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I was wondering if you use proportional dividers or not.  Also, does anyone know where to get a decent one for a decent price.  I have read several posts but the opinions are mixed.  Some say you will never put them down while others say they are a waste of money.  Looking online, I saw some for $50 but they looked cheap.  Others were up and over the $200 mark. Micro Mark has them at $100.

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I think the point of proportional dividers is to scale up and scale down, though they can be used to transfer lengths from plans to materials. I have a set of the micro-mark ones and I have not used them for kit building (though I have used them to practice lofting frames from plans - I can see how for a scratch build they would be very useful to have).

hamilton

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I bought a pair years ago from Micro-Mark, but I don't remember them being $100 -- more like $50. Must be inflation. As stated previously, not only are they useful fro scaling up and down, they are also very handy for taking measurements off plans.

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They're like any other tool. It depend what you are doing and what tools and methods you "like." If you buy plans of the same scale of the model and if you are convinced that the plans are accurate, then you will not need them.

 

If you redraw plans from archival materials then they might be useful, although more accurate methods exist such as using a pair of regular dividers to determine a measurement on the drawing's graphic scale, then using an architect's scale to plot the dimension on the new drawing or part. This system is preferable because drawing distortion is often not uniform. If you are redrawing a drawing without a graphic scale then proportional dividers are more useful.

 

Roger

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I use mine all the time. They make easy work of finding the center of something, or dividing a length into any number of parts. The slide adjusts for the number of increments you want then presto. You can find centers without a measuring tape and division. Quickly, easy, and without math errors.

 

I bought mine used on eBay and are Weems and Plath. These are a fine tool that cost nearly $200 new but I paid less than $70. A good set is solid steel and nothing to wear out. The case is worn but the instrument is in perfect condition. I never knew how valuable a tool it was in the workshop until I got one.

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I bought one on eBay.  Good ones are not cheap, which is amazing considering the general demise of manual drafting and the availability of cheap digital calipers.  However, after examining their construction, I can see why they're not cheap - if there are errors in certain lengths and positions then the scale settings will be off enough to be very exasperating.   They are a very different animal from regular dividers.  

 

There are some plastic versions available - I have one of these as well, but I think they are more for artists to scale a picture rather than for drafting.  The major limitation of mine is that the ratio is adjusted by moving the pivot to holes of fixed locations so that ratios of only 1:1, 1:2, 1:3 are possible.

 

I use them fairly often, and not just for model building.   As others have said, if you're working a kit boat, you won't need proportional dividers.   But if you're mashing drawings from different scales, they're a real time saver.  

 

As a poor-man's option if you only have standard dividers, I've attached an example of a grid I use for a converting between 1:72 and 1:96. I used a CAD program, but you can make a satisfactorily accurate version by hand.

 

72_96Scale.pdf

  1. Set the dividers on the dimension on the 1:72 drawing
  2. Place the dividers on horizontal base line
  3. Pivot from the right point of the dividers 
  4. Set the dividers to span up to the diagonal line
  5. The dividers are now at the distance needed for the 1:96 drawing
Edited by lehmann
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I've had a pair for many, many years.  I use mine mainly for planking. Simply set the proportion to the number of planks remaining in a planking section and measure the width of the plank at each frame directly off the hull.

 

John

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I can see the uses for it and it may be a nice tool to have for the quality of being a nice tool. However, with computers, pocket calculators, spreadsheet programs, scanners, and (laser) printers around, so far I did not have a real need for a pair. I would rather invest the 100€ into something else ...

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I'm afraid I have to agree with Wefalck. I actually have a beautiful pair of 10" dividers - rack and pinion, 110 division scale, with right-angled tips so that you can use the instrument parallel to your work rather than held vertically - and very seldom use them.

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I bought mine on E-Bay and like everything on E-Bay sometimes they go at a very reasonable price and other times way out of range.  Once you get them you will not know how you lived without them.  Get a good pair, rack and pinion, I bought a pair from MicroMark years ago but I do not think they are rack and pinion.  In my opinion you would be better off with a good used pair from E-Bay.  

