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Join Date: May 2008
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[CAM] pressure angle vs beamlength

05/10/2008 7:25 AM

Does it matter which configuration I use?

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#1

Re: [CAM] pressure angle vs beamlength

05/10/2008 7:48 AM

The two configurations put different stresses on the parts.

Config 1 has a much 'harder cam' with higher stresses on the cam and follower...I theenk..but hey I'm a cat that designs electronics...so maybe you'd better wait for the mech engs to turn up.

Del

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#2

Re: [CAM] pressure angle vs beamlength

05/10/2008 12:57 PM

What are you trying to achieve? How much force are you trying to overcome? How much room do you have? What are the parts made of? The list goes on. More info please.

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#3
In reply to #2

Re: [CAM] pressure angle vs beamlength

05/11/2008 7:37 AM

The cam shaft is rotating slowly (maybe once every 6 seconds) so acceleration is not a big issue. And the other forces are quite low also (acting upon springs, but quite light).

Though, space is limited (so I would like the cams to be small). And I would like the movements as fast as possible (steep pressure angle) because other processes must wait for it (I can not use this time for anything else)

So, within a certain angle of the cam I can use a pressure angle of 30 degrees with no scaling of movement. Or I can use say 15 degrees pressure angle and scale the movement by extending the beam. Which one is preferable?

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#4
In reply to #3

Re: [CAM] pressure angle vs beamlength

05/11/2008 2:05 PM

How critical is the acuracy at the beam end farthest from the cam? The farther out you extend from the fulcrum, the more tendancy there is for backlash; so then you will need to have stronger retention springs. From what you describe, my judgement, from practical experience, would be for the top diagram with the fulcrum centered on the beam.

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#5
In reply to #4

Re: [CAM] pressure angle vs beamlength

05/11/2008 2:29 PM

I'd go along with that...

As the whole thing is under a fairly light load it prob' doesn't matter much.

If using the top diagram, how about having the pivot for the beam on the same level as the base circle of the cam? e.g raise the beam pivot a bit this would give a smoother angle of attack on the follower.

Dunno if it helps, but it looks better to me if the follower touches the cam at top dead centre, and the beam extends horizontally away from that.

Hope this makes sense... go gently with me I just a Cat

Del

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#6
In reply to #5

Re: [CAM] pressure angle vs beamlength

05/11/2008 3:10 PM

Yeah, the accuracy gets worse in the second configuration

The idea (I think, and that's why I'm asking) is that when you increase the pressure angle to 90 degrees, the cam won't work at all. While at a small pressure angle, say 10 degrees, the cam works very well. So my gut feeling tells me to keep the pressure angle as small as possible (so the opposite of what you think actually, hmm...).

btw the angle in the drawing is not the pressure angle, just the angle of the follower (a little bit confusing maybe)

<quote>If using the top diagram, how about having the pivot for the beam on the same level as the base circle of the cam?</quote>

Yeah, but this effectively means that you're extending the follower arm and decreasing the ouput movement. (because if you're not changing the length, then you can rotate the image and end up with the situation you started with)

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#7
In reply to #6

Re: [CAM] pressure angle vs beamlength

05/11/2008 3:34 PM

Sven,

My experience is in food processing equipment and automotive (and a lot of other stuff that doesn't figure in here). Dels is in electronics. You haven't told us what field this applies to but it sounds more like Del can probably give you the best advice here. I will defer to the wisdom of 'El Gato Supremo'.

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#8
In reply to #6

Re: [CAM] pressure angle vs beamlength

05/11/2008 4:11 PM

I think you are misinterpreting what I'm saying.

What I think is ...

If you draw a line from cam centre to follower, this should form a right angle with a line drawn from cam follower along the beam, when the cam is on the base circle. Dunno if there is a sound reason to this but it seems right to me, with things acting at or near 90o to each other where possible. Same at the other end of the beam, in the 'neutral' position the linkages should be at 90o. Or is this just a foible of a cat?

Del

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#9
In reply to #8

Re: [CAM] pressure angle vs beamlength

05/11/2008 4:55 PM

My reasoning being..the geometry is much easier to do if the angles are approx 90o.

Del

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#10
In reply to #9

Re: [CAM] pressure angle vs beamlength

05/11/2008 5:18 PM

you mean that

center base circle -> center follower wheel -> pivot

should form a right angle.

One should say it should. It's something I didn't even think about.

The field it applies to is hobby. It will become some sort of orrery.

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Del the cat (4); Shadetree (3); sven2000 (3)

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