Lenght of the pipe in the cutlist

juha_hoo

I'm modeling a pipe with bendings by using sketch, frame-tool and pipe profile. Then I create cutlist. For some reason the lenght of the pipe is wrong in cutlist compared to mesured in the sketch. Can one help me how I could get the right lenght to the cutlist.

jnewth_onshape

Hi there-

Im Josh, one of the Frames devs. First, I agree that it's confusing, but both numbers can be considered "correct". They are just measuring different things.

The measurement tool's value is the sum of the length of the path.

The cutlist's value is an overestimate-but-not-a-ridiculous-one of the straight stock required to manufacture the segment.

So the measurement tool is trying to measure a sketched quantity, but the cutlist is trying to help you actually manufacture the part. Different goals.

Let me give you an example:

We have a frame sweep path 2m long. I create a frameTrim that splits it in half. I create two cutlists, one pre-trim, one post-trim. We now see 3 numbers in the screenshot:

Path length, regardless of trim: 2m

Pre-trim length: 2m

Post-trim length: 1m

The situation gets more complicated when there are curved segments, splines, or trimmed ends. In all cases, the path measurement will only provide the length of the path centerline. Cutlist lengths always take in to account the actual geometric state of the segment.

In your specific case, there are no trim operations, so you might wonder why the numbers still don't match? Good question. One could argue the centerline is the neutral axis of a stressed beam, which is the simplification a stress & strain textbook will make. In manufacturing, I've found the best straight length cut estimate is to use the "outer path" of an arc, and to "add a little" for things like chopsaw operations.

Our cutlist length calculator tries (very hard) to make its length approximation a useful one _for manufacturing_, so that if a person simply cuts to the lengths specified in the cutlist, their subsequent tube bending / end trimming operations still produce useable results.

The best way to think about it is this: The cutlists are primarily in service of manufacturing. It's easy to trim beams down if they are a little too long - much harder to stretch them out if they are a little too short!

In sum: The cutlist length is not going to match the path centerline. If you need the path centerline, the measurement tool or a custom feature is a better solution.

juha_hoo

Ok. Thanks for the answer!

shawn_crocker

jnewth_onshape said:

In manufacturing, I've found the best straight length cut estimate is to use the "outer path" of an arc, and to "add a little" for things like chopsaw operations.

@jnewth_onshape
I'm wondering why in this example, the cutlist is showing a smaller length then the center sweep path?  If the calculation is done on the outer arc of the sweep, shouldn't the cutlist length value be greater than 657mm?

jnewth_onshape

shawn_crocker said:

jnewth_onshape said:

In manufacturing, I've found the best straight length cut estimate is to use the "outer path" of an arc, and to "add a little" for things like chopsaw operations.

@jnewth_onshape
I'm wondering why in this example, the cutlist is showing a smaller length then the center sweep path?  If the calculation is done on the outer arc of the sweep, shouldn't the cutlist length value be greater than 657mm?

Yo @shawn_crocker
Sorry for delay in replying. Perhaps I've misunderstood your comment, but in the above example the cutlist overestimates at 675mm, the centerline is 657 (swap the two last digits), so the cutlist is an overestimate. It's not _exactly_ the outer arc of the sweep (for a circular profile I have no swept edges that can give me the largest radius directly so I have to use a heuristic).