Grinding Cam profiles on a DeskCNC 4 axis mill

[Paraprop]

I am presently upgrading my mill to 4 axis.

On the spindle head (Z axis), I am going to add a diamond wheel grinder.

Right now I am not too sure how to scan an existing cam profile (from an engine intake/exhaust camshaft) into the system.

I am using a 2500 CPR encoder on the A Axis. so I would like to take a measurement for up to each of the 10000 steps in a 360 degrees rotation by a linear encoder head putting out a signal onto the encoder input of the DeskCNC controller card (same as used as feedback for the lathe spindle application). The output of this linear encoder (I still have to purchase it) has a resolution in the 0.001mm range. Then I would like to graph the resulting cam profile, eventually modify it and then produce a G code file to grind another camshaft lobe based on it. The grind is done just by rotating tha A axis and moving the grinding wheel on the Z axis. No need to move the X axis for it.

Is it actually possible to do so ? I could not find any hint on the docs. Available on the web. If yes, is there somewhere a similar application I could use for reference ?
Until now I can only find samples of scans done with the touch probe connected to the Lim input but I am afraid this method is not as accurate as if I go for the linear encoder even though I already got 2 sets of the IMservice touch probe. Also in the literature nothing hints about using the touch probe for parts rotating on the A axis.



Thanks in advance for nay hint.

Paraprop

Daniel

[NC Cams]

Andrews Products makes and sells a device (EzCam) that does EXACTLY what you wish to do. Audie Technologies does so as well as does Performance Trends. There was also the "Cam Doctor" sold at one time but they are no longer in business as far as I know.

They people currently selling machines do NOT however, provide any DIY "how to's" especially with regard to the software - some won't even sell the software without purchasing a machine.

Some of your ideas are valid - some, however, some will simply not work. The why's/wherefors behind both is far to complex to delve into in a message board thread.

For insight into cam reading "how to", contact the SAE and obtain some papers written by Jess Nourse. They were written in the late 60's or 1970's. The Nourse articles are/were what these same people used to create their cam reading machines.

There are also a number of other cam design articles that are mentioned in a "cam design" thread that is/was ongoing on the Zone. Do a search and it will come up near the top.

That's as much of a hint as I can offer.

[toastydeath]

For a hobbyist, it is easier to grind a cam on a manual mill and grinding machine than it is to make a CNC to grind an acceptable cam. You're not going to get a smooth, long wearing surface with the intermittent step-cutting you're going to get from an ad-hoc CNC grinder unless you really know how to design a machine.

There are a lot of old books and articles on grinding cams via manual methods. These methods are certainly not as accurate as a even an okay CNC cam grinder, but they're going to give you a longer wearing and smoother running cam than what you're going to get how you've proposed to do it.

I would take the more inaccurate cam with a great surface over the slightly more accurate cam that breaks everything that comes into contact with it.

I might not know what goes into designing a cam, but I have a much better idea of what goes into building a CNC grinder, and it's not something that you're going to be able to easily finagle.

[NC Cams]

There have been numerous attempts at making CNC cam grinders attempted over the years. I don't know of any that achieved commercial success outside of the Landis 3L. This machine is far, far and away too expensive however for the hobbyist to even consider.

We grind cams as a profession. We've tried to mill cams with 4th axis machines. WE even tried to create plate master cams with a 2D machine. After spending lots of time and money, we finally did it but it takes a VERY, VERY expensive CNC and one in very good condition to do it - a home brew CNC does NOT have the accuracy. The smootheness issues illuded to in the prior post are but a few of the problems that preclude the use of milled lobes for high speed cams - there are more and they are substantial....

There is a model size cam grinder that was made for/by a DIY'er - it was featured in a past issue of Home Shop Machinist and was a cover story as I recall. The machine did model engine size cams. I suspect it MIGHT be upscaleable to do Briggs or other one cyl cams but you'd still need to have a master cam created to grind from.

The cam arc and protractor design method used for the model engine cam will not create a profile that is smooth or dynamically stable enough to live in even a lawn mower engine. Again, the issues outlined in the prior post are harbingers of things that will happen.

Shameless plug: We do grind masters as a service to our clients. Although we haven't designed or cut any "model cams" like those used to on the HSM grinder, we theoretically could once we got the linkage geometry provided from whatever HSM adaptation is attempted.

