Beyond system limits

don_howe

I created a simple test using full size dimensions that layoff the gun deck of a 18th century 74 gunship. The length between perpendiculars is 176 ft. Draw a straight line and erect perpendiculars at each end of the line and make their height 24' 6". Call the line on the right the foremost perpendicular and call the line on the left the aftermost perpendicular. From the foremost perpendicular set back 66 ft and erect another perpendicular, call it dead-flat and make it's height 22' 6". Draw a curve to pass thru all three spots at the heights of the perpendiculars. Simple enough. However OS chokes on this. I suspect OS has same operating environment that early versions SW did, a cube of 500 meters. The radius generated by my simple test would be 21,792 inches. This tells me that OS cannot be used to build full size structures.

I would request that this limitation be removed asap

https://cad.onshape.com/documents/a1fc976bf226407397f33f31/w/90826e06b9ad4756b85c88f8/e/96c44f0cef8346249af131c6

shashank_aarya

I just tried to access your document but sketch was empty and in failed condition. However based on the profile what you mentioned for 18th century 74 gunship I just followed the steps and built a sketch as shown below. But there was no problem.

I am not sure if I missed anything while creating it. If possible can you suggest if anything I need to correct in this sketch to reproduce the situation you faced?

If I am not missing anything then you can check the graphics performance recommendations here
https://cad.onshape.com/help/#webgl.htm?TocPath=Welcome%20to%20Onshape|_____2

Also can you once again elaborate the details of 500 meters cube. I will try that scenario also.

Thanks

don_howe

OK first, all the heights are measured from the same base line. Second, did you make the heights and lengths in feet and inches? Meaning, 176 ft = 2112 inches, 24 ft 6" = 294 inches, etc.?  

The system environment or operating range of OS is a cube of 500 virtual meters.

nav

Hi @don_howe I have never thought of the limits as I we don`t usually model anything that big, however I just played around to see what the limits were; as far as sketching only, drawing a line in each direction centered at the centerpoint you can draw a line of a length of 999 Meters, if you enter 1000 Meters you get a system error.



The maximum build volume is ->

shashank_aarya

@don_howe I tried putting the value in inches as suggested by you. Below is a result.



Regarding limit I definitely agree with you. The limit of Onshape is different from unit to unit.

don_howe

shashank_aarya   The 270 dimension (the middle perpendicular) comes from the same base line as the 294. Doing so will invert your curve.  Remember this is the line that will represent the deck of the ship. I will try this step again during my lunch hour and see what happens. 

don_howe

Well, I just tried again here at work. I set up my perpendiculars, used a 3 point arc to draw my radius and it gives me the following error.

nav

Hi @don_howe anything drew outside OS systems limits will result on an error no matter how small the object you are drawing is. Verify your sketch is contained in the 999m x 999m (or equivalent units) square area. (Centered to the origin)

lougallo

It seems like you may not be in the correct units. You can type in the unit or set it in the hamburger menu in the upper left.. 176ft is well within the limit of the system. 

_Ðave_

@lougallo it appears the issue is with the size of the radius and not the size of the ship

dennis_20

Would the center of the radius be outside the working envelope?  Could that be why it is failing?

shashank_aarya

@don_howe You are correct. I also tried exactly same thing what you shown and it given same results to me. After this error I increased 270 inch value incrementally and found that error occurs up to 320.5 inch. Error will not come when the value is greater than 320.5 inch. So, in such case you can raise support ticket for the same.

andrew_troup

Don's example seems to suggest that it is not just entities, but also the centre of all arcs which needs to be within the cube. Which seems to me to make sense.

andrew_troup

Forum software screwing up again (not refreshing, losing posts)

I suggest using a spline instead of a three point arc.
 I  doubt a naval architect would use a trammel to construct a sheer line, even if his studio was big enough.
The character of the curve, in the case of a circular arc, is unsuited to the circumstance.
The very word "spline" originally came from the flexible battens used as drawing tools for lofting ship hull shapes, I seem to recall.

_Ðave_

too bad on the center of arc in the cube, I could see that as being an issue if I needed a large arc. I suppose a spline would suffice when/if it ever comes to that.

_Ðave_

@andrew_troup I'm developing an admiration and respect of how full of amazing relevant trivia you are.

andrew_troup

@da_vicki
y2k 
the splines (wooden battens) used for lofting sheerlines were generally thicker aft, because the nature of a sheerline is typically straighter aft of the inflection point, which itself is generally aft of midships. (by way of explaining what I said earlier about a circular arc having the wrong 'character', which extends to any conic I'm aware of)

Whereas I seem to recall the splines used for "diagonals" were thick at both ends ....

I wonder if specialised CAD apps for marine architecture provide a simple way of capturing the character of a spline.
Unrelated (or barely related) point: I imagine Beziers might be more suitable than B splines...

_Ðave_

@andrew_troup I understand where your coming from about a circular arc from another thread But am inclined to disagree as to a spline being a preferred arc. The only reason being that in my world (CNC Machining) the dreaded spline will create multitudes of programming lines of code and whenever reasonably possible (even required on older machines) gets converted to a circular arc which creates only one line of code with a much smoother finish.

nav

andrew_troup said:

Don's example seems to suggest that it is not just entities, but also the centre of all arcs which needs to be within the cube. Which seems to me to make sense.

da_vicki said:

too bad on the center of arc in the cube, I could see that as being an issue if I needed a large arc. I suppose a spline would suffice when/if it ever comes to that.

You guys nailed it, indeed the center of the arc its outside OS drawing limits. That`s why you get an error.

EDIT: Is not the center of the arc, just did a test to put the center in the drawings limits and still did not work what I believe its happening even though its an ARC the projected geometry is a circle if I want to close the ARC. And parts of the circle are outside the drawing limits.

andrew_troup

da_vicki said:

@andrew_troup I understand where your coming from about a circular arc from another thread But am inclined to disagree as to a spline being a preferred arc. The only reason being that in my world (CNC Machining) the dreaded spline will create multitudes of programming lines of code and whenever reasonably possible (even required on older machines) gets converted to a circular arc which creates only one line of code with a much smoother finish.

I was talking in a narrowly specific context, @da_vicki, pointing out that the constant curvature of a circular arc is not very useful in describing the curvature of ships and boats, whereas you seem to have read my recommendation as being general in some way.

But maybe I misunderstand, because I can't work out what you mean when you say "...from another thread" 
 
Setting that aside: your point is well taken... and I guess those whose CNC capabilities extend to full size shipbuilding would have to take particular note .

don_howe

I'm a little disappointed that I can't do this full size. I know I can reduce the scale to 1:48 which was typical of 18th century draughts but I have learned that certain errors can creep in at 1:48 even with CAD because of the rounding of dimensions. The early days of SW had the same problem and I don't know when they corrected it but SW2015 didn't have any problems putting in an arc with the requirements I specified. Splines are not the answer as has been pointed out for various reasons. There is a time and place for splines but I don't believe this is one of them. I think based on the feed back I will submit a ticket that is, if someone else hasn't already done so.