Strange behaviour of SU when molding a door

Charlie__V

Luca,
Others have described better than I could, what/why.

Attached shows how I might overcome SU Follow Me.

Basically make the "tool" that would perform the cutting in real worl.
Orient the arc segments to the rail/stile. and "quarter it".
Intersect the "tool" with the problem corners and follow me to complete.

Or create a solid using the same "quarter" of the tool, and subtract from ea. component.

Best,
Charlie

Sportello_Tool_Intersect.skp

mac1

Brandy20
Another comment. Make the model like one will typically build the door. Assemble the rail and stiles first and then do the moulding cut just like you would with a real door. It seems to me cutting the individual rail and stile components would be difficult and dangerous if possible at all. If you do it this way the follow tool will work very nicely.

jeff hammond

@mac1 said:

Brandy20
Another comment. Make the model like one will typically build the door. Assemble the rail and stiles first and then do the moulding cut just like you would with a real door. It seems to me cutting the individual rail and stile components would be difficult and dangerous if possible at all. If you do it this way the follow tool will work very nicely.

actually, it won't work very nicely.. i'm telling you, follow-me is junk.. (see attached .skp)

sporty_follow_me.skp

Jean-Franco

First, thank you to all for this interesting problem analysis.

If you do that in your shop, in reality the corner will appear a little different as what Jeff describe.
Using the router after assembling the frame is effectively the way to go.
But you'll use a router bit with a bearing at the bottom, having a special radius.
How would you represent this in SU ?

Jean Lemire

Hi folks.

The Follow Me tool, when used to extrude a profile around a curved path may produce these problem if you extrude the profile inside the path. If you use it outside, the problem don't show.

However, with some combination of arc radiuses and segmentation for the path, it is possible to get good result, even if the profile is inside the path.

See all the scenes of the attached SU file for ideas.

Door panel molding.skp

jeff hammond

@jean-franco said:

First, thank you to all for this interesting problem analysis.

If you do that in your shop, in reality the corner will appear a little different as what Jeff describe.
Using the router after assembling the frame is effectively the way to go.
But you'll use a router bit with a bearing at the bottom, having a special radius.
How would you represent this in SU ?

if you used one of those bits to cut the profile after assembly, it wouldn't turn out too sweet..

sporty_bearingbit.skp

brandy20

This discussion is getting more and more interesting

I found Jeff and Charlie's approaches very clever, even if I still haven't tried Charlie's at the top of the door, where the molding should also be curved.

I knew about TIG's Extrusion Tools but never found an application for me with the Lathe tool. So I spent some time in getting to grips with it. I think it is a very good tool but I'm experiencing some troubles with the angles of the curved top molding. After having extruded the two corners at about 79,371° ( )I found the centre of rotation of the arc (Point a centre) and tried to extrude every section corresponding to each segment of the arc. The arc angle is about 21.258°, there are 12 segments for the arc, so every extrusion should measure 1.7715°. But I can only write 3 values after comma, this means adding some more imprecision to the angle. After three extrusions I notice that the segment of the extruded profile is not following the segment of the arc. The difference is very small but, after 12 extrusions the difference increases and this causes (at least to me) problems when intersecting geometries to clean up the molding.

Where am I wrong?

Jean (Lemire), thank you for your hints, but as far as I can see, your example ends up with rounded corners also internally, where they should be squared instead. Unless I didn't go deep enough in your example, I don't think it's the right solution.

Luca

mac1

We have to agree to disagree. Follow me has been around for some time and as with many things they get over taken by progress. To call it junk I think does a disservice to the creator. If the model is made carefully it works fine. As posted many times you must scale up by a relative large number for that to happen. More than the OP.
I have posted many times there is no tangent in SU by the mathematical definition ( unless you think a straight line is appropriate for consideration.). The designers have come up with an approach and if you don't like that why use it?
TIG's tools are very nice because they are adaptive in the sense a relative fixed geo is not required.

jeff hammond

@brandy20 said:

I knew about TIG's Extrusion Tools but never found an application for me with the Lathe tool. So I spent some time in getting to grips with it. I think it is a very good tool but I'm experiencing some troubles with the angles of the curved top molding. After having extruded the two corners at about 79,371° ( )I found the centre of rotation of the arc (Point a centre) and tried to extrude every section corresponding to each segment of the arc. The arc angle is about 21.258°, there are 12 segments for the arc, so every extrusion should measure 1.7715°. But I can only write 3 values after comma, this means adding some more imprecision to the angle. After three extrusions I notice that the segment of the extruded profile is not following the segment of the arc. The difference is very small but, after 12 extrusions the difference increases and this causes (at least to me) problems when intersecting geometries to clean up the molding.

Where am I wrong?

instead of measuring and entering angles etc for those (unless you know the angle is 90.0º, or 25.0º etc.... try this:

-start the lathe tool
-choose rotation axis
-enter desired # of segments (12s <enter> for 12 segments etc..)
-enter 0 (zero) which will allow you to graphically choose the angle instead of entering the # in degrees..
(if the extrusion is rotating in the wrong direction at this stage, type <shift>C which will reverse the direction)

jeff hammond

@jean lemire said:

.

