Chamfer Calculation 2

[eliot15]

Hi,

When I need to chamfer a bolt hole, I use the following formula:

(Chamfer Diameter - Bolt Hole Diamater)/2/tan(Chamfer Degree/2).

I add this amount to the distance my chamfer tool travels into the bolt hole before scraping the sides. That becomes my negative Z depth.

But suppose I want to use a ball nose end mill to do the chamfer. Does anyone know a formula for calculating chamfer depth when using a spherical raidus like a ball nose end mill??????

Thanks

[Kiwi]

Give this a try.
Add to your negative depth:
(Ball Mill Dia/2) - (Sine(Chamfer Deg./2) * (Ball Mill Dia/2))

[eliot15]

Only problem is I'm not given any information about the chamfer degree in this case. All that's typically called out on the print is:

CTSK. 14mm SPERICAL RADIUS x .945 +30/-0 DIA.

So I just throw in a 28mm ball nose end mill and adjust it deeper untill I get the diameter I need.

I could ask around and maybe get some information about the angle of the tool. Maybe it is 45 degrees or something. Someone at work could probably point me in the right direction there, if thats the way I'd need to go.

Thanks for your reply.

[Kiwi]

This is what I make from the specs.
If the angle is 90deg (half 45deg) the depth should be 1 + 4.1005 = 5.1005.

[eliot15]

Thanks for that. Its helpful to see it layed out that way. I'll have to play with it for a bit, and see what I come up with.

[eliot15]

I'd really like to try this again, and hope that some others are up for it. Its an interesting problem to me, but I'm not making much headway.

Notice that the bolt holes on the plate below are chamfered. I cut the chamfers with a 14mm spherical radius ball nose end mill. For the purposes of discussion, however, lets talk in inches. I used a 0.5512" radius, or 1.1024" diameter, ball nose end mill.



Here are the specs:



You can see that the 7 bolt holes have a .734" diameter, and the diameter of the chamfers is .945". Only the spherical radius is given in metric, which I'm just going to convert to inches for the moment.

I WOULD LIKE: a formula that will allow me to calculate the Z depth for a G-code canned cycle when cutting a chamfer of any diameter with any spherical radius tool.

I can do this easily with a standard 60, 82.5, 90 degree chamfer tool. You all know the formula: (Chamfer Dia. - Bolt Hole Dia.)/2/tan(degrees/2). Then you take this value and add it to the Z depth value at which your chamfer tool scrapes the bolt hole.

MY PROBLEM: I can't seem to get my formula for a spherical cutter using simple trig. As the 1.1024 ball nose end mill approaches its final depth, any known angles are constantly changing.

In the image below, the 1.1024 diameter ball is just scraping the edges of the .734 bolt hole. The adjacent and opposite angles to the perpendicular depth of cut line are 69.1274 degrees and 20.8726 degrees, respectively.



When the 1.1024 diameter ball reaches its final depth (i.e., the chamfer diameter is at .945), the adjacent and opposite angles to the perpendicular depth of cut line are 60.4970 degrees and 29.5030 degrees, respectively.



So SOHCAHTOA won't work. What else is there, short of firing up GibbsCAM as I've done above and drawing geometry. I want a formula I can plug a chamfer diameter, cutter diameter, bolt hole, etc. into and work at the machine.

Any thoughts greatly appreciated. Thanks for plowing through this if you took the time.

And if anyone can think of a more appropriate forum to post this in, I'm all for it.

[Kiwi]

Try: (1.1024/2) - (Sqr( (1.1024/2)^2 - (0.945/2)^2))

[eliot15]

I get 0.2675, which I'd have to say appears to be right. I'm showing a final depth in my second drawing of 0.2674.

But how does your formula work? It looks kinda' like you're working Pythagorean theorem backwards, or maybe inside out...

Are you by any chance able to draw what you're doing??

Thanks

[eliot15]

Actually looks llike I get .2674.

(.267359922)

[eliot15]

I see. The radius of the cutter is the hypotenuse of a right triangle of which the base = .4725 and the side = a.

So...

a^2 + .4725^2 = .5512^2
a^2 = .5512^2 - .4725^2
a = Sqr(.5512^2 - .4725^2)
a = .2838

Then subtract .2838 (the portion of the radius above Z0.) from the full radius (.5512) = .2674, the portion of the radius below Z0.

Brilliant. Thanks a million. Got a good feeling about it. Should work.

[eliot15]

[Kiwi]

1.1024/2 = 0.5512
0.945/2 = 0.4725
Sqr(0.5512^2 - 0.4725^2) = 0.2838
0.5512 - 0.2838 = 0.2674