Quote:
Originally Posted by JesseK
Qty 1: Silver & Demming 1-1/16" Drill Bit
Qty 1: 1-1/8" Reamer, exactly 1.125"
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The Machinist in me tells this is absolutely the right way, however I know the price of a reamer that big costs about as much as as most team's drill presses, and I've never seen a reamer larger than an inch with a 1/2" shank. Only the beastly industrial chucks go bigger than 1/2 shank"
Drills inherently do not drill precise holes. It is just not the nature of the tool, drills make 'close enough' holes. When using a drill for bearing holes you can expect a loose fit. When I use a drilled bearing hole I always use rivets or bolts hold it in place, as well as press it against a preferred side. some de-burring is to be expected.
Here are some tips for running monstrously large drills, but this applies to most machining operations. It amazes me how many "senior mentors" with years of experience in first/engineering/shop don't know these simple machine shop practices
-Predrill,centerdrill
This is more for location, I wouldn't predrill much more than 1/8 as doing so can lead to more vibrations later on. A drill is supposed to make a hole where there is no hole, if you prefer to step up the drills that is fine, but drill points actually do a pretty good job of starting the cut if used correctly.
-Use the right speed
Different diameter tools, and materials require different speeds(rpm). Basically small diameter tools go fast and larger diameter tools go slower. for your 1.125 HSS drill the right speed would be around 600rpm any faster and you are creating too much friction which creates excessive heat. Aluminum has a low melting point and likes to gall on hot tools that are not going the right speed. aluminum galling on tools has to be the leading cause of tool wear in first.
-Use coolant
Unless using carbide tooling, always use coolant. not only does it lower the temperature to prevent galling but it also adds lubrication for the chips to clear faster.
-Adjust feed/use peck drilling
I know plenty of people that punch their way through material with a spinning drill, instead of letting the drill actually cut as intended. If the above rules have been followed the drill should actually cut. there should be enough force to create a chip, but no more. If the material is getting stuck like you mentioned, there might be too much force applied for too long, and chips are not clearing as they should. Try peck drilling, this is when you drill for maybe a second or two, then back out allowing for the chips to clear, and re enter. rinse(with coolant) and repeat.
-Clean/sharpen the cutting edge
There's a high chance the cutting edge has already been galled, so clear it of any aluminum before attempting to cut again, use pliers not your fingernails please! Only attempt sharpening the tool if you have somebody on board who actually knows how to do so. Beware! a lot of people think they know, but actually make it much much worse.
-Good work holding.
If the part is not held securely on a vise it will wobble around, making the already oversize drill hole even bigger. Should also help with vibrations. Also safety! can't stress the work holding enough!
Drilling a 1.125 hole into 1/8 aluminum plate will never be perfect, but hopefully those suggestions help.
As mentioned above, never do this in a hand drill, and if a mill is available that will provide a much better work holding than a drilling press.