DIY Mini Lathe Build Log (Photo Heavy)

[mako]

After turning a lot of labor-intensive valve stems on my drill press and wasting hours trying to find hardware store parts that suited my purposes, I decided I really, really need a lathe. Unfortunately, even the cheap ones are expensive and the really cheap ones ($100 - $200) have way too much plastic in their construction for me to risk trying one.

The solution, obviously, was to build my own mini lathe. Of course, 90% of building it is because I want to build one. The other 10% is that I need one. So, here's the build log for my first mini lathe; if you can learn from it, feel free. If you've got helpful input, fire away!

Disclaimer: I don't know much about lathes and haven't ever used one, but I've done my research and I'm happy to learn by trial and error. I'm well aware I'd get better results by buying a lathe instead of building one. If you're on this forum at all, it's because you'd rather build it than buy it. 'Nuff said.

The planning process was as follows:
1. I need a lathe.
2. I can't afford a normal lathe.
3. But I bet I can make a serviceable (for my purposes) lathe for under $200.
4. Where are my car keys? I'm ready to go to the hardware store.

So... yeah, that's about the extent of the initial planning process. What can I say.

I was initially going to build it along the lines of this Bolt-Together Lathe, until I got to looking at the pipe section in the local hardware store. Those 2" pipe fittings were a little more expensive than I wanted to pay for. Besides that, the store doesn't carry plate steel thick enough AND wide enough to work as the lathe bed.

After perusing the metal section, I decided I'd try a slightly different tack. The 1/2 inch steel rod they carry is quite stiff (according to the ISO "stand on it and see if it bends" test ). It has a certain amount of flex to it over a 4 ft length with 140 pounds on it, but I think over 18 inches it should be stiff enough to do the job. I grabbed a length of it and a length of .95" steel square tube.

The plan is to use three 6-inch lengths of steel tube to support two 1/2 inch steel rods as the lathe 'table'. At five inches apart, with the maximum distance between supports being 18 inches, it should be stiff enough to work aluminum and brass at the least. I'm hoping it'll be able to handle iron and softer steels , but I won't be too disappointed if it can't.

Here's the schematic I've come up with so far:

I'm planning to improve the stiffness of the overall design by bolting the entire assembly tightly to an extremely smooth concrete block. I think the concrete will help prevent a lot of bending and twisting. Even if it doesn't help (but it should) it'll add some mass to the lathe and keep it from sliding around, so I won't have to bolt the thing to a table. Win!

I decided to cut the steel square tube with a hacksaw instead of my angle grinder. A little more finesse is never a bad thing.

Pardon the poor picture (cell-phone camera). Anyhow, never ignore the usefulness of a good centre punch; drill bits have a tendency to wander, even if you have a drill press.

One of the steel rods, with just enough chamfer to allow it to start in the holes in the steel tube, but still achieve a tight fit.

This was about as far as I've gotten as of this evening.

I'm leaving the parts as they came from the store until the lathe is almost completely finished. I figure if I give the whole thing a good tight fit, any moving parts (the tailstock sled and the tool carriage) will be nice and snug - but still movable - after I polish everything down.

[mrfoo]

a : your pictures aren't visible
b : Concrete's great. Don't underestimate its usefulness. http://opensourcemachinetools.org/concrete-lathe/

[jackssmirkingrevenge]

You can't use dropbox as an image host, best to use the spudfiles uploader and place the images inline.

[mako]

Oops. I'll fix that in a bit. Thanks.
Edit: fixed. Pictures! I love pictures! Drinks all 'round!

@mrfoo: COOL!! I may try that next.

@JSR: I tried that, but the uploader wouldn't work...

[mako]

I went down to the hardware store and got a piece of 3/4 inch steel square tube to make the tool carriage from.

