GD&T Datums

[Magnum]

I just downloaded the software and started looking through the process. I am honestly surprised I stumbled across this company, very impressed so far.

However, I generally do a lot in GD&T as the main goal is to eliminate rejections. I do have a few questions. I called up one of the sample parts and tried adding a datum place. It stated the X&Y are default in the front and z in the side.. No problem.. But how do i see the actual datum? I wanted a box with A & B datums in the front view. But could never see the actual location...

Second. How are hole patterns or parts established with GD&T verified? At what point would a go-no-go tool be used and is there a cost associated with it?

Also, can I apply a datum to a circle? I tried adding a datum and when I tried to go into 3D, it stated the circle needed a Z depth, but that was already defined.

is the problem I am using the part to try and associate the datum and I should have a separate line?

[Tech2]

The Datum capability currently only allows you to draw lines that define the origin of measurement of the overall part. For example, consider a rectangular box lid with 4 corner holes. If you draw datum lines along the lower and left edge, the part will be measured accordingly. If you draw datum lines thru the centers of the lower and left corner holes, the part will be measured that way. GD&T symbols are not displayed or interpreted automatically but they can be added using Comments To Machinist. Costs for Comments To Machinist are handled manually by eMachineShop Staff. Costs for tight tolerances are handled automatically for the built-in tolerancing features. The specific tools used in inspection are at the discretion of the inspector unless specific instructions are provided via Comments To Machinist.

[Magnum]

Thanks for the quick reply. I think I understand. Here is a small example, maybe you can let me know the best way to proceed. I come from the aerospace industry where everything is just about GD&T on every part.

I have a small rectangular plate that has three holes in line through the middle of the plate. I need these holes at a close tolerance, first guess would be about +/-.003 to the center hole.

The overall dimensions of the plate I could care less about and could be +/-.030 or even +/-.08. But The holes must be within the above tolerance to each other. Would it be better to try and describe as GD&T or simply just hold a tighter tolerance on the holes and leave a note to the machinist?

I would think a situation like that would not really increase the cost at all, as it is simply a different reference point for centering/measuring?

[Tech2]

1) Draw a vertical and horizontal line meeting at the center hole.
2) Set line type to Datum.
3) Set Job | Settings | Auto | Tolerance to say .03.
4) Add Comments To Machinist with appropriate arrows for the hole positions.

The additional cost would be minimal for a small run.