30+inch+TROK+grinding+machine

The images below show the completed grinding machine in it's new garage in October 2001. The text below these images are of the making of this machine.
 * __October 2001__**

This machine was used to make the 30 inch TROK mirror. It has now been dissasembled and a new machine that is easier to use and can make larger mirros now exists. Follow this link to the new machine.





**__February 2001__**

Construction of the grinding machine
 

Overview
 Work began in the middle of February on the construction of the new grinding machine. It would essentially be similar in design to the smaller machine used for the 6, 8 and 16 inch mirrors recently completed, but would be much larger and need to have much more power. The machine would be 6 feet by 4 feet on plan dimensions. The table height would be a suitable height to handle the mirror at around 2 feet from the ground to the top of the table. At one end would be two drives for the table and the overarm, each driven from a separate motor. At the other end would be the pivot for the overarm. The table would be supported on a central shaft held by two large bearings within housing. This shaft, bearings and associated housings actually came from my de-commissioned 18inch Newtonian. The Machine would be capable of Grinding and polishing mirrors up to and including 30inches. It could easily be modified at a later date for larger mirrors to over 40inches.

 The machine frame
The frame for the machine would be constructed from 3inch square fence posts. These posts are relatively cheap to buy, easy to handle, easy to drill and fix too, and are treated for being in contact with water. The frame was bolted together with M10 coach bolts 7inches long and using large repair washers to spread the load when tightening the coach bolts up. Some lengths of M10 threaded rod were also required for some connections that where longer than 7 inches. The frame was given a coat of woodstain for aesthetics and to provide additional water protection. This coating would be renewed for finer grades and polishing to 'seal in' any unwanted loose grains of grit. 

Table construction
The table itself would be made from many layers of plywood cut into discs and then glued and screwed together. Two 40mm thick worktops 24inches in diameter would be used for connection to the shaft flange. Two discs of ¾ ply 30inches in diameter would be used for the large pulley ontop of these two discs. The edges of these two 30 inch discs would be cut to a 45-degree angle to centre the large belt to dive the table. This was done by angling the jigsaw to 45 degrees when gutting. The jigsaw also had a homemade attachment to cut discs. This used a piece of aluminum angle with a number of holes drilled in it to allow for different sized discs. The top three discs are also cut from ¾ ply but are 32inches in diameter. The whole table was then sealed with two layers of fiberglass resin and left to cure. 

Drive for the table
The drive for the table is a 1/3hp single phase 240V motor. The has a 1 inch 'V' pulley that drives a 7inch 'V' pulley on the input shaft of a 30:1 gearbox. The gearbox is a none reversible on the output shaft and assumed to be a worm and wheel arrangement. The output shaft of this gearbox has a 2inch 'V' pulley that drives, via a LONG belt, the 30-inch wooden pulley that is part of the table. This can bee seen in the above picture in the section about the table construction. The final drive gives a table speed of approximately 0.7rpm. Backlash is minimal when the belt is tensioned and no trouble has been experienced so far when using the machine.

The image above shows the arrangement of the drive. 

Drive for the overarm
The drive for the overarm is again another 1/3hp single-phase 240V motor. The has a 1 inch 'V' pulley. This pulley drives multi-diameter pulley (8inch, 6inch and 4inch) on the input shaft of a 15:1 gearbox. The output shaft of this 15:1 gearbox is direct onto the overarm drive rod. The gearbox is reversible on both input and output shafts. This gearbox is also much larger than the 30:1 gearbox for the table drive. It is intended to add a larger pulley to the input of the 15:1 gearbox for polishing to slow the drive dive and get more torque.

The motor also during the hogging out stage was getting a little too warm. The image below shows the high tech solution employed to keep it cool!!



 Overarm and pivot
This itself is made from wood. The main driven arm is a piece of 3x3inch fence post. The pivot from the dive arm from the 15:1 gearbox is a universal joint with a ½ inch shaft. The pivot onto the driven arm is from a car half shaft. The universal joint was included to:- · Allow for the driven overarm to sit on the tool under it's own weight · Allow the arm to move up and down a little due to the curve of the mirror · Allow for easy removal of the driven arm from the tool The drive arm connected to the 15:1 gearbox is adjustable for length of stroke. This is simply achieved by having a slot in the arm and held in place by two brass M12 wing bolts. The pivot at the opposite end from the drives is a simply M10 piece of stud fixed into a 3x3inch cross piece at the upper end of the machine. The position of this is variable to allow for different start positions of the tool.

Building the New garage
The garage we used to do the hogging out work was sufficient for that puprose. But is was not long enough or clean enough for polishing, figuring and testing.

The sectional garage was demolished in April 2001 and a new block wall garage 32 feet in length was built by myslef, my Dad, Geoff, Steve King, Dave Owen and others (including Mike next door in laying the foundaions). We completed the garage in September 2001.



 Material list
Existing bearing housing (RA drive) from 18inch telescope (4inch solid steel shaft) 1 x 7 inch flange for over arm connection 1 x 8/6/4 inch multi diameter pulley for i/p to 15:1 gear box 2 x 1 inch V pulley's for motors 1 x 7 inch V pulley for i/p to 30:1 gear box 1 x 2 inch V pulley for o/p of 30:1 gear box 9 foot V belt 15:1 gearbox 30:1 gearbox 2 x 1/3 horse 240V motors 1 x 4 foot length (3x1) C section beam 8 x 8-foot lengths of 3inch square fence post Approximately 40 M10 coach bolts 2 x 3-foot lengths of M10 threaded rod 2 x 6 foot lengths of white worktop 2 x (8x4) sheets of 3/4inch ply 100 wood screws 2inches long 500ml of water proof PVA 500ml of fiberglass epoxy resin 2 tubes of hardener Off cut lengths of shag pile carpet