# Cutter speeds - where is an authoritative table or formula?



## WobblyHand (Apr 25, 2020)

I thought I looked in the right table... An old Machinery's Handbook (17th edition).  I'm looking at the table "Speeds and Feeds for Milling, Drilling and Turning".  It says 700-900 FPM for aluminum using HSS cutters.  If I worked out the math right that yields 6100 RPM for a 1/2" mill (800 FPM).

The basic formula should be: 
FPM [ft/min] = circumference of bit [ft/rev] x RPM [rev/min], correct?  So solving for RPM we get: 
RPM[rev/min] = FPM [ft/min]/(pi x D [ft/rev]) = 12 [in/ft] x FPM [ft/min] /(pi x D [in/rev]) ?  (I put in the units to make sure the math is ok.  It does clutter the equations, sorry for that.)

Could someone set me straight?  Is this the right formula?  Is the advice just to run aluminum cutters fast, or as fast as your machine will allow? Thanks.  The 17th ed. Handbook claims this is conservative, modern practice.

Moments after posting, I see there is a sticky.  Doh!


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## WobblyHand (Apr 25, 2020)

I see there is a tooling correction factor which appears to reduce the RPM.  Where does this term come from?  3.82 is a funny number.


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## ThinWoodsman (Apr 25, 2020)

One thing I found helpful was to make my own feed/speed tables.

The first is a table of feed and SFM for different metals, which is basically a range from Roughing (low) to Finishing (high), with an all-purpose number that usually lies in between.

The second is a table of RPM for different SFM and diameter (tool or workpiece) combinations. The diameters will increase by 1/8 or 1/4 until 1", then by 1/2" until 4", then by 1", and so forth. You'll find that the small-diameter RPMs are impossible to achieve, and the large-diameter RPMs tend to converge.

Print it out, hang it by the lathe or the mill. Becomes pretty simple to choose an SFM, from that, select an RPM by interpolating from known diameters. If you have a fixed selection of speeds (e.g. a pulley system), then you can alter the second table to only include the RPMs you have available.


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## benmychree (Apr 25, 2020)

Some of the tool companies make a slide rule type of speed/feed calculator out of hard cardboard, so no need for calculations.
In school we used a formula;  RPM= cutting speed X 4, divided by the diameter of the moving part, the cutting speed for soft steel being 100 FPM.


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## Cadillac STS (Apr 25, 2020)

Take a look at G-Wizard at CNCcookbook.com

speeds and feeds all done in a nice easy app

no table needed.


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## WobblyHand (Apr 25, 2020)

Ok, now I know where 3.82 comes from...  That's just 12/pi.  12/pi = 3.81972...


benmychree said:


> Some of the tool companies make a slide rule type of speed/feed calculator out of hard cardboard, so no need for calculations.
> In school we used a formula;  RPM= cutting speed X 4, divided by the diameter of the moving part, the cutting speed for soft steel being 100 FPM.


And the 4 is just an approximation of the 3.82.  Got it.  It seems the units for your equation are ft/min for the cutting speed and inches for the diameter.  Makes sense now.  So my equation is correct, unless there's some kind of efficiency or fudge factor, I've left out.

Still think 6100 RPM is fast.  I've only got 3100 RPM available, so that will have to do.


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## WobblyHand (Apr 25, 2020)

Cadillac STS said:


> Take a look at G-Wizard at CNCcookbook.com
> 
> speeds and feeds all done in a nice easy app
> 
> no table needed.


Need to make an account to do anything on that website.  Pass for now.  Maybe later.  I'll bet it's easy to use.  Me, got a calculator and the Handbook.


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## WobblyHand (Apr 25, 2020)

ThinWoodsman said:


> Print it out, hang it by the lathe or the mill. Becomes pretty simple to choose an SFM, from that, select an RPM by interpolating from known diameters. If you have a fixed selection of speeds (e.g. a pulley system), then you can alter the second table to only include the RPMs you have available.


That's a pretty good idea.


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## ttabbal (Apr 25, 2020)

Niagara Cutter, LLC
					






					www.niagaracutter.com
				




I got one of these and use it when I need suggestions. It seems to work pretty well.


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## Cadillac STS (Apr 25, 2020)

If you have a smart phone type feed speed in the search of app store and pick which app you like


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## Aukai (Apr 25, 2020)

This person has charts for wall mounting depending on lathe size.








						WALL CHART for 10in 12in ATLAS METAL LATHE - CRAFTSMAN - 16 Speed  | eBay
					

Each is FULL-SEAL HOT LAMINATED with heavy duty (5-mil) FILM. The chart is totally sealed for years of use and wipes clean with a soft cloth. Using one chart, you can easily find the correct tool cutting angles and the proper cutting speeds for any of 22 different materials.



					www.ebay.com


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## mikey (Apr 25, 2020)

Formulas and charts are good to have and you should know how to calculate speeds but ... they are just starting points, not written in stone. For every speed, there is a feed; finding that combination is what you're looking for. If you calculate a speed and it is too fast or too slow for your lathe, you can still produce an accurate cut by adapting the feed to accommodate that speed, at least on a manual machine. What you're doing here is really learning how to cut metal on a lathe. If you watch, listen and feel the lathe as it cuts, it will tell you what it wants from you.

For example, say you calculated the speed for mild steel but then dialed in a big depth of cut. This will likely chatter so your response is to reduce depth of cut and reduce your speed or increase feed and the chatter will resolve. The lathe will tell you what it wants.


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## KMoffett (Apr 26, 2020)

Online calculator


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## BGHansen (Apr 26, 2020)

Google "Tom's Techniques" and watch his video on speeds. I didn't write down the recommendations for non-ferrous materials, but the simple formula for mild steel is (as mentioned above), 400 divided by the diameter.

