Linear Sketch vs Linear Pattern

Which is better to use a liner sketch or a linear patter? Where is the best
situation to each tool? Why?

Nathan

 

According to some tests done last year a feature pattern rebuilds faster and
create smaller files then a linear sketch step and repeat

Krister L

 

For many of the previously stated reasons, I vote for the feature pattern. I
don't know if it will always rebuild faster than the sketch pattern but I
would recommend selecting the "Geometry Pattern Only" option whenever
possible.

JJ

 

Matt Lombard has this written down in his Rules of Thumb.....there You can
compare file size and rebuild times for different kinds of patterns.

http://www.frontiernet.net/~mlombard/

Krister L

 

An advantage of feature patterns may not be apparent at first. Just this
morning one of our guys here had created his base extrude with several holes
in it. (Ok, fine, stuck ACAD user, he'll learn.) But then he put in some
Hole Wizard tapped holes, patterns, etc. Now, today he wants to remove one
of the original holes in the extrude sketch. Upon editing that sketch and
deleting the circle, apparently the base extrude rebuilds with a different
ID, as the child features don't like it anymore. No sketch relations at all
to the circle in question, just a circle in the sketch. Remove it and other
things fail.

So, the moral of the story is that features are easier to manage later when
changes are implemented.

WT

 

Could one way of solving a problem like that be to simply pick the
cylindrical face of the hole in and select "delete face" instead of editing
the sketch.?....But I'll also put the feature patterns before the sketch
ditto though

Krister L

 

I just tried a test part on what I described here about taking a circle out
of the base extrude, and it worked just fine. He must have had something
else goofy in there that we didn't find. Sorry. :-|

WT

 

feature patterns are very effecient when populating assemblies with
fasteners

 

One problem with patterns inside sketches is that you can not add
entities to the pattern once the pattern is made.

 

Hopefully you can benefit from my painful experience. I just finished
a part. A hat channel 90" long with 58 pairs of hooks to be punched
out from the inside of the hat. (And two other configs with short
length and fewer hooks.) The hooks were 90 degrees down and 85
degrees up. I spent long hours getting it "right".

Initially, I cut the outline (material removed by the punch) I "knew"
enough to use symetry so that my my Extrude-Thin1 was half the part. I
made it sheet metal and rolled back to make the cut. The first outline
cut was patterned the 58 instances. Then I mirrored. So far so good.

In my ignorance, I edited the Flat-Sketch1 in Process-Bends1 to make
the bends for the hook. (I had a another part with a modeled by
another to go by. This was how he did it.) I In the Flat-Bend1 sketch
I again used symetry by first sketching a centerline to use two lines
across the pre-bent hook area. I then did a step and repeat for 58
instances. A step and repeat in one direction needs a dimension
manually added between one step and another to constrain the pattern.
(You would think Solidworks would do the dimension for you because it
knows you only went one direction)

Imagine waiting for that rebuild only to find that the 116 hooks were
pointing the wrong way. I was able to determine that I could select
and edit the bends to make the second bend opposite to get them to
point "right". Each Sketch bend had to be edited by itself. I needed
to do 116 of them! each rebuild took about 7 minutes. 7 x 116 = 812
minutes. 812 minutes/60 = 13.53 Hours! After 5 hooks I realised i
had nother problem. How was I going to make the other bends not 90,
but 85 degrees! Not counting the time it would take to figure out how
to do that, my task would take 27 hours! It was time to call my VAR
for help.

He explained I should make it two individual "Sketched Bends" Using
SolidWorks Help this was simple. This gave me the hooks with the
proper direction and angle without having to manually edit each one.
But, I know had two features with linear step and repeats in them.
Rebuilds still were irratating.

At this point, managment forced me to send the drawing off to the
vendor to get the punch tooling ordered. This was before I knew if
the hooks would be strong enough. Off the files went. I made a
smaller version of the hat channel to run CosmosExpress. I was
pleasantly surpised with margin of safety.

I called the vendor this morning to see how he liked my rebuld time.
He said he spent a hole day making his shop drawing. He made a couple
of passes with Pallet Forming tools. The first one made the outline
and the hook and the second made the hook and then he cut the outline
after. Both versions of course eliminate the linear sketch and
repeats, replacing them with a sing feature linear pattern. I asked
him for the forming tool he used.

He sent me both explaining he used the second because it was closer to
my model. He could make neither exacthy the same as mine because of
the minimum radius limitation when modeling the forming tool (another
subject).

I made a new configuration of my part and did the form and then the
cut. Rebuilds are now seconds instead of minutes. He called asked
how I did. Of course I was very thankful. I told him we could both use
the quicker of the two because the tool was made per my original. If
my hook design doesn't prove out I have to buy new tool anyway.

A really big payoff will follow whan I make the configurations of the
shorter versions. I would have to supress the Sketched-Bends made for
the 90", and make new Sketched-Bends for each new config because you
can't change the step and repeats.

Now the downside. Had I gone the feature pattern up front my FEA
results would have been different. Maybe time consumingly different.
Both forming tools produced an ugly mess of surfaces exactly where the
highest stress was. I haven't done the FEA on the "new" hook but I
know the results will not be the same. I may have had sleepless
nights.

I have to admit I chose the sketch linear step and repeats because of
my lack of success making forming tools, and the management pressure.
(I'm self taught user with little training. This ng helps a lot.
Through it, (Paul Salvador's link) I knew of the Lombard Rule uf Thumb
for this was. Thanks all.) and was hoping in advance for the help I
received from the vendor. He is a much better modeler than I am.
Design was more important. I'm convinced things worked out the best
they could. The linear step and repeat produced a model closest to
the real world for tooling and FEA, and the feature linear pattern
gives much better productivity now.

I hope this helps.

 

Actually You can....easily.....highlight one of the patterned entities ...it
shows up in the property manager like "PatternedX"....rmb that one and
select edit pattern....now You can increase or decrease the number of
entities
Or...rmb one of the patterned entities ...and select "Edit Linear Step and
Repeat
If You wanna change the distance between the entities, just put in a
dimension and adjust it...same goes for angles


Krister L

 

I am curious to see the part - would you please send me a copy.

WT

 

Sorry...language confusion...after reading again I see what You mean....and
yes You're right ...You can't add more entities

Kriste