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Drilling ID of small diameter steel tube

cobalt327

Plastic
Joined
Apr 27, 2016
I am enlarging 5/64” ID x 2” long mild steel tubes having no visible seam to 7/64” ID. I am using a very rudimentary method- a drill press spinning the bit 1750 rpm (I can go as high as 2600 rpm max) with the tubing held stationary in a Jacobs chuck. I am using a 135 degree cobalt bit and 5w 20 synthetic motor oil for lubrication, applied every pass. I am taking an average of 8 passes per tube, feeding “gently”. Each pass I back the bit out and clean the chips and reapply lube to the tube ID and the bit. Early in the hole, I am getting long strands that are ejected from the tube, later when the 1.4” long flutes are inside the tube, the chips are much smaller. I am getting around 40 pieces before I feel the bit dulling.

Should I increase the speed to 2600 rpm?
Is there a better lube that I can apply manually? How often should I apply it?
Would 118 degree bit be better? Would it work at all?

Thanks in advance for any help!

AIR TUBE B.jpg
 

spaeth

Hot Rolled
Joined
Jan 28, 2008
Location
emporium pa
Cobalt327,
I've had good results with both COOL TOOL and TAP MAGIC.
You can usually get a standard Cutting Oil at any hardware store which would probably be better than motor oil. Apply the lube with a plumbers acid brush to minimize usage and try every other retraction and a drop or two in the hole as you go deeper. Experiment with the RPM and the peck feed, if you get away with six pecks by the end of the hour you will have gotten more parts.
spaeth
 

cobalt327

Plastic
Joined
Apr 27, 2016
Thanks, all- I appreciate it.

Any opinions on RPM? I'm at 1750 rpm now but can go as high as 2600 rpm. Or slower, if need be.

And, is a 135 degree point preferred over 118 degrees?
 

Milland

Diamond
Joined
Jul 6, 2006
Location
Hillsboro, New Hampshire
A 3 or even 4 flute drill does a much better job in enlarging existing holes

Peter

At a cost of available flute volume for chip evacuation and higher drill cost. At 7/64 (~2,8mm), a quality cobalt drill is probably as good as he's going to find for this application.

I'd avoid carbide due to brittleness and the sketchy setup and machine process.

Change to a good cutting oil (whatever's available at your hardware store will likely do), and concentrate on removing chips from the drill flutes during the "pecking". As for drill life, I'd say (given the circumstances) you're doing pretty well.
 

Milland

Diamond
Joined
Jul 6, 2006
Location
Hillsboro, New Hampshire
Thanks, all- I appreciate it.

Any opinions on RPM? I'm at 1750 rpm now but can go as high as 2600 rpm. Or slower, if need be.

And, is a 135 degree point preferred over 118 degrees?

Stay with the 135/cobalt drills. As long as you don't get excessive heat buildup or faster drill dulling, sure, speed up to the max.
 

BT Fabrication

Stainless
Joined
Nov 3, 2019
find a reamer and slow it down a touch as you are at the high end of the sfm at 100. manually id be in the 80-90 so 10-20% slower, heat is all that gets produced when going too fast and that is what kills drill bits.
 
Joined
Jan 15, 2005
Location
The Netherlands
At a cost of available flute volume for chip evacuation and higher drill cost. At 7/64 (~2,8mm), a quality cobalt drill is probably as good as he's going to find for this application.

I'd avoid carbide due to brittleness and the sketchy setup and machine process.

Change to a good cutting oil (whatever's available at your hardware store will likely do), and concentrate on removing chips from the drill flutes during the "pecking". As for drill life, I'd say (given the circumstances) you're doing pretty well.


Well I am a metric man I had no idea it was that small:D
Should have done the math
sorry
But for bigger holes I stick to my statement

Peter
 

dgfoster

Diamond
Joined
Jun 14, 2008
Location
Bellingham, WA
Setting up a small tube/nozzle blasting compressed air across the tube opening can aid chip removal. The chips get blown out of the flutes instantly and completely where brushing them out is tedious and incomplete. A lube mister (Noga) can double as chip clearer and lube applicator. Koolmist is a safe(vegetable oil-based) and effective lube.

