I really didn't expect that to work...

[Dr.Al]

This was an experiment, mostly to work out ergonomics and dimensions before designing something suitable for machining from lots of bits of aluminium. However, I think I won't bother with the aluminium now.

The experiment started with two left-over bits of walnut (from when I made a lot of chisel handles a couple of years ago):

They both got turned into cylinders with a roughing gouge:

I then got the spindle gouge out and attacked one of them in a rather random manner and with no particular shape in mind:

Off the lathe it came and a contraption that was almost entirely made by my 3D printer got mounted onto the lathe:

The only bits not 3D-printed are a cheap insert cutter from ridethebevel.co.uk, the four steel bars along with the LM10UU linear bearings that run on them, the two centres (turned on the metalworking lathe) and lots and lots and lots and lots of brass threaded inserts and steel screws. The linear bearings allow the tall bit of the assembly to move smoothly along and across the bed. The tool post thing has a pointy-out bit that touches the first (lower) turned part and stops the tool post (and hence the cutter) from moving too far in.

I was expecting it to shake itself apart or just vibrate too much to be of any use, but it just worked, with the cutter easily skimming down the workpiece to the right size:

The finish isn't amazing, but it's good enough that it wouldn't take much sanding. If/when I use it for real, I'll probably leave sanding of the "master" part until I've done all the duplicates and then everything will be sanded from the same base shape. A more direct comparison of the two parts:

Tonight I'll print version 2 with a few minor changes (mainly increasing the maximum part diameter to about 70 mm instead of the current 40 mm, but also making the tool post and cross-slide narrower). One nice thing about the design (and my new big 3D printer) is that all the parts fit easily on the printer bed in one go:

 

[daedalusminos]

What are you using, PLA? I assume you could also print the master object.

 

[Dr.Al]

What are you using, PLA? I assume you could also print the master object.

PETG (same thing I use for almost everything). Specifically this stuff, which is easy-ish to transfer to a Bambu reel to keep cardboard out of the AMS & which can be printed on the super fast Bambu PETG-HF setting.

The only time I ever use PLA is as an interface material for supports.

The model was printed with lots of perimeters (8 or 10 I think) and 40 or 50% infill to help with strength. Whether that was needed or not I don't know.

Yes, I could definitely print the master object but I'd make it flat rather than round (to make it easier to print). There are two holes (with threaded inserts) just underneath the hole that has the centre in it) for mounting something flat.

 

[hotponyshoes]

The equivalent of a pantograph arrangement for a lathe?

As you say, the master could be printed flat.
You could also print the inverse of a master slightly undersize, glue a strip of sandpaper along the face of it, then mount it in place of the insert cutter for the final finishing.

I don't know anything about wood but the insert cutter in those photos looks like it's for metalwork?
Wonder if it would be possible to mount something like a belt sander/router/Dremel instead and use that for the cutting? (Although that cutter looks like it's worked pretty well?)

Or, if you are making loads of them, could you not just make one big long blade from some tool steel and feed the whole thing in at once?

 

[roofman]

Men in sheds could easily re-build the planets infrastructure...great job @Dr.Al

 

[Dr.Al]

The equivalent of a pantograph arrangement for a lathe?

Yes, but without any scaling capability.

As you say, the master could be printed flat.
You could also print the inverse of a master slightly undersize, glue a strip of sandpaper along the face of it, then mount it in place of the insert cutter for the final finishing.

I'm sure that would work (as long as the sanding was done very gently to avoid melting the plastic) but it's probably not worth it really - if the size is close enough then you're just sanding enough to get rid of any tool marks. I can't think of a situation where wooden bits would need to be that precisely the same.

I don't know anything about wood but the insert cutter in those photos looks like it's for metalwork?

I don't know much about woodwork insert tooling but I bought the insert from a company that sells insert tooling specifically for wood lathes so I assume it's intended for wood. It seems to work well enough anyway.

Or, if you are making loads of them, could you not just make one big long blade from some tool steel and feed the whole thing in at once?

I doubt I would ever make enough of anything to be worth it, but I guess it would be possible. I'm not sure I'd look forward to the job of sharpening that cutter though!

 

[Dr.Al]

Version 2 has been printed and fitted:

View from the rear of the lathe:

As you can see, the tool post now rotates, thanks to a conical washer in the base:

It's stiff, but I see that as a good thing: less likely to rotate when I don't want it to.

After the first test, I also had to replace a part that I never expected to last at all:

The steel replacement was made from a bit of 10 mm square bar using hacksaw, file, pillar drill and M4 tap.

To test out version 2, I thought I'd print a template instead of using a turned part:

With a template like that and the rotating head, I can hold a bit of wood in the chuck and turn to match:

I'm pleased with how it's turned out. I might do a version 3, but the only thing I'll change is to round over the corners of the lower part of the tool post (and perhaps the base that it slides along). That'll give a bit more clearance from the reference part when rotating the tool.

In practice, I'm not really expecting to use this very much. It's been a fun design challenge to come up with a design, but I'd rather be doing things manually and I'd rather be making one-offs rather than lots of the same. Nevertheless, I'm sure it'll come in handy now and then. Given how infrequently I expect to use it, it was nice to be able to print the parts rather than spending ages plodding away with the milling machine chewing up aluminium.

 

[MysterG]

You are a clever chap

 

[DeanH]

Fantastic work. I have some staircase spindles to make and I was going to make a similar thing from plywood. Think I'll have a go at 3D printing the jig now...