A New Method for the Design of a Three Arc Cam Lobe

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carlw

Member
A few years ago, 'awake' posted his algebraic and CAD drawing solutions of the geometry of a three arc cam here: Cam Calculations SOLVED! (But is there an easier way??). He asked if there was a simpler method. Well, yes there is. I've attached the .pdf file below.

The article concentrates on the design of the three arc cam using a new to us concept, Acceleration Ratio, which is an older concept used in cam design in the 1930's and possibly earlier. Originally, cam design was done at the drafting board - this was a defined shape method. During the 30's articles were published giving methods of calculating the motion of the lifter and it was increasing clear that acceleration was the most important parameter. While cams were still designed by their shape - their lift, duration, base circle radius, flank radii, and nose radius - the design was then evaluated by the acceleration of the lifter. Someone developed the new parameter Acceleration Ratio. I have not yet found the source of that concept. It is at the core of the defined acceleration method.

Designing a cam by either the defined shape or defined acceleration ratio begins with the values of three initial parameters: cam lift, cam duration and base circle radius. A fourth initial parameter is necessary to begin the design process and this is where the methods diverge. For the defined shape method, the fourth parameter is nose radius and at this stage is a guess. The design is completed using the equations in p. 5 of the pdf. The acceleration ratio is computed and the suitability of the cam design is determined by a rule of thumb. The nose radius may then be changed to bring the acceleration ratio within the guidelines.

In the defined acceleration ratio method, the acceleration ratio is assigned based upon the desired performance of the engine and the design process is completed using the equations in p. 4. These equations are simpler than those for the defined shape method and there is no need for further validation of the design.

At one time spreadsheets based upon both methods were available on the Model Engine Builder Magazine website and on my personal website. They are no longer available on either site. They may become available on the MEB website at some time. I have submitted an article to MEB with the information necessary for a reader to build his/her own spreadsheet(s) and if perchance this is not published, I will post this information on HMEM.

CarlW

Attachments

• Equations for three arc cam BAEM.pdf
519.5 KB · Views: 0

krypto

Well-Known Member
HMEM Supporting Member
Awesome but way over my pay grade. I'm just happy to hear another issue of MEB is in the works.

Nerd1000

Well-Known Member
I've knocked together a spreadsheet from this and can confirm that it seems to give sensible results. I could post it, but I'm unsure if there are copyright issues with doing so?

carlw

Member
Nerd: I'm unsure how to proceed myself. My intent was to make it possible for a model engineer to generate his own spreadsheet and had not given any consideration to it being published.

I sent this thread to MIke Rehmus, editor of Model Engine Builder Magazine. He has more experience in copyright. I appreciate that you raised the issue and will get you an answer ASAP
Carl

ajoeiam

Well-Known Member
Nerd: I'm unsure how to proceed myself. My intent was to make it possible for a model engineer to generate his own spreadsheet and had not given any consideration to it being published.

I sent this thread to MIke Rehmus, editor of Model Engine Builder Magazine. He has more experience in copyright. I appreciate that you raised the issue and will get you an answer ASAP
Carl
If you 'give' it to MEB - - - - they own the copyright - - - - for a very very long time.

carlw

Member
ajoeiam: That is not my understanding. I believe that I retain copyright ownership of the original material. MEB owns the new formatting if any. As the spreadsheets were not changed by MEB. I retain full copyright. I believe that the same logic applies to publication on HMEM: the forum made no changes in the material and it has no copyright. I will have to check that out.

Nerd 1000: Mike Rehmus has no issues, so you are clear there. I've given some thought to this and here is what I think would be a good way to go:

My thought is that you may use my equations to generate your own spreadsheet(s) without copyright problems. Therefore, you may publish your material on HMEN. Because we are using the same equations, our spreadsheets will have similar structures. I have no problem with that. I am looking forward to seeing your material.

Carl W.

GreenTwin

Well-Known Member
HMEM Supporting Member
With articles published in Live Steam Magazine, you retain the copyrights to all of your material, however you cannot use the unique arrangement that the magazine uses to publish your material, ie: you can't just distribute copies of the article that Live Steam creates, since that arrangement is unique.

But you can do whatever you want with your original material, and you retain the copyright to it.

This is with regards to Live Steam Magazine.

I am not sure about other publishers, but this is the only agreement that I have ever signed into, and it seems fair to both myself and the publisher.

Pat J
.

carlw

Member
Pat: Thanks, you explained the subject very clearly. Carl

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