turning a large diameter

Following a current discussion on the "clocks" forum here, I would welcome .any suggestions on the best way to form a piece of steel, about 2" long by 1/2" wide into a section of a circle with a 39" outside radius. The finish has to be good, at least ground.I have an old Myford lathe.

dave8

Edited By david bennett 8 on 04/09/2023 23:57:52

I would start by melting down the lathe

O.K, I amend my question to "any sensible suggestions"

dave8

Suggest providing a fully dimensioned sketch with critical parameters and finishes if you want sensible suggestions. Ground finish on a part that is formed metal seems contradictory. " 2" wide x 1/2" thick " describes 2 dimensions - at least three dimensions are needed to describe even the simplest 3D objects.

As Jeff says we really need the 3rd dimension.

If you hade a 40" length of 2 x 1/2 and needed the radius on the end it would be easy to put a pivot hole at one end and cobble something together so the other end could be swung against a moving tool then a grinding wheel / sanding disc held in the lathe chuck.

If you need the radius on a shorter piece of metal then it is just a case of mounting it to an arm that can be swung as above

Also what sort of Section of a circle once the radius is done is it pie shaped or cut along a cord

Edited By JasonB on 05/09/2023 06:51:41

.

Just for clarity, Jeff … he actually wrote: about 2" long by 1/2" wide

no mention of thickness

MichaelG.

Edited By Michael Gilligan on 05/09/2023 06:55:59

Cnc mill the profile. Polish by hand. Actually 1 metre approx outside diameter.

That's why I melted the lathe down, for more metal

I suppose you could roll it out into foil to get 39"

A ground 1 meter diameter is going to take some doing if we assume a 1/2 by 2 strip, like the outside of a large clock

A blacksmiths bar roller and nice shiny chrome coating would be easier

Edited By Ady1 on 05/09/2023 08:58:23

A much longer piece than necessary, roll it to radius and machine to size (likely sawing and then finish-machining to size).

Nearly 2m, in diameter - and only about 50mm long- is not a great deal of change from straight, flat or with a bit of a filed ends?

Depending on the surface finish required, maybe even surface grind the section required, before bending - and protect that surface during the bending operation.

OOPS. The sector is going to be about a metre long? Just use a linisher for the very slight curved end?

Edited By not done it yet on 05/09/2023 09:12:03

We don't need a 1 metre dia bit of metal, we need a small bit with a radiused face with 50cm radius of curvature on it, which would need to be about 4cm long. and maybe 6 to 10mm thick. Width behind the curved face wouldn't need to be large, less than 10mm I'd guess.

Quite easy really.
Solder the target block to the end of a piece of angle iron (just because it is probably a readily available cheap item) that is about 42 ins long.
Remove tailstock from lathe and clamp on convenient slab to extend bed so that you have a support point 1m from chuck. Drill the angle iron and seat up pivot point etc.
Arrange to camp the angle iron to the cross slide but with some flexibility to control its sideways movement and height across an end mill held in collet/chuck. After rough forming move to a small grindstone.

Like this - not to scale. Upper surface 500mm radius, exaggerated width but ~40mm, thickness into page say 10mm. There would be a blind hole in the lower face for a pendulum rod to fit into, probably carbon fibre for minimum mass. Assume the bob is on the lower end of that rod so its CG is 100mm from the top face. Material has to be steel or iron so it can be attracted to the lower face of a strong magnet that will support the bob weight. Within the above limits the amount of material in this needs to be minimised so the pendulum approximates as closely as possible to "simple".

Just for information, the reason for the circular arc on the top is so the CG of the bob will swing in a cycloidal path at least up to +/- 10 degrees from vertical.

Aha!

The amount needing removed is pretty minute

One square is 0.05" (1.27mm)

Edited By Ady1 on 05/09/2023 09:59:24

Exactly.

One I made earlier

As I said earler clamp/screw your bit of metal to a longer piece that has a pivot hole, provide a pivot which will be approx 500mm from the cutting tool then sanding disc held in the lathe chuck. Simples.

Moral of the thread is "ask old guys technical stuff at 9am and not 11.45pm"

Here you go.

Pivot at far end will need to be something clamped to the bed.

If you put a slot towards the other end to take a pin fitted to a cross slide tee nut then winding the cross slide in and out will move the workpiece on the end of the bar in an arc.

Could also be arranged vertically with the pin that goes into the slot mounted on a vertical slide and the pivot 500mm out to the front of the Myford anyone who has read the Minnie book will know the method as it is the same for the expansion link machining.

PS Younger guys will give an answer before 7.00am

Edited By JasonB on 05/09/2023 10:15:29

Edited By JasonB on 05/09/2023 10:22:10

  removed

Edited By Paul Lousick on 05/09/2023 10:47:57

Yes but there is a good chance that alot of them will have woken up grumpy lol

Pete