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I might add a couple comments about the way I measured the planking problem I showed above.

The length of the two openings (4.85 and 4.00 inches) was measured by using a piece of stiff paper. You can see that in the photograph. These dimensions were used in the calculation. 

The width of the planks was measure with a dial set of calipers (with a dial indicator) that is accurate to within 0.001 inch.
post-246-0-51940900-1486065717.jpg

There is no way that you can be that accurate with the proportional dividers.

To pace off sets of repetitive dimensions on a chart it is cheaper and easier to use a simple pair of dividers:post-246-0-15033200-1486065455.jpg

 

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Tools are tools, which to use is a mater of preference, confidence, knowledge and the availability of tools to choose from. I may choose to measurement using cubits, 'IE 14.7 cubits, the .7 being an eyeball best guess', and a slide rule for the math or a calculator if I need to measure that result somewhere using a measuring device marked in meters. I prefer to work in decimals, decimal feet unless I need decimal inches, you will find lots of little pencil marks around my fabrication projects. I may measure using a decimal scale with 10, 10 or a thousand divisions regardless of scale, imperial or metric, scales are a simple conversions, divisions are visible things that create refinement in the eyeball reading of a measuring tool and are the single most used method of refinement in any measurement until needing to think about technique to avoid repetitive and cumulative errors. Wife was an inch, foot girl, a defect in her early potty training, had to rid the place of such marked measuring devices, until the lesson was absorbed with comfort, that the end of fractions did not destroy her world, only requirement, was to be aware of the division, inches or decimal feet, I have pocket tapes with both, amazingly the foot marks are common, not double. Why pick on the wife? She wanted, and did help me in my work, Inches were a problem in a decimal world.

Edited by jud
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I've had a set of proportional dividers since my drafting days.  I look at them once in a while.  Never use.  If I need to resize a plan I find it much easier to have it scanned in and reprinted. 

 

Bob

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So I won the Ebay auction and have the proportional dividers heading my way.  I paid a lot more than I should have but I realized the cost of buying new ones was very expensive.  They are made by Dietzgen so I know they are quality.  Hopefully I can put them to good use.

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It is interesting to see the two sides of this 'coin'.
If you have used the proportional dividers for a long time, I can appreciate that you like them for various reasons.
In my case, I have a pair and seldom use them, but so be it.
When Jud mentioned his liking for the decimal system (rather than fractions, I suppose) I agree. But when he talks about using a slide-rule - - - - I have to grin because those are dinosaurs in my college collection. Slide-rules are as accurate as proportional dividers and even more difficult to use and understand (I know Jud, you add or subtract logarithmic values, etc.).

The upshot is: if you like the tool you have, use it. If you want accuracy, calculate.

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I was rather surprised that some modelers weren't familiar with the proportional dividers.  I find them essential. I suppose because I do a lot of scratch work and I find myself redrawing lines published in old books (Chapelle, etc.) that will be prints of larger drawings reproduced without regard to scale.  With a good set of proportional dividers, all you need is a single identified measurement (a non-fractional measurement is best) and with your dividers set to your working scale, away you go!  Just take a distance from the page in the book and the other side gives you the distance to the scale you've set.  There are, as mentioned, a lot of other things you can do with them as well, such as drawing a square with the same area as a particular circle and vice versa, but I've yet to learn who really needs to do that.

 

I collect fine drafting instruments for my own use.  Most I've bought on fleaBay and I check for listings frequently.  I'll pass on that the prices do vary wildly, depending on condition, quality and rarity.  Condition may not always be a relevant factor if you are looking for a "user."  Some oaf may have scratched his name into the instrument and/or the case may be in rough shape.  That can mean a $100 or $150 reduction, leaving what would be a "mint" $200 instrument going for only $50, yet be entirely satisfactory for use nonetheless.

 

The proportional dividers that you want to look for are the 10" pairs with "110 scaling" or "decimal scaling."  This scaling permits setting proportions in "decimal equivalents" (e.g. 1/2 = .50)  These instruments will have rack and pinion geared adjustment and Vernier adjustment to decimals out to .0005 (If memory serves... perhaps there's an extra zero in there... don't hold me to it.)  These instruments will be manufactured by Keuffel and Esser and Bowen in straight point configuration and right angle point configurations (as pictured above.)  You will likely never see a right angle pointed set on fleaBay.  They are extremely rare.  I expect that at some time Dietzgen made decimal equivalent scaled proportional dividers, but I've never seen a set on fleaBay.  The most commonly offered are the K&E 10" "Paragon" decimal scaled models.  "Paragon" was K&E's top of the line series of instruments and the "110" decimal equivalent scaled dividers were only offered in the "Paragon" line.  They are made of "German silver," which is an alloy of nickel and copper, much similar to monel.  Their "Parogon" were made of cold rolled German silver and hand fitted. (Each will bear matching part serial numbers.  They were sold in silk velvet lined cases. The back of the case in newer production has a metal plate on the bottom with all the various decimal equivalents etched in it, which is quite helpful.  Older models have a cardboard insert (often missing) that has the same information. (The information is easily found on line in any event.)

