Drilling 10,000 7/8" dia holes

[brgrii]

I have to drill 2 7/8 dia holes in 5000 pcs 6" x1.5"x1/2" thk hrs. I would just as soon save a step and not center drill them all. Any suggestions on the best way to go about this? I will be using a 12x25x6" CNC knee mill.

[Geof]

I think it is a toss up between using a short carbide drill and interpolating.

Through holes can be problematic because as the drill breaks through everything gets very hot; if you do not use coolant it can be hot enough to burn the cutting edge off the drill in addition to throwing up a horrendous burr. If you do use coolant then the intermittent cooling thermally shocks the cutting edge and you get microchipping and early failure.

I would be tempted to try one of the drill/mill cutters that has a drill point on the tip and milling flutes further up. Something like a 1/2" could possibly be punched through fairly quick just using a powerful airblast for cooling, then the same tool interpolates the hole out to 7/8" again with the airblast. A distinct advantage to this approach would be an absolute minimal burr on the underside.

[DareBee]

Sorry Geof - I believe this is the first time I have ever disagreed with you.

I say RotoBrute CT150 all the way.
http://www.championcuttingtool.com/rotobrute.html

Although - I would have tried to design the parts to be laser cut out of Plate stock.
Would save big bucks.

[Geof]

Sorry Geof - I believe this is the first time I have ever disagreed with you....

I'm not sorry, it just shows that I was taking a blinkered aproach. Yes an annular cutter is the way to go on that thickness. Truth of the matter is I have never used them so they do not come to mind.

[Caprirs]

What kind of tolerances can be held with those types of cutters?

[xclr82xtc]

waterjet...

[HuFlungDung]

I'm not sorry, it just shows that I was taking a blinkered aproach. Yes an annular cutter is the way to go on that thickness. Truth of the matter is I have never used them so they do not come to mind.

I used one of them once, in a setup on the mill. The cutter lasted all of 30 seconds before it shattered like a cheap toy. I didn't even begin to enjoy its functionality. I seem to recall some horrid stringy chips, though.

For this job, an insert drill would be great on a real machining center, but this is a quite small machine. So I'd use helical interpolation, with about 1/2" diameter carbide, to make the hole, then add a cleanup pass while the tool is extended through the part. It would be quick, the chips would not snarl up, and the thrust requirement is minimal, and no slug to contend with.

[xclr82xtc]

how many can you get in the machine in one go??? i would just try to do 10-12 at one time and run the center drill first. the cycle would be long enough to let you go do something else, but not so long that it hurts production.

[TheBigJW]

What about punching the holes on a punch press.

John

[DareBee]

I used one of them once, in a setup on the mill. The cutter lasted all of 30 seconds before it shattered like a cheap toy. I didn't even begin to enjoy its functionality. I seem to recall some horrid stringy chips, though.

You must have used the wrong brand Hu. A RotoBrute is definitely not cheap.
We can hand drill with these and not chip the carbide.
Very fast throughput in 1/2"
Yes; chip control requires a break-chip cycle

[brgrii]

Thanks guys . . .
1. I plan on stacking and drilling 8 at a time.
2. Unfortunately, the mill is old enough that it does not have helical cutting ability (Fanuc 3 control), it does have coolant though.
3. Laser cut has been quoted at 3 bucks each, holes and profile (2 corners have rads that I will cut later).
4. What about these drills with insert-able cutters?
5. I have my cutter tool guy looking into turning a 7/8 drill bit into a step drill with a smaller start hole, as well as some other options.
6. Our Whitney punch won't handle 1/2" material, besides methinks it would bend the stock anyway.

Thanks again, I'll let you know how it goes - If I fail, we will go to the laser quote.

br

[Geof]

Thanks guys . . .
1. I plan on stacking and drilling 8 at a time.....

4. What about these drills with insert-able cutters?

br

Stacking hrs can be problematic. It is not flat so once you go through the top piece you can have a little gap that tends to snag chips coming out of the hole on subsequent plates. In addition as the drill passes through from plate to plate it encounters the hard scale surface and can tend to wander. Over a distance of 4 inches this wander can build up to a considerable distance.

Insert drills may do it but I would not try stacking plates for an insert drill as they sometimes 'trepan' out a little disc of material as they break through. This disc then gets trapped and spins under the drill on the next plate down and everything can go downhill very quickly.