Box joint table saw jig

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Probably the mistaken presumption of a shared understanding that the role of the gears in precisely positioning the work implies a free turning, backlash free mechanism. ;) I think I would have just cut a hob on the knee mill and made the plywood gears that way. Very little drawing or figuring involved, obviating the obvious problems.
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Swingman wrote:

My apologies - I was experiencing an adversity/frustration overload and shouldn't have posted anything anywhere...
...and MikeWhy was right that one of the headaches involved backlash in a trough-type reflector tracking mechanism subject to (mostly) unpredictable wind loading.
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Morris Dovey
DeSoto Solar
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Meshy business, that.
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I haven't actually ever made a hob, but know of the general principles. If your gears are non-metallic, wood or GRP, the problem might be even simpler. Better still, if the geartrain is a worm gear, a simple tap -- the things used to cut internal threads -- are perfectly serviceable hobs for cutting the worm wheel.
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"MikeWhy" wrote:

Hobbing is the least accurate but highest production rate process for making a gear.
Least back lash is with a worm/wheel drive.
The higher the ratio, the less the back lash.
Lew
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MikeWhy wrote:

Your suggestion is appreciated, but this thing needs to be thermally driven (as opposed to motor driven) - and if I need to use a geared approach, it will probably be a sliding rack with one or two simple spur gears.
It's one of those problems that /seems/ like should have a simple and inexpensive solution, but every attempt so far has led to unacceptable complexity and/or cost.
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Toothed belt? A la printhead on an inkjet? Bicycle sprocket parts....VERY universal and cheap. Or
Those nodding oil pump things I see all over the country-side around Petrolia? Your reciprocal motion on one end, the same, but fulcrummed (LOL) on the other as a pump?
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Robatoy wrote:

Hmm - I hadn't though about this, but will.

This comes closest to what I'm working on - except that that the power source is solar heat. I think I can make it work with a flat panel, but the efficiency (which translates into ROI here) goes way up if high-temperature heat is used. That requires a collector aiming mechanism to track the sun.
Recently I got a video of the first engine actually pumping water (not doing a very good job yet, but still not bad for a first try) in Pakistan.
http://www.iedu.com/DeSoto/Projects/Stirling/Elsewhere /
The sight glass on the piston shows the pump displacement, and the pumped volume should match that. I think their problem is check valves with too-strong springs.
The sun-tracker will, of course, need to make one (controlled) cycle per day, and somehow (automagically) start out facing east in the morning.

Exactly! The same, only different! (ROFL)
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DeSoto Solar
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[snip]

That's an easy one. Expanding gas cylinder like the greenhouse people use to open a vent. Hide it in the shadow of the collector itself, so when the sun peeks around, it starts expanding till it creates its own shadow again sortakinda like a wheatstone bridge but mechanical. When the sun stops playing peek-a-boo with the cylinder at night, it is brought home by its own collapse, perhaps helped by a counterweight/ spring. The cylinder would sit lengthwise along the obvious edge. It could sit in a slot in the collector itself for extra intensity. The mechanical challenge is minimal.
Maybe something bi-metal?
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Robatoy wrote:

I've been considering /two/ such gas cylinders (so that operation isn't air temperature dependent) - one on each side of the collector, each side connected to opposite ends/sides of a double-acting hydraulic or pneumatic cylinder. That setup would allow for an eastward pressure bias that would be overridden during the day, but would cause the tracker to revert to east-pointing at night, pretty much as you describe.
The major drawback appears to be instability in gusty winds due to the gas' compressibility.

Maybe, but I think your first idea is a better match to the problem.
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DeSoto Solar
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Locking against heavy loading would seem to suggest a worm. PV? ;) A Stirling pumped "hydraulic" motor/water wheel? I know... complexity.
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MikeWhy wrote:

PV plus motor plus worm drive is certainly an attractive route, but too expensive and not suited for local production and maintenance.
It needs to be really simple and so inexpensive that it's not worth stealing. For context, rural Somalia might be one of the target "market" areas.
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Morris Dovey wrote:

Offhand I'm not sure how one would design such a thing but rather than using shaft work could you pump water from one plastic bag to another, with appropriate levers and paddles resting on top of the bags?
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J. Clarke wrote:

Maybe. I've been too involved in trying to help get the engine working to worry about the tracking system until now. Nearly all of my past experience with control systems has been digital, and I'm really in over my head on this one.
It seems to me that if I can choose one side to pump to, then I should be able to pump to a cylinder/piston linear actuator of some kind (thinking of a reworked shock absorber or strut) to do that job.
Hmm - if I use robatoy's gas cylinder idea to control a valve to direct part of the pump flow to one of your actuators, I might be on a better track than I am now, even though I'll still need to figure out some reliable way to make it face the morning sun without being vulnerable to nighttime gusts.
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As though I/we needed taunting... ;) Give credit where credit is due. The man's an obvious genius, and his workmanship is topnotch. I was about to remark on replacing the gear drive with a DC servo motor, ground ballscrew, and linear slides, but I see he already did one with a stepper. It wouldn't take much to put a microcontroller on it to drive it without a PC. I have an old AVR Butterfly sitting around unused...
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MikeWhy wrote:

Hmm - if you're going to do that, why not add a second motor to move the stock over the blade too? Then you could do something else while it makes the joint for you...
...and if you do that then you might as well add a third motor and build
http://www.iedu.com/DeSoto/Projects/JBot /
so that it can make about any kind corner joint you can think of.
Pull out that Butterfly and a soldering pencil. :)
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DeSoto Solar
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Morris Dovey wrote:

Did you see what he did at?:

http://www.youtube.com/user/Matthiaswandel

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www.e-woodshop.net
Last update: 10/22/08
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http://woodgears.ca/jenga_pistol /
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Here, Sketch this: http://woodgears.ca/schulteiss/index.html
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Everytime I see a Leigh jig, I think an X-Y table, and a router motor for the spindle. One of these days, I'll actually do something about it. The last time this came up, I ended up with a boxful of dozukis and waterstones instead, which obviated the need (for the time being).
The single axis jig, as here in the box joint cutter, is a special case in simplicity. It should work equally well on the router table, doing the job of an Incra-style jig. The full set of Incra templates could reasonably be stored in flash. The more I think about it, the simpler it seems and the more generally useful (in the same way that an Incra jig is useful).
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