Rotary table

Wish I had taken the time to listen to the maths teacher now !

Then why not make the 133 hole with your DRO and only get an error of 0.00011deg, eight times better than the 46hole and that is not cumulative.

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Thanks, Richard

MichaelG.

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Interestingly ... it took only moments to find this:

http://gzkds.en.alibaba.com/product/60164547519-219208401/133_tooth_gear_for_HP_5200_Printer_RU5_0546_020CN.html

So now we have a new exercise: WHY does HP [for example] use a 133 tooth gear ?

Edited By Michael Gilligan on 30/04/2018 10:26:25

Yes Jason, got bogged down with the maths! yes I could make the 133 plate on the dro and then transfer it to the vertex looks like thats the way to go for least error.

Thanks for all you great help have learnt more about it all.

Regards

Richard..

Howard is right just checked my chart on the vertex and there are some errors so always worth checking before cutting!

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

pgk

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That seems a jolly good start

MichaelG.

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'.

Perhaps they made the prototype using meccano and then just productionised what they had in the lab. I wonder what pitch the OP's friend wants his gears.

Suggestion:

Download the HV6 spreadsheet and expand it cover the numbers of holes in the plates for the HV8?

The formulae will update themselves for the new cell locations. (They did when I expanded it for 133 divisions). It could then become a useful item, to correct any errors or omissions in the chart for the HV8.

Howard

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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 21x7 is 147 (too high).

Happy to be told this idea is complete rollocks!

Dave

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.