, finger tight on the barrel ID, dial in the muzzle, then snug up the screws.

 

[Road_Clam]

Do you guys use jam nuts to lock your spider jack screws or are they not necessary ? The bolts wont back off from rotational forces and vibration ?

 

[DaveTooley]

Not necessary

 

[skeeljc]

I believe that this setup would spread the load and preclude the problem because of the lower unit loading required to secure the barrel. I don't remember where I got this picture, but I first saw this setup in a post by Alex Wheeler and I still think that it is a very good design, the best of its type.

These long blocks will spread the clamping pressure but they must slip where they contact the barrel to allow the other end to move and that will cause a bend in the barrel.

 

[BoydAllen]

These long blocks will spread the clamping pressure but they must slip where they contact the barrel to allow the other end to move and that will cause a bend in the barrel.

It would seem to me that the primary purpose of these sorts of setups is to be able to adjust the lateral position of a barrel at a given point, and to resist loads applied by cutting tools, preventing the barrel from being moved by those loads. Based on reports from reliable sources the setup that I posted a picture of does both very well. As far as sliding goes, I believe that this would take place before the final tightening, and that that would actually prevent the barrel from being bent, as adjustments are made.

 

[DShortt]

It appears to me that the spider Boyd pictured has ball ends within the blocks on the tips of the screws to allow them to move in whichever direction they need to in order to match the barrel contour. Hard to tell without seeing it first hand but that's what I pictured in my mind.

 

[DShortt]

I am using this inboard spider. It uses a 5mm Allen. Sounds like yours, @DShortt, has thumb screws or the like?

View attachment 1425557
Hank

Very similar except that I have two sets of screws in mine as I haven't figured out a practical way to mount an outboard spider on my SouthBend Heavy 10. I don't really like that much hanging off the front of the spindle but it doesn't seem to cause me problems and small equipment has limitations you have to deal with one way or another.
The only other difference is the tips of my screws are aluminum and half round. Made them myself.

 

[BoydAllen]

It appears to me that the spider Boyd pictured has ball ends within the blocks on the tips of the screws to allow them to move in whichever direction they need to in order to match the barrel contour. Hard to tell without seeing it first hand but that's what I pictured in my mind.

There are conical seats for the balls in the tips of the screws. Any sliding, caused by muzzle end spider adjustments, would take place under light tension as the barrel's position is being adjusted, before final tightening.

 

[Road_Clam]

We use spherical Jergen nuts and washers frequently in the heavy hydraulic machining industry. Solid means of clamping off cambered or irregular (other than perpendicular) surfaces.

 

[LVLAaron]

I use a nut on my outboard spider, with an o-ring under it. It's not needed... but keeps them from rattling around and coming out when I'm not working on barrels.

 

[Judd]

I use a nut on my outboard spider, with an o-ring under it. It's not needed... but keeps them from rattling around and coming out when I'm not working on barrels.

I use a nut on my outboard spider bolts…I didn’t, right up until the first one came loose haha…then I started religiously using the nuts. Mine are just the factory brass tipped bolts that come with the Grizzly gunsmithing lathe.

 

[LVLAaron]

I use a nut on my outboard spider bolts…I didn’t, right up until the first one came loose haha…then I started religiously using the nuts. Mine are just the factory brass tipped bolts that come with the Grizzly gunsmithing lathe.

Are they fine thread?

 

[SKWERLZ]

Are they fine thread?

I went fine thread on mine
They don’t budge.

 

[Carl S]

Its tightening them down to get that last few thou thatll get you

Yes ya gota be real steady on them.we don't want to be forcing,bending or inducing any stress on the barrel.

 

[B Nettesheim]

You can easily distort the bore with your clamping force.

Easily!!

 

[INTJ]

I use 1" x 1/2" x 1/8" aluminum shims under both inboard and outboard spiders. I tighten them snugly with allen wrenches so they will hold. This method won't dimple a carbon barrel.

I also use a Grizzly rod to determine what bushing to use on the reamer when cutting the chamber. I look for a snug but smooth fit on the bushing. I have never noticed a tight spot anywhere along the shims, so I guess my MK-1 hand feel is about right.

The nice thing about the brass tipped screws on the aluminum shims is they will only allow so much tension before they squish a bit, so as long as I am reasonable with my tightening there shouldn't be an issue.

I think the final check of too tight may be the Interapid itself. On a decent quality cut rifled barrel, the rifling should be extremely close to even. If the Interapid confirms that when the barrel is dialed, then there must not be any over-tightening.......or else they are all over-tightened the exact same amount......

Thinking about it, probably the worst way to hold a barrel--in terms of potential over-tightening--is with a 4-Jaw with small aluminum shims at the end of the jaws....the shims we use to allow the barrel to articulate. Those small contact points with the clumsy way we have to tighten a 4-Jaw would seem to easily allow over tightening.

I guess this makes a good case for a Set True chuck........

Then again, I have shot several screamer groups at 1000 yds with barrels I have chambered using a 4-Jaw with small shims, so maybe none of this is a big deal......

I guess I'll know in two weeks when I take my best chamber job yet to a match. Of course, if I do shoot better, it could be my deeper inlet and rebedding of the action, or the better designed Alex Wheeler reamer, or better conditions, or??????

 

[Judd]

Are they fine thread?

No, course.

 

[Road_Clam]

Educate me ... What are "Grizzly rods"?