[Paraprop]

Thanks for your input.

Right now I would like to start with digitizing an existing cam profile with the DeskCNC controller.
Haven't yet received an answer from the manufacturer if it possible to use the encoder input normaly used for threading on a lathe, to read the cam profile data relative to each of the 10,000 rotary encoder steps per revolution on the A axis.

Indeed, there are a few hardware and software vendors who already do this and If I can access the data received by the encoder input of the DeskCNC controller, I may be able to do the same I guess.

For grinding I had already build a duplicator which worked quiet well. There was a follower on the master cam lobe and a diamond wheel on the raw cam. The whole thing was sliding on roller bearings and a weight pulled it towards the cam lobes.

Now the challenge is to do it on CNC. Even if it may not turn out well, it is a good learning experience.

[Switcher]

There have been numerous attempts at making CNC cam grinders attempted over the years. I don't know of any that achieved commercial success outside of the Landis 3L. This machine is far, far and away too expensive however for the hobbyist to even consider.

We grind cams as a profession. We've tried to mill cams with 4th axis machines. WE even tried to create plate master cams with a 2D machine. After spending lots of time and money, we finally did it but it takes a VERY, VERY expensive CNC and one in very good condition to do it - a home brew CNC does NOT have the accuracy. The smootheness issues illuded to in the prior post are but a few of the problems that preclude the use of milled lobes for high speed cams - there are more and they are substantial....

There is a model size cam grinder that was made for/by a DIY'er - it was featured in a past issue of Home Shop Machinist and was a cover story as I recall. The machine did model engine size cams. I suspect it MIGHT be upscaleable to do Briggs or other one cyl cams but you'd still need to have a master cam created to grind from.

The cam arc and protractor design method used for the model engine cam will not create a profile that is smooth or dynamically stable enough to live in even a lawn mower engine. Again, the issues outlined in the prior post are harbingers of things that will happen.

Shameless plug: We do grind masters as a service to our clients. Although we haven't designed or cut any "model cams" like those used to on the HSM grinder, we theoretically could once we got the linkage geometry provided from whatever HSM adaptation is attempted.

Here is the link to the Home Shop Machinist "Building a Model Engine Camshaft Grinder" click the link below, & wait till the page loads the back issue database, then scroll down to & click "Volume 23 Issue 6, Nov 2004", it's the 3rd article on the list, by "Jerry Kieffer".

I'm not sure how to order the back issue, the store isn't working ( http://store.homeshopmachinist.net/ ).




Link to back issue:
http://www.homeshopmachinist.net/art...M&method=ISSUE


.

[Switcher]

Google has a bunch of links for "Jerry Kieffer".

http://www.google.com/search?sourcei...=Jerry+Kieffer

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[Switcher]

This shows the actual cam grinder.

1) http://craftsmanshipmuseum.com/images/camgrind1.JPG

2) http://craftsmanshipmuseum.com/images/camgrind2.JPG

3) http://craftsmanshipmuseum.com/images/camgrind3.JPG

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4) http://craftsmanshipmuseum.com/Kieffer.htm

JERRY'S CAM GRINDER

In order to be able to make proper cams for his running engines, Jerry designed and built this camshaft grinder. He used the cast iron base from a discarded table saw. A Federal dial indicator was a $10.00 flea market purchase. The rest was made from bar stock. The power is supplied by the headstock/motor/speed control from his Sherline lathe. Total cost was under $60.00 not including the Sherline power unit. With it he can grind just about any model engine camshaft.

Specifications:
Max. cam length: 6.00"
Max. cam diameter: .750"
Grinding accuracy: .0003"

For his seminar at the April, 2004 North American Model Engineering Society Expo in Detroit Jerry will be detailing the construction and use of this tool.

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[Paraprop]

Thanks for that Switcher.
Very kind of you.

[Switcher]

I figure If that guy can make cams that small, maybe the machine could be scaled up to fit your job?

.

[Switcher]

More links (ideas).

1) http://www.strappe.com/grinder1.jpg

2) http://www.strappe.com/grinder2.jpg

3) http://www.strappe.com/grinder_notes.html


Scroll 1/2 way down the page:
4) http://www.strappe.com/hsm.html


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[NC Cams]

The Keiffer mini grinder is essentially a scaled down table top version of a number of "rocking table" cam grinders.