If using a 1/2" end mill, 400 divided by 1/2 or 800 rpm. Same for drills on the mill or lathe. 

If turning a 2" round on the lathe, 400 divided by two or 200 rpm.

The numbers for brass and aluminum are something like 1000 instead of 400, but take a look at Tom Griffin's videos for the actual numbers.

Bruce


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## ThinWoodsman (Apr 26, 2020)

WobblyHand said:


> That's a pretty good idea.



Here's an example I made up for the lathe. 

I based the per-material feed and speed ranges on a few textbooks, erring on the slow side because I don't run a production shop. That is something to keep in mind: most speed and feed recommendations are calculated to minimize labor hours, with little regard for tool life. For a home shop, you can stick to the low end for roughing and maybe the middle for a finish. You 'll probably want to make some test cuts on different materials to get a feel for which part of the range works for you, given your machine and tooling.

I would advise making your own chart against downloading one, as you are very likely going to have a limited set of tools and a limited range of materials or diameters, so you can reduce the information overload like in that colored chart posted above.


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## Tozguy (Apr 26, 2020)

A lot of the published charts and tables are to indicate maximums for the production minded.
Hobbyist can use any speed and feed that works for them, often much below the maximum speed shown on charts.
What is important is chip formation and heat control. As a hobbyist I found it more useful to learn to read chips and as mikey wrote find what works best with my own set of tools and equipment. A log book can help you record what works and what doesn't for future reference.
If you have a QCGB then it is easy to try different speeds at the start of a job to find what works best.


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## Tozguy (Apr 26, 2020)

This fella offers many good videos. A couple of videos in particular on chips feeds and speeds were very helpful when I was starting out.


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## diamond (Apr 28, 2020)

Tozguy said:


> This fella offers many good videos. A couple of videos in particular on chips feeds and speeds were very helpful when I was starting out.


Great share. I needed that.  When it comes to speeds/feeds/DoC I'm a complete new guy.   I'll need to watch it a couple times I think to sink in.

Observing chips makes total sense.  At the risk of thread hijacking I'm curious about how his approach applies with carbide inserts and chip breakers.   When it comes to the 416 I'm usually cutting I've been going for nice golden brown "C" chips rather than the long continuous shiny curly chip.   Is this wrong?  In fact I hate the long spiral stringy things that often turn into a birds nest when I have to do a shallow cut.

For example to get that I turn a 1.250 diameter rifle barrel tenon cut down to 1.0625 at 850rpm using .020 DoC with the gear box set to D3.  The chart on my lathe (PM1340GT) says .001"-.00055"/rev for the D range.   I'm not exactly how to read that to know exactly what my feed rate is.  I assume it's something between 1 and .5 thou/rev.  By trial and error I discovered that gave me a decent finish and that golden brown "C" shape chip (or also like a "6" shape).   I do cut dry and my part does get a little warm.   This is with a DCMT 32.51 55 degree diamond insert.   

I'd love to know if I'm doing that right or if I could improve on it.  Burned up some inserts getting to this point and it's ok but if I could do better I'd like to know.


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## Tozguy (Apr 28, 2020)

Marc, the author of that video will also answer questions for you. I think that you can get his addy from the website. Not that the fellas here can't help but Marc is available too (at least he was the last time I emailed him).


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## MrWhoopee (May 13, 2020)

benmychree said:


> Some of the tool companies make a slide rule type of speed/feed calculator out of hard cardboard, so no need for calculations.
> In school we used a formula;  RPM= cutting speed X 4, divided by the diameter of the moving part, the cutting speed for soft steel being 100 FPM.



This ^^^^

*RPM=Cutting Speed x 4/diameter.* 

Commit it to memory, your wife should hear you mumbling it in your sleep. 

Rough cutting speeds:
Mild steel = 80-100 sf/m 
Aluminum = 2x to 10x mild steel (160-1000 sf/m)
Stainless = 40 sf/m
Tool steel = 40 sf/m

These numbers are rough approximations for HSS and subject to change based on the actual alloy. They WILL get you making chips very quickly without trashing your tool. Feed rates are a matter of finding out how much the machine will take. Start low and keep turning it up until you hit the limit of rigidity or power. CNC programming for production requires calculating maximum metal removal rates, manual machining not so much. 

It's been at least four decades since I've needed more than a calculator, and usually not even that.


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## aliva (May 13, 2020)

Toms Techniques has a downloadable chart will give a good starting point


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## erikmannie (May 13, 2020)

I have this under my belt for HSS cutting tools, but I don’t know much about carbide, which I use half the time.

Edit: Apparently you multiply the HSS RPM by a whopping 4 for carbide!


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## erikmannie (May 13, 2020)

That link to That Lazy Machinist video was appreciated. I hope everybody watches that video. Here are some fun screenshots:


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## erikmannie (May 13, 2020)

Like many others said, in school they taught us Maximum RPM = (CS X 3.82) / diameter.


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## Illinoyance (May 18, 2020)

There are a lot of apps for your phone.


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## GunsOfNavarone (May 18, 2020)

Cadillac STS said:


> Take a look at G-Wizard at CNCcookbook.com
> 
> speeds and feeds all done in a nice easy app
> 
> no table needed.


This looks intriguing...you ca't buy this program, rather, you have to pay a subscription? Are you a member?


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## OTmachine (May 18, 2020)

Look here: https://archive.org/details/DTIC_ADA092695/mode/2up


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## Cadillac STS (May 18, 2020)

GunsOfNavarone said:


> This looks intriguing...you ca't buy this program, rather, you have to pay a subscription? Are you a member?



Yes I have used it the last couple years. You do the subscription or can buy it lifetime I think. He does ongoing work on it and you can get all upgrades free along the way. I think the price is ok and I like to support someone’s work on a project like that.


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