Rotary table

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Bazyle on 30/04/2018 11:31:43:

Posted by pgk pgk on 30/04/2018 10:56:44:

A quick dig about on google tells me that HP Designjet 50PS in Color Magazine mode does 133 LPI

pgk

but is that a result of using the 133 gear, or did they decide on this obscure LPI to start with? I don't think it aligns to printing 'points'.

.

Eureka !!

**LINK**

http://facweb.cs.depaul.edu/sgrais/color_line_screen.htm

MichaelG.

[SillyOldDufferModerator @sillyoldduffer]

Posted by Michael Gilligan on 01/05/2018 19:21:49:

Posted by Bazyle on 30/04/2018 11:31:43:

Posted by pgk pgk on 30/04/2018 10:56:44:

A quick dig about on google tells me that HP Designjet 50PS in Color Magazine mode does 133 LPI

pgk

but is that a result of using the 133 gear, or did they decide on this obscure LPI to start with? I don't think it aligns to printing 'points'.

.

Eureka !!

**LINK**

http://facweb.cs.depaul.edu/sgrais/color_line_screen.htm

MichaelG.

Ah but isn't that just kicking the can down the road? Now we know that 133lpi is a printing standard, some awkward cuss is bound to ask why 133lpi was chosen for magazine quality printers.

My hypothesis is that it comes from the practical limitations of spur gear ratios:

• Best to distribute wear on a spur gear by having an odd number of teeth (so the same pairs of teeth don't re-mesh continually.
• A pinion must have a reasonable minimum number of teeth, perhaps 10 to 25, with pinions cut with smaller numbers of teeth liable to wear quickly.
• 19 is a decent number of teeth to put on a pinion.
• 19 : 57 gives a 3:1 ratio
• 19 : 113 gives a 7:1 ratio

I suggest 133 lpi was chosen because it's a resolution suitable for magazine quality printing that can be achieved with standard gears. 17 x 7 is 119 (too low), and 21×7 is 147 (too high).

Happy to be told this idea is complete rollocks!

Dave

[Michael GilliganParticipant @michaelgilligan61133]

Dave,

I think your 'hunting tooth' hypothesis is sound.

We have at least one forum member with practical experience of printing machinery, so hopefully he will be along with a definitive answer.

MichaelG.

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