How to Drill STRAIGHT Long Holes?

[Phil3]

As a novice hobby machinist, this may be a very basic question, but how does one drill a very straight, long hole? For instance, how is a rifle barrel bored? This may be just a .220" diameter hole that is up to 30" long. I figure if it goes off center a bit the barrel can be turned to be concentric around the bore, but what if the bore starts to curve? I am not making barrels are anything, but as a firearms enthusiast, just wondered how this was done.

Phil

 

[Tom Griffin]

Phil,

Deep holes are drilled with a special carbide tipped single flute drill that is also hollow so pressurized coolant can be used to flush out the chips. They are aptly called gun drills. Once the drill is started, it is self aligning and can drill straight over long distances with very little wander. I have used them to drill deep holes in wood, but so far not metal. That may change however since I am contemplating making the barrel for my Steven's Favorite project.

Tom

 

[DMS]

There is also something called a "d bit". They are shop made, basically a rod the diameter you want the hole, with a D shape cut on the end. They cut _verrrry_ slow, but give an finish akin to a reamer, and go straight as long as you get them started straight.

Here is a pretty good discussion of them

http://www.homemodelenginemachinist.com/index.php?topic=5251.0

 

[Kevinb71]

Don['t mean to steal this thread, but do you actually "drill" the hole with the d reamer? Or does it just finish it to size. Oh and yes I am a newbie

 

[12bolts]

...they can bore straight down and then make a right hand turn...

Sorry this is the best picture I could find at short notice.

This is not a very good picture, and is only a model of the real thing but the three cutting heads can be controlled independantly and extended and retracted radially. This allows the drill head to cut on one side only, thus enabling directional boring. They are driven on long shafts that allow flexibility, but wont make a right hand turn, just a right hand curve.

Cheers Phil

 

[Tom Griffin]

Rotating the work self centers the bit. Rotating the bit can lead to interesting results, with well drilling in mind. An article I was reading said they can bore straight down and then make a right hand turn. It didn't say how that was done, but I want one.

Yes, gun drills are normally used that way; with the drill held stationary and the part rotated.

Tom

 

[4GSR]

Sorry this is the best picture I could find at short notice.
View attachment 35535
This is not a very good picture, and is only a model of the real thing but the three cutting heads can be controlled independantly and extended and retracted radially. This allows the drill head to cut on one side only, thus enabling directional boring. They are driven on long shafts that allow flexibility, but wont make a right hand turn, just a right hand curve.

Cheers Phil

Those can drill "Doglegs" too!!! If not controlled properly.

 

[DMS]

Don['t mean to steal this thread, but do you actually "drill" the hole with the d reamer? Or does it just finish it to size. Oh and yes I am a newbie

Yes, you actually drill the hole with the D bit. You do need to start the hole with another drill so that it is the right diameter, and so that the hole is deep enough for the D-bit to enter up to the solid part (the part after the "D"). The main thing to remember is to use lots of cutting fluid, and clear chips OFTEN, as they have a tendency to bind in the hold if you don't.

 

[kdupuis]

For 12bolts picture you would use a mud motor that has an angle to drill an oil well with a kickout to go horizontal.

 

[brucer]

gun drill,

The gun drill I ran, the part did not rotate..

We used a gun drill to drill waterlines in mold bases and cores and cavities..

the gun drill looked somewhat like a boring mill but it has a guide bushing that the shank of the drill ran in for alignment..

You bolted the part to the table, we used alignment blocks in the keys of the table, they would also act as positive stops...
We used single point carbide tipped drills, they were also hollow.. We used a high pressure cutting oil, and the drill is feeding quite fast like 10-15ipm, and it would leave a mirror finish in the holes.. the brand of drilles we used were Sterling..




We also had a gundrill attachment for a cnc boring mill..


also if the gun drill was passing all the way through the part, you had to have a piece of stock clamped on the back of the part, if not the cutting oil would blow all over the place.

http://gundrillingsolutions.com/index.html