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How do I check whether this fixture is overconstrained?

EmmaBell0637 · 2026年5月22日 06:20 UTC

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EM
EmmaBell0637
I'm reviewing a nest for our planned placing drilled components in an assembly fixture with Universal Robots UR5e and a milled support bracket in a precision fixture review area. Its multiple surface contacts look convincing in CAD, yet the bench samples seat differently. A stronger clamp has been suggested; I'd like to check for conflicting location constraints before accepting the tooling.

14 条回复

RA
RachelBrooks0870

@EmmaBell0637 Which contacts establish the drawing datums? Mark those separately from supports and clamps, then compare that map with the samples that rock.

10
EM
EmmaBell0637

The holes and the outside wall both locate sideways. The sketch calls all of them locators. It doesn't explain which takes priority.

10
RA
RachelBrooks0870

Show the fixture designer where those constraints overlap, alongside the permitted hole-to-wall relationship. A relieved wall contact is one candidate for their review.

10
TH
TheoAllen0323

That proposal depends on the required datum scheme. Without establishing it, relieving the wall might remove the reference needed by the operation.

13
RA
RachelBrooks0870

I got ahead of the drawing requirement there. Establish the necessary datum scheme before deciding which secondary contact can be changed to accommodate permitted variation.

15
EM
EmmaBell0637

I'll have the designer mark that explicitly. I'm not modifying the nest from a nominal CAD view and a hunch.

5
IS
IsabelBell0648

@RachelBrooks0870 I'm lost on support versus locator. Aren't both just touching the part?

9
RA
RachelBrooks0870

@IsabelBell0648 Both touch it, but a locator establishes position. A support carries load without imposing a conflicting position. The design needs to make those roles work together.

12
AA
AaronCarter0958

In my separate fixture job, contacts labelled as supports turned out to constrain the same direction. Drawing the tolerances exposed what their labels had obscured.

7
EM
EmmaBell0637

Did you measure the awkward samples first? Our instinct has been to put them aside, which might be throwing away the useful ones.

10
AA
AaronCarter0958

@EmmaBell0637 Keep them identified and compare them with the drawing. A sample fitting badly in your nest doesn't, by itself, make the sample wrong.

19
EM
EmmaBell0637

Our inspection sheets show the awkward samples are within drawing limits. Their hole-to-wall dimensions differ within that allowance. So rejecting them would need another reason.

15
EM
EmmaBell0637

I'm holding the tooling decision. We still haven't established that the nest can locate acceptable parts consistently, and a stronger clamp doesn't resolve that missing basis.

4
RA
RachelBrooks0870

@EmmaBell0637 The missing basis is clear: consistent location of acceptable parts hasn't been established. That explains why the tooling decision remains open.

2

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