Mitering on a Curved Path
SOLIDWORKS Forums
2 months ago

Hi all

 

I had a bit of unexpected time this Sunday morning so I had a little play to see how SW handles curved mitres.

Consider this profile running round a segmental arch

Here is what SW produces with a Single Group/Structural Member - a little disappointing!

 

Any old joiner worth his salt knows that there are two ways around this problem.

 

The first solution is to cut a curved mitre.  I found this way pretty easy, by creating a curved surface passing through the intersection points and using a trim/extend

 

The second solution is to keep a straight mitre but adjust one of the mouldings.

This again was pretty straight forward by creating an intermediate sketch and editing the weldment profile sketch in the second member, and driving (over-riding) some dimensions with sketch relations

 

That's the two techniques out of any joinery text book - the thing that surprises me is that it's only for the most high quality work that these solutions are required, normally we just do a straight miter like this, which whilst not perfect is generally acceptable.

 

Here's SW solution and your average joiners solution on top of each other

By the look of things it appears they construct the miter plane using a mid plane as opposed to the intersection of equally offset geometry

The reason I got into all of this was because at first I used a sweep and noticed SW very cleverly cheats


Categories: Modeling and Assemblies, Weldments

Comments
Last comment By: Rob Edwards   Thu, 05 Apr 2018 10:54:07 GMT
Re: Mitering on a Curved Path

Just a question?

 

Why not just use the Sweep Feature ?

 

 

 

By: John Stoltzfus  Mon, 27 Mar 2017 10:47:57 GMT
Re: Mitering on a Curved Path

Hi John

 

I used a sweep to begin with and noticed it was producing an impossible to manufacture solution (in our workshop anyway, we've got a 50 year old overhead router).  I didn't experiment with all the settings, or additional guide curves, but I noticed that the sweep adds extra material in the corner.  Maybe if I was using a CNC it would do but if you look carefully at the image you can see the curve is flattened off towards the end?

 

 

It's a trivial matter but I'm always looking to make improvements to our efficiency.  We don't own a CNC machine ourselves but have occasional access to one to use for cutting jigs.  I was wondering about the possibility of cutting the perfect miter on the computer and then using a template trim in the shop.  As it's always tricky laying out these joints at a minimum an accurate 1:1 drawing would be a good time saver

By: Rob Edwards  Mon, 27 Mar 2017 12:25:59 GMT
Re: Mitering on a Curved Path

If it flattens out - you could extend the sweep beyond and then miter it further back.. 

By: John Stoltzfus  Mon, 27 Mar 2017 12:28:38 GMT
Re: Mitering on a Curved Path

I'll have a play with sweep again, to see if it can be accurate as well as fast and easy.  Weldments are good though.  I'm happy enough creating my own mitre plane.  I made this post just because I thought it was curious.  I can't imagine why anyone would cut a mitre the way SW does.

By: Rob Edwards  Mon, 27 Mar 2017 12:38:53 GMT
Re: Mitering on a Curved Path

Ok - did the perfect result - I did try this a few more ways... 1st way was to do the Top arch as a Revolve at about 180 degrees from center out and then trimmed the ends where the connection is, did not look clean at all - not as bad as your first attempt but almost..

 

Next I tried making the two vertical side pcs, First I made the right side & cut it at the angle based on a sketch part in the assembly, then I made a mirrored part and mated it in place.

 

Next I added a new component and used the miter cut on each vertical pc and inserted a sketch at both seams, then I added another sketch directly in the top center.  Then used those 3 sketches using the loft feature and using the Sketch Part Arch sketch as the Guide sketch, that is where it came out the cleanest, which would work perfectly on a CNC Machine

 

 

By: John Stoltzfus  Mon, 27 Mar 2017 17:00:36 GMT
Re: Mitering on a Curved Path

Ah a loft!

 

I tried again with sweep, seeing if there is anything can be done with guide curves, but I couldn't get anything to work.

