Drilling metal - speed charts vs reality

[zze86]

Looking at drilling into steel and aluminum. Mainly plates and sheet.

So I was looking up some speed charts to put next to my drill press and found that many of the speed charts recommend high RPMs. I was always under the impression, as a general rule, that the harder the material and the larger the hole the slower you wanted to go. So I was kind of surprised that many of these are recommending 1000rpms for 1/4"-3/8" holes and 3000rpms for anything below that.

Seems high and likely to produce a bunch of heat...? Doesn't that kill the drill bit? Should I be going with these recommendations or backing off the speeds a little? What has experience shown you?

Forum won't let me link sites so here's a pic of one I grabbed off the net.

for

 

[woodchucker]

Looking at drilling into steel and aluminum. Mainly plates and sheet.

So I was looking up some speed charts to put next to my drill press and found that many of the speed charts recommend high RPMs. I was always under the impression, as a general rule, that the harder the material and the larger the hole the slower you wanted to go. So I was kind of surprised that many of these are recommending 1000rpms for 1/4"-3/8" holes and 3000rpms for anything below that.

Seems high and likely to produce a bunch of heat...? Doesn't that kill the drill bit? Should I be going with these recommendations or backing off the speeds a little? What has experience shown you?

Forum won't let me link sites so here's a pic of one I grabbed off the net.
View attachment 404161
for

That seems about right.
Larger bits slower.
3/8 is not big


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[woodchucker]

That chart is incorrect, I believe. Steel should be slower than al.
1/2 I spin just under 1000. In al it cuts easily without overheating. Steel more force lower speed.

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[MrWhoopee]

Get rid of that chart, it's far too general (and inaccurate) for metal-working.

Cutting speed x4/dia.=rpm

Here's a good cutting speed chart.

Cutting Speeds

This page gives cutting speeds for turning, milling, and drilling of several different materials. It includes a calculator to figure the spindle speed required.

littlemachineshop.com

Just for starters, in 1018 steel a 1/4" bit should run about 1200-1300 rpm, 900 rpm for 3/8" and 600 rpm for 1/2"
Harder/tougher steels, run slower.

 

[woodchucker]

Where'd that chart come from?

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[zze86]

Where'd that chart come from?

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Image search on Google. Googled "drill speed chart" and it was the second image. But again, multiple charts were similar.

 

[zze86]

Get rid of that chart, it's far too general (and inaccurate) for metal-working.

Cutting speed x4/dia.=rpm

Here's a good cutting speed chart.

Cutting Speeds

This page gives cutting speeds for turning, milling, and drilling of several different materials. It includes a calculator to figure the spindle speed required.

littlemachineshop.com

Just for starters, in 1018 steel a 1/4" bit should run about 1200-1300 rpm, 900 rpm for 3/8" and 600 rpm for 1/2"
Harder/tougher steels, run slower.

Thanks! I'll have to play with that and make my own chart then.

 

[zze86]

Is the drill bit type important when drilling metal? Seems like a 135* bit is preferred for metal but wasn't sure about the "twist" vs "bullet point" like in that chart.

 

[MrWhoopee]

Is the drill bit type important when drilling metal? Seems like a 135* bit is preferred for metal but wasn't sure about the "twist" vs "bullet point" like in that chart.

I've never seen bullet point drills used in metal. They're generally for wood and plastics AFAIK. I wouldn't bother simply because of the difficulty of resharpening.

 

[ErichKeane]

I think that chart has odd numbers as well... I checked on FsWizard (BTW, the 'pro' app is also really useful!), and for a 3/8" HSS Twist Drill, 6061 is 4280 RPM, and 1018 is 786 RPM. So that chart would have you spinning quite a bit slow for aluminum, and a bit fast for steel.

For a 1/8" drill bit, my app says 10,000 and 2359 (though 10k RPM seems to be the app's max RPM).