Tuesday, February 2, 2016

Building The Handy Lathe



The following instructions describe how I built my own lathe, as shown in the videos.  My design was dictated by the tools and materials that I happened to have around, since one of the major goals of the project was to build the lathe for the minimum possible cash outlay, using mostly junk and leftovers from other projects.  If you build your own lathe it will undoubtedly be different.  Part of the charm to home made tools is the uniqueness of each one. 


Part I of the Video

The Head Stock

The head stock consists of a bicycle bottom bracket held in a sturdy wooden frame.  There are at least half a dozen configurations of bottom brackets out there, many of which can probably be made to work.  The kind I used, which is the most common on adult bikes of the '80s and '90s, has 10mm male threads on the spindles to which you can screw adapters for the pulley and chuck (or face plate, live center, etc).  A slightly newer design, also very common, has female threads to which you can attach things with a bolt.  Either one should be pretty easy to work with.  My bottom bracket is old enough that it uses loose ball bearings with adjustable cones, which means I can adjust and/or repack the bearings dozens of times as they wear in.  Newer units have sealed bearings which last a bit longer, but you need to replace the whole unit when it wears out. 

If you don't have the tools you need to adjust or dismantle a bottom bracket (which vary depending on the type) it will be cheaper to bring it into a bike shop than to buy them.  I do have the tools, though, because I used to work in a bike shop.

The bottom bracket shell fits tightly into a hole in a wood glue up and is held in with a 1/4" lag bolt that engages one of the holes in the shell.  Precision is very important when building the head stock--more so than with any of the other assemblies.  You want to start by finding well-seasoned, straight-grained wood.  Hardwood--perhaps maple or white oak--would be ideal.  I used a chunk of old-growth fir which I have been saving for something special ever since I sawed it out of a 1940's house. 

After the glue dries you will want to carefully plane all of the surfaces to get them absolutely square, since everything else you build will be squared against the face of the head stock.  This is one of those tasks for which there is just no substitute for a well-tuned smooth plane and a little patience. 

You will probably not have drill bits that are the right size for the holes for the bottom bracket and pipes.  For the bottom bracket hole I used an adjustable bit to bore it slightly (about 1/32") under-size.  Then I very carefully enlarged it with a half-round file

Optional:  So I wouldn't have to remove quite so much material, I used a rabbet bit in a router to remove some of the wood from the sides of the inside of the hole. 

Once the bottom bracket would go in I mounted an old crank and checked everything for square against my table saw by rotating the crank and measuring it.  I was only off by a fraction of a degree and was able to correct it by a little more filing and scraping.  If end up taking off too much material you will need to shim the bottom bracket square with pieces of shim stock (a.k.a. beer can). 

I followed a similar procedure for the holes that received the pipe ways, except that I was able to use an adjustable hand ream to enlarge the holes.  A bicycle seat tube ream is a good size for this. 

Optional:  You can cut a shoulder on the ends of the pipes using the pipe grinding jig that I showed you how to build two episodes ago, which will give a very nice fit and allow you to use a 1" drill bit. 

The small counter-bored hole in the lower center of the head stock isn't mentioned in the video.  Its purpose is to receive a lead screw later when I add a sliding carriage for metalworking, but it's easier to add it now before the lathe is assembled.

The last step is to use a router or a file to round off all the exposed corners, which will keep them from splintering.



The Ways

The ways are made of 3/4" schedule 40 water pipe.  Actually, 1" or 1 1/4" would have been even better, since it would be stiffer, but 3/4" was what I had.  You need to find the straightest pieces of pipe you can.  An old trick is to role them on a flat surface and listen for clicks, which means that they are bent.  If you have access to another lathe it would be a great idea to take a pass along each of them to true them up.  Ironically, someone gave me a long-bed lathe a couple weeks after I had already installed them...that's the way these things seem to go. 

The bracket that holds the tail end of the ways is just a piece of straight-grained 2x4 with holes that line up with the ones in the head stock.




Assemble the ways to the head stock, square everything, then glue and screw it to a piece of particle board.  Why particle board?  Because it is very dimensionally stable and you don't have to worry about it warping and bending your ways out of alignment.


