Good example of engineering drawing

[ant77]

Hi all,

I'm looking for a good sample part drawing done to Y14.5M.

Can anybody supply a drawing, or show me where I can download one?

Thanks,

ant77

 

[aardvarkdw]

CBL,

You may be right, but that really wasn't what I was intending to demonstrate. Depending on what sort of tolerance is required, you may want to dimension between the holes like Ant showed in his post, but the method of showing Symmetry is sound.

Pdybeck,

Being as I don't know how the part is to be used I didn't include datums and such. I was just trying to show the ASME Y14.5M-1994 method of denoting Symmetry.

 

[Finethread]

Greetings,
I recommend you take a look at the Drafting Manual Pocket Companion. You can find it on the Genium Drafting Zone site. I have been providing these to designers and engineers for years. There are good examples of GDT, delineation, hole callouts, often used formulas and tables etc. It's all based on ANSI.

 

[ewh]

I would establish your 3 primary datums as the face of the part (A) and two perpendicular sides (B and C). then use basic dimensions from B and C to locate your holes, using a positional tolerance (value of which determined by need) to A, B and C.

 

[ctopher]

ant77,
Please read faq559-1100.
Your picture makes all posts cut off the right side. I can not read everything.
Thanks.

Chris
Systems Analyst, I.S.
SolidWorks 06 4.1/PDMWorks 06
AutoCAD 06
ctopher's home (updated 06-21-06)

 

[MechNorth]

I think some of the responses are getting a bit off-topic. The original question was regarding how to dimension in Y14.5M, not whether the method used was legal or consistent with any other standard, whether or not such standard is referenced within Y14.5M.

I've posted a (hopefully) clean drawing for ant77's geometry on my site

http://www.profileservices.ca/files/tidbits/tidbits_missc.html;

download it and review it with the following text:

Where to begin ... with datums! The most fundamental benefit of GD&T by ASME Y14.5M-1994 or any other standard, is that you can repeat the inspection process because you have datums to establish the origin of measurements. Your likely Primary Datum (let's call it Datum-G) will be the back face of the U-channel. This is better than the two feet of the channel because it minimizes the effect of warpage in the center panel. Put a Datum-G symbol on the back face or on a leader from that face (see Y14.5M-1994-Fig. 4-2, Datum-D, -E, -F). Next, the symmetry is visually about the centerline, so that is the desired location of the Secondary Datum (let's say Datum-A). To do that, put a Datum-A symbol inline with the arrow of the dimension line (see Y14.5M-1994-Fig.4-19, Datum-A or Datum-B). This indicates that the mid-plane is the datum feature, and that is where the locations will be measured from, and hopefully where the features will also be dimensioned from. The Tertiary Datum should be the face from which the 10,20,30 dimensions originate; label it as you would for the Primary Datum, indicated above, but call it Datum-K.

As the symmetry is visibly about the centerline, you do not dimension both of the symmetrical holes, just the location of one of them, with the dimension starting at the centerline (per Y14.5M-1994, if features on a workpiece appear to be symmetrical, they are assumed to be symmetrical, and those features not complying with a symmetry would need to be individually dimensioned). You will also need a Positional Tolerance on the 6X Dia2.50 callout (drop "HOLE"). A diametral tolerance zone of whatever tolerance size would be applied wrt Datum Reference Frame [G|A|K].

Of course, overall dimensions are needed, and a general tolerance covers all features not otherwise directly toleranced. Note that the trailing zeros are omitted and the C/L symbol is also omitted. You need to indicate the dimensioning standard under which the drawing was created.

Jim Sykes, P.Eng, GDTP-S
Profile Services
CAD-Documentation-GD&T-Product Development

http://www.profileservices.ca

 

[ewh]

MechNorth,
My understanding of establishing datums is that they "shall not be applied to centerlines, centerplanes, or axes", as these are not true features. How is it allowed in this case?

 

[pdybeck]

ewh,

The datum A in Jim's example is not the centerline. The centerline is defined by Datum A surfaces, which are the edges of the part in this example. This is a key difference and is defined under ANSI Y 14.5. The same would be true for placing a Datum on a diameter. The actual datum surfaces are the cylindrical surfaces and they are used to set up center planes which can be referenced by other features. That little centermark that we all place on our drawings for cyclindirical features is a theoretical intersection of planes that are defined by the outside edges/surfaces. I agree with Jim's approach to this drawing and was as I suggested (for establishing Datum A at least). We use this method on our machined casting drawings where we desire a set of machined holes to be centered within outside features of a casting. The drawing is correct to ANSI Y14.5 and is clean and concise to all our personnel who use the drawing.

 

[ewh]

pdybeck,
You are right. I was just starting to post a "nevermind" but you beat me to it. I had posted before I looked at the example.

 

[aardvarkdw]

Based on my post I may not be the best to nit-pick but shouldn't all the dims that locate the holes be basic as well?

