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Countersink question

LAMPSguy

Well Known Member
Please reference page 11-03 Rev 1 or see the photo if you can read it

676q12.jpg


Two questions:

I am instructed to countersink the screw holes IAW Figure 3 and 4. Those figures show the skins being dimpled. I read ahead to see that the tanks use #8 and the access plates use #6 screws. What is the best method to determine countersink depth? Take a .032 piece of Al and drill, deburr, and dimple for the #40/#30/#8/#6 hardware and use THAT as my countersink go-nogo gauge or just use a precision instrument to measure per the specs in the figures 3/4 as stated above?

Also, it says to "machine countersink in all rib locations" I have highlighted this in green. Do I just countersink the flanges, or does it really mean ALL locations and I should CS the whole spar web as well (also highlighted in green).

I am probably over thinking all this, but I have already screwed up by not looking too closely tat the instruction so I am a little gun shy now.
 
What is the best method to determine countersink depth? Take a .032 piece of Al and drill, deburr, and dimple for the #40/#30/#8/#6 hardware and use THAT as my countersink go-nogo gauge or just use a precision instrument to measure per the specs in the figures 3/4 as stated above?
I kindof did both. I primarily used calipers (and magnifying glass) to get the dimension correct as per the figure. I measured the OD of the countersink and figured the smaller diameter would take care of itself. Then I checked with a piece of dimpled 0.032.

Also, it says to "machine countersink in all rib locations" I have highlighted this in green. Do I just countersink the flanges, or does it really mean ALL locations and I should CS the whole spar web as well (also highlighted in green).

The holes in the web are #30. And I believe the drawing says something like "CS all #40..."

By the way, I like your idea of printing reved pages on yellow. I think I'll start doing that, I'd been hilighting the title block but I like the yellow paper better.
 
Wow. Dimensional specifications for countersink diameters. I guess Van must have gotten tired of answering the "how big" question from builders of earlier designs. I think I used a dimpled skin to get the size right on mine.

As a side note: There is such a thing as a countersink gage. I got one from mil surplus many years ago. It is a springloaded cone that is placed in the hole and gives a reading of top diameter.

The tank countersinks have been talked about many times on VAF but since you are prepping, I though it would be good to bring it up again. Please make sure to have some sort of guidance for the countersink pilot to keep it from wandering. I think Van may say to install the nutplates and use them for piloting. He has done so on some print/instruction sets. Other builders have made a steel jig and moved it from hole to hole before installing the nutplates.

Enjoy. I remember getting these done and being proud of the work. Hope you are too.
 
Why #30/40

Why does Vans have us use #30/40 countersinks for the screw holes on the spar flange? Shouldn't there be an appropriate countersink for a #8 and a #6 screw?
 
Why does Vans have us use #30/40 countersinks for the screw holes on the spar flange? Shouldn't there be an appropriate countersink for a #8 and a #6 screw?

There's really nothing different about the countersink itself as long as its a 100 degree head, right. It's only the pilot stud that makes it a #30 or 40.

My guess is: works good enough
 
Per plans

So I assume you did it per plans, drilled and riveted in the nut plates first, then CS the screw holes. All without a problem? I have seen others talk about other possibly better methods.
 
Step seven

I can't help but think that I am overthinking this...but the helpful people at VAF seem to remind me that at least one other has thought the same!

In step seven in the pic at the start of the thread, it says to countersink the remaining holes just deep enough for the skin dimples. Looking ahead, the skins are two different thicknesses. Do you make a couple test pieces of the correct thickness and dimple them...then figure out where the skins of the appropriate thickness go and CS specifically for each?
 
I can't help but think that I am overthinking this...but the helpful people at VAF seem to remind me that at least one other has thought the same!

In step seven in the pic at the start of the thread, it says to countersink the remaining holes just deep enough for the skin dimples. Looking ahead, the skins are two different thicknesses. Do you make a couple test pieces of the correct thickness and dimple them...then figure out where the skins of the appropriate thickness go and CS specifically for each?

You can do this, but you are looking to account for an extreemly minute difference. I think you are far more likely to make a mistake and over do it for some holes, than you are to gain any bennefit from it.
The prototype was built by adjusting .007 " deep for any hole that received a dimple (regardless of the skin thickness). I doubt you could tell the difference if it was done differently.
 
Deeper

Are you saying wherever the project needed to be countersunk, it was just adjusted .007" deeper (7 clicks on a countersink cage) than what was required for a rivet to sit flush?
 
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Why does Vans have us use #30/40 countersinks for the screw holes on the spar flange? Shouldn't there be an appropriate countersink for a #8 and a #6 screw?

May be because the assembly instuctions have you intall the platenuts before countersinking for the screw. The platenut serves as a guide for the cutter. The #30 countersink cutter pilot fits the #8 screw platenut, the #40 fits the #6 screw platenut.

Are you saying wherever the project needed to be countersunk, it was just adjusted .007" deeper (7 clicks on a countersink cage) than what was required for a rivet to sit flush?

Maybe as a general rule, however the the thickness of the dimpled material will influence the depth needed for a good fit.
 
Countersink question ? supplemental

I'm a bit confused with this one; On step 2, 3rd paragraph, instruction says NOTE: Machine countersink in all rib locations. What does this means? I find that a little bit vague.
Qonpg11-03_zpsdd33c69d.png

The rest is pretty much strait forward but this. Is this referring to the pair of holes that match the rib tab (top & bottom of the rib) or else? It can't be the holes matching the forward flange of the rib holes since you need to install AN470 rivets there to attached them to the spar (step 3 pg 12-07).
 
I'm a bit confused with this one; On step 2, 3rd paragraph, instruction says NOTE: Machine countersink in all rib locations. What does this means? I find that a little bit vague.
Qonpg11-03_zpsdd33c69d.png

The rest is pretty much strait forward but this. Is this referring to the pair of holes that match the rib tab (top & bottom of the rib) or else? It can't be the holes matching the forward flange of the rib holes since you need to install AN470 rivets there to attached them to the spar (step 3 pg 12-07).

Marc, here is how I took it. Any time I see the words NOTE:, I believe it is basically referring to or a part of the step directly below it. So in this case, I believe it to refer to step 3 and step 3 has the directions for what to do along with the illustration.
 
Tom,

Seen that way it makes sense. I guess there are many ways of expressing "NOTES" on a specific set of instructions. In this case, it precedes the instruction. Being a professional engineer myself, I usually provide a NOTE after an instruction set. There's the confusion. Just need to adapt! Besides, this may have been explained in the section 1 to 5 of the manual and as usual, we tend to overlook what we've read previously. :rolleyes:

Thanks for the remark.
 
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Marc, here is how I took it. Any time I see the words NOTE:, I believe it is basically referring to or a part of the step directly below it. So in this case, I believe it to refer to step 3 and step 3 has the directions for what to do along with the illustration.

Tom has it right.
 
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