Home Made Metal Spinning Lathe

My Metal-spinning LatheA Home Workshop Guide

Last Updated: 13 February, 2002

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Why Build A Metal Spinning Lathe?I guess I could have gone out andbought a commercial wood-lathe andused that for metal spinning but I havehad an old budget-priced drill presssitting here for a couple of years and Ireally wanted to put (at least parts of) itto good use.

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

Design ConsiderationsObviously some of the designconstraints and parameters were setby the parts I was re-using from thedrill press. This did introduce someless than optimal limitations -- suchas the use of 19mm bearings,meaning that the mains-shaft of thelathe was also limited to 19mm indiameter. If this turns out to be tooweak I'll just go buy some biggerbearings and make a new shaft.

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

Apart from the main-shaft, just abouteverything 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 towork with than plain old 1020. The chips from 1214 are small and blunt and -- unlike the razor sharpshards that come off 1020 when it's milled or turned. If you're planning to turn anything out of steel, doyourself a favor and get some free-machining stock such as 1214 or 12L14.

01/07/2010 Home Made Metal Spinning Lathe

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Tools UsedMost 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 timeand work within their limits.

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

Unlike a metal-turning lathe, these machines don't have a cross-slide or compound, so they don't needaccurately 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 HeadstockI decided to start with the headstock and designed it sothat the center of the backplate would sit 180mm (7inches) above the lathe-bed. This provides enoughclearance to spin a disk of metal 14 inches in diameter --plenty large nough for my purposes and probably morethan the little 1/2HP motor is capable handling.

The basic design of the headstock is very simple -- it'stwo pieces of 50x25mm (2"x1") which hold the shaftbearings 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 14mmand then bored out to 36mm, the outside diameter of thebearings used. I'm not too happy with the results hereactually -- I was trying out new carbide inserts and didn'tfind a satisfactory combination of insert, sfm and feed rateuntil I'd done the first hole -- but they're okay.

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

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

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

There are then two horizontal pieces of 50x25 barwhich bolt to the headstock so as to connect itfirmly to the bed of the lathe.

These have 25x25mm notches cut in the bottomedge (these were hacksawed and thensquared/finished with the mill). They also have a1mm deep slot milled in them so that theheadstock is firmly keyed in place.

I was very pleased with the level of accuracyachieved with machining the headstock






components -- they all fit together very snugly -- requiring just a light hammer-tap to seat everything inits groove. After that you can pick the whole thing up and it won't fall apart -- even without the bolts inplace.

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

Firstly -- because the pulley salvaged from mydrill press was designed to fit on a 22mm shaft --but the bearings only allowed the maximumthickness for the shaft on that side of thebearings to be 19mm, I had to make it in twoparts.

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

Of course the parts of the shaft where the bearings sit also had to be machined for a close interferencefit 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 sothat it didn't have room to wobble or slip. I was thinking of turning a taper here to ensure good centeringand maximum grip -- but I decided to try a straight shaft first and see how that turned out.

The BackplateWith a metal-spinning lathe there is no need for achuck. Instead of gripping the work as you wouldon a metal lathe, the work is actually clampedbetween a specially turned form and a live-centeron the tailstock.

So -- the backplate is simply a place where thenecessary form can be bolted or keyed to stop itshifting about.

I decided to turn up the backplate from a 20mmthick piece of 100mm diameter 1214 steel I hadsitting on the shelf. This makes a pretty heavyitem but the extra thickness ensures goodalignment on the shaft and resistance to skewingdue to the high side-loads imposed by thespinning operation.

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

The backplate is retained on the main shaft by an 8mm high-tensile bolt that screws into a matchingthread 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 halfthe edge, I had to remount it and set the runout to zero. Any axial run-out would have manifested itselfas a discontinuity or lip along the edge of the backplate where the two machining operations didn't lineup.






After spending a little more time than usual, I got the plate lined up so that the dial-indicator didn'tbudge and, although there's a slight visible difference between the two halves, there's no discernable lipor edge to the touch.

The BedOne of the nice things about wood and metal-spinning lathes is that the bed exists only to providesupport 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 allpretty basic stuff.

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

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

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

Milling these slots was a good test of the RF30's ability to put its 2HPmotor to work. I used a 16mm 4-flute cobalt end-mill running at around500 RPMs to move the metal.

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

I'm pleased to say that the tailstock base was a perfect fit on the bed -- andmoves smoothly enough and with so little slop that it would indeed be a nicesetup for a saddle on a conventional-type lathe. In fact, based on myexperiences with this little lathe, I'd say that it would be quite practical to buildyour own accurate metal turning lathe from scratch at quite a low cost andwithout 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 toprovide the clamping force.

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

Because the alignment of the tailstock is critical to accurate work-holding, the decision was made touse 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 maincross-member. The height can now be adjusted by shimming, the angle and horizontal alignment canbe set by loosening the mounting screws, moving and retightening.

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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 whichpasses 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. Iwanted to be able to use different sized centers for different sized forms.

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

The final piece is the clamping bar whichholds the tailstock from sliding along the bedas clamping pressure is applied through thelive-center. This was made from a singlepiece of 25mm (1") sq which has the endsmilled as you'll see in the picture.

This cross-piece simply clamps the tailstockto the bed by tightening two bolts that passthrough from above. There was no point inbuilding any fancy cam-lock mechanism forthis (although it would not be too hard)because the talistock is only moved whenchanging forms.

The ToolrestAs mentioned above, the tooling for spinning orwood-turning is hand-held -- so this requires theaddition of a toolrest.

By the time I got to this part of the lathe, theprospect of having to mill out another cross-pieceand clamping bar was all to much -- so instead thetoolpost 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 postand it has a slot milled into it so that it's a nice snug(but sliding) fit over the bed-rail. Another smallerpiece of 50x25 is also slotted and fits on the otherside -- the clamping pressure being provided by twobolts that pull the two pieces together with the bedrail firmly held between.

On top of the toolpost is a cross-piece made from25x25 (1"x1") which is retained by a single bolt sothat it can be swiveled and locked to make toolmanipulation easier against the form.

Several holes have been drilled and vertical pinsinserted to give leverage points for the hand-heldtooling.

The Drive SystemI'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 alittle mounting block that is in turn bolted to a mounting plate that is (in turn) bolted to the lathe bed. Icould 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 onthe 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 steelwith a metal bar while the whole lot spins around at several thousand RPMs then a little old pulley isn'tmy biggest worry ;-)

Unfortunately the belt that came as standard is a piece of crap and seems to have been spliced inabout four places. This makes it alternately stiff and flexible -- something that causes vibration. I'llreplace 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 bandsawor 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'tbe miserly -- cutting steel with a blunt blade is a dumb thing to do -- it wastes time and invites poorresults.

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

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

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 somenew 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 perhapscreate 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.






Home Made Metal Spinning Lathe

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