Surface high speed pencil

[BenK]

I have read the help section on bitangency angle for the pencil toolpath and could use a better explanation. Could anyone elaborate more on how this setting effects the toolpath?

[Redfire427]

Bitangentcy is the maximum acute angle where the software still looks for material. If you draw two line at a 90 degree angle and put a fillet of say .125" between them, you will clearly see the "remaining material". Now if you draw another two lines where the angle between them is say 120 degrees and fillet them with the same .125" rad, you will see much less "remaining material. As this included angle increases to 180 degrees ( a straight line ), the fillet gets smaller and smaller. Once you get to roughly 170 degrees, the remaining fillet would be "almost" zero. Basically, by setting the bitangentcy angle, you are telling Mastercam to ignore the small amount of leftover material. I think 170 degrees is default, but you can set it to whatever you like. I think an appropriate value would be between 160 and 170 degrees.

 

Carmen

[BenK]

That's a great explanation. Thanks.

[David Conigliaro CNC Software Inc.]

Has nothing to do with material, I'll try to explain. It's a bi-tangency angle, 'bi' meaning 'two'. Your selected tool makes contact on 'two' tangent locations of the tool's radius along a corner with a sharp or a radius less than the tool's radius, that is where it chooses to pencil trace or 'roll the ball'. The bi-tangency angle is the max angle between the two tangent lines extended from these two tangent locations on your tool. The angle must be less than the bi-tangency angle to consider it a corner to receive the pencil trace. Please understand that there is no material in the game.

 

Think of it as rolling a ball along the corner of a shoe box. That's where pencil chooses to trace, then it ensures the angle between the walls and floor is less than the bi-tangency angle. So you have two criteria that control the pencil. Imagine rolling a 1in diameter ball along the corner of a shoe box with .25in fillets, it would be easy because the ball can touch the wall and the floor surfaces and roll nice and straight. The bi-tangency angle is what gives the ball it permission to roll there. The angle between the wall and the floor surfaces between the two tangent points of the ball must be less than your bi-tangency angle. Now try to roll the 1in diameter ball along those same corners if there was a 2in fillet between them. It would be difficult to roll straight as the the ball is not able to make contact with the wall and the floor with two tangent locations rather it is using only 1. In this case there is no bi-tangency angle to check to see if it has permission to roll there. So first it must be able to roll with two points of tangent contact and then it must ensure the angle between those walls are less than the bi-tangency angle in order to have permission to roll there.

 

Hope this helps

[Redfire427]

My explanation was a layman's explanation, but I disagree that it "has nothing to do with material". One of the main functions of the pencil tool path is to calculate the "remaining material" leftover from previous operation/s so that Mastercam can calculate multiple passes. When you adjust the bitangentcy angle, you also affect the tool path based on the calculated "remaining material". We are both right, but two different ways to explain it.

[David Conigliaro CNC Software Inc.]

Please don't think material is in the mix here, it is absolutely not. Multi passes are simple 3D offset passes out to where the reference diameter would have made its two tangent contact points if you are auto-calculating, of course you can simply tell it to offset a hard number of passes if you wish. I assure you it is not using a material model I just received an email from one our Mill programmers responsible for 3D toolpaths telling me my explanation was correct, no material model in play. He did say your explanation was pretty good, not too far off

[BenK]

Lets see if I understand you correctly. The reference tool diameter is applied to the corner and the bitangency angle is determined off that diameter?

[David Conigliaro CNC Software Inc.]

close, draw the tangent lines at the tangent contact point of the tool and part.

[David Conigliaro CNC Software Inc.]

This might help. This video will self destruct in 1 hour...

 

http://www.screencast.com/t/dClWCCIK

[crazy^millman]

Great Video David and that makes sense.

 

RedFire you have a good explanation that helps people see some principles, but I can see where David is showing the difference.

[Glenn Bouman]

Regardless how you explain it, making the number bigger will let it into get more areas and make it smaller if you do not want to cut those nearly flat areas. As shown in this example.

BI-TAN-ANGLE.MCX-7

[BenK]

Thanks for the explanation. This is a tool path I haven't used too much in the past but I'm running into situations where it will be useful.

[crazy^millman]

Ben I have not used it thank mush either, but after this topic and some of the different parts I have had to cut lately I am starting to see a good use for it. Why I like this forum always a place to learn something for me anyway.

[Thee Rickster ™]

I use it all day everyday,

 

To add some strategy...

 

If you were machining a fairly deep, tapered cavity box, type enclosure, a good

strategy is to do a waterline rest (I zig zag them) with the smaller cutter first, leaving say a couple

thou, then copy the path and run a pencil path that David shows in the video.

 

Great for mould making tricky parts.

[Thee Rickster ™]

I made a video, but I cant upload it.

Its an .swf.

[Thad]

How big is the video, Rickstrap?

[Thee Rickster ™]

How big is the video, Rickstrap?

 

3.3 meg

[Thad]

Can you email it to me and I'll host it and post a link to it? I'd like to see your video.

 

Thad

[Radical1]

This might help. This video will self destruct in 1 hour...

 

 

 

David that is a great video! I have a drawing that I use to teach with that could use this, I am going to give it a try on Monday.

 

On an other note I noticed that the version of Mastercam that you used in the video has MU2 but my search for MU2 turned up nothing. Is it comming out shortly or did I miss something?

[Mick]

Pencil is a very handy toolpath, especially for cleaning out material corners machined by a larger ball nose cutter.

 

I used it regularly.