Information abot cylindrical cam design

[escalatorman]

Hello everybody,

I'm a R&D mechanical engineer and I must design a cylindrical cam with a variable pitch helix machined on it, in order to get a linear accelerated movement with a constant rotational speed.

I'm thinking about a two meters length shaft with 150 mm of diameter. The rotational speed should be about 500 r.p.m. The initial pitch of the helix would be 75 mm and the final 225 mm. I don't know which is the maximun angle permitted for the helix in order to get a good transmission of the efforts and avoid the block of the follower.

Does anyone have experience about this matter?
How the follower should be?
Can the cylindrical cam be used as a shaft in order to transmit power as a rigid transmission?
What about the supports?
If I would need more length, can be possible to manufacture them in order to get two pieces assembled?
Does anyone know any manufacturer of this kind of parts?

Thanks for you attention.

 

[grinderguy]

How will you decel or stop the screw? Does the follower return?

Robert Setree

http://www.advanced-grinding.com

 

[escalatorman]

The screw doesn't stop (unless the machine stops). It is always rotating at constant speed. The follower returns by other way, not using the cam.

 

[EdDanzer]

It might be less expensive to use a ball screw and servo motor or hydraulic cylinder and servo valve driven by a motion controller. Machining this size of part with a variable pitch helix will be very expensive. Unless you know all the parameters for design, including force generated by acceleration and deceleration, and force required during different sections of the travel your chances of failure are good. Any machine shop with a large enough mill/turn should be able to make the helix if properly described.

 

[escalatorman]

I can't use a ball screw because two or more pieces must be engaged to the cylinder cam at the same time, and each one must have different speed. If someone as an idea to met these requirimet, I have my mind open.

 

[Iskit4iam]

I think what you're describing is a variable pitch screw, not a cam. A cam typically goes through its full range of motion in one revolution while your description seems to indicate multiple revolutions.

I've seen similar devices in the conveying and packaging industries used to space products out. The screw engages the body of the item.

You could make it in multiple pieces but I wouldn't. Any shop with a cnc lathe long enough to chuck the piece can make this. I've been able to find lathes with 240" inch beds with little difficulty.