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jmattsson

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Reply with quote  #1 

I build all my projects using Baltic Birch plywood.  I like there are few if any voids and at least one side has no imperfections.  For years, if I bought a piece of plywood marked as 1/4" thick, it was 1/4" thick.  The last two times I bought plywood none of sheets of plywood were the exact thickness as advertised.  It now appears that there is no plywood available in imperial inches (1/4" for example).  Instead, it appears all plywood manufacturers are making plywood using metric dimensions.  Recently, I built the Jeep Grand Wrangler using the plans designed by Lloyd Watson and sold here on the Toymaking Plans.com site.  The plans called for 7 1/2"pieces of some material to make the frame of the body.  Using the 1/2" plywood I had, I cut out and glued up the 7 pieces only to discover I was 1/4" shy of the necessary 3/ 1/2". I cut out two more pieces out of 1/8" stock to make up the differences, but that now meant I had to glue up 9 pieces of stock to make up the body.  Trying to manage that many pieces to get a reasonable clean line over that whole piece is difficult. 
All of this rambling is to ask, should the designers now start giving its directions in metric rather than imperial-inch?  Mr. Watson's plans may have started out using metric measurements as there are many mistakes in the plans particularly involving the diameter of some parts that need to be drilled for matching dowels. (see xihunter posts)  Just converting all the imperial measurements to metric doesn't necessarily work as I found out with the body of the Jeep.
Turning the question directly to you, Mr. Lewman, since there is not any imperical-inch dimensioned plywood stock available, should you adjust your plans to reflect what is out there for the toy builders to use?  If it is known that when you call for a 1/4" piece of material to be used in one of your plans, then the plan calls for a 1/8" hole to be drilled in the thickness of that piece of material, even if the stock is a true 1/4" there is little room for error.  This further complicated when that 1/4" piece of plywood is not 1/4", but something close to 6mm.  Do I try to drill the 1/8" hole, or switch to metric drill bits and compensate when the 1/8' dowel no longer fits.  I don't know where one finds dowels in metric sizes.
I really enjoy the plans offered on this site.  The detail for most of the plans make them fun to build and produce a project I can be proud of; however, this plywood issue is becoming an increasingly frustration problem.

Wombat

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Reply with quote  #2 
Welcome to the world that we in countries other than USA live in.

Dowel, timber (lumber) even MDF sheet is only available in metric sizes here, and none of it matches size for size what imperial finished dimensions are. 

eg:
If we want 1 1/2" (38mm) dressed wood, we have to machine down the available 45mm stock or compromise the plans to suit the 32mm DAR stock available.
When we buy CraftParts wheels, local metric dowel never fits snugly in the imperial holes.

Getting around these issues is just a part of the challenge involved making toys from these plans. 
Step 1 - make lumber / adjust plans
Step 2 - Build  the toy.


I note that John's plans do not specify materials to be used, just a set of sizes that, if followed, work.
If John switched to metric dimensioning, I have no doubt he would alienate all his loyal US customer base.
It's a no win situation.

If your material of choice no longer comes in imperial sizes, can I suggest respectfully that you do what we do.
Either scale the plans down slightly so all the proportions are correct, or change materials.



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kenistheguy

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Reply with quote  #3 
Go to http://www.makecnc.com and select "scale calculator". It will calculate + or - adjustment in % to add or reduce print. Think it still sells for $5 US
AES

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Reply with quote  #4 
It's not really a HUGE problem. As someone who learnt the Imperial system and now works in Metric 90% of the time, the above calculator, amongst other solutions (such as simply measuring thicknesses, and using a pocket calculator) will all work.

BUT what you have to be VERY careful about is that even good quality Birch ply (for example) or even MDF (as another example) is NOT always the exact thickness stated. For example I've had some Birch ply sold as 19 mm which was actually 21.1 mm and other ply, also sold as 19 mm, which was 18.5 mm thick! It seems that there is a manufacturing tolerance (and I bet there was in the old Imperial inch fraction days too) and it also seems that different manufacturers' tolerances vary. As I buy most of my ply from what the Americans call the local big box store (what I call the local DIY "Emporium") it also seems that the buyers for these big chain stores buy mainly on the price, which seems to mean that you can get ply (for example) from different manufacturers in stock at different times or even at the same time - often with slight thickness variations.

IMO there's a lot to be said for using the sheet itself, and a simple sliding gauge (doesn't need to be digital or even vernier - use it as a simple comparator) to set out critical dimensions such as slots, etc, direct on to the job. Saves a lot of problems.

HTH 

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BadBob

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Reply with quote  #5 
You haven't bought plywood in a long time, I am guessing.  1/4 inch plywood hasn't been 1/4 inch in years in the US.  So long that router bit manufactures sell undersized plywood bits for plywood.
 
Wood moves. It expands and contracts according to its moisture content. It also move when stresses are relieved.  I always cut to fit and dry fit before glue up.  

I would not buy plans that were metric only. I have few tools that are metric. I don't want to buy more expensive measuring tools, and I don't want to do conversions that don't convert to fractions. I may not buy plans that have both. I find this sort of plan to be confusing and error-prone.




 

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Wombat

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Reply with quote  #6 
I am fortunate to have been raised with the imperial system of measurements, the changeover to metric occurring as I entered adulthood.
With ongoing work-related ties to both UK and USA during my lifetime, I have learned to think interchangeably.  (I have been known to refer to something as 1" x 20mm)
My tape measures, rules and vernier callipers are all dual scaled, and were no more expensive than single scaled versions.

Thinking about it though, few people under the age of  50 here will have had any daily exposure to imperial measurement. Lucky for John, most of us toymakers are old farts eh?

I imagine that as these (relative) youngsters advance to retirement age and take up toy making, John's plans will have less relevance for them, but then again, by then I also imagine John will be hanging up the drawing board himself.
Hopefully not before doing another Noah's Ark set that is dimensioned in Cubits. ( another outdated measurement) [biggrin]



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Being equally inept with either hand is NOT the same as being ambidextrous!
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