Inventor General Discussion

Inventor General Discussion

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*Wally
Message 1 of 12 (267 Views)

Can't get Insert Constraints to remove all degrees of freedom.

267 Views, 11 Replies
10-14-2007 03:39 AM
Hi,

I usually start out designing and assembling things using Mate constraints.
Later I add fastener holes, as required, remove the Mate/Flush constraints
by replacing them with Insert Constraints. I've been having issues getting
the parts to assemble in this way, due to error messages. If I check the
alignment of holes, using full precision, the parts line up perfectly.

I can't submit any of my designs due to confidentiality concerns, but would
like to know if anyone else is experiencing this. The workaround I'm using
is to use one Insert and either a Flush constraint, or an Angle constraint.
If anyone has found a reason for the software not being able to remove all
DOFs with Inserts, could you please explain what you did? Is there any way
to set the software to allow, perhaps, a certain amount of assembly error so
the parts will assemble with Insert constraints? I looked for this but
couldn't find any indication that this was possible.

Wally
*Dennis Jeffrey
Message 2 of 12 (267 Views)

Re: Can't get Insert Constraints to remove all degrees of freedom.

10-14-2007 06:25 AM in reply to: *Wally
When I'm constraining holes, I never use the mate constraints... Why create
twice the constraints in a design? My insert constraints always work unless
there is an error in the spacing. If you need to constrain two parts and
there is an error, then use one insert and a single angle. If I had errors,
the I would take the time to find them.

Since you cannot share any parts for an example, it would be impossible for
anyone here to see where you are going wrong.

--
Dennis Jeffrey, Autodesk Inventor Certified Expert
Autodesk Manufacturing Implementation Certified Expert.
260-399-6615
Instructor/Author/Sr. App Engr.
AIP 11SP3, AIP 2008 SP1, PcCillin AV
HP zv5000 AMD64 ( modified)
Geforce Go 440, Driver: .8185, 2GB RAM
XP Pro SP2, Windows Classic Theme
http://teknigroup.com
"Wally" wrote in message
news:5749180@discussion.autodesk.com...
Hi,

I usually start out designing and assembling things using Mate constraints.
Later I add fastener holes, as required, remove the Mate/Flush constraints
by replacing them with Insert Constraints. I've been having issues getting
the parts to assemble in this way, due to error messages. If I check the
alignment of holes, using full precision, the parts line up perfectly.

I can't submit any of my designs due to confidentiality concerns, but would
like to know if anyone else is experiencing this. The workaround I'm using
is to use one Insert and either a Flush constraint, or an Angle constraint.
If anyone has found a reason for the software not being able to remove all
DOFs with Inserts, could you please explain what you did? Is there any way
to set the software to allow, perhaps, a certain amount of assembly error so
the parts will assemble with Insert constraints? I looked for this but
couldn't find any indication that this was possible.

Wally
*Expert Elite*
JDMather
Posts: 28,250
Registered: ‎04-20-2006
Message 3 of 12 (267 Views)

Re: Can't get Insert Constraints to remove all degrees of freedom.

10-14-2007 08:40 AM in reply to: *Wally
>I can't submit any of my designs due to confidentiality concerns

Can't you reproduce this behavior in a dummy assembly that does not use your proprietary designs?
Please mark this response as "Accept as Solution" if it answers your question.
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Distinguished Contributor
gnrnr
Posts: 319
Registered: ‎12-11-2003
Message 4 of 12 (267 Views)

Re: Can't get Insert Constraints to remove all degrees of freedom.

10-14-2007 04:40 PM in reply to: *Wally
An insert constraint will always leave the rotation of the bolt of part free. If your'e using the insert constraint to place parts then just use two insert constraints on two of the holes. The combination will remove any remaining DOF.

Regards

Steve
*Wally
Message 5 of 12 (267 Views)

Re: Can't get Insert Constraints to remove all degrees of freedom.

10-14-2007 07:43 PM in reply to: *Wally
Hi Dennis,

As I explained: "I usually start out designing and assembling things using
Mate constraints. Later I add fastener holes, as required, remove the
Mate/Flush constraints." Unless I misunderstood, you also have to align
your parts in some way before you add the holes. I assume you don't do this
visually, as this could impact the accuracy of how other things align. So
I'm not sure what you mean when you say: "When I'm constraining holes, I
never use the mate constraints... Why create twice the constraints in a
design?" Fasteners are the glue that hold things together. When loads are
calculated, that is what determines how many fasteners, and where they are
placed. Therefore I assume you must have to always include mate or flush
constraints as an interim step. Otherwise it might become a problem with
complex assemblies, because if the fastener constraints ever become removed
for any reason there is the danger that it could impact many other parts
making recreation of relative part positions impossible.

