I am going to split off a topic that was posted in another thread, since I think we drifted too far off of the original subject that was posted.
Constraints/Dimensions or No Constraints/Dimensions in 3D Modeling
- Thread starter GreenTwin
- Start date
Help Support Home Model Engine Machinist Forum:
JasonB asked:
So Pat how do you know what size anything is on your 3Dmodels. lets take two simple parts one shaft and a block with a hole in it.
you select circle and click and drag a circle but what diameter is it. You then extrude it but have to enter a length or do you just drag it to some unknown length.
The other part how do you get the hole in it to fit the shaft if you don't dimension it or give it a size. And how do you position the hole in the block if you can't dimension it from an edge or ctr line.
I'm constantly using various constraints particularly concentric, parallel, symmetrical, tangent, colinear, right angle. Some come up automatically others I add as needed
My first response is:
I am sort of puzzled, because I always assumed that everyone does 3D just like I do 3D, so it is a surprise to find out that others do it some other way.
I really don't have good feel for how others use 3D.
I have done 3D for so long that I don't even think about how I am doing it, so I will have to think about it.
Sometimes I have drawings, such as the Mississippi marine engine, and sometimes I start from a raster image inserted into Autocad.
Lets assume we start with a raster image of an engine, and insert that into Autocad.
I try to get a square side view photo if possible, but usually the photo is skewed.
If the photo is skewed, I interpolate.
If I can find out one dimension on an existing engine, such as flywheel diameter, I scale the raster image so that the flywheel is actual size.
I usually start with the base or frame, and try to find a 2D sketch that gives me the most "bang for the buck", ie: a shape I can extrude that captures as much of the base/frame geometry as possible in one extrusion.
I draw that starting 2D sketch in Autocad, generally beginning with horizontal and vertical X and Y lines, and then offsetting from that line some relatively rounded number that is close to the raster image.
I keep offsetting from centerlines, and then round out the sketch with arcs, circles, splines, chamfers, etc., trimming overlapping lines almost always.
Copy that 2D sketch from Acad to SW, paste it on one of the three planes, depending on what makes sense.
If the sketch is the side view, I put the sketch on the side plane.
If the sketch is from the bottom of the base/frame, I put the sketch on the top SW plane.
I like to keep the part symmetrical with the X,Y,X origin, and I often extrude from the center out in both directions from either the X, Y or Z axis.
The distance I extrude is based on some rounded number that I measured from the raster image in Autocad.
.
So Pat how do you know what size anything is on your 3Dmodels. lets take two simple parts one shaft and a block with a hole in it.
you select circle and click and drag a circle but what diameter is it. You then extrude it but have to enter a length or do you just drag it to some unknown length.
The other part how do you get the hole in it to fit the shaft if you don't dimension it or give it a size. And how do you position the hole in the block if you can't dimension it from an edge or ctr line.
I'm constantly using various constraints particularly concentric, parallel, symmetrical, tangent, colinear, right angle. Some come up automatically others I add as needed
My first response is:
I am sort of puzzled, because I always assumed that everyone does 3D just like I do 3D, so it is a surprise to find out that others do it some other way.
I really don't have good feel for how others use 3D.
I have done 3D for so long that I don't even think about how I am doing it, so I will have to think about it.
Sometimes I have drawings, such as the Mississippi marine engine, and sometimes I start from a raster image inserted into Autocad.
Lets assume we start with a raster image of an engine, and insert that into Autocad.
I try to get a square side view photo if possible, but usually the photo is skewed.
If the photo is skewed, I interpolate.
If I can find out one dimension on an existing engine, such as flywheel diameter, I scale the raster image so that the flywheel is actual size.
I usually start with the base or frame, and try to find a 2D sketch that gives me the most "bang for the buck", ie: a shape I can extrude that captures as much of the base/frame geometry as possible in one extrusion.
I draw that starting 2D sketch in Autocad, generally beginning with horizontal and vertical X and Y lines, and then offsetting from that line some relatively rounded number that is close to the raster image.
