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From: Richard Smith <null@void.com>
Newsgroups: rec.crafts.metalworking
Subject: Re: boat propulsion - miniature computer-controlled steam plant?
Date: Sat, 09 Mar 2024 20:19:20 +0000
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"Jim Wilkins" <muratlanne@gmail.com> writes:

>> "Peter Fairbrother"  wrote in message news:usi5v7$2ea8v$1@dont-email.me...
>>
>> On 07/03/2024 00:51, Jim Wilkins wrote:
>>
>>> You machine each blade with two hole saw cuts like this into the rim
>>> of the disk:  ((
>>> with a smaller radius on the back one so the blade has a crescent
>>> moon profile and sharp edges.
>>
>>
>> I tried that, but couldn't get it to work with a suitable geometry (for
>> an impulse turbine) - I had problems with the back edge of the holesaw
>> hitting the workpiece. If the saw was small diameter it would intersect
>> the workpiece on both edges, and if the diameter was large enough that
>> it didn't interfere the turbine blade was too straight.

> 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.
>
> I design things like this graphically by drawing the separate shapes
> in CAD and moving them to touch, for example the front and back
> circles intersecting at the blank edges, then recording the center
> coordinates. Trigonometry can refine the precision without much risk
> of gross error.
>
> 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.

Hi Jim, Peter

This and the previous "machining and eccentric" (with mention of model
aeroplane "peg out of a disc" crankpins) - has really dug up something
from my youth - mid teenage.  Now 60 years of age.

I was obsessed with getting a lathe (how met Tony of lathes.co.uk) - and
wanted to become a machinist.

Word was - no this is not a credible job.
etc.

Thing is - a structured mission is better than "kicking your heels"
ostensibly doing something you have no interest in.
ie. a "lowly" (sic.) mission might get you on a path, where being
defeated out of "wrong choices" and adrift without purpose, structure or
direction is going to put you six foot under.

I am still here - and this is the first time someone has spoken to my
15-year-old-ish self - and I now at 60 years of age see what I was
trying to do.

I would have been drawn in to a world of vast knowledge, been "hot on
the trail" taking-up mentoring, and had a life expanding open from that.

When everything came crashing down, I passed off as a welder and rebuilt
a life.  So I still had to travel a similarish path.

I recently went and for the first time discussed with some family
friends now elderly about their son my contemporary who died by suicide
35 years ago.  I am a living link to their son.  I had to profess I
didn't know much; hadn't seen anything "dark" in the time I was nearby;
have some knowledge of such things yet still was without basis to
comment.

Well; I am here.  And thanks for these interesting responses.

Best wishes,
Rich Smith