Rick6a
Well Known Member
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/productselect.asp?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.
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/productselect.asp?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.
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