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Drill bit recommendations

abstruse

Plastic
Joined
Jul 24, 2020
Greetings. I have to drill 35, 13/16" holes in a 6" mild steel pipe, .430" wall thickness. I want to be able to drill completely thru the pipe to insure reasonable hole alignment. I'll be using a magnetic drill.

Should I use a conventional twist drill or a core/shell drill for easiest drilling?

Thanx.
 
Core. But if you want to retail good hole alignment, you may want to make a drilling template first on a mill to help get the spacing right.

Do you need overall C-C accuracy, or just pitch (hole to hole)?
 
You are talking about an overall depth of 6 5/8". No mag drill I know of has that kind of spindle travel. Bridgeports could do the job if you don't mind cranking the knee up and down a lot. The ideal machine is a radial drill. You need an extended length drill to go all the way through the pipe. A conventional drill point is OK. A core drill is for opening up an existing hole.

If you are stuck with a mag drill you can make a jig that has bushings to line up a punch to mark the locations of both holes. Use an annular cutter to do each hole in one pass.
 
Look at the drill bits & core bits, as well as the mag drill travel (as mentioned above)
and walk thru the job. Taking everything into account.

I have an old B&D with a #3 morse taper, along with a tall column.
It might doo that job from one side, but only with a long twist drill, no core drill.

What is the job ?
 
I have a twist drill that will drill to 8". I didn't think about the quill travel limitation -- thanx!

I can make a jig that will clamp around the pipe and have a guide that will insure centered, perpendicular holes on both sides.

This is for a zip line for my grandkids. It's the second one I've made for them. It'll be 180' long.
 
Curious as to how you're using these on a zip line. I have a 400' line. I like to limit the rider's weight to 250#s. The riders sit in a bucket seat and I pull them up with an ATV so they get to ride both ways. Speed depends on line tension and rider weight but they come down 20 to 25 mph. A brake is essential. My 6 year old grand daughter has many 100s of rides and mastered the braking when she was 4.
 
I have a twist drill that will drill to 8". I didn't think about the quill travel limitation -- thanx!

I can make a jig that will clamp around the pipe and have a guide that will insure centered, perpendicular holes on both sides.

This is for a zip line for my grandkids. It's the second one I've made for them. It'll be 180' long.
Wrap around template and a plasma cutter....
 
Sounds like manual layout followed by centerpunching would locate the holes close enough.

When using my mag drill on round pieces, I have a piece of steel channel cut square and about 6" long. I tack that to the piece on both sides, at the end next to the hole. Then I fasten the mag drill to the (flat) channel top and use the tit on the pilot to pick up the centerpunched hole, then drill. A rotabroach style bit would work great for your purpose.

This isn't channel, but it's equivalent:

cleanoutHoleCutSetup.jpg


Note that the mag drill in the above picture has a Morse taper spindle so I can use a chuck in it - very handy indeed.

metalmagpie
 
You are talking about an overall depth of 6 5/8". No mag drill I know of has that kind of spindle travel. Bridgeports could do the job if you don't mind cranking the knee up and down a lot. The ideal machine is a radial drill. You need an extended length drill to go all the way through the pipe. A conventional drill point is OK. A core drill is for opening up an existing hole.

If you are stuck with a mag drill you can make a jig that has bushings to line up a punch to mark the locations of both holes. Use an annular cutter to do each hole in one pass.

I think you should use the core drill.
Get an extension for the bit, after the first hole pull the drill up on the quill, and insert the core and extension.

Might be easier to have 2 of the same core, and one with the extension already mounted.

Just my opinion, like everything else you mileage may vary.
 
I think you should use the core drill.
Get an extension for the bit, after the first hole pull the drill up on the quill, and insert the core and extension.

Might be easier to have 2 of the same core, and one with the extension already mounted.

Just my opinion, like everything else you mileage may vary.

Is the OD of the core extension going to be smaller than the hole ?
 
You are talking about an overall depth of 6 5/8". No mag drill I know of has that kind of spindle travel.

Some of the lighter drills, like the Milwuakees, let you slide the power head up and down and then clamp it in place.

Have you asked your local steel yard what it would cost to have it drilled on their beam line?
 
cleanoutHoleCutSetup.jpg


Note that the mag drill in the above picture has a Morse taper spindle so I can use a chuck in it - very handy indeed.

metalmagpie

I am looking for a more modern (and lighter) mag drill, have not seen that one before.
Is there a manuf name ? a website ?
 
I am confused. I see core drills mentioned. Is the term core drill used with respect to an annular cuter? To me core drill refers to a multi flute drill that is not center cutting.
 
in the pipe world, there is a thing, ususally found at a welding supply shop. its called a pipe wrap for doing this exact thing. wrap, scribe a line and it has measurements on it also.

and yes, go mag drill and annular cutter, or torches or plasma cutter. all will work.
 
My 35 yr old import mag drill will certainly drill 7 - 8” deep with one reposition of the drill motor in the T_slot carrier. One of the reason I bought an import at the time. But it can be a factor for some models.

A roto-broach style tool has a small enough 3lobe shank that it could be used first in the chuck for the face side hole. Then removed & put in the end of a purpose built shank with set screw drive to continue through the other side.

If you drill through 2 sides of anything, be sure the nest of shavings and the slug are not laying in a position on the bottom to snag & break the center drill or broach. Also be sure on the bottom with a concave surface or possibly even the weld that the center/pilot drill projects far enough to guide the rim of the broach before it contacts & initially feed the rim gently on the uneven surface until it is cutting all the way round.

Alternately drill a 6mm hole (pilot drill size for that size rotobroach IIRC) with a short drill, then a longer drill to pop out the other side. Then use the rb through the pilot from each side. Don’t get sloppy - rb types at least carbide versions are somewhat delicate.

smt
 








 
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