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# Understanding assembly relations

Genius

Hi all

I have an instrument, which fits with 1mm clearance into a cylinder shaped housing. Trying to insert the instrument can work on several ways.

The combination of one 1 times Axial Align plus 1times Mate works fine

The combination of one 2 times Axial Align does not work but gives an error message.

From my geometric understanding it should be fine a well, as the instrument is inserted along its symmetry axis into the housing and rotated to make the crossing holes in the housing being in line with the hole in the instrument where a bolt will be inserted to fix the instruments position.

Any ideas what's wrong with two times Axial Align, where each individual Axial Align works, but between them a collsion of relations is reported.

(view in My Videos)

best regards

Hans

25 REPLIES

# Re: Understanding assembly relations

Gears Phenom

you are correct that 2 axial aligns should work...

I have had similar issues in the past and almost always have found geometry error(s).

Your 1 part looks like it was imported geometry...  I bet a closer inspection will find some sort of deviation out some .00000000x decimals

you can test this theory by re-creating an oversized cross hole in the imported geometry and see if the then can align...   if so then edit the newly created cross hole to the proper size.

Also as a test.   Can you over-constrain via the 1st method.   can you place the thru hole,  then the mate,  now can you add the main axial align,  and if so then delete the mate?

===================================================
Matt Johnson
Solid Edge Certified Professional (ST7 & ST8)
Solid Edge ST9 (SEEC) - Production
NX11 (Tc Integration) Pre-Production Testing
Teamcenter 10.1.7

# Re: Understanding assembly relations

Genius

Is there a way to set the required precision of axial align's orientation, may be to limit it to 0.1° or so ?

Might it help to measure if the angles of the cylinder's axis and the bore hole axis are vertical to eachother?

If this was the not perfectly the case, that might be a reason of conflict.

But right now I did not succeed to measure the angle between two axis. I didn't find how to use this menu point.

best regards

Hans

# Re: Understanding assembly relations

Gears Esteemed Contributor

And you have to ask if it's worth worrying over a 7th place decimal out of alignment. The trouble with using two axial constraints on a single item is that one or more degrees of freedom get constrained twice. I guess it's good for discovering small misalignments but it violates the limit of 6 degrees of freedom maximum to fully constrain a part. That's why datums are set up as 1st to constrain three axes, 2nd to constrain two axes, and 3rd to constrain 1 axis for a total of six.

Bruce Shand
ST10 MP7 - Insight - Win10 - K4200

# Re: Understanding assembly relations

Gears Phenom

Us

Unable to play video. Please try again later.
(view in My Videos)
e 3D Measure

===================================================
Matt Johnson
Solid Edge Certified Professional (ST7 & ST8)
Solid Edge ST9 (SEEC) - Production
NX11 (Tc Integration) Pre-Production Testing
Teamcenter 10.1.7

# Re: Understanding assembly relations

Gears Phenom
no way to give assy relationships any tolerance... Must be theoretically and geometrically perfect!
===================================================
Matt Johnson
Solid Edge Certified Professional (ST7 & ST8)
Solid Edge ST9 (SEEC) - Production
NX11 (Tc Integration) Pre-Production Testing
Teamcenter 10.1.7

# Re: Understanding assembly relations

Genius

Hi Bruce,

What was Your suggestion, what I should do?

best regards

Hans

# Re: Understanding assembly relations

Genius

Hi Matt, thank You for preparing, but unfortunately I cannot view Your video. Will it just take some time or was it an error during upload?

# Re: Understanding assembly relations

Gears Phenom

video is either still uploading or failed..   see screen shot...  use 3D Measure

===================================================
Matt Johnson
Solid Edge Certified Professional (ST7 & ST8)
Solid Edge ST9 (SEEC) - Production
NX11 (Tc Integration) Pre-Production Testing
Teamcenter 10.1.7

# Re: Understanding assembly relations

Gears Esteemed Contributor

Hi @Hans11

don't conentrate on angular tolerynce only.

If those axis will not cross each other exactly, then the 2 axial alignements can not work.

So consider and take care that for both parts the hole axis will cross exactly.

What I remember is, that You are working synchronous, so select the smaller holes and use the steering wheel to move it to the center of the larger hole.

Do this for both parts and try again.

As soon as the geometry is correct, it will work.

If it will not do so, then try the parallel relation instead of the axial.

Here You can allow an range for the fit.

I suppose that then the angualr tolerance must be exacgtly too, but not the position.

regards
Wolfgang