On Thu, 5 Apr 2012 08:25:49 -0700 (PDT), Bob La Londe
wrote:

On Apr 4, 10:09*pm, Bob La Londe wrote:
If you needed to put a hemisperical end on a bunch of 1/4" stainless
dowels how would you tackle it? *Say 400, give or take.

No. They don't need to be terribley accurate. This is just to make
the non press fit end of alignment pins a little faster to start.
They do need to be pretty and smooth though.

My thoughts were to make a lathe bit to round or cut and round out of
HSS. Past experience has shown I am not all that good at grinding
lathe bits, but I did say it doesn't have to be too terribley
accurate.

A CNC lathe would be the easy answer for starting with long stock.
Two problems. I have about 400 pins already, and that will last me a
while. I don't have a CNC lathe... or do I?

I thought about using a round over end mill. Either by chucking a
rotary tool up in my tool post. (A mount to do this is on my to do
list.), or by mounting the pin in a vise vertically and circling it
with the round over mill on one of the mini mills. I had not thought
about using it in a fixed configuration, but I can see how it would
work.

A ball turner was on my consideration list. I can make either a
stacked bearing type or a wishbone type. I think I have a tube of
cheap all stainless skate bearings a buddy of mine gave me around
somewhere I could use for the stacked bearing type, and I think I have
some bronze sleeves I could use for the pin bushings in the wishbone
type. My thought on that though are because of the lack of rigidty in
my lathes (the 8x18 is better) and the additional flex of the ball
turner itself those would require light cuts, which is both time
consuming and a bad idea on stainless.

I had not even considered using a concave hemispherical end mill.

I had not even thought of (or new about) the free hand method using a
drilled piece of HSS. While intellectually it intrigues me, on a
practical level it scare the crap out of me. Kinda like metal
spinning with a 4 or 5 foot long lever/shaping bar. LOL. Awesome to
watch somebody else do.


Back in the day it was quite common to see a "turning tool" in a
machinist's tool box. Usually used to make ball ends for vice handles
and such non-precision things you just put the tool holder in
backwards for a tool rest and went at it - about like turning maple on
a wood lathe.

Mine was about 12 inches overall made from a length of 3/8th drill rod
with a spiffy aluminum handle I turned up one lunch hour and shrunk
on. But really just a steel rod with the end ground flat with a bit of
an angle for clearance, and hardened.

The battery drill method would make them roughly uniform, but I think
it would take a while. It would work. If I were making just one I
might do it that way. Inpsite of my poor skills at making lathe bits,
I am pretty decent at that type of "freehand" work.

Cutting them from bar stock makes perfect sense. 12' probably not so
much in my shop with the equipment I have and the way its layed out in
the shop, but cut down to 2-3' with a wood notch rest sitting on the
next bench over to prevent whipping of the free end would work. That
is probably what I will do in the future. I can also select free
maching alloys of stainless for it then. It would also allow me to
more easily customize my pins using some other ideas I have for making
them easier to seat and keep straight on the press fit end. Being
somewhat frugal (ok cheap) I'ld like to save the box of pins I already
have first.

Here are the solutions I am going to try in order:

1. Put the dowel in the spindle of one of the mini mills. Put a
small vise on the table. Clamp a lathe bit in the vise. Cut the end
of the dowel just like on a CNC lathe. For the precut pieces I have
this should be fine if the collets will hold them well enough and
leave out enough to cut. (I'll try it with the cabinet doors closed,
LOL) For using this method for longer stock I would need to put the
original spindle back on the Taig. (it is hollow and I can feed
stock through it).

2. If one doesn't work, I will already be setup for (2.) Use my mini
mill to cut a lathe bit to shape. Do them on the lathe.

Current headaches with both of the methods I plan to try first. My
spindles are really way to fast for this type of work. I do have a
PID speed controller sitting on the shelf for one of them that could
theoretically get me down to 5-6000 RPM (realistically more like 8000)
and still have good power since the PID will automatically compensate
for any drop in RPM. Still awfully fast, but I might be able to make
it work.

For the future... I am accumulating parts to do a CNC conversion on
the 8x18 anyway, which would be the best tool for the job of those I
have as far as just making the cuts at the right speed. The 7x14
would do it, but now that I have it "pretty good" I want to keep it
manual just for those occassional quick small pieces that are easier
and faster to do manually. Becasue it has a 4 jaw it will be the one
I use if I cut the dowels manually with a self cut lathe bit. I think
it will hold the piece better.



2. Use a

Or use a form tool with an extended lip used as a cutoff tool.
Probably grind one up out of HSS in 20 minutes.

--
Cheers,

John B.