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Cam and Shape Grinding

lathehand

Cast Iron
Joined
Jan 31, 2005
Location
San Francisco Bay Area
I would like to obtain an original or a photocopy of the book "Cam and Shape Grinding with Norton Cam Grinders" by C. J. Green, published by the Norton Company. I have tried all of the book searches available to me via the web and the local public library without success. The Norton factory library does not hold a copy. Time to expand the search and try here. If someone on this forum is knowledgeable about rocking bar cam grinders, I'll post my questions here.

TIA
Carl
 
Carl, please persist with the general topic of cam grinding and shape grinding so that those who don't know can gain an appreciation of the process.

I would be grateful for information that expands my knowledge which is sadly deficient in this area.
 
Rocking bar???? As in the valve train of an engine?

Are you needing to know how to grind a single cam shape, or a camshaft with multiple cams?

(I'm not familiar with the Norton cam grinders)
 
I think he is referring to a cam grinder where you produce a negative form for a follower to trace, transferring the movement to the grinding arbor. We had a cam grinder at one company I worked for and used it to grind form punch shapes. Kind of a lost art since most people buy their punches from a central supplier now. But if you are R&Ding designs it sure comes in handy. -Mike
 
Yep... Some of the punch grinders used a cam following fixture on a surface grinder for punches. Today they're pretty much all computerized.
 
rj newbould, cam gruinders are STILL being used today to make shape punches. They normally get half the time a CNC gets for the same shape. Why are they slowly phasing them out you ask? ;) It takes more operater skill than CNC to get a "perfect punch" and shapes other than rectangles and elongs take job specific cams.

Most all of the can work punches are made with cams as you can get dead true blends in less time than doing by hand. Quite frankly, the CNC's we have can't hold the finish requirements and tend to "butt check" radiuses when check with .0001 indicators.

You'd be VERY surprised to see how many shape punches are made. Most one off's and specials are still made on manual surface grinders, at least in our shop.
 
rj newbould, cam gruinders are STILL being used today to make shape punches. They normally get half the time a CNC gets for the same shape. Why are they slowly phasing them out you ask? ;) It takes more operater skill than CNC to get a "perfect punch" and shapes other than rectangles and elongs take job specific cams.

Most all of the can work punches are made with cams as you can get dead true blends in less time than doing by hand. Quite frankly, the CNC's we have can't hold the finish requirements and tend to "butt check" radiuses when check with .0001 indicators.

You'd be VERY surprised to see how many shape punches are made. Most one off's and specials are still made on manual surface grinders, at least in our shop.

I wouldn't say I'm VERY surprised. It's been a quite a few years since I visited the shops that were using my spindles for punches.

At that time (about 15 yrs ago) they were strongly leaning towards CNC, and making some progress. I had assumed that in that length of time the CNC would be more predominant. Can't say that I know the current ratio of manual to cam to CNC.
 
rj newbould,
Probably most companies phased them out as you say but a lot never had them to begin with. Cam and split cam machines were normally built in house. The main problem I have seen with CNC and shape grinding is the constant changeover that is demanded. If you were running the same shapes all day you could make fixtures to support that. But when your switching from a part that is 1.2500 in diameter and then run a .1875 you can see the problem. On skinny stuff it is still mainly done a manual machines. Even with centers on the end of the parts they flex and bow and give too much crown to have good parts on cam and CNC.

Another problem is the finish. Most all CNC machines don't move in and out and you end up with grind lines that can't be polished to a 4 - 8 micro. I'm not saying they aren't out there, it's just that I haven't seen one.

Industry wants CNC so they can take the skill level out of the mix so the can pay any Joe Blow of the street to Plug and play 4 machines at once. Probably happen eventually but for now we are still hanging on, fixing all their screw ups and stuff they don't want to do ;)
 
A cam and shape grinder is, in general, a cylindrical grinder with an attachment on the table that carries the master cam and the cam(shaft) to be ground. The attachment is mounted to the grinder table by bearings that allow it to rock toward and away from the grinding wheel. This motion is controlled by the shape of the master cam which bears against a roller follower. All of the details of the cam, e.g., angle of cam action, timing, and lift profile, are machined into the master. Polygonal and irregular shapes can also be ground into a rotating workpiece: note that convex curves must have a radius greater than that of the grinding wheel.

You guys who are grinding punches: tell me about the machines that you are using. I am mostly familiar with the automotive grinders: Norton, Landis, Berco, Storm-Vulcan. These use master cams that are substantially larger than the workpiece. Their shape is derived by adding a fixed amount to the normal tangent to the cam/shape profile at each point. Thus an automotive master cam looks very much like a circle - essentially it is out of round by the amount of the lift. The extra radius is subtracted from the master by the difference between the location of the center-line of the roller follower and the grinding wheel. The diameter of the follower and wheel must be the same within a small allowance.

The profile of the master is exactly the same as that of the center-line of a large mill cutter that would generate it: the process of generating the master is analogous to that of CNC cutter diameter compensation. A example: the master for a square punch would have four flat sides connected at their ends with tangent arcs (one quarter of a circle.)

