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prkaye

Well Known Member
If I wanted to accurately measure the height of a driven shop-head, what kind of caliper would I need? I know it would need to be sensitive to at least 1/128 inch. I've never used a caliper, but from what I've seen to measure the thickness of a part you have to put it between these two jaws, and close the jaws up on the part. But this won't work for measuring the height of a shop-head. Is there a special kind of caliper I can get for this purpose?

I'm still very concerned about my rivets being too short, and I'm hoping that it's just because my little rivet gauge is too fussy. My procedure is to set the rivet just enough so the rivet gauge will not slip over the shop head. But many times when I do this and then check the height, the shop head will slip under the height gauge, meaning the rivet has come up too short. My gauge seems to have virtually no margin between correct height and correct diameter. So I'm hoping with a caliper I will find that I am indeed within tolerance in spite of what that little rivet gauge is telling me!

(has anyone else experienced this phenominon, or is it just me??)
 
If you have full access to the shop head, use the "back" side of the caliper (technically, the depth gauge). Open the caliper and push the back part into the piece until the slide part of the caliper hits the shop head. Then read it off.

By the way...I'm not suggesting that we measure our shop heads with calipers. I'm just explaining how to use them for depth measurement :D
 
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>> By the way...I'm not suggesting that we measure our shop heads with calipers

Why, is this a bad idea?
 
Where to measure...

Phil... if you are measuring the shop head of a rivet in a dimpled hole, then the little "tab" rivet gauge may be off.

See the picture on my web site.... The shop height needs a little estimating in this case.

http://home.earthlink.net/~gilalex/

gil in Tucson
 
Nothing bad about it at all. It's probably a good idea to do a couple of practice rivets, measure them and then compare them to the MIL spec. You'll be surprised how bad a rivet has to be to be out of spec. The little anodized gauges are pretty conservative IMHO.

I just didn't want to give the impression I thought it was nescessary to mic every rivet. You'd have the most perfectly built RV in the world assuming AVGAS is still available for your first flight in the year 2025... :)
 
That (measuring from the end of the dimple) means that the situation is even worse... if the rivet isn't high enough from the base of the dimple, it's certainly not high enough from the tip of the dimple!
The thing is, according to my gauge, if I'm high enough, my diameter is too small! This is my dilemna... if I set the rivet so the diameter is large enough, the height is too short!
I don't think I'm crazy, although this is driving me crazy...
 
If you call Vans (or read the preamble to the preview plans) you'll see that sometimes the right size rivet isn't available and they use the next shorter size.

Call them up...it'll make you feel better. It made me feel better. They told me to squash'em until they passed the width gauge and move on (assuming you're actually using the right size. Make sure you didn't mixup the rivets when you sorted them) Don't take our word for it, though. Call them...they're nice folks! :D
 
Yeah, I'm using the right size rivets. For things like stiffeners to be honest I'm not too worried about slightly over-set rivets from a safety standpoint. But I am worried about my subassembly inspection. I have this fear of the inspector saying "look at all these over-set rivets, you have to re-build these elevators!" (and then I cry). If I get a good caliper and the mil-spec, if I'm within spec and the inspector is using one of those cheap rivet gauges, I can show him that according to mil-spec the rivets are ok.

Perhaps I'm being way too paranoid... I haven't gone through the inspection yet, but I feel like I always did in university right before a big exam. Only if I screw this up, it's hundreds of dollars and hours in re-building empennage parts!

So, this Caliper is what I need? It will let me measure the height of shop heads?

Avery caliper
 
It is not just you. I ran into this same problem. The TC that looked at my riviting showed me how to use a caliper for rivits (using MIL spec #'s). This is now how I check all rivits and I find it quick and accurate. The Avery gauges seem to be "rule of thumb" devices. Using the MIL spec #'s gives me an acceptable range which I understand clearer than Avery's gauge. I found the Mil Spec #'s for rivits with a Google search.
Not knocking Avery - there stuff has been great!!!
 
Oh, that's right. You're in Canada. DOH! How do you use calipers to measure the rivet heights that are buried in the middle of the structure? That'll be a cool trick!
 
T.S., when you measured with the caliper, did you find that rivets that the guage said weren't high enough were actually within spec?

Do you use a caliper like this one?
avery caliper

I'm not sure whether Canadian inspectors go by the mil spec or what, but I imagine if I'm within the mil-spec I should be fine.
 
They should

prkaye said:
....
I'm not sure whether Canadian inspectors go by the mil spec or what, but I imagine if I'm within the mil-spec I should be fine.
Click to expand...

They should... the Mil-specs drive the design handbook for strength of aerospace structures that the FAA accepts..... this is what the RVs were designed with...