Spindle Adapters

Now you need to figure out how to get a pulley on one end of the spindle and whatever chucks or other accessories you will be using on the other.  In my case the pulley I was using accepts a 5/8" shaft with a key-way and my chuck goes on a 5/8" plain shaft typical of accessories that are meant for ShopSmith machines), so both adapters are basically 5/8" metal cylinders that screw onto the threads on the spindle.  If you are using a threaded chuck then you will need to thread the adapter.  This job is best done on a friend's engine lathe, but is possible with a die if you are careful. 

The adapters can be made out of, in decreasing order of suitability, brass, pot metal, bronze or steel.  The reason brass is the best because it is reasonably strong and threads nicely.  Pot metal and bronze are even stronger, and thread nearly as well.  Steel is the strongest, but it is hard to cut really nice threads in it, especially with a crappy tap and die set like mine.  You can buy short lengths of brass round stock from Online Metals, a company with which I have done business off and on for years.  I'm poor though, and didn't want to wait for delivery, so I melted down scraps of pot metal and cast my own adapters. 

Metal casting is both an art and a science, and I don't pretend to be an expert.  However, this is just about the simplest casting that I can imagine, and is well within the abilities of a handyman.  The amount of metal involved will melt on an ordinary camp stove and the "mold" is little more than a hole poked in some dirt.  The most important advice I can give you is to poor slowly otherwise you will end up with bubbles in the metal that will create voids and ruin the casting. 

Also, remember that molten metal is hot!  You definitely want to wear sturdy leather boots and gloves and long pants.  Welding gauntlets and leathers, if you have them, would be even better.  Also, be aware that when molten metal spills on concrete it sometimes causes it to spall, sending high velocity chunks around the shop, so casting over blacktop or dirt is safer.  Always plan your motions ahead of time and know what you are going to do before you have a crucible of metal in your hands, and never rush; it's better to screw up a pour than to go to fast and end up hurting yourself.

Once you have your castings done, or cut your round stock, you will need to do some work to turn them into adapters.  A drill press, though not absolutely necessary, is quite useful for these steps. 

The first step is to create a flat reference face on one end of the casting.  I started by hack sawing off one end as square as I could get it.  Then I put the casting in a vice and cleaned it up with my belt sander (a file would work too, but I'm really good with a belt sander).  Then I clamped the piece in a drill press vice with v-blocks and faced it up with a stiff sanding disk that I made.

Next I located the centers and drilled with a tap size drill bit (9.5 mm for the 10 mm fine threads on the bicycle spindle.  In precision work like this it is best to drill first with a smaller drill bit and then "follow the hole" with your final size bit. 

Next I tapped the hole in the drill press.  The center in the drill chuck holds the tap square and make it less likely that you will get a "drunken" thread.  If you don't have a tapping fixture for your drill press you can just put a center in the chuck and wrap a bungee cord around the feed handle to apply even pressure. 

Once you have the threaded hole you can screw the blank adapter onto the spindle and turn it to the final size.  "But wait," you say, "we don't have a pulley on the lathe yet, how do we make it rotate for turning?"  I solved this problem by powering the lathe with my half inch drill and a flex shaft made out of some hose.  You could also use the actual lathe motor and a slightly bigger diameter hose.  Either way you want to clamp the drill/motor down pretty securely.  Otherwise it will pull towards you and whip the hose around at high velocity. 

For adapters that need a key-way, like the one on my pulley, you can cut it with a small chisel then clean it up with files.  Back in the days of yore all key-ways were cut this way and it isn't difficult, just time consuming.






Part II of the Video


The Tool Rest

The next step is to build a tool rest which is sturdy enough to last and adjustable enough to get you into all the positions you need for hand turning.  I opted for a fairly short rest, since my lathe will mostly be used to turn fairly small objects.

Of course the eventual plan is to put a sliding carriage on this lathe, but even for metalworking hand work is more convenient for certain tasks...such as the spherical sections on almost any piece.  And nearly all wood turning is done with a hand rest.

The bracket that holds the tool rest to the ways is made by gluing up some pieces of 2x4, then drilling a hole and sawing down to it.  Make sure you use pieces without any knots, or they will break when you try to clamp them.

The socket that holds the tool rest is a piece of 3/4" schedule 40 pipe left over from cutting the ways.  Use a round file to deburr it and smooth out the inside, then drill and tap for a set screw.  I used the set screw from an electrical conduit pull box which I had already melted down for its pot metal.  If you want, you can solder on a wing nut or half a dime to make it a wing screw, like I showed you how to do two episodes ago in the pipe grinder video.