Let's see how this description goes before I ask the main question.

Carl
 
A cam and shape grinder is, in general, a cylindrical grinder with an attachment on the table that carries the master cam and the cam(shaft) to be ground. The attachment is mounted to the grinder table by bearings that allow it to rock toward and away from the grinding wheel. This motion is controlled by the shape of the master cam which bears against a roller follower. All of the details of the cam, e.g., angle of cam action, timing, and lift profile, are machined into the master. Polygonal and irregular shapes can also be ground into a rotating workpiece: note that convex curves must have a radius greater than that of the grinding wheel.

You guys who are grinding punches: tell me about the machines that you are using. I am mostly familiar with the automotive grinders: Norton, Landis, Berco, Storm-Vulcan. These use master cams that are substantially larger than the workpiece. Their shape is derived by adding a fixed amount to the normal tangent to the cam/shape profile at each point. Thus an automotive master cam looks very much like a circle - essentially it is out of round by the amount of the lift. The extra radius is subtracted from the master by the difference between the location of the center-line of the roller follower and the grinding wheel. The diameter of the follower and wheel must be the same within a small allowance.

The profile of the master is exactly the same as that of the center-line of a large mill cutter that would generate it: the process of generating the master is analogous to that of CNC cutter diameter compensation. A example: the master for a square punch would have four flat sides connected at their ends with tangent arcs (one quarter of a circle.)

Let's see how this description goes before I ask the main question.

Carl

Although I'm familiar in general with the machines you describe. I'm most familiar with grinding shapes on a surface grinder.

One of the fixtures used (in the past at least) was a simple spindle mounted on a vertical slide. On the back side would be mounted a cam, the part on the front side. As the operator slowly rotated the spindle, it would rise up and down on a stationary finger riding on the cam, to create the shape on the part.
 
We have both types of cam grinders. What rj newbould refers to is what we call a hand fixture. You just use a normal surface grinder for that but it uses the same cams as on the dedicated units. Cams are around 6 inches and like you say, they look basically round. They use split cams as well on the dedicated machines. Set the spread with gage blocks to adjust finish size differences.

Nice thing about grinding a cam is that you basically can't junk it. Just take off equal amounts to finish size and reswing. Hard to explain but if you've worked with them you know what I'm referring to.
 
Carbide insert grinders are commonly referred to as cam grinders because the non-cnc ones use a master cam to generate the insert profile.
A master cam for the correct insert shape (TPG-321, SNG-432,etc.) is attached to one end of the workhead and the workhead either rocks on pivot bearings or slides in and out on linear bearings to generate the insert shape.
They are also sometimes used to make carbide punches.

When I still had cam operated machines I had over 350 master cams.
These cam operated machines are still quite popular especially in the smaller carbide shops.
Bob
 
No time on the 'puter today: I'm off to pick my wife up at the airport. I will have a longer post later tonight or tomorrow about making the master cams. Please check back.

Carl
 
I'm glad that people are prepared to discuss general operations of machines rather than a question about a specific problem with a particular machine.

Having a browse of the posts was enough to realise that some careful reading is going to be needed here.

I feel like a lazy school child who gets all his information provided without any thanks to the teacher who might have had to research and find the information. That being admitted may I ask for PICTURES please? I realise that this might not be so easy since it probably involves the boss's machine and the time he pays you for working not taking pictures.

I think this could develop into an interesting topic and good for referral from time to time.
 
1tsb4z.jpg

This is a Berco camshaft grinder that has been converted to CNC operation in-house, one of 8 we have, two of which I operate simultaneously. As far as I know these are the only such Berco machines with a CNC conversion, and the only CNC cam grinders in the 'aftermarket' industry here in Australia. We also have a surface grinder that has been converted to provide CNC shaping of 'master' cam lobe shapes that are designed on computer - these 'master lobes' are then used in the Berco machines to grind the master patterns used for grinding cams, by a reversal of the normal grinding process. This works by the same method used to 'copy' the profile of an existing cam, by having the following wheel follow the lobe on the cam while the grinding wheel grinds the master, rather than having the following wheel follow the master and the grinding wheel grind the cam.

Any questions about things you see in the pic let me know, if I have some spare time I might be able to add some graphics to the pic pointing out the important features so it is more clear just how it operates.
 
Let's start with MorganGT:

"these 'master lobes' are then used in the Berco machines to grind the master patterns used for grinding cams, by a reversal of the normal grinding process. This works by the same method used to 'copy' the profile of an existing cam, by having the following wheel follow the lobe on the cam while the grinding wheel grinds the master, rather than having the following wheel follow the master and the grinding wheel grind the cam."

Your description of the process is excellent and makes it easy for me to proceed directly to my questions:

Why are masters made from the master/model lobe (I prefer to use the term model lobe for clarity: so the word master is not used in two senses) and then the masters used on the production machine? It is clear that the master cam could, in principle, be replaced with the model lobe. Here goes the first question: why is the model lobe enlarged into the master and then reduced in grinding the cam?

