Amateur question: drill press speeds

[ajchien]

Ok, ive got an amateuristic question ...

Why is the recommendation for drilling wood and softer materials high in the 2000-3000rpm range?

What happens if you try to drill wood at say 400-700rpm? For a 1/8" bit?

(When I use a handheld cordless or corded drill, I pay no attention to the rpm speeds ...)

 

[KinzeMech]

Time. You don't have to drill it at speeds that high, but when the equipment can take it, why not?

You can drill wood at 2000-3000rpm all day long, and you are not likely to overheat or break your bit. Drill steel at a speed like that, and it won't be long before the bit overheats, loses it's edge, and you're basically done cutting at this point.

It's probably worth noting, what kind of drill bit you are using makes a difference as well. (Note: I'm not a carpenter) From what I have observed, a twist drill doesn't much seem to care, but a spade drill really seems to smooth out at high speed, and be less likely to grab, especially while pushing through the backside.

 

[zkling]

In a word, efficiency and balance between work output and tool life. What you are asking about is called cutting speed, which is specific for each material. RPM is just a calculation of cutting speed and cutting tool geometry. IE why a 0.5" bit should spin slower than a 0.125" bit even when drilling the same material.

Here is a decent read

http://en.wikipedia.org/wiki/Speeds_and_feeds

http://www.wisc-online.com/Objects/MTL8202/mlt8202.htm

If you run too slow you are just not being efficient. If you run too fast you could damage the tool and the work piece by overheating.

Actually drilling speed is also a function of feed rate. You will see large CNC machines running 1000's of RPM to drill steel, something that would be absurd for a home DP. They can do this because the automatic feed is super fast. It's over before the drill even realized what just happened

 

[MFolks]

If you drill metal, use some form of coolant, to prevent overheating. For Aluminum, I use a squirt of WD-40 before, and during drilling.

Steel will require cool tool II(a coolant sold at machine shop supply stores). Check the label on the coolant, as some are not compatible with Aluminum.

And if tapping Aluminum or steel, use the correct tapping fluid, to reduce the chance of tap breakage.

 

[lilredex]

My drill presses never get out of first gear......and drill all sizes in wood and metal. The only time I use cutting oil is for spring leaves, etc. Most mild steel drillled is 3/8" max. thick and is drilled dry.....................works for me.

 

[kc-steve]

I agree with everything said above, except I will use a cutting oil when drilling steel because I never know when the drill bit overheats until it is too late. That saves me money from having to buy a "drill doctor." Am I cheap or what?

I have a lot of old unused oil sitting around worth using.

Steve

 

[R W]

Use the 2nd speed for up to 1/2". Use the slowest speed (125 rpm)for any drill larger.

 

[Trey T]

Drill speed vs manual feed rate is one of those question that's hard to answer and your solution is to experiment. Drill bits are relativelly cheap and you'll break the bits long before you can break a drill press.

Try it out!

 

[Ign]

Why is the recommendation for drilling wood and softer materials high in the 2000-3000rpm range?

What happens if you try to drill wood at say 400-700rpm? For a 1/8" bit?

I'm gonna argue it has little to do wth efficiency (science doesn't care if you get your work done quickly) and more with the realties of physics (term used broadly as I know nothing of physics per se).

Ever wittle wood with a knife and have the blade auger in? With time and skill you might correct this but the machine and the drill bit have no feel. Plus for heavy shaping cuts you might learn to go fast, but for fine tuning light cuts you can go slow.

Likewise, an 1/8" bit will "auger" into wood at 400 rpm, essentially trying to thread it's way into the hole. Eventually the wood gives or the bit breaks. If the former happens, you wind up with a poor finish in your hole. If the latter happens, you're probably not happy. This is even more true if you drill polyethylenes or brass.

I didn't click on the wikipedia links above, but there's also a concept known as tool pressure which has more to do with milling than drilling perhaps, but (some of) the concept is that sometimes it's better to quickly rip or cut something than to slowly do the same cut. Think pulling a bandaid off your hairy arm.

 

[offroadsteve]

I am going to agree with Ign and zkling ... what you are really looking at is the speed that the tool cutting edge moved over the material in inches / minute. This is a funciton of your feed rate, the material you are cutting, the size of your tool and your tool material. A larger drill bit needs to run slower because the tangental velocity of the cutting edge (at the outer diameter) is faster than a smaller bit for the same RPM.

Feed rates are a balancing act which tries to optimize surface finish, tool life, and cutting speed. Similar to the saying: you can get it fast, cheap or right. Pick 2.

This is all in the weeds for most woodworking since basically any tool is much harder than the workpiece, and surface finish isn't much of an issue. The only real problem you run into is what Ing pointed out above where if you run the drill too slow with a fast feed rate you will "auger" instead of drill.

Where all of this matters is cutting precision surfaces on harder metal workpieces. If your feed is too fast you will burn up the tool, too slow and the tool chatters and your surface finish is awful. The only application I can think of in woodworking is turning very hard wood on a lathe, feed rate starts to matter here as well.

The Machinery's Handbook has an entire section (over 300 pages) on feeds and speeds and optimizing cutting efficency. Very useful if your in the buisness of machining metal, not so much for anyone else.

 

[RogueFab]

Most of these guys have it covered. It is all about how much material the cutting edge of the bit is removing (thickness). I seem to remember .015" per pas is where you want to be on steel. I don't cut wood.

I have never used a drill press above about 1000 RPM on anything. I do like to go down to about 50 RPM for some metalwork though.

 

[Ign]

Most of these guys have it covered. It is all about how much material the cutting edge of the bit is removing (thickness). I seem to remember .015" per pas is where you want to be on steel. I don't cut wood.

I have never used a drill press above about 1000 RPM on anything. I do like to go down to about 50 RPM for some metalwork though.

I just drilled 460 holes thru aluminum with a #21 bit (roughly 5/32) at 1800rpm. Parabolic bit and I dunno what the formulas say about helix angle, but either way I bet I was running slower than would be recommended/calculated for such a small hole in a soft material. I could just pull out my references and figure it, but I don't care that much.

That said, the quality of your machine matters as much as anything. A nice rigid radial drill press or quality mill will out-perform a cheap bench top drill press and allow for higher feeds and speeds, all other things being equal.