# Caliper - measuring descrepancies

Discussion in 'General Card Modeling' started by Lionheart, Jan 10, 2005.

1. ### LionheartNew Member

I have a good set of calipers that I am using for the build of the Halisnki P-51 D. I know that .20 = .5 mm (If memory serves....). So when I put 2 pieces of this stock together they should equal .40 on the caliper which is 1 mm, no? I put 2 pieces together and I measure .45-.50..... Add a third piece and the error gets even bigger..... What gives? And this is without any glue. Just piled on one another and measured. The calipers are not digital. They have a dial on it which I have "zeroed out" before measuring. I'm stumped.
2. ### BernhardMember

Lionheart

I try to help but first I need to understand your problems.

First problem, you measure the thickness of a sheet of paper and (with properly zeroing the instrument) it reads 0.20. Measuring increasing numbers of sheets of paper stacked on top of each other does not give you readings close to multiples of 0.20 such as 0.40, 0.60, ... and so on. Is that correct? If so, (and given all the sheets were from the same ream), your caliper is probably crap. Buy or borough another caliper and repeat the exercise. In any case, the last digit of such a measurement is not very precise. The best way to measure the average thickness of your paper is to stack a large number of sheets (try 10 and then 20), measure the thickness of the stack and divide by the number of sheets.

Second problem - unit conversion: You are measuring 0.20 of what unit? I assume you are talking about inches. 1.00 inch is about 25.4 mm. Thus, 0.20" = 0.20*25.4mm = 5.08mm. That doesn't seem right. Card used for models is normally more like 0.20 to 0.15mm thick, copier paper is even thinner. You might be measuring in mm already, 0.20mm makes perfect sense for paper.

By the way the caliper I use only allows to measures to the nearest 0.1mm despite the fact that it is a nice and precisely machined piece of steel. Maybe your caliper displays more digits on the dial then it can actually measure with precision.

Bernhard
3. ### Jim NunnMember

I think you miss spoke .020 ~. 5mm. 67 lb paper (HammerMill White Cover Stock) is around .009 inches and 110 lb paper (Georgia Pacific Image Plus Card Stock) is around .010 in I also use 44Lb Epson Matte Photo Paper and this is .009 thick. I have also noticed what appears to be an increase in thickness as I laminate the paper to make .5 and 1 mm stock. If you measure paper stock at several locations on the same sheet you would find that the thickness varies I have seen +/- 10 % (.002 in) on the same sheet and not all of the sheets in a package are the same. When you measure paper you must apply the same amount of pressure so we have lots of variables and remember paper is sold by weight not thickness.
Then we have the glue and it will add a few mills to the thickness. I would suggest that you use a mix of 110 and 67 lb papers to make the .5 and 1 mm stock. I would not go over size my impression is that it is better to be just a little under sized.

And we cannot forget the moisture on dry days the paper is thinner.

And we call this a hobby

I would like to hear from the other modelers who make their own .5 and 1 mm card stock.

Jim Nunn
4. ### MauriceMember

The correct approved interpersonal relationship you require between the two systems is that (approximately - but good enough for here) -
0.04" = 1mm (or 1mm = 40 thou. of an inch)
so that
0.02" = 0.5mm
Pedantic perhaps but best to be clear before you start measuring, that way you run the risk of getting it right.

If you have moved your sheets around you may well include some air in your measurement.
If you use callipers you will measure the thickness of the edge of the sheet.
If that has ever been cut it may well be swollen.
If not it may well taper off.
Better to use a micrometer and reach in past the edge.
With air excluded, measuring several sheets is, as suggested, the best way to go.

If you stick glue on the sheets you add some glue to the resultant thickness as well as swelling the bascic sheets. I agree that it's best to err a bit on undersize - that allows for if something else swells somewhere else - which it will.

An amusing combination of precision and iffyness.

Maurice
5. ### AtomskMember

You need to remember that even "smooth" paper isn't exactly smooth. The surface has some ripple and fuzz, that your caliper might be able to smush down, but will add to the thickness where two sheets meet.

This is even more true for cardboard.

I don't have any way to measure it, but I'd find a discrepency of 0.1mm (per lamination) believable, for 0.5mm "Cerial Box" cardboard.

Try gluing two sheets together, and pressing them with a couple of heavy books until the glue sets. That might result in a thickness that's closer to 2x the thickness of the original sheets.
6. ### LionheartNew Member

I probably didn't do a good job explaining this. Let me see if I can clear up some things. I am using cardboard from a single source, in this case a gift box from Christmas. The individual pieces measure out ok to .20 mm in thickness time and again. If I take two pieces of the same stock, they logically should measure out at .40 mm, three should measure out to .60 and so on. They do not. Two pieces stacked and measured will usually run at about .43. 3 pieces can run up to .7 mm. This is without glue, mind you. Nothing but air (or error, as the case may be). I freely admit, I am a novice in all aspects of card modeling. So, I imagine it's something silly on my part. By the way, I've been using Tacky Glue to laminate the card stock and I've been using a wallpaper roller to roll over the laminations. I've been getting good results with it. Hope I've made myself a little clearer and thanks for all the help.

8. ### cecil_seversMember

Lionheart,

It's seems rather than an error you may have simply encountered an unexpected result due to the way card stock fits together. If you want to calibrate the accuracy of your calipers, borrow a spark plug gapping tool. The kind which use various thicknesses of metal stock should make a good calibration gage. If you really need a precise thickness for the combined stock try lightly sanding the surface of each side first.

Honestly though, I don't see an need for such precison since most of the time parts are doubled for strength and stiffness, or for cross section bulkheads, not to achieve a perfect fit. Even a 0.1 mm "error" is about 0.004". And fitting parts is more about careful cutting, dry fitting and sanding to fit or making other corrections, dare I say it, such as filling gaps with an appropriate medium like colored glue or artist gesso.

Hope these comment help. BTW, nice catch Gil on the digital calipers. Makes me almost want to replace my vernier set.

Cecil
9. ### GilActive Member

Cecil,

I got tired of having to find the magnifying glass to read the vernier..., the digital caliper can be read with the poorest of eyesight and changes from English to Metric at the touch of a button making for a sweeter sort of life.

Best regards, Gil
10. ### AshrunnerMember

Ain't nothing like a good digital caliper. A friend gave one to me for Christmas in 2000 and I have gone through a dozen batteries on it. Have a tendency to leave it on and mine doesn't have auto off. But it is still a lot easier to read than any other caliper I have used.
11. ### LionheartNew Member

We have a Harbor Freight here. Think I'll make a trip over there a pick up a digital.
12. ### LionheartNew Member

Well fellas, I did go to the Harbor Freight store and picked up the digital cali's. Just like Gil said. Thanks for the tip, buddy! They work great, no more guess work! I wanted to get a mic' too but they didn't have any at that store. I'll just order from the website, I guess. Can't beat the price either!
13. ### AtomskMember

I went 'n' bought one too, at the Harbor Freight just down the road.

These'll come in useful for lots of things.