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MotorradMike
09-05-2012, 09:01 AM
Hi guys:

I'm trying to locate an edge with an obtuse angle so I can't use the edge finder.
The best I've come up with is a small point spinning in the chuck and eyeballing it.

I'm thinking there must be a better way.
???

Lew Hartswick
09-05-2012, 09:30 AM
One of those "Optical" do-hickeys. :-)
...lew...

TGTool
09-05-2012, 09:43 AM
Ah, the "sticky pin". It has a long history in edge or feature finding. How close does the location need to be?

Jaakko Fagerlund
09-05-2012, 09:44 AM
What are your objectives? Drilling/tapping holes or something that requires precision?

Do you have any other edges to pick up from or can your workpiece have a locating pin hole on the opposite side?

If just drilling/tapping, I just eyeball those situations, but mainly my work involves pieces that have no way of picking up an edge and both sides have features that have to align, so I usually just drill & ream a small hole for a pin that is mounted on my mill table and picked up as my X0 Y0 after doing the first side holes etc.

One option is to make a piece that has the same angle as your workpiece and that way you get a straight edge to pick up from when you put this new "tool" against your workpiece. And you can easily measure the tools length so you know your offset.

rkepler
09-05-2012, 09:50 AM
I'm assuming that the corner you can indicate on has a broken edge with an unknown radius. Most of the time you can just 'assume' the radius of the edge and take it into account after indicating. In the worst of these cases the only solution is to install a tooling ball at a known location and reference off it after it's in the fixture or vise and at an angle. In the middle ground you can mark out the work before fixturing and use a wiggler to find the centers, but in my experience that's usually about the same as the first solution.

Forestgnome
09-05-2012, 09:51 AM
A wiggler will get you damned close. It's amazing the accuracy you can get to by eye.

MotorradMike
09-05-2012, 09:58 AM
One of those "Optical" do-hickeys. :-)
...lew...

The optical ones still need a vertical edge right?
As well, this is in Delrin so non-conductive.


Ah, the "sticky pin". It has a long history in edge or feature finding. How close does the location need to be?

Sticky pin???



If just drilling/tapping, I just eyeball those situations, but mainly my work involves pieces that have no way of picking up an edge and both sides have features that have to align, so I usually just drill & ream a small hole for a pin that is mounted on my mill table and picked up as my X0 Y0 after doing the first side holes etc.


I like the pin locator idea for when I need more precision. I can use that.

This problem was encountered while trying to locate a hole on the opposite side of the part after machining an angled face so I lost all references when I flipped and rotated it in the vise..
I'm sure I got within .010" and that's fine for this job.
This will come up again though and now I have more ideas to work with.
Thanks guys.

oldtiffie
09-05-2012, 10:01 AM
If you have a "good eye" the "poiner" on a cheap "wiggler" set can be quite accurate - with practice:

http://i200.photobucket.com/albums/aa294/oldtiffie/measuring/Centring5.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/measuring/Centring6.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/measuring/Wiggler1.jpg

Rustybolt
09-05-2012, 12:37 PM
Cigarette paper works too.

Dan Dubeau
09-05-2012, 12:40 PM
If it's a tight tolerance than you can hold a 123 block (or suitable setup block) against the edge, along with a dowel pin (or gauge pin). If you know the angle, and the dia of the pin, you can trig out the edge (or just use cad like I do). I had a setup like this last week, and it worked fine. Other way is to eyeball it. Like said above, you'd be surprised how close your eye can be sometimes. I routinely have funky setups like this at work.

http://i48.photobucket.com/albums/f224/danrdubeau/th_angleedgefind.jpg (http://s48.photobucket.com/albums/f224/danrdubeau/?action=view&current=angleedgefind.jpg) Just a quick example i just drew up. #'s totally arbitrary. Edit: I just reread your post, and noticed the "obtuse angle" part. This will work for an obtuse angle too.

MaxxLagg
09-05-2012, 07:09 PM
Assuming you know trig you can still use an edgefinder by picking up at least two points each along two lines that intersect into the point you wish to call zero. Note their locations, either off the dials or the DRO, depending on your machine. Do the math. PITA but can be done.

TGTool
09-05-2012, 09:03 PM
Sticky pin???

Thanks guys.

That's a field application of a wiggler. A piece of modeling clay stuck on the end of the spindle with a convenient pointed wire stuck in it. You can get it "zeroed" with your fingernail while the spindle is running like the more official version.

I can't remember what story that "sticky pin" showed up in, but it was the foreman's standard method of location without resorting to actual fancy tools or indicators.

LES A W HARRIS
09-06-2012, 10:06 PM
Hi guys:

I'm trying to locate an edge with an obtuse angle so I can't use the edge finder.
The best I've come up with is a small point spinning in the chuck and eyeballing it.

I'm thinking there must be a better way.
???

Turn up a pickup button made a nice dimesion, mill angle to suit, can magnetize for steels, if none magnetic, temporary glue to part, pickup edge of button, figure c/line of edge.

Pickup button..
http://i37.photobucket.com/albums/e97/CURVIC9/2010%20GENERAL/Fullscreencapture96201273409PM.jpg







Cheers,

Jaakko Fagerlund
09-09-2012, 04:27 AM
Although this doesn't probably help in a case of obtuse angle, but with an opposite situation where you need to find the edge but there is a chamfer or rounding on the edge to fool your readings: Put some modelling clay or that two part "chemical metal" on the edge, file or sand or use a stone to flatten from both planes that make the edge and hey, you got a sharp edge! :)