Mini-lathe inboard spider project

[Ian]

So I had this original idea to make a part for my mini-lathe so I could thread the muzzles of rifle barrels too long to fit between chuck and tailstock center and too large in diameter to pass into the spindle bore. After doing some research, if appears that my idea was a long way from original but still a solution to the problem: An inboard spider which acts like a cathead in a steady rest, but instead of having fingers riding the OD of the cathead, it has a bearing positioned precisely on the spindle/tailstock centerline, square to the bed, and has a spider hub pressed into its center. Four clamping screws instead of eight, and ball bearing support so no wear, chatter, fighting to get the steady fingers exactly on center, or tendency to fret out of the chuck. Very clever. Not so easy to make without a mill, but my lathe came with a steady rest suitable for mounting a flanged bearing with a couple of bolts, so I got a bearing and started engineering the cathead/ spider/steady rest thingy.

Pictures speak better....

Setting up on bullnose live center after aligning bearing in the housing square and plumb to lathe bed:



After drilling and tapping the steady rest base and bearing housing. Due to lack of material on top of the steady, I had to put the bolts through from opposite sides and d/t the bearing housing. I made the bolt holes oversized so that slight alignment corrections can be made to center the bearing bore.




Now to make the spider part. The bearing bore is only 1.25" and I plan to make the spider ring press on the OD of the bearing race so I can use most of the bearing hole diameter.

 

[freebullet]

Seems like your really making the most out of that little lathe. Excellent work.

 

[Ian]

Just trying to stretch its capabilities enough to do a couple more projects that would typically require a $5,000 machine or paying a gunsmith over $100 each. Looks like a few hours and $20 in parts will get me there.

 

[RicinYakima]

Very clever! Just with I need for my old Atlas that only has 20" of work length and 5/8" spindle bore.

 

[JWFilips]

Ian,
Wish I had a lathe but I still love reading about you & others making all these extra tools for it !
Excellent
Jim

 

[smokeywolf]

I used to work with a Japanese engineer who was a bona fide mechanical engineer, electronics engineer and optics engineer. Ian seems well on his way to qualifying as that type; a jack of all trades and a master of all of them.

 

[Pistolero]

Very good, Ian. Should be a real winner, and do a fine job. An aluminum muzzle spud,
groove diameter, tapped into the bbl to broach the grooves into the spud should drive the
barrel just fine if you keep the cuts light. Works fine for trimming shoulders on S&W pistol
bbls to remover the restriction.

Bill

 

[Ian]

Started making the spider tonight. Faced both sides, turned the OD, and bored the back side for a press fit on the bearing.



One thing I'm learning is to take deeper cuts. I ended up being pretty happy running .025" Depth of cut at 400 rpm on a 1.5" diameter. That might not sound like much, but this lathe has a 3" chuck and I'm using 5/16" tooling.

 

[freebullet]

Very helpful details, much appreciated by those learning along.

 

[Ian]

FINISHED!!

Spider was coated in sleeve retainer, pressed onto the bearing hub, and the grub screws tightened from the inside with an Allen bit and 1/4" box end wrench. If I ever have to replace the bearing, I'll have to make a new spider. I didn't get a photo, but the 1.25" ID of the spider and the bearing ended up concentric and made a seamless tube when pressed together; not particularly important, but satisfying anyway. I didnt drill the bolts for brass buttons, but I did true and crown them.


I put a 3' stick of 3/4" rod in it for the photos.

 

[Brad]

Damn fine work Ian.

 

[Ian]

Wish I had a gizmo like you got for indexing and drilling the spider bolts. The way I do it is a pain in the neck and only reasonably precise.

 

[Brad]

My collet block wouldn’t hold something that large. Could you get a good 90° chunk of angle iron and temp affix the round to it? That lets you drill at a true 90° angle.

 

[Brad]

Take a look at this Ian,lots of good ideas here.

 

[Pistolero]

Good idea, and well executed, Ian. Should let you do those
muzzles now.

Bill

 

[Eutectic]

You are doing nice work Ian! And you will find our 'hobby' will suck you into tool & die work like a vacuum!

Heck...... Seems like only yesterday that several of us worked on convincing you that YOU needed a lathe.... Now let's see..... who's left? Oh yeah! fiver!

Pete

 

[Ian]

Now for the nitty-gritty......putting it to work.

Double-checked the spider bearing was on center, turned a sacrificial muzzle pilot per Bill's suggestion, popped the Rock Creek 5R Bisley .308 heavy barrel off the Savage 11 receiver, padded it in the spider with dead-sot aluminum, and tapped the muzzle onto the pilot.



I made the pilot .3075" this rifle runs a couple tenths under .308" in the grooves. Not really knowing what to expect, I made the bearing surface of the pilot .300" long, with a slight relief at the shoulder for peelings to go, and faced it slightly concave. Turns out none of that was necessary, after oiling and tapping the barrel with a 2# deadblow and block of pine, it seemed very happy to be on there only about 2/3 of the way, so I stopped there. Then I indicated the last few thousandths out of the chamber end and gave it a go with a razor sharp HSS bit. The stainless cut like butter, fed by hand at a snail's pace. .010" depth of cut at 250 RPM seemed to be the happy place and just keeping constant pressure on the carriage handwheel let it cut the amount it wanted to. A few decades later I got it down to .623" X .600" long, Griffin Armament's spec. Still need to cut the thread relief and chamfer, then grind a thread form tool to get in close to that right-hand shoulder, then it will be threading time.

 

[Ian]

Oh....forgot to mention. The barrel profile was evidently achieved with a belt sander, and the barrel has a thick spot running most of the length, making an indicator needle trace out about .004" off the base circle in a narrow band, and easily felt with the fingers. This would never ever have worked using a steady-rest directly on the barrel. Other than the bump, the chamber was within .005" of concentric to the barrel OD at the spider. Not terrible, but it does reinforce the notion that we should never be using the OD of a barrel as a reference for ANY sort of work which must be co-axial with the bore center.

 

[Ian]

Done threading.

 

[Brad]

My steady rest has a much larger opening. Might still be able to mount a flat 1/4 plate on it that could accept a bearing mount like that.

Great idea and execution Ian.