Everything was going great until the pilot on my #40 countersink bit broke while countersinking the rivet holes for the nut plates in the back side of the spacer. I was wondering when/if this might happen after experiencing several ocassions where inserting the pilot through a freshly drilled # 40 hole sure seemed awful tight. Either I torqued on the bit causing it to snap, or the base of the pilot had worn a groove in it from rubbing against an undersized hole over and over again, to the point where it could take it no more. It almost buggered up the countersunk hole beyond repair, but I think I can still salvage it. I had to use a 3/32 inch punch to get it out of the rivet hole, and that went OK.
Step one
Drill the bolt holes through each spacer, without the tie down bracket. Had to align them according to the plans, flush with the outer edges of the top and bottom spar bars:
Step 2
Using my large metal clamps and two pieces of wood, one on top and the other underneath to prevent damaging the metal with the clamp heads, I clamped the spacers in place tightly so they would not move while drilling the holes.
Step 3
You will do this a million times - turn the spar over and drill through the first hole, then put a 3/16 inch (gold) cleco through the spar web and the spacer hole to hold it in place. Repeat for the 3 remaining holes (2 per spacer).
Notice in this pic how the 1/2 wood block I am using completely cover the holes on the opposite side. I took care of this later by taking a thin strip of left over 3/4 inch plywood and cutting two very skinny clamping blocks on my band saw. I also cut them just a bit longer so they would fit the inside width of the spar almost from flange to flange.
Next pic shows the relative position of the nut plate after drilling the first hole. Note how close to the edges everything is. Precision is needed here to avoid messing things up. IN reality, as long as you clamp everything in the proper position securely, drilling the holes goes pretty smoothly.
Step 4
Once the two holes on one side are drilled and clecoed, reposition the clamping blocks as necessary to drill the other two holes on the opposite side. Clecoes will keep te spacers from moving out of position if you need to reposition the blocks. SHown in this next pic is one of the two freshly cut and much skinnier clamping blocks that I fabricated.
Some of the rivet holes may end up very close to the edge. When drilling, go slowly and ensure that you are drilling as straight as possible (something that apprently is almost impossible for me to do when drilling through thick material for some reason.
Remember to click on the pics for larger more detailed image.
And another pci showing both of my clamping blocks. The trick to this is ensuring that the blocks run straight across from one end to the other. Took me a few tries to get the hang of how to place the blocks, using a combination of inserting clecoes or bolts on one side or the other as holes were drilled to keep the parts from moving during clamping. I only ad one problem using these blocks during the tie down bracket drilling, but I used a skinnier piece of particle board which worked out fine.
Step 5
Debure the holes in the spar web and the spacers, and label the spacers so you know which one goes where
Not very impressed with the holes in the spar web - slightly enlarged a couple of them. Not concerned about this because they are sandwiched between several layers of other parts that are secured to the spar web, but sure wish these looked a little better. Spacer holes looked OK - go figure.
Step 6
Now it's time to drill the remaining holes in the tie down bracket. The trick here is to align the spacers so that the holes will be properly match drilled through the tie down bracket. You cannot use clecoes in the spacers as this will interfere with the tie down bracket. First, however, you focus on the bracket attach holes on the outside edges, which do not require any spacer alignment. Do these first.
I needed to find something that was absolutely square to ensure that the bracket was square to the spar. I found the following trim molding ends that I had intended to use in the basement at one time, but never got around to finishing it up. These were about as square as anything I could find, and they fit almost perfectly in between the two spar bar bars. Sometimes you just have to use some imagination and use what's available. INsert the bolt in the first hole that was already drilled per the specs in the plans, and then square up the bracket.
The first hole I decided to drill with the bracket clamped in position was the one that is diagonal and opposite the one that was drilled initially. This provides some stability to the bracket by allowing you to insert bolts in the holes temporarily during all the clamping and flipping of the spar that occurs during this process. You have to keep flipping the spar over because when you clamp everything you are on the front side of the spar, but to drill the holes you must turn the spar over to access the predrilled holes which are used to match drill the holes through the spacers and the bracket. Also note that this is where I had to use a skinnier piece of wood so that it would not interfere with my square block against the inside edge of the bracket. Worked out great. Keep clamping and drilling until all 4 of the bracket attach holes have been drilled.
Here is the opposite with the bracket attach holes ready to be drilled.
And a shot with the drill in position. I made sure it was straight in the hole before I actually drilled it!