The old designation was MIL-HDBK-5 - it now has a commercial designation with essentially the same info. Search the VAF archives for more details...

The Canadians never published their own design guidelines AFAIK...cheaper to use the US ones paid for by our taxes.... :)

gil in Tucson
 
A dial caliper is one of those tools that you don't know how you lived without once you have one. I HIGHLY RECOMMEND every builder (or every handyman, for that matter) buy one and you'll be surprised how often you'll use it. I use mine all the time for measuring small round objects, inside diameter, wall thickness, depth, etc...
I just have a simple plastic one and it has served me very well. I'm sure you can find better ones too.
It actually might not be the best tool for measuring rivet head height.. but it will work.
Pick one up at any home center:
http://www.lowes.com/lowes/lkn?action=productDetail&productId=186523-56005-142
 
I found that rivits I had thought were too flat OR too tall (and I drilled out) were most likely within spec. I ended up with a digital caliper for an extra $6 upgrade from dial type and use it constantly - total cost $27. It is on the top of the tool heap all the time. I do not measure every rivit - anymore.
 
unfortunately HF does not ship to Canada. There's an automotive place in town that has a lot of tools "Princess Auto", so I'll check there.
 
I've seen calipers at most hardware stores and definately tools stores. I'd suggest avoiding plastic calipers. Also, make sure to get either digital or dial calipers. The old fashion vernier calipers are basically worthless IMHO. One advantage of digital is you can switch between inches and millimeters, which could be useful if you want to use it for other things, otherwise there is nothing wrong with a decent dial caliper. Like most tools, it doesn't pay to get the cheapest thing that you can find.

One thing that I've found over many years of using calipers is that measuring depth has more uncertainty than measuring width with the jaws. You have to make sure that you are squared up and that both surfaces are touching. Make sure to repeat measurements a few times to see how repeatable you are.

In any case, try not to worry about the rivet size too much or it will drive you crazy and you'll never finish. I always remind myself that A) There is a fair amount of design margin built into riveted joints, B) The strength of a rivet is not that sensitive to the amount that it is driven (within reason), and C) I've never heard of a plane falling apart in the sky because of a few imperfect rivets.
 
So I picked up a digital caliper last night at Canadian Tire. I took it home and measured my little rivet gauge. You guys were right, the rivet gauge is way too conservative.
For a 3/32 rivet, the mil-spec says the minimum driven head hight is 0.038". The notch in my rivet gauge has a height of .050". So a rivet can be high enough for the mil-spec and still slide easily under the rivet gauge. Actually, .050" is the MAXIMUM heigh according to the mil-spec, so if a rivet doesn't slide under the rivet gauge, then it is actually OUTSIDE the mil-spec... go figure!

The minimum mil-spec for diameter of the shop head is 0.122". The diameter of the hole in my rivet gauge is 0.144", so the guage could easly slide over a shop head that is still within the mil-spec.

My little rivet gauge is useless! Glad I got this caliper though :)
 
Phil, listen to Eric. I own a very fine Mitutoyo depth mic that will quite readily measure to the ten-thousandths of a inch, but I use only the Avery "rule of thumb" gauge to check the rivets. And as for using the "correct" rivet, that would be the one that works in the particular spot. I routinely use rivets 0.5 longer than the plans callout, in order to get the desired shop head diameter without it getting too flat. I consider the plans rivet callouts to be a "no shorter than" spec.

I think you're being too hard on your little gauge by calling it useless. ;) It's just not a minimum spec gauge! Get a test rivet set to the specs you want, then put your gauge on it and see how it looks (height) and feels (wiggle the hole back and forth on the shop head). Your gauge is now calibrated, and away you go!
Years back, I examined the interior of a CAF Heinkel HE-111. I looked at the shop heads of literally hundreds of rivets, and the overwhelming majority were so bad that I would have never allowed them to pass, yet after 50 years the airframe was still holding tight.
 
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Be careful of el cheapo calipers

I was given some Chinese knockoff of a digital Mitutoyo. It was off as much as .025" over the scale. Made some expensive (non airplane) mistakes using them before finding that out. Ate batteries like crazy too.

I agree with William, a rivet guage and Mark I eyeball are adequete for rivets but a good set of calipers is indispensable. For accurate measurements, though, you'll have to spend some money. Just because it reads to .001" doesn't mean its accurate to .001"

I love my Mitutoyo Digimatics:

Mitutoyo Digimatic

Other options:
If your eyes are good, a vernier caliper can save you some money.
Dial calipers are easy to read but also have to be well made for accuracy and are not as rugged as the others. Any of them can be used as a depth guage.

John
 
Make your own gauge...

