Newsgroups: rec.crafts.metalworking
Subject: Self adjusting steady
From: Robert Bastow <teenut@home.com>
Date: Sun, 26 Sep 1999 08:54:12 GMT

I have seen a self adjusting, travelling, three point roller steady used for
turning the outside of rifle barrels.  This is a hydraulic device and try as I
may, I can't figure out how it works...unless there is an accumulator or
pressure make-up supply.  

I want to make one!  

Any Ideas or sources?

teenut

Newsgroups: rec.crafts.metalworking
Subject: Re: Self adjusting steady
From: Robert Bastow <teenut@home.com>
Date: Sun, 26 Sep 1999 18:27:11 GMT

Yup!  Plumb wore out my hand.

No "stiffening" is required..just dampening.

I do quite well with an oiled softwood wedge betwixt tool post and barrel.  The
tapers involved are gradual enough that periodic adjustment works fine.

Howerver this is only good for light finishing, and a 3 point fixed steady is a
pain-in-the-a$$ necessity when roughing.  This has to be shifted and reset
several times and I want rid of it!!

I think I am going to scratch about with the Idea of three cylinders, cross
connected with bleed orifices, and fed from a gas pressurised accumulator. 
Heck, I think three stiffly spring loaded fingers might even do the job,
especially if they had replaceable UHMV tips.

The whole thing can be self contained and quite compact I think.

The device I saw, briefly had three HINGED arms, with the tool side one curving
up, under the job..looking almost like a scissor type knurling tool.

Thanks to all for your suggestions..More are welcome.

teenut

Jack Erbes wrote:
> 
> Robert Bastow wrote:
> >

> If the barrel was between centers the steady would only have to provide
> a little extra stiffening near the cut to work well.  I am sure with
> your experience playing around with guns that you have experimented with
> using your hand to damp out vibrations when turning barrels.
> 
> --
> Jack in Sonoma, CA, USA (jack@vom.com)

Newsgroups: rec.crafts.metalworking
Subject: Re: Self adjusting steady
From: Robert Bastow <teenut@home.com>
Date: Sun, 26 Sep 1999 22:37:05 GMT

tonyp wrote:
> Now the "gearing" between the three arms _might_ be done hydraulically.

The "gearing" is certainly not done mechanically!


> What you'd need is a slave cylinder on each arm, each connected to its own
> separate master cylinder.  You then mechanically tie the three master
> cylinders together, and drive them as a group with whatever you want --
> screw, air piston, deadweight, will power :)
> --

DUH!  Maybe I am being real dense here..But how would three masters tied
together differ from just one big one?

BTW.  This type of steady is used on longer bed CNC lathes and other than
longitudinal positioning, and "Open/close" commands there is no regulation of
the jaw positions.  I believe some are operated by coolant pressure...on lathes
without a separate hydraulic system.

teenut

Newsgroups: rec.crafts.metalworking
Subject: Re: Self adjusting steady
From: Robert Bastow <teenut@home.com>
Date: Mon, 27 Sep 1999 01:11:32 GMT

The more I think about a hydraulic solution, the more I realise I am missing a
fundamental operating principle that IS being used here.

Think of it as a ring with three (or four) equally disposed fingers, each free
to slid in and out and each impelled (inwards) by equally strong springs or
equal pressure on hydraulic pistons.

If you imagine the workpiece as being pushed away from center or even rotated
precessively, then in the above example, while all the fingers would remain in
contact, there is no resistance to the displacement of the center line.  This
system can accomodate changes in diameter..but cannot resist changes in the
center of rotation. (Which is, after all, the primary function of a steady!!)

A mechanical solution might be to have the jaws/fingers under control of a lever
operated cam ring or scroll..exactly like a lever operated scroll chuck but with
the "tommy bar" actuated by spring or hydraulic pressure.

This would remain centered as the jaws closed..I am not sure it would work well
or efficiently as the jaws were forced open.  (it is usual to have the thick end
of the barrel up at the headstock end)

Now,  The examples I have seen, (Oh how I wish I had taken better notice at the
time) all had three rollers which impinged upon the workpiece in the customary
12, 4 and 8 o'clock positions BUT all three rollers were mounted on arms that
pivoted (one above the other) at the REAR of the workpiece..in the 3 o'clock
position if you wish.

The three arms were therefore of disparate lengths.  No 2, at 4 o'clock being
the shortest and no 3, at 8 o,clock being the longest as it had to curve right
round under the work piece.

I doo not recall seeing any separate hydraulic cylinders, certainly not one per
finger and no obvious sign of interconnection....

AHAH!!  A crack of light methinks (or a train coming)..

If the "butt ends" of the three pivoting arms are controlled by the SAME cam,
cone or wedge, then their movements must always remain RELATIVE TO EACH
OTHER..Exactly as in the case of scroll operation. pre-supposing that the wedge
or cam has ONLY one degree of freedom of movement.

Now, the three fingers are free to move IN or OUT if the diameter changes..but
like the scroll chuck they cannot move INDEPENDANTLY..ie. there common center
cannot be displaced.

Now...And I am thinking on paper here..While the scroll chuck actuats easily in
the inward direction..it does not happily work in the other..the scroll can
drive the jaws..but the jaws cannot drive the scroll. Friction and relative
degrees of mechanical advantage being in play here. (think of a worm and wheel)

However, in our lever steady system the friction and mechanical advantages are
the SAME, whether the jaws are being forced open or closed. (And now I am
assuming that the Butt ends of the levers have rollers impinging on an operating
wedge or cone.)  Because the workpiece side of the levers is so much longer they
have a powerful mechanical advantage when it comes to being forced open,
conversely the will need a powerful push to translate into any useful force at
the workpiece.  Our (single) hydraulic cylinder can provide that force or
resistance.

Now it occurs to me that the arms must each have the same RATIO of mechanical
advantage..but not necessarily the same physical lengths.

So the actuating "side" must be a MIRROR, but not necessarily same SIZED image
of the operating side!

Dawn begins to break!!

I am going away to scratch on paper after giving my poor aching brain a rest!!

teenut