Machinability of Drill-Rod

Lobate is tehw ord for teh symptom, not the actual shape. But 'trochiod' isn't correct either, the shape is a Reuleaux polygon.**LINK**

Neil

Reuleaux ... as mentioned, and linked, in my post.

Correct me if I'm mistaken but, in the case of centreless grinding; I believe it's specifically "triangle" because there are two grinding wheels ... same effect as you sometimes get with a two flute drill.

MichaelG.

Looking here, perhaps I am wrong about the triangle.

... Although this seems to support my belief that "triangle" is the typical fault condition.

Edited By Michael Gilligan on 27/09/2012 20:56:46

Edited By Michael Gilligan on 27/09/2012 21:06:14

Drifting even further from the original topic ...

This is worth a look

As, most definitely, is this.

MichaelG.

Edited By Michael Gilligan on 27/09/2012 21:17:26

> Reuleaux ... as mentioned, and linked, in my post.

You don't seriously expect me to re-read the entire thread before replying

Neil

No ... but I would recommend you look at the second link in my post, above [just edited]; especially the bit about the Wankel engine.

MichaelG.

Hi Michael,

I skipped the maths, but interesting to see the theory about how a lobate broach can be used to make a square hole.

I used to have a MKII RX7; if people think silent electric cars are spooky they ought to try being in a wankel-engined car when the over-rev warning goes off. Bicycle clip time!

Neil(Why does "fixed centrode" make me think of Stanley Unwin?)

Edited By Stub Mandrel on 28/09/2012 20:56:22

I always fancied one of those Mazdas ! ... Somewhere in my archives I think I still have an article from "Cars & Car Conversions", where they tuned-up the early saloon, simply by fitting a free-flowing exhaust system. If I find it, I will let you have a copy.

MichaelG.

On the subject of constant-width sections, it is worth noting that a 90 degree V-block will not always detect this deviation from roundness. For example, a 7-sided constant width section will show zero deviation in a 90 degree block as measured vertically above the V. (If you doubt this, those in the UK can try it with a 50p piece.) A similar false pass will apparently be recorded by shapes with 9, 15 or 17 undulations, though I haven't tried this.

There is in fact a British Standard setting out in great detail the tests required to establish roundness (BS 3730, 1987, if you are interested). You may need to use several V-blocks of different included angle to establish true roundness, though a block of 72 degrees will work for all symmetries up to and including 18.

There is an infinite family of constant-width shapes, of which the symmetrical examples are only special cases.

David