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Suspect that the use of proportional dividers becomes a habit, the tool you automatically reach for. I remember sitting in the Student Union doing some homework and a very simple division question came up that was a step in a solution, something like 12/3, I reached for my slide rule, that stopped me and got me to thinking about what I had just done, looking around and such things happen all around us. Dependency or habit?  I like to think habit but I know the panic when I find my pocket knife is not in my pocket. Creature of habit, I think we be.

 

jud

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I have a pair and use them when planking a hull, but in my opinion, they are overkill for someone new to the hobby. As others have said, they are expensive and not as frequently used as other things you might spend that $100 on. You can easily determine plank widths by using a planking fan such as the one Chuck Passaro has posted on the site - http://modelshipworldforum.com/resources/Framing_and_Planking/plankingfan.pdf

Instructions for using the fan are found in his excellent planking tutorial - http://modelshipworldforum.com/resources/Framing_and_Planking/Lining%20Off%20your%20hull%20for%20planking.pdf

 

One must be careful when using proportional dividers to take measurements directly from a frame or bulkhead if the bulkhead has much curvature. You wind up measuring the chord of the arc rather than the length of the arc itself. That can result in planks that are narrower than they should be. When I'm determining plank widths, I lay a tic strip in the space to get the overall length, then use the proportional dividers to determine the individual plank widths.

 

Of course, there are other uses for them than in just planking, but again, there are probably better things to spend your money on when you're getting started in the hobby.

 

Cheers -

John

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Hhhmm, just thinking about error addition/multiplication ... using proportional dividers to mark out n equal divisions for planks along e.g. the circumference of a frame requires that you apply the dividers n times, thus likely adding n times an error of similar magnitude, e.g. because the dividers slip a bit on the woodgrain, parallaxes, etc. If you were lucky, you would make as many positive as negative errors, so that you would end up at the desired end-point. You could do the same process from the opposite end again and then middle out the differences. Not sure one gains a lot of time.

 

Today I think I would take a paper strip and place it around the frame, marking the desired end-points. I would then measure the distance with a vernier caliper and take this measure to my drawing programme on the computer, that has been calibrated agains the printer to give a dimensionally correct print-out. I would then draw a long rectangle and have it subdivided into the necessary equal parts digitally and print this out. The cut-out strip of paper is then taken back to the frame.

 

Alternatively, if you was to use paper templates for the frames, the subdivisions for the frames can already drawn onto the templates and no additional measuring on the model itself would be required.

 

There are various other strategies I suppose.

 

This is not to say that I don't find these instruments attractive as instruments. If they weren't so expensive, I probably would have got one myself already ...

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Pleased to oblige, Wefalck. Pictures as requested. They certainly are attractive instruments. There is a table of figures for setting every conceivable proportion one might want.

 

I use similar strategies to yourself when subdividing distances, especially on curved surfaces such as hulls.

post-635-0-22805100-1485971764_thumb.jpg

post-635-0-72675300-1485971766_thumb.jpg

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A number of years ago I thought to buy a set, but cost put me off. So I made a set. Not as accurate maybe, and with fixed ratios, but they worked until I found a 'real' set on ebay at a good price. I wrote it up as an article for 'Bottleship', the quarterly magazine of the 'European Association of Ships in Bottles'. This subject cropped up on 'Bottled Shipbuilder' a few weeks ago as well. If memory serves me, I believe that this article was uploaded to this site as well before the crash, so here it is again. If you want the quick way, skip to the end.

 

Regards

 

Alan

Proportional Dividers Kind Of.pdf

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As said by others eBay is the way to go to get a good pair without breaking the bank.  I bought an excellent set for less than $40 including shipping.  Well worth the cost.  However be wary of the ones being sold from India.  They are very cheap copies.

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Hhhmm, just thinking about error addition/multiplication ... using proportional dividers to mark out n equal divisions for planks along e.g. the circumference of a frame requires that you apply the dividers n times, thus likely adding n times an error of similar magnitude, e.g. because the dividers slip a bit on the woodgrain, parallaxes, etc. If you were lucky, you would make as many positive as negative errors, so that you would end up at the desired end-point. You could do the same process from the opposite end again and then middle out the differences. Not sure one gains a lot of time.

