Questions on connector cut out 2

[KENAT]

I’m looking at a bracket that has a couple of mating pairs of D type connectors that mount to it. The location of the cut outs in the bracket isn’t too important but the size/shape of the cut-outs, and the holes associated to the cut-outs are more critical. See attached sketch.

I’m thinking this is an ideal case for composite profile like ASME Y14.5M-1994 fig 6-25 for the cut-out. However, I’m not over confident on then relating my holes to follow the cut-out. I found a similar example in some training material from Gary Whitmire but my cut out is a lot more complex and I don’t fully understand the datum structure regarding use of D-E rather than D|E.

Q1: Which of the hole feature control frames in my sketch makes more sense or is there another better way.

Q2: Where symmetrical I’ve given overall dimensions for the cutout, like you would for a simple slot. However some of the examples around here that my previous checker did have additional dimensions to relate the overalls to the ‘center’, e.g. a .656 dimension from the center to one of the holes and similar for the width and height of the slot. Are these extra dimensions really needed?

(Please note I haven't properly calculated the values of the positional tolerances yet, I probably should have made them the same for the sketch.)

Thanks.


KENAT, probably the least qualified checker you'll ever meet...

 

[drawoh]

KENAT,

Your specification looks okay to me, although it is a little complicated. I take it your Datum_D is the outside quadrant of your radii.

I think you can make the drawing views simpler. Apply positional tolerances to the jack screw holes with respect to the main drawing datums. Apply the profile tolerance all around the big hole, showing the boundary outside. This makes your nominal dimensions the MMC. All you need to do is make sure your D-sub poke out through the hole when it is located by the jack screws.

On main drawing views, I tend to dimension to one of the jack screws. On my detail view, I can use the jack screw as a datum. Unless your D-sub is fixed to a printed circult board, its location is not nearly as critical as the location of the pattern elements to each other. You can buy D-sub hole punches, so there is a way a fabricator can take advantage of well prepared drawings.

Your form obviously is symmetric, and you cannot measure from a centreline, anyway. I think you are right to leave of the centring dimensions of the jack screw holes.

JHG

 

[KENAT]

Thanks Drawoh,.

I take it with your proposed scheme the profile FCF would also refer back to the main drawing datums.

In this case how do you propose to take advantage of the fact that the connector cutouts positions can vary a lot with respect to the main drawing datums but that that the shape/size of the cutouts and the position of the holes reletive to them must be more more closely controlled?

I've updated my sketch to show what I understand of your proposal.

KENAT, probably the least qualified checker you'll ever meet...

 

[Xplicator]

If you can could you include the A|B|C datum features in your sketch so I can get clearer understanding. Off the cuff, I'm thinking fig. 6-19 in conjunction with fig 5-28, the kicker would be declaring the two hole pattern as a datum as well and position the cutout wrt it. Although that might be to much for what you need. This is just a knee jerk until I see what else you've got going here.

 

[powerhound]

I think your original print was good except that I would have repeated all the datums in FRTZ of the composite profile tolerance. Also, don't forget to add the "all around" circle to the elbow of the leader line.
I don't understand the alternative method that you show on your drawing at all. I've always understood that type of callout to apply to axes or planar features but have never seen it used like this before. I'm curious to know how that method even works.
As for your second question; if you position the hole pattern relative to D and E and show no dimension from center of D to the center of the hole and from the center of E to the center of the hole then the dimension is an implied zero and thus "centered". You don't have to add dimensions to show it centered.

Powerhound, GDTP T-0419
Production Supervisor
Inventor 2008
Mastercam X2
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[powerhound]

KENAT,
Check out the March tip on the tec-ease website that I frequently refer to. It directly addresses your second question.

Powerhound, GDTP T-0419
Production Supervisor
Inventor 2008
Mastercam X2
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[KENAT]

Xplicator, I looked at those figures. I'm not sure 6-19 actually achieves what I want, in fact it's almost opposite. If I understand correctly it has a relatively lose profile and then puts a tighter position. I effectively want the opposite, relatively tight profile to control size & shape but looser position. I don't see what you're referring to on 5-28.

