GB2417305A

GB2417305A - An elevating device having a conical worm engaging a rack

Info

Publication number: GB2417305A
Application number: GB0418304A
Authority: GB
Inventors: Roger Harvey Slee
Original assignee: Individual
Current assignee: Individual
Priority date: 2004-08-17
Filing date: 2004-08-17
Publication date: 2006-02-22
Also published as: GB0418304D0

Abstract

An elevating slide 2 or column (eg. a screw jack) has a gear rack 6 with helically cut teeth fixedly attached in the plane of intended elevation, and a captive but conical worm gear 10 rotatably engaged with said rack 6 so as to cause the rack 6 to rise or fall as the conical worm 10 is rotated. The axis of the worm 10 inclined with respect to the longitudinal axis of the rack 6 when viewed along the plane parallel to the engaging surface of the rack 6, and when viewed from the plane which is normal to it and parallel to the longitudinal axis. The worm 6 may be slid angularly to fully engage the rack 6. Backlash between the worm 10 and rack 6 can be adjusted to maintain a minimum working clearance. The rack/column may possess a clamp 24.

Description

24 1 7305 Improvements in Elevating Mechanisms The use of a Screw Jack for

Elevating and lowering heavy objects in a controlled manner is well known.

A common form of this mechanism comprises a base,an axially constrained internally threaded nut,and a co- operating screw which can move axially (but not radially), when the nut is rotated by a bar or gearing.

An inclined plane is formed by the helical thrust surfaces of the nut and corresponding screw,which upon mutual movement, are caused to slide relative to one another. If the helix angle of the thread is large relative to the thread axis, which is usual, frictional forces between the sliding elements reach a peak value and the efficiency is low; in this condition the mechanical advantage or jacking capacity is high, and the tendency to 'slip back'is minimal.

Notwithstanding the effectiveness of the Screw Jack,it is sometimes inconvenient to provide for rotation of an orthodox screw and nut, where the constraints of space or access to a control device may intrude.

The aim of the present invention is to provide for a mechanically or manually operated Elevating and lowering mechanism for use in machine tools,where access to the actuating system is required from above or to on side of the elevating element, and in a relatively safe position for the machine operator.

I,Dr.Roger H.Slee, a British subject, of 28, 0akwood Grove, Warwick, England, hereby declare this invention, and request that a Patent be granted to me, and the method by which it is to performed, to be particularly

described in, and by the following statement:

The present invention relates to Elevating and lower- ing mechanisms used in machine tools where a sliding part or column is required to be moved vertically or obliquely in relation to other machine elements, and comprises in a gear rack having helically cut teeth attached to,or otherwise integral with, the machine element to be moved, the said helically cut gear rack being positioned in the plane of required sliding motion,and having its helical rack teeth engaged with a conical worm gear,the axis of rotation of which is inclined in two planes, such that the teeth on the conical worm lie complimentary to those of the helix angle of the rack gear,and the axis of the conical worm is inclined away from the helical rack gear at an angle equal to half of the inclusive angle of the conical worm, thus ensuring several rack and worm teeth are always in mutual engagement and that by adjusting the position of the conical worm on its axis, backlash between the rack teeth and conical The invention will now be described with reference to the accompanying drawing (Figure 1) wherein: A Column (2) is slideably engageable in a Housing (4) and is provided with a Helical Rack (6) which is fixedly attached to the column (2) by means of screws (8). A Conical Worm (10) is mounted on a Shaft (12) and provided with Bearings (14,16) and located within a Sub-housing (18) and provided with adjusting shims (20). The Sub-housing (18) is attached to the Column Housing (4) such that the Conical Worm (10) meshes fully, engaging with several rack teeth at once.

The Shaft (12) has a handle(22) at its upper end to effect changes in the column position with respect to the Housing (4). Once the Column (2) has been moved into its desired position,it may be locked by means of a split clamp (24) or similar clamping means.

One complete revolution of the Handle(22) causes any one tooth on the conical worm (10) to advance or receed by one full tooth pitch,thus causing the helical gear rack (6) to rise or fall accordingly.The handle may be attached to a graduated scale(26) to accurately quantify the change in elevation of the column (2).The helical gear rack (6) may provide the additional function of radial location of the column (2) within the housing (4).

Because a gear rack of standard form and 20 degree pressure angle has straight sided tooth flanks,it is quite straightforward to design and cut a conical worm to provide contact along each tooth flank using an equivalent thread angle of 40 degrees, with a radiussed root and truncated crest.

Unlike a parallel worm gear,which is usually cut on a Thread Milling machine,or Hobbed, a conical worm will present problems due to its exaggerated conicity, which is beyond the capability of taper thread turning attachments fitted to normal screwcutting lathes. It may also have an assymetric tooth form when viewed in profile.However,it may be successfully cut on a CNC (Computer Numerically Controlled) Lathe,using a form tool for the helical tooth.

Claims

What I Claim is: 1.A machine element of an elevating slide or column

having a gear rack with helically cut teeth fixedly attached in the plane of elevation,and a captive but conical worm gear rotatably engaged with said rack so as to cause the said rack to rise or fall as the conical worm gear is rotated.
2 A machine element as disclosed in Claim 1 wherein the conical worm gear is inclined in two planes such that its teeth lie complimentary to those of the helix angle of teeth on the rack,and that the axis of the conical worm gear is inclined away from the helical rack at an angle equal to half of the inclusive angle of the conical worm.
3.A machine element as in Claims 1 and 2, wherein the conical worm teeth may be slid angularly into full flank engagement with those of the rack, such that several teeth are always in mutual engagement.
4.A machine element as in Claims l to 3, wherein the backlashbetween the conical worm and helical rack is adjustable to maintain the minimum working clearance.
5.A machine element as in Claims 1 to 4, wherein the elevating slide or column is provided with a clamp.
6.A machine element as in the foregoing Claims, and

according to the accompanying specification and

drawing.