Spar page 11-03 step 5

Hi group,

I'm on step 5.

This is the step to machine countersink the fuel tank attach screw holes. Is there a particular reason why this step would follow the riveting of the nutplates? It seems like it could have been done before step 4. I suppose its not that big of a deal, but was concerned about any shavings that might be left over inside the nutplates themselves. I can blow them out.

Further, the instructions nor the illustrations do not say what screw will be going inside the nutplates. This would be helpful in determining the depth of the countersink. Can I presume that the screws that came inside the same bag as the nutplates will be used? (bag 3007).

Finally all the way at step 8 says to prime the areas where countersinking took place, however the nutplates would already be on by this point.

I know there have been revisions to this page, but I believe I am on the latest.

Tom

Page 16-09 Figure 1 shows AN509-8R8 fasteners. Be sure to use a CS cutter for a #8 screw.

The nutplates must be on to keep the countersink cutter centered in the hole while you cut. Practice on some thick scrap angle or something. I got some angle aluminum from Lowe's aviation supply.

Thanks KC. Those in fact are the screws that come in the bag with the nutplates so that is good.

Regarding the priming, I presume I should be priming the rivet countersink holes prior to actually riveting them as shown all the way down in step 8

KC, as I look at the directions closer, I'm in fact countersinking for a dimpled .032 skin to sit on top and not the screw head itself. When you say get a scrap piece of angle, do you mean get a scrap piece of aluminum sheet to dimple and then test fit inside of the countersunk hole?

Tom

propsync said:

KC, as I look at the directions closer, I'm in fact countersinking for a dimpled .032 skin to sit on top and not the screw head itself. When you say get a scrap piece of angle, do you mean get a scrap piece of aluminum sheet to dimple and then test fit inside of the countersunk hole?

Tom

Click to expand...

You're correct. And get both, a scrap piece of angle to get the CS set up and practice and a scrap piece of .032 to dimple and use as a depth gauge. I think you can get both at Home Depot / Lowes. If you can't get 032, I'm sure something like 025 is close enough.

propsync said:

Thanks KC. Those in fact are the screws that come in the bag with the nutplates so that is good.

Regarding the priming, I presume I should be priming the rivet countersink holes prior to actually riveting them as shown all the way down in step 8

Click to expand...

I primed all CS holes in the spar, whether for AD3 rivet or #8 screw/skin before I riveted anything. I think the #8 holes are most important and that may be all the instructions tell you to do ( don't have book in front of me)

Read ahead

Tom, you will find many of these answers, as well as insight by reading ahead. Wen I got to the same point, I just looked forward in the plans to figure out what went in or over those holes. If its .32 skin, then I cut some scrap, drilled, debarred, dimpled, and countersunk to fit that...reading ahead will also help understand the whole project better.

I went to lowes and bought cheap aluminum angle...think it cost $18 total, clamped it beneath the spar web, match drilled, then countersunk for the nut plates using the "throw away" angle to drive the CS pilot. This allowed me to get around some of those pesky problems you are tackling about.

KCBerner said:

Page 16-09 Figure 1 shows AN509-8R8 fasteners. Be sure to use a CS cutter for a #8 screw.

The nutplates must be on to keep the countersink cutter centered in the hole while you cut. Practice on some thick scrap angle or something. I got some angle aluminum from Lowe's aviation supply.

Click to expand...

KC, I wanted to check this step with you. You mention to use a countersink cutter for a #8 screw. Looking at my chart, that would mean using a #19 cutter. The tip of the #19 cutter will not fit in the hole. Anyway, the instructions do say to use a #30 so I think I should stick with that unless you know otherwise, since you mentioned it I thought I would double check.

Also, I'm doing a few practice dimple runs on some scrap aluminum from Home Depot. I found this conversion chart online if it is helpful to anyone. http://www.unc.edu/~rowlett/units/scales/sheetmetal.html

.032 sheetmetal converts to 20 gauge (they show gauge not inches). Unfortunately, the closest I could get is .019 which is about 1/2 the thickness. When I dimple this scrap piece, the screw head does not seat flush, but I suppose that is to be expected since its half as thick. Going to try Lowes tomorrow to see if I can get closer. Or, I might try doubling it up as that would get it closer.