11 Replies Latest reply on Mar 3, 2015 8:53 AM by John Stoltzfus

# How to I write an equation that controls multiple parts within an assembly?

I am fairly new to Solidworks and have been self teaching myself the information that I need to know for my project. I am designing furniture using one model by where you can change the dimensions of the top and the supporting structure will scale accordingly. I have written simple equations to make this work, however there is one piece that is not working.

This is changing the height of the table/desk. When I change the dimension shown at 730mm the beam across the centre needs to be scaled accordingly, so that they leg stretchers remain in the same place, but the beam across the centre also needs to be dimensioned in relation the top of the table/desk.

The problem I am having is that I have an equation that controls the length of the beam in the centre in relation to the top dimensions which works, its just when I change the height (730mm) to any other dimension one of the leg stretchers stays put in the correct position whereas the other moves as it is being driven by the dimension of the centre beam in relation to the top.

I hope all this makes sense. I would appreciate any help with how to figure this out.

Thanks

• ###### Re: How to I write an equation that controls multiple parts within an assembly?

Nathan, can you post the part or at least  a screen capture of the error condition?

I'm not certain which part of the table is a leg stretcher.

It sounds like the issue is in the way one of the legs is constrained.

• ###### Re: How to I write an equation that controls multiple parts within an assembly?

Yeah no worries, the images below show the problems I am having.

This image shows the correct positions of all the parts - when the leg is at 730mm - the top is 1200mm x 600mm

I can then scale the top accordingly - shown is 2000mm long - the supporting structure moves with the desk and scales according to the equations.

Then this is the problem I am having -the top of the table is still 2000mm long, but when I adjust the height - shown here is 500mm the stretcher on the left side moves away from its position.

I hope this is clearer.

Thanks

Nathan

• ###### Re: How to I write an equation that controls multiple parts within an assembly?

It would help if you upload the original files.

• ###### Re: How to I write an equation that controls multiple parts within an assembly?

Hi Nathan

I am also a joinery designer and have suffered all kinds of troubles trying to utilise the power of solidworks

From my experience I think for models like you show it is a lot easier to make a multibody part.  if you would still like individual parts it is possible to do this by saving out the bodies and it can also make the assembly for you.  INSERT>FEATURES>SAVE BODIES...

Include a weldment and create 3d bounding box is also useful to us joiners who want cutting lists

I show an example of a bench i did, similar to your design.  If you have instant 3d turned on, simply clicking the part you want to change allows you to alter dimensions etc and everything will update quickly and consistantly.

With assemblies i find i often have to open the parts and force a rebuild (CTRL-Q).  This could well be your problem too.

anyway heres my model, i hope it is useful to you

• ###### Re: How to I write an equation that controls multiple parts within an assembly?

Hi Rob,

Thank you very much for your reply and your advice, I really appreciate it and I will give that a try within my model.

Thanks agains

• ###### Re: How to I write an equation that controls multiple parts within an assembly?

No worries, the model was never really finished but i hope it shows 1 way it can be done, there seems to be so many ways to do anything in solidworks its all a bit bafflin when u get started hey? If you're like me you're happier with a saw in your hand than sat at a screen, all the best any questions please fire away, us joiners need to stick together

• ###### Re: How to I write an equation that controls multiple parts within an assembly?

Sorry. SolidWorks 2012 installed.

• ###### Re: How to I write an equation that controls multiple parts within an assembly?

If the piece is scaling correctly but not going where you intended, the problem could be a relationship problem.

so that when sketching the part, relationships got defined on one side of the stretcher that where not defined on the other side.

look in the display/delete relations command

• ###### Re: How to I write an equation that controls multiple parts within an assembly?

Nathan,

I design furniture everyday using SolidWorks, I use very very little equations or configurations..  What I use is a Base Part that is full of sketches and planes.  This part is the top part in every assembly and sub-assembly and all the components are built using the sketches and planes from that part.  I set it up that all I need to do is change the height, width and length and the entire model moves accordingly.  Kind of hard to explain, but it works really well and the rebuilds are good.

• ###### Re: How to I write an equation that controls multiple parts within an assembly?

This is exactly what I am trying to achieve, thanks for your advice

• ###### Re: How to I write an equation that controls multiple parts within an assembly?

Feature Tree Pictures of my assemblies - sub assemblies

you can also put the features in different folders to organize it better