GB2433454A

GB2433454A - Tap or reamer coupling

Info

Publication number: GB2433454A
Application number: GB0526264A
Authority: GB
Inventors: Terry Smith; Steve Browning; Michael Bernard Coupla Quigley
Original assignee: HIGHTOWN ENGINEERING Ltd; QUIGLEY ASSOCIATES
Current assignee: HIGHTOWN ENGINEERING Ltd; QUIGLEY ASSOCIATES
Priority date: 2005-12-21
Filing date: 2005-12-21
Publication date: 2007-06-27
Also published as: GB0526264D0

Abstract

The coupling 2 is flexible to allow a tap 6 or reamer to accommodate small variabilities in set up. In an operation to tap or ream a pre-drilled hole 7 the tap or reamer does not break. A sensor 5 indicates whether the load on the tap is too high and provides a feedback system. The feedback enables a feed to the tap to reverse and pull the tap out thereby reducing the chance of breakage.

Description

1 2433454 Improvements to the production of reamed and tapped holes in

metals This invention relates to the production of reamed and tapped holes in metals particularly but not exclusively in holes of diameter less than 2.5mm.

When conventional reaming and/or tapping of holes of diameter less than about 2.5mm is carried out by conventional mechanical means it is found that the reamer or tap can break easily. This can be due to any small asymmetries in the angle of tapping or in ensuring that the tap rotates and also progresses through the pre-drilled hole both at the exact rates suitable for the thread characteristics.

There can also be a problem when the procedure is reversed and the tap is withdrawn from the hole. In all of these circumstance a broken tap or reamer can result in the whole job being scrapped leading to a significant financial loss.

There are systems already in the market that can deal with this problem to an extent but only for the larger holes. These typically have a clutch system and are big and bulky, far too large for the small holes being considered.

In this invention a small, less than 10mm diameter, very flexible coupling is proposed which allows the tap or reamer to accommodate the small variabilities in the set up that normally cause the problem. The tension put on that coupling by the tapping operation is taken up by an elastomeric coupling material which allows for minor changes of the tapping characteristics. The soft coupling material reduces the tension that might otherwise develop if the tapping process was going slightly off axis or the feeding characteristics were not exactly correct.

A high tension might indicate a tendency to break the tap and the soft coupling system proposed will reduce that tendency. Some coupling systems exist, typically for the larger holes described, in which a very coarse spring like body is used to make a helical coupling which takes up the slight imperfections. However these systems are too coarse for the very small holes under consideration here.

Other systems have feedback control, again for the much larger holes, in which a large CNC machine, for example, carries out the tapping operation. The current to the machine is monitored and if it rises to too high a level the machine cuts out. This is fine for large holes but the inertia of the large machine is far too great for the hole sizes being considered here. The changes in current caused by the imperfections in the tapping process are very small compared with the current used to drive the whole machine.

One embodiment is to use a soft rubber or elastomeric material as the coupling medium. The elastomer is glued to the body part that holds the final tap. Apart from the benefit of taking up slight mismatches and tolerance errors a possible other benefit is anti-shock, as there is an amount of give'. This may prolong the life of the tap. The proposed system will be far smaller and lighter than current systems that are not suitable for this size of hole and will result in far fewer failures of the tap or reamer in holes leading to less waste of expensive parts.

A strain gauge is fitted to the elastomenc coupling to indicate when there is too great a twisting motion on the coupling. The signal from the strain gauge is fed back to the spindle drive via electronic circuitry. If the load gets too high the circuitry then sends a signal to stop the forward pressure and automatically reverse the spindle so feeding the tap back out.

One embodiment is to arrange for the signal produced to be compared with a standard signal produced by a tapping operation in which there was known to be no difficulty i.e. a reference standard. These signals can then be compared electronically and the settings for the tapping operation then changed automatically. The proposed system will be far smaller and lighter than current systems that are not suitable for this size of hole and will result in far fewer failures of the tap or reamer in holes leading to less waste of expensive parts.

Referring to Figure 1 as an example the proposed design of a novel tap can be seen. I refers to the drive part of the tap, 2 refers to the elastomeric insert, 3 is the adhesive joining the insert to the rest of the tap, 4 is the small radial gap that allows for axial and radial mis-alignment 5 is the strain gauge, 6 is the tap and 7 is the hole to be tapped.

Claims

The Claims What we claim is 1. A device for ensunng that in an

operation to tap or ream a pre-dnlled hole the tap or reamer does not break.

2. A device as in claim I in which a small, less than 10mm diameter, very flexible coupling is used to allow the tap or reamer to accommodate the small variabilities in the set up that normally cause the problem.

3. A device as in claims I and 2 in which a sensor indicates whether the load on the tap is too high and provides a feedback system to make the feed to the tap reverse so pulling the tap out and reducing the chance of breakage.