...But I succeeded with an extrude and revolve up to a curved surface, although SW is being fussy about fully defining the sketch for creating the arc surface, sometimes its black, sometimes its blue

 

edit: I deleted the right hand blue segment and it appears to be working now

By: Rob Edwards  Mon, 27 Mar 2017 18:19:25 GMT
Re: Mitering on a Curved Path

Not sure I ever want to see a segmental arch again,,, but following your lead for the loft I got a sweep to work.

Thanks John

By: Rob Edwards  Tue, 28 Mar 2017 06:59:26 GMT
Re: Mitering on a Curved Path

Just a question Rob - How do you plan on making this pc?  Here we would have the raw material steam bent and then machined that way your grain follows the profile, or do you plan to just take a chunk of wood and machine it?  There are a few really good steam benders we work with that would be capable of doing the work, wasn't sure how you have it in the UK....

By: John Stoltzfus  Tue, 28 Mar 2017 10:26:11 GMT
Re: Mitering on a Curved Path

I'd just do a swept path and split the body on the mitres????

By: Jason Young  Tue, 28 Mar 2017 12:15:48 GMT
Re: Mitering on a Curved Path

That is what Rob Edwards did - check his first post...

By: John Stoltzfus  Tue, 28 Mar 2017 12:22:45 GMT
Re: Mitering on a Curved Path

For me this is by far the easiest solution.

By: Jason Young  Tue, 28 Mar 2017 12:23:06 GMT
Re: Mitering on a Curved Path

Rob,

use the external profile to define the path??

By: Jason Young  Tue, 28 Mar 2017 12:28:28 GMT
Re: Mitering on a Curved Path

I was reading this and thinking to myself (as a wood machinist), yeah, it's okay for SolidWorks to just pump out the image, but you've got to think of how cutters work on curved surfaces. You would either have to do that multiple passes with different tooling on CNC, or, as suggested, use the traditional steam box technique. The mitres are easy peasy..........

 

 

Dave.

By: Dave Bear  Tue, 28 Mar 2017 12:33:41 GMT
Re: Mitering on a Curved Path

me a machinist too pal.....

back in the old days I would of developed cutters and done it using saddles and dumplings.

yeah, 2 sets of cutters required though

By: Jason Young  Tue, 28 Mar 2017 12:35:14 GMT
Re: Mitering on a Curved Path

That's the best way John   I don't know of any steam benders near us, we have done a little bit ourselves but nothing this wide, it would be nice to have a specialist near us.  For the run of arches we have just made we jointed a single piece to form a V which is then cut out, the grain is a bit short in the corner which caused a few problems (fixed with miter fast)

 

We have some difficulty sourcing straight grain air dried but one of our upcoming jobs is a gothic arched door and I was suggesting to the boss just yesterday that we should have a go at bending some 2.5" and 3" for the jambs then laminating them up and forming a rebate... I think that's my project now so watch this space.

 

The piece I've shown in this post was just an example, it isn't for a live job but I guess if I was the one making it and it had to be good, I would look at getting some bland straight grain and ripping it down into strips, then laminating it back together in the correct order.  Not as good as steam bending (and probably more work) but I know I could do it. 

 

As for the machining it's a perfect arc so I'd probably look at spinning it under the overhead router and doing multiple cuts with various bits, then finish by hand.

 

getting me quite excited just thinking about it, nice to see so many woodworkers on the forum

By: Rob Edwards  Tue, 28 Mar 2017 15:12:40 GMT
Re: Mitering on a Curved Path

Thanks Jason.  I'll give it a try but I guess it will distort the inside of the moulding, I think the main point of this post is that SW mitres on the mid plane of the two normals at the intersection and this is not correct for curved work, where a curved mitre or two subtly different profiles is required.  Maybe I should just leave it to the lads in the shop to work out, I guess I'm just missing my tools instead of this computer

By: Rob Edwards  Tue, 28 Mar 2017 15:24:50 GMT
Re: Mitering on a Curved Path

Looks pretty good from the piece I knocked up pal.