The tool rest itself is a section of a 1" pipe nipple brazed or welded to a piece of 1/2" pipe. 

First you will need to turn down the bottom two thirds or so of the vertical piece down so it will fit in the socket.  You can do this by roughing it out with a file and then chucking it in the lathe.  You will need to kludge a temporary tool rest up out of scraps--it doesn't need to be fancy, since you'll only be using it once.  For the actual turning use a diamond point tool and take many light passes, then smooth it up with 120 grit sand paper.

Note: If you don't have lathe tools yet, I will be giving you some tips on how to make them in an upcoming episode. 

The horizontal piece can be cut out of the 1" pipe using a hacksaw or abrasive cut-off disk in your angle grinder. 

You need to cope the vertical piece so it fits against the bottom of the horizontal piece.  You can do this by eye, but I also made this template which you can print, snip out, and use to mark the cut line.  Rough it out with grinder, then use a half-round file to finish it. 

Then drill and tap for a little 3/16" bolt or machine screw to hold everything together while you braze or weld it.  If you own an acetylene torch fillet brazing with brass rod is the way to go:  it looks better and will be less likely to deform the pieces.  Arc welding is also fine.  If you own neither a torch nor a welder, then you do what I did and just fill the inside of the rest with molten pot metal.  I buried the whole assembly upside down in a can of dirt, added some vents by poking with a piece of coat hanger, and slowly poured in the metal.  The result probably isn't as strong as torch brazing would have been, but I haven't had any trouble with it. 

Clean up your welds/brazes with files and smooth out the top of the rest with a fine file.

The clamp that locks the tool rest is a quick release from a bicycle hub.  Quick release skewers are made of heat-treated steel which is hard to cut or thread, even with carbide tools, so use the whole skewer and make a spacer out of pipe fittings or a block of wood. 

This tool rest looks like a jury-rig, but actually locks up faster and tighter than the one on my big Harbor Freight lathe and about as well as the one on the old 1930's wood lathe that I owned before.

Detail at Bottom of Tool Rest


The Tail Stock

The tail stock is the single most complicated sub-assembly in this lathe. 

The body of the tail stock is a glue-up made from pieces of wood.  Ideally, you would make the whole thing out of some sort of tough, dimensionally stable hardwood like white oak or maple.  Hardwood is expensive, though, and I made it out of dry construction lumber and only used maple for the pieces which will actually contact the ways. 

Start off by gluing up two rectangular slabs, then plane them flat.  Next, drill the holes for the ways, and cut off the waste piece at the bottom.  Then saw out the shape on each piece.  A band saw is ideal, but a portable jig saw, or even a coping saw, will work.  Next, cut one of the pieces in two and glue the two pieces onto the other piece.  Sand everything flush and round off exposed corners.

The next step is to make sure the half holes in the bottom of the tail stock match the ways and that it sits absolutely square.  To do this, stick some PSA sandpaper on the ways.  Then mark the surface with Sharpie pen or pencil and scrape the tail stock back and forth over the sandpaper for a few minutes, holding it as square as possible (it helps to clamp a square to the ways that you can eyeball on).  When you turn the tail stock over you will see where the ink or pencil has been sanded off.  Attack these high spots with a half-round file and/or a scrap of pipe with sandpaper wrapped around it.  Repeat as needed.  For the last few passes forgo the file and use the sandpaper itself to lap the holes for a really good fit.

The next step is to make the clamp that locks the tail stock in place.  I cut and bent an old iron plant hanger and added a bicycle seat post quick release.  This setup works well.  My only complaint is that I need to bend the strap when I take the tail stock off the lathe for chuck work, and I'm afraid it will eventually work harden and break off.  A better design would incorporate a hinge on the bottom piece of strap.  Maybe you could weld in a small gate hinge?

The next step is to bore the hole for the tail stock ram.  Do this by chucking a spade bit (not a self-feeding bit, a cheap spade bit) in the lathe chuck and slowly sliding the tail stock into it.  Like the other holes in this project, you will need to enlarge this one to the precise diameter of the pipe.  You could use a hand ream again, but it is easier to make a boring bar and use the lathe.  In this case the boring bar is just a scrap of 1/2" EMT conduit with a sheet metal screw in the end.  The end of the screw is plenty sharp enough to scrape out the inside of the hole.  Take several back-and-forth passes, calipering the hole frequently until it is the right size.

