Lofting in TurboCad

Lofting by AndyUK

Icon: Image
Menu: Insert / 3D Object / Lofting
Insert a 3D object by consecutive connecting of 2D profiles

<table style="width: 400px; text-align: center;" border="0" cellpadding="2" cellspacing="2"> <tbody> <tr> <th>Designer</th> <th>Deluxe</th> <th>Pro Basic</th> <th>Pro Platinum</th> </tr> </tbody> </table>

To Download a TCW v10.2 file of Loft examples 152k TCW please click here
and lastly a small(ish) PDF to accompany it, 324k here

Curved Stair beams example adapted from a design by
Lisa Schneider: Lofting Beams

<font style="font-family: helvetica,arial,sans-serif; font-weight: bold; font-size:20px; color: red;">Lofting with TurboCAD</font> by AndyUK

The following Do's and Don'ts reproduced with kind permission from a lofting master
and an inspiration to us all, Mr. Henry O. Hubich

  1. Don't try to loft a Group.
  2. Don't bother drawing symmetrical profiles to make a symmetrical object. Model half the object, then mirror-copy it.
  3. Do draw a single profile, then place a copy where you want the next profile to be and then edit it as necessary. Repeat for each successive profile.
  4. Do make the profiles as simple and clean as possible.
  5. Do be aware of the Format|Create solid|From surface option, new in v10. In many cases, you can use open profiles and then invoke that option to fill in the resulting hollow shell. (Doesn't always work well.) Also be aware that a hollow shell is acceptable in some cases.
  6. Do consider alternative approaches to profile arrangement — e.g., terrain can be lofted from contour lines or from cross sections.
  7. Do anticipate adjusting your profiles to repair imperfections in the finished loft.
    Lotsa luck.

  • Do you need to loft, - Can a form be better achieved using extrude with a twist, extrude along path, or boolean, these are lofts that may be better extruded ---- I lofted them just for fun
  • Profile -Think of yourself as a navigator, and Genie (the heart of TC) as the driver, your job is to guide her using the best and smoothest route, if Genie thinks your navigation (profiles) are crap she will cut corners, come to a stop and complain, (throw up self intersecting error), or put in a few dents and scratches and blame it on you… hmm - does that scenario sound familiar :-)

  • Quantity and positions of profiles is trial, error, and experience, I use guidelines to roughly tell the positioning, quantity is guesswork, but try not to overdo it, too many profiles can actually cause problems.

  • What can be lofted - "all Open" or "all Closed" 2D profiles, be they polylines, arcs, circles, spline, bezier, and 3D spline's in v10.2 pro on, (not sure about v10.1) But not if they are a Group, Region, Block or Symbol, these must either be exploded down, or groups and block can be lofted in their own edit mode, You cannot loft between an open and closed profile.

  • Drawing guidelines - My personal approach is to draw spline guidelines for the profiles to follow, this helps to simplify alignment, most often it is just one or twp spline guides, be they hand drawn or offset. I usually eyeball most things see Pic - below left
    One note if you use Offset tool, if you use the offset to get different sized profiles, and your shape has tight corners, the offset tool may round these over, as in the cloud below, this is not a bug, but the way TC calculates the offset centre, Its better to draw the inner first and offset and node edit the outer, or scale the image and node edit, Click below for page 2

Genie makes nice clouds - shame to let offset mess them up


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Join Polyline tool: Its OK on Arcs and lines, but use sparingly IMO on splines , I dislike all the lines it produces,
using join Polyline on a spline or bexier, converts it into lots of little Polylines, i.e. too many nodes, which can give Genie a headache as she tries to work out what goes where. If you have to use join Polyline, then try the Convert to Curves tool on a copy of the objects to see if its OK; often it will work OK, but sometimes yuk,


Tweaking: Tweaking of the profiles is nearly always needed after the first test loft, , As can be seen from the gray render below-left, I messed it up, this has a big bulge at the end. Mine's around my waist, but I'll not go into that. - simply re-scaling the profiles sorted it out.


