Best material for a spider?

I used 7075 aluminum for my spider and it works well. 7075 is a very strong and relatively hard aluminum alloy similar to some mild steels. I under bored the spider, heated it and slipped it onto the spindle for a very secure shrink fit.
It helps that I already had the 7075 stock on hand.

I will use 7075 if/when I decide to do a spider for my 1340GT. 7075 is more than strong enough, and a spider isn't carrying that much in the way of centrifugal force if correctly set up anyway.
 
I just checked out your new lathe. That is a nice machine!
My old 13X42 South Bend is still making parts even after 71 years. You are gonna love that lathe!
What add-ons did you get?
Back to the post. I made a spider out of aluminum, my fault, bad design. My spindle hole is just a tad over 1". I have no way of attaching it to the spindle OD. I decided to make a slip-in but, that's just not practical. It was a good lesson.
I have seen plenty on this forum and youtube using 7075 though.
 
I've got a number of pieces of 6061 to play with/practice and mess around with. Got that piece of 4140 from David to make the permanent spider.

Janderso I got the preferred package in 3-phase. It's coming from Matt with a DRO and an upgraded 4-jaw chuck. Going with the full-on Mark Jakobs VFD control system upgrade with his proximity stop design as well. Can't wait to get that all set up.

Lathe is still a few weeks out, don't have a confirmed delivery date yet. Still working on setting up the shop area. Basically enclosing one corner of a 40x50 metal building to be my shop area. Building is too dang hot this time of year. I'll want to be able to have some climate control in there.
 
You can use any material at all thaq will hold a thread. I use wooden collets instead of a spider and they work very well. Even junk aluminum will hold the pressures if the length of the thread is greater than 2 times the diameter of the thread.
 
For chambering, the outboard spider is just there to dial in the barrel, if you loosen any of the outboard spider screws and the runout as indicated on the chuck side spider moves, you are bending the barrel. The outboard is not there to tightly hold the barrel, snug is all you need, aluminum is plenty good. There are a few schemes out there that allow the chuck side barrel to pivot or gimbal. Find out for yourself what works best for you and your machine.

If you are interested I can send you a copy the compiled chambering discussions on benchrest forum, it is too large to post. Send me an email bambanbarrelbarn@gmail.com
 
Thanks Bamban. I'll take you up on that because I like to learn from others. FWIW I ended up making one out of aluminum and it's working great and I'm really happy with it. As noted a lot of force is not needed for this specialized purpose (rifle barrel chambering). Just light finger pressure on the screws (which I tipped with brass) is really all that's needed to support the muzzle end and dial in the chamber end. Then I just snug up the lock nuts to keep anything from moving. I'm using a bit of #4 copper wire wrapped around the chamber end to allow it to pivot and not put any bending forces on the barrel. If I'm concerned about anything with the aluminum it's the 1/4x20 set screws that lock it down on the spindle. That area of the part is only about 1/4" thick so there's not a lot of thread there. But for now they seem to be doing well and again, not a lot of force is really needed. I have to just remember not to go all out when I tighten those. It only needs to be snug to keep stuff from moving.
 
Last edited:
Document sent.

One way to check how solid is your workholding, after dialing the barrel, part of small section, face it off, and check the bore for runout. In my case, the finger clamps with ball bearings provide the best holding power with no change after parting. Another check is after threading, run your dial test indicator tip on the thread, with the same threading set up run the lathe backwards at slow speed and see if the runout is the same at bore runout. Just an unsolicited input.
 
I would not use aluminum, too soft and also you can get corrosion/oxide formation where it slides on
Mark
Absurd, this has been installed and removed from this lathe many times in the last 25 years or so, being made from aluminum has never caused a problem. I have only used this machine for the last 5 years but remove it and reinstall once per week or more.

This is an extension to the stop for a long part.
 
Not your typical thin walled spider. To each their own, you may have had one experience with aluminum, others may have had a different experience. I have had numerous cases where aluminum has oxidized and frozen onto other metals. It can also gall when threading screws and does not hold up as well as steel with regard to deformation, in particular when the spider wall is like 1/4"and you thread and add lock nuts. I have not seen any commercial spiders that fit onto/thread into the spindle made out of aluminum. If your spider is not heavy walled, I would use steel.
 
Back
Top