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Drilling Holes In Carbon Steel

fstdril

Plastic
Joined
Feb 18, 2020
Hi,

I am looking for the most efficient way to drill approx 65 - 7/8" dia holes in flat, 1 1/2" thk carbon steel plate on a CNC mill. We currently use a high speed drill for this operation which seems time consuming with the pilot holes, pecking, and slow feed drill rate.

We have heard the Sumitomo 3xd replaceable thru coolant w/ 7/8" dia drill tip inserts would work best for this operation.

Is this the way to go? Other suggestions?

Thanks,
 
Sounds good, Thank you. Ever had any issues with the tips breaking midway through a hole?

So far only when an operator isn't paying attention to their inserts or when through spindle coolant isn't available. Once you get your speed and feed dialed in with either of those drills they have great life. The Iscar 2 flute Sumocham drills come in a fairly wide variety of geometry designs, so if one of them isn't quite working you can try another.
 
We have heard the Sumitomo 3xd replaceable thru coolant w/ 7/8" dia drill tip inserts would work best for this operation.

Never had any luck with the Iscar Chamdrills I'd stay away from those, they just haven't worked like they claim, at least for me.
However the Sandvik 870 drills are really, really good! And don't forget to look at Kennametal etc.. each big name brand has their own replaceable tip drill and they are all pretty much similar in performance.

Do you know the exact type of steel you're drilling? Carbon steel plate can mean a million different kinds of steels.
 
Straight shank, 3/4 or 1/2" shank S&D 135 deg HSCO 7/8" drill - 442 RPM 7.2 ipm. 7/8" does not need a pre-drill. G73 high speed peck to eliminate any long errant chips. Try 3-5 pecks total to start.

Drill time - 0.1 clearance plain - 0.18 tip length plus over-drill - 1 1/2" stock - 1.9" cut length X 65 = 123.5" LOC / 7.2 ipm = 17 minutes.

4 pecks costing you maybe 0.4" X 65 = 26" / 7 = 3 3/4 minutes.

Let's call it 21 minutes.

Chamfer both sides with long neck 1/2 carbide DA cutter from Harvey or the likes. (3.1415 X 0.375 tool path D) +(0.2 lead in lead/out) X 65 X 2 = 179 LOC / 30 ipm = 6 minutes.

In the cut time for job around 28-30 minutes.

In short, if you had just loaded a drill on hand and started drilling instead of posting here you would already be done and on to the next job.

With a rigid setup and proper coolant concentration the drill should make it through the whole job without a problem.

If this is a repeat job and you have no drill yet on hand then by all means, go the high route. But remember the basics is just about a half an hour w/ 2 sided chamfering.
 
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