A proposal.....

Since we only deal with basically two rivet sizes, why not make our own gauges?

For -3 rivets

Take a small piece of 0.040 alum. (say 0.4 by 2.0 inches) and file one end down to the 0.038 thickness, and drill a 0.122 hole (#31 is 0.120 - use a hand held drill and it will be close) in the other end.

The hole will be a no-go measure, if it slips over, hit the rivet more.
The 0.038 end can be used with your calibrated Mk. 1 eyeball... if the height is less than the thickness of the strip.. reject the rivet as over-smashed.

If you want to be a bit conservative, use the 0.040 strip full thickness and drill a 1/8 hole.... this gives your rejection criteria at 0.002 over the specification.

It would take you about 5 minutes to make the custom no-go gauge described. Bend the two ends about 45 degrees to make it easier to place over/next to the shop heads.

For -4 rivets

Hole size #20 drill = 0.0161 (min spec. is 0.0162) and use 0.050 stock (min. ht. spec. is 0.050)

Will try it this weekend...

gil in Tucson
 
Max. diameter

JonathanCook said:
I think that making your own tools is great, and I do that my self when needed. For a rivet guage I recommend clear air tools rivet reader. http://clearairtools.com/Merchant2/merchant.mv?Screen=CTGY&Store_Code=CA&Category_Code=MM

This reader can not be beat. Check it out. It also can be ordered from Aircraft spruce.

Jonathan
Click to expand...

Neat tool... and Fred K. certainly knows his air tools.....

I'm a little confused where he gets the MAX. shop head diam. from... the Mil-spec. has no maximum diameter.

http://home.earthlink.net/~gilalex/rivet_spec/rivet_a.htm#TABLE III

On a cursory glance, it looks like it might be the optimum 1.5 D diameter, but bigger is OK as long as the shop head does not get too flat.

UPDATE - 6:00 pm MST

I spoke to Fred Kunkel at Clear Air Tool in Tulsa (he moved) and he said the max. number came from the Allfast company and is 1.5 D
Since the FAA documents all use 1.5 D by 0.5 D as a "perfect" rivet, I would recommend using the larger shop head diameter gauge slot as an "optimum" measurement rather than a maximum. With that criteria, Fred's tool looks very useful.



Like an earlier message said, I prefer rivets 1/2 a size longer than Van specifies... this gives more tolerance on the timing of the rivet hitting...

The tool looks good and has more info. on it, but making your own is still easy.... :)

gil in Tucson
 
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az_gila said:
Phil... if you are measuring the shop head of a rivet in a dimpled hole, then the little "tab" rivet gauge may be off.

See the picture on my web site.... The shop height needs a little estimating in this case.

http://home.earthlink.net/~gilalex/

gil in Tucson
Click to expand...

Sorry to bump an old thread, but gil I have a question regarding this.

I'm setting rivets in my horizontal stabilizer now. Unfortunately I have used the substructure dies for all the ribs/spars/etc, and the 3.5 rivets are coming out right at the minimums for shop head diameter and height. I suspect it's due to the substructure dies opening the hole a tad bit more. I've tried -4s but they don't set very well. Quite frankly, having every single rivet shop head at the mil-spec minimums doesn't sit very well with me, and I'm contemplating a re-do of my horizontal at the end of my project if I'm still not feeling good about it.

I'm wondering how the little tab rivet gauge could be off? What kind of estimating should we be doing? Unfortunately after all these years your website is inaccessible anymore.

Here's a picture for reference. I measured (as best I could) the rivet shop head height from the top of the dimple on the bottom rows.

VJ0asTl.jpg
 
Joness0154 said:
Quite frankly, having every single rivet shop head at the mil-spec minimums doesn't sit very well with me....
Click to expand...

Don't let that concern you. There is no loss of fastener shear, joint shear or fatigue allowable properties at mil-spec minimums compared to anywher else within the mil-spec tolerance band. In fact, there is very little loss of properties well outside of minimums/maximums. Anywhere within the mil-spec tolerance band (even at the min/max limits) is perfectly acceptable for any and all rivets. You should be very proud if 100% of your rivets meet the mil-spec.
 
The rivet head gauges sold by the popular tool companies are typically sized to check for the .5 D X 1.5 D rule of thumb. This is not the Mil Spec minimum.

You can check the actual Mil Spec values for minimum head diametetr and thickness on the chart in THIS document.

BTW, just based on an eyeball check looking at your photo, the shop heads look fine to me.
 
Dead End Links

Hmm... Looks like some of the older posts have some inactive links. Can the original posters or someone edit the links to point to the correct web pages?
This would maintain the value of this thread. I've found three bad links so far.
 
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