Profile of Coplanar Mating Surfaces

[koorookoo]

Hello! I have 3 identical parts (see attached image), which need to be intimately mated using a clamp.

ALL mating round surfaces must be in contact WITHOUT any gaps once the 3 parts are clamped. Before clamping, a very small gap can be tolerated (0.002") and thanks to clamping forces we expect to close the gaps. Note that if profile is used on these 7-inch tall parts, some of the round surfaces could be on their max side or min side, so some will be in contact and some will not until they are clamped.

QUESTIONS:

1) What is the best way to dimension the 3 faces on each side of the part for machining?
2) Should the RIGHT faces (3X) be PERPENDICULAR to the part floor to minimize tilting with PROFILE as additional control (w/ or w/o continuous feature?) ?
3) Should the LEFT faces (3X) be PARALLEL to RIGHT faces?

Thank you!

 

[drawoh]

koorookoo,

Is the base of each piece mating with the floor? Is this critical?

Why do the faces need to mate accurately? Is this structural, or do you need a thermal or electrical contact?

--
JHG

 

[koorookoo]

The base will be bolted down as well (bolts and details are not shown in the diagram). So, somewhat might have an impact on the above mating surfaces.

Also, the face need to be in contact for vibration (i.e., structural) reasons. If they are in contact, the parts would be more stable as they'd be considered to have a wider base, as opposed to individually, where they'd wobble.

Thanks,

 

[drawoh]

koorookoo,

You need to think your design through quite a bit. I don't think this is a drafting problem.

If your pieces are rigid and you are straining them .002" on assembly, you may be imposing high stresses, at assembly. To get around this, you may need to specify ultra-tight tolerances. Any stresses in service will be added to your assembly stresses.

Consider using side plates to connect your pieces. This will be flexible at assembly time, and it will be rigid when you clamp the bolts down.

--
JHG

 

[koorookoo]

Thank you drawoh, your advice is well taken into consideration. However, we would still like to know, as originally asked, if all's acceptable structurally, how would one dimension the part?

Profile and perpendicular for one side and what about the other faces? Parallel or profile to first faces?

Thank you again.

 

[3DDave]

Profile can control perpendicularity, so only profile is required. Since the faces on each side are otherwise independent, independent profile tolerances can be applied on each side to the faces; there is no reason to chain the tolerance build-up from one side to the other. Each individual face (6 per part) will need a refinement, such as flatness.

Your original goal is going to be difficult to realize. You need a strain analysis to determine if the parts will deform enough to close the gaps.