My issue is that when I use the software's Measure tool, after I've aligned
with an insert constraint and an Angle constraint, for example, the second
set of holes lines up perfectly using full precision. Therefore I shouldn't
have to use the Angle constraint. But I have found, on a couple of
occasions, that this is necessary. This is not a big issue, but it is
curious, because the parts fail to mate with 2 Insert constraints when there
is no calculable error between the holes. It also detracts from progress,
since the reasons for the failure have to be tracked down for significance.

The above is the reason I asked if there is any way to adjust the software's
precision for constraining parts to exclude the occasional times when mating
errors occur. Usually I create hole patterns off of the hole pattern of
another using the Geometry Projection tool. Then I remove all Adaptive and
Reference listings from the Browser followed by constraining the holes with
dimensions to lock the holes in position. My reason for doing this is to
keep the files as lean as possible. Maybe this is where the errors creep
in.

Wally



"Dennis Jeffrey" wrote in message
news:5749204@discussion.autodesk.com...
When I'm constraining holes, I never use the mate constraints... Why create
twice the constraints in a design? My insert constraints always work unless
there is an error in the spacing. If you need to constrain two parts and
there is an error, then use one insert and a single angle. If I had errors,
the I would take the time to find them.

Since you cannot share any parts for an example, it would be impossible for
anyone here to see where you are going wrong.

--
Dennis Jeffrey, Autodesk Inventor Certified Expert
Autodesk Manufacturing Implementation Certified Expert.
260-399-6615
Instructor/Author/Sr. App Engr.
AIP 11SP3, AIP 2008 SP1, PcCillin AV
HP zv5000 AMD64 ( modified)
Geforce Go 440, Driver: .8185, 2GB RAM
XP Pro SP2, Windows Classic Theme
http://teknigroup.com
"Wally" wrote in message
news:5749180@discussion.autodesk.com...
Distinguished Contributor
Josh_Petitt
Posts: 5,400
Registered: ‎09-21-2004
Message 6 of 12 (267 Views)

Re: Can't get Insert Constraints to remove all degrees of freedom.

10-15-2007 05:31 AM in reply to: *Wally
>I usually start out designing and assembling things using
Mate constraints. Later I add fastener holes, as required, remove the Mate/Flush constraints.

When constraining most parts (excluding fasteners and round parts meant to be inserted), I would use mate and flush constraints. After the holes are added, I would not remove the mate and flush constraints between the parts. I would only use the insert constraint to add the fasteners. This may seem counterintuitive, however, your holes can be moved and are considered (by me) to be more variable than other more important aspects of the geometry.
*Expert Elite*
JDMather
Posts: 28,250
Registered: ‎04-20-2006
Message 7 of 12 (267 Views)

Re: Can't get Insert Constraints to remove all degrees of freedom.

10-15-2007 05:38 AM in reply to: *Wally
>the second set of holes lines up perfectly using full precision.

>is no calculable error between the holes. It also detracts from progress,

>constraining the holes with dimensions to lock the holes in position.

It sounds like you are doing everything right.
Can you zip and post a non-proprietary dataset that exhibits this behavior?
Please mark this response as "Accept as Solution" if it answers your question.
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*Gary R Smith \(Autodesk\)
Message 8 of 12 (267 Views)

Re: Can't get Insert Constraints to remove all degrees of freedom.

10-15-2007 06:30 AM in reply to: *Wally
Hi Wally,

Inventor does not currently provide you with a tolerance preference on
assembly constraints that would allow you to: "...ignore anything after 4
decimal places on INSERT constraints..." or "...ignore anything after 6
decimal places on MATE constraints..."

We have been looking at ways to provide more error tolerance in assemblies
but have not yet decided on the best approach to maintain confidence in the
result while allowing practicalities to be taken into consideration.

--
Gary R. Smith
Autodesk Inventor Team
Portland, OR
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*Teun Ham \(IV10 SP3 / IV2008 SP1\)
Message 9 of 12 (267 Views)

Re: Can't get Insert Constraints to remove all degrees of freedom.

10-15-2007 06:38 AM in reply to: *Wally
Our designs are also being bolted together, but I use ZERO insert
contraints...

Skeleton Modeling only requires Flush Constraints (Origin to Origin)

--
T. Ham
CAD Automation & Systems Administrator
CDS Engineering BV

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--
*Dennis Jeffrey
Message 10 of 12 (267 Views)

Re: Can't get Insert Constraints to remove all degrees of freedom.

10-15-2007 07:00 AM in reply to: *Wally
"When I'm constraining HOLES......"

--
Dennis Jeffrey, Autodesk Inventor Certified Expert
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