I keep offsetting from centerlines, and then round out the sketch with arcs, circles, splines, chamfers, etc., trimming overlapping lines almost always.
Copy that 2D sketch from Acad to SW, paste it on one of the three planes, depending on what makes sense.
If the sketch is the side view, I put the sketch on the side plane.
If the sketch is from the bottom of the base/frame, I put the sketch on the top SW plane.
I like to keep the part symmetrical with the X,Y,X origin, and I often extrude from the center out in both directions from either the X, Y or Z axis.
The distance I extrude is based on some rounded number that I measured from the raster image in Autocad.
.
Lets assume I am sketching in Solidworks:
I pick a plane, either Front, Side, or Top.
Draw a circle on that plane.
Whenever possible, I put the origin of the circle, or at least the origin of the part at the X,Y,Z intersection.
There is a window on the left side of SW, and when you draw a circle, the window will show the circle origin, the circle radius, and some other info.
You can manipulate any of the circle info in the window, but I only change the radius to my desired dimension.
Typically I extrude from the center out equally in both directions, and again there is a window on the side that tells me how long the extrusion is.
I extrude out to some random length, and then edit the value in the window.
Or sometimes I extrude out, and then trim off with a second sketch used as a cut.
For a shaft, again draw a circle, and edit the radius in the box on the left.
Extrude the shaft out to some dimension, again controlled by what you type in the box.
I always draw a centerline at the X,Y,X axis, and then offset that centerline over a specified distance.
Then I draw the circle on my offset line, and extrude or cut.
Maybe I am using those without knowing it, but I really don't think I ever use any of those.
The only time I can recall using constraints like that is when building an assembly of multiple parts.
.
In Solidworks, there is a little popup avatar next to the cursor, and it tells you if you are vertical, horizontal, or many other things.
I ignore all of the popup avatars except horizontal or vertical.
The thing I don't like about doing 2D in SW is that after I have drawn a few lines, and then perhaps I want to do an offset of one line, SW offsets all the previous lines, not just the one line I select.
AutoCad only offsets the line I select.
Or if I draw a few lines, and then stretch out a line, or drag it, all of the previous lines are stretched/distorted, even though I only want to drag one line.
Again Autocad will drag one line without affecting any other line.
The only way I can overcome the problems that SW causes is to pick each line and try and delete all of the relations that SW is creating automatically.
I don't want the relations created, but don't know how to turn that feature off.
The automatic relation creation really causes me a lot of problems.
It is suppose to help, but it almost stops me from sketching.
I think much of it relates to learning to draw in 2D in Autocad, which is quite different than drawing in 2D in Solidworks.
I learned Autocad first, and that is what I can use very quickly.
Maybe I can make a video of some typical sketching I do in Autocad, and in SW.
.
I ignore all of the popup avatars except horizontal or vertical.
The thing I don't like about doing 2D in SW is that after I have drawn a few lines, and then perhaps I want to do an offset of one line, SW offsets all the previous lines, not just the one line I select.
AutoCad only offsets the line I select.
Or if I draw a few lines, and then stretch out a line, or drag it, all of the previous lines are stretched/distorted, even though I only want to drag one line.
Again Autocad will drag one line without affecting any other line.
The only way I can overcome the problems that SW causes is to pick each line and try and delete all of the relations that SW is creating automatically.
I don't want the relations created, but don't know how to turn that feature off.
The automatic relation creation really causes me a lot of problems.
It is suppose to help, but it almost stops me from sketching.
I think much of it relates to learning to draw in 2D in Autocad, which is quite different than drawing in 2D in Solidworks.
I learned Autocad first, and that is what I can use very quickly.
Maybe I can make a video of some typical sketching I do in Autocad, and in SW.
.
I started leaving a paper trail as I create models in 3D, and I use the "PrintScreen" button to copy the screen and paste it into a photoshop program.
