Effective Training Inc. Message Board

I am currently working with a product that has a tapered blind hole. The taper is called out by two diameter limit dimensions one at the top and one at the bottom as shown in the top picture.

The problem is that, IMHO, this dimensioning scheme doesn't give any position tolerance, doesn't well define how the taper of the hole should look and is difficult to gage.

Two options were developed as shown in the bottom picture. But I don't know if they are proper to address the three concerns stated above. The top option on attachment looks like it gives no positional tolerance compared to the ID. I understand the intent of the bottom option but I don't know if it is correctly using the standards. Maybe there is a third option that someone sees for this. Thanks in advance for any assistance and please let me know if you have any questions.

_________________
Anthony J. Weaver
Supplier Development Engineer
BorgWarner Drivetrain Systems

Here is one suggestion. Since it is very difficult to measure at "corners" it might be better to dimension to a point on the tapered cone where there is a continuous "flat" surface. This suggestion uses a toleranced diameter coaxial to Datum A and an associated Basic depth dim from datum surface B. The Profile of a Surface is then applied to the tapered conical surface of revolution with respect to Datums A and B. The toleranced diameter dimension could also be Basic which would then only allow the position, size, form, and orientation error to all be contained within the fixed Profile tolerance zone. As shown here however, the actual cone can grow and shrink within the size limits and the profile zone moves with it. Inspection would check diameter at the Basic depth such that it would have to be within the size limits. The actual entire conical surface would then have to stay within the profile zone tolerance limit. If dimensioned as shown in this sketch then the total diameter tolerance would typically be greater than the profile tolerance zone width. Otherwise, you'd have to make the diameter basic and use the profile tolerance to control all variation.

(Couldn't get the JPG image to upload! I'll try it on a separate reply.)

_______ _______B
\ /
------- \---------------- /----------------
\___ ___/
| |
| |>--A

The stinkin jpg file still won't upload to this site. Maybe its the firewall here or something. Oh well.

Sorry for the crude sketch here. It will have to do. The dotted line above is at a Basic depth from the top surface (B). And it has a toleranced diameter where it intersects the cone. It also has a Basic angle dim. The overall depth of the conical hole can be a toleranced dim as well. Profile of a surface spec applied to cone with respect to A and B.

Sorry, the crude sketch lost all of its "spaces" when the reply was submitted. Now it really looks goofy. If you put spaces in the appropriate places in each line the image will come to life!

Joeyd,

No problem about the attachment. I am having the same problem. I just have been linking to an outside site for the photos.

I understand your comments above. Thanks for your input.

Attached is the pre-release of the new dim scheme that was presented today. Better than the old, but the profile of a line call out is throwing me off a little. I am going to have to look into that one to make sure that I am ok. I don't think it violates the standard but it’s not make sense to me readily. I see what the intent is but I don’t know what it means for my suppliers gauging method.

_________________
Anthony J. Weaver
Supplier Development Engineer
BorgWarner Drivetrain Systems

AWeaver,

What your drawing details for the conical hole might be considered as a "True Profile" in that it has been defined by Basic dimensions. There is a basic radius (diameter) and a basic angle (and perhaps a basic depth... or could be a coordinate ± tol on depth). At any rate, no part will be truly perfect (at true basic form and size) so the Profile of a Line (PoL) control is an attempt to limit the variation. The problem is that usually the application of PoL control to a feature like this implies that, while trying to control a "line element" along the axial length of the conical surface, the form and size AROUND the cone (circumference) is controlled by a diameter tolerance or some other limits. But, in this case your drawing also has a Basic radius (diameter). So, circumferential form and size would also have variation but you are trying to control that with an axial "line element" control. My suggestion would be to change the control to a Profile of a Surface (PoS) and then let it control all aspects of the hole's variation. You could have a larger PoS control and then apply a smaller PoL control to further limit the axial form error. Or have the larger PoS control and then apply a Circularity to control form around the hole circumference.

Again, PoL is not necessarily wrong here, its just not as clear or complete as would the PoS control.

Joeyd,

Here is the final released design that will go for quote and feasibility to the supplier. Through the collaborative efforts of product engineering and supplier development we have found we don't need a taper but rather a chamfered hole will do just fine for the functionality of the part and improves all the concerns that we had with the tapered hole gauging. We are expecting a reduction in the cost of gauging and tooling in the next quotes as well.

Thanks for all your input.

_________________
Anthony J. Weaver
Supplier Development Engineer
BorgWarner Drivetrain Systems