Drilling holes accurately for aligment pins

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compact8

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This is the need for some of the parts I am planning to make and I am wondering how it can be done accurately.

On one side the hole should be light press fit and on the other side a sliding fit. The pin size is 3 mm. Controlling the fitting is not too difficult with reamers but I expect the accurate alignment of the holes on the two sides to be challenging. My mill is just a hobby-grade EMCO FB2 so there are plays here and there. Even if spot drills are used, there is always some errors in the position of drilled holes. If it is within 0.02 mm I will be happy. Are there any methods to ensure good hole alignment with such a machine ?
 
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I assume you must not be able to clamp the parts together and drill through in one op - easiest way.

How about a transfer plate? Drill the holes in it, make sure the drill holes are a tight fit to the spot drill - ream if necesary. Then clamp the plate to each part as the drill guide. A spotting drill should be used here.
 
Sounds like you're making a split mold ? If so , drill and ream both parts while together to the press fit diameter and then re-ream one half to the slip fit diameter . That's IF this is what you're looking to accomplish . How about a sketch ?
 
compact8 said:
This is the need for some of the parts I am planning to make and I am wondering how it can be done accurately.

On one side the hole should be light press fit and on the other side a sliding fit. The pin size is 3 mm. Controlling the fitting is not too difficult with reamers but I expect the accurate alignment of the holes on the two sides to be challenging. My mill is just a hobby-grade EMCO FB2 so there are plays here and there. Even if spot drills are used, there is always some errors in the position of drilled holes. If it is within 0.02 mm I will be happy. Are there any methods to ensure good hole alignment with such a machine ?
Click to expand...

If it's possible to assemble the parts, and drill both halfs of the hole in one go, then that's your answer. Drill once, then the reamer will follow the existing hole. One half just under, and one just over. I'm sure your mill has what it takes, as this works well on a floppy old crooked drill press. Well, provided that the actual position has some wiggle room. It'll get both halves lined up quite well.
 
If the whole assembly is to big to fit on the mill is the smaller part able to fit on the mill?
Drill the pilot holes in the smaller part and then assemble the smaller part to the big part and at this point you can even use a hand held drill to drill the big part using the holes in the small part as your drill bushing. Dissassemble and then just ream your over and under finish sizes.
 
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