Which way to Make a Hole

[Andrew R Stewart]

I have a very basic question about which way to cut an aprox 2" hole in 1/4" 6061 plate. The two abilities I have are:

A rotary table and use an end mill. Drill a hole to admit the end mill and slowly spin the table around cutting the circumference. I suspect a smaller diameter end mill, maybe 3/8"?

Or using a boring head. If I went this way i would think about hole sawing first, I have a 1.75" hole saw as example.

Backround. I am no machinist (as you all can tell by what I ask and how i ask it) but am muddling along. I have a bicycle floor pump (Zefal Double Shot, out of production for a couple of decades but perhaps one of the best bike pumps made) which has too much plastic in its construction. One of the folding feet broke off and I want to make a new base that will sandwich the existing base. The base is about 2" in diameter. There's no need for precision, pre mill days I would run a series of small drill holes around the hole's ring, punch out the blank and file the rough edge to fit. Now that I have a mill I have a good excuse to use it with this repair.

So the question is which way is easier, faster, stupid to consider... Andy

 

[Dhal22]

Will a hole saw work?

 

[jwmelvin]

Hole saw works pretty well. Even better if you can drill some smaller holes around the cutting path, to give chips a place to go. Otherwise, withdraw the cutter frequently and clear its teeth of chips. Then use a boring head if you need a better hole (size, circularity, finish, etc.).

 

[RJSakowski]

Either the end mill/ rotary table or the boring head will give you an accurate hole. 1/4" 6061 is no problem for either. A 3/8" end mill will work fine. You could use a 1/4" too. If using the end mill I would cut the hole slightly undersized and finish to size. Ise WD40 or other suitable lubricant t prevent galling. An undersized hole saw could be used to cut a starting hole bit isn't necessary,

 

[Winegrower]

I have a 1.5” end mill that I start these kind of operations with. Drill a smaller pilot hole, run the end mill through, then enlarge as needed with a boring head. Also, you might use a 4 jaw or faceplate on a lathe, and if that was feasible, would be my first choice.

 

[MrWhoopee]

Hole saw and bore. Much faster to set up and finish.

 

[mksj]

Annular cutter and boring head depending on the accuracy of the hole needed. Annular cutters give a very clean hole, I have bored 1.5" x 2" from two direction to core (4") from solid steel rod. Aluminum, rough cut with a hole saw and followed by a boring head, or use an orbital jigsaw with a metal cutting blade to rough out the hole and then a boring head. Worked with another forum member just recently that needed several 2 7/8" hole in 1/2" steel plate, ended up using a 2 3/4" annular cutter followed by the boring head. He initially tried it with the boring head alone which didn't work in steel. End mill in a rotary table, will most likely give a poor cut if cutting both sides of the hole at the same time, but would work as a finishing diameter with climb cutting.

I have used hole saws in plate aluminum, up to 3.25" holes, cutting was not so good and the teeth tend to load up. Annular cutters you use much lower speed with even continuous pressure and get long ribbons of metal peeling off. Do not peck with an annular cutter, but back out occasionally to break the swarf.

 

[Lo-Fi]

I've used the end mill and rotary table approach many times myself with excellent results in both steel and aluminium. The biggest challenge is work holding, but it's nothing a few strategically placed holes in the waste stock and a sacrificial layer on the table can't solve. Annular cutters are great, but a 2" one will cost you a small fortune.
I've had success with HSS hole saws in thicker stock too, the trick with them is to clear the teeth regularly.

 

[Batmanacw]

An annular cutter will usually make a hole within a few thousandths of your desired size. I stop feeding every few seconds to break the chip so you don't birds nest. Buy the cheapest one you can find on Ebay. Lots of wd40.

Of your options I'd drill and bore.

 

[Mini Cooper S]

Hole saw and bore. Easy setup and much faster. I make parts for a customer that requires just that, biggest problem is clearing the chips while sawing. I use a course tooth blade and lub with TapMagic (For aluminum) and a brush to clear chips.

Richard