How to make a cam grinder?

[RotaryNut]

Additional to the above post(#12)

E.T.Westbury's 'SeaLion' cam article appeared in Model Engineer #3021, 16th April 1956, pages 462 - 464.

The article can be downloaded at the yah00 group: 'mlprojects1'
The entire 30cc 'SeaLion' article is available, spread over 12 articles.
The Cam grinding article is in file: 3021-Sealion-08.pdf

Simo

[pastera]

Because of some moron selling copies on Ebay, the publisher revoked the agreement with JW Early (the person scanning the articles) that allowed the posting of the articles.
Most if not all articles have been removed from the groups.

Aaron

[NC Cams]

Over the years, a number of methods have been used to design cam profiles. In the early days, a simply protractor, french curve and straight edge would suffice - and do so quite readily.

HOWEVER, as speeds got higher and valvetrains got heavier and durability issues became more critical. The old "cut and try" protractor/straight edge profiles gave way to much more scientific and thus more dynamically stable methods of cam design done via the use of more sophisticated design processes.

The "golden years" of cam design evolution pretty much took place during the 50's and 60's. This was when simple flat head engines were giving way to OHV pushrod/rocker arm engines. During this time, it was learned (often the hard way via breakage, noise and/or other carnage) that french curve profiles may have "looked nice" but they could easily and actually be real parts breakers.

I'm not saying that you can't take and make a cut and try cam for a hobby engine. Not hardly. HOwever, you really shouldn't think that one that's been crafted out of whatever will outperform something that is well and fully engineered.

For grins, we've duplicated some of the plate cams that were listed as being "patterns" for the model engines as cited in one of the reference articles posted. We then dynamically evaluated on our cam design and analysis software - the same ones we use for the race and OEM prototype cams we suppply.

Will/would the cam move the valvetrain? Yes.

Would it live? Perhaps.

BUT Not only were the dynamics pretty violent but they would make high speed grinding marginal at best. It a light valve train with low/moderate stresses, the thing might work OK.

However, based upon our years of OEM and aftermarket engine experience, the profiles could not help but tear up either themselves, the followers or perhaps and including the valves during sustained high speed operation. Spring surge in concert with the attending noise and durability problems would be all but GUARANTEED over time.

I"m NOT trying to disuade the hobbyist from making cams. However, I am trying to point out the realities that mere "oversimplification" can create. This is especially true when simple cam grinders get made and out into the hands of creative people. We've seen too many "I can do that's" applied to cam profile designs and applications - some work and most don't.

Sadly, when you start to get REAL serious with the process, the empirically designed and manufactured ones do NOT tend to work as well or as long as ones made using good/sound desgn and manufacturing processes. They simply can't due to horrible dynamic integrity of the motion curve being asked for.

You can pound screws with a hatchet all you want. But, trust me, the use of screwdrivers does a much better and more consistant job.

To the comments about trying to wring the most amount of profit and/or performance out of a cam, yes, we do try to do just that. Our client base expects and pays for performance and we charge a fair/reasonable price for our grinding, design, manufacturing and valvetrain engineering services.

We liken it to going to going to an emergency room when/if you wake up with a cramp in your heart - when you have the cramp, you really don't try to practice self medication and/or look for lowest cost care provider. YOu seek out the best care money can buy when it really matters.

Should your priceless/time critical hobby be treated with any less care or attention????

Something to think about (just a bit) when you try to "create" your own cam via some of the cut and try methods published in the hobbyist IC engine magazines.

[pastera]

NC

If one were to map out the cam profile based on a smooth acceleration curve (low jolt) would that work for a hobby engine cam?

Or should there be defined regions of acceleration that are different (taking up valve lash, valve approaching seat, etc) that should have distinct velocites that are then smoothed together?

Aaron

[NC Cams]

Different engines want and/or need and/or can tolerate different things at different points of the lift curve. Small light systems can tolerate things that heavy big systems can't. Stiff/rigid systems can do things that flimsy/light systems can't stomach. You can't over simplify the process simply because it is a hobby engine although people will do just that to get stuff to run.

Frankly, it isn't that much harder to make something well designed/engineered once you know how but it sure is nicer because it will inevitably work better and for longer, more trouble free periods.

You have to take into consideration materials, system stiffness, dynamics and/or performance requirements when designing the lift, velocity, acceleration and jerk profiles for each section of the profile.

Whenever you affect a compromise (lift, duration, violence, etc) when you design a cam, you will ultimately compromise performance, durability,noise and/or emissions output of/from the engine. There is no free lunch.

Like I said, it is easy to simply open and close a valve.

When you want to do it with style, verve, performance and/or with low noise without affecting durability, the devil is definitely in the details.

[camshaft]

Originally Posted by j45acp Does anyone out there know where I can get a GOOD set of plans to make my own cam grinder for some model engine projects I would like to start. I would try to design one but i have never used one so the working theory of the machine is non-existent at this point.

There is a website with a small cam grinder at www.quarterscalecamgrinder.com/. We have some large manual and CNC cam grinders for industrial engines, but we haven't built one and we don't have any plans for one.

-Clay
Kams, Inc. - cam grinding for industrial engines

[stevehuckss396]

You can make nice cams using a simple fixture. If you don't want to spend the time making a cam grinder this is a good alternative.

Here is some info on how to use the fixture.

http://www.mikes-models.com/camarticle.html

[artform]

What about using a full size cam, and have a grinder follow the profiles, but at a different scale, is that possible ?, I think i have read somewhere here that it works ?

If anyone could draw a simple diagram that would make it easier to understand the principle, it would sure help me

[miniengine]

The Cam Grinder in Strictly IC Issues 39, 40, 41 by Gene Switzer is a great item. I built it about 4 years ago and it works great.

[miniengine]

j45acp, I was wondering what you ever did about a cam grinder? Your post back in 3/24/04.was your first question about it. Thanks, Ray