Cap strip drilling.

[hausburn]

I am searching for entries of stack drilling and haven't found any. In my picture I have a stack of 4 aft spar caps to drill rib placements. Accuracy would be great, does anyone se a problem with this? Mind it is just for rib placement.

[Chris In Milwaukee]

I set up the longest cap strip first and drilled all of the holes in it. Then I used it as a template to match-drill the other strips. I did them one at a time, though. When I stack-drilled my root attachment plates, I broke drill bits pretty often. It was annoying. I wasn’t using any sort of lube, though.

[S Lathrop]

I took a piece of steel that was 18 inches long and made a drilling template. I did this on a CNC machine. I used this template to drill all the holes on the spars and cap strips. I drilled the holes 3/32 diameter. The strip was the width of the main spar cap strips but I milled the ends down to the width of the rear spar so I could align the template with both cap strips.

Just as a note, I found that if I used distance of 1.0268 between the rivet holes, all the major components of the wing would line up exactly (per the drawings) with the rivet holes. This is why I made the drilling template on a CNC machine.

[BTAZ]

I made a "master" like S Lathrop described. A bit of work in Excel to get the numbers. Drilled with my mill to get the spacing accurate.

I then stacked up all the cap strips at once and drilled them using my drill press and a temporary extended table/fence, indexing the master to the capstrips as I went.

Then I positioned the capstrips on the spar and match drilled.

[hausburn]

I took a piece of steel that was 18 inches long and made a drilling template. I did this on a CNC machine. I used this template to drill all the holes on the spars and cap strips. I drilled the holes 3/32 diameter. The strip was the width of the main spar cap strips but I milled the ends down to the width of the rear spar so I could align the template with both cap strips.

Just as a note, I found that if I used distance of 1.0268 between the rivet holes, all the major components of the wing would line up exactly (per the drawings) with the rivet holes. This is why I made the drilling template on a CNC machine.

Are you building a patrol?

[S Lathrop]

Are you building a patrol?

Sorry, I should have said that I am building a 4 place.

[N3UW]

I had a similar setup to yours on the bench. I setup all the cap strips in the order they would be install on on the spar. I took a marking gauge and with a sharpie drew a centerline on the cap strip. I then used a plastic template that was the length of one rib opening and marked all the rice locations. This is also the time to mark the necessary no-drill locations. I then center punched the holes and used a air drill with a bubble level bondoed to the top to make sure i was plumb. I also used boelube on the bits that helped a lot. Worked out great and the holes were perfect as if i had used a drill press. I did initially undersized the holes and drilled to full size when i attached the spar web. I believe i show some of this in one of my videos I have listed in my signature. Happy drilling.

[Chris In Milwaukee]

I have noticed that a lot of people are really getting hung up on this 1.026" business. The important measurement is the distance between the ribs (14-3/8" on the 4-place), 7-3/16" center-to-center on the lightening holes, as well as the spacer bars that go between spar caps top to bottom. Once you have those laid out, set up your rivet fan so that your spacing is the closest thing to 1" (which will be about 1.026"-ish). There's only one spacing on your rivet fan that will get you close to that. But if you've got a CNC drill available to you as one has above, then it should match.

As John said, though, you definitely want to make sure you've got those "special" locations accounted for.

Here's my version of the story:

https://bearhawkforums.com/forum/bea...645-spar-party

Page #2, Post #22 is where my spar caps begin.

[BTAZ]

As Chris mentioned, the critical thing is the rib spacing. If you use a template, it needs to be precise. If your rib spacing holes on the template are off .010", by the time you stack that error 20 times you will be off almost a 1/4". That accuracy is easy to achieve on a mill but not with a tape measure and center punch. Once you have the end holes of the template worked out, the in-fill holes are just a division problem.

One could avoid the tolerance buildup if the rib locations were laid out on the cap strips and the template was only used(like the rivet fan) to locate the in-fill holes.

Like N3UW noted. as you drill, be sure to skip holes as needed(particularly in the spar web splice area) where the rivet locations would interfere with the strut attach brackets and the pulley brackets.

Always keep in mind the bigger picture. At some point, you will have a spar web sandwiched between spar cap strips with the spar cap strips spaced apart by spacer bars at each rib location. Each rib location will also have attach angles on either side.

