In computing the surface feet per minute of a given diameter drill bit at a given rpm, normally the drill outside diameter is used. Since the drill bit cuts along its entire cutting edge, would it make more sense to use 1/2 the drill diameter for the computation? Or do the recommended-rpm charts take this into account?
-
Welcome back Guest! Did you know you can mentor other members here at H-M? If not, please check out our Relaunch of Hobby Machinist Mentoring Program!
Drill SFPM
- Thread starter 02vito
- Start date
- Joined
- Jun 7, 2013
- Messages
- 10,089
Use the drill diameter for computation; the same with any rotating tool or rotating part being machined. To make it easier, get a slide rule type calculator.
What you suggest makes sense. Thanks.
Agreed. Too fast burns up tools. The surface speed of a drill bit goes from it's maximum at the outside diameter, to zero at it's absolute theoretical center. You need the speed at the outside. In order to work with that, you need to use the actual circumference. To get to that, you could measure all of your drill's circumferences, you could use diameter, radius, pi, tau, or you could measure a chord along the flutes and work it out that way... any way you wanted really. Since the diameter is the most accessible dimension on virtually every drill, it just makes the most sense to base the calculations on that in most cases. You'd get the same result no matter how you did it.
Our BP has VFD with single pulley, so we need back gear for good torque at slower speeds.
We found that slower speeds seem to work very well when drilling.
For hobby folks, there is no reason for too fast as it just damages the tool.
Do not measure RPM, more of a know from the look of it thing.
When using a drill press like tool and not using a portable device, you can actually drill to the capability of the tool.
Often with portable drill folks drill small hole then step up, fine but take too many steps.
The steps only need to be as large as the web.
We often drill 1/2 inch in one shot.
Slow RPM with good feed and oil.
Changing bits takes time...
If not sure what rpm to use, just start at some slower speed and see how it goes.
If it's too slow, it will cut just fine, and the chips curl out.
Too fast, and it cuts fine for a while, then not so much.
Sent from my SM-G781V using Tapatalk
We found that slower speeds seem to work very well when drilling.
For hobby folks, there is no reason for too fast as it just damages the tool.
Do not measure RPM, more of a know from the look of it thing.
When using a drill press like tool and not using a portable device, you can actually drill to the capability of the tool.
Often with portable drill folks drill small hole then step up, fine but take too many steps.
The steps only need to be as large as the web.
We often drill 1/2 inch in one shot.
Slow RPM with good feed and oil.
Changing bits takes time...
If not sure what rpm to use, just start at some slower speed and see how it goes.
If it's too slow, it will cut just fine, and the chips curl out.
Too fast, and it cuts fine for a while, then not so much.
Sent from my SM-G781V using Tapatalk
- Joined
- Nov 23, 2014
- Messages
- 2,606
Hit the website:
Tom Griffin is a great instructor; gets to the point quickly. Youtube video link for cutting speeds is below:
Here's a snippy of the chart for different materials from the video:
The formula is:
RPM = (SFPM from chart above x 4) / diameter
Couple of examples:
You want to drill a 1/2" hole in aluminum on the mill or drill press:
RPM = (250 for aluminum x 4) / (1/2" drill diameter) = 2000 RPM
You are turning a 1" mild steel round on the lathe:
RPM = (100 for mild steel x 4) / (1" diameter round) = 400 RPM
You want to mill a pocket in a chuck of cast iron on the mill using a 3/8" diameter end mill:
RPM = (60 for cast iron x 4) / (3/8" diameter end mill) = 640 RPM
Guys will typically double the RPM's if using carbide tooling vs. high speed steel. These speeds should be considered guidelines. If taking a deep cut, back off the RPM's; finishing light cut, bump it up.
Bruce
Instructional Videos - Tom's Techniques
https://tomstechniques.comTom Griffin is a great instructor; gets to the point quickly. Youtube video link for cutting speeds is below:
Here's a snippy of the chart for different materials from the video:
The formula is:
RPM = (SFPM from chart above x 4) / diameter
Couple of examples:
You want to drill a 1/2" hole in aluminum on the mill or drill press:
RPM = (250 for aluminum x 4) / (1/2" drill diameter) = 2000 RPM
You are turning a 1" mild steel round on the lathe:
RPM = (100 for mild steel x 4) / (1" diameter round) = 400 RPM
You want to mill a pocket in a chuck of cast iron on the mill using a 3/8" diameter end mill:
RPM = (60 for cast iron x 4) / (3/8" diameter end mill) = 640 RPM
Guys will typically double the RPM's if using carbide tooling vs. high speed steel. These speeds should be considered guidelines. If taking a deep cut, back off the RPM's; finishing light cut, bump it up.
Bruce