Newbie- Calculating end mill sizes for toolpaths

[George777]

I'm generating tool paths for surface contours in Mastercam. The contours are organic in shape. (see the pic). Of course during tool path creation Mastercam asks for the tool size and at this point I'm taking a trial and error approach for selecting the right size tool. I've read that tool size is dictated by the smallest radius in the tool path. Is there an effective way to calculate the best tool size for the tool path.

[HuFlungDung]

Well obviously the tool must fit the smallest radii profile or you'll have to rest machine it later, but sticking with that small tool could be a collossal waste of time if a larger stiffer tool will clear the bulk of the material more quickly.

What one might look at is the general dimension of the area to be roughed. If it is more than 6 to 10 tool diameters wide (3 to 5 loops around) then it probably makes sense to double the diameter of the endmill from the minimum required. The deeper you can cut per pass, I think the sooner you might want to increase diameter to improve stiffness.

I generally would not step through a whole series of endmill diameters in roughing unless extreme depths of the part gave a significant advantage that way.

The machine you will be running the path on probably has tool driving limitations as well. Broad areas can use face or shell mills at moderate depth of cuts and easily consume all the horsepower available. Deeper sections probably will be cleared with some sort of 'favourite' tool, which might be anywhere from 1/2" to 1" diameter, depending on what you are used to dealing with. The maximum material removal rate per horsepower(for a given type of material) for the spindle in use should give you a rough guideline on largest tool to be used.

The style of toolpath also affects what the tools can physically handle. If you've got a high speed toolpath option which controls the tool engagement, then you can adjust the rules a bit, allowing smaller diameter tools to cut deep but at shallow engagements, at high feedrates and high rpm.

[thebowman]

Originally Posted by George777 I'm generating tool paths for surface contours in Mastercam. The contours are organic in shape. (see the pic). Of course during tool path creation Mastercam asks for the tool size and at this point I'm taking a trial and error approach for selecting the right size tool. I've read that tool size is dictated by the smallest radius in the tool path. Is there an effective way to calculate the best tool size for the tool path.

Are you using Analyze Dynamic to interrogate your organic part model first?

[chuy]

Originally Posted by thebowman Are you using Analyze Dynamic to interrogate your organic part model first?

OK what is analyze dynamic?

[thebowman]

Originally Posted by chuy OK what is analyze dynamic?

Analyze Dynamic presents you with an interface that you can use to dynamically drag an arrow over a surface or solid model to see what radius's the model contains. This way you know what cutter size you need to use. I find it to be an indispensable tool and I use it all the time on surface and solid models.

[BobWarfield]

Originally Posted by George777 I'm generating tool paths for surface contours in Mastercam. The contours are organic in shape. (see the pic). Of course during tool path creation Mastercam asks for the tool size and at this point I'm taking a trial and error approach for selecting the right size tool. I've read that tool size is dictated by the smallest radius in the tool path. Is there an effective way to calculate the best tool size for the tool path.

Interesting. I can see where having a general purpose software feature that tells you the smallest endmill diameter needed to machine an area within a particular accuracy would be very handy.

It would also be helpful if that tool could tell you what % or some such of the feature could be done with a tool that is "too big".

In other words, the software should be helping us to make more optimal tradeoffs on what to do when roughing versus rest machining to get to the final result.

Doesn't sound like anyone has software that does this yet, however.

Cheers,

BW

[Mike Mattera]

I know this is after the fact, but you can use an STL compare to determine if stock was left on the part. Then you can run a Rest Mill toolpath or Leftover to get the rest of the stock.

Mike Mattera

[George777]

So, let's say I'm doing a simple surface pocket that has an hourglass shape with straight walls and flat floor. The first step in the tool selection process is to check the dimensions with analyze dynamic and select the largest tool that will work within the upper and lower large areas of the hourglass. Run a tool path and then go back and use "Restmill" with a smaller tool that will fit within the neck of the hourglass. The restmill toolpath will only go over the areas that the original toolpath did not cover. How do you initiate an "STL compare" ?

[lovecnc2003]

thanks

[chuy]

Originally Posted by thebowman Analyze Dynamic presents you with an interface that you can use to dynamically drag an arrow over a surface or solid model to see what radius's the model contains. This way you know what cutter size you need to use. I find it to be an indispensable tool and I use it all the time on surface and solid models.

Oh cool...That's sweet I'll keep that in mind...Thanks.

[thebowman]

Originally Posted by chuy Oh cool...That's sweet I'll keep that in mind...Thanks.

Glad you think this tool is as cool and as helpful as I do.

I learned what to use Analyze Dynamic for from watching Mike Mattera's Mastercam 3D Surfacing CD.