drilling long thin holes

[jtrout13]

Hi all, sorry to bother, but could not find any good info on this..

I am building a Elmers #2 wobbler, which requires me to drill a hole
through the column for air intake. It is 1/16 diameter, and 1.25 inch
deep. I have broken 4 drill bits already, and remade the part twice
because I couldn't get the bits out. Even the electron discharge
machine couldn't burn them out.

Do you guys have any suggestions on how to prevent this breakage?
This operation is being done on a Smithy Granite series combo machine,
although if necessary I suppose I could do it on the Bridgeport mill. The
workpiece I am drilling is 6061 T6 Aluminum.

Do you think spindle wobble is to blame, or heat? I am using cutting
oil to lubricate, and am only drilling 0.1 inch at the time before pulling
the bit back out, clearing chips, and relubricating. Nonetheless, the bits
break around 0.6inch depth. I can't even get halfway, so I can't really
flip the part over and drill halfway from both sides.

Help a student engineer/ self proclaimed machinist out!

 

[don-tucker]

I don't know the exact application but with drilling small holes you must keep the speed up high and easy on the feed,is it possible to drill from each end,keep withdrawing the drill to clear the chips and use some lubication.
Hope this helps
Don

 

[jtrout13]

What speed do you recommend? I was drilling at 1500 rpm. I know the
speed/feed chart says you can do about 6500 RPM in Al at that size drill.
Machine maximum speed is 3000, do you think that would really affect it?

I was afraid that the faster I went, any spindle wobble would flex the
shaft of the bit faster and faster as RPMS increased, leading to a fatigue
failure.

 

[arnoldb]

Hi jtrout13

How fast are you running the drill bit ? - small drills want a lot of speed.
Did you start the hole with a punch mark or center drill and exactly on center of such start ? - if you're not working very straight, the drill will also break.

For small drills, you need a "light" feed otherwise the drill will bend and surely snap.

What cutting oil are you using ? - is it synthetic and rated for aluminium ? - try some paraffin or WD40 as alternatives.
I work aluminium with methylated spirits (rubbing alcohol) as lubricant, but it is a bit flammable - so use at own good sense.

If you still find it happening, try to take and post a photo when you had part-drilled the hole, so that we can get an idea of your setup.

I see Don posted while I was busy, and you answered - go up to 3000RPM - once you start the hole, the high speed actually helps keep the drill straight.

Regards, Arnold

 

[bearcar1]

JT, here is a posted response to another member a few days ago encountering the same problems.


........ the major factor that contributes to drill bit breakage is advancing the quill too fast. What happens here is that the flutes of the bit get packed with metal bits and do not have time enough to be ejected clear the hole site and ultimately, as more and more cut metal packs into the already confined space it reaches a point of "no where else to go" and essentially binds the bit to the hole wall and *SNAP* scratch one drill bit. Not having the part being drilled securely held will couple with the bit flexing and will also lend itself to disaster. All of this may sound scary as the dickens but it does not have to be that way. #1, allow the drill bit to do the work, not the ham fisting that some operators employ. Be sure that the bit is sharp, if it is throwing a chip it is cutting, be gentle and apply only enough downforce to sustain the cutting action, no more, no less. #2, don't be in a huge rush to finish drilling the hole in one fell swoop, take your time and back the bit completely out of the hole to clear the chips out, both in the hole, as well as any that have built themselves up on the drill. Do it often and in shorter intervals as the hole depth increases. Use a lubricant (ooohhh ), this will help to wash chips away as well as reduce the heat buildup. #3, hold the part securely in a vice and provide some means of securing it down, remember, you're not boring holes in wood but are attempting a deep drilling operation in a piece of metal. Doing this will keep the piece from applying any side loads to the bit in use. If you follow these steps your chances of success will increase ten thousand fold. Take your time, clear chip build-up, and keep the piece rigid at all times. You'll do just fine, good luck and let us know how you made out.
Regards
BC1


BTW, just how much spindle wobble are you speaking of? A higher RPM spindle speed would certainly help, but it will not overcome obvious machine defects.

BC1
Jim

 

[mklotz]

Three thoughts...

Get one of these...

http://www.littlemachineshop.com/products/product_view.php?ProductID=3790&category=

(less expensive versions are available)

Use kerosene as your drilling lubricant for aluminum.

Clean the drill thoroughly with a toothbrush every time you withdraw it.

 

[SAM in LA]

I just had the same problem that you are having while building the same engine. :wall:

First, save the broken bits, you can use them for the crank pins. :idea:

I used WD-40, very light pressure and with drew the drill and cleaned it frequently.

Make sure that the work piece is held securely and center drill the hole location.

Slow feed, lots of lube and frequent cleaning.

SAM

Just been there and done that.

 

[kvom]

Another idea is to determine if the plans permit a larger hole, and increase the size of the drill bit for more rigidity. Possibly drill part-way with a 5/64 (for example) and then 1/16 the rest of the way.

Definitely crank the speed as high as you can.

 

[jtrout13]

SAM, what speed did you use when drilling? I am center drilling
my holes as well. I don't really want to have to get on a Bridgeport
to do this, I am considerate and would rather let guys with larger
projects use them.

 

[mocaquita]

Drilling small holes can be tricky. Most of the problems involve getting rid of chips. Bearcar1 covers it pretty well. I would like to add that small drills need to be running true. Small drills do not handle runout in the chuck very well. Use your best chuck. Drilling down .100 at a time is too much. Try going only .020 or .030 for a peck depth, use a lubricant, a light feed and if available, air will help to get rid of the chips. You may have to take a peck without cutting to make sure the hole is clear. When breaking through the bottom be very careful and go slow. This is another good spot to break drills.

Dave

 

[rake60]

I remember fearing the deep 1/8" holes the Elbow Engine.
They were somewhere around 2-9/16" deep in aluminum.

I borrowed a 3" long 1/8" drill bit from a maintenance man at work.
He loaned it to me on the condition that if I broke it he'd.....
We'll there were conditions.

First I drilled the hole as deep as I could with a standard bit.
Very light pecks, fully withdrawing the bit between pecks and if the chip
was spinning on the bit, I'd stop the machine to clear it.

Personally, I don't use a lubricant to drill aluminum. I run it fast and
take little bites. You can't get greedy!

Rick

 

[SAM in LA]

SAM, what speed did you use when drilling? I am center drilling
my holes as well. I don't really want to have to get on a Bridgeport
to do this, I am considerate and would rather let guys with larger
projects use them.

The speed was approximately 2000 RPM.

I broke 4 bits.

I went and bought 4 more and didn't break any more after that.

 

[substandard]

You might want to check the run out on your set up. The smaller the bit size the more sensitive it becomes to run out. Somewhere in my buying/trading of shop treasures I ended up with a small Jacobs brand drill chuck mounted on a 0 morse taper arbor. It was meant for a Sherline or similar machine.

I chucked the arbor in the lathe and turned the morse taper into a straight length. It ended up being a 13/32 diameter, which is an odd size, but I have a 13/32 R8 collet for the mill. I have drilled as small as #56 with no broken bits. Following the same advice given above about slow feed, hi speed, pecking etc.

Another tip when using a drill chuck and a small diameter bit, is to tighten the chuck all around. Use your chuck key to tighten the chuck at all three holes on the chuck body.

Oops just saw that DaveB had already mentioned the run out..