Edge finder on a non-perpendicular edge?

Taking a machining class and have a few projects that involve manual milling at 45 degree angles. Basically a cube that I need to locate center on while mounted in a vise with V blocks so the block is 45 degrees to the table. Was told to just use the center finder against the edges even though the travel of the table is not perpendicular to the face that the center finder will be hitting. Seems like the angle might make the tip move sooner in one direction than the other.

I tried it and used both slopes to try to see the difference. Seemed pretty accurate. Is this generally accepted to locate? Is there some rule of thumb to the amount of angle where it gets unacceptable?

If the V-blocks are exactly the same, and the part is symmetrical, then measure the distance between the vice jaws and divide by 2

I'm a bit confused that a face is not perpendicular to a table axis. It at least must be perpendicular to the vice jaws. A picture of the setup would help my confusion.

Yes, I suppose I could measure from the vise jaws. I hadn't thought of that and it's a creative solution. And for the y direction I could edge find both sides of the V block and take the center of that. The part is 1.25 square. I was machining on the end of it (actually had two the same that were thin and put one at the bottom of the V block and the one being machined at the top but the issue would be the same with a longer part and working on the end). I used two V blocks (one on each side of the part with the V vertical) to hold the part so the vertical faces of the part were at 45 degrees to the table axis. Hope that is clear. I don't have a picture.

Still curious about using the edge finder on an angled surface. I am having a hard time imaging a case where I would need to do that and the part not being symmetrical though...

I guess you could edge find on an angled surface if you were exactly the same height on both sides, and the sides are symmetrical. I have never actually tried it.

hy jim & jim :) most discusions on this topic are about how to locate accurately a tilted edge, or how a part got machined wrong because it was probed on a tilted edge

yours, is different :

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Seemed pretty accurate. Is this generally accepted to locate?

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you made it work, but why did work, right ? haha

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Is there some rule of thumb to the amount of angle where it gets unacceptable?

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is all tolerances; let's imagine a tilted part :
... if there is enough stock to machine, you may simply don't care about edge finder accuracy
... if you need to aling at 0.01/500, would you still use an edge finder ?

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I am having a hard time imaging a case where I would need to do that and the part not being symmetrical though...

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there are probing macros, that simply allow you to mount your part/vice arbitrarely on the table ( thus you no longer loose precious minuteswith alignment ), and the probe will find the center in a few seconds; even posible to reach few um accuracy with a probe that has run-out

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Still curious about using the edge finder on an angled surface

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run your own trials, gather data; for example, use a rotary table, and begin with 0* then increase steps 5 10 15 ... 45 - 50; it may take you a while, but at least you will gather experience

or let's go for another one : try to rotate the cube, so it is no longer at 45*, but let's say 30 ? thus position it in such a way that it's axis of simetry are no longer aligned with machine axis, and then try to find it's center with the edge finder; pull this out, and trust me, you will have your answers

if you wish, i can help you; check attached image ( left ) :
... touch 1 & 2, among y axis, and find center M
... touch 3 & 4, among y axis again, then find center N
... touch 5 & 6, among x axis, and find center P
... cube center is P projection on MN
right side of image shows skematic, how is possible to find the center using only 3 points, with a probe that can detect also edge tiltness / kindly :)