A note about start and finish profiles, the "O" below is one loft, and normally one can click the same single profile to start and finish a closed loft, but occasionally TC will throw this up as an error, reason - no idea, at least I'm honest, but if this happens simply find a suitable hidden point and create a separation with two profile very close together, do the loft and do a second loft between the two profiles and add together,


Occasionally a loft will take a very long time, and give the appearance that the program has "hung" or crashed, whilst I don't rule it out, it is often caused by a bad profile, and is simply taking genie a very long time to decide if the loft is possible, on one such occasion, pictured below I was re-scaling, and hadn't realised I had typed in a big figure, fortunately it was late at night, so I left TC working on the loft overnight, the result I found in the morning showed why it took a while, good job I wasn't designing a toilet seat - ouch.

img/wiki_up//Bad loft1.jpg

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Profile direction: when going round a bend think of the car scenario, you are looking forward towards the bonnet, your are sitting at '0' and the bonnet is at +Z, now you do a 'U' turn, you still want to be looking at +Z i.e. where you are going, not -Z where you've been or you'll crash.
In below left, two profile are facing the wrong direction, whilst all the profiles look perfect it results of a bad loft, this is not always the case as, Genie will try her best to accommodate the profiles, but sometimes things get into a spin, but if your careful when aligning the profiles errors can be limited

To avoid this, keep in mind the +Z direction If the loft is to do a "U" turn the profile also does a "U" turn, not simply copied into position. It doesn't usually matter which direction you select the profiles when lofting. (but see page ?).


Equal Node Count: Genie finds it much easier if the node count is the same for all profiles, this can helps limit tears in the loft, I find the easiest way is to create the most complex profile first thus the maximum node count needed, then copy this profile to other positions, and simply edit the nodes as necessary, if more nodes are needed, add same to all profiles, below -, two extra nodes where added to the opposite sides of 2 profiles, none added to the rest of the profiles, with disastrous results note - I did his deliberately - honest


Sudden changes in direction: Trying to take a bend too tight without adequate profile setup can cause distortion, and may result in "self intersecting error" or tears in the loft, if you have to take a bend tight, use plenty of profiles (but don't overdo it), and make sure they don't touch.
OK I know this could be extruded but its just an example


Change of profile shape: a sudden change in profile shape (I.e. Profiles close together), without adequate intermediate profiles may distort the loft '2nd left' , it is necessary to either - add and edit extra profiles to smooth out the change - by that I mean, each transition profile, is slightly different from the last, in the example '2nd right' it took ten profiles with each one node edited to be different, or loft as two separate pieces and Boolean add. Occasionally if the change is too dramatic, lofting as separate objects and adding is the only way (got this one right in the end though :-)


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Change in profile type, - changing profile type will disrupt the node count, do a test loft on that section, and add profiles to compensate, the biggest problem on my system is changing from rectangle to a spline or bezier, the image below 'left' is lofted as one, and clearly shows the twisting, if your lucky the nodes may actually line up, but unlikely, so best to do this as two separate lofts, if possible try to go from a square to a circle first then circle to spline / bezier where the transition is much smoother, the center image is done as two lofts. (Oh and the shape is actually suppose to look like that, I call it my contribution to modern art)


Loft direction: occasionally even when things have been set up perfectly, all profiles aligned correctly, etc. The loft will go bad, its just one of those internal program things, the problem is that these type of blemishes are often zero thickness, and cannot be removed by subtraction

simply try to loft in the opposite direction, I.e. From finish to start, before moving or tweaking profiles, often this simple remedy will work wonders. In this example it lofts ok '2nd right', but there Is a blemish on the curve, which is not present in the wireframe, but lofting in the opposite direction cured this, and no blemish occurred 'far right


Self Intersection: this is a common one, to my way of thinking its when the profiles are positioned in such a way as to cause the loft to overlap or crash, but the reasons don't always appear obvious on screen, the best method to finding problems is to do test lofts at various stages, this should soon find any culprits,

Some causes are:
  • incorrect profile positioning on a curve,
  • accidentally selecting profiles in the wrong order,
  • incorrect scaling causing the loft to go from big to little to big in too short a space,
  • changing shape, I.e. loft leading into the shape "bashes into" loft leading away,
  • profiles out of alignment,

With self intersecting its trial and error, and can be frustrating) to find the cause and remedy. Basically you're on your own with this one.