Optional:  If you drilled the holes in for the lead screw, you can insert a piece of 3/8" all thread rod and use it to push/pull the head stock back and forth for the boring steps.  A ratchet and socket on a double nut on the end makes a handy crank.  This is slower but should result in a slightly more accurate hole.  Besides, it looks awesome while you're doing it!

Next, you will need to cut a key way slot in the hole to receive the 1/4" feather on the bottom of the tail stock ram.  You can use a coping saw to cut the edges of the hole, then clear out the waste with a 1/4" chisel. 

The tail stock ram is yet another piece of 3/4" pipe (marvelous stuff, pipe, and you can find hundreds of feet of it abandoned in the crawlspace of any house that has previously been re-piped!).  It has a 1/2" hex nut pressed into each end.  Because this is an interference fit, you will need to either hammer in the nuts or press them in with either an arbor press of a pipe clamp.  I also put a blind rivet in each nut to hold it in.

To do a blind rivet, cut a short chunk of a nail (10d common nails are about the right diameter for this).  Drill through both pieces, but don't go through to the other end.  Then insert the little chunk of nail, cutting it if necessary so it sticks up less than 1/16" of the surface.  Then peen it with a ball-peed hammer until it squishes into the hole and locks the pieces together.  Finish by filing it flush with the surface.  With larger rivets it is helpful to heat the rivet cherry red with a propane torch before peening, but it isn't really necessary with little ones like this.

The tail stock ram also gets a feather at the bottom made from 1/4" key stock, which keeps it from turning in the hole.  I also attached this with blind rivets, but brazing would be another option.

A bit of paste wax on the ram makes it much easier to shove into the hole.  You want a tight running fit with no side play. 

The ram feed screw is a piece of 1/2" all thread rod with hex nuts and washers.  It passes through a wooden plug which you can turn in the chuck (the easiest way is probably to drill the 1/2" hole first and stick a 1/2" dowel through it so you have something to grab in the chuck. 

The knob on the end of the feed screw is turned much the same way.  I had originally had trouble with it slipping on me, so I mortised in a short piece of left-over key stock which engages a notch I cut in one of the nuts.


Accessories

Dead Center

You will need a dead center for any kind of spindle turning.  I make them by cutting off a short length of all thread rod or a bold and fixing a hex nut in the middle with a blind rivet.  Turn a point on one end to about a 60º included angle.  Whenever your center starts to get dull or beat up (which happens often when you are turning metal) just put it in the chuck and turn a fresh point on it. 

Tail Stock Chuck

Most types of drill chuck can be adapted to this tail stock.  Probably the easiest is a chuck with 1/2" threads, since you can just the head off a half inch bolt and use a die to thread one end of it to the 1/2" NF threads in the chuck.  Riveting a nut in the middle gives you something to hold onto when you screw it in to and out of the tail stock.

A chuck that is meant to go on a Jacobs or other taper is going to require some more complicated turning, since you will need to exactly match the taper for it to fit on.  Your best bet is to turn it a few thousandths oversize and coat it with Sharpie or machinists' dye, push the chuck on to see where the high points are, and use a very light pass to adjust.  Repeat until the chuck goes on all the way and stays on.

Drive Center

I don't actually recommend hand made drive centers, since they don't usually work as well as even the cheap store bought ones.  Of course if you have a milling machine you can make as many high quality ones as you need--but since you are reading about how to build a lathe out of junk, I assume you don't have a mill either.  The basic procedure is to start with a cylinder of steel (part of a large bolt works) and drill and tap it to go on your head stock spindle.  Then mark out the spurs.  Four is the most common number, although I have seen centers that use anywhere from two to twelve.  Then carefully carve out the metal with a grinder and files. 

It is easier to make the center pin separately and then press it into a hole in the center.  This avoids the problem of turning the pin without wiping out the spurs, which can be quite a challenge with hand tools.

Other Accessories

Look in any machine tool or woodworking catalog and you will see literally hundreds of different accessories for lathes.  Many of these are fairly simple and, with a little ingenuity, you can probably build your own versions...especially now that you have a lathe.  It's also worth diffing around in pawn shops and flea markets.  Dig around in the junk boxes they usually have in a back corner and you can find all sorts of bits, centers, chucks, and other useful parts that can be adapted to your own setup, often sold for pennies on the dollar.
 

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