Squaring an Engineer’s Square

Oct02
by Thomas Yoon Chee Tuck on October 2, 2019 at 10:50 pm
Posted In: CNC, DIY

When I am cutting materials by hand for my projects, a lot depended on whether I can mark out the designs accurately, particularly the right angles. I have a cheap engineer’s square (L-square) which I used for my projects, which I later found was not completely square.

There are many youtube videos that teaches you how to check whether the square is actually square by comparing lines drawn when the square was placed first on one side and then on another side on a fixed straight table edge. That is the easy part.

From what I could see, very often the engineer’s square needed to be trued. And the recommended practice was to drag a file over the edges by hand from progressively different locations so that essentially the edges of the ruler would be filed at an angle – to the correct angle. This was a time consuming process, depending on how much the fault to be corrected was.

Since I had a movable gantry cnc machine, I thought it would be a good idea to make use of it for this purpose. A mushroom type grinding head could be used to spin at a high speed by the machine spindle and then made to travel in a straight line perpendicular to one of the L-square’s legs in order to grind off any imperfection in the L-square ruler.

But first, I needed to make sure that my machine itself was moving perfectly square. In order to do this, I squared up my machine first.

This was how I did it. I used Trigonometry in Mathematics for this, particularly the right angle triangle formed when the sides consisted of 3-4-5 units. To fit my machine, I had selected multiples of 113 for my calculation. For the x axis travel, the indicator was made to travel a distance of 113 x 4 = 452 mm. For the y axis travel, the indicator travel was chosen to move 113 x 3 = 339 mm. If the movements of the x and y axes were true, the “Hypotenus” line would measure exactly 113 x 5 = 565 mm. This was confirmed by measuring with a normal steel ruler.

Since the accuracy would depend very much on the human eye reading the markings on the ruler scale, which could also be subjected to inaccuracies during manufacture, the distances to be measured were chosen to be as long as possible to fit the dimensions of the machine table (wasteboard).

Before this, I actually had to calibrate my machine, so that I could be quite confident that what was shown on the computer screen was the physical position of the indicator at the machine table. Using the computer screen movement figures as representing the actual physical dimensions on the machine table, I would then have no need to measure the triangle physically with my steel ruler, thus saving me some time and effort.

Once the cnc machine was deemed square enough, the L-square was clamped in position and the grinding tool was programmed to move slowly to cut away the imperfections. I had to do this slowly so that very thin layers were removed each time. In this way I could be sure that the grinding abrasives would not have dislodged during the whole process of cutting from begin to end making the grinding even.



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Cyclone Dust Collector

Sep02
by Thomas Yoon Chee Tuck on September 2, 2019 at 4:54 pm
Posted In: DIY

I managed to pick up a discarded vacuum cleaner quite sometime back. It was a simple vacuum cleaner that had just a flat filter screen between the dust compartment and the motor. Looking at the construction of this vacuum cleaner, I reckoned that it would only be suitable for use if the dust to be sucked were quite large, like in a barber shop, where the “dust” were the hair that was lying on the floor. And since the dust compartment was rather small, the collected dust would have to be emptied quite often. And since there was no bag to collect the dust, the latter had to be emptied from the vacuum cleaner itself into an external dustbin or bag for disposal, possibly by digging around with a stick. No wonder the previous owner did not want it anymore. It was too difficult to maintain. When I found it, it was heavily choked.

But the motor and the vacuum fan was working alright, although the wire return spool spring mechanism was not working. I decided that it would make an excellent workshop tool for me if I could manage to improve on it.

This I did, by adding a cyclone and a container for it. I had to fabricate some supporting structures for them in order to work. My plan was to use it for dust extraction of my movable gantry cnc machine because some of the cutting jobs did generate a tremendous amount of wood dust.

The dust extractor would be fixed on a wall beside my cnc machine. Therefore I did not even need to have a spool to store the electric wires. The wires could be managed well by just hanging loose. The functions of the supporting structures were designed:

  • To allow the assembly to be hung on the wall so that it could be removed easily.
  • To secure the vacuum cleaner with motor to the assembly. Operation vibration will cause it to move away
  • To secure a cyclone dust collector to the assembly so that it could be connected to the vacuum cleaner
  • To be able to collect the dust in a removable container. This would eliminate the need to clean the filter/filter bag
  • To be able to remove the container easily so that the dust can be emptied easily

The supporting structures were made of wood, plywood, steel rods, and springs. The connection hoses were cut from original. Some pvc pipes had their diameters enlarged by heat treatment or reduced by sandpaper so that they could fit the cyclone/vacuum cleaner.

Originally, the cyclone was just enclosed with a open top canister, pressed seal with the help of two spring loaded compression rods to maintain the vacuum. It did work, but because of the limited space available for dust collection, I decided to add another screw cap bottle at the bottom of the assembly so that I could have more space to collect the dust before I needed to empty it. Also it would become easier to remove by just unscrewing the bottle from its cap.

So