GT2 3mm Pulleys

[Paul Jeran]

I am working on a rotary engraver using parts I had laying around and unfortunately, I need a slightly different tooth count pulley than what I have on hand.  Given that I have a laser cutter, it would be great if I could cut a new pulley.  How difficult would it be to add the GT2 3mm profile to the options for GT?

I have seen on thingverse http://www.thingiverse.com/thing:16627/#files that the parameters have been figured out.  Instead of loading SCAD up, it would be nice if I could work in a program I already have.

Thanks,

Paul

[ArtF]

Paul:

Ill see what I can do, often the problem is the numbers arent there, an STL doesnt help much in getting proper spec numbers..
but Ill see if I can interpolate something ,,

Art

[ArtF]

Paul:

  As I figured, the actual specs of the 3mm are not easily found. The complexity of the specs is surprising in a gt2 , the 5mm for example
is speced at no fewer than 10 arcs with 12 intersection points specified. Much more complex than one would think. I dont like ot guess abotu such things
as it truly bothers me when someone counts on my numbers being proper and then finds they are not. (That costs people time and money and I DO
lose sleep over such things so I try very hard not to fudge unless its obvious to the fudger that he's explorin new territory. ).

  If I may make a suggestion. I did some research as to the rate of change of the GT2 pulleys from size to size. As you go from 8mm to 5mm there is a
great amount of change in the radial sidewall nature, however, as you go from 5mm to 3mm that rate of change stops.. so I very much suspect
that if you were to put out a 5mm pulley of the correct tooth count and scaled it by the correct amount as a dxf, you'd have a 3mm pulley.
  I cant really add such a loose spec without more testing, but were I needing a 3mm pulley, Id make a 5mm, and then scale it to the same OD as a same tooth count 3mm pulley. (Easy to find OD of pulleys online, its just the curvatures that difficult..)

Art

[Mooselake]

Art

OpenSCAD is a programming language that generates 3D models, so you can determine what criteria they used to create a GT2 3mm profile by looking at the OpenSCAD file.  Of course, there's no guarantee they did it right.

I've done some modest projects in OpenSCAD, including a few that ended up on TV(erse), but am not even close to being proficient with it.  It is pretty easy to install if you want to try that route.

Kirk

[Paul Jeran]

Art,

Thanks for the thoughts.  I can understand wanting to do it right.  I will give the 5-3mm conversion a shot.  If you do get the info you need to generate the tooth profile, I will also look forward to that.

Paul

[ArtF]

Paul:

  They are in todays release, BUT be cautious, they look a bit off to me, might not matter, that happens in interpolated data,
but let me know how they stack up.. Thx for the pointer to the data...

Art

[Paul Jeran]

Art,

Thanks!  I will generate some gears and let you know how they work.

UPDATE:  Tried to generate a 10 tooth gear - yes pretty small.  It looks like a series of vectors that don't quite tie togehter.  I will try to attach a PDF of what the DXF looks like.

When I try to generate a 25 tooth gear I get a Error Found Gearotic:11, Attempt Recovery? - I tried several times to recover and it just loops around to the same error.

Paul

[BobL]

Paul;

Have you tried switching over from inches to mm in your setup?


Bob
Cheers
:)

[ArtF]

Paul:

  I did discover inch mode wasnt working, a fix was generated so redownload and you should find its fine..

Art

[Paul Jeran]

Art,

After too much business travel got back to the gears.  The profiles look a bit flat on the tips compared to the other GT profiles.  When I cut a 55T gear, the mesh was off with the 180* of engagement.  I went to the GT2-5 profile and re-sized it to the proper diameter and it seems to be working fine.

Thanks again for the effort on this.  It is pretty nice to be able to knock out a gear for a project as needed.

Now that the rotary is complete, time to get back to the clock!

Paul

[ArtF]

Paul:

  Yes, tyhe shaping can be difficult to get right  if the spec isnt just so.. Its why I always hesitate to try to
duplicate a shape unless I have something more definitive. The GT2 I did was based on a belt apparently, so
I expect its a bit off. Ill wait and see what feedback occurs over the years.. :) , eventually Ill find the
right data. Glad to hear the 5mm works when scaled.. Maybe Ill just change the code to scale the 5mm ..dunno why I didnt
just add it that way..

Art