My
Metal-spinning Lathe
A Home
Workshop Guide
Last Updated:
13 February, 2002

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Copyright © 2001 - 2004 to
Bruce Simpson

Why Build A Metal Spinning Lathe?
I guess I could have gone out and bought a
commercial wood-lathe and used that for metal spinning but I have had an
old budget-priced drill press sitting here for a couple of years and I
really wanted to put (at least parts of) it to good use.

So, I scrounged the motor, pulleys, drive belt, power wiring/switch and
bearings from this drill press and built a lathe around them!

Design Considerations
Obviously some of the design constraints and
parameters were set by the parts I was re-using from the drill press. This
did introduce some less than optimal limitations -- such as the use of
19mm bearings, meaning that the mains-shaft of the lathe was also limited
to 19mm in diameter. If this turns out to be too weak I'll just go buy
some bigger bearings and make a new shaft.

Other than the legacy components, there was the issue of exactly what I
had sitting in my metal rack and scrap bin -- which wasn't much.

Apart from the main-shaft, just about everything on this lathe was made
from 25mm square or 25x50mm CRS 1020 steel bar stock.

There are no castings -- it's just cut to size and bolted together.

The main spindle and the backplate were turned from 1214 free-machining
steel which is much nicer to work with than plain old 1020. The chips from
1214 are small and blunt and -- unlike the razor sharp shards that come
off 1020 when it's milled or turned. If you're planning to turn anything
out of steel, do yourself a favor and get some free-machining stock such
as 1214 or 12L14.

Tools Used
Most of the
operations required to build the lathe were done on my 7x10 minilathe and
my RF30 mill-drill -- it's quite impressive what these bits of oriental
iron can do if you're prepared to take your time and work within their
limits.

General Layout
Let me say
right now that building a wood lathe or metal-spinning lathe is a whole
lot easier than building a metal-turning lathe.

Unlike a metal-turning lathe, these machines don't have a cross-slide
or compound, so they don't need accurately ground ways and all the extra
parts and machining that such pieces entail.

In effect, these lathes consist of little more than a headstock and a
place to rest your tools.

The Headstock
I decided to start with the headstock and
designed it so that the center of the backplate would sit 180mm (7 inches)
above the lathe-bed. This provides enough clearance to spin a disk of
metal 14 inches in diameter -- plenty large nough for my purposes and
probably more than the little 1/2HP motor is capable handling.

The basic design of the headstock is very simple -- it's two pieces of
50x25mm (2"x1") which hold the shaft bearings and are separated by a piece
of 25mm (1") square down the middle so as to make an 'I' beam.

The holes which retain the bearings were drilled to 14mm and then bored
out to 36mm, the outside diameter of the bearings used. I'm not too happy
with the results here actually -- I was trying out new carbide inserts and
didn't find a satisfactory combination of insert, sfm and feed rate until
I'd done the first hole -- but they're okay.

The 36mm hole doesn't go right through of course -- it's recessed to
12mm -- the thickness of the bearings.

Rather than just bolt the two pieces of 50x25 to the central 25x25mm
center-piece, I milled 1mm deep slot in the 50x25 pieces so that the
centerpiece was held snugly in place.

I can't imagine any casting being more rigid
than this beefy item once it's all tightened up snugly.

There are then two horizontal pieces of 50x25 bar which bolt to the
headstock so as to connect it firmly to the bed of the lathe.

These have 25x25mm notches cut in the bottom edge (these were hacksawed
and then squared/finished with the mill). They also have a 1mm deep slot
milled in them so that the headstock is firmly keyed in place.

I was very pleased with the level of accuracy achieved with machining
the headstock components -- they all fit together very snugly -- requiring
just a light hammer-tap to seat everything in its groove. After that you
can pick the whole thing up and it won't fall apart -- even without the
bolts in place.

The Main-shaft
The lathe
shaft was turned from 1214 mild steel and it required some careful
attention to accuracy in several places.

Firstly -- because the pulley salvaged from
my drill press was designed to fit on a 22mm shaft -- but the bearings
only allowed the maximum thickness for the shaft on that side of the
bearings to be 19mm, I had to make it in two parts.

A smaller 22mm OD collar was machined to fit very snugly over the end
of the main-shaft and it is secured with a grub-screw.

Of course the parts of the shaft where the bearings sit also had to be
machined for a close interference fit so that the shaft doesn't spin
inside the bearing.