 

Learned long ago when laying out multiple points along an object, not to measure and mark each one individually, error in the measuring device will multiply and accumulate. Determine spacing, use a measuring device that will reach the full length, pick a scale that has the most number of divisions per inch, determine how many of those divisions equals the desired distance. With that lay your measuring device out with the beginning end securely held and mark the first distance, move nothing but your marker and mark the next point by adding the first distance to the next and mark the sum, continue adding and marking the sums and you will have well spaced marks, may be some random isolated errors but they remain where they occurred. Amazing how fast errors can accumulate by repetition. A method taught in basic surveying. not appreciated until you see it at work, matters not if you are laying out stations on a highway or stations on a model, same factors and principles at work.

jud  :pirate41:

Edited by jud
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Derek I went to eBay and searched as follows:

 

 http://www.ebay.com/sch/i.html?_nkw=dietzgen+proportional+dividers

 

It shows PDs from $21 to over $300.

Most important feature of a PD is the accuracy of the measurements.  Dietzgen is a premier maker of all sorts of engineering and drafting tools. I've used the same pair for over 40 years and they are still accurate. 

Good luck

Tom

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Thanks for all the advise everyone, and Tom, last night I put a bid in for a set of Dietzgen's on Ebay.  They are older but look to still be true and accurate.  I still have to wait a few days to see if my bid gets accepted.

 

Fingers crossed.

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I have two types of proportional dividers.

The one shown below is a lot more accurate than my mechanical type and faster too.

 

 

The accuracy required is not only that of the calculation, but also in the transfer to the work-piece ... how does this happen then ?

Edited by wefalck
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Here is the main application why I do not use a ruler, but a proportional divider.

 

I use 1/48 set of plans to build a model at 1/24 scale. 1/48 scale plans are easier to manipulate than at 1/24. When I want to cut to size a part from the measure of the 1/48 plan. I can take the measure : 1 inch 27/32, multiply it by 2 with the calculator or calculate by hand and obtain the value. Or there is also the fast way. The use of the proportional divider is not only to divide or multiply but it can also be use as a ruler. For the same operation, I measure with 1 end of the proportional divider and with the other end I transfer the measure immediately at 1/48 scale in multiplying the number automatically by 2.  I did transfer a measure and multiplie dit by 2  and I did have any calculation to do.For the model I am actually building from plans this is the same procedure which has been applied for 5 years. Did I save some time? Was is worth to use it? I guess I probably ask myself the same question the first time I saw a calculator. Is it worth to buy one? Will I save time ? At least I will not do mistake of hand calculation! And I can continu and ask myself the same question again and again…

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Ok, let me explain. Let me do this with an example, the hull planking of my cross section. 
 

If the planks need to be tapered because the space or opening as shown in the picture below changes along the hull lines, it is necessary to use the 'proportional method'. In this case, you measure the two dimensions of the opening and they are 4.85 and 4.00 inch respectively. Let's say the planks you have are 0.121 inch wide. What should the plank width measure at the other end? Obviously smaller if you put the wide end to the left in the picture. 

 

The proportional ratio is 4.00 divided by 4.82. Now multiply that ratio by the 0.121 and you get 0.100 inches, the width of the narrow end.

Now you could have done this with the mechanical divider, but the accuracy becomes questionable because of the big difference in the size of the opening and plank width.
post-246-0-36592900-1476724674.jpg   post-246-0-36486600-1476724821.jpg

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Much of this focus has been on planking. Yes, proportional divides can help immensely when setting up planking. You could also use just a fan ray. However, I completed planking on my Eagle many months ago. I still use the proportional dividers a great deal. So it is not just about planking. there are many instances in models where we need to divide a space into parts, or find the center. Yes there are many alternatives for each of these however a good set of proportional dividers come in handy in many areas outside of just planking.

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Before CAD, when I was a pen and paper draughtsman, proportional dividers were an essential bit of kit and I own an expensive pair.

They are little used these days, but I would not be without them.

One word of caution when using them for planking (as has been mentioned above). When measuring from the frames or bulkheads, you are measuring the chord- a straight line between two points on the circumference of a circle or arc- not the length of the arc itself= the width of the plank. In most ship model situations the error will be so small as to be irrelevant, but it is there.

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I have a good set and never found them accurate enough at 1:48 scale.  I was taught (by David Antscherl) that there is a lot of error in a pencil width (sharpen it more often) and by Ed Tosti who got his (CAD) lines down to one pixel width.  All a matter of personal level of acceptance.

Maury

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