Are my calipers off? Can't I cheat?

[Don Quixote]

I used these non-digital callipers to measure all the wood from the kit. When I planked around the gun ports and sweeps it looked to me like I was missing more than half of the planks I needed. Got 'em from Model-expo. Now, when preparing for the planking of the hull, I need 8 1/16"X3/32" for each side for the first strake "A". When I started measuring out the battens and verifying with the width of the planks I started having problems. Things weren't adding up. The 8 planks I needed totalled more than what the plans call for. Thinking WTF? to myself, looking over and over I noticed an oddity in the callipers I used. See I have it set to 5 mm, but look at 10 mm and it's a mm off. 10ths of inches appear to me to be off too. I bought some considerably more expensive callipers and to me it looks like what should be 1 cm is off by .137 mm. (lighting is playing trick with the shadows in the picture) But the original callipers say something about .002mm. More, WTF?

 

Thing is, converting metric to inches, I get what *I* thought was 3/32" is, according to the new callipers, actually .101" or 7/64" Bottom line, I have no more 3/32"X1/16" planks, and I'm anxious to learn to plank.

 

Question is, the plans call for 8 - 3/32" planks at bulkhead H, strake "A", but all I have are 7/64". Can I change the .75" strake called for in the plans in section A, to accommodate the 7/64" planks I have? Seems to me I can modify all the strakes because the 4th strake "D" has the garboard strake which is the odd man out anyway.

 

I'm out to lean "how to", I don't care about authenticity. Yet.

[druxey]

Have you calibrated your callipers by adjusting them at zero?

[SketchupModeller]

The divisions on the sliding and fixed parts of the caliper are, by design, not spaced identically (this is why your caliper is aligned at 5mm but not at 10mm in the first picture).  This is known as a Vernier scale, and allows for precise measurement.  Put simply, the human eye can tell, at a very high precision, when two lines are aligned.  On a Vernier scale, at any time, there will only be one line on the slide that is aligned with a mark on the fixed part of the caliper.  Depending on which lines are aligned, it is possible to read a metric caliper to the nearest 0.02 mm.

 

Here's the best tutorial I could find quickly on how to use a vernier caliper: http://www.technologystudent.com/equip1/vernier3.htm  The Wikiipedia page for Vernier scale (http://en.wikipedia.org/wiki/Vernier_scale) is also very good.

[DaveF]

To check calipers is an easy process. The faces you use to measure by wear naturally. the move you touch metal surfaces. But I have also come across new calipers that were not ground properly.

 First thing to do before any callibration is to close the cliper faces and then hold them up to the light. You should see no gaps or spaces between the anvils. If there is a space then get new ones, if there isn't a space calibrate. Set to zero.

 If you find any movement in the sliding caliper part( a rocking motion) then they are not adjusted right  Everything has to be snug but not over tight. Some have tiny screws on the bottom that can be used for adjustments but be careful that you adjust both EQUALLY or you will always get miss measurement.

 Dave

[Don Quixote]

Thanks y'all. The callipers that were (I thought) giving me trouble, were not the digital, rather, my very old callipers I got from my dad after he passed. I went and spent $150 on the digital, and after receiving them started measuring everything in site with both callipers. Always came up with the exact same answer. NOW, WTF? They can't both be off the exact same amount, so I'm thinking I'm missing something in the design of a calliper. I even measured the distance between an inch on my big table saw. It was... An inch.

 

Google told me about this phenomenon called the Vernier scale. Sounds kinda familiar now... Brandon

Years ago I worked at a factory and we always used digital callipers, and never manual. Trust me, our tolerances were sometimes 1/64" We learned to zero out every freaking time we used them.

[dgbot]

It has been years since I used a vernier.  I use a digital and it makes my life and my eyesight easier.  Plus I can convert from decimal to mm with a touch of a button.   And you can always take a wider plank and narrow it down.  Whenever you plank the hull always try to use the widest planks possible, that way you can modify them as needed.

David B

[AndrewNaylor]

Well some times real good European /USA companies need to make even more money and so they look to other countries to make there products.  So we have BIG Box stores full with stuff ( possibly made the other side of the Pacific /indian ocean ) not naming any one specifically. OH yes thats right there is a ban on kits from certain countries well you get the gist 

Andy

[Gaetan Bordeleau]

usually calibration is done with a gage block

you measure a known value

you check if you have the good reading

[dgbot]

At work QC uses Mititoyu digitals for the final inspection.  For handcut we use a less expensive model.  The reason is if you drop the QC version it has to be calibrated for final inspection.  You pay for what you get.  For what we do a .0001 readout is all you will ever need and that can be overkill at times. 

David B

[Don Quixote]

We had to use the block at the factory I worked at years ago. For the purposes of this project it occurred to me and just now confirmed that the wood isn't even consistent in the same strip. In one spot a strip is .095, and another on the same strip is .092. Should be .09375 or 3/32" And, I just though. I need to taper a 1/8" strip to 1/16" I'm sure what I'll end up with is a tooth pick.

 

Real question was, can't I make up for any discrepancies with the garboard plank? Can't I adjust the width of that?

[DaveF]

It would seem that we can get off topic real easy here.

 To me since you want to use a certain size plank say 1/4" and the kit supplies a 3/16" plank then obviously it would make sense that the size of the  Garboard strake would be altered for the number of runs for the larger plank.

Dave