Finally, the end of the shaft to which the backplate is attached also
needed a close interference fit so that it didn't have room to wobble or
slip. I was thinking of turning a taper here to ensure good centering and
maximum grip -- but I decided to try a straight shaft first and see how
that turned out.

The Backplate
With a metal-spinning lathe there
is no need for a chuck. Instead of gripping the work as you would on a
metal lathe, the work is actually clamped between a specially turned form
and a live-center on the tailstock.

So -- the backplate is simply a place where the necessary form can be
bolted or keyed to stop it shifting about.

I decided to turn up the backplate from a 20mm thick piece of 100mm
diameter 1214 steel I had sitting on the shelf. This makes a pretty heavy
item but the extra thickness ensures good alignment on the shaft and
resistance to skewing due to the high side-loads imposed by the spinning
operation.

To make it easier to center the form on the backplate, I turned a
number of concentric rings into the face of the backplate.

The backplate is retained on the main shaft by an 8mm high-tensile bolt
that screws into a matching thread in the end of the shaft.

One of the nicest things about making this part was that I had to turn
it in two operations on the 7x10. The jaws in my 4" 4-jaw chuck had to be
reversed to hold it and then, having turned one face and half the edge, I
had to remount it and set the runout to zero. Any axial run-out would have
manifested itself as a discontinuity or lip along the edge of the
backplate where the two machining operations didn't line up.

After spending a little more time than usual, I got the plate lined up
so that the dial-indicator didn't budge and, although there's a slight
visible difference between the two halves, there's no discernable lip or
edge to the touch.

The Bed
One of the nice
things about wood and metal-spinning lathes is that the bed exists only to
provide support for the headstock, tailstock and toolrest.

There's no need for precision ground and hardened ways to guide a
saddle and cross-slide -- it's all pretty basic stuff.

Since the tooling on these lathes is hand-held, there's no need for
absolute rigidity in the lathe bed either -- so I just used 25mm (1")
square section laid out into a rectangle.

The Tailstock
The job of the tailstock is to apply the
clamping pressure that holds the metal disk (which is to be spun into the
final shape) firmly against the face of the form.

To acommodate different length forms, the tailstock needs to be able to
be shifted along the bed -- as with a regular lathe so the base was made
from a piece of 25mmx50mm (1"x2") CRS into which two slots were milled so
that it would ride on the 25mm (1") sq pieces that make up the bed.

Milling these slots was a good test of the RF30's ability to put its
2HP motor to work. I used a 16mm 4-flute cobalt end-mill running at around
500 RPMs to move the metal.

I took off 2mm at a time and, although there was some vibration (as
you'd expect), it breezed through without any problems.

I'm pleased to say that the tailstock base was a
perfect fit on the bed -- and moves smoothly enough and with so little
slop that it would indeed be a nice setup for a saddle on a
conventional-type lathe. In fact, based on my experiences with this little
lathe, I'd say that it would be quite practical to build your own accurate
metal turning lathe from scratch at quite a low cost and without a lot of
difficulty.

The tailstock vertical is another piece of (you guessed it) 25mm x 50mm
(1"x2") CRS.

At the top of the tailstock is the adjustment screw and live-center
needed to provide the clamping force.

The clamping mechanism consists of a 10mm cap-head bolt which runs in a
threaded hole drilled at the top of the vertical. It is locked in position
by another cap-head bolt (6mm) that screws down and presses a brass pad
onto the main bolt.

Because the alignment of the tailstock is critical to accurate
work-holding, the decision was made to use an adjustable mounting system
for affixing the vertical to the tailstock cross-member.

This was done by mounting the vertical to a smaller cross-piece that is
in turn bolted to the main cross-member. The height can now be adjusted by
shimming, the angle and horizontal alignment can be set by loosening the
mounting screws, moving and retightening.

The live-center was made using one of the other spindle bearings out of
the drill press.

The static side was machined from 6061 aluminum and screws onto the end
of the 10mm bolt which passes through the tailstock. It also holds the
bearing.

The rotating part of the live-center is also turned from 6061 and is
designed to be easily changed. I wanted to be able to use different sized
centers for different sized forms.

A sharp center is used to firmly secure the
wood when I'm turning up the initial form for later use in the spinning
process.

The final piece is the clamping bar which holds the tailstock from
sliding along the bed as clamping pressure is applied through the
live-center. This was made from a single piece of 25mm (1") sq which has
the ends milled as you'll see in the picture.

