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It Looks Like Cheating, but Feels Oooh, Sooo Good: ST6 Synchronous Boolean


What is this, has Matt turned to writing bad country songs? Maybe a hedonist manifesto? No, it’s not any of that. It’s just a confession. Like most long-time history-based CAD users, I have an overactive conscience. I feel guilty when I take the easy way out. If your CAD program isn’t difficult to deal with, it must not be very good. Yeah, I’m the same guy who wrote the BrandX Bible, and I’ve been known to write history-based best practice rules like they were the 10 Commandments.


Letting go of all of this judgmentalism is difficult for history-based users who are so used to feeling guilty for just about anything that might constitute a crime against the unnecessarily harsh rules that your modeler inflicts on you. We have this need to feel that things can’t be right unless they were hard. You need to let go a little. Loosen up some, and get a little synchronous mojo.SNAG-0000.png


Synchronous Boolean functions can be used in multi-body parts as well, but in this article I’m going to focus on the application in assemblies. It  was added in ST6. I didn’t really pay much attention to it at first because it looked like an old SolidWorks feature.


The Boolean functions are of course Union, Subtract, Intersect, and Split. I didn’t think they were much of a big deal until I heard Bob Mileti going off about them somewhere. At first I said “Bah, excitable Italians! We had that in ‘Works last century.”   And that much was true, but what I wasn’t getting was that this wasn’t really the same thing. This was all the chocolate with none of the calories. All of the sin, without any guilt. It’s a feature between parts in an assembly without any in-context relationships to maintain. And yes, in case you’re wondering, that is something to get excited about.


Let’s look at this motor assembly we’ve worked with a few times. There are a lot of opportunities here to fix things, if you’ve had a look at it. The engine cover part runs into the block casting in a couple of places, and gives us a chance to subtract one part from the other.


Here’s how you make the magic happen:

  • In the assembly, right click on the part you want to add the feature to and select Edit
  • On the Ribbon, go to Home > Solids > and under the Add Body icon, click the dropdown arrow and select Subtract
  • Follow the Prompt Bar, and select the main body of the Engine Cover part, right click to accept to make this the part to subtract from (Target).
  • Select the Block Casting part as the part to subtract (Tool), and right click. Done.

2.pngNow you can (save the assembly first, and then ) open the Engine Cover part and edit it independent of everything else. So you can make a gap around the places where the Block Casting intersect.


One thing you might ask is if you can use the steering wheel to change the offset distance. Well, no. Not that I know of. You can’t just pull on an arrow and make all 3 faces of this slot offset. That might be a good enhancement request, though.


You can make the offset type edit happen with dimensions, though. Notice the way the red arrows are situated, and remember that double arrows mean symmetric change, and single arrow means change just in that direction.


Now I can hear all you haters out there saying “yeah, but now you’ve got this dead feature that isn’t related to anything,” and I’ve got two responses to that:

  1. Yes, and isn’t it beautiful? I can make it related to something in the assembly when I need to make a change relative to something else, but I don’t have to “pay the taxes” on that (incur rebuild overhead) until I need it.
  2. Solid Edge still has all of those history-based features that work just like the old-fashioned ones in SolidWorks. We call them InterPart, and they work in a similar way with the external relations and only update with the assembly.

3.pngSo if you really do want a part feature driven by something in the assembly, you can always use the traditional InterPart (in-context) type history-based tools to do that. Or you can create guilt-free features, and use all of the power of Synchronous to decide the design intent at the time you make the change.


The ability to use either method is the real beauty here. One method is the way you are accustomed to working with features in order where you establish your design intent up front, and the other way is a more freeing way to work where you establish your design intent when you need it (no crystal ball or decoder ring needed). Geometry is geometry. You don’t get extra points for setting up complicated schemes that just make it more difficult than it needs to be.

Gears Esteemed Contributor

Matt, there is a Synchronous Inter-Part feature in the Relate section of the Main ribbon of Assembly called "Create Inter-Part Relationships"  Basically relates faces of Synchronous parts together.  You should check it out as it gives you the best of both worlds, but only when you want it!


What, me be excitable.... fugetaboutit!


Now if only I could find a way to use a Boolean Subtract to remove those 2 cannolis I just had for Breakfast from my waistline...  maybe the good Dr. Versprille can do the Math!



That's what I love about this blog so much, I'm always learning stuff. Thanks for pitching in with more in-depth information.



Yeah, tell me about it. I need to subtract several holidays of southern cooking.

Siemens Valued Contributor

Matt,I've never used this before until about 3 weeks ago when  I wanted to subtract a bolt from a nut. I'm itching to go play with some of the other options now.




When my ship comes in I'll fund the research for the "BobLEAN" Subtract Operation. It can't be too hard since I already use the "Add Body and Union Operations" daily. My other option is to just have my mouth sewn shut!


"My other option is to just have my mouth sewn shut!"


I'd be willing to bet that you might find some donors to help pay for thatSmiley LOL

Gears Esteemed Contributor

Here is the first donation Smiley Tongue


Valued Contributor

Hi Matt,

  Looky, I am here now!! Talking to people who have had a chance to observe newbies to CAD learning ST is interesting. A common comment is that those who are new to it all automatically love ST and wonder about the old timers that can't seem to get it. I know when I first saw it there was an awakening and I knew there was power there and even if I did not know how to use it I could see the potential and determind to have it. But many are a little tired of having to learn things, again and again, to arrive they feel at the same end result. Then there are those who are just two busy and these two categories are the major reasons seasoned CAD users do not try ST. It is funny to see these straight history guys at places like the Summit where thay are exposed to someone using ST for the first time and you can see the wheels start to spin. That new subtract thing is cool and I make vice jigs in a heart beat for machining and it is quick and easy. Hedonism nothing, how about an eminently practical use of my time to have learned ST.