 

[pdybeck]

aardvarkdw,

Good catch, they should be basic. I would also dimension between holes and not from center of the datum reference out to the hole. So you would see 20, 30, and 40 dimensions between holes and they woud be basic.

 

[ewh]

... and shouldn't the hole centerlines be connected horizontally (or the dimensions be appended with 2X)?

 

[ringman]

Ant77,

If your company has a drawing standard tha is referenced on your drawing, it might sork for your case. However I doubt that lacking that, there would be anything close to a universal interpretation.

 

[KENAT]

In answer to the original post:

You could also look at something like the Genium manual which expounds upon Y14.5 & associated standards. Again though it's specific examples more than full drawings.

http://www.draftingzone.com

However maybe the applied suggestions to your sketch are more usefull.

 

[MechNorth]

The hole-locating dimensions are basic, as indicated by the note "NON-TOLERANCED DIMENSIONS ARE BASIC". This is very common, and reduces the workload a bit (see Y14.5M-1994, Sect. 1.4-a, and Fig.5-1(c)).
You could dimension one hole from the other, but the typical and common method is to dimension from the datum (in this case, represented but not physically embodied by the centerline) to reduce math errors in programming or machining. Similarly, you can connect the holes by centerlines, but it's not necessary and can lead to a very messy drawing (I had a situation where 144 pattern locations pitched 60mm apart were on a single plate about 1.5m x 1.5m, with 5 holes per location ... that's a lot of centerlines covering the page). Again, if the features are visibly symmetrical about a common and obvious centerline, you don't need to go any further than that. As a result, you don't need to add 2X for each of the lateral dimensions either.
In a previous work environment, we focused on minimal detailing as a cost-savings measure. While I didn't agree with everything that was done under that label, it was fairly obvious that anything that legitimitaly reduces detailing time and the risk of mistakes adds value to the engineering. It's not incorrect to add the extra dimensions, center-lines or quantities, but they add work and increase the risk of making a mistake (e.g. quantities). As a side-benefit, detailing the "odd" features that don't meet the symmetry will make them stand out and reduce the likelihood of being overlooked.

Jim Sykes, P.Eng, GDTP-S
Profile Services
CAD-Documentation-GD&T-Product Development

http://www.profileservices.ca

 

[namdac]

In answering to the original question: According to the freedom of information act, you can get standard drawings on everything from Apollo to Atlantis. I have a copy of the details and specs regarding the Shuttle. All I did was ask. No body gets in trouble, They want thier information in a certain format and they provide a standard outline. Just as ANSI, FAA, NASA, FEMA. Pretty much anyone who utilizes consultants provides guidelines and examples of what and how they acccept the final product.
Have Fun Out There,
Regards,
Namdac

 

[ewh]

MechNorth,
Seems like good reasoning to me. Old habits die hard though.

 

[MechNorth]

I hear ya, ewh. I resisted GD&T for a while, even when I was put in charge of it...little by little, and a whole lot of studying, applications and mentoring, I got there. The plate I described was a nightmare for design & manufacturing, not to mention inspection. People were convinced that I'd redesigned and simplified the plate when I cleaned up the drawing and circulated it with minimum dimensions & reduced clutter. To loosely mis-quote former Canadian Prime Minister, Jean Chretien, "The proof is the proof...when you have the proof, you know it is the proof, and there you have the proof."

Jim Sykes, P.Eng, GDTP-S
Profile Services
CAD-Documentation-GD&T-Product Development

http://www.profileservices.ca

 

[ringman]

Ant77,

One other question please. Is interchangeability a requirement for this part?

 

[ant77]

Thanks everyone for your feedback!

Firstly, apologies to you all for the large JPEGs in my post - please put this down to me being a first timer.

MechNorth, thanks for all your feedback and the sample you posted. This is exactly what we needed to see, and as you say it takes a lot of studying and mentoring to get to that level, so your feedback is very valuable.

I agree with pdybeck that seeing the actual distance between the hole centers would feel more 'natural'. What would you do on the drawing if you wanted the hole centers inspected, because the 40mm hole centers on this part match a 40mm hole centers on a mating part (or is this a naieve question?)

I love the note 'non-toleranced dimensions are basic'!

Unfortunately Ringman our company is not large enough to have it's own documented drawing standard, hence our need to rely on published standards. This part is not interchangeable.

 

[MechNorth]

ant77,
The datums and feature control frame establish how to set up the workpiece for inspection. That's a little beyond this lesson. Are the 40mm holes clearance holes (for a screw fastener) or a tighter fit as for dowels? If the entire assembly is located based on those two holes, then the datums can be changed to reflect that, but it won't make much difference if the holes are a loose fit.

Jim Sykes, P.Eng, GDTP-S
Profile Services
CAD-Documentation-GD&T-Product Development

http://www.profileservices.ca