Feed Rates

[wwheeler]

With all the money going into this project, I'm worried about breaking bits or projects by setting the wrong feed rate.

Just where can I find the details on figuring this and the stats I would need for the bits?

[Tom Walter]

On the feed rates, I can give you a ball park.

Post up details on:

A What router/spindle you are using.

B. Details on the cutting bit.

C. Material being cut.

From those inputs we can give you a ball park rpm and feed (ipm) rates.


Oh, just accept you'll break 10 bits in your first week, so when you only break 6 you will feel pretty good about everything! (I hate that snapping sound of realizing I gummed up a bit with aluminum, then it just snapped).

[wwheeler]

Sorry Tom,
I'm jumping the gun a bit on it. we're still building the CNC. It will be a Hitachi router (the one referred to on the site here. 12dvc?)

I'm just trying to find a formula I can use.

[jkube]

I get a sense of what to do by reading about people's projects at cnczone or other similar websites. Michael usually has the feeds and speeds posted on his projects here which is helpful.

I've broken a few bits and it's always been from starting out too aggressive. I think just about everyone will tell you to start out slow on a new material. Don't be too afraid to break a bit or two though. You learn just as much from that as anything.

[Tom Walter]

I'm running the CNC Machinist Cookbook to calculate speeds.

Bob Warfield is the person behind www.cnccookbook.com He does allow you to "try before buying" by downloading a limited time use software. Do NOT download it just yet -- wait until you have gotten the machine up and running and a feel for cutting rigid foam.

Having said that, for the 50x50 wood router, with a 1hp router....

Cutting MDF, using a two flute 1/4" HSS cutting bit:
Tool width: 0.25"; Tool Depth 0.25" (that is a lot!), stick out 1"

Conservative: 17,121 rpm. Fee rate 186 ipm. Plunge 93 ipm
hp required: 0.94 hp

Aggressive: 14,683 rpm Feed rate 383 ipm. Plunge 191 ipm
hp required: 1.91 hp
WARNING TOOL DEFLECTION is 0.0019"
(You are on the hairy edge of snapping a bit.... )

He has a spent a time developing the software, but it is amazing to go back through and look my list of speeds & feeds from 20 years and compare it.... I probably would have saved $5000 in milling machine bits over the years with his calculators. Highly recommended!

[wwheeler]

Well, I've continued my hunt for feed rate information and stumbled across this article.

http://www.precisebits.com/tutorials/ca ... speeds.htm

While it's talking about micro bits, it still seems a great bit of advice for anyone starting out with a CNC system. Particularly about finding nodal points in the router spindle and collet combination.

Precise Bits is bit store but there are other articles I'm finding interesting on the tutorial page.

http://www.precisebits.com/tutorials.htm

[kono0014]

I have just started using Vectric VCarve Pro and it calculates the feed rate based on the bit you select. It does not seem to be a scientific calculation in that the tool database seems to favor around 100 IPM for most bits. I am intrigued now on what the proper feed rates but would assume that most software packages that have a tool database will give you a starting point. I am surprised that the tool database is not more sophisticated in how it calculates the feed/plunge rate. Of course there are so many factors that can be taken into account you need to be a rocket scientist to come up with the optimum feed rate so I will try to pay attention to the feel of routing as that is what you do when operating a router by hand.

Tom, I am curious why the router/spindle would make a difference. If you are sure your router has little to no runout then it should not be a factor given all of the routers are near equal on HP that go on the KRMx02.

[Tom Walter]

Tom, I am curious why the router/spindle would make a difference. If you are sure your router has little to no runout then it should not be a factor given all of the routers are near equal on HP that go on the KRMx02.

On the router/spindle.... HP rating is what I was looking at. My Bosch Router has a big fancy "2.25 hp" rating, but that is probably very optimistic.

If you look at the example I listed for conservative 186 ipm feed it requires 0.94hp. Aggressive at 383 ipm requires 1.91hp. I'm pretty sure the Bosch router will not keep up and will be breaking bits with the aggressive feed.

For production you really want the best feed rates. For a Hobby shop, conservative will give the best tool life.

The calculator is a cool tool. Bob Warfield makes it so if you buy a "3 year software" it is good for a 3hp motor. If you buy one year software, it is limited to 1hp.... but the software never expires, just defaults to 1 hp rating.

[msimpson]

First let me say, once you build your CNC, you will be faced with the process of learning feeds and speeds. Yes, you can calculate the feed rate, or RPM of a bit, but you must know the loading for the flute. This is a number that is provided by the manufacture. Un fortunatly they can be hard to come by, so you must experiment your self.

Here is a catalog for Haurlauer bits:
http://www.hartlauer-bits.com/HartlauerBitsList.pdf

In addition to the bits it also contains some useful information.

Here is some feeds and speeds information that might also be helpfull:
http://www.cnccookbook.com/CCCNCMillFeedsSpeeds.htm


Online calculators:

http://www.hougen.com/tech_tips/speeds/speed.html

http://www.monstertool.com/monster_tool ... ators.html

http://www.daycounter.com/Calculators/G ... ator.phtml

http://janproducts.com/Speeds_and_Feeds_calculator.html

http://www.custompartnet.com/calculator ... d-and-feed

More Formulas and information:

http://www.dapra.com/tech/dloads/Dapra- ... rmulas.pdf

http://www.dapra.com/tech/calculators.htm

http://its.fvtc.edu/MachShop3/SpeedCalc ... tecalc.htm