Problems drawing connected arcs

[DickB]

I was working on a wabble drive: https://www.youtube.com/watch?v=KCLrzAtq3j4

I'm making the gears - if you can call them that - with a series of precisely-placed connected arcs:
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I had lots of trouble doing this. I finally succeeded after much trial and error regarding the sequence of arcs to draw next to get it to work.

Here is an illustration of the problem. I had these two segments drawn, and I wanted to connect them together with an arc:
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When I drew that connecting arc, things went haywire. Connections that were tangential clearly became non-tangential. One of the arc's radius constraint was removed. And the arc that I drew ended up with a radius constraint that I didn't specify:
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I'm curious if others have this problem. I've uploaded the mpc done with Designer 3.102. I started this project with Designer 1, but it misbehaved so badly I could not get very far. At first Designer 3 worked better, but it too had issues. BTW I have had similar problems in the past when drawing other complex connected lines.

[bergerud]

I have always had trouble drawing with arcs. My method is to draw the whole thing first with segments and then convert the segments to arcs at the end. There are certain tangency conditions which cause Designer to crash when converting segments to arcs, so, save often.

In this case, I think I would have drawn all the segments to make a regular polygon. Convert every second segment into an arc (adjusting the radius of each). Then convert all the segments between.


Edit: I should also add that I stay away from constraints. I type a radius and then remove the constraint.

[SteveNelson46]

I think all of us that have tried to draw anything sophisticated using the Designer have had problems. Especially arcs. Even converting line or arc segments doesn't always work correctly. Considering time as a factor it's just easier to use Corel Draw or Adobe Illustrator and then import as a DXF.

[DickB]

My method is to draw the whole thing first with segments and then convert the segments to arcs at the end. I went back to Designer 1 to try your method and it worked. I did also have to follow this sequence:

Draw a polygon with the Connected Lines tool.
Convert all segments to arcs, positioning each radius to approximate location.
Set x and y constraints on the radii.
Specify and constrain the radii.
Convert Free connections to Tangent.

If I tried converting the nodes to tangent and then setting the radii, in some cases it was not allowed. (Error message "The constraint you entered could not be completed because it conflicts with another constraint." Clearly not the case, as I was able to make the same constraints in a different order.) These constraints are all necessary to make the "gears" with the required precision.


In this case, I think I would have drawn all the segments to make a regular polygon. Convert every second segment into an arc (adjusting the radius of each). Then convert all the segments between.I tried that and it didn't work. At one point I got the non-tangential tangents.


There are certain tangency conditions which cause Designer to crash when converting segments to arcs, so, save often.I have not had crashes so much as misbehavior or an inability to draw correctly.


Edit: I should also add that I stay away from constraints. I type a radius and then remove the constraint.That didn't work for me. If I removed a radius constraint, then changed the Free node to Tangent, the radius was altered.

I'm attaching the Designer 1 version of the ring in case anyone wants to play with it.

[DickB]

I think all of us that have tried to draw anything sophisticated using the Designer have had problems. Especially arcs. Even converting line or arc segments doesn't always work correctly. Considering time as a factor it's just easier to use Corel Draw or Adobe Illustrator and then import as a DXF.Problem is I'm cheap. I don't have Corel Draw, Adobe Illustrator, or DXF Importer. And if I did there's another learning curve that will take time. I really think these bugs should be addressed. One should be able to design parts such as mine with Designer IMHO.

[bergerud]

Here is a simple crash example. Try and convert the middle segment to an arc.

[SteveNelson46]

Problem is I'm cheap. I don't have Corel Draw, Adobe Illustrator, or DXF Importer. And if I did there's another learning curve that will take time. I really think these bugs should be addressed. One should be able to design parts such as mine with Designer IMHO.

Dick,

I agree but if we carry this too far we will soon experience the wrath of LHR

[DickB]

I don't think so. Just pointing out a bug and my opinion that it should be fixed.

[lynnfrwd]

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"The Wrath of LHR"

(Sorry, couldn't help myself...but this is what I conjured up in my mind. It doesn't help the arc issue, but I can't do anything about that and I don't think LHR has any plans of software updates any time soon. We will keep it in mind for when we do.)

[JLT]

Dick,


Saw your post, and took a quick hack at a Radial Vector script (see attached, which you can sinply drop into the RadialScripts folder). Basically it treats every tooth and trough as a tooth, drawing either a convex or concave arc as the tooth. (So for example, if you want a Wabble gear with 11 teeth, you need to enter 22 as the total number of teeth + troughs.) Based on the following video https://www.youtube.com/watch?v=2shapHAanIU , it appears that the outer disc is basically the same profile, with one more tooth & trough, and of course a larger diameter, but cut on the inside of the gear profile. So, when using this script to generate the outer disc, simply make the cutting bit diameter "-1/8", which will draw the cut profile on the inside of the gear...


(BTW, my apologies if I took some of the fun out this. The math was kinda interesting to me! Yes, I'm an odd duck...)


R, Jon

[DickB]

JLT, that's awesome! I'm busy right now, but will definitely look at this later. I've made a few changes to your scripts, and have wanted to dig in more to see if I could make some more extensive modifications. I'd really like the ability to produce involute gear sets.

Dick

[JLT]

Dick,

Oddly enough, when I first put together the radial vector generator, I began with involute profiles till I did some research and realized that cycloidal profiles were typical for clock works. I'll dig up the involute profile work that I had done before (which I seem to recall was much simpler than the cycloidal!) and pass it along this weekend...

