nuts & bolts

shop talk Magnetic Duplicator KEN WHITE, EA A 660371

I

n aluminum aircraft construction, drilling rivet holes in your wing and fuselage skins that match up with the holes in your ribs and bulkheads can be a challenge. You want the holes in the flanges of the ribs or bulkheads to be the proper distance from the edge for maximum strength, so it is always best to drill those before you apply the skins so you can carefully measure and place them. This also keeps you from accidentally drilling into fluting. I like to drill through the back side of the skin using a 12-inch long aircraft drill. Using the aforementioned hole in the rib or bulkhead as a guide ensures perfect alignment because you are match drilling the skin hole to the rib or bulkhead hole. Sometimes you do not have access to drill the hole from the back side because other structures are in the

way. When this happens you can use a tool called a duplicator to position the hole. A duplicator is a tool made of two straps of steel that have a pilot pin on one strap and a drill guide bushing on the other. The straps are welded together at one end and resemble gigantic tweezers. To use this tool, pull the skin away from the rib or bulkhead enough to slip the pilot pin strap behind it and pop the pilot pin into the hole in the rib or bulkhead. This aligns the drill bushing to the hole in the rib or bulkhead so that you can drill the skin hole from the outside. Drill the hole part way through, then remove the duplicator before you finish drilling to keep from drilling into the duplicator. The reach on the duplicator is around 6 inches. If you have to reach beyond 6 inches, you have a problem that I have solved using what I call a magnetic duplicator.

Using two round neodymium magnets, a magnetic duplicator makes aligning rivet holes between the skin and a rib or bulkhead flange much easier.

98

NOVEMBER 2008

My magnetic duplicator consists of two round neodymium magnets that have a hole in them. (Neodymium magnets have been around a little while but are still relatively new. They are very strong. If you have never been exposed to neodymium magnets, you will be surprised at how hard it is to pry two of them apart.) One goes on the rib or bulkhead flange and is aligned to the rivet hole with a pilot pin. The other magnet goes on the outside of the skin and is aligned only by the magnetic field of the piloted magnet. The alignment is pretty close if you use a spot of light oil on the skin magnet so that it can slide into magnetic alignment. It helps to rotate the skin magnet a few degrees to help it seek its alignment. Once you have the magnets in place, carefully insert a center punch into the skin magnet and lightly tap it once with a hammer. I start drilling with a 1/16-inch diameter drill, so that if the alignment is a few thousandths off, there’s a better chance of the holes being aligned after drilling them to their final size. As with any new aircraft construction process, you will want to try this

out on scraps a few times before you drill holes in your skins. You can purchase the magnets from K&J Magnetics at www.KJmagnetics.com. The part number is R636, and you will need two of them for $1.05 each. The pilot pin and the center punch must be made from 3/16inch diameter non-magnetic material, such as 304 stainless steel. I got mine from McMaster-Carr at www. McMaster.com; the part number is 89535K24, and it’s $9.36 for 6 feet. You will need access to a metal lathe to machine the pilot and center punch as shown in the sketch. The 304 stainless cannot be hardened, but it will see light service so hardening is not necessary. If you do not have access to a lathe or would rather purchase the tool, Noah Industries of Melbourne is manufacturing them and plans to distribute the tool through aircraft tool and component distributors. You can contact Noah at [email protected]. Ken White is chief mechanical engineer for Noah Industries. He owns a Beechcraft Skipper and is building a Mustang II.

STATEMENT OF OWNERSHIP, MANAGEMENT, AND CIRCULATION (Required by 39 U.S.C. 3685). 1. Title of Publication: EAA Sport Aviation 2. Publication No.:0511-720. 3. Filing Date: 9/26/08. 4. Issue Frequency: Monthly. 5. No. of Issues Published Annually: 12. 6. Annual Subscription Price: $30.00 in U.S. 7. Known Office of Publication: EAA, 3000 Poberezny Road, P.O. Box 3086, Oshkosh, WI 54903-3086. Contact Person: Kathleen Witman, Telephone: 920-426-6156. 8. Headquarters or General Business Office of the Publisher: Same as above. 9. Publisher: Thomas Poberezny. EAA, P.O. Box 3086, Oshkosh, WI 54903-3086. Editor: Mary Jones, same address as above. Managing Editor: Kathleen Witman, same address as above. 10. Owner: Experimental Aircraft Association, P.O. Box 3086, Oshkosh, WI 54903-3086. 11. Known bondholders, mortgagees, and other security holders owning or holding 1 percent or more of total amounts of bonds, mortgages or other securities: None. 12. Tax Status: Has Not Changed During Preceding 12 Months. 13. Publication Title: EAA Sport Aviation. 14. Issue date for circulation data below: September 2008. 15. Extent and Nature of Circulation (Average No. Copies Each Issue During Preceding 12 Months/ No. Copies of Single Issue Published Nearest to Filing Date): a. Total No. of Copies Printed (130,432/125,797) b. Paid Circulation (By Mail and Outside the Mail): 1. Mailed OutsideCounty Paid Subscriptions Stated on PS Form 3541 (Include paid distribution above nominal rate, advertiser’s proof copies, and exchange copies) (117,179/114,589). 2. Mailed In-County Paid Subscriptions Stated on PS Form 3541 (Include paid distribution above nominal rate, advertiser’s proof copies, and exchange copies) (0/0). 3. Paid Distribution Outside the Mails Including Sales Through Dealers and Carriers, Street Vendors, Counter Sales, and Other Paid Distribution Outside USPS (8,940/9,183). 4. Paid Distribution by Other Classes of Mail Through the USPS (e.g., First-Class Mail) (352/361). c. Total Paid Distribution (Sum of 15b (1), (2), (3), and (4)) (126,471/124,133). d. Free or Nominal Rate Distribution (By Mail and Outside the Mail): 1. Free or Nominal Rate Outside-County Copies Included on PS Form 3541 (0/0). 2. Free or Nominal Rate In-County Copies Included on PS Form 3541 (0/0). 3. Free or Nominal Rate Copies Mailed at Other Classes Through the USPS (e.g. First-Class Mail) (200/200). 4. Free or Nominal Rate Distribution Outside the Mail (Carriers or other means) (3,275/395). e. Total Free or Nominal Rate Distribution (Sum of 15d (1), (2), (3), and (4) (3,475/595). f. Total Distribution (Sum of 15c and 15e) (129,946/124,728). g. Copies not Distributed (See Instructions to Publishers #4 (page #3))(1,396/200). h. Total (Sum of 15f and g) (131,342/124,928). i. Percent Paid (15c divided by 15f times 100) (97.33%/99.52%). 16. Publication of Statement Ownership: Publication required. Will be printed in the November 2008 issue of this publication. 17. I certify that all information furnished on this form is true and complete. I understand that anyone who furnishes false or misleading information on this form or who omits material or information requested on the form may be subject to criminal sanctions (including fines and imprisonment) and/or civil sanctions (including civil penalties). Interim Director of Publications and Editor, EAA Sport Aviation, Mary Jones, 9/26/08. PS Form 3526, September 2007

EAA Sport Aviation

99