Need help with Randall Cox cam cutting

[cessna]

Hi, I am attempting to cut cam lobes using the method by Randall Cox. I have the mill, turntable, boring tool etc. and understand the principle. What I don't seem to get is the setting on the boring tool. The write up in the mag says the radius of the cam flank determines the radius you set on the boring bar. Looking at the enclosed drawing, what would you set the boring tool to?
Thanks for any help you can offer.
Terry

 

[Swifty]

The left drawing is showing a 10mm rad, while the drawing on the right is showing a 11mm rad. I can only assume the one is inlet and the other exhaust.

Paul.

 

[cessna]

Thanks for the reply Paul, I was confused because the radius shown do not start at the center of the cam, I think however you are right, will give it a try.
Terry

 

[Jasonb]

The flank radius "circle" touches the R5 and R2.31 "circles" so cannot be central to the cam for the radius given. As Paul says the 10mm and 11mm dimensions are the flank radii.

J

 

[Swifty]

Terry, once you have the boring head set to the correct radius, you will have to offset the part to the sizes shown and then start boring.

Paul.

 

[cessna]

Thanks again for the help, I tried cutting another lobe, it makes a great shaped cam but the hole for the shaft is away off center, obviously I must be setting the offset wrong, when measuring the offset for the boring bar where do you measure from and to ?
Terry

 

[Cogsy]

As long as you have set the correct radius for the boring head, for the left one you offset the tool by 4.83mm from the centre of the hole and the right one 5.66mm. (at least thats what the plans say)

Good luck!

 

[Swifty]

As long as you have set the correct radius for the boring head, for the left one you offset the tool by 4.83mm from the centre of the hole and the right one 5.66mm. (at least thats what the plans say)

Good luck!

AND also 2mm lower for the right one, and an unknown amount for the left one, I cant see the offset.

Paul.

 

[Swifty]

Just did a quick CAD drawing, the left one, the exhaust cam, is 1.29mm lower from the centre.

Paul.

 

[Cogsy]

AND also 2mm lower for the right one, and an unknown amount for the left one, I cant see the offset.

Paul.

Well spotted, I didn't see that at all until you pointed it out

 

[Brian Rupnow]

Where can I get some more thorough information on the Randall Cox method of cam cutting?---Brian Rupnow

 

[Cogsy]

I have his email if you want to drop him a line. He feely distributes it on Youtube vids about his engines. [email protected]

 

[Brian Rupnow]

Thanks Cogsy--I will contact him.---Brian

 

[cessna]

Like sand in an hour glass it is slowly sinking in to this fuzzy old brain. I really appreciate all your help.
Terry