SFM RPM Chart

[whydontu]

So I've been pucking around with an Arduino-based calculator to calculate SFM / RPM for different material for my lathe and mill. I have a version that works for the mill, and in the process of putting together one for the lathe.

Here's the mill version. Two dials, one sets material, one selects cutter diameter.

Tonight, assembling the lathe version, while sticking jumper wires into a proto board, I managed to fry some pixels on the LCD display I'm using. No big deal, the display is worth $8. Then I started thinking, this is dumb. The math is pretty simple, I can do simple math in my head, and I have some very nice engraving machines. A 3"x5" chunk of 16ga aluminum and an Excel spreadsheet makes a RPM SFM chart that won't ever burn out, short when hit with cutting fluid, and if it gets scratched to poop I can just make a new one.

Excel chart:

I'll post a photo of a completed plate once I have one done.

 

[jorogi]

Fabulous, sign me up.

 

[Dabbler]

This is the best!

 

[Susquatch]

That's REALLY COOL! That's the kind of thing I would just print and tape to the wall beside my machine!

Currently, I use a wall chart with graphed curves on it from little locomotive (or something like that). I like your idea better!

I'd love it if you shared the spreadsheets themselves with the rest of us when you are done!

In a similar vein, I've been thinking about writing an RPN module for HP Calculators to do this kind of thing. I have several HP Emulators that run on my Android phone that can run such a program. The HP41C platform would add alpha characters to the input process.

The other idea I've had for a little while now is a speeds N feeds system for carbide inserts based on the manufacturers recommendations. I would imagine that this would probably be a lookup system of some kind with the oem recommendations for the inserts I already own but be flexible enough to add more as I acquire them. The program would then output the required speeds N feeds for my lathe and/or mill.

Cool idea @whydontu!

 

[whydontu]

Suggested other materials? I have four lines available to make the card a more balanced layout.

I’m using the mid-ranges SFM values from Little Machine Shop. If I get really ambitious I could have the spreadsheet calculate a range of values.

 

[Susquatch]

Suggested other materials? I have four lines available to make the card a more balanced layout.

Here is what my little loco wall chart does. You might get a few ideas including materials on it. Just zoom in.

In case it's not obvious, you select material colour at the bottom, then work diameter on the left side, scan sideways to the desired colour, then read speed (sfm) in the boxes, or scan up to the top for rpm.

 

[DavidR8]

Something wacky is going on with pics today as I was viewing the post @Susquatch just made and suddenly the image disappeared.

 

[YYCHM]

Something wacky is going on with pics today as I was viewing the image @Susquatch posted and it suddenly disappeared.

That's been happening for a couple of months now

 

[Susquatch]

Something wacky is going on with pics today as I was viewing the post @Susquatch just made and suddenly the image disappeared.

I agree with Craig. This is a months old problem with still no fix in sight.

That said, I fixed the post a bit by adding both thumbnail and full image.

 

[YYCHM]

I agree with Craig. This is a months old problem with still no fix in sight.

That said, I fixed the post a bit by adding both thumbnail and full image.

And when you try to zoom in on your thumbnail you get "Image Not Found"

 

[whydontu]

Today's version, split out turning and milling SFM, added a few materials. Any and all critiques gladly accepted.

 

[DavidR8]

Today's version, split out turning and milling SFM, added a few materials. Any and all critiques gladly accepted.

View attachment 53260

For my own edification let's make sure I understand this correctly.
Workpiece is 1" diameter mild steel. Using HSS tooling in the lathe.
Left columns say 380 rpm will get me 100SFM
The material column for turning says for mild steel it should be 215 SFM. What is the 2x multiplier for?

 

[whydontu]

For my own edification let's make sure I understand this correctly.
Workpiece is 1" diameter mild steel. Using HSS tooling in the lathe.
Left columns say 380 rpm will get me 100SFM
The material column for turning says for mild steel it should be 215 SFM. What is the 2x multiplier for?

So you double the RPM given in the left-hand chart. 1" mild steel as 380 RPM at 100 SFM, but a good starting point for mild steel is 215 SFM. Roughly 2 times 100 SFM. So if you spun your 1" mild steel workpiece at about 800 RPM you'd be a little above 200 SFM cutting speed.

