Tip: Transfer Punches
 

If you can lay the undrilled sheet on top of the drilled sheet, can't you do the opposite? And then all you gotta do is back-drill. I'd much prefer back drilling, personally. Results will be more accurate imho. If you can't back-drill for some reason, then ok...

That's the point.....situations in which back-drilling is not possible. If faced with a situation in which you need to use a strap duplicating tool, consider using transfer punches as an alternative. I mentioned installing floor panels placed atop pre-piloted floor ribs as one example. In repair work, you may have to remove and replace a skin but the underlying ribs or stiffeners remain in place. Fitting a new skin and lining up the existing holes in the structure is made far easier using transfer punches.

There is also a threaded version of the transfer punch--or center as I know them as----for use in threaded holes. The raised point has a hex shank so it can be screwed in and out.

Try machinest supply stores.

One other handy tool tidbit is Bristol key, also known as spline key wrench.
Very simmilar to Allen wrenches, commonly used in radio know set screws.

Mike

Mike,
Threaded transfer punches can be easily made, using a lathe. I simply cut the head off of a bolt, say 3/8" X 16 tpi (for the tie down ring skin holes). Mount the bolt in the lathe and machine the cut side down to a point. Cut a slotted notch, off center on the end with the point. Remove from the lathe and install the the required hole. In this case, that would be the tie down bracket. Use a straight slot screw driver to insert and remove the transfer punch.
Cleco the skin or part over the transfer punch to locate it. Smack the skin (or other part) with a plastic mallet above the punch. Remove the skin (or part) and drill out using your newly created punch mark.
If you don't have access to a lathe, mount the headless bolt in your electric drill. Spin the bolt in the drill and place it against the spinning stone of your bench grinder. With a steady hand, you can do a very nice, low tech job of creating that point.
Charlie Kuss

Charlie----------good tip. Might be a bit soft, but should be fine for aluminium.

I still have a set from a prior life as a machinest. Very useful, specially for blind holes.

Mike

Mike,
They are reasonably hard if you use grade 8 bolts. However, for use on aluminum, common grade 5 bolts work fine AND are much easier to cut a notch in with a hand hacksaw. I spent 4 years doing Aerospace machine assembly. That is where I learned this trick.
Charlie

Rick, is there a transfer punch that works with a dimpled hole? I've dimpled a few parts sooner than I should have, only to find that I needed to use the dimpled part to match-drill another part. Sure, you can stick a felt pen in the dimple and mark the new part, but it sure would be nice if there was something more accurate like a transfer punch that would nest inside the dimple.

Yes, in the case of AD3 rivets, a standard #40 transfer punch will set inside the dimple. A #30 transfer punch will work in an AD4 rivet dimple. They may move about ever so slightly but for all intents and purposes will produce a reasonably accurate mark to match drill your new part. Because the punches will sit inside the dimple a bit, the mark left after tapping with a mallet may be a bit fainter than if the material was not dimpled, but will still work. Way more accurate than the felt pen approach.

Transfer punch
 

Mark ... this might work....

http://www.aircraft-tool.com/shop/de...x%3fPageNo%3d1



Available in many sizes... should also be available from a machinists tool supply place near you....

gil in Tucson