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I have had a brief discussion in the reloading section about barrel spiders so I thought I would create a post here so I can ask a few more questions of OVENPAA just some random questions for OVENPAA. They are not aimed at anybody specifically any one can feel free to chip in. You get my drift.
Materials of construction.
I have had a look I have access to
Aluminium most grades.
Mild steel and Bright steel.
Stainless the common grades of.
PTFE round bar.
PEAK round bar.
Lots of grades of Nylon type bar stock of experimental grades they machine like peak.
I have a lathe as you know and a pillar drill in my shed bench grinders vices the usual stuff. I am kitted out well with HSS stuff and I have carbide inserts of every description falling out of my pockets as well as the holders. I also have access to a milling machine all though this is in the workshop at work. The milling machine is a huge computer controlled thing so it would probably be cheating to use that.
Iv scoured the internet I have pictures of barrel spiders coming out of my ears.

Phew so what should I make it out off is my question. Yeah I know what a let down.

A lump of a reasonable grade of aluminium would be my choice as it will easy to machine and cope with the tightening forces of the M8 grub screws or similar that you use. Getting the O ring groove depth right is going to be the challenge, it can be calculated however you have things like material compression to take into account.

I would start by accurately confirming the bore of the spindle, then machine a short length of material to the same internal diameter to use as gauge. Now machine the spider major diameter, frill and bore it. Turn the work piece around finish the bore if necessary and machine the minor diameter supporting the work piece with the tail stock until it is easy sliding fit of around .003" smaller than the diameter of the spindle (Use your gauge to confirm this) Machine a square bottomed groove into the spider which leaves the O ring standing proud by around .012" inert the O ring and slide the gauge over the minor diameter of the spider and O ring, it is probably going to be a tight fit/will not fit, remove a bit more material from the bottom of the groove until you can slide the gauge over the O ring with a rotating action, it should be a snug fit.

The purpose of the O ring is simply to hold the spider into the rear of the spindle if you do not have a shoulder to clamp the spider to. Once the spider is pushed fully home to its own shoulder and the barrel inserted through and centred in the 4 jaw the spider should have no lateral forces exerted on it hence a simple O ring to hold it in place is fine.

Find some suitable 1/4" diameter brass and cut it to 1/2" lengths with a chamfer at both ends. Now take your chosen grub screws and place them in a chuck with the bottom standing out by around a 1/4" and machine them flat, pilot them and drill a hole around 1/4" diameter by 3/8" deep in each and glue a length of brass into the hole. Let the glue set and you have some nice soft faced grub screws to prevent marring the surface of the barrel and save faffing around with slips of soft shim.

Remember, this is just my take on things and you can build spiders in many different ways.

What's a barrel spider?

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It is a means of accurately centering and supporting a barrel on a lathe.

To accurately chuck up a barrel you must ensure that the end of the barrel NOT being machined which goes through the headstock of the lathe is fully centred where it emerges from the tailstock . for this to occur you either need an adjustable device which holds the barrel truly central or a dead centre which fits into the rear of the headstock . If the bore is fully concentric with the outer diameter then a 4-screw "spider" is all that's needed along with a good dial gauge .If the bore isn't truly concentric , and I have found many that aren't , then I use a solid fitting in the end of the tailstock taper cut for a No. 2 mt dead centre . Check between centres and adjust the 4-jaw to hold true after clocking and if necessary turning the out to true it perfectly. Works for me .

I'll have a go at making the spider but I'm not sure I am skilled enough to re crown the barrel.

Come on Dave, I've seen it Bubba'd on Youtube loads of times with a drill and sandpaper, I'm sure you could manage

Waterford, I do agree however the bore is seldom concentric to the OD and problems arise with very long barrels as it can be problematic to clock the bore. I spent some happy evenings designing an independent fixture that would be bolted to the back of the lathe and would allow for even the longest barrels to be supported and clocked plus give a rotating fixture for pressurised cutting fluid to be recycled through the barrel bore. I never did get around to building it

Equally I can think of a few people who simply use a bush in the outboard end of the spindle, arguing that it is merely there to offer some support to the barrel. Horse for courses really, I know what I prefer to do.

I fished this lump of aluminium out of the scrap bin. its 3"x 2.5". Ill have a play with this over the weekend and see how I get on. Hmm

It will be interesting machining a square section, make sure you pilot one end and support it with the tail stock and carefully centre the other end in a 4 jaw chuck. You also need to keep the speed down as the cutter is going to bang around as it hits the edges until it is reduced to round, at that point I would pop the round section into a 3 jaw and again support the end and reduce the remaining diameter to suit the section which fits inside the spindle.

Take some pictures, wear some safety glasses and keep you fingers clear!