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camshaft machining

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djc:
OK, I found the seal drawings on the Model Engineer website.

Attached are some rough sketches (inlet only, right hand sketch). First, because Uncle Ed. did not have the benefit of CAD, his dimensions do not quite work. The combination of 11/32" base, 9/16" flank radius, 1/32" fillet and 5/64" lift do not give a smooth curve. In my sketch, I have used the radii as given: with everything properly tangential, it results in 0.004" less lift. If the lift is critical, you will have to alter one or other of the dimensions.

The cam is symmetrical and only composed of circular arcs. For 240 degrees of its circumference, it is a circle (constant radius) so that bit is easy.

To calculate the Z-dimensions as above posts, the left and centre sketches may help. Start with the centre one. For any angle a [from 0 to 20.4 degrees], measured from the start of the flank radius, you use the cosine rule to calculate x, the distance from the centre of the cam. You also need to calculate the angle from the cam centre at which that distance applies (I did not show that as the sketches are too messy as they are).

Similarly (now use the left sketch), you can calculate y, the distance from cam centre when traversing the fillet radius. Cosine rule again, using angle b [from 0 to 39.5 degrees]. Again, calculate angle from cam centre at which that distance applies.

Now, the most important bit: you will not be able to cut the flank and fillets using a flat-bottomed cutter as the edge of it will dig in where you do not want it. You need to use a ball-ended cutter and then it is always tangential to the cam profile.

philf:

--- Quote from: djc on August 10, 2019, 04:31:16 AM ---........................

Now, the most important bit: you will not be able to cut the flank and fillets using a flat-bottomed cutter as the edge of it will dig in where you do not want it. You need to use a ball-ended cutter and then it is always tangential to the cam profile.

--- End quote ---

I'm puzzled - I have only seen a low resolution section through the engine and the cam follower seems to be flat. For the cam to work properly with a flat follower then that would mean that a cutter could be the same diameter and shape as the follower.

chipenter:
Those angles don't add up the 11/64" radius at 30 degrees the other should be 50.4476 by my reckoning , if using the A and Z axis G2 or G3 I would file the 1/32 radius .

djc:

--- Quote from: chipenter on August 10, 2019, 03:31:19 PM ---Those angles don't add up the 11/64" radius at 30 degrees the other should be 50.4476 by my reckoning.
--- End quote ---

The three angles on the sketches each have a different vertex. The 30 degree relates to the 11/32" diameter; the 20.4 degree relates to the 9/16" radius; the 39.5 relates to the 1/32" radius.

As you traverse the 9/16" arc and the 1/32" arc, you will subtend an angle of 60 degrees measured from the centre of the 11/32" diameter.

djc:

--- Quote from: philf on August 10, 2019, 01:42:21 PM ---I'm puzzled - I have only seen a low resolution section through the engine and the cam follower seems to be flat. For the cam to work properly with a flat follower then that would mean that a cutter could be the same diameter and shape as the follower.
--- End quote ---

I see what you are saying and in my initial reply, I thought a flat cutter would be OK. It is only when you draw the geometry that you see what is going on.

There is a difference between a follower moving on a cam and a sharp rotatey thing cutting chunks out of a cam blank to produce a defined shape.

Using a flat follower on this cam will result in the fully closed or open position varying depending on the width of the follower. If the follower is of zero width, fully closed will be at the 30 degree position. If the follower is quite wide, the edge of it will start to ride up the 9/16" radius before its centre intersects the 30 degree position. If the edge of it is sharp and not able to ride, it will cut out part of the cam.

There is one of the old Machinery's yellow cover textbooks on the Internet Archive that covers cam design. It is an interesting read. Varying the position and shape of the follower on the same cam can make a big difference to its movement. You have to start with either a cam geometry or a movement profile and then design the rest to suit. Here, we are wanting to reproduce as accurately as we can, what Mr Westbury first drew.

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