This cross-piece simply clamps the tailstock to the bed by tightening
two bolts that pass through from above. There was no point in building any
fancy cam-lock mechanism for this (although it would not be too hard)
because the talistock is only moved when changing forms.

The Toolrest
As mentioned above, the tooling for
spinning or wood-turning is hand-held -- so this requires the addition of
a toolrest.

By the time I got to this part of the lathe, the prospect of having to
mill out another cross-piece and clamping bar was all to much -- so
instead the toolpost clamps to the closest rail of the lathe bed --
halving the number of machining operations required.

A 50x25mm (2"x1") piece of CRS serves as the post and it has a slot
milled into it so that it's a nice snug (but sliding) fit over the
bed-rail. Another smaller piece of 50x25 is also slotted and fits on the
other side -- the clamping pressure being provided by two bolts that pull
the two pieces together with the bed rail firmly held between.

On top of the toolpost is a cross-piece made from 25x25 (1"x1") which
is retained by a single bolt so that it can be swiveled and locked to make
tool manipulation easier against the form.

Several holes have been drilled and vertical pins inserted to give
leverage points for the hand-held tooling.

The Drive System
I'm using
the motor and pulley system from my drill press so this was fairly simple
to set up and gives me a choice of 5 speeds.

I was going to just weld up a motor mount -- but ended up doing things
the hard way and milling up a little mounting block that is in turn bolted
to a mounting plate that is (in turn) bolted to the lathe bed. I could
have made this thing in about half the time if I'd welded instead of
bolting everything.

The motor is a 1/2 HP unit and speed is changed simply by moving the
belt to the required grooves on the pulleys. I'm probably breaking about a
million different laws by not having a cover over the pulley -- but that's
another project. If I'm brave/stupid enough to attack a rapidly spinning
disk of stainless steel with a metal bar while the whole lot spins around
at several thousand RPMs then a little old pulley isn't my biggest worry
;-)

Unfortunately the belt that came as standard is a piece of crap and
seems to have been spliced in about four places. This makes it alternately
stiff and flexible -- something that causes vibration. I'll replace it
shortly with a decent quality belt.

Do Yourself A Favor!
Just
a word of warning -- this project involves cutting a hell of a lot of CRS.
If you don't have a bandsaw or power hacksaw before you start a project
like this then you will live to regret it.

I'm still nursing a sore shoulder from all that manual hacksawing.

And... if you're a masochist like I am -- have a good supply of nice,
sharp 18 tpi blades on hand. Don't be miserly -- cutting steel with a
blunt blade is a dumb thing to do -- it wastes time and invites poor
results.

And don't think you're going to be able to move even a little lathe
like this around too easily. It's actually heavier than my 7x10
metal-turning lathe!

I've already started spinning up some aluminum and stainless using this
lathe and although I'm pretty low on the learning curve, it does the job
just fine and it's already become an indispensible part of my workshop.

Coming Soon(ish): Learning To
Spin!
I'm always keen to share my successes and failures
with others so I'm in the process of creating some new pages that will
document what I've learned while learning to spin.

There aren't a lot of good tutorials or metal spinning info sites on
the Web so I'm hoping I can perhaps create some interest.

Until I get these pages up, those interested in spinning might want to
check out this guide (PDF file) which has some great stuff.

Meanwhile -- here are some of the intake venturis I've been spinning
for my pulsejet engines.

These were spun from 1.2mm 1100 alloy
aluminum which was anealed by heating and quenching prior to use --
because the local merchant couldn't supply in anything other than H12
temper.

In order to spin a shape like this which would otherwise get "stuck" on
the form, it's necessary to make the form so that it can be broken into
two parts for extraction purposes.

Home | Project Diary |
My Tools | Contact
Me | Links | My Gas Turbine
Project | The
Afterburner
Turboshaft
Engine | Jet-kart | Pulsejet-powered
Kart | Kitsets | Troubleshooting
pulsejets
Valveless
Pulsejets | Ramjets
Explained | 100lbs-thrust
pulsejet | Turbo-turbine FAQ

Chrysler's
Turbine-cars | How Pulsejets Work
| Flying Platform
| Metal Spinning
| My
Lockwood engine
Starting a
pulsejet | Making
Reed-valves Last | Pulsejet-powered
speedboat | The PDE
Thrust
Augmentors List of
Sponsors | Master Site
Index | The
Pulsejet FAQ | DIY Cruise Missile

Copyright © 2001 - 2004 to
Bruce Simpson