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From: Peter Fairbrother <peter@tsto.co.uk>
Newsgroups: rec.crafts.metalworking
Subject: Re: boat propulsion - miniature computer-controlled steam plant?
Date: Sun, 10 Mar 2024 16:36:59 +0000
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On 09/03/2024 19:11, Jim Wilkins wrote:

> I can visualize what you mean, interference limits the blade depth. The 
> blades could be cut deeper with a small end mill if the rotary index 
> holding the disk blank was in a swivel vise (or rotary table) manually 
> turned only far enough to make the cut. The setup might be easier if the 
> disk blank was fixed to a drilled index plate that took up less space, 
> mounted on a vertical surface of a block that centered (or offset) the 
> blank over the vise swivel axis.

Nowadays I only cut ceramic turbine wheels on a CNC mill [*] - it has 
five-and-a-half axes, but I only use three (plus a rotary table) for 
turbine wheels, that's good enough, so the result is similar to your setup.

For ceramics, don't buy the "machinable" ceramics, they are horribly 
expensive and their properties are lesser. I get most of my alumina from 
a no-name chinese source, can be brittle but it is usually ok if yuo 
keep that in mind. Also Morgan ceramics for high tech and high 
reliability stuff (Si3N4, ZrO2).

Diamond tooling is not expensive if you a) buy the tools in reasonable 
quantities and b) keep the water flowing, or even just there. Been 
meaning to make my own diamond tooling, but I don't know how and haven't 
really tried - anyone?


> I would rough out the gaps first, milling an arc with hand feed pressure 
> doesn't allow much depth of cut and NO climb milling.

NO climb milling is always good :) even in ballscew equipped CNC mills. 
Somewhat less important when you are using abrasive rather than cutting 
tools, but still.

Keeping diamond and abrasive ceramic containing slurry out of ballscrews 
is also good, damhikt.



Peter Fairbrother

[*] technically it's a CNC-converted BCA jig borer, but it has hefty 
upgraded ballscrews, improved lateral stiffness and is pretty much only 
used on ceramics with abrasive diamond tooling; though I can fit an ER20 
collet shaft and a slower motor. I also have a manual BCA.