Good to see an artisan woodwork shop doing well.

By: Jason Young  Wed, 29 Mar 2017 07:18:27 GMT
Re: Mitering on a Curved Path

I think he set his guide path to the centre or inside edge.

that will be why SW added the extra material??

By: Jason Young  Tue, 28 Mar 2017 12:32:56 GMT
Re: Mitering on a Curved Path

Thankyou.  I tried sweep again with external path and as you say it's pretty good, about 1.5mm discrepancy in this case.  I suppose normally I would never be as accurate as SW but in this case I wouldn't even have to sharpen my pencil. ;p

 

For woodwork it's a minor issue but I can imagine in other fields of design 1.5mm is a big number

 

By: Rob Edwards  Wed, 29 Mar 2017 12:27:04 GMT
Re: Mitering on a Curved Path

LOL...we deal with tolerances in the range +/-.0002" (yes, that's 3 zeroes) on a regular basis.

 

So yeah, 1.5mm is a football field.   *grin*

By: Dan Pihlaja  Wed, 29 Mar 2017 12:30:09 GMT
Re: Mitering on a Curved Path

can you upload the sample part on here please??

By: Jason Young  Wed, 29 Mar 2017 12:30:19 GMT
Re: Mitering on a Curved Path

Not sure how your overhead router is setup, but just thinking that getting your profile should be fairly easy if you set up your cutting jig using the vertical pcs as your set point.  The vertical pc would have to be mitered and set exactly in position from the router pivot point, then you could set your router tip flush with one of the vertical moulding profiles and then just swing the radius.  

By: John Stoltzfus  Wed, 29 Mar 2017 12:49:35 GMT
Re: Mitering on a Curved Path

As Rob has mentioned here, it is really cool when you can see an pure example of what is or isn't possible on the computer as opposed to what can or cannot be produced on the shop floor. It also highlights one of the first things that the members of the forum here got me to think about when using SolidWorks and that was "How will it be made in the real world?".

 

Being that this related to 'wood' I could envisage everything without blinking and real-world mitres Vs. dysfunctional computer mitres actually became astounding! Hence Rob's post I imagine.

 

It was just nice to see something that I totally related to in both contexts.

 

Dave.

By: Dave Bear  Wed, 29 Mar 2017 04:01:33 GMT
Re: Mitering on a Curved Path

Yes, makes a lot of sense. I normally pencil the profile from the master onto the end and creep up to the line, leaving just a hair for cleanup.  I'd be worried about spelch so would want to leave the pieces oversize.  Swinging it would be good fun, a job best for 2

By: Rob Edwards  Wed, 29 Mar 2017 13:34:27 GMT
Re: Mitering on a Curved Path

Rob, How much of an arc is it? What would be the dimension from bottom of mitre to bottom of mitre (Inside width) and bottom of mitre to bottom of inside arc (height of arc). For the straight pieces, have you got the cutters for these yourselves? Spindle moulder, four sider, router, etc.

 

My apologies, haven't downloaded your file.....

 

Dave.

By: Dave Bear  Wed, 29 Mar 2017 13:37:17 GMT
Re: Mitering on a Curved Path

Of course.

The actual value changes depending on the width of the profile and the radius of the arch - It seems to be between 1 and 2 mm. 

It'd be nice if there's a setting I've missed somewhere

By: Rob Edwards  Wed, 29 Mar 2017 13:50:31 GMT
Re: Mitering on a Curved Path

you have an issue with the radii, they should differ by 12mm??

By: Jason Young  Wed, 29 Mar 2017 14:01:10 GMT
Re: Mitering on a Curved Path

How strange....

looks likw SW is creating a spline to make the shape up?

there must be another parameter that it relys on.

ive tried a few things and still get a 'splined' effect.

By: Jason Young  Wed, 29 Mar 2017 14:13:49 GMT
Re: Mitering on a Curved Path

We'd use various router cutters for the arch and depending how many to be made spindle knives for the straight.  If only a couple we'd probably rout the lot.  Our workshops pretty basic, old Wadkin stuff mostly. 

