Reamers and Bolt Holes

[rebel280]

Hello :-)

I am starting to build an airplane of 6061-T6 aluminum. Some folks use reamers, some drills for their bolt holes. I will be making holes for bolts of the following sizes:

Bolt min to max reamer considered
AN4 0.2460-0.2490 0.2500
AN5 0.3090-0.3120 0.3125
AN6 0.3710-0.3740 0.3750

I don't know what the tolerances of the reamers are, but aren't they -0.0000 and +0.xxxxx? So it looks like there would be at least 0.0005-0.0010 difference. Would this be enough to slide/tap the bolt through without rubbing off the cadmium plating on the bolt?

There will be thick stock between 0.090 and 0.1875 joined to thinner sheets, 0.025-0.060 for the most part. I will be match drilling pilot holes, then making them bigger either on a drill press if possible, or by hand if not possible.

I've never used a reamer before. The ones I have available are chucking reamers that have a 45 deg chamber for ~1/8". I also have a hand chuck. Could I use this to ream them by hand? I've heard that's not a good idea.

Any other suggestions are welcome. I understand I should under drill by 1/64 before reaming.

[hardtailjohn]

Rebel, what are these holes for? What airplane are you building, and what does the plans author suggest?
JH

[Randall]

Hi Dan
A 1/4, 5/16th, and a 3/8 chucking reamers will work but for this thin of material I would suggest hand reamers. The longer taper of a hand reamer will help you get started in the predrilled holes. 0.001 inch is not very much to fit a bolt in (this is considered a drive fit) so the cad will come off. You must remember that either the hole or the bolt just has to be off somewhere on the diameter to keep the two from sliding together. And I hope you will be putting a little zinc chromate in the hole before you install the bolts and this takes up some of that clearaqnce. The main thing will be keeping the sheets in alingment, with two or three sheets this can get tricky.

Now for my two cents worth

I would try a few holes on some scrap and see if it is worth the effort to ream. I have never reamed a bolthole in sheet metal. Even a closr tolerence hole in a block of material will have 0.004 to 0.005 inch of clearance. A normal bolthole will have 0.015 inch clearance, this for alignment. I think ( and I can get in big trouble doing this) that using the same size drill for the same size bolt should yield good results if you take it slow. If you can't get a round hole than a reamer may be the way to go, but I think you will need a 0.002 inch or so oversize reamer.

Hope this helps more than confuses

Randall

[rsanter]

the need for drilling verses using a reamer depends on the application area. even for a plane some areas do not need the hole reamed

bob