Drilling deep holes without high pressure coolant

[Just a Sparky]

Just doing some brainstorming for an upcoming project.

I will need to drill a 1/4" blind hole 12" deep into a length of 1/2" O.D. aluminum round bar for a fluid passage. I've heard a little about gun drills, but my understanding is that those rely on high pressure coolant injection for chip removal. I will be doing this operation on a 13" South Bend toolroom lathe not rigged for coolant.

Is it possible to get a nice straight hole that depth with a progression of twist drills? Are 1/4" twist drills available with flutes that long? Or am I going to have to peck in 1/16th increments?

Suggestions welcome.

 

[john.k]

as soon as the flutes load up ,the drill is forced off course.....consequently must be removed and cleaned before that happens......A straight flute,one edge drill will clog immediately ....a spiral flute will take a bit longer before the force required to move swarf along the flutes becomes excessive ,and jams up.

 

[muckalee]

What alloy is the shaft? Some aluminum is difficult to machine.

 

[Karl_T]

mcmaster sells 1/2 OD .26 ID tubing

 

[boslab]

We often cobbled a gun drill to a cheap pressure washer in work, sorry not a gun drill a through coolant drill, it’s jankey but it works, last go off we chucked 5 % dromus oil in the water, it’s bloody messy but works, trick was drill, ream to size then shove the cooled drill in, the reamed section guided the long drill.
Mark

 

[crossthread]

You asked if you could make a "nice straight hole". How nice and how straight? I have drilled plenty of holes that deep even using extended bits but how nice and straight they were is debatable. You said it was for fluid passage so I don't think the niceness or straightness is much of an issue. Yes you will have to do a lot of pecking but nowhere near 1/16" increments. Retract the bit and see how your flutes are loading up. That should determine when it is time to peck. Lubricate the heck out of the bit while it is out so the chips will slide up the flutes instead of jamming. My best guess is that you could go 1/2" between pecks. In my experience it is best to go with high revs and slow feed. The hole seems to stay straighter and the chips tend to feed better into the flutes.

 

[Gordon Heaton]

I personally don't think you'll get anywhere near 1/2" per peck. I typically get 1XD on deep holes but the alloy, lube and drill all have a lot to do with real life results. Most long drills still only have a few inches of flute which is just as well since chips won't clear any more than that without through-coolant pushing them out.

Like crossthread said, straight it won't be, and the more you cut between clearings, the further off it'll go. You also need as perfect a grind on the drill as you can get. If chip load is uneven side to side, the working flute will load up real fast and push things off even more.

 

[Scottl]

Try to find the old Popular Mechanics article Deep Hole Drilling online. They showed ways to make homemade deep hole drills used without pressure lubricant. I used the article as the basis for a tool made from drill rod to bore a .50 ca. brass cannon barrel. You do need a properly sized staring recess as the drill geometry is not self centering. Also, don't completely retract the bit from the bore when flushing chips or it will cut oversize.

PS: The article could also give hints on grinding angles for commercial single-point bits if you go that route.

 

[Karl_T]

What Karl said. One-thou over on the bore. Plug one end of the bore.

Now it is blind. Also faster and cheaper that making the bore.

D'you really think you will be able to hold to anything closer than one-thou?

Or even half as good?

Anyone else, I'd let it go. But since you are consistently a total jerk, do you not know .26 is 10 thou over not 1 thou?

 

[crossthread]

Gordon...I agree after putting my brain in gear. 1/2" would be wishful thinking. Maybe 1/4" but it still would be best to check the chip load to see how long you can go between pecks. patience is a virtue that escapes me from time to time.

 

[Just a Sparky]

Anyone know how feasible making a little plug weld in 1/4" aluminum pipe would be with a scratch start TIG torch? Sadly I don't have access to a foot pedal welder these days. I imagine timing and amperage would be everything. Too low amperage/too slow and the whole thing will puddle... too high amperage and I won't have time to work before the same thing happens.

I've got some beefy-ass contactors lying around. Big 150 amp things. Wouldn't give me amperage control, but I could rig footpedal start/stop. Better than nothing when dealing with aluminum?.

Or maybe I'd be better off drilling and tapping the end for... what? 1/8" NPT? 1/16"? Just plug it and be done. Trouble is the end of that part needs to have machine threads somewhere on it for a mechanical hold-down. NPT plug on the inside and NC machine threads on the outside? I'd need small enough OD threads to fit an o-ring over, but not so small as to interfere with the ID threads. Methinks some CAD visualization is in order.

 

[Gordon Heaton]

Hmmm. If I were going to try a weld without real-time current control, I think I'd torch preheat to at least 400F and try a relatively low amp setting. Current sufficient to use for preheat will almost certainly be too high for the weld.

 

[DDoug]

Anyone know how feasible making a little plug weld in 1/4" aluminum pipe would be with a scratch start TIG torch? Sadly I don't have access to a foot pedal welder these days. I imagine timing and amperage would be everything. Too low amperage/too slow and the whole thing will puddle... too high amperage and I won't have time to work before the same thing happens.

I've got some beefy-ass contactors lying around. Big 150 amp things. Wouldn't give me amperage control, but I could rig footpedal start/stop. Better than nothing when dealing with aluminum?.

Or maybe I'd be better off drilling and tapping the end for... what? 1/8" NPT? 1/16"? Just plug it and be done. Trouble is the end of that part needs to have machine threads somewhere on it for a mechanical hold-down. NPT plug on the inside and NC machine threads on the outside? I'd need small enough OD threads to fit an o-ring over, but not so small as to interfere with the ID threads. Methinks some CAD visualization is in order.

Use a drive in plug.
The Lee Company - Lee Plugs