Ordinate dimensions... need guidance 1

[USAeng]

Our owner has all of a sudden come to us saying he wants all of our drawings to be dimensioned using ordinate dimensions. I am a little freaked because I've never done it but I will do it since he said to.

Is there anything I should watch out for while converting all of our thousand some drawings to having the ordinate dimensions?

This is all coming about because he wants to make things easier on the machinist.

Thanks.

 

[CorBlimeyLimey]

First of all, there is no need to convert all of your drawings. Just convert on an as-needed basis.

 

[MadMango]

Make sure your 0-0 origins on different parts make sense in the overall assembly. Ordinate dims love stack-up tolerances.

"Art without engineering is dreaming; Engineering without art is calculating."

Have you read faq731-376 to make the best use of these Forums?

 

[MDGroup]

Another quick item to note on tolerances, the tolerances might doubel up.

Say on your current drawing, you have a critical dimension between 2 holes of Diension +/- tolerance.

If those holes are now both dimensioned from the origin, one could be -tolerance and the other could be +tolerance. So now the distance between holes is dimension +/- 2x tolerance.

Ordinate dimensioning is a very effective way to dimension, and it is easier to read for machinists/CNC.
As long as you maintian your design intent, everything should be fine.

 

[USAeng]

yeah I was worried about the tolerance stacking up

I imagine using the ordinate dimensioning for the majority of the noncritical dimensions and then when it comes to critical dimensions doing those seperately...

I will get the hang of it... and he does want us to do it project by project, but eventually all of the drawings will be changed over

 

[ArtL]

Mr USAeng I usually set up my drawings with the upper left hand
of the part as the 0,0 position. Reason being on a mill, useing a vice, the back jaw is the fixed jaw, and the quill handle is on the right side of the mill. So its easier to dial off ordinate dims without rotating the print so the 0,0 is upper left. With just about all work being done on CNC's now I don't know if it really makes a difference any more. If you set up some sort of standard to start with, there is less chance you will be bit in the butt down the road.Ordinate dim the first hole and go point to point for the close tolerence between holes.

 

[SnowCrash]

I've used these for shop drawings for several years. It is handy for milling and drilling, and some lathe work.
I handle tolerance build up by using normal dimensions between features and making the ordinals (reference) dimensions where there is a conflict. Of course, Geometric Tolerances of features would be better.
It takes some understanding of your shop practices to determine the best 0,0,0 for each part. Generally I put it on the upper left side of the part as oriented for machining. I use the same position for the coordinate system for BobCAM.
When I get a lot of holes in a part, I use the hole table instead of a web of dimensions, anyway.
I think I've read that you can use coordinate in sketches and features and then import into the drawing, but I have not tried it.

--
Hardie "Crashj" Johnson
SW 2011 SP 2.0
HP Pavillion Elite HPE
W7 Pro, Nvidia Quaddro FX580

 

[fcsuper]

Ord dims actually limit stack up over other methods of dimensioning. It just depends on how you implement it. I covered this is some brief detail last month:

http://www.fcsuper.com/swblog/?p=2440

Matt Lorono, CSWP
Lorono's SolidWorks Resources & SolidWorks Legion
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[SnowCrash]

fcsuper,
I was actually thinking of your blog when I responded. The issue for me comes when the position of the holes mates with something, but the position of the pattern is wide open. Like I need +-.005 to mounting holes, but the pair can be +- .050 on the plate.
Geo is better for that.

--
Hardie "Crashj" Johnson
SW 2011 SP 2.0
HP Pavillion Elite HPE
W7 Pro, Nvidia Quaddro FX580

 

[fcsuper]

Yup, but it can be difficult to convince some engineers to accept GD&T. Either way, function and design intent should be the primary determinations of any dim scheme. The beauty of GD&T is that is factors in some degree of design intent. Function is still up to the engineer to address.

Matt Lorono, CSWP
Lorono's SolidWorks Resources & SolidWorks Legion
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[USAeng]

Another thing to mention- I was told that I should place the outside dimensions above the part and the inside dimensions below the part. This would be for a cylinder with varying diameters outside and inside. Is this an industry standard or something? Thanks for the replies

 

[SnowCrash]

Don't know nuttin about no standards ;-) , but I do often put in two sets of dimensions above & below, sometimes from both ends of a cylinder which might require two setups in the shop.

--
Hardie "Crashj" Johnson
SW 2011 SP 2.0
HP Pavillion Elite HPE
W7 Pro, Nvidia Quaddro FX580

 

[fcsuper]

No, that's not a standard. There are preferences that some people that and try to pass off as rules. The drawing should be well organized, but rules like that one will often exceptions (which means it isn't much of a rule).

Matt Lorono, CSWP
Lorono's SolidWorks Resources & SolidWorks Legion
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