Indicating & reaming throat under jaws/spider

[Henryrifle]

I am not unnecessarrily cranking down the inboard spider on the barrel but it is directly over the throat area. I do, however, grip the barrel tight enough to keep it from moving when turning and threading the tenon. Of course it measures 0 runout after you ream it but once you relax the spider/jaws does anything undesired happen? Will try to measure that next time. I've only reamed a few chambers this way and so far, so good. I do see that some of y'all have made aluminum blocks radiuses to match the barrel contour that are placed between the spider and barrel. That seems like a good idea.

Thank you,
Hank

 

[Dusty Stevens]

A good test is to slug it while clamped on it. Then youll see. Gotta figure out how to test everything

 

[DShortt]

A good test is to slug it while clamped on it. Then youll see. Gotta figure out how to test everything

Excellent response. I only tighten mine down enough to hold them which is really little more than finger tight. It's not hard to deflect a barrel blank believe it or not. Learned that the hard way. If you're setting it with an wrench of any kind you're probably getting things waaaaaay too tight unless you're only using a couple of fingers.

 

[SKWERLZ]

I’ve always feared I’m overly tightening my spider screws on barrel but have made a rod to fit reamer bushings in the barrel before and in the spider and couldn’t feel a tight spots, not super accurate but within a few tenths.
I should experiment on how tight I need them for cutting and reaming on a smoked barrel.

 

[Alex Wheeler]

You can easily distort the bore with your clamping force.

 

[Henryrifle]

Fortunately, I am not a gorilla and have built things like airplanes and race cars. I do have a good understanding of materials, deflection, torque and etc. I flew and raced them too. None fell out of the sky or failed to perform due to mechanical issues. While I don't have your experience regarding barrel making, I do have a good sense about machine setup.

I use an inboard spider that is tightened by a small Allen wrench. No worries about extreme over tightening.

Thanks for the good pointer, @Dusty Stevens.

Sounds like chucking the barrel a little ahead (towards the muzzle end) might be better than directly over the freebore area?

Hank

 

[762plinker]

You can easily distort the bore with your clamping force.

so alex,, which do we do
just lite force..defined s ???
move to keek the throat out of the jaws ?? how far out ?
or ??
thanks

 

[Alex Wheeler]

You grab them where you need to. Like Dusty said, slug them to know how much grip they will take. Spreading out the force is key as well. Small contact points are not the best. Cant descride it, you just need to learn your setup.

 

[Dusty Stevens]

Just get a grizzly rod, find a perfect bushing, then clamp it and try that bushing again. Its easy to test things multiple ways. The grizzly rod is faster than a slug

 

[DShortt]

So if you're using inboard and outboard spiders how much/little pressure does it take to deflect the bore of a blank? If your chamber area is indicated true, what happens to that same area when the spiders are loosened?

I'm asking because I ask myself these same questions and I'm not set on what reality is.

 

[DShortt]

I personally have not noticed any constrictions introduced to a barrel using a spider, but the only way I've found to detect them is by using slugs and I've never tried that while I had a barrel mounted in the lathe for chambering. I probably should try that a couple of times just for my own knowledge if nothing else.
I did notice early on that it doesn't take much pressure at all to deflect the barrel blank between spiders. Now days I am very careful to apply only enough pressure to keep the barrel from spinning within the spiders, which isn't much at all. I've not tested this with a torque driver but perhaps I should for the sake of consistency if nothing else.

Do any of the rest of you have a torque reference you use for spider screws? Mine are 1/2 -20 with aluminum ball tips if that matters/helps.

 

[BoydAllen]

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.

 

[Henryrifle]

@DShortt - I don't know and it is a good question if it makes a difference down range. I am only now coming back around to think about these things.

I chamber barrels because I don't want to have to wait months for that work to be done, and, like all of you, I too am an OCD perfectionist. The barrels I made and shot in competition shot to a standard - 2" groups at 600 yards for 10 shots. Now I am wondering if I can do better than that and am just starting to look critically at all my chambering processes.

Hank

 

[Henryrifle]

@DShortt - guessing that deltronic pins are an easy way to find out if the bore is tightened while in the spiders/jaws.

Hank

 

[DShortt]

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.

I would think that such a setup would require even less pressure than mine does and even then it's little more than finger pressure. That's simply because the contact area would be greater with blocks rather than ball tips.

 

[Henryrifle]

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


Hank

 

[Dusty Stevens]

The more surface area you have for clamping the tighter you can get them. You can feel a clamp on rimfire tuner and you can feel those spider points. All we ever do here is encourage testing. Again, a grizzly rod is the fastest way to test or you can slug it in the lathe while trying different things. Youll find out in minutes then back up and devise yourself a good method that will pass your tests. Being a good machinist is being able to test your work, id say in chambering its the number one requirement if you want to rise above the garage fitters on every corner these days

 

[DaveTooley]

Just get a grizzly rod, find a perfect bushing, then clamp it and try that bushing again. Its easy to test things multiple ways. The grizzly rod is faster than a slug

If you have a lathe make your own rods. I made a set for 1,2&3 size bushing. Maybe 4" long back when I though bushing fit was important.

 

[SKWERLZ]

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

That’s similar to the spiders I use.

 

[LVLAaron]

One day I'll get around to making an inboard spider... It will incorporate elements from this "thing" I made for actions and dies. There's a thick/removable aluminum split bushing in the center that fits close around the object and has ~30 thou of clearance between the bushing and steel fixture.


I would think for barrel work you want the least amount of screw sticking out and sharp little contact points as possible... if anything to reduce chatter/harmonics.