Thread: Milling an inside radius

Originally Posted by Anorak Bob

( I know this will be a shock to Stuart but I don't own an 800mm diameter rotary table let alone a machine to mount it on! )

Well not yet you don't, but now you have the perfect excuse to go buy one. Problem solved.

Doesn't the table on your mill pivot? Just bolt it to the table and pivot the table by hand.

If not you could mount the plane onto a piece of square tube clamped in a swivel base vice. If you make the tube long enough to come out the other side of the vice you now have a handle to pull the work past the cutter. Get what I mean?

Stuart

On edit, I removed my comment because now I realise what you are talking about. I'll be back.

Stuart,

I understand, but the pivot point or centre point is beyond the end of the table.

BT

Here is the best picture I have of what I was talking about.
The 25mm SQ black bar is about 3ft long, the swivel base is loose enough that you can move it but wont lift. The radius would only be about 100mm but your cutters are likely sharper than that one

With your MDF idea you would just need an up side down L bolted to the fixed board hoooked over the end of the moving board to stop it lifting.

Stuart

How long is your table? Maybe you pictures make it look bigger than it is
Stuart

I like Stu's idea. In fact, if you had a rigid enough tube you could fashion a pivot point out of a stud, a tee-nut and a bearing or two. If long enough (2 metres?) you could probably control the feed by hand.

OK, I see you've mentioned that the table is too short to allow the pivot being on the table. Maybe a metal version of your MDF idea might afford more rigidity? Probably still not enough though.

Roughly 600mm. It rotates about it's centre and while I can move the entire table along the vertical face of the longitudinal slide, I can't get it anywhere near the position I need it in to be able to use it as a "rotary table"

The vise as a pivot makes sense. I have a little Hercus T & C vise that could be well suited to the idea. Another way might be to buy a piece of 400 x 150 x 10 flat bar and fix it per GQ's suggestion with some kind of extension handle.

Does it have to be milled on a milling machine?
What about doing it on a face plate on a lathe, admittadly setting it up at the requisite 392mm radius might be fiddly

Pete

There may be another way of achieving the rigidity required. The 13's dividing head and tailstock sit on a 540mm long swivel saddle. This is a tee slotted cast iron beam. I could come up with some Heath-ish adaption that might allow the mounting of the plane body. This beam has a pivot to enable partial rotation on the mill table.

Could be the answer.

I see there have been a few posts put up while I have been drawing.
Something similar to this would work and could be made up to be bolted together.
The bottom tube could be bolted to the table and use thread rod with double nuts on it to lock either side of the block near the handle.



Dave

Originally Posted by pjt

Does it have to be milled on a milling machine?
What about doing it on a face plate on a lathe, admittadly setting it up at the requisite 392mm radius might be fiddly

Pete

An impossibility Pete. My lathes only have a nine inch swing. If you have a look at the last photos in my post entitled "Adventures with cast iron...", the intended curved surfaces are next to the frog. I can only use a mill to achieve the curve.

BT

Since your table is to short, having the tube raise the long piece off the table would allow room for another piece of tube to be bolted to the table out to the pivot point.

Dave

"I see there have been a few posts put up while I have been drawing.
Something similar to this would work and could be made up to be bolted together.
The bottom tube could be bolted to the table and use thread rod with double nuts on it to lock either side of the block near the handle."

Thank you Dave. The advantage of the screw feed is being close to the action. I'll slip up to the shed tomorrow to see if I can conjure something up from the bits and pieces I have.

Bob.

If the extension for the pivot point can be set up on your table like below, it will save having to weld a T bar across and will give more support bolted across a couple of T slots.
Sorry for the rough pictures.



Dave