Do you really need a spring loaded pinion drive?

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12 Dec 2016 11:21 #83940 by rodw
Andy, Tommy, thanks again for your ongoing guidance and advice given I am just a self taught hobby machinist who knows nothing about what he's doing.

I had a bit of a Google and am satisfied the machine specs to date well exceed many commercial offerings. I am sure some commentators with commercial interests on other forums overly complicate this stuff in the hope that it remains shrouded behind smoke and mirrors. One particular finding was the use of a new (to me) term of measurement called milligees. On further research, 1 milligee = 0.001 G forces. Those of us who are blessed with SI units will know that the apple was accelerating at 9.81 m/s/s when it hit poor Einstein on his head under the power of 1 G force.

So it seems that this axis is accelerating at about 90 milligees using a common approximation assuming 1 G roughly = 10 m/s/s. Now these commentators say that you need acceleration of about 30-40 milligees to do a decent job on a plasma table and some high end tables reach 70-100 milligees. One manufacturer even stated his machine accelerated at 40 inches /sec/sec.

So now I have a difficult choice to make. What should I set the acceleration to:
1. Leave unchanged as Tommy suggests secure in the knowledge that it is 3 x better than other commercial offerings.
2. Increase it to 981 mm/s/s so that I can claim 100 milligee performance
3. Adopt 1016 mm/s/s which for the SI challenged is 40 inches/s/s
4. Shoot for the stars and see what can be achieved on scratch built hardware before it shakes apart...

The experimenter in me really wants to pursue option 4 but I have some recollection of applying this approach to a small air driven steam engine I made some years ago that would run happily on 3-4 psi and all but disintegrated at about 16,000 RPM when driven at about 80 PSI (oops, should be using kPa shouldn't I? Call it 550 then)

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12 Dec 2016 12:22 #83942 by andypugh
It might be instructive to see how many milli-ells it takes to get up to full speed.

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13 Dec 2016 08:38 #84017 by rodw

It might be instructive to see how many milli-ells it takes to get up to full speed.


Andy, I've given your suggestion due consideration and with deference to my Scottish ancestry, it seems the Scottish unit you suggested was outlawed in 1824. The equivalent British yard without the extra inch was only bannned in the colonies down under in 1970. It is also clear that Einstein was not sitting beside a Scottish Loch when the apple fell upon his head. I also note that the ell was used in some circles to measure cloth and tapestry and despite the fact that my real name means "famous weaver", I will defer to the law of the colonies. Therefore, I am unable to perpetuate this unit of measure in the famous plasma table I am constructing.

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13 Dec 2016 14:14 #84037 by tommylight
Dang, wrote quite some funny stuff regarding Einsteen and Newton and apples and got a call so failed to post it.
Well apple has to do Newton, not the hairy grey genius.

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13 Dec 2016 20:13 #84054 by rodw

Dang, wrote quite some funny stuff regarding Einsteen and Newton and apples and got a call so failed to post it.
Well apple has to do Newton, not the hairy grey genius.


I hate that too. Well enough diversions, I gotta get some limit switches finished and work out how to mount the 80x40mm gantry cross member to the yet to be designed uprights at each end.

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