Lathe foot pads, matching the pad to the screw

[WobblyHand]

Now that I faced the steel foot pads for my lathe, I'd like to machine a dimple for the "spherical" head screw to rest in. Is there some rule of thumb for the radius relative to the screw head radius? Say the radius of the screw head was 1", then the dimple radius would be? Obviously greater than 1", but not infinite radius (flat). 10% or 20% greater? 100% greater? Something else?

I don't yet have a comfortable way to machine this, but have an idea that might work. The required radius might change the answer, hence the question.

 

[RJSakowski]

I used a shallow cone head on my adjusting screw with a cup with a matching conical depression cut into it. As I recall, the cone angle was the same for both.

On the Level: Further Adventures with the G0602

When I built the stand for my G0602 lathe, I made leveling adjusters for the four legs. They were simple in design; a 1/2-13 bolt and jam nut threaded into a plate at the bottom of each leg. However, in trying to precision level the lathe, I ran into some issues. When adjusting the height...

www.hobby-machinist.com

 

[jwmelvin]

I really don’t see why you’d bother. A conical seat will work fine.

 

[jwmelvin]

Hm, I didn't mean to be dismissive. I think you have to first decide what you want out of the interface. I'd think here you want the position to be stable, so you want a centering feature and you want rotation to not create axial position changes between the screw and the pad. A cone that mates with the spherical screw will provide centering. A spherical cup would provide much less centering, but would have the advantage of a contact point that limits torque on the screw. As the screw walks (because there isn't much centering force), it changes axial position; that seems counterproductive. To me, the centering effect of the cone is what you want.

You get better centering with a steeper angle of contact, but more sensitivity that creates axial displacement. You are relying on an averaging effect to minimize any influence of the interface, and an average that includes more surface area is better in that regard.

Since your screw head has a pretty large radius, I'd go for a relatively shallow cone that centers the screw and contacts not too far from the center.

 

[WobblyHand]

I like the idea of using conical heads and sockets, easier to make than spherical, especially if one doesn't have a ball turner. Thanks for saving me a bit of time!

 

[benmychree]

I used a shallow cone point on the studs and a drill point on the pads; to keep things from moving around under vibration, put a piece of tarpaper under the pads, assuming that you have a concrete floor.

 

[Nutfarmer]

I used a carriage bolt for the adjusting bolt. For the base plate I ground a drill to match the curvature of the bolt head. Has worked on and after releveling in a month has not moved.