Note how the ends of the bracket are short of the edges of both spar bars - this is according to specs. This whole business about ensuring that the tie down bracket is square to the spar has to do with the placement of the Eye bolt that will screw into the bottom of this bracket. Apparently if this is not square the eye bolt end up cockeyed and will not sit correctly with the wing skins that are applied later. Squared it as best I could. I am happy with it.
Step 7
Looks like I missed a pic of this. Once the bracket attach bolt holes have been drilled, remove the bracket, grab the spacers that were drilled earlier, place in their proper positions, using a straight edge to ensure that they are aligned properly. Then carefully take the tie down bracket and place it over the spacers and the spar, being careful NOT to upset or move the spacers in any way. Then you need to carefully clamp one side of the bracket so that the spacer holes on the other side can be drilled. Make sure that your clamps are placed over the area where the spacers are located, and NOT on the ends of the tie down bracket. This will ensure that the spacers are clamped tightly between the spar and the bracket, and they will not move during drilling. I think the above pic shows this.
Step 8
Now for my little trick that I came up with. So after clamping everything in palce, how can you be really sure that the spacers are in the correct location. The answer is simple:
Turn the spar over to expose the holes in the spar web. Then take the bolts and insert them into the holes. Remember that the spacer holes have already been drilled, so the bolt should drop down into the hole of the spar as well as the hole in the spacer of everything is aligned correctly. If not, then reclamp the spacers and the brackets until this step is acheived. This is how you know that the spacers are aligned correctly.
Next, remove the bolts and drill the holes the rest of the way through the tie down brackets. Worked pretty slick, if I do say so myself.
Check the holes by inserting the bolts through each of them
Step 9
Remove the clamps and bolts and reposition the clamps to the other side of the bracket, and repeat the alignment and drilling process in step 8 for the other side.
Step 10
Whne all the holes are drilled, remove the bracket and the spacers from the spar, debur the remaining holes in all parts as needed. Now its time to drill the holes for the nut plate rivets. My solution was to place one of the spacers in its correct position behind the bracket, then take an AN3 bolt and a nut plate, and partially insert the bolt through the spacer, the tie down bracket, and hand tighten it into the nut plate. Neither 1/8 inch or 3/16 inch clecoes will secure the nut plate (either too small or too big), so you are left with clamping things into position once again. What a pain. The next pic shows how I did it with some small bar clamps these worked quite well. I thought I had positions the nut plates relativey vertically, but as my next pics will show, it wasn't perfect. So much for eyeballing it!. This is not important as long as the nut plates can still be securely fastened to the spacer and the tie down bracket. Also remember that you are NOT riveting this assembly to the Wing spar. This is by design so that you can remove the tie down bracket and replace the nut plates if necessary after the plane is flying.
This is important because these nut plates will be securing the bolts that hold the aileron belcrank bracket in place. So if these start to come loose, that could be a very bad day indeed.
Next is how I set up everything to drill the #40 rivet holes, using the nut plate holes as a drill guide:
Once one side the nut plate rivet holes are drilled, clecoes can hold the assembly in place so that the holes on the other side can be drilled. Once this is done, remove the spacers and nut plates from the tie down bracket, debur the rivet holes,and prep them for countersinking on the back side of the spacer. I shoujld also point out that I used additional spacers under the tie down bracket to help stabilize it on the drill board while I was drilling the rivet holes for the nut plates. The problem with countersinking the rivet holes is that you are right on the edge of the spacer, adn the countersink cage has no real estate to rest on to stabilize the tool while countersinking the hole. My solution again was to use additional spacers by butting them up against each other to create an even platform of metal that is now large enough to support the circumferance of the countersink cage. This was working just fine right up to the point where my countersink pilot broke off while doing the first hole.
Then the thunder boomers showed up so it was a quick dash to clear the shop and put the cars in the garage before they got hailed on. SO I need to order a new #40 countersink bit and still need to tap the bottom of the tie down bracket for the eye bolt, which takes a 3/8 x 16 tap. Then, once that is all done, I need to repeat this same 10 step process for the right wing tie down bracket and spacers. Then its prep for primer, prime, and bolt it all together.
How's that for two hours worth of work? I don't know how others drill the holes for these things, but I suspect a lot of folks are clamping the hole shebang together and drilling through everything. I just did not like that approach very much because there is too much room for error or mis-aligned holes. I like the way that I broke this down to a series of sub-steps that ensures that all the holes are where they are supposed to be, and all the parts are lined up correctly as well.
Till tomorrow, KPR.
No comments:
Post a Comment