 

There are also commonly 6" and 7.5" proportional dividers.  The 7.5" models do come with rack and pinion adjustment but not with the more accurate Vernier adjustment feature.  They are, however, useable.  The 6" models do not have rack and pinion adjustment and neither do some of the 7.5" models.  Don't waste your money on anything that does not have rack and pinion adjustment.  While useable, the "slide" adjustment models aren't anywhere near as accurate.  Similarly, pay the few extra bucks for the "110" decimal scaling.  The other proportional dividers have scaling that corresponds to fractions 1/2, 1/3, 1/4 and so on, and settings in between are "by guess and by golly."  Also, you will see "Russian Navy" and "Weems and Plath" proportional dividers offered.  Take a pass on these because they are "navigational dividers" and, although they work the same and are useable, they are scaled for "time" and "distance" proportions for use on maps and their scaling isn't useful for modeling measurement conversions. (You can adjust them for plans measurement conversions by comparison to a rule and/or tick strips, but this is rather tedious)

 

In summary, what you want to look for on eBay is a Keuffel and Esser 10" "Paragon" proportional divider with "110" decimal scaling.  They are relatively common because they were the "professional's choice" for many years.  A "mint" example with an excellent case will sell for as much as $225, but very "clean" examples regularly go for around $125 at the moment.  Examples that are a bit "rough," mainly due to a work case, can be had for $75 or even $50.

 

If you work from drawings to the scale you are building (i.e. as with kit plans,) you can live without a proportional divider, but if you are working from plans in one scale (or no scale, as in many lines drawings found in old books,) you will be amazed at how you ever before lived without them.  Yes, you can measure a distance and then punch that into a calculator and then measure off the result, over and over again, or you can set your dividers once and then simply measure the drawing at one end of the dividers and have the proportional distance simultaneously provided between the points of the other end of the dividers.  It doesn't get any faster or simpler than that.                                                           keuffel-esser-k-e-806-paragon-proportion

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40 minutes ago, Bob Cleek said:

I was rather surprised that some modelers weren't familiar with the proportional dividers. 

Yeah I bought a Dietz set some years ago that had a rough case and didn't look terribly good for $40. I don't care about the case and all it took was some 1500 grit sandpaper and it looks great and could be used another 100 years.

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Hi Bob;

 

Thank you for the long and informative post.  I wasn't aware that proportional dividers could be had with such a fine adjustment.  I'll keep an eye out for a set.  It is also kind of you to let us know what to avoid.  

 

All the best,

 

Mark P

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Greetings Druxey;

 

Thank you for the additional tip.  I will keep this in mind.

 

All the best,

 

Mark P

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On ‎4‎/‎21‎/‎2017 at 4:52 PM, druxey said:

Make sure that the set comes with the tables for setting any proportion you wish. (The photo above shows the paper chart.)

Yes, it's easy to do the math to get a decimal equivalent, but there are a lot of other settings where the chart is really handy.  Older K&E 10" Paragon decimal scaled proportional dividers came with a fabric-hinged folding cardboard chart (which is often lost and missing) and the later models have the settings "cheat sheet" on a piece of metal attached to the bottom of the case.  If all else fails, a bit of googling should turn up a copy of the "cheat sheet" easily enough, or, at worst, a photo of the bottom of the case with a readable settings plate.

Image result for Keuffel and esser proportional dividers

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Once again this forum and the older archived messages are proving to be a valuable resource.  After reading about the use of proportional dividers for planking, scaling plan measurements and a multitude of other uses in our model shipbuilding hobby, I started trolling eBay for a nice set...today I managed to win an auction for a very nice set of K&E Universal Paragon Proportional Dividers...same as the ones pictured by Bob Cleek above, just the earlier case with the paper insert of charts rather than the metal base.  This particular model seems all over the map...I paid $74.95 for mine in very nice condition with a great case....but just a month ago a set sold for nearly $200...so go figure.  I suppose it pays to have patience not only for building our models but also when it comes to acquiring tools!.....

 

Now if I could just locate a set of K&E Copenhagen Ship Curves......

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