These are/were made for the camshaft industry by Berco, Storm-Vulcan, Landis and a number of other companies who've long since faded from memory. It should not be impossible to scale up the Kieffer but, in doing so, you scale up the need for rigidity and accuracy - the larger the grinder the more substantial the error potential becomes - take my word, we've been down that path during our grinding and in-house master creation process.

The rocking table grinders all take a master and via a follower/linkage mechanism, trace the master onto the cam via the grinder. The conversion from simple design data to the master and then back thru the linkage geometry to the finished cam can be mathematically challenging.

Unless you have all the linkage geometries known and slop/clearances minimized, the design data and finished cam will not even be close to each other - moreover, the relationships ARE NOT 1:1!!!!!.

Heidenhain has multi axis rotary and linear encoders and counter cards that plug into a PC. The expense/complication comes in when you try to take data of the fly and turn it back into a meaninful cam follower motion curve. THIS CONVERSION FROM COUNTS TO DYNAMICS IS NOT EASY.

Even the seemingly simple task of finding the lobe center (point of max lift) can be challenging, especially if the cam has dwell at the nose or runout in the base circle (all cams do to some extent).

At one time Heidenhain offered DOS based ISA slot counters. Not anymore. They've gone to PCI which means you pretty much have to use Windows. Not only are the counter cards and encoders pricey but the development kit to write programming for Doze is not cheap. Hence, unless you plan to do a lot of cams, the cost to do what you're trying to do could turn out to be QUITE prohibitive.

We tried to do the same thing on the cheap as I was not bucks up when I started my cam company. Luckily, I struck a deal with a guy who made some table top measuring equipment and was able to buy some scratch and dent equipment that he'd developed for market. We then adapted it to some of our own fixturing and learned lots more about what counts when it comes to reading cams.

Even though I got a deal, it was expensive. I had little choice as I did not have programming nor much reverse engineering analysis experience, especially when it came to turning cam motion into engineering data - I could to the work once I got values but couldn't get values.

If you want/need a few cams measured, we offer the service and it is far less costly than making your own machine. However, being in Thailand does pose a transportation challenge.

Cost wise, your best bets are as follows:

cheapest: see if you can find a used "cam doctor". These were made at one time but have become a bit rare as the company is no longer in business. THey were the racers dream and relatively affordable at the time. Not suited for production validation measurement but better than a degree wheel.

Less cheap: Check out Audie Technologies. Not suitable for production QC validation and/or all-out killer reverse engineering but OK for racer analysis - probably as cheap as I'd go if I were an engine builder and was going to get serious. Have not used one but it is far better than a dial indictor and degree wheel.

High end, pro racer and production prototype suitable: Andrews Products Ezcam. These are superb, precise devices and they are doing world wide distribution of their machines. They are shop floor rated and also suitable for tool room inspections.

They have accuracies traceable and comparable to the Adcole - the Adcole is THE Rolls Royce of cam measurement devices. Ezcams are NOT cheap but considerably less than an Adcole and almost as good. Far better inspection device than a lot of aftermarket cam grinders and refinishers use even today.

Rolls Royce: get an Adcole.This is THE ONLY device recognized as useabla/suitable by the OEM's. PERIOD.

If you're bound and determined to make your own, do a search thru the SAE for any/all articles written by Jess Nourse. He wrote the articles that most of the cam measuring machine guys used to craft up their machines.

There are also a 3 article series written in the 1950's in Machine Design Magazine. One of the authors who wrote the article was Stoddard. This article, too, should be helpful in providing you with some of the math that you will need to take your encoder data and turn it into the measurement data you're seeking.

A simple tough point encoder WILL NOT BE SUITABLE to read a cam. Why? Tell me the true shape of an oblong American football when you only touch 3 points on the OD. Can't be done. Unless, you MEASURE the cam accurately, you can't simply touch random points and let some geometric mumbo jumbo program guesstimate via geometric curve fits what's happening inbetween.

With the encoder resolution you're talling about, you're going to be swamped with data. You can either process and interpret it properly or else why bother??? WIth the resolution you're talking, you're easily in the ball park of what Andrews Products machine already does.

All in all, it may be cheaper for you to buy one of the Ezcams and have a turn key one shiped to you than to reinvent the wheel. If you do buy one, tell Dave or John that you heard about it from NC Cams.