Powerhound, I looked more closely at 6.5.9 after what you put about the lower profile size/form/orientation refinement control and I'm tempted to think I don't necessarily need to add them as I'm not too concerned about orientation to A & B. However, the fact I'd put this already was more by luck then understanding, having looked at it again I better understand it and will think some more about adding them. Given that D & E are derived from the cutout itself I don’t think having loose orientation of the cut-out will negatively effect the location of the holes relative to the cut out, but please correct me if I’m wrong. Thanks for prompting me to take another look.

I realized the all around symbol was missing after I posted the sketch, thanks for reminding me though.

I was lost by the second option on the FCF for the holes too, it didn't make sense to me in this application but I thought maybe I was missing something. I know there's a couple of errors in the material I was looking at, maybe that's one of them.

On my second question what you, drawoh and tec-ease say confirmed my understanding of things. I was doubting myself because the other drawings were done by someone who really knows their stuff and if he'd put it I was thinking maybe I was missing something.

Attached, is updated sketch again with the all around symbol & datums A & B shown. C is the far side face of the tab that the cut outs are in, so is normal to them. It’s slightly higher resolution so hopefully clearer where leaders/dim lines are going to (I’ve cramped it up to keep the file size down, on the drawing it’s more spread out).


KENAT, probably the least qualified checker you'll ever meet...

 

[powerhound]

KENAT,

The reason I would have repeated the datums in the lower portion of the composite profile FCF is not as much for orientation as it was to maintain a smooth profile. As it is the profile would have to be perp to C within .010 but the profile itself can still wander within .050 of the true profile. For example the vertical line across the top of the cutout can still wander + and - .025 from the true profile, making for a potentially jagged line. If this is not a concern then never mind.
Something I just noticed about the print is the feature that makes up datum D. It is comprised of 2 tangent points on the arcs. It might be better to make datum D the .875 dimension instead...just an observation.

Powerhound, GDTP T-0419
Production Supervisor
Inventor 2008
Mastercam X2
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[KENAT]

Powerhound, are you sure about the profile still being able to wander the .05 rather than .01 effectively wrt istself (not quite the right terminology I suppose sorry)? I'm looking at 6.5.9 and especially at figure 6-25 and that isn't my understanding of it.

You'd be more likely to know than I but I don't see it matching what the standard says or figures show.

KENAT, probably the least qualified checker you'll ever meet...

 

[CheckerRon]

Regarding the implied symmetry tolerances that powerhound and Kenat mention. The March Tec-ease tip does clarify that a dimension off a centerline isn't needed but the tolerance definitely is.
I often get drawings where the designer assumes symmetry on a linear feature dimensioned with a ± tolerance and shown symmetrical to a feature centerline, but without giving either a GD&T tolerance or a toleranced dimension to the centerline. As I understand the tec-ease tip, you need one or the other. Agree or disagree?

 

[KENAT]

If you're not using appropriate GD & T to apply the tolerance then yeah, I'd say you need a dimension to center it.

The examples I was looking at (CCA faceplates if that rings a bell Ron) had both GD&T and centering (basic) dimensions.

However my main concern now is that I'm using the composite profile properly and that my holes are following it.

KENAT, probably the least qualified checker you'll ever meet...

 

[drawoh]

KENAT,

Yes, in my first proposal, the outline usually would be controlled by the main drawing datums. My second suggestion accounts for the possibility that the location of the hole is controlled separately from the profile.

I agree that allowing the D-sub pattern to float is good practise, but fabricators cannot always take advantage of this. The more complicated drawing would not help a machine shop at all. Now on the other hand, it looks like you have a bent sheet metal part there. Dimensions from the bend can be fabricated to +/-.015".

