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Gary's RV8 Construction Log
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Date:  1-5-2010
Number of Hours:  3.00
Manual Reference:  
Brief Description:  Countersink Main Spars

I started by placing some masking tape over the area spar and the spar stiffeners to stop all the alumium filings finding there way in there and causing havoc. Because of the depth of the countersink required (especially the #8) the is not enough material to keep the countersink bit dead center towards the end of each countersink. Many have reported oval holes subsequent to countersinking as a result of this. Vans suggest using the nutplates with smaller countersink bits to assist in this regard. I chose a different route and started by clamping a piece of aluminium flat bar under the flange and match drilled all the #6 and #8 to the flat bar.

Then using a scrap piece of aluminium, I drilled test countersinks to get the depth exactly right. For the #8 countersinks, Van suggests no more that 0.375" (or 3/8) diameter on the final countersink so this is what I shot for, carefully adjusting the microstop countersink deeper a click at a time until I was happy.

Using an electric drill, I then countersunk all the #8 holes in both spars so that I didn't have to re-adjust the countersink cage. I was able to re-use the aluminium flat bar in all instances, clamping it to the relevant spar flange each time. Every singly countersink was perfectly round and just a hairs breadth under 3/8ths. Very happy with the results!
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Stock aluminium flat bar clamped under the spar flange ready to be match drilled

Stock aluminium flat bar clamped under the spar flange ready to be match drilled

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Really glad the masking tape is there!

Really glad the masking tape is there!

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Setting the countersink depth for the #8 holes

Setting the countersink depth for the #8 holes

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