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Drill It & Pin It

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From time to time I have somebody ask me to make a mold like an existing readily available cheap mold with the only difference being an eye socket.  This may not always be the most satisfactory answer, but quite often it will work and its an order of magnitude cheaper than having me make a custom mold.  Drill it and pin it.  That can be scary I know, but if you mess it up the mold was cheap anyway.   You can always just try again.  


This is how I would do it.  I would definitely do it on a drill press, but I won't discredit anybody else's skill with a hand held drill.  



A.  Drill Press. 

B.  Fine Point Felt tip Marker 

C.  Center Punch (I like a spring punch for this)

D.  2 Drill Bits - 1 the largest you can start easily in your punch mark.  I would suggest staying away from tiny bits as they are easily broken and difficult to dig out of metal mold when they are.  1 a few thousandths smaller than the finished hole.  Maybe a third drill bit 

E.  Light cutting oil suitable for aluminum.  I like Tap Magic All Metals formula, but any decent quality cutting oil will work fine.  

F.  Maybe a reamer under size to your pin or a third drill bit.  I have a set of over and under reamers for standard sizes.  I've found a 1/4" pin can be press into a hole in upto .004" smaller with extruded aluminum.  With cast aluminum I would go for a size .002 smaller than the pin as I would not want it to crack when I pressed in the pin.    

G.  Some type of clamp to hold the mold to the drill press table.  Bar clamp, table clamp, swivel pad welding clamp, etc.  I hesitate to suggest a vise because so many inexpensive molds and cast molds do not have square sides to clamp to.  

H.  Something to press in the pins.  Arbor press, bench vise, even a hammer if you have the confidence.  


Mark one side of the mold with your felt tip marker on the inside where you would like your eye socket.  Hold one of the pins there to make sure it fits nicely.  


Center punch the the location.  


Set your drill press on a high speed.  3000 RPM is not too fast.   Use the smaller of the two drill bits.  For something like this I like to clamp the mold down after I can feel the drill bit is set in the center punch mark.  Apply cutting oil liberally to the location to drill.  You will want to drill with positive pressure.  You may want to peck drill to clear chips and add lubrication.  You DO NOT WANT TO RUB.  You want to cut.  If you peck drill instantly reverse your feed.  Don't sit there rubbing the metal.  Aluminum work hardens.  You want to be either cutting or pulling out.  You never at anytime want to let the drill just spin in the hole.  


After you have successfully drilled through the first side close the mold.  Place the closed mold hole side up.  Lower the quill until the drill bit is in the hole.  Clamp the mold to the table so that the drill bit goes easily in and out of the hole you drilled.  You may want to check that the other side will now drill through in a manner that you will like.  A hole center punch (aligning punch) would be handy, but a tiny drill mark with the drill bit will also do.  If you chose to double check that the other side will drill in a good spot unclamp the mold and check your mark.  If it looks good reposition and reclamp the mold in place as described above.  Add more cutting oil and drill all the way through.  You can check your work at this point or if you are confident you can just change drill bits and drill to the larger size.  


Drill bits tend to drill holes larger than their markings, so check your pins at this point.  If the feel like they might start then press them in.  If not then a slightly larger drill bit or a reamer might be in order.  If the pins go into the hole by hand the hole is too big.  All may not be lost  A bearing and sleeve locker like the old Loctite Green might save you.  If you feel the hole is to big to use bearing and sleeve locker you can try making some peen marks around the hole on the outside with a punch.  It may be just enough to hold the pin in place.  


Make sure you set the pin at the depth you want, and test the mold.  


This may work on aluminum molds for lead casting items like jigs and spinner baits or for soft plastic molds for swimbaits and worms.  


WARNING:  You may very well destroy a mold or three learning how to do this and getting the knack for it, but its still cheaper than having a custom mold made.


If you find this post useful I would appreciate if you share it with others.

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