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Any suggestions running a spade drill for this application.

INCONELDAVE

Aluminum
Joined
Mar 29, 2014
Location
PA
Before I start I claim complete ignorance never having used a spade drill! that said.

Machine VMC no TSC ,no High pressure coolant. I am drilling it to dia. 1.40 +- .010
about 6" inches deep in an aluminum forging

Only 7 PCS total.. picture a 1.71 dia held in a fixture(No it wont fit in a lathe)

also was planning on altering the insert grinding the dia from a stock 1.406 dia to 1.394 dia
with .12 rad on the 2 corners for the form at the bottom of hole.

what happens if I drill a smaller pilot hole (I cant visualize this being a good idea) or just go for it?

My smaller machine has thru spindle high pressure but I have the larger basically ready to go setup wise.(not a deal breaker thou)

So anybody???? fire away!
Thank you
 
I've only played with a few spade drills, but I'd imagine if you keep a few things in mind, it'd go fine. I know that spade drills take a large amount of Z force to cut good but your diameter is not that big for a spade, it's aluminum and I don't know why a pilot drill wouldn't work fine to get the spade humming. I imagine you would need a good chip load to break the chip. Are you boring it after drilling or holding size with the drill?
 
I've only played with a few spade drills, but I'd imagine if you keep a few things in mind, it'd go fine. I know that spade drills take a large amount of Z force to cut good but your diameter is not that big for a spade, it's aluminum and I don't know why a pilot drill wouldn't work fine to get the spade humming. I imagine you would need a good chip load to break the chip. Are you boring it after drilling or holding size with the drill?

Hopefully, Drill and done 125 finish
 
Most spade drills do not like pilot holes. If you look at the AMEC catalogs, they tell you not to drill pilot holes for most of their lines of spade drills.

If you must, spot drill using a shallower drill tip angle than your spade drill so the spade starts cutting at its center rather than its edges.
 
Just go for it... poke that sucker...

You shouldn't have any problems holding a 125 finish with a spade drill and usually they drill pretty close to size of the bit. You might get away with it in aluminum but I've never had much luck trying to sharpen or alter the corners, may cause it to want to walk a bit opening the hole some. Only time I use a pilot is when drilling 3" and bigger. Good luck!!


Brent
 
I drilled a 2"+ hole in A36 3 1/8" through but drilled a 1"pilot first for the larger spade pilot arbor. Hole finish was not important as further work was to be done. This was on a BP clone with 3HP. Your machine should be able to screw a larger spade through without the pilot. Some of those drills are rated to almost cram through. I would ask your tool pusher what the advised speeds & feeds to use, he should know or figure out the best starting points.
 
I was also wondering about chips not evacuating? I have the option of drilling a .94 hole first from the other end giving chips a place to go.
I just dont see good things happening when that spade drill breaks into the .94 hole.

After reading your replys I thinking go for it and may the chips be damned.
Thanks guys
 
Followup!!
So I finally got to this project Thanks for the info everyone.:cheers:DSCN1157.jpg


800 rpms 12 ipm 6.149 deep . no thru the spindle coolant.
Had to alter the width of the insert (1.406 to 1.395 dia) and .120 radius on the corners.

one shot ran fine ,I closed the doors glued my eyes to the spindle meter with my finger on the reset button.

also used a boring cycle so the spindle shut off at the bottom of the hole after a .5 dwell (had to hold depth)

I experimented with a scrap block ...definitely cant peck or dwell a spade drill.

I also rounded the flutes to the .120 radius .Dont know if it made any difference ?
 
i have used spade drills with spot holes all different angles, pilot holes, and peck drilling mode on easily tens of thousands of holes without the slightest problems.
.
yes if you have a long spade drill it is normal to use slow rapids to help hole reentry. obviously a long spade drill sagging or bouncing around from coolant hitting it should not be slammed at high speed at a hole reentry during peck drilling. i drill plenty of deep holes over a foot deep with spade drills and the full peck getting chips out of the hole and coolant washing the spade drill is necessary or better on deeper holes
.
on long over 18" long twist drills it is common when after a shorter drill was used for the longer drill to be fed in the hole at 2" a minute at slow rpm to help hole reentry, then obviously feeds and speeds are increased once in to hole. sure a 18" long drill bouncing over 1/4" from coolant should not be slammed into a existing hole at high speeds.. thats does not mean peck drilling is not used millions of times a year without problems if done properly.
 
I have only used spade drills on screw machines and on them the spot drill would have a steeper drill tip angle for the following drill to follow. I would appreciate your thoughts on this.
Most of what I (think I) know on the subject is taken directly from the drill maker's literature. Most spade drill designs do not guide well on their lips, so it is preferable to use a shallow spot drill so the following spade drill will guide on its point. Ultimately, production is the proof, so if you've got a routine which works, then it works.
 








 
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