It was a sample so I just made up a moulding. As for sizes it would depend on the job, I guess it looks good shallow but not too deep or you should probably go all the way round.  Probably anywhere between these two.  I'm seeing a nice sash window here .  I think it could take a 5" architrave.  That'd be a nice job.  Get's me giddy thinking about it, don't you miss it? 

 

 

By: Rob Edwards  Wed, 29 Mar 2017 14:23:48 GMT
Re: Mitering on a Curved Path

revolved cut is very very close...

but still not perfect

 

By: Jason Young  Wed, 29 Mar 2017 15:10:29 GMT
Re: Mitering on a Curved Path

I'm not sure if you're on 2017 or not but I have an assembly attached how I would model it and from the arch part is what I would send to the shop..

By: John Stoltzfus  Wed, 29 Mar 2017 16:33:31 GMT
Re: Mitering on a Curved Path

I'm on 15 but thanks John.  Im guessing If the job were made the way you suggested, using the straight moulding to create the curved piece no one would ever notice...

By: Rob Edwards  Wed, 29 Mar 2017 19:35:30 GMT
Re: Mitering on a Curved Path

i find it really strange that the loft does not give you a radii that can be measured??

By: Jason Young  Thu, 30 Mar 2017 07:12:13 GMT
Re: Mitering on a Curved Path

Yes, From my assessment weldment, or revolved cuts/extrudes best to replicate manufacture

By: Rob Edwards  Thu, 30 Mar 2017 08:01:39 GMT
Re: Mitering on a Curved Path

That's because it turns everything to a spline and you would need to make a cross cut section and add a sketch...

By: John Stoltzfus  Thu, 30 Mar 2017 10:31:43 GMT
Re: Mitering on a Curved Path

that's still a very strange behaviour though?

why should it need or want to do that?

TBH its not something I have ever noticed before, are you able to dimension it in a drawing??

By: Jason Young  Thu, 30 Mar 2017 10:50:50 GMT
Re: Mitering on a Curved Path

No not really, because of the way it was developed, the vertical trim pcs are created with lines and circles and then I cut those pcs on with a miter cut, therefore the radius's were cut on an angle and that makes the circle development an ellipse. So when you select the end cut and convert the entities it turns the geometry into an un-measurable spline...

 

Here is the Auxiliary View of the miter

By: John Stoltzfus  Thu, 30 Mar 2017 11:07:51 GMT
Re: Mitering on a Curved Path

you are not even able to dim the internal / external radius??

By: Jason Young  Thu, 30 Mar 2017 11:14:59 GMT
Re: Mitering on a Curved Path

As in any spline creation - you would need to add sketch arch's to fully dimension that part, the best way would be to show the Guide Sketches used in the loft, make them the same color as the part lines and you're good to go...

By: John Stoltzfus  Thu, 30 Mar 2017 11:18:53 GMT
Re: Mitering on a Curved Path

It's a pity you don't have the climate that we do. You could use your standard straight-line cutters on a piece that had extra meat on both out side edges (allow for clamp damage). Place outside on the driveway in the sun with 3 sash clamps, put a sprinkler in the middle (set to low) and then just wind the centre sash clamp up slowly a couple of turns every half hour! Reach desired arc, leave to dry in shade the next day (not too quickly), trim off excess side timber, mitre, join, VOILA !!!!!!

 

 

Dave.

By: Dave Bear  Thu, 30 Mar 2017 13:28:44 GMT
Re: Mitering on a Curved Path

Another example of sweep not working for me...

Yes of course I want a straight line added to the top of my arch.  One to look out for maybe?

 

 

 

EDIT:  I replaced sweep with multiple extrude/revolves...

Not so bad on this example, but would be a PITA for anything more complex

By: Rob Edwards  Thu, 05 Apr 2018 10:54:07 GMT
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