New+grinding+machine

The new grinding machine replaced the old wooden grinding machine the made the TROK. The old machine worked great, but was large, heavy and took up too much space in the garage. It was also limited to 30 inch mirrors.

The new machine was designed to be compact, easy to clean, more flexible in operation and easily moved. It would also be capable of making mirrors up to 48 inch (1.2M) in diameter.

The over arm motor is a variable speed drive that can vary the rate of the over arm. The table speed is fixed, but could be changed quite easily by changing one of the external pullies. The table spped is a little under 1 rpm. The over arm can be between 1 stroke every 2 seconds to 1 stroke every 6 seconds.

The table is made of layers of plywood and sealed with fibreglass resin. This, it's solid steel 4 inch shaft and associated bearings were taken directly from the old machine. A new wooden frame was made to support the bearings and covered in sheet plastic for both protection and to reduce contamination. The machine table can be hosed down when required.

It is belt driven. The motor is contained within the casing of the table. The table has 4 nylon wheel in which it may be easily moved to enable the TROK trailer to be stored in the garage.

The overam mechanism stays in place at all times. The overarm sections are all made frm light box aluminium.The length and stroke of the overarm are all variable to enable the tool to be placed in varied positions on the mirror depending on what work is required.

A number of additions are planned for the machine including a driven tool. This will allow the tool to be driven left or right on the overarm, either auromatically using limit switches or my the hand controller. Another modification required is to put jacks on the table. This will remove the need to block the table in place during polishing when the friction is at it's highest. The table can move if it is not blocked up as in the image below.

Videos of the new machine




The power to bothe the motors is control via a central control panel. An old microwave controller/timer enables power to the machine when the timer is set and the reset button is pressed.

If the time runs out then the timer needs to be reset. This enables the machine to be set to run for controlled periods of time.

The machine has two emergency stops. If either of these is pressed then the machine will stop. The machine will need to be reset after an emergency stop to re-enable the power. This is prevent inadvertant start up of the machine.

Only one slight issue is the the variable frequency drive for the overarm has olding capacitors and takes a few seconds to loose its charge after an emergency stop. So long as you wait for the power to dissipate from the motor controller, then it is safe to reset.

Relays that control the mains power to the motors and variable speed controller are 24V. A 24V mains supplied power supply is required. This was obtained from Maplin. It is shown next to the power control panel in the image below.

The supply to the overarm can be isolated seperately so that the table may be sued for hand work (sub diamter laps, figuring etc) without the need for the overarm.

Typically, the time for each grinding/polishing session is around 10 to 15 minutes before the mirror is turned onit's support on the table. This is to prevent astigmatism being ground/polished into the mirror.



Image below is of the pendant control panel to start and strop the machine.







During the making of the 30 inch F3 in 2015, the machine table was modified to include a 1 metre Aluminium table. Also a new large DC gear motor to give more torque and to make the machine quieter. The gear motor was from an old stair lift.





Image below (Summer 2014) shows the new 1.0M aluminium table and 3 x lateral supports in place. Polishing of teh 30 inch F3 is being done in this image.