chamfer into radius

[Tucker84]

how do i program a .25 radius off of a 30degree chamfer without G41 or G42? it blends to a 90 up the face of the part. when i graph it on the control the radius looks odd. i'm not using any cam software, programming it manually. thanks.

[307startup]

Depending on your control, this should be an I,J,K function...your radius stay the same, but the arc start point and end point will change in relationship to these. This will determine the odd radius your graphing shows.

[Tucker84]

i tried using an I value, and it corrected it to a certain extent. when i tried to enter a K value it threw an alarm. i don't know enough about I,K,J values to experiment. are the I,K values tool tip to radius center?

[307startup]

No...I,J,K values are related to X,Y,Z orientation. Basically how the arc tangents are in relation to the X,Z path on a lathe. That is why you can get funky shapes when graphing.

Do you have a copy of a newer Machinist Handbook, or the Modern Machine Shop's Handbook for the Metalworking Industries?

There is a great CNC section in there that can give a much better definition than I can. Unfortunately my copy is in my toolbox, and that is on the other side of town or I would give you the "proper" definition.

[Tucker84]

the latest book i have on the subject is 2006 machine tool practices. it is only a general overview. do you have any recommendations or suggestions on how i may solve or start to fix the problem?

[307startup]

I will try to give a brief, though I hope helpful, explanation.

The tool tip to radius center idea is close, but due to some vagaries in application, not quite correct. As you know all inserts have a nose radius, so when hand-coding you have to use trig to figure out the actual "point" of the insert in space.

When dealing with I,J,K values an -/+ sign can have a huge impact on where your arc travels...as well as tool nose compensation.

That being said...I have no real idea where your radii are in Cartesian coordinate "space". Is there any chance that I could see a photo of your graphing, to get a rough idea?

I haven't programmed on a lathe in about a year, so bear with me for not having all the answers on the tip of my tongue.

[Tucker84]

unfortunately i don't have a picture. i could give you dimensions of x and z coordinates if you think that could help. thanks

[Tucker84]

Thanks for your help 307startup I really appreciate it. I actually ended up calling a shop down the road that uses gibbs cam and they helped me with it. but your definitions helped and i'm still on the path of enlightenment so if you come up with anything else that would be useful I would like to hear it. Thanks again

[modoleinad]

see if your machine has a fillet command; many do.