# How to measure faces 45 degrees apart?



## Ngray (May 1, 2014)

So I have a piece of plate, and I need to cut a 45 degree bevel around the top edge. The bottom of the bevel needs to come down half the thickness of the plate. Problem is, I just can't visualize how to measure that, because any way I slice it, there are no parallel faces to measure. The only thing I can think of is to use the calipers by 'feel', opening them til the ridge of the bevel falls in.

Note that I have no problem making a 45 degree bevel. I just don't know how to make it deep enough, accurately. This is for fun, but I'm trying to learn as I go. Thanks for the help in advance.

On another note, I just got my one-knob indicator holder from LMS. Oh my God it's so much better than my old cheapie.


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## TOOLMASTER (May 1, 2014)

45 is as deep as it is wide...so if you go in on the side 1/4" it will be 1/4" deep


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## John Hasler (May 1, 2014)

Ngray said:


> So I have a piece of plate, and I need to cut a 45 degree bevel around the top edge. The bottom of the bevel needs to come down half the thickness of the plate. Problem is, I just can't visualize how to measure that, because any way I slice it, there are no parallel faces to measure. The only thing I can think of is to use the calipers by 'feel', opening them til the ridge of the bevel falls in.
> 
> Note that I have no problem making a 45 degree bevel. I just don't know how to make it deep enough, accurately. This is for fun, but I'm trying to learn as I go. Thanks for the help in advance.
> 
> On another note, I just got my one-knob indicator holder from LMS. Oh my God it's so much better than my old cheapie.



Set your square over the bevel and measure inside it with the knife edge of your caliper.


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## Ngray (May 1, 2014)

In as deep... Makes sense. I see how the square/knife edge would work as well. Thanks to both!


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## easymike29 (May 2, 2014)

Ngray said:


> ....I just don't know how to make it deep enough, accurately. This is for fun, but I'm trying to learn as I go. Thanks for the help in advance.....



What do you mean by "accurately"?

Gene


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## JohnG (May 2, 2014)

When I worked as a design engineer, drafting standards would not allow me to dimension a detail like your edge bevel in a drawing except as a "reference dimension" for just this reason:  standard tools won't measure it reliably.  Reference dimensions in drawings are just there for the draftsman or designers use; the production of the part ignores them.  It's a common problem, and it requires industry specific regulations.  For example, aluminum extrusions which may have multiple internal cavities require more elaborate rules than wood moldings for reference dimensions in cross section drawings.

Critical geometric details that can't be measured by the rules are gauged.  If your edge bevel is a critical detail, you could make a simple gauge for it by grinding a short piece of 1/8" key stock diagonally to a 1/8" x 1/8" right triangle and using it inside the corner of a precision square.  Notice that the critical dimensions of this gauge can be measured by standard tools.  A step up in accuracy would have you grind steps of suitable height into the two 1/8" sides to make a go/no go gauge which would fit-or not-into the gap between your plate and the square.  Volume production would justify more elaborate gauges.  

The accuracy of gauged details is determined by conformance to the gauge, and gauges make the transition from dimensional tolerances to more complicated geometric tolerances.  We could go on from here on the principles of gauge design, but I think you get the idea.  You've had your first encounter with a common problem which does have a well developed solution, and you're wise to consider it a learning opportunity.


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## Tom Walter (Aug 16, 2014)

OK, Old thread.

If I need to measure a beveled edge.  Slide the work piece up to a 90 degree plate, drop a dowel in.  You now can measure the height of the dowel pin... and with a little trig know exactly the bevel dimensions.

I made up a simple fixture to do something like that.  In my case trying to determine to corner location (but it had been rounded off, yet I needed to drill a hole based on the location of the missing corner!

https://www.youtube.com/watch?v=D79lmmnJRoA&list=UUsbR-x5FrR8bE30_1f6Dc8A

Tom


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