collars

[ArtF]

Steve:

  I understand what your saying, ( you explained it quite well for a non engineering type.. )

  Reviewing them here the teeth look near identical for all tooth counts. BUT, I did do
multiple changes in there.. so by all means take a photo so I can see if it looks different than mine. We'll go from there..

  As to the arbor issue, typically even with large ratio you'll get several teeth engaged, the math just works out that way, but in extreme cases an idler would be used to press the chain into a further engagement  on either one side or both...

Art

[Stephen Fornelius]

This photo shows the difference between the two types of teeth that I've been generating.  Both were DFX exported to BobCAD/CAM.  Generally only did rough profiling on the larger gear with 3/16" end mill.  I would think that doing a final profile with a smaller diameter end mill might change the profile of the tooth.  I also had to "reverse the start point", otherwise the cutter tried to work within the part and not the waste area.  BobCAD doesn't seem to think this is an issue.  Changing the tool offset doesn't seem to work.

[ArtF]

Hi:

  Well those small ones look odd..but the large one just looks...wrong..

Does the DXF show those sharp points? I cant find a type or size that makes that...
It looks very much like the tool size was off or something.. At a minimum the large one should match its dxf exactly.. Were these cut 2.5D?

Art

[Stephen Fornelius]

I didn't like that one either.  Here's the profile I'm probably OK with.  Its my 7 inch sprocket and the weight chain sprocket.  Wrapping the chain around these seems to tell me they're ok.

[ArtF]

Yes, those look much better. In the end the best test is as you noted if the chain fits them, if it rides well the sprocket is fine generally..

Art

[Stephen Fornelius]

Ran the sprockets with collars per my prior posts.  I'm going to forget using BobCAD/CAM to do the machining - the reason? - your cnc works MUCH BETTER.  Nice teeth, no drama (except for having to put in M3 and M5), and instead of one or two teeth engaging the chain, I can wrap the chain around the sprocket engaging a typical 4 teeth.  Drill and thread for a 4-40 set screw and they should be ready for testing. 

Notes:  It seems that a sprocket with less than 10 teeth needs a relief cut on the collar to allow the chain to fully engage, otherwise the inside portion of the chain can't seat.  Some filing is required to sharpen the tooth, but basically just clean up the milling marks. 

[ArtF]

Stephen:

  Always nice to hear. lol

I think if you use a slightly lower radius %, the filing wont be necessary..

Art

[Stephen Fornelius]

I see what you mean, however, the drawn part with collar doesn't seem to go over to cnc well.  The collar isn't there at all as far as I can tell.  Is this something you had planned to do?  I would think that it would be something like I'm doing now - mill the whole part as a sprocket so its something like 3/4" thick, then mill away 1/2" into the collar shape.  The problem I can see immediately is that the cutting tool would have to be WAY too long. 

A couple of other things - I see in your demos that you can use the mouse to spin the part around, but I only have headly and related selections - is this something only you can do?

2nd - I can't seem to get my material color to correspond to what I select in options.  For example, the raw material is black, but the cutting lines are fluorescent green - great contrast but I can't see the part too well!

Made all my pinion sprockets.  Rough cut the driver sprockets yesterday, but still have to mill the thickness down and debur/file the teeth a bit to clean them up.  Next is the collars - I may try to do them like a lantern pinion so I can use the CNC again.  Otherwise its all drill press work

Steve

[ArtF]

Steve:

>> the drawn part with collar doesn't seem to go over to cnc well. 

  Very true, the collars are not considered at all in making a cnc program. The collar
for such a thing would be considered a part of making the blank , G2 only puts out code
to do the actual teeth for any gear, it ignores collars and spokes ( unless in 2.5D). In 4th
axis, only teeth are cut.

>>A couple of other things - I see in your demos that you can use the mouse to spin the part around, but I only have headly and related selection s - is this something only you can do?

No, anyone can. I use the middle mouse button to rotate the screen, if yu dont have one, you can press and hold ctrl-shft and click the left mouse button to rotate. The shift and ctrl key mixed with the left mouse can pretty much do anything.

>>For example, the raw material is black, but the cutting lines are fluoresce nt green - great contrast but I can't see the part too well! Smiley

  I will be redoing the cutlines so you have some selection, I know its sometimes hard to visualise currently..

  I think with collars Id cut them separatly and weld or silver solder them to a sprocket..might be easier..

Art

[Stephen Fornelius]

control-shift-left mouse works.  I'm gonna have to go back through the tutorials I think and pick up some more hints.

I'm using aluminum for the prototype, so I'll probably have to either epoxy the collars to the sprockets or use socket head cap screws to hold the collar to the sprocket and then one to hold the assembly to the shaft. 

I'm really happy with the sprockets I made yesterday.  I'm using 8 tapered spokes for all 6 to give some continuity to the look of the project.  I think by next weekend, I'll have the escapement parts together - only have the escape wheel so far, but I don't think cutting the pallet is going to be too hard.  Depthing is something else though, not to mention the crutch, pendulum leader, suspension spring and pendulum itself.  Just more fun and games!

Steve