Milling round stock to square, on center

[ccfl]

I'm still working on making a beefier drill press spindle from scratch. This one part has me stuck. Material will be 1/2" OD 1144.

Test piece in aluminum:

Round parts & threading will be done between centers on the lathe. My obstacle is milling the square while keeping it reasonably on center. I'd like it to be +/- .001" because I'm weird.

My test piece was just held in the vise, resetting the Z for each flat. Not nearly precise enough. The drill press has a primitive depth stop but it's not graduated, I have to just do an approximation by zeroing the tool against the part and fitting a shim or drill rod of the right size under the depth stop and then locking it.

I do have a H/V rotary table - but no tailstock for it. If I did that would be ideal. Set the Z by sneaking up on it on the first side and then don't touch it again until all 4 are cut.

The least-worst options I have come up with are:
1. Make two 1" square blocks with tight-fitting 1/2" holes+setscrews, place a length of round stock between the two square blocks, then clamp blocks to the table and whittle away. Flip to the next flat of the square and whittle some more, so on. I have used that method for making trapezoid gibs from round stock (with the correct angles on the fixture blocks to suit) and it works fine.
2. Use the rotary table, and make a temporary pseudo-tailstock to support the free end. Just a vertical support with a reamed hole at the right height, fixed to the table.

Any other clever and non-machinery-intensive (cheap/free) suggestions?

[NP317]

Acquire that tailstock you wish you had.
It will make the job much simpler, and you'll have the tailstock for those other projects in your future.
Just pretend you are Steve and get more tooling...
!RN

[Magicniner]

Get a good milling vice and a set of parallels before fancier kit, it's all you need for the job,

- Nick

[Mr Ron]

It appears to me that you are working backwards. You should have started with a square piece of stock a bit larger than 1/2"; milled it down to .360, then mounted in a 4 jaw, zeroed in and thread cut. How do you register the flat on the square with the thread; looks like the threaded portion screws down hard against the 1/2" dia flange.

[SteveHGraham]

Rotary table with a screw jack to support the free end of the work?

[ccfl]

I didn't mention in my first post but my intended order of ops is:
-Cut to length, leaving ~1" extra for ease of holding and whatnot.
-Pop center holes in both ends.
-Mill to square.
-Mount between centers on the lathe and do the round features.

NP317- I have seen tailstocks for 4" rotary tables, but the cheapest (around $100 delivered) is $40 more than what I paid for the RT when new. No thanks. I don't have tons of money though I can rationalize spending when it's really worth it, but that's just too far.

Magicniner- I have a 3" Kurt-style milling vise & parallels, that's how I made the test piece. The loss of accuracy I ran into is that the first cut is fine, the second cut is fine too (part is rotated to index the 1st cut against the rear jaw, required Z doesn't change, same round diameter sitting on the parallels). But cuts 3 and 4 put a flat face down against the parallels, the centerline drops accordingly, and so the required Z height changes and the drill press (not a real mill!) has to be reset, and it's near impossible to hit the same number again.

Mr Ron- Where oh where do I buy square Stressproof? I have looked. Nothing but round. I do have a 5" 4-jaw but the jaw faces are not 100% (or even 99%) parallel with the axis, so I get axial runout or whatever the proper name for it is. Zero runout at the chuck is not zero runout 4" out from the chuck. I don't trust it enough for this type of job. (There will be a stepped/flanged washer between this square drive piece and the main spindle/upper bearing inner race - it's a goofy cobbled design but I think it will work. The too-small diameter of the flange is intentional, it has to be inset into the washer, and the washer has to be inset partially into the bearing inner race, for overall height reasons. I tried more sane designs and the dimensions just wouldn't fit without sacrificing something else.)

Steve- That's the spirit! Though I would take it a little further, without turning it into a full-blown tailstock-from-scratch project. 1/2" round hanging out ~4" will need lateral support too, not just vertical. My idea was a T-shape assembled from 1/2x1 AL bar. A foot that can clamp to the table, a vertical that can be bored for the round stock to pass completely through. The part can have extra material on both ends for holding, it can be chopped off later.

[spro]

I'm glad you posted this reply when you did. I couldn't see how the square shaft would apply to a drill press quill. I was about to mention earlier drill presses with a tapered square hole in the spindle and they had power ratchet feed while the flywheel was turned.

[ccfl]

This is a bottom of the barrel import Skil (or that's what it started life as). The square works the same as the more common splined shaft in the drive hub. This one is just too small to use splines, it's only .430" round (corner to corner) on the ID of the square drive hub.

Making it two piece like this solves two problems. Provides a way to apply bearing preload (the original spindle uses a single circlip and wishful thinking), and allows the main shaft/collet part to fit between centers on my baby lathe. I think I have a clever way to make sure the bearing journals are on center with the 7/16-20 tapped hole at the top - tap that hole first, then screw in a grub screw with an accurately located center hole, then finish the bearing journal. If the thread fit is good enough it shouldn't throw anything off. I hope!

[ccfl]

This is the original spindle. Garbage!

[ccfl]

These are the blocks I made to make gibs out of round stock:

Think square collet blocks, without the collet part.

[spro]

Okay, one section and the end attaches to the bearing/quill section. Got it
Then the next pics. Seeing generation here. Very above all, the thought process and execution. You don't lack momentum.

[Magicniner]

the required Z height changes and the drill press (not a real mill!) has to be reset, and it's near impossible to hit the same number again.

That kind of explains it.
Make up a Z axis DRO using a digital caliper so you can read actual Z position, use any of the common methods of setting your cutter to the top of the work and you should be able to get close enough.

- Nick