Overlapping when mirrored and patchwork pattern: as can be seen 'below left', on the straight section (wide part) there is solid red in the blue section and vice-versa after mirror copy + a patchwork pattern on the edge.

The solid is mostly caused by incorrect profile, this occurs after editing half a profile, ready for loft / mirror copy, but after alteration the half of the profile is not within the boundaries of an equivalent full profile, i.e. It sticks out a bit.

The simplest method to get rid of it is Slice the lofting before mirror copy, but there are the odd time, when a slice down the center line will, actually cause damage to the object, in these instances slice slightly over center,

another way is to redo the profiles, which, as all the legwork has been done already with profile alignment, etc. it only take a few minutes to adjust or replace the profiles, There are many times when no action at all is needed as this cannot be seen in the final render.

The Patch pattern is often due to 2 faces occupying the same space:

the pattern will also disappear with slicing, and can occurs on any object whether lofted of native TC, like boxes, where two faces coincide, If you find this pattern when you don't expect it, it is likely that there is a duplicate object with a different or no material, to check simply drag a selection window around the whole object (or part of it if open window mode is used) and check in selection properties how many objects there are, - though what I often just do is just click one select it and hit delete an see if one remains, then use undo


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Full profile, - - - closed rectangle / circles:
these are the simplest profiles to loft, and very few problems should occur, except self intersection, for reasons stated earlier,

Full profile, - - - closed Spline / bezier:
A few drawbacks to this method, are - - -
  • It can takes longer to loft a full profile if it has any complexity so the delays between loft / tweak / loft / tweak can become tedious and lead to errors,
  • The more complex a profile is, - the more nodes it contains, the more chance of errors creeping in, - remember - keep the node count the same if at all possible.
  • If the profile is symmetrical and one needs to edit some nodes its more difficult to alter both sides exactly the same

These mostly give very good results but if you hit problems, then try simplify the profile or choose a different method of lofting, sometimes one can get round some problem by lofting in stages and Boolean adding, this may produce a seam, but choose a hidden positions preferably a straight section, also choice of material will dictate if seams are obvious, Of course these seams are no good for production purposes, but for that you would probably use a dedicated solid modeling program anyway, its all in the mind, if people can't see it - it ain't there,.

Segments between control points - beziers: One thing to try when drawing the profiles is to go into properties 'below left', experiment with the number of segments between controls points, in some circumstances it may make a difference especially if exploded, as to how good it looks when rendered, below right shows an object made with 20, 8 and 2 segments, in A, B, C the bezier is exploded to a polyline before lofting, and clearly shows the difference in facets, D, E, F are not exploded and actually make no difference as to the setting in V11, if using an older version than v11, I suggest testing it to see if there is a difference in render times,


Symmetrical lofting - 'half of a' closed Spline: Its often not necessary to draw a full profile if both sides are symmetrical, the profile is drawn as half of the object, and mirror copied, It is generally necessary to move the reference point to lie at the point it will be sliced / mirrored, unless the profiles are all the same size, (in which case better to use extrude along path),


Problems: Ref point not at desired location, this will mean that selecting the profile and snap to a line, it will be positioned wrong, this can be caused by
  • activating default ref point (local menu or button) - clumsy,
  • occasionally happens on opening file, unlucky
  • re-scaling unequally in z and y direction.
  • stretching the profile
  • node editing
  • can occasionally occur when moving file to different version of TC

some solution -
  • Draw a cross inside the profile where the ref point is to be, relocate ref, group the profile and cross then before lofting ungroup, - doing this means that should you need to tweak a profile after lofting, one can see of the ref point has moved away from the cross.
  • keep a single master copy of the profile (inc cross if used) on separate layer, then if the worse happens sooner or later it will, and it proves difficult to realign, its a simply a matter to making a new profile from the copy,

Symmetrical profiles - half closed Bezier: One advantage of a bezier curve is that tight corners in the profile can be utilised, but there are drawbacks, .the main one being editing the nodes, its often more fiddly to alter the control points of a bezier whilst avoiding too much shape change.

