Drilling Speed Chart

[Randy_]

I just received a solicitation for a magazine subscription and included was a drilling speed chart.

The question of correct drilling speeds for pen blanks is controversial and there is significant disagreement of what is best. I recognize that not everyone is going to agree with the information in this chart; but thought I would post it anyway since there are so many questions asked about this subject. For people who are unsure about drilling speeds, this will represent a starting point if they are having problems and if they are unhappy with the results, they can experiment with speeds other than what are suggested.

It is worthy of note that that all of the speeds recommended in the chart are for new drill bits in face grain drilling. There is a note that speeds should be reduced for drilling in end grain (which is what about 99% of pen blank drilling is); but there no recommendation of how much of a reduction is needed.

There are a couple of mistakes/omissions in the chart and I am currently in contact with the editors about fixing these. There is also another chart with more extensive information; but is has so many mistakes, I really don't trust it very much. If the editors can get that one cleaned up, I will post a link to it later and/or put it in the IAP Library.

Here is the chart:

http://www.ibiblio.org/twa/info/drillSpeedChart.pdf

 

[Paul in OKC]

Wow, I wonder if anybody tried those out before putting them on a list! There are some pretty fast speeds in there, especially for steel. I wouldn't run any of the speeds they recomend even as a starting point, but hey.... As for the wood speeds, like you said, there are many different opinions about that, but I think the chart is a bit fast for them as well. I drill at around 750-850 for all woods and acrylics.

 

[Randy_]

The speeds for drilling steel certainly do look a little fast; but I looked at the chart that came with my drill press and they were even higher?? Other than drilling a little sheet metal around the house and a few bed rails for home projects, I have little experience with steel so you are certainly the expert.

I know there is a handbook for machinists. It would be interesting to see what they have to say about drilling speeds for the various metals listed..

I wonder who might be considered an expert (or at least highly knowledgeable) about drilling wood and what their recommendations might be??

 

[Daniel]

I'm not an expert but I do know quite a bit about why a drill bit is made the way it is and how it is meant to work.
First and most obviously it is supposed to make a hole in various materials. so take the standard twist bit that is good for wood, plastics and even metal. It is a fairly good bit for general use although you could easily get a better bit specifically for any of those materials.
Most people would think the very end of the bit is doing all the work of making the hole. But it is not. the sides of the bit are what actually determine what quality of a hole you end up with. they are not only making the last little bit of cut, they are burnishing the walls of the hole and making it smoother.
The very end of the bit or chisel edges is actually hogging out all the stuff that needs to be removed from the hole.

there is also the twist in the flutes of the bit. the truth is that a bit does not need these at all to cut a hole. what they need them for is to remove all the waste wood pieces. this workes better at some speeds than others depending on the size fo the bit (size of flutes) since forces tend to cause the chip to want to stay at rest, a faster moving bit has a better chance of scooping it up and getting it to slide up the flute against gravity and out of the hole. but his effect has a limit so at a point faster is not better. having the bit removing chips at it's max helps reduce friction and heat it also allows the energy applied to the bit cut hole and not drag debris around the walls of the hole.
In the end drill speed actually has more to do with how much you will have to attend to the bit clogging, which in penturning it is going to do at any speed, than anything. you can actually get a bit so clogged it will damage the walls of your hole. anyone actually melted the walls of an acrylic blank? or burned the walls of a wood blank.
I have drilled blanks with my press at top speed and at it's slowest speed. there is a difference but either works.

 

[Paul in OKC]

Don't mean to disagree, Daniel, but the very end of the bit can determine the size of the hole. I can make a hole drill abit oversize by grinding it a tad off center which causes one side of the bit to 'swing wider' than it would on center (at least in wood). The sides of the bit and twist are to evacuate the chips, and as you said, they don't need the twist, but works better with it. When drilling metal. I don't want the sides of the bit to touch the sides of the hole, you get heat build up, and seizing if you're nont careful!

 

[Mudder]

Don't mean to disagree, Daniel, but the very end of the bit can determine the size of the hole. I can make a hole drill abit oversize by grinding it a tad off center which causes one side of the bit to 'swing wider' than it would on center (at least in wood).

It works in metal with bits up to 3/16". We have a drill grinder at work that can be set to do this. Comes in handy for some odd size holes that there is no "close" conventional drill for.

(Note: It might even work with bits bigger than 3/16" but that's the largest that I have experience with.)

 

[Daniel]

Paul, You are correct except I am describing how a bit is "Intended" to work. the discussion on how they "Actually" work can get pretty long.
I also was not so much thinking about metal as I was wood either. actually the side of the bit is not always rubbing in wood either or it would also bind and heat up. but it does cut and burnish the walls. Drill bits actually taper buy just a couple of thousandths of an inch from tip to shank just for this reason.
On the subject of metal. I have noticed two types of material that a slow speed actually works much better. One is metal and the other even more noticeably is concrete. I am not really sure why the slower speed helps but i know it does. In concrete I have time and time again been drilling along getting nowhere so I start slowly start backing off the speed, the bit will suddenly dig in and start drilling 2 to three times as fast. Variation in how a bit preforms best is limitless and in actual practice is a matter of trial and error. But as far as wood speed is not nearly as critical if you realize what to expect and tend to it. slower speed simply peck more often etc.

 

[TellicoTurning]

At lot of what you guys are talking about (well, actually most) is Greek to me, but from my past experience, I know that if I drill too fast in Acrylics, I wind up with melted acrylic seizing my drill bit and I have to buy another bit... DAMHIKT... Also know if you don't clear the chips out with a spade bit, you can wind up binding the bit in a perfectly good peppermill blank and it can take up to an hour to get it out.. DAMHIKT..

I find it to be a real PITA to change the speed on my little HF drill press, so I've set it at 1100 and drill everything there and clear chips very often.... on the lathe I drill at 450 and again clear chips often... seems to work best for me. Of late, I do most of my drilling on the lathe.. except for the antler.. haven't quite figured out that yet.