The carriage is 8 inches long and 4 inches wide. Unfortunately, due to some wobble in my drill press (and difficulty getting accurate measurements) the holes in the carriage slides weren't aligned with the "table" rods. A little work with a file fixed that. (if the lathe works, I'll be rebuilding it with tougher parts anyway, so perfection isn't the goal here)

I couldn't find a piece of steel at the hardware store wide enough and thick enough to work as the top of the carriage. Since it has to bind the two 3/4 inch square tube pieces together AND hold the tool, it needed to be at least 1/8 thick, if not more. Luckily, I found a piece of stainless steel from a boat conversion kit I had and cut it to fit.

It wasn't quite long enough to cover the whole thing, but it gets the job done. I'll add another section to complete the tool carriage top. To tell the truth, I actually bolted the steel to the wrong end of the tube steel, but after thinking about it for a while, I decided to leave it. I think it'll make the carriage a little more stable in this position. (again, if the lathe works, I'll buy a piece of steel big enough to cover the whole carriage)

The tape is there for scale, for those of you of the measurementally curious. Next, I'll be drilling the holes for the lead screw for the tool carriage and tail stock. The lead screws on this will be standard all-thread. It's not perfect, but it'll do for now. If this were a more precise lathe, I'd be worried about backlash in the all-thread.

I'll pick up the all-thread and nuts for the tool carriage when I go get the glass I'm casting the concrete slab on. I was discussing with my mom how to get a perfectly smooth surface on the concrete slab (she used to work for company that tested the stuff) and she suggested pouring it in a form with bottom made from a piece of sheet glass. We'll see how that goes.

[tigerblues28]

Do a google search for a "gingery lathe".

I started thinking about doing the same and building a lathe.



Nick

[mako]

Actually, the Gingery has been at the top of my 'want to do' list for a long time. I ultimately decided to try this first, since the Gingery lathe requires more casting skill than I currently have (ie, none) as well as needing access to a fair amount of aluminum raw. I'll probably try one someday, after I get some aluminum casting experience under my belt. I've been planning to build a foundry, anyway...

Well, I hope my learning experience helps you out some!

[mrfoo]

You will almost certainly find that your current design is not stiff enough. It will chatter, probably even cutting plastic.

It's a good learning experience, though.

[mako]

That's a distinct possibility, but as you say, good learning experience.

How are you concluding that, btw? Is the 1/2 stock not stiff enough at all, or is it the way I'm supporting it?

[mako]

I had a meeting at work today, so I dropped by the hardware store at the way home and grabbed some parts to make the lead-screw for the tool carriage.

The lead-screw is 5/16 inch all-thread.

The shaft-collars hold the lead-screw in place fairly tightly with minimal slip when I reverse directions. I can cut down on what slip there is by clamping the shaft-collars against the tube steel before tightening them.

I think this is called a flange nut (not sure, but that's what I'm calling it) and it was ridiculously expensive. $1.84 for the little thing (almost as much as 3 feet of all-thread!) but it saved a lot of trouble. It's screwed to the tool carriage.

Here's the assembled tool carriage lead-screw. Since it's just hardware store grade all-thread and fittings, it's got a fair bit of backlash, but it's not to bad, all things considered. The thread pitch on the all-thread is low enough that it takes a lot of turning to get the carriage to move an inch, but that's okay. If I need faster carriage movement later on, I'll gear an electric motor to it. I had the electric drill on it earlier and boy, did the carriage fly! I think I clocked it in at two or three feet per minute at one point.

One thing is worrying me, though; I'm going to be using a standard drill chuck for the lathe chuck at first (until I determine if spending the money for a real lathe chuck is worth it) but I'm having trouble finding a spindle/shaft that will fit the drill chuck.

I currently have a 3/8 inch carriage bolt I cut off screwed into it, but it turns out the bolt has slight bend in it, which is tough to see, but becomes very obvious when I put a work piece in the chuck. Fortunately, a long, boring search online led me to an Ebay shop that sells taper-less threaded shafts of the correct length. http://www.ebay.com/itm/3-8-Steel-Shaft ... xydlFSr64c

Now, I've got to figure measure the chuck for thread size and pitch...