If you could set up in a lathe, a micro chuck adapter might make things go quicker and with fewer broken bits.
Denis
 

thermite

Diamond
find a reamer and slow it down a touch as you are at the high end of the sfm at 100. manually id be in the 80-90 so 10-20% slower, heat is all that gets produced when going too fast and that is what kills drill bits.

^^^ THIS ^^^

Helical twist drills are mean to GENERATE a hole. Not to enlarge one.

Everything about their working geometry is wrong once centre support no longer exists.

Try a common reamer, "core" drill, or "plunge" end-mill, given they are short holes..

"Piloted" reamer with high-pressure coolant might do very well.
 

Milland

Diamond
Joined
Jul 6, 2006
Location
Hillsboro, New Hampshire
^^^ THIS ^^^

Helical twist drills are mean to GENERATE a hole. Not to enlarge one.

Everything about their working geometry is wrong once centre support no longer exists.

Try a common reamer, "core" drill, or "plunge" end-mill, given they are short holes..

"Piloted" reamer with high-pressure coolant might do very well.

At that size and for that depth, a reamer will have the same issues a core drill will - too little flute space and poor chip evacuation, even with pecking. Higher cost per reamer and greater friction also are negatives.
 

cobalt327

Plastic
Joined
Apr 27, 2016
Thanks for all the replies.

The reason I was asking about the bit tip angle is to determine what drill bit sharpener I could use.

I'm guessing many of you sharpen bits by hand. I have a good bench grinder, maybe getting a fine grit stone for it and learn to sharpen my own bits is the way to go?

I have tap magic but thought the motor oil was doing fine, but I guess not! FWIW, doing it the way I am, the work is slightly warm to the touch immediately after finishing a hole. Might have something to do with flooding it with oil.

Oh, and the bits are $3.50 each after tax and shipping.

ETA, re cutting oil- I read the following from member '9100' about using a cylinder hone.: "Motor oil is formulated to stay in between the rubbing surfaces under all possible conditions. The cutting oil they used was designed to break down under the concentrated pressure at the points of grit. I was using an oil that did its best to keep me from removing metal."

If true, I suppose this make sense for a drilling operation as well as a hone...

Thanks again.
 
Last edited:

rogertoolmaker

Cast Iron
Joined
Jan 3, 2016
I am enlarging 5/64” ID x 2” long mild steel tubes having no visible seam to 7/64” ID. I am using a very rudimentary method- a drill press spinning the bit 1750 rpm (I can go as high as 2600 rpm max) with the tubing held stationary in a Jacobs chuck. I am using a 135 degree cobalt bit and 5w 20 synthetic motor oil for lubrication, applied every pass. I am taking an average of 8 passes per tube, feeding “gently”. Each pass I back the bit out and clean the chips and reapply lube to the tube ID and the bit. Early in the hole, I am getting long strands that are ejected from the tube, later when the 1.4” long flutes are inside the tube, the chips are much smaller. I am getting around 40 pieces before I feel the bit dulling.

Should I increase the speed to 2600 rpm?
Is there a better lube that I can apply manually? How often should I apply it?
Would 118 degree bit be better? Would it work at all?

Thanks in advance for any help!

What have you changed? You have been doing this for a while, so "what is different". Look at your old drills and compare to your new drills. Pay attention to the flute spiral and the cutting-edge differences. Maybe take an oilstone to the corners of the drill cutting edge to knock off the sharpness. Or resharpen the drill bit to reduce the rake. Change your lube? Maybe Lard in oil? Your RPM is O.K.
All the best.
Roger
 

dlaw

Plastic
Joined
Jul 27, 2012
Location
Minnesota USA
? Rig compressed air to the bottom of the jacobs chuck to blow out the chips & cool the drill. Adjust your feed so you do not get long chips & by all means ware face protection. With cobalt drills i would try 2600 rpm & see how it goes. How many of these have to be drilled out?

Good luck
Doug
 








 
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