trouble with loft

hi you guys doing,

I've used this site a few times to help me with my CAD homework. This time around I couldn't find what I was looking for so, I'm creating this thread.

I'm making a c-clamp. I think I have everything together and it's time loft the objects. They seem to loft together, but when I try to choose the polyline for path, it tells me this isn't valid. I've taken a screenshot if you guys need more angles, just let me know.

Thanks,

Jay

Welcome to CADTutor Jay.

I would use the SWEEP command for this.

If you have any problem doing it, read this...

http://www.cadtutor.net/forum/showthread.php?87802-Relatively-Painless-3D-Modeling-of-A-Potentially-Troublesome-Unistringer&highlight=unistringer

Attaching the .dwg would be more helpful than the screenshot, as forum members can then open it and more quickly diagnose the problem.

It's difficult to tell from the image, but it's probably because your path is not at the center of the Loft extrusion. It appears that your path line is touching the outside edge of the cross sections. Try offsetting it so that it is in the exact center of the cross sections.

I agree with Dadgad though. Sweep would be a better option.

man you guys are quick! I wasn't expecting replies till tomorrow.

Okay what I did was loft it piece by piece, then moved the each piece into place. I wish I would've held off a minute. Here's what I have so far.

cad final.dwg

Here's a pic of my assignment.

I have been playing around with your drawing, with remarkably little luck, and rather intermittent output from my software.

I now understand that the sections being used are different, which means that LOFT is a better choice than SWEEP, which would be used if the shape remained constant along the entire length of the path.

I was confused, and assumed you had made a mistake, as the ends of the clamp are not parallel, but now that I see the assignment, and it is drawn as being at 100 degrees, I am even more confused. I used to run a factory wherein we had and used lots of clamps, and as a devoted tool junkie of many years, and I am curious how this is meant to work.

Overall I would say you have done a very good job thus far, better than I have been able to.

I may try redrawing your drawing from scratch, and see if I have better luck.

Perhaps there are some settings in my ProSteel of which I am not aware, which are making this more problematic than I would expect it to be.

I think the way you did it (loft piece by piece) is fine. Did you ever stop to think why some AutoCAD commands have more than one option? The flexibility of the software allows us opportunities to use different methods to solve problems.

I revisited this, and painfully and laboriously lofted the individual bits, like you did.

It definitely looks more like it is meant to, although there are inherent problems in the design, as dimensioned.

The axis of the center of the screw thread housing needs to be aligned as on the assignment image you posted.

I have changed that section color to red, and show it rotated into the described orientation.

Clearly the two sides of the clamp need to be parallel, meaning the face of the round pad shown at the bottom of the 3D isometric view needs to align with the center of the screw thread which will penetrate the part at the top.

They should both be concentric to the orientation of the center of the screw thread.

In the screenshots I have highlighted an area which is still problematic, due to the stated diameter of the flat face being 1".

The last screenshot demonstrates why I say there is a dimensional issue with the drawing, because with the diameter being only 1", the lofted part of the clamp, which is profile D, will stick out past the pad, in at least one point, which suggests to me that either Profile D has to be shortened (as shown in yellow), or the diameter of the pad needs to be increased to a minimum of about 1.05", or some combination of the two.

The larger red circle merely indicates that the alignment has been corrected.

Nothing on my desk at the moment, so I played a bit more with the model, and shortened the height of the D section by .25, and relofted the corner bit, and increased the diameter of the pad on that jaw to cover the lofted profile. After which I had to change the position of the tube through which the screw threads on the other jaw.

Must be time for me to step away from the magic box!

I think the way you did it (loft piece by piece) is fine. Did you ever stop to think why some AutoCAD commands have more than one option? The flexibility of the software allows us opportunities to use different methods to solve problems.

how do you you loft it all together at once?

I revisited this, and painfully and laboriously lofted the individual bits, like you did.

It definitely looks more like it is meant to, although there are inherent problems in the design, as dimensioned.

 

The axis of the center of the screw thread housing needs to be aligned as on the assignment image you posted.

I have changed that section color to red, and show it rotated into the described orientation.

Clearly the two sides of the clamp need to be parallel, meaning the face of the round pad shown at the bottom of the 3D isometric view needs to align with the center of the screw thread which will penetrate the part at the top.

They should both be concentric to the orientation of the center of the screw thread.

 

In the screenshots I have highlighted an area which is still problematic, due to the stated diameter of the flat face being 1".

The last screenshot demonstrates why I say there is a dimensional issue with the drawing, because with the diameter being only 1", the lofted part of the clamp, which is profile D, will stick out past the pad, in at least one point, which suggests to me that either Profile D has to be shortened (as shown in yellow), or the diameter of the pad needs to be increased to a minimum of about 1.05", or some combination of the two.

 

The larger red circle merely indicates that the alignment has been corrected.

 

Nothing on my desk at the moment, so I played a bit more with the model, and shortened the height of the D section by .25, and relofted the corner bit, and increased the diameter of the pad on that jaw to cover the lofted profile. After which I had to change the position of the tube through which the screw threads on the other jaw.

Must be time for me to step away from the magic box!

Thanks dadbag, I was wondering if I did something wrong. This isn't a shop class, so this item will never be made which is probably why the design has issues.

how do you you loft it all together at once?

I'm not sure it is possible.

Thanks dadbag, I was wondering if I did something wrong. This isn't a shop class, so this item will never be made which is probably why the design has issues.

DadBAG? I like that!

You're welcome. I expected to be able to do a continual LOFT along the path, but could not get it to work.

Whether or not it will ever be made, had the person who posed the problem tried to do it, it should have been caught, and remedied.

In the problem it suggests using the POLYLINE as a GUIDE CURVE, which I had never heard of, nor done.

When I tried doing that it was rejected with a comment

Modeling Operation Error:

Centerline is not G1.

I googled this, and saw lots of references to it, with no clear answers to getting around it, other than doing it in pieces.

If your instructor grades you down for it, ask your instructor to try and do it, to prove that it can be done in a single pass.

To do all sections in one shot you need to have a spline path not a pline

1- draw a spline as a path

2- place each section where you need it to be

3- use command loft and select each section in order then press ENTER

4- Chose "Path" from "Loft" sub menu

Voila

as mentioned - Sweep will work best - you could also use extrude and select a path

But if you insist to use loft and do all in one shot, then you need to have a SPline as a path not a Pline

1- draw a spline as a path

2- place each section where you need it to be

3- use command loft and select each section in order then press ENTER

4- Chose "Path" from "Loft" sub menu

Voila

Attached is the CAD file with final result

If you need more precise model then add more points to your Spline path

Adsk

cad final-SPline.dwg