However, with some combination of arc radiuses and segmentation for the path, it is possible to get good result, even if the profile is inside the path.

even then Jean, there are errors.. and if you're using sketchup as a drawing tool for real world construction, these errors are huge..
if you just want something to look neato on the screen then i guess you can get away with using but if you're trying to make accurate drawings, stay away from that tool unless it's being used for straight extrusions.. same goes for the offset tool (and actually, quite a few other circumstances/plugins have this problem)

see attached skp.

followMe_error.skp

jeff hammond

@mac1 said:

We have to agree to disagree. Follow me has been around for some time and as with many things they get over taken by progress. To call it junk I think does a disservice to the creator.

it's nothing against the creator.. all i'm saying is that it is not accurate and anyone that needs accuracy in their drawing should steer clear of the tool..

@unknownuser said:

If the model is made carefully it works fine.

see, that's not true.. look at the examples i've posted and tell me where i went wrong or wasn't careful in the setup..

better yet, how about posting a carefully made model which shows accurate results with the follow-me tool on a curved path..

@unknownuser said:

As posted many times you must scale up by a relative large number for that to happen.

huh? that's nothing to do with it..

@unknownuser said:

I have posted many times there is no tangent in SU by the mathematical definition ( unless you think a straight line is appropriate for consideration.). The designers have come up with an approach and if you don't like that why use it?

i don't use it.. but when people are wondering why they're getting messed up results when using the follow me tool, i'll try to point out that the problem lies in the tool itself..

brandy20

@unknownuser said:

@brandy20 said:

I knew about TIG's Extrusion Tools but never found an application for me with the Lathe tool. So I spent some time in getting to grips with it. I think it is a very good tool but I'm experiencing some troubles with the angles of the curved top molding. After having extruded the two corners at about 79,371° ( )I found the centre of rotation of the arc (Point a centre) and tried to extrude every section corresponding to each segment of the arc. The arc angle is about 21.258°, there are 12 segments for the arc, so every extrusion should measure 1.7715°. But I can only write 3 values after comma, this means adding some more imprecision to the angle. After three extrusions I notice that the segment of the extruded profile is not following the segment of the arc. The difference is very small but, after 12 extrusions the difference increases and this causes (at least to me) problems when intersecting geometries to clean up the molding.

Where am I wrong?

instead of measuring and entering angles etc for those (unless you know the angle is 90.0º, or 25.0º etc.... try this:

-start the lathe tool
-choose rotation axis
-enter desired # of segments (12s <enter> for 12 segments etc..)
-enter 0 (zero) which will allow you to graphically choose the angle instead of entering the # in degrees..
(if the extrusion is rotating in the wrong direction at this stage, type <shift>C which will reverse the direction)

Jeff, that's great, thank you! It works very nicely,

brandy20

Molded door, using Extrude Edges by Lathe. Works very well and the workflow is pretty fast.

I'll also try Charlie's trick.

TIG

AND please remember that whatever method you use to make 'moldings', or any other swept-form for that matter, IF it will result in tiny facets it will fail. Sketchup and OpenGL don't like faces <~0.5mm or 0.01sq". Scale up. mold, scale down. Small facets can exists quite happily...it's just the accuracy issues in creating them in the first place that makes things fall over...

Jean Lemire

Hi Jeff, hi folks.

I agree with you about the use of SU for real world construction. After all, SU is a sketching program.

However, with carefull use, as is the case with all tools, it can be used to some extent.

See attached SU file for ideas.

followMe_error 2.skp

jeff hammond

@jean lemire said:

Hi Jeff, hi folks.

I agree with you about the use of SU for real world construction. After all, SU is a sketching program.

i dunno, sketchup is super accurate in most cases (especially when dealing with mid to large size construction drawings)..
i use the app with full confidence in my work.. it's just that over the years, i've learned (often the hard way ) where it breaks down and how to avoid the problems..

over the past couple of years, i've learned another app (nurbs based) which picks up the slack when sketchup fails.. using the two apps together instead of one OR the other is seemingly one of the smarter work related decisions i've made lately

but when it comes to situations like these, Rhino doesn't even bat an eye

jeff hammond

@brandy20 said:

Molded door, using Extrude Edges by Lathe. Works very well and the workflow is pretty fast.

there are a couple of improvements/changes in the way EEbL works that would make my life a teenytiny bit easier but..
i feel like i've bugged TIG enough on the lathe tool already.. i'll give it another couple of months before i start with another round of suggestions

mac1

Per request http://sketchup.google.com/3dwarehouse/details?mid=97f6c7269341fe93483a6eca16661274 below the OP scale the model starts to have SU size issues.
Barndy20 please reconsider trying to mould the component approach it is dangerous

jeff hammond

@mac1 said:

Per request http://sketchup.google.com/3dwarehouse/details?mid=97f6c7269341fe93483a6eca16661274 below the OP scale the model starts to have SU size issues.
Barndy20 please reconsider trying to mould the component approach it is dangerous

lol.. i don't really know what to say.. maybe i'll just go with..

you're absolutely right! follow-me is awesome!

jeff hammond

if anyone other than m1 is actually interested in seeing the follow-me problem in another circumstance, have a look at the attached file..

this time, i use the offset tool as an example.. it shows the same exact error as with follow-me but with , it's easier to understand/explain where exactly the software breaks down

offset_problem.skp