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Fallback wobbler

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PaulR:
I was hoping to find a bit more time to come up with an idea that's been knocking around but it's just not to be at present so I'm going to whip out the usual old chestnut and make another super simple wobbler just to keep my hand in.

It'll be a small single acting engine, 8mm bore, 18mm stroke horizontal jobbie with minimal parts 9and even less interest for most here I expect!).

Snagged an hour and a half this afternoon and made the frame from some brass angle, the cylinder from some hex, the piston from some silver steel and a block of brass for the bearing. A bit of soldering next I think.

While I'm here, can anyone suggest a simple way to mark a centre line on the flat face of a piece of hex (along the side, not across the end that is) without using a machine tool? Best I've got is laying it against a vertical flat and scribing using a surface gauge but it's tricky to get it dead centre. Maybe I should scribe then flip it over and do it again, as I often do with Jenny calipers.

crueby:
The way that I learned to scribe centerlines on boat spars will work here as well. For them, a block of woood several times longer than the width of the piece to be scribed, length does not matter. Add blocks at either end taller than the piece to be scribed. Then measure from the insides of each block to the other, mark the center, and drill a hole for a pencil or scriber. To use, position this 'tool' onto the piece, rotate it till the two blocks touch the side, and lower it till the pencil/scribe touches the surface. It will self center the scriber - then just push it along the length, marking the piece. Very simple to make, works great.
Here is a link to something of the sort, made from a single block and having two scribers to lay out for making an octagon (this is not my site, found it by searching for 'spar gauge' ). Same thing works with one scriber in the center for your use.
https://hub.shapertools.com/creators/5e4d9fa3c8f2b1000fb45be5/shares/63bc94f950c65c5f829cddbe

crueby:
Oh, and for the 'no machine tools' part, to take it to an extreme, one could be put together with a few bits of wood/metal, a pencil, and some tape!

PaulR:

--- Quote from: crueby on August 14, 2026, 08:50:09 pm ---The way that I learned to scribe centerlines on boat spars will work here as well. For them, a block of woood several times longer than the width of the piece to be scribed, length does not matter. Add blocks at either end taller than the piece to be scribed. Then measure from the insides of each block to the other, mark the center, and drill a hole for a pencil or scriber. To use, position this 'tool' onto the piece, rotate it till the two blocks touch the side, and lower it till the pencil/scribe touches the surface. It will self center the scriber - then just push it along the length, marking the piece. Very simple to make, works great.
Here is a link to something of the sort, made from a single block and having two scribers to lay out for making an octagon (this is not my site, found it by searching for 'spar gauge' ). Same thing works with one scriber in the center for your use.
https://hub.shapertools.com/creators/5e4d9fa3c8f2b1000fb45be5/shares/63bc94f950c65c5f829cddbe

--- End quote ---
Thank you Chris - that is a great gadget and one that I imagine has been in the craftsman's armoury for aeons! I couldn't quite fathom it from your description but read while looking at the picture in the link it's very clear. Definitely going to make one of those when time allows!

crueby:
Yeah, been around forever. It works on straight or tapered pieces, I made one for making masts and booms on my sailboats decades ago. The two pencil version can mark out octagons, so you can plane off corners from a tapered mast blank  then you round off those corners by eye, and a mast appears!

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