Tip: Transfer Punches

Rick6a · #1 10-23-2006, 07:54 AM

Okay...You are faced with a build situation in which you need to match holes in a new part with existing holes in an assembly. An example: You have decided to install nutplates instead of pop riveting the floor in place. You have carefully laid out and pilot drilled the floor ribs for nutplate spacing, but how do you transfer that pattern to the undrilled sheet that lays atop it? Commonly, for this situation and similiar tasks we may employ the use of a strap duplicator such as this one.

Less commonly, but the way I almost always prefer to accurately locate blind holes is with the use of transfer punches. Think of this type of transfer punch as a strap duplicator without the strap. Quality can vary among manufacturers and this little tool goes by many names including being referred to as "transfer pins," "sheet back markers" by Wicks and Spruce, and "blind-hole spotters" by Spellmaco http://www.rlspellmanmfg.com/blinds.html and Brown Tool http://www.browntool.com/productsele...?ProductID=480. Whatever you call them...they work.

You simply insert these little punches one or more at a time into the existing holes, and then lay the undrilled sheet (or replacement part) in place atop, and gently tap around the general area with a rubber mallet. The punch will leave an unmistakable mark upon the undrilled material assuring its precise mating alignment with the underlying structure. I keep a healthy stash of transfer punches stored in a 35mm film canister. Available in all common nominal diameters, I have loaded up an assembly with up to a couple dozen transfer punches at one time to make short work of transferring an entire hole pattern in one step. For sheet metal repair work, I consider these diminutive bits of hard steel an indispensable tool.

I once asked a major RV tool vendor why they did not sell transfer punches and replied at one time they did, but most builders did not know what transfer punches are and as a result, sold very few...a pity. Transfer punches are perfectly suited to work in difficult to reach areas that the average strap duplicator, limited by throat depth simply cannot reach.

dan · #2 10-23-2006, 08:43 AM

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...

Rick6a · #3 10-23-2006, 09:34 AM

Quote:

Originally Posted by dan

........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.

Mike S · #4 10-23-2006, 10:04 AM

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

chaskuss · #5 10-23-2006, 11:31 AM

Quote:

Originally Posted by Mike S

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

Mike S · #6 10-23-2006, 11:44 AM

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

chaskuss · #7 10-23-2006, 12:05 PM

Quote:

Originally Posted by Mike S

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

rv9builder · #8 10-23-2006, 04:33 PM

Quote:

Originally Posted by Rick6a

Okay...You are faced with a build situation in which you need to match holes in a new part with existing holes in an assembly.

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.

Rick6a · #9 10-23-2006, 05:12 PM

Quote:

Originally Posted by rv9builder

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.

az_gila · #10 10-23-2006, 05:19 PM

Quote:

Originally Posted by rv9builder

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.

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