topic Re: Fillet with decreasing radius? in AutoCAD Forum

Fillet with decreasing radius?

masterenol — Wed, 16 Aug 2017 02:29:59 GMT

Hi everyone,

Is it possible to fillet a part with a starting radius and an ending radius? For example in the object pictured below, I can create fillet of radius 3 shown in red.

I want to use a starting fillet of radius 3, and have the fillet gradually decrease to 0.001. Anyone have any ideas on how I can go about doing this?

Re: Fillet with decreasing radius?

BeKirra — Wed, 16 Aug 2017 05:12:14 GMT

Maybe you give a try of "sweep" command?

Edit: look into "scale" option before selecting the sweep path.

HTH

Re: Fillet with decreasing radius?

masterenol — Wed, 16 Aug 2017 05:12:24 GMT

I've tried using SWEEP with Scale, it is very difficult to achieve the result I want. With SWEEP and Scale, I end up with sharp edges where it should be smooth.

Re: Fillet with decreasing radius?

BeKirra — Wed, 16 Aug 2017 05:42:28 GMT

Please find the sample attached. I used a scale of 0.2

The right hand side is the profile and path used for creating the sweep model on left hand side.

HTH

Re: Fillet with decreasing radius?

Michiel.Valcke — Wed, 16 Aug 2017 06:28:22 GMT

Hi,

Have you tried using _LOFT.

You make your cross-sections and connect them with a guiding arc. Once you use the command loft you will see that the profile does not follow the guiding arc. If you finish the command with an 'enter' it will ask you one of the following [Guides/Path/Cross sections only/Settings] If you select guides you can pick the arc as a guide and the profile will change to follow the arc.

Do notice that this will create a surface and not a solid. If you wish to create a solid with the _LOFT command you need to make your cross-sections closed polylines or splines.

In attachment you can see my results.

Re: Fillet with decreasing radius?

BeKirra — Wed, 16 Aug 2017 06:43:58 GMT

Can you upload your drawing if the samples (both of mine and Michael's) attached are not what you want.

By looking at your screenshot again, I am not sure if I understand the geometry you want to create.

Re: Fillet with decreasing radius?

masterenol — Thu, 17 Aug 2017 00:03:35 GMT

Here are 3 pictures of the drawing I want to modify.

Picture 1: A yellow solid object with a cyan plane.

Picture 2: A White Curved Line is shown between the Cyan Plane and the Magenta Plane. Shown in red is a cross section of the yellow solid object that I want to fillet. I want to fillet so that the fillet curve is tangent to the White Line as shown in Picture 3.

Picture 3: Shown in Green is the fillet curve that is approximately tangent to the White Line. I was not able to get a perfect tangent fillet curve, it is something I am struggling with as well. I made a fillet of radius 4.5.

I want to fillet the top of the yellow solid object so that the left side shown in the Red Cross Section has a fillet radius of about ~4.5 and gradually decreases down to 0 or 0.001 fillet radius as it approaches the right side of the yellow object shown in the right Red Cross section. I would like all fillet curves to be tangent to the white line.

I greatly appreciate all the help you all can give. I'm still experiment tips given to me by both BeKirra and Michiel.Valcke and I'll let you know if I make any progress.

Re: Fillet with decreasing radius?

BeKirra — Thu, 17 Aug 2017 02:41:01 GMT

Ok, I have done an excise and the drawing file is attached.

I can't make the model perfectly.

The reason is that there is a difference when talking about "geometrical" theory and "AutoCAD" theory.

In your case, we can imagine that a sweep created from an end profile to an end point can be done and this is "geometrical" theory.

On the other hand, AutoCAD doesn't allow user to set the sweep scale to "0" as the end point is a perfect point and this is "AutoCAD" theory.

On the drawing file, the '01" solid is a copy from yours on its left just in case I might make a mistake. "04" is the profile I created a perfect tangential curve and the sweep path copied from yours. "02" and "03" are the solids using different sweep scales. When you have a close look at the end point on "02" you will see it is not perfectly formed. "03" solid created by "0.001" sweep scale seems ok to me. Back to the "01" solid now, your solid is subtracted by "03" solid and obviously it is not the result you expected. I then created a curve solid "05" which sweep scale is 1. As you noticed "05" solid has a offset from the profile and the sweep path. The sweep path (magenta) on this one is a copy from the top edge of your solid. This explains the result of "01" solid cut. Furthermore, having a close look at the "03" solid, you will also see there is an offset from the sweep path (white) and the solid bottom edge.

All these can tell the reason which we will not be able to create a perfect cut or trim that you descripted.

Hope this explains but not "HTH".

Re: Fillet with decreasing radius?

beyoungjr — Thu, 17 Aug 2017 03:36:32 GMT

Hello,

Loft was your answer in a previous response.

I used your file and I copied your line/arc profiles away from your working area. I set my UCS to World just to be sure everything was in my comfort zone. I used Join to make each of your profiles a Polyline (joined polyline will be solid vs surface). I used fillet to create the R3 on one profile and R.001 on the other. I created an R34 arc between the bottom inner corner of the profiles.

Lastly, I pre-selected the two profiles and clicked the Loft command on the Solid ribbon (drop-down under Sweep). Since the profiles were valid and pre-selected the command prompts asked for a method and I chose Path. Selected the R34 radius and voila, a solid.

Remember that the profiles are absorbed by the Loft command (similar to Revolve and others) so if you wish to keep the profiles you should copy a working pair to a distance away and maybe save them on a working layer.

You dwg attached back.

Cheers,

Blaine

Re: Fillet with decreasing radius?

BeKirra — Thu, 17 Aug 2017 03:56:40 GMT

Ha, forget avoiding to use trim method.

You are right. The loft is the answer.

Cool.

Re: Fillet with decreasing radius?

masterenol — Fri, 18 Aug 2017 01:20:42 GMT

blyoung, that's pretty much exactly what I wanted. Thanks!

Thanks for your help as well BeKirra.

Re: Fillet with decreasing radius?

BeKirra — Fri, 18 Aug 2017 02:50:34 GMT

Just a sidenote and may be off topic.

I tried to get the fillet/trim solid part by subtracting the loft from your solid. (see the drawing file attached)

It doesn't give a perfect cut and leaves very thin solids on left and right sides of the trim solid.

It confirms that loft and sweep functions do not perfectly form the expected solid.

In other words, it again tells that AutoCAD has accuracy issues.