The idea behind the papertrail is to help me remember how I got from the beginning of the model to the end, and also to capture dimensions in the dialog box on the left of the screen, so I can quickly see what dimension I used for any sketch.
The approach I take for each part varies, depending on what the part looks like.
Here are some screencaptures of some 3D models for the Mississippi.
In this case there is a shaft, and I have accurately drawn half of it in Autocad, and imported that sketch into Solidworks, where I rotate the sketch to make the complete and finished shaft.
The idea behind the papertrail is to help me remember how I got from the beginning of the model to the end, and also to capture dimensions in the dialog box on the left of the screen, so I can quickly see what dimension I used for any sketch.
The approach I take for each part varies, depending on what the part looks like.
Here are some screencaptures of some 3D models for the Mississippi.
In this case there is a shaft, and I have accurately drawn half of it in Autocad, and imported that sketch into Solidworks, where I rotate the sketch to make the complete and finished shaft.
Here is the beam.
I was not sure of the best approach on the beam, so I just blindly started out, and made things up as I went.
When I finished this beam, I did not like they way some of it turned out, and so I started over with a new beam model, and that model was much better.
Generally I can get a pretty good model the first attempt, but for a complex shape, it may take two or more attempts.
Again the initial sketch is made in Autocad, and then imported.
I can sketch extremely fast in Autocad, and the same sketch very slowly in Solidworks, so I try to to most of my sketching in Autocad.
I was not sure of the best approach on the beam, so I just blindly started out, and made things up as I went.
When I finished this beam, I did not like they way some of it turned out, and so I started over with a new beam model, and that model was much better.
Generally I can get a pretty good model the first attempt, but for a complex shape, it may take two or more attempts.
Again the initial sketch is made in Autocad, and then imported.
I can sketch extremely fast in Autocad, and the same sketch very slowly in Solidworks, so I try to to most of my sketching in Autocad.
More beam work.
Beam
Beam
More beam
Beam
beam
beam
I was having problems with the approach on this beam, but I kept going, just because I did not have any better ideas at the time.
I ended up discarding this beam and started it all over again.
This design meandered quite a bit, but I had never done a beam before.
I ended up discarding this beam and started it all over again.
This design meandered quite a bit, but I had never done a beam before.
beam
I got to the point where features added would damage previous features, and that is not a good thing.
I got to the point where features added would damage previous features, and that is not a good thing.
I was struggling at this point, but nothing to do but keep trying to hash it out.
I see some dimensions in some of these sketches, but typically I offset a plane a given distance, and then verify that with a dimension.
I typically erase the dimensions if I do check them.
In this case I left the dimensions in.
It should be noted that the sketch was created, and then checked with dimensions.
The sketch is not driven by the dimensions, and nothing happens when I erase the dimensions.
I see some dimensions in some of these sketches, but typically I offset a plane a given distance, and then verify that with a dimension.
I typically erase the dimensions if I do check them.
In this case I left the dimensions in.
It should be noted that the sketch was created, and then checked with dimensions.
The sketch is not driven by the dimensions, and nothing happens when I erase the dimensions.
beam
In the 4th image down, I can see that I drew a centerline, offset that line, and then used the endpoint of the offset line as the starting point for my circle.
I could not use the standard fillet on some of the pieces of the beam, since that produced the opposite curve that I wanted, and opposite the curve shown on the original 1840 drawings.
In the 4th image down, I can see that I drew a centerline, offset that line, and then used the endpoint of the offset line as the starting point for my circle.
I could not use the standard fillet on some of the pieces of the beam, since that produced the opposite curve that I wanted, and opposite the curve shown on the original 1840 drawings.
beam
beam
My beam design was not going well, and I was unhappy with it.
Sometimes you have to see what does not work well in order to think of a better approach.
I could have drawn a more simple beam more easily, but I was trying to match the original 1840's Mississipi beam drawing exactly.
Sometimes you have to see what does not work well in order to think of a better approach.
I could have drawn a more simple beam more easily, but I was trying to match the original 1840's Mississipi beam drawing exactly.
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