Topics

Marking Cam

Gus
 


Hi All,

I was interested to read the explanations by Marc in the magazine  for his method of markings cams. My method differs in that I use a direct means of marking, directly to the cam.  ( I often suspect that this is because I don't have the mathematical mindset needed for anything but the practical )
The character which I am wanting to animate is already attached to its cam follower, usually by wire, always within the body, dislike visible external controls. The cam is a blank ply disk. The cam follower is a lever, pivoted at some point, with a 10mm bearing attached via a brass or timber dowel, directly under the shaft center. The first photo shows the bearing attached. It is removed, and a small block, photo 2,  is fitted to the dowel, with an adjustable length piece of pencil lead. As I turn the cam, using the follower, I move it to the positions I want the character to do, so marking the cam. Modification is rarely required if I got the complete  cam markings correct. 






Thanks for looking,
Regards,
Gus

V Bass
 

Great idea! Thanks for the photos; they really help understand how you arranged the tools.

 

Hi Gus...
Excellent idea.  Thanks for sharing.  I'm dealing with a cam right now on the automata that I am building...will give your idea a try.  I think it will work well.
Cheers
--
-Jim Coffee-
creating automata near San Diego, California
one of the group moderators
JamesCoffee.com

Gus
 

Hi Jim,

Please report on how it went, maybe a photo of the outcome ? I would especially like to know if the descriptions were in any way difficult to decipher.

Regards,

Gus

 

Good evening...
Well, my report is that I was not able to mark the cam while it was installed.  Just a complication of this particular cam.  I think that the concept of marking the cam with a pencil attachment is a good idea and I will use it in the future I am sure.
I've included several images that show what I did do:
  • This is a test stand...not the final automata.  The test stand is built for the purpose of ensuring that the biped is properly jointed and to burn it in for a couple of thousand cycles.  Each time I create this particular automata (I call this model "Inclined Slide") the biped will need to be able to function in this test stand (without any test stand modifications) before it goes to the final automata assembly.
  • The white cam follower is plastic, with a 1/4"OD X 1/8"ID ball bearing assembly at it's hub.  
  • The cam is 3/16" Baltic Birch plywood.
  • The cam axle is 3/16" and you can see that I've constructed an axle clamp which is glued to the cam.
    • The axle clamp is glued at the non-slotted end to the cam.  By being glued at just the end the fingers can flex and tighten.  The tighteners are #2 pan head screws that thread into t-nuts.
    • Just a side note...I don't think I'll use a 3/16" dowel as an axle again.  I'll use 1/4" instead...the clamp will have much more clamping power.
  • For this cam I needed a "fall off" that occupied 2/5 of the cam, and a "lift up" which occupied 3/5 of the cam.  So I marked the segments on the cam and then used a french curve to connect the dots.
There are certainly many ways to do this.
IMG_20190923_175204-1000.jpg
IMG_20190920_100849-1000.jpg
IMG_20190923_175059-1000.jpg

Cheers
-Jim Coffee-
one of the Automata Group Moderators
I create automata near San Diego, California



On Thu, 19 Sep 2019 at 15:54, <klekner@...> wrote:
Hi Jim,

Please report on how it went, maybe a photo of the outcome ? I would especially like to know if the descriptions were in any way difficult to decipher.

Regards,

Gus

Gus
 

Hi Jim,

Thanks for that detailed explanation. It looks like the input  pulley behind the cam, is that right ? If it is fixed to the camshaft using the same method as the cam, could it, and the cam, be moved to the left or the right temporarily, to allow a pencil block sized to the inner groove of the plastic follower, to mark the cam ? The  marking block could be fixed by a self tapper to the outside of one of the arms. I often move a cam one way or the other to allow for marking.  Perhaps I see it incorrectly.

Regards,
Gus

 

Hi Gus...
The problem is not the marking concept...the problem is that I used a one time cam follower and that I needed just simple timing.
What I did last night was investigate the sourcing of cam followers that I can use going forward (that can be ordered again and again over the years).  I've settled on screen door rollers with a 1/4" ID.  These have roller bearings in them, are sturdy, and are reasonably priced.
I'll make a cam marking device such as yours that will work with these screen door rollers and I am sure that it will come in very handy many times over the years.
Thanks for your input.
Cheers
-Jim-

On Tue, 24 Sep 2019 at 20:58, <klekner@...> wrote:
Hi Jim,

Thanks for that detailed explanation. It looks like the input  pulley behind the cam, is that right ? If it is fixed to the camshaft using the same method as the cam, could it, and the cam, be moved to the left or the right temporarily, to allow a pencil block sized to the inner groove of the plastic follower, to mark the cam ? The  marking block could be fixed by a self tapper to the outside of one of the arms. I often move a cam one way or the other to allow for marking.  Perhaps I see it incorrectly.

Regards,
Gus