Sheet Metal Tab - Subtraction Scope & Offset

matthew_stacy

Wow!  Just figured out what subtraction scope and subtraction offset are for in the sheet metal tab tool.  In a free moment this morning I was googling "sheet metal" "subtraction offset" and asking myself, "is that really a thing?"

Then I stumbled onto one of @cody_armstrong 's tech tips and learned that it's not a thing, except in Onshape.   This is absolutely brilliant to be able to use a tab profile sketch that is NOT necessarily coplanar with the flange to be merged with.  And to be able to merge that tab with one sheet metal part while subtracting it from another (subtraction scope) and specifying the kerf width (subtraction offset) in a single feature is icing on the cake.

I realize that I am only 2 years and 364 days behind the curve in singing the praise of this tool now (https://www.onshape.com/cad-blog/tech-tip-creating-sheet-metal-tabs-in-onshape ).  Old dog, new trick.  If you haven't played with the sheet metal tab tool yet, I strongly encourage you to do so.

My compliments to the OS crew for developing the sheet metal tab!  This is a very powerful tool.

MBartlett21

@matthew_stacy
It also can add multiple tabs at once (from the same sketch, but on different sheet metal faces)

matthew_stacy

Thanks @MBartlett21, that is another great aspect of the sheet metal tab tool.

But I still miss tools like unfold/refold from SolidWorks.

MBartlett21

@matthew_stacy

What do you want unfold and refold to do?

We can sketch on the flat pattern and cut the flat pattern.

matthew_stacy

@MBartlett21 that is very interesting that OS will sketch and cut on the flat pattern.  I appreciate the tip.  Feature tools like Holes, Chamfer/Fillet, etc. don't appear to be available though.

I mentioned unfolding as a possible modeling approach for the Book End that @mark_leger posted recently.

I succeeded in creating a fully parametric model for this part (omitting the formed ribs for now) with the dimensions of the flat tab directly-associated with the cutout in the parent flange (uniform kerf width all the way around).  The flat pattern automatically updates with the width and height parameters for the cutout (#width and #height)  But the only way that I have been able to do this by creating variables for critical sheet metal parameters (thickness and k factor).

https://cad.onshape.com/documents/6aa160088e284fef5cdf3a09/w/f319ffa7931bcaec9193141d/e/280fd3af0f2f54730d922087

Unfolding (if we had such a tool in OS) might offer a simpler alternative.  Cut the kerf region out of the flange.  Then unfold the central region of that flange.

I also tried to model this part using the Fold SM feature script (that I believe you wrote) to bend after cutting the kerf from a flat sheet.  Ultimately this sequence would be the most consistent with a likely fabrication sequence, which I believe is generally a good modeling ideal to strive for.  No luck yet, but I may not be using the feature script properly.

Thoughts?  Suggestions?

MBartlett21

@matthew_stacy
The Fold SM feature (that I wrote) currently only works for bends with only one segment.

Henk_de_Vlaam

matthew_stacy said:

@MBartlett21 that is very interesting that OS will sketch and cut on the flat pattern.  I appreciate the tip.  Feature tools like Holes, Chamfer/Fillet, etc. don't appear to be available though.

I mentioned unfolding as a possible modeling approach for the Book End that @mark_leger posted recently.

I succeeded in creating a fully parametric model for this part (omitting the formed ribs for now) with the dimensions of the flat tab directly-associated with the cutout in the parent flange (uniform kerf width all the way around).  The flat pattern automatically updates with the width and height parameters for the cutout (#width and #height)  But the only way that I have been able to do this by creating variables for critical sheet metal parameters (thickness and k factor).

https://cad.onshape.com/documents/6aa160088e284fef5cdf3a09/w/f319ffa7931bcaec9193141d/e/280fd3af0f2f54730d922087

Unfolding (if we had such a tool in OS) might offer a simpler alternative.  Cut the kerf region out of the flange.  Then unfold the central region of that flange.

I also tried to model this part using the Fold SM feature script (that I believe you wrote) to bend after cutting the kerf from a flat sheet.  Ultimately this sequence would be the most consistent with a likely fabrication sequence, which I believe is generally a good modeling ideal to strive for.  No luck yet, but I may not be using the feature script properly.

Thoughts?  Suggestions?

@matthew_stacy

You can make this part fully 'design intented' without variables with only 5 features instead of 7.

https://cad.onshape.com/documents/205790153bf985484ba7fc4f/w/3189789ec786e8b0eec93c6b/e/cde6358549db8712223bcf4e

matthew_stacy

@MBartlett21 , it is a very handy tool and greatly appreciated.  I haven't ventured into the deep end of the pool yet, so feature scripts are still magic to me.

I noticed that your Fold SM feature will accept a custom bend radius.  Consider adding a custom k-factor, if you're ever inclined to circle back on that one.  In a recent thread about bend-specific sheet metal parameters it was noted that different pieces of equipment, even in the same shop, will each have their own k-factor. 

MBartlett21

@matthew_stacy
In order to use the Fold tool, the part has to already be converted to sheet metal, which is where you would put the default bend radius and k factor.

Currently, Onshape does not support having a custom k factor for a bend, so I cannot do this in the feature at the moment.

matthew_stacy

@Henk_de_Vlaam well played sir!  That is a very elegant solution.  Your Extrude1/Extrude2 approach on the flat pattern is the key to this puzzle and definitely beats the Tab tool.  My compliments.  (PS:  I experimented with eliminating your Extrude2 and revising Extrude1 to match, but your exact method is the way to go.  Your record stands at 5 features.)

steve_shubin

@matthew_stacy

Yeah — using extrude is better than tab

Thanks to @MBartlett21 for the sketch in flat view window tip