I should note that there are at least two different ways of "assembling" the master cam. The Berco and Storm-Vulcan, intended for the aftermarket grinding market, use two masters keyed onto a shaft: one for the intake and one for the exhaust. The master lobes are timed exactly as the final camshaft with the difference between the opening of the two valves. The master lobes are carried on an mechanism that is indexed to the required angle when going between the lobes for each cylinder. Production grinders such as the Landis and Norton use a master with the same number and phasing of lobes as the workpiece.

Typical practice appears to be to make the model cam first, then the master. The same process could be used to make the master directly. Why is is the master ground from the model cam?

I am interested in the non-CNC methods of grinding cams and shapes and the next question will reflect that interest. However, for this discussion to be complete, I wish to gain some knowlege of the CNC methods.

What methods are used to make the models? Some shapes can be generated by relatively simple methods such as the Harig Grind-All. IC engine cams are another problem as even the simplest ones have four arcs and 2 spirals of various shapes. I believe that these must be "sliced and diced" into tables of lift at each increment of rotation and machined (rotary table and mill) or ground (spin jig and movement of wheelhead??) to those dimensions. That will leave either flats or scallops between each cut that must be hand blended. The accuracy of the final model is then dependent upon careful measurement and hand work.

CNC: the dimensions of cams are tighly toleranced. I understand that the development of CNC grinders was delayed because of the difficulties encountered in eliminating the problems associated with reversals in the direction of movement. (CNC grinders are linear slide machines except for rocking cradle retrofits such as MorganGT's.) Any comments on your experience with this?

RJ and Kevco and CarbideBob all commented on linear slide machines or attachments? Any further information on these? Manufacturers, pictures, sketch, or general comments?? Same question on rocking cradle machines. Were they small model cylindrical grinders or special purpose machines? Info/pics on linear slide attachments used in surface grinders?

Kevco: Can you tell us more about split cams and adjustment with gage blocks. And I do not understand your last comment about "reswing."

MorganGT: I use the search function on the forum and appreciate that all this is being archived and will be indexed by the search engines etc. It will become a valuable source for someone who also has these questions. Should you have the time and interest, I would appreciate having labels on the photo, and further comments on the subject of cam grinding.

CarbideBob: I had no idea that inserts were ground on similar machines. Can you supply some more info?

Strictly IC, a magazine in the US for builders of model and small size IC engines published a design for a cam grinder that used a geometric reduction. Instead of adding and subtracting going from the model lobe to the master and back to the workpiece, this design reduced the size by a ratio. None of the commercial machines that I know of use this principle. It would appear that it would have the advantage of reducing errors in the dimensions of the master by the reduction ratio. The rocking cradle and linear slide machines will replicate any errors in the master directly into the workpiece as well as any errors introduced by the machine and process. On the other hand, the geometrical reduction design required separate shafts to carry the master and the workpiece and these had to be connected together with gears or chain. This connection would itself introduce errors. Any comments on this?

This has been a big one and is enough for this morning. I've got to go dig a big hole.

Carl
 
On split cams: They made these up for doing rectangles and oblongs of various sizes. Each set of cams had a range of size, or spread, that allows them to be used for different sized shapes. They also have a selection of "shoes"(part that rides on the cam) that effects the shape somewhat. The shoe rides over the small gap and not effect the flats. 2 gage blocks would be put between the cams and snugged up. Size depends on the spread you need. Backs of cams have grooves in them to align one way and you indicate the up and down central and tighten.

We grind all the cams out of a small Harig and that is what I was refering to when I mentioned "reswing". Meaning, reswing the radius between the flats when downsizing the cam. As long as you keep it proportional, a smaller cam can grind the same shape as a larger one. You just adjust for the difference when your infeeding grinding wheel.

These machines were all made in house.

Honestly, I don't know whether the hand fixtures were made here or bought. I'll have to look about that.
 
Kevco: Thanks for the explanation. Just to check that I understand, an example: an obround punch could be ground from a two piece master with say .500 gage blocks inserted between the halves. It could be reground to a smaller center distance, but the same end radius, by changing the size of the gage blocks. It could also be reground to a smaller overall size, i.e., shorter center distance and smaller radius (each reduced by the same amount) by "reswinging" and infeeding the grinding wheel by the amount to be subtracted.

Carl
 
Yes, I believe we are on the same page as far as split cams go. What you are dealing with is the measured difference between the top of the oblong and the 2 narrower flats. We refer to this as "spread". Here's an example: Oblong measures .500 x .400 would have a .100 spread. The SAME cam set EXACTLY the same can grind a .400 x .300 oblong because it is all proportional, just push the grinding wheel in farther. make sense?

I checked last night and the hand fixtures we have were made in house.
 
Kevco: I got ya! And you didn't even notice that I made a mistake on my previous post where I said the center distance is reduced. You are calling the center distance the "spread" and as you explained it does not change.

Carl
 








 
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