How to Make a Clean Hole with 1 1/8" Dill Bit?

[swwrobotics]

Hey everyone, so for our practice bot, our team was having trouble drilling the 2014 KOP chassis with a 1 1/8" bit, similar to the one shown here: http://drillsandcutters.com/dwdrsd1-...hlOgode FEA_A. We need to fit bearings into four holes we drill so they need to be precise.

When we tried drilling a practice hole in the 2014 chassis, the drill bit jumped around a lot, got stuck every once in a while, and in the end we ended up with a piece with a very jagged hole in it. Is there a way to fix this problem? Like squirt a bunch of lube on the piece while drilling it? Or buy another type of bit? Any advice would be appreciated.

Also keep in mind we're just using a normal cheapo drill press and none of that fancy CNC machine stuff (which I wish we had). Thanks!

[pfreivald]

Originally Posted by swwrobotics

Also keep in mind we're just using a normal cheapo drill press and none of that fancy CNC machine stuff (which I wish we had). Thanks!

In that situation, I'd use an appropriately-sized hole saw, lube, and sufficient patience. (Heating can be a problem when trying to precision-drill holes on a less-than-stellar drill press. Consider taking more time than you want to!)

[cgmv123]

Start by using a center punch to accurately place the center of the hole. Then drill through with a bit like 1/8". Then use the 1 1/8" bit. Remember to properly align the workpiece under the drill press each time. Cutting oil will help too.

[mrnoble]

We have used step drills, such as the Irwin Unibit. Grainger has an assortment of them, with some going up to 1-1/8" and larger. Harbor Freight has a set for cheap, but they don't last and are a bit dull.


http://www.irwin.com/tools/browse/dr...it-step-drills


http://m.harborfreight.com/catalogse...obile_redirect

[AlexH]

i'd start with something like a #4 center drill go up to a 1/2" , then a 3/4" and then the 1 1/8.

also check your RPM against this SMF calculator. you might be going too fast or slow.

[pfreivald]

Originally Posted by mrnoble

We have used step drills, such as the Irwin Unibit. Grainger has an assortment of them, with some going up to 1-1/8" and larger. Harbor Freight has a set for cheap, but they don't last and are a bit dull.


http://www.irwin.com/tools/browse/dr...it-step-drills


http://m.harborfreight.com/catalogse...obile_redirect

Yes, I absolutely meant a step drill and not a hole saw. Hole saws are notorious for their inaccuracy. Step drills (with a properly punched, piloted hole) are much better, and we've used them for bearings for years.

[mrnoble]

Originally Posted by pfreivald

Yes, I absolutely meant a step drill and not a hole saw. Hole saws are notorious for their inaccuracy. Step drills (with a properly punched, piloted hole) are much better, and we've used them for bearings for years.

I wondered.

[swwrobotics]

Originally Posted by cgmv123

Start by using a center punch to accurately place the center of the hole. Then drill through with a bit like 1/8". Then use the 1 1/8" bit. Remember to properly align the workpiece under the drill press each time. Cutting oil will help too.

Oh thanks. I'm actually not sure if we'll be able to center punch the piece though since the area we're drilling already has a bunch of holes around it (I know, its a bad idea) but we'll give it a go.

Originally Posted by mrnoble

We have used step drills, such as the Irwin Unibit. Grainger has an assortment of them, with some going up to 1-1/8" and larger. Harbor Freight has a set for cheap, but they don't last and are a bit dull.


http://www.irwin.com/tools/browse/dr...it-step-drills


http://m.harborfreight.com/catalogse...obile_redirect

Also, thanks! We'll definitely look into these.

[JesseK]

Qty 1: Silver & Demming 1-1/16" Drill Bit
Qty 1: 1-1/8" Reamer, exactly 1.125"

Haven't had a bad hole since.

[rkbot]

Would work best to do it on a mill, but without access to one use a center punch and then drill holes starting at 1/8 or so and work your way up to 1 1/8. Using a 1 1/8 drill bit in a drill press can be very scary if taking a lot of material out. or just using it in there period. they get stuck a lot and if used, what your drilling needs to be clamped very well because they can grab and turn something very easily.

[pfreivald]

Originally Posted by mrnoble

I wondered.

In the future, please don't be shy about calling me out for something that's O.o-worthy! My brain thought one thing, my mouth said something else. (And I use Voice Recognition to type, so that's not a typo!)

[mrnoble]

Originally Posted by pfreivald

In the future, please don't be shy about calling me out for something that's O.o-worthy! My brain thought one thing, my mouth said something else. (And I use Voice Recognition to type, so that's not a typo!)

[Oblarg]

Use a step bit to get up to 1 inch or so, finish it off with the 1-1/8'' bit.

You can, of course, use the step bit for the whole thing but I've always found they don't leave the nicest finish on the hole (lots of burrs, and if you go too far you end up widening one end).

Edit: As for general drilling practice, you should always have a bottle of cutting oil handy when you're using a drill press. It almost always gives you better results. It's not always necessary on aluminum (I tend to skip it for the 1/4'' or 3/16'' holes we drill loads of to save time), but it's an absolute must for getting good results on steel and it really does help for larger holes on aluminum as well. I went a long period of time not knowing this, to my detriment.

[DonRotolo]

Originally Posted by cgmv123

Start by using a center punch to accurately place the center of the hole. Then drill through with a bit like 1/8". Then use the 1 1/8" bit. Remember to properly align the workpiece under the drill press each time. Cutting oil will help too.

Good advice, except for the part about going from 1/8" to 1-1/8" directly. You absolutely need to work your way up to 1.125 as others have noted. PM me if you want to know why.

You cannot hand-hold a drill to make such a hole. This is dangerous. A drill press is the only safe way to make that hole with a drill bit. Your jagged hole is from the human inability to keep the drill perfectly centered on the pilot hole. As the bit bounces off the walls of the hole, you get chunks taken out instead of slivers.

[AndreaV]

Originally Posted by JesseK

Qty 1: Silver & Demming 1-1/16" Drill Bit
Qty 1: 1-1/8" Reamer, exactly 1.125"

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.