ninjabadger
Industrial
- Jun 26, 2015
- 2
Hi All,
I'd like your help on how to datum this part (or if how I'm thinking of doing it is legal)
First off 95% of the parts / drawing here don't have any datums specified. Occasionally a bore will be called out as a datum, and a c'bore or groove given a concentricity to it.
I'm really pushing for the use of proper datums and more GD&T, the design department and others are quite receptive to this but not that clued up on it, so I'm kind of showing them how I think it should be done.
I'm a CMM programmer BTW.
We've potentially quite a bit of work coming from some customers whose drawings contain some quite involved call-outs, so they realise they can't continue to shy away from it too much, but they're also mindful of a workforce who will need educating on this. i.e We want to keep it all fairly basic to start with.
We're working to ISO (Although I don't have access to all the standards - ISO is a pain unlike ASME it's not all contained in one nice document)
The attached drawing (not a real part, I just knocked it up for demonstration purposes) is typical of the type parts we make. We manufacture pumps and similar products.
The Three large bores are for the pistons (they actually house cylinders which the pistons go in but that's not important) - these are tight limit in both size and position.
The three smaller holes are flow holes - there's nothing important about these other than they're there.
The 6 smaller holes around the outside are bolt clearance holes.
In the assembly the part will mate on what I've defined as datum A and locate on Dat B (which has a groove / seal which I've not modelled).
Timing wise the orientation would really be controlled by the three large bores.
I believe the correct way to define this would be....
3X 20.0±0.02
[POS|Ø0.05|A|B] (Correct position of group to Face/Locating Diam)
[POS|Ø0.05] (Correct position to each other)
V
|
|
[C]
i.e. Datum C is defined as the group of cylinders.
I know however this will not be well received (too complicated).
They (Design) want to use one of the cylinders as Datum C - but on a rotationally symmetrical part depending on which of the three (or in some cases 6) you picked you'd get different results.
We've come up with the idea of having some identifying feature to identify which is to be used - in this case a countersink on one of the flow holes. So I could show the bore CW of the countersunk hole Datum C.
The problem then comes in the detail section view I want to call the c'bore out to the cylinder.
I guess my question is can I label the bore (in the 'Typical 3 positions' detail section) as Datum D, even though it's already been called out as C elsewhere?
At the moment all holes are called out as toleranced PCD & Angular locations, but obviously the next logical step is to use Position to define them - so even though we'd not have anything called out the ABC just yet, I'd like to get a good system of working in place now. For now though I'd simply like a fixed DRF from which to generate repeatable results.
I'd like your help on how to datum this part (or if how I'm thinking of doing it is legal)
First off 95% of the parts / drawing here don't have any datums specified. Occasionally a bore will be called out as a datum, and a c'bore or groove given a concentricity to it.
I'm really pushing for the use of proper datums and more GD&T, the design department and others are quite receptive to this but not that clued up on it, so I'm kind of showing them how I think it should be done.
I'm a CMM programmer BTW.
We've potentially quite a bit of work coming from some customers whose drawings contain some quite involved call-outs, so they realise they can't continue to shy away from it too much, but they're also mindful of a workforce who will need educating on this. i.e We want to keep it all fairly basic to start with.
We're working to ISO (Although I don't have access to all the standards - ISO is a pain unlike ASME it's not all contained in one nice document)
The attached drawing (not a real part, I just knocked it up for demonstration purposes) is typical of the type parts we make. We manufacture pumps and similar products.
The Three large bores are for the pistons (they actually house cylinders which the pistons go in but that's not important) - these are tight limit in both size and position.
The three smaller holes are flow holes - there's nothing important about these other than they're there.
The 6 smaller holes around the outside are bolt clearance holes.
In the assembly the part will mate on what I've defined as datum A and locate on Dat B (which has a groove / seal which I've not modelled).
Timing wise the orientation would really be controlled by the three large bores.
I believe the correct way to define this would be....
3X 20.0±0.02
[POS|Ø0.05|A|B] (Correct position of group to Face/Locating Diam)
[POS|Ø0.05] (Correct position to each other)
V
|
|
[C]
i.e. Datum C is defined as the group of cylinders.
I know however this will not be well received (too complicated).
They (Design) want to use one of the cylinders as Datum C - but on a rotationally symmetrical part depending on which of the three (or in some cases 6) you picked you'd get different results.
We've come up with the idea of having some identifying feature to identify which is to be used - in this case a countersink on one of the flow holes. So I could show the bore CW of the countersunk hole Datum C.
The problem then comes in the detail section view I want to call the c'bore out to the cylinder.
I guess my question is can I label the bore (in the 'Typical 3 positions' detail section) as Datum D, even though it's already been called out as C elsewhere?
At the moment all holes are called out as toleranced PCD & Angular locations, but obviously the next logical step is to use Position to define them - so even though we'd not have anything called out the ABC just yet, I'd like to get a good system of working in place now. For now though I'd simply like a fixed DRF from which to generate repeatable results.
