Lathe Design

[Jeremy Maso]

Hi,

We're working on our own lathe design and are looking for feedback on it. Here's the page with pictures of the second design, which we changed it to after some feedback:
Open Source Lathe Design 2

We're using the entire shaft to mount the spindle, and the bolts from each section adjust the level to keep anything from coming loose and to add extra support. The far bolts can be set to the correct height and left there while the near ones can be loosened to adjust the slide distance and then tightened so that the far bolts keep their height set and the cross slide and tail stock keep their alignment with the spindle.

It's somewhat similar to these lathe designs:
Drummond
Scope
Kneller

I will write up a list of what we are going to be doing with the lathe later, so we can see if what we are building will meet our needs. Basically we're looking to bore out steam engine parts.

Pictures:
http://openfarmtech.org/images/3/3e/Lathe_2.0_1.jpg
http://openfarmtech.org/images/6/69/Lathe_2.0_2.jpg
http://openfarmtech.org/images/9/9c/...0_XYZ_3D_1.jpg

The hydraulic motor is powered by the LifeTrac engine (LifeTrac - Open Source Ecology).

Is it going to work? Are we missing anything critical?

[RICHARD ZASTROW]

Depending on how much force exerted in the Z axis (toward the spindle), there could be bending on the plates supporting the spindle bearings. The same problem exists for the tailstock.

Easily solved with supporting elements to prevent lateral motion such as a plate between the front and rear bearing of the headstock (spindle) end, creating a "box".

Some angle brackets?

The tailstock will need to be supported to prevent it from pivoting by the engagement force of the center itself.

These are all addressed in your examples by the castings that perform these functions.

Kepp working at it.

Dick Z

[RICHARD ZASTROW]

You will need some method of moving you tool(s) toward and away from the workpiece in the cross (X axis).

The cross slide will have to be guided along the Z axis to prevent it from twisting due to cutting forces. Some method of preventing the the cross slide from lifting is required as well.

You may want to study your example machines a bit more.

Dick Z

[handlewanker]

Hi Jeremy, I would use twin bars for the bed.

One to guide the saddle and the other to prevent the saddle rotating round the first bar.

If you take the design of the Unimat modelers lathe, (the original Unimat with the twin bar bed), and scale that up you might just achieve something, but as I see it, and I've been in the engineering trade for 50 years as a fitter and turner, this design is too crude to justify spending a lot of effort for little return.

I'm not sure what facilities you have for working with metal but it would appear that this is a farmyard project, using minimal machinery if any.

However if you have access to a machine shop, even if with minimum tools available, then a far better design would pay dividends, and I'm sure there are lots of budding machine tool designers that would steer you in the right direction.
Ian.

[John Welden]

You'd be better off buying a cheapo lathe.

[Jeremy Maso]

Thanks Ian, it looks like two bars wouldn't cost much more, and would add a lot of stability.

We might look closer at buying a cheapo one if we really need one asap for another project. I don't know if the prices are reasonable for the sizes we're looking at though, a 12" chuck with about a 2 foot slide.

Thanks for the advice Richard, it does looks like the spindle bearings need better support. I'll add something there, maybe just a plate across the top attached with angle? Maybe something to attach them lower as well. I'd also like to add a threaded rod to adjust the x axis.

[RICHARD ZASTROW]

Jeremy, A plate across the top would reduce twisting in the horizontal plane. A vertical plate securing your existing plates to each other would reduce vertical twisting or parallelogram type movement.

An angle iron type support connecting your existing vertical plates to each other both on the top and sides would reduce all right to left (front to back) motion of the headstock end. The same could be true of the tailstock end if constructed similar to headstock.

Hope that isn't too hard to understand.LOL

Dick Z