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

[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.

[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.

[philso]

Originally Posted by AndreaV

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.

The other night, I made a pair of bearing holders for our collector rollers doing what Andrea described (except I used new drill bits and no coolant) and the bearings were a perfect slip fit. I did the work on a no-name floor standing drill press much like the ones you can buy at HF and no fancy or expensive equipment. The following expands on what Adrea suggested. It isn't the only way to do it but I think it illustrates how to apply the principles she outlines. The only suggestions I would add to Andreas list would be to use templates where appropriate and to take the time to do the job well enough that someone else does not have to spend more time afterward to make corrections and adjustments so that what you made will actually be useable.

I clamped a stack of 5 blank 1/8" aluminum plates and the template in a drill press vise to drill all 19 pilot holes (some were for mounting to the collector arm, some were for mounting the spacer made from 2 " x 1"tube). Fortunately, the plates were cut out by the sheet metal shop at work and they matched each other very closely. I also used 2 C-clamps to clamp the stack of plates down in the vise and to the drill press table.

I used the template to drill the 3/16" holes to clear the 10-32 mounting screws with all 5 plates in a stack. The template was removed. I then drilled the one bearing hole to 1" with the 5 plates still in a stack. I set the belts on the drill press to give the slowest speed possible to avoid any chatter once I went past 1/4". The height of the drill press table was set so that the shortest and longest bits would all work.

To go from 1" to 1 1/8", I clamped one plate in the vice, centered the workpiece using the 1" step on the step drill, clamped the workpiece down in the vice and to the table with a C-clamp and added a second C-clap to help steady the vise. The resulting hole was just under the size needed to insert the bearing.

I deburred the 1 1/8" hole and carefully adjusted the hole size by "scraped" the inside of the hole to get a slip fit on the bearing. The scraping was probably the most tricky part of the operation needing 3-4 iterations to get the right fit. It was done with a Spyderco folding pocket knife with a 2 1/2" stainless spear-point blade that was sharp and stiff. I have used for many things for over the last 15 years. I would not use a snap-off utility knife nor would I use a box cutter since those blades are not stiff enough for me to do this successfully.

I used a second template (made from the first) to drill the spacer made from a 3" long section of 1" x 2" rectangular aluminum tubing. I clamped the spacer in the drill press vise. and clamped the vise to the table with two C-clamps. I ensured that the spacer was seated on the flat section of the vise so that the hole would be as close to perpendicular as possible. The 19 holes were drilled to 11/64 since the mounting screws were 10-32 thread-forming types. All holes were drilled through both side of the tubing. As I moved the vice around the table, I kept the workpiece pointed in the same direction. The table and vice are not perfectly perpendicular to the drill bit. Drilling each hole with the workpiece held in the same orientation means that the hole in the back side of the tube (1" away) would be offset by the same amount. I then drilled the bearing hole out to 1/4". I then used my Blue Mol 1 1/8" hole saw to drill through each side. I know that my hole saw "wobbles" and give a slightly larger hole than the nominal size. This was so that the hole would clear the bearing.

The end result was that hole pattern on any mounting plate (9 mounting holes, 1 bearing hole) would match up with hole pattern on either side of any spacer. The parts were all interchangeable. When assembling the plates onto the two sides of the spacer, all 18 screws went in straight and bearings also went into the mounting plates without interference from the spacers, indicating that the clearance holes were sufficiently concentric with the tap or and slip fit holes. In all, this work took about 5 hours though I actually made four sets of spacers. I still have to make a second set of mounting plates for our other robot.


PS: Andrea, I just looked up the team you mentor. If we had not moved away from TO, my son would likely be on our team. We were living in a house just south of Yorkdale Mall. Congratulations to your team for making it to the finals of GTRE and winning "Highest Rookie Seed".

[roystur44]

Use a drill press with a c'bore tool like this one

http://www.mscdirect.com/product/006...&026=-99&025=c

drill a .250 pilot hole and use the pilot hole to guide this tool.

[catacon]

We have had great luck with carbide hole saws like this one. They get expensive in larger sizes, but they cut extremely nice holes.
http://www.grainger.com/product/IDEA...511?s_pp=false

[AndreaV]

That counter bore(basically a giant end mill) and carbide hole saw are beautiful!

I love machining! Just when you think you know what you're talking about there's a cool new toy or way to do the same job easier!

[pmangels17]

Whatever option you choose, if it is not carbide, make sure you use oil! Also, we bought a cheap mega-box of chip brushes at harbor freight. We use them to brush away chips whenever we are cutting anything. It helps the drill cut more efficiently and prevents chips from getting in the way of the oil (sometimes it helps if there is oil on the brush). Also, please be really careful to secure your work onto the machine otherwise it will wobble.

[Greg Needel]

I have had good luck with step drills and we use them quite often, specifically when just cleaning up holes cut on our cnc plasma.

A few years I found this http://www.mcmaster.com/#4080a26/=r1d6zv It works well if you are trying to drill a hole from nothing, I do recommend using a drill press for this, as it can still walk out like a regular hole saw, but the finish is much better.