Problem - tweaking the "control points" of a bezier node, once all the profiles are in position, especially if done on a few profiles,
the Solution is care, pure and simple, there is no magical solution that I know of with bezier control point editing, just experiment on a few copied profiles to see if the desired shape in possible, using grid snap with a fine grid, will give indication and possibly something to snap to,


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Simple Open Profiles - - sheet object:

In many cases it is not necessary to have a closed "solid" object, a mirrored open "sheet" will do.

These can often look just as good and sometimes loft a lot better than a solid, one can still do a Boolean add if its necessary to join two bits together, and if a solid is found to be needed later on, it might be able to convert it to solid using the surface to solid tool., - often works ok, but not always,

the decision as to solid or sheet, depends on the use, If one lofted a garden and wanted to dig a pond, this on its own is no good as you would fall through as soon as you cut the surface away, but if no digging was required this would produce a quick and accurate top surface,

  • Problem: after snapping all the profiles to a guideline the Back of loft is not flat, and Boolean add shows a gap
  • Cause: snapping the profiles to a guideline inaccurate
  • Solution: there are times in TC where the snaps "miss" their target, in 10.2, the "N" SEKE is notorious for this on my system, it is often necessary to zoom in to ensure the SEKE goes when one wants it, Zooming in side view will show if this has happened, if not corrected there may be a gap when mirrored, simply find the offending profile and re snap it the guide, and re-loft, or if the loft looks ok, - cheat and slice off the extra bit


Self intersection - revisited:

Certain shapes that are drawn will immediately self intersect, this is not a TC error, but due to the shape required, The shape in Fig.1 below, has an obvious self intersection where the green line crosses, this requires lofting in two stages, shown below are a couple of ways to achieve this, One is to draw overlapping profiles, Fig. 2, the either add together, Fig 3, or slice both between the overlap and then add, Fig 4 shows a second method, there the same single profile is used to start two lofts, in opposite directions, with the result in Fig 5,

Both these methods have a drawback, they produce a seam, shown by the arrows in Fig's 3 and 5, and there is no 'best' method, in this example the overlap is better, but in other lofts the single profile method will be superior, my advice is to try both and see which is best, However there is an extra advantage to using a single profile in some situations, i.e. if one also utilises the compound profile option, - see section on compound profile


Won't loft:

Sometimes things just won't work, in this example I was trying to get one of the profiles 'tight in' so it would look like a sort of carving when lofted, but as soon as I try to move the nodes inwards, it won't loft in v10.2 , indeed no matter how it was altered, copied, redrawn it wouldn't loft, on testing this and after cursing a few times at the screen I ended up using v10.5, where it will loft but only by using the ' use compound profile ' option, the result is mirror copied.

If you use the compound profile option, you must select the 'finish selecting button' after each profile is clicked,
  • Problem: can select first profile but can't select a 2nd profile.
  • cause: compound profile button,
  • solution: if you can't click on a profile__, check the compound profile button on the inspection bar, for quick lofts where one can be reasonably sure the profiles are correct, I would try lofts with this button off, and turn it on if post loft editing is expected, or if the standard loft won't work.


Compound Profiles:

This item was new in v10.?, and can be another good addition to the lofter's toolbox, whilst not as quick as the normal loft, it allows for changing the shape of the loft after the initial loft has been created, (with care), an example being if you need to loft the object as 2 separate lofts, the same profile can be used to edit both lofts, but use it with caution, too much editing, or editing in ISO view, may cause severe shape change, and may also cause a crash, if editing, use an Ortho view and avoid using snaps when editing,

  • Problem: if you try to move the loft without also moving the profiles the loft will snap back to where it was, doing this too many times may crash TC,
  • Cause: this is because the loft is directly linked to the profiles,
  • Solution: either - select the loft and profiles and move as one, or select the loft and explode once, this will sever the link with the compound profiles.

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