Re: [CAD_CAM_EDM_DRO] Re: Why dovetails?

kmslinda <gerry@...> wrote:


--- In CAD_CAM_EDM_DRO@yahoogroups.com, R Rogers
wrote:

> Andras:
>
> Why dovetails? Three reasons 1) stability and accuracy thru length

and mass of high tolerance dovetail connection 2) The design
inherently "locks" the two mating surfaces together eleminating the
requirement of any other method of maintaining engagement of the two
surfaces. 3) surface area of the mating joint, distributing the load
over a much larger area.

>
> Traversing a carriage etc. over lengths of any type geometry

supported at both ends will produce an undesirable surprising amount
of deflection. Its lack of unsupported mass, deflection in the rails
and surface area that are the culprit. I design and build line-side
automation tooling and toil with traversing end effectors etc. Even
using THK rails in parallel and two cars per side with a substantial
moment in between them, Deflection is still a persistent problem. I
then must make the end effector "float" as to overcome the deflection
and engage the assembly operation. Ball bushings traversing on a
round shaft are the worst about this.



I can't think of a modern CNC Machining Center or Lathe that uses
dovetail ways. They either use "THK" style linear bearings or
"Box" ways! We have 20 CNC machines in our shop and none of them
have dovetail ways. Our Bridgeports are the only mills that have
dovetail ways.

Gerry

/// We are discussing a home made machine. The original poster was inquiring about the feasability of linear slides versus dovetail ways for stability. We shouldn't mislead him by using an expensive commercial machining center as an example. I know the THK style bearing that is referred to in a machining center and it is in no way comparable to an off the shelf THK component other than in principle. Box ways are cheaper to manufacture. It's certain if Bridgeport felt that Box ways and THK arrangements were better they'd be using them. They've been building machine tools for 80 years and regarded as the best mill that money can buy. Ask any machinist. They still use chrome lined dovetails. It's comical actually with all the alledged "improvements" that the import clones have made to the originals copy, Bridgeport never adheres to them. They come and they go.

Ron




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