Laser centreing device
There are many laser centre finders on the market. As far as I am aware these are static devices that fit into the spindle or collet or chuck and they are used to indicate when a point or an edge is on centre. Any inaccuracies in mounting these devices result in inaccurate location of the point or edge
This device is different. It to is mounted in the spindle, chuck etc. but it is used with the spindle rotating. In the photo above the device is mounted in the drill chuck on my mill. It consists of four main parts. The spindle mounts in the chuck. The spindle is cross drilled for the cross bar. The cross bar can slide in the spindle and can be fixed using the knurled thumb screw at the end of the spindle. The cross bar is joined to an aluminium block that holds an ordinary laser pointer which is inclined at 60 degrees to the cross bar in the photo. The laser is adjusted so that the light beam intersects the axis of rotation.
This device is different. It to is mounted in the spindle, chuck etc. but it is used with the spindle rotating. In the photo above the device is mounted in the drill chuck on my mill. It consists of four main parts. The spindle mounts in the chuck. The spindle is cross drilled for the cross bar. The cross bar can slide in the spindle and can be fixed using the knurled thumb screw at the end of the spindle. The cross bar is joined to an aluminium block that holds an ordinary laser pointer which is inclined at 60 degrees to the cross bar in the photo. The laser is adjusted so that the light beam intersects the axis of rotation.
When the device is rotated the laser generates a cone of light and if a sheet of paper is placed on the milling table it will draw a circle. The axis of the cone will be exactly the axis of rotation of the mill spindle. Starting with the headstock near the top of the column the circle will be large. As the headstock is moved closer the circle will become smaller and smaller until it eventually become a spot. This spot will be centred exactly on the axis of rotation of the mill spindle. Further movement towards the paper will cause the circle to reappear and it will become larger as the headstock approaches the paper.
The device can be used for other purposes. For instance the circle will always coalesce to a spot at the same distance from the headstock. so that the vertical co-ordinate of any point on the work can be measured. Holes can be accurately centred by allowing the circle to disappear into it. Once a symettrical circle forms inside the hole the the hole is centred on the spindle axis. If the beam hits a round surface of a cylinder then a symettrical pattern when the axis of rotation is directly over the cylinder axis. Thus the device has many uses apart from just centre finding.
The device can be used for other purposes. For instance the circle will always coalesce to a spot at the same distance from the headstock. so that the vertical co-ordinate of any point on the work can be measured. Holes can be accurately centred by allowing the circle to disappear into it. Once a symettrical circle forms inside the hole the the hole is centred on the spindle axis. If the beam hits a round surface of a cylinder then a symettrical pattern when the axis of rotation is directly over the cylinder axis. Thus the device has many uses apart from just centre finding.
In this photo the cross bar has been unscrewed from the 60 degree position and it has been screwed into a different hole that sets the angle of the laser to crossbar to be 45 degrees. There is a further hole available that sets the angle to 75 degrees.
The aluminium block is 38 mm diameter and 17 mm thick. It was cross drilled 9.5 mm for the laser pointer. The hole in the centre of the round face is of no significance. The block was from the scrap box and was a hole saw cut out from a thick aluminium sheet, hence the hole!
The aluminium block is 38 mm diameter and 17 mm thick. It was cross drilled 9.5 mm for the laser pointer. The hole in the centre of the round face is of no significance. The block was from the scrap box and was a hole saw cut out from a thick aluminium sheet, hence the hole!
The laser pointer is 9.5 mm diameter and about 50 mm long. The on button is located half way along the body. What appears to be a small hole near the right hand end of the pointer is a window that glows red when the laser is on. The left hand end has an attachment for a key chain.
This shows the cross drilled hole for the laser pointer. Note the small cut out on the left hand side of the hole. This slopes in to join the main hole. It was made using a round file. The function of this cut out is such that when the pointer is inserted into the hole the on button pushes into the cut out and this keeps the button depressed.
One of the M5 threaded holes that are used to attach the cross bar is visible just to the right of the large bore for the laser pointer.
One of the M5 threaded holes that are used to attach the cross bar is visible just to the right of the large bore for the laser pointer.
The other components are the spindle, the cross bar and the thumbscrew.
The spindle is a length of 10 mm round bar cross drilled near the end with a 6 mm hole. There is an an axial M3 tapped hole for the thumbscrew.
The cross bar is a length of 6 mm bar. The end is turned down to 5 mm and threaded M5. This threaded end screws into the aluminium block at one of the three possible attachment points.
The thumbscrew is simply a short length of M3 studding loctited into a knurled knob.
The spindle is a length of 10 mm round bar cross drilled near the end with a 6 mm hole. There is an an axial M3 tapped hole for the thumbscrew.
The cross bar is a length of 6 mm bar. The end is turned down to 5 mm and threaded M5. This threaded end screws into the aluminium block at one of the three possible attachment points.
The thumbscrew is simply a short length of M3 studding loctited into a knurled knob.
This device has some interesting uses but it is difficult to show them on this page. However, this youtube video shows a similar device being used by Dan Gelbert.
Disaster strikes.
The laser centring device worked well but eventually the batteries need replacing. The threads at both ends of the laser pointer would not undo with finger pressure and in trying to undo the threads using tools the pointer was damaged and was unusable.
I searched local shops and ebay for a similar pointer but they seem to be no longer available. The commonly available type is now multifunctional and incorporates not only a laser pointer but also a LED torch. It has a much larger diameter than the 9.5 mm original unit.
A new unit has been constructed which is built around a cheap, readily available laser diode, see here.
I searched local shops and ebay for a similar pointer but they seem to be no longer available. The commonly available type is now multifunctional and incorporates not only a laser pointer but also a LED torch. It has a much larger diameter than the 9.5 mm original unit.
A new unit has been constructed which is built around a cheap, readily available laser diode, see here.