If your 1" workpiece is aluminum you'd go 5 times the 380 rpm, so spin at about 1500 RPM. Or whatever you feel safe standing next to.

Maybe the milling numbers are more intuitive. Aluminum workpiece, 1/2" cutter. Left-hand chart says 760 RPM for a 1/2" cutter at 100 SFM, aluminum is rated 165 SFM, so the 1/2" cutter could run at about 1100 RPM (1.5 x 760 RPM) and be at a good working speed. Mathematically it could be 760 x 1.65 = 1254 RPM but that's too much mental math and just using 1-1/2 times the chart SFM is easier on my brain.

 

[Susquatch]

What is the 2x multiplier for?

Allow me to try so I can burn it in to hard memory (no such thing here but for me, understanding is everything.)

You picked 1" mild steel. If you had picked 2" its easier to explain and understand. So going with 2".

Pick material on RHS. Mild steel is 215 which is roughly 2x 100.

Pick diameter on LHS. 2" in my case. Rpm for 100 sfm is 190 rpm from the left side. But we need 215 sfm which is 2x 100. So multiply 190 rpm x 2 = 380 rpm.

Basically, he put the round number multipliers there to make the math easy.

He also says carbide is 2x hss which is 760 rpm. I assume that is brazed carbide.

I see he posted while I drafted so now I get to see if I actually understood.......

 

[DavidR8]

So you double the RPM given in the left-hand chart. 1" mild steel as 380 RPM at 100 SFM, but a good starting point for mild steel is 215 SFM. Roughly 2 times 100 SFM. So if you spun your 1" mild steel workpiece at about 800 RPM you'd be a little above 200 SFM cutting speed.

If your 1" workpiece is aluminum you'd go 5 times the 380 rpm, so spin at about 1500 RPM. Or whatever you feel safe standing next to.

Maybe the milling numbers are more intuitive. Aluminum workpiece, 1/2" cutter. Left-hand chart says 760 RPM for a 1/2" cutter at 100 SFM, aluminum is rated 165 SFM, so the 1/2" cutter could run at about 1100 RPM (1.5 x 760 RPM) and be at a good working speed. Mathematically it could be 760 x 1.65 = 1254 RPM but that's too much mental math and just using 1-1/2 times the chart SFM is easier on my brain.

Ahh that makes sense now.
For my brain, the third box is the starting point. and the left and second left boxes are SFM per diameter to rpm references

 

[Susquatch]

Ahh that makes sense now.
For my brain, the third box is the starting point. and the left and second left boxes are SFM per diameter to rpm references

That's cuz you think milling. I think turning so start is second box not third.

 

[DavidR8]

That's cuz you think milling. I think turning so start is second box not third.

No it's because in my mind the third or fourth box is the outcome and the first and second are the means to get the outcome.

Easy enough to swap the columns around

 

[Susquatch]

No it's because in my mind the third or fourth box is the outcome and the first and second are the means to get the outcome.

You lost me.

In my mind they are all inputs the 3rd and 4th are inputs (the SFM for the material for Lathe or mill.

THEN you go to the first and second box to get the rpm for 100 SFM at a given diameter and

THEN you get the result which isn't anywhere, you have to calculate it by multiplying the rpm in the first and second box by the multiplier in the 3rd or 4th

 

[DavidR8]

This is the column order that makes sense for my brain.
(grouped them into turning and milling so I can print one for each machine)

Convo in my head goes like this:
Am I at the lathe or the mill?
You're at the lathe stupid...
OK, then what's my material?
Bronze you big dummy. so you need to hit 200 SFM
How big is it?
1" according to my eyecrometer
Ok , well 380 RPM will get you 100 SFM and you need 200 so what's 380 times two?
Last I checked it's 760.
Ok, so set the lathe to spin 760 RPM or thereabouts and get on with the dang job!

 

[Susquatch]

This is the column order that makes sense for my brain.
Am I at the lathe or the mill?
You're at the lathe stupid...

Too funny!

Yup, I'm the idiot at the lathe.

So what material?

Bronze you hairy old fart

How big is the part?

2" Multiply to get answer.

Where is my calculator?

I dunno, use your phone.

Where is my phone?

In your hand, you blind hairy idiot.

Where is my hand?

OMG

Damn right, I forget the numbers now. And it's your damn fault David.