JHG

 

[KENAT]

drawoh, on your second idea how does making the first hole the datum and positioning the cutout and other hole from it work better than positioning the cutout and then the holes from it as I've effectively done?

I'm not sure I understand what you mean by coming off the profile being more complicated, there's not much in it is there? The holes are tied to the cutout. The cutout is relatively free to float but the holes and the form/size of the cutout must be more closely controlled.

The +-.015 you mention is fine for me for location but no good for the size of the cut out. (Well it might be but I don't have the information to be sure, my information says +-.005 which I've put in as surface profile to better control it).

KENAT, probably the least qualified checker you'll ever meet...

 

[drawoh]

KENAT,

I think one of the jack screw holes makes a better location datum than parts of your cutout would. The jack screws are what will locate your connector. Either method is valid according to the standard. The standard D-sub cutout for front mounting is sized to allow you to insert the connector from the rear, with the cable attached. This is gross oversizing.

If my part is being machined, or it is a flat piece of sheet metal, I tend to not worry about patterns. I would rather have a simple drawing that the fabricator does not spend too much time studying. Everything will be accurately located.

If the sheet metal is being bent, or one or more datums are controlled by welding or casting, then I worry about patterns. It is easy to design stuff that cannot be fabricated.

JHG

 

[Xplicator]

After looking at your last drawing spec I believe that what you have will probably work fine to get by but with some risks. Here is what I would question, which of the features in this collection constrains the next component. Is it the cut out or the mounting holes? Next would be the second cutout/holes collection, what are they to be controlled wrt? Since the detail is in two places are we to assume that it is a separate requirement and that it also has replicated duplicate datum(s)?

It would be my guess only, that the mounting holes are your constraints here and dictate assembled orientation and location of the connector to the bracket. The cutout is merely a relief and must allow clearance albeit minimum when the connector is constrained. Now a connector to connector may be an entirely different story but that isn't what this is.

My proposal is that you locate the mounting holes wrt the main DRF. Make the pattern of the two mounting holes your sub-secondary/tertiary datum leaving C as primary. Then locate the cutout with respect to it using Surface profile to refine the size, form and orientation to your liking. You can now call the second collection wrt this "sub-datum scheme".

This is not complicated neither just thorough. If I am wrong about the intended function which I could be, in the dynamic of speculation about intent in this forum then I'm sorry, But if not, these are a couple things you should consider.

 

[KENAT]

Hmm, I've been thinking about it a bit more and you may both be right about the holes being the real location feature.

Nominally I care where the connector itself ends up not the mounting screws but the screws probably do define that more than the cutout.

One of the examples I looked at was mating to a CCA where the connector location was driving it. The other was just a generic example in some training materiall.

I'll think about it some more and may post again.

Thanks,



KENAT, probably the least qualified checker you'll ever meet...

 

[TheTick]

I understand your plight.

I am not comfortable with using the cutout as a datum to locate the holes or vice-versa. Unless I am mistaken, datums are fixed and do not "transfer" from one instance to the next. Even though your meaning is clear, I do not believe it is correct.

I can not find a precedent for using a single position on the cutout. If you can do this, then you could cover the holes and cutout with the same composite position callout.

 

[powerhound]

Tick,

While this may not apply to what KENAT is trying to do, you can, in fact, transfer datums as shown in Fig. 5-39. An extension of this principle can be used as shown in the following tec-ease tip:

http://www.tec-ease.com/tips/march-01.htm

This kind of looks like what KENAT is doing but he only has 2 cutouts to deal with and it's hardly worth the effort.

Powerhound, GDTP T-0419
Production Supervisor
Inventor 2008
Mastercam X2
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[TheTick]

Simple enough to understand. I still have doubts as to how kosher it is w.r.t. the actual standards. Can anyone out there find chapter and verse?

 

[powerhound]

Section 5.7 in the standard...Fig. 5-39

Powerhound, GDTP T-0419
Production Supervisor
Inventor 2008
Mastercam X2
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II