R, Jon

[DickB]

Cool! I have projects in mind other than clocks, and the involute profile seems more appropriate. I know a few other forum members were looking for gear design tools as well for different gadgets.

[oscarl48]

And here I go getting back sucked in on trying to learn how build clocks again.

I typically don't have such problems learning stuff but for whatever reason clock design and gearing seems to be my current nemesis. All these designs and ideas are very inspirational though.

A sincere big thanks for bringing it back up. I do have a growing pile of gears just sitting in a corner.

[DickB]

The wabble gearing simplifies clock design. You need only one 12:1 wabble set for minutes to hours and one 60:1 set of seconds to minutes.

[JLT]

Dick,

I've uploaded the latest Radial Vector Generator v1.5a at the original post http://forum.carvewright.com/showthread.php?17794-Make-Gears-with-Radial-Vector-Generator , as I realized that the Wabble script I provided earlier wouldn't work with the older version. The new zip file contains both the Wabble Gear and the Involute Gear profiles. I haven't actually cut either the Wabble or Involute Gears, so you might be off roading a bit when you first go to use these profiles. Also, in playing around with the Involute Gear generator, I noticed that large gears didn't generate well with the normal pressure angles of 20+ deg, so I incorporated a check in the Involute script to ensure that the base diameter (where the involute profile begins) is larger than the dedendum circle, and if not, throw out a new recommended pressure angle... The discussion on the involute gear profile might eventually warrant another thread...

R, Jon

[DickB]

Thanks! I only got a chance to take a quick look - I wish I didn't have other projects in the queue right now! This will definitely be a big help.

FYI, there are cases where one would want to adjust the percentage of arc on the wabble gears to less than 180 degrees - does this make sense?
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[JLT]

FYI, there are cases where one would want to adjust the percentage of arc on the wabble gears to less than 180 degrees - does this make sense?


Yes, makes perfect sense... easy enough to incorporate as another parameter, presuming the profile is always an arc, and not a sinusoidal wave... Although off the top of my head, I can think of a few ways to incorporate the parameter...

1) As the range of the arc, from 0 - 180 degrees, with 0 of course being a flat line, and 180 being the full arc.

2) As the height to the "tooth tip" away from the pitch diameter. Of course, this would be bounded by 0 and whatever height represents the radius of the width of the tooth.

3) As a percentage from 0% to 100%, basically being translated to an arc from 0 to 180.

Not sure what my inclination is, as I haven't dabbled in wabble gears, but suspect #3 is most intuitive to interpret the outcome...

[DickB]

You and me both - I'm just starting in wabble gears. Haven't cut one yet, but will do so soon.

[JLT]

Dick,

Uploaded the next iteration of the Wabble script, including it in a re-upload of the v1.5a zip file at the original post http://forum.carvewright.com/showthread.php?17794-Make-Gears-with-Radial-Vector-Generator.

In addition to the parameter to control the height of the tooth arc, I also incorporated the generation of the Ring Gear with an additional parameter to permit adjustment to the Ring Gear diameter to provide some clearance between the Wabble and Ring gear teeth as they pass each other. My intuition tells me there's more math to the profiles than simple arcs (kinda like the rolling action of the involute and cycloidal profiles), but I could be wrong...

R, Jon

[Rocketman]

Very interesting thread. We truly have some talented people on this site. I've played with early Ely Terry clocks. I've got two of his early designs in pieces now. It's a shame how little value they have considering their age and the hand work that went into them. My father was a watchmaker and one of the first clocks I ever tinkered with was his old wood gear clock my mother had hung in the living room for decoration.

Some of the wood gear clocks being made today are beautiful works of art! People often give Henry Ford credit as being the creator of the modern day assembly line. I think Eli Terry should get the credit for all the clocks he turned out decades before Henry's cars. They say they cost about a years wages back then and he would drop one off at a farm and let them test it out. When he went back to see if they wanted the clock very few were returned. It would have been as ground breaking as an Iphone was when it was introduced.

I'm looking forward to seeing what kinds of creations develop from these gears.

Brad

[BOB D]

This is a timely discussion for me. DickB posted a link to a wooden clock previously (http://www.scrollsawer.com/2015/10/0...-gadgets-2015/ (http://www.scrollsawer.com/2015/10/02/gizmos-gadgets-2015/)) and I couldn't resist building it. 79652
Converted the patterns to DXF and used the Carvewright to cut them out. I had difficulty in understanding the mechanics behind the conversion from minutes to hours. The designer called it a "daisy". Makes a lot more sense now.
Bob D

[DickB]

Nice job on that clock Bob. How did you convert the patterns to dxf? That daisy is similar to the wabble.

[Rocketman]

If the pattern is in pdf form you can convert it online for free here: http://www.pdftodxf.com/

Brad

[BOB D]

Dick,
There was no easy solution for me. I scanned the scrollsaw patterns from the magazine, loaded them into Turbocad, scaled, then either traced or re-drew the component. Saved as DXF and imported into Designer. Not a simple process but it worked.

Bob

[DickB]

Dick,
There was no easy solution for me. I scanned the scrollsaw patterns from the magazine, loaded them into Turbocad, scaled, then either traced or re-drew the component. Saved as DXF and imported into Designer. Not a simple process but it worked.

BobThanks Bob. Every once in a while I come across a scrollsaw project that I get interested in tring with the Carvewright, and I'm always looking for ways to make the conversion.