Either you will want to fabricate and drill all of these parts precisely enough that they are interchangeable across location OR you will want to drill each in situ and then keep track of them as you go through the deburring, corrosion protection, and re assembly step.

I chose the "interchangeable route" simply because of my background and tools on hand.

Others have placed everything in the spar webs and hand drilled all at once.

Neither way is particularly better from an end product point of view.

"Should I drill this now or should I wait and match drill to the mating part?" is a very useful question.

[geraldmorrissey]

The only problem I see is that if you screw up one hole you screw up four capstrips.
Good Luck
Gerry
Patrol #30

[S Lathrop]

The necessity of accurately locating all the critical components of the wing is undeniable. I chose to use a drill jig as a way to assure the necessary accuracy. From years of experience doing layouts, I felt most comfortable using the rivet holes that I laid out with the drill jig assured that accuracy. It also saved a lot of time. I setup to drill all the cap strips first and then used them to layout the spars. Bottom line was that all the individual parts of the wings were interchangeable.

My drill jig for the cap strips was 18 inches long. I would overlap existing holes about 5 inches and then drill the next 12 inches. The drill jig was the same width as the cap strips. This helped assure that the holes were centered on the strips.

I drilled all the holes 3/32 diameter. Then I assembled the spars with the undersized holes. The last step was to drill the holes to size.

I did the large aluminum plates ( the splice plate and the wing mount) on the mill. Again this assured accuracy and saved time.

I also made drill jigs to do the angle brackets and rib stiffeners. Any thing that I had to drill a pattern more than twice, I made a drill jig. The jig for the rib angle brackets also serves to check the spacing of the cap strips along the spars.

[Chris In Milwaukee]

I'd certainly love to learn how to use a mill and similar tools one day. There's no denying that you can create some really cool stuff when you have crafty tools.

[S Lathrop]

I'd certainly love to learn how to use a mill and similar tools one day. There's no denying that you can create some really cool stuff when you have crafty tools.

My mill is a 1978 Bridgeport Series 1 CNC mill. You can find these things for less than the cost of moving it to you shop. They have no hand controls so very few people want them. My mill was not working when I moved it to my garage. There is a company, Mach Motion: https://machmotion.com . They have a conversion kit to replace the original control system with a new PC based system. I have an early version of this conversion. For about $7000 to $8000, I have a 3 axis CNC mill. I do use this thing in my day job.

Many of the fixtures I made would be very cost effective to have a local machine shop do for you. The advantage I probably have is I think about making fixtures and other ways to make parts than simply walking out to the shop and cutting metal.

One resource I have found invaluable is a water jet cutting operation. The aluminum plates that are part of the wing construction, I had many of those done on a water jet cutting machine.

[N3UW]

As Chris and BATZ mention...rib spacing is critical. In addition to what i said above. I took a single cap strip and laid out all the critical measurements including rib positions, splice plates, attach fittings etc. I then used this to transfer to the other cap strips so i was consistent from one wing to another, top and bottom cap strips and front and rear cap strips. I then used my simple plastic template to setup rivet spacing between ribs. it would be just as easy to use a rivet fan but at this point in my build i did not have one yet so i printed one out on my printer. That spacing does not have to be exact just close enough. Worry about the critical measurements but not everything. There are many ways to build this plane. Pick the way that works best for you.

[sjt]

I copied N3UW for the most part.

I dedicated a single tape measure to be my master tape measure. The rib locations are the critical measurement - not the 1.021 spacing number.

1) Buy an extra length of cap strip dedicated as the master. $20
2) Do not drill the holes at the support bracket locations.
3) Do not drill holes near the Web splice.
4) Do not drill holes near attach plate

As an aside, you think you will remember not to drill the locations, but the process of drilling all of those holes is so monotonous that you will not be able to stop yourself.
It is best if the template does not contain those locations and the problem is avoided.

5) drill undersize with #40.
6) epoxy a bubble level on drill.

7) It was my preference to transfer punch - using my master cap strip (with missing holes) . I drilled one at a time -undersize #40. A broken steel fragment in aluminum is hard to fix.

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Do not install rivet at rib locations since a bracket must be installed at those locations.