Chamfer calculation

[eliot15]

I'm trying to figure out how to calculate the 'Z-depth' value on say a G73 canned cycle for a .75" bolt hole. Lets use a chamfer diameter of 1.5".

If I were doing a 90 degree chamfer, I'd just bring my counter sink down till it touches in my bolt hole, take that depth (say -.123) and add it to (1.5 - .75) /2. So we get .375 + .123 = .498. So my G73 Z address value would be Z-.498, plus a little tolerance.

How do I do the same sort of calculation with an 82.5 degree counter sink?

Any help much appreciated.

e

[Eurisko]

That requires a little trigonometry.

First, divide 82.5 by 2, then find the tangent of that angle:

82.5 / 2 = 41.25

tan(41.25) = .8770 ( to 4 decimal places )

Take the diameter of the required chamfer, subtract the hole size, divide by 2, then divide by .8770

for example, your 1.500 chamfer would be :

(1.500-.750) / 2 / .8770 = .4276 ( to 4 decimal places)

This is the amount you would feed in Z with the chamfer tool just touching the hole.

[eliot15]

Thanks a million!

This is the amount you would feed in Z with the chamfer tool just touching the hole.

Just to be sure I undestand, I'm using an indexable countersink. I'm assuming I would have to bring the tool down to part zero, then drop the countersink into the hole until the inserts touch the sides of the hole, then add that distance to .4276 in the eample above.

Here are the numbers I actually worked with today:

My countersink inserts touched at Z-.168.

Chamfer (1.38) - Hole (.755) / 2 = .3125.

.168 + .3125 = .488.

So I initially set my Z-depth to Z-.488. That gave me a chamfer diameter of about 1.32. I finally got the chamfer diameter I wanted by increasing my Z-depth to about .538.

So, using trig:

(1.38-.755) / 2 / .8770 = 0.3563( to 4 decimal places)

Adding .168 to 0.3563 = 0.5243, which gets me just about to .538.

I wasn't sure if your remark:

This is the amount you would feed in Z with the chamfer tool just touching the hole.

was assuming that .168 was added in or not. Just wanted to be clear. I need a Z depth of about -.540 to get the 1.38 chamfer.

Is that all correct??

Thanks for your time.

e

[Eurisko]

I think you've got it. Yes, you would have to add the .168 (Z position with chamfer touching hole) to the trig calculation to get the final Z value.

It could be that the chamfer angle isn't exactly 82.5 degrees, that would explain why a little more depth was needed. Also, a chamfer diameter is tough to measure exactly. That throws another variable into the mix. Add tool pressure & flexing, and the numbers make sense.

[eliot15]

Great. Thanks again for that. I'll be using it constantly.

Also, .168 + .3125 doesn't = .488. My bad. It equals 0.4805. I threw in about .008 to shoot for the middle of tolerance.