End of Slot as Datums? 7

[SDETERS]

I have a part that has two protuding slot features on it. The part is made of Rubber. The two protruded slots are what locates this part in the assembly. I want to call out a profile of these slots but I also want to call the end radius as y and z datum Please See PDF. What is the proper way of doing this? Will the R.16 be basic or have a tolerance? Should I say three surfaces on the profile instead of all around? Suggestions. Wow two questions from me in same day. Sorry.

 

[KENAT]

Hmm, what you have is 'orrible at first glance but I'm trying to properly understand your intent before I say too much.

Certainly if you want to use the surface profile all around you either need to make the entire slot controlled by it and make the rads basic or, explicitly identify which surfaces it applies to as per Fig 6-13 from ASME Y14.5M-1994.

Can you explian really what you mean by using the end radii as datums? I think your secondary and tertiary datum between them want to fix it's translation (top to bottom and side to side as shown in the print) and its orientation (rotation).

Given the way one of the slots is angled to the other and to the overal part, I wonder if you'd be better using the horizontal slot feature to get both your secondary & tertiary datum and then relate the other 'slot' to it.

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[SDETERS]

I agree it is not the best way of doing things. By using the end of the radii on the two slots the CMM can easily pick up one radius as the Y datum and the other as the Z datum. I am up for suggestions here. I just need to make sure this part fits in to a channel. I could change the slots to protruded pins,But the ENg likes the looks of the slots and wants to keep them. I understand I need to make the R.16 basic. But can you attach a Y datum to a basic dimension. I guess this is where I am getting confused. Looking at 6-13 now.

 

[KENAT]

Using a cylindrical feature as a secondary datum feature typically fixes translation but leaves rotation unconstrained, you get two theoretical plantes intersecting at right angles to the datum axis but not oriented to the overal part. Take a look at section 4.4.2 7 figures 4-5, 4-7 & 4-9 in ASME Y14.5M-1194 and associated text.

To get the rotational orientation you add another datum (4.4.3). My Concernt is how your Z is interpreted in this context.

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[TheTick]

Looks like the GD&T equivalent of moving across state lines in order to marry a cousin.

 

[SDETERS]

Thanks for that comment so what is your suggestions? These features are the only features that locate this part. I do not need to use surface profile. I would like to get the best Datum structure as possible for this part. How you would set the y and z datum structure up?

Kenat I looked at the veiw you mentioned. All the datums are in the same plane.

 

[TheTick]

I forgot to type the first part...

Some things are "legal" but very questionable.

I would use the width of the "Y" slot as the horizontal datum and the length or an edge as a vertical datum.

-OR- use the straight edges as datums and constrain the slots as a pattern, perhaps with a composite tolerance.

The slot ends are not going to be easy to pick up with any accuracy, even with a CMM.

Given the generous tolerance you have on the profile, I would wager there are many better ways to dimension and inspect this part and get a good result, even if the scheme is not 100% aligned with your design intent.

 

[KENAT]

The last sentance of my first post was meant to be something like Ticks 1st suggestion. Use the horizontal slot, either width or length, I'd suggest length as it's a longer feature to give you orientation, as your secondary datum. I'd then maybe use the width of the slot as my tertiary datum.

However, this is assuming the fit to the next part is very much constrained by the location of the slot.

Given that you say it's rubber, and the fairly loose tols, I wonder if this is a case as Tick says where you don't have to stick really close to theoretical function in order to get a workable solution.

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[fcsuper]

The tolerancing of the slots is incomplete. Also, Y and Z are to the center of the slot radii to which they attach. I'm guessing you actually want there farthest points to be the constraint? For this, you'll need verbage on the drawing, because (correct me if I'm too lazy to look this up) I do not believe there exists a standard method to create a datum to a "farthest point from such and such" on a curve.

Also, I ASME has a method that better controls slots, though it is a bit more work to set up, and profile allows you to short cut your datum scheme (if you want the centers of those radii to be your datums).

For style, attached the Z and the Y to the bent portion of the radius leader. This is a bit cleaner than globbing it directly onto a radius.

Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
and Mechnical.Engineering Yahoo! Group

 

[fcsuper]

..sorry, for your other question, R.16 does appear to be a basic dimension since you are using an all around profile FCF.

Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
and Mechnical.Engineering Yahoo! Group

 

[Belanger]

Tick -- moving across state lines; flogging; you're a riot!

John-Paul Belanger
Certified Sr. GD&T Professional

http://www.gdtseminars.com

 

[SDETERS]

Great feedback all thanks

I will review these suggestions and update the drawing. Maybe GD&T with datums do not need to be used. I am going to review this with the eng and post the results when we get something that can agree upon. Thanks again.

 

[KENAT]

Hang on, no one said not to use GD&T here. I suspect the use of it is entirely appropriate. The thing is you were trying to use it wrong, or at least unusually.

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[SDETERS]

Oh ok This is an unusally different part. That is why I come here to the people who know the standards inside and out. I think we are going to call out how kenat talked about using the width and the length of the horizontal slot as the y z datum. I think I am going to set the datums up this way. Thanks again.

 

[TheTick]

correct me if I'm wrong...

If both slots are controlled by the same control frame (w/ two arrows), then you can control their relative position to one another with just the "X" datum (maybe add a second datum for orientation). Then a second frame to control the position of the pattern on the plate.

Can composite tolerancing be applied to profile?

 

[PeterStock]

Attached is how I would dimension the OP's part.

Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services
www.infotechpr.net

 

[tk369]

sdeters..
i would caution you that the horizontal slot is actually a TAPERED slot as shown. even changing the r .16 to basic leaves you with a tapered slot.

that said, the y14.5-2009 standard will allows the use of a 'linear extrusion', i.e. the horizontal slot, as both secondary and tertiary datums. this allows you to locate the angled slot with basic dims, and gives you rotational control of the entire part (after locating the slot to one of the edges of the part, of course.)

teddykaye

 

[SDETERS]

TK369 I will look into the 2009 standard about this. We have to stay with the 1994 standard but it does not hurt to look at the new standard.

Peterstock.
Thanks for that feedback. I was thinking that same thing and I am moving torwards that way of setting the datums up.
I have taken that type of info from Kenat you and thetick and assumed that it meant what you have posted in your file. Thanks for all the help

 

[KENAT]

Peters is pretty much how I was going to do it. One thing though, I think it still needs an "R" pointing to thes slot end radii. No value, just R to incicate it is a true full radii.

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[axym]

sdeters,

Before recommending a datum structure, I would need to know exactly how the part's degrees of freedom are constrained when it interfaces with the mating part. Specifically,

1. What is the geometry of the features that the slots mate with? From your descriptions, it sounds like the mating part has two pins, with basic spacings of 5.444 in the X direction and .398 in the Y direction. Is this correct?

2. What is the size tolerance of the mating features? Or are they adjustable in size to achieve a snug fit with the slots?

Once these questions are answered, then the datum features (or possibly datum targets) can be specified appropriately. Tolerances can then be applied to the various slot surfaces and to the features that need to clear the channel.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca