DROs speed proptotype production

Following the retrofitting of four-axis digital readout units to three Bridgeport turret mills in Taylor Hobson's toolroom, time savings of some 10% have been made on prototype part production.

Following the retrofitting of Heidenhain's Positip PT 855 four-axis digital readout units to three Bridgeport Series 1 turret mills in Taylor Hobson's toolroom, the company reckons time savings of some 10% have been made on prototype part production.

However, it is the elimination of calculations, the ability to break down jobs for more urgent tasks and quickly pick up data, and the accuracy improvements gained through Heidenhain's linear measuring scales now fitted to the machines, that the first complex job through the toolroom virtually paid for the installation.

The Leicester-based manufacturer of precision measuring systems for surface topography and roundness has quite a large need for prototype and special one-off component production.

This is required to customise existing units or meet the on-going demands for development of new devices.

Here the toolroom has proven to be a central resource and therefore has to have as much flexibility in the equipment it uses to keep its response time as short as possible.

Steve Edwards, Taylor Hobson's machine shop manager, comments: "Our regular production is centred on CNC machines and we have invested quite heavily over the last few years, since we gained our independence from the Rank Organisation in the mid 1990s.

However, in the toolroom, production has kept its manually operated machines as these ensure we have optimum flexibility for very small batch requirements".

He follows on to describe how replacing previous two-axis point-to-point digital readouts (DRO) with the systems supplied by Heidenhain (GB) of Burgess Hill in West Sussex has, however, made the machines easier to operate.

"This is especially so on those occasions when the toolroom has to produce a small number of identical components", he says.

Jeff Tonks, one of Taylor Hobson's toolmakers, explains: "We need the capability to tackle a wide range of work with component size up to 450 by 300mm.

While some is straightforward, a large proportion of prototype development can be very complex.

For example, a recent job we had to do involved manufacture of a two-piece assembly for a new instrument.

Between the body and a mating component there were around a dozen holes of various sizes, some of which were at angles.

Now that the prototype is complete and the components are fully productionised, it requires some 40 tools on a four- axis machining centre to produce them, so you can gauge how complex the original parts we had to make were", he says.

This type of work could have been carried out with the previous setup, using the table x and y axes which were serviced by the DRO.

The quill and knee settings remained, literally, in the hands of the operator using the machine's standard micrometer dial and feedscrews.

In addition, there was no facility to reset data in-process, and while a skilled operator was capable of achieving excellent results it took considerable time and demanded a lot of calculation, in-process dimensional checks and very high levels of concentration to prevent errors.

Local Heidenhain agent ACC Systems of Coalville, Leicester installed the PT 855 DROs which were selected following an appraisal of the market.

To complement the DROs, Heidenhain linear scales were fitted on the x and y table axes, the knee z axis and quill.

Installation was carried out on one machine at a time so as not to disrupt activity in the toolroom.

The Positip 855 uses flat screen display and graphical features with conversational guidance and contextual help.

The logically laid out keypad makes operation easier while the amber readout helps the reading of data.

Display steps are five or one micron and the DRO is able to hold 99 datum points and 99 tools in memory.

As Taylor Hobson's toolroom has found, the distance to go display has proven very useful in their tasks of operating the Bridgeport machines.

As Steve Edwards reflects: "By upgrading the DROs we were aiming to relieve the operator of a lot of the nonproductive tasks associated with using the machines.

The objective was a system that provided most of the facilities associated with a CNC machine.

I think we've been very successful because the Heidenhain PT 855 has a lot of useful features such as semiautomated positioning for pitch circle diameter drilling and pocket milling, and an onboard calculator for feeds and speeds".

For Jeff Tonks, a key facility is the subdatum as it allows multiple setups to be maintained on the machine table.

"Before we had the Heidenhain system installed, we used to spend a lot of time finding and calculating datum positions from which to machine.

With the PT 855, I can set fixtures or vices up at various points on the table and quickly move between them with ease, as the DRO automatically 'knows' where they are.

This is a major advantage if I'm working on a job and have to stop and break down to do something that is more urgent.

Usually I can leave the setup in place and come back to it without having to set up again".

In addition, he maintains: "We can record and teach-in a sequence of movements that can subsequently be used to guide the operator through a cycle from the 20 program memory, if he has to repeat a machining operation".

Jeff Tonks maintains: "This capability certainly makes repetitive machining tasks faster.

However, the confidence we have in the accuracy of positioning is the key advantage as we now work religiously from the read-out because we have total confidence in what it displays.

As a result, the amount of in-process checking has significantly decreased".

A further addition that Taylor Hobson's toolroom is considering is the inclusion of Heidenhain's KT 130 three dimensional triggering probe which will be used to capture datum points prior to machining and hence further improve setup.

Steve Edwards reckons that the overall time saved on a typical job is easily 10%.

To which he concluded: "The investment on this upgrade programme was recouped very quickly.

As soon as the first complex job went through the toolroom we essentially recouped the cost due to the ease of use and that it allows the machinist to concentrate on the job rather than the machine operation.

Moreover, because the Heidenhain linear measuring scales provide absolute, backlash-free high accuracy measurement, confidence levels are really high".

Back to top