[mrfoo]

How are you concluding that, btw? Is the 1/2 stock not stiff enough at all, or is it the way I'm supporting it?

A bit of both, really. You don't have enough rigidity or mass.

Confession time - my build, which is currently torn down, failed due to massive chatter and accuracy issues. I was taking a similar approach to yours, except I was using 40mm OD tube packed with sand as my ways, and 40mm bored hardwood blocks as the riders.

Issues you will have are:

You need to have your ways aligned exactly. Not "near enough", but "within 1/10 mm or so". Without that kind of accuracy, you'll have to have so much slop in your carriage that you'll be seeing 1mm or so play at the tool. Leadscrew backlash is not an issue, of course, as long as you only drive one way. Allthread is fine.

Make your headstock separate to the bed, you can then adjust alignment WRT the ways. You'll never get it accurate enough to make decent cuts any distance from the chuck, otherwise.

Don't bother with a chuck to start with. Certainly not a drill chuck. It won't be accurate enough. Go centre-to-centre with a drive dog.

[mako]

Fortunately, based on tests last night, I think I've got all those problems covered. My ways are solid steel 1/2 inch thick and supported in three (soon to be four) places, bolted VERY securely to an 80 lb concrete bed. Rigidity may still be a problem, but I think steel rod is a far cry from even 40mm tube. Mass, hover, isn't anywhere close to a problem. The completed. assembly is likely to weigh over 150 lbs, twice the weight of a Grizzly mini-lathe.

Good point about the alignment; the good thing about this design, though, is that it doesn't need to be perfect. It just has to prove that the design is feasible. If it works, I'll be rebuilding it with 3/4 or 1 inch drill rod ways and solid steel supports. Instead of simple bored holes, the ways will be adjustable by screw-positioned blocks within the supports. Anyway, for some bizarre reason, the current ways actually came out remarkably well aligned. They're within a 0.5 mm of each down their 18 inch length. I may put an adjustment screw in one later on to fix even that.

I'd already figured out that a chuck might be out of my reach for now. In my case, tho, it's because of the difficulty finding a spindle. A good quality drill press chuck will be every bit as accurate as a lathe chuck; if they weren't, drill presses would be useless.

[mrfoo]

Rigidity may still be a problem, but I think steel rod is a far cry from even 40mm tube

Unfortunately, not in the way you think. Rule of thumb is that a given length tube is up to* twice as stiff as the same length rod of the same mass. Stiffness varies with (IIRC) the cube of diameter.

Unit area of 12mm od rod is πr^2 = 113mm^2
Area of 40mm x 2 tube is π(r₁^2 - r₂^2) = 238mm^2

To get something like the same stiffness as 40mm OD, 2mm walled tube, you'd need rod of around 18mm**.

The completed. assembly is likely to weigh over 150 lbs, twice the weight of a Grizzly mini-lathe.

How much of that is useful, though? The thing about real lathe beds is that the ways are effectively part of the bed, meaning that the mass of the bed is useful (other than for keeping the thing on the ground). My problem was that my ways weren't attached enough, or stiff enough, to damp things down. All combined with too much slop. The end result wasn't pretty. But, y'know, learning experience.

My plan for spindle was (once I'd got a temporary headstock and spindle up and running) to turn down some bar stock to diameter for my "real" bearings, put it in place in the "final" headstock, and then bore a morse taper into it. That plan still holds, its only the bed, ways, slides and temporary headstock that need changing

* Limit case, infinite diameter tube with infinitesimally thin walls.
** If you ding the tube, of course, all bets are off.

[Gun Freak]

Interested to see how this ends up homemade lathes have always been a fascination of mine, so much so that I built one and never actually used it to make any parts

[mrfoo]

Interested to see how this ends up homemade lathes have always been a fascination of mine, so much so that I built one and never actually used it to make any parts

Photos!

This has triggered me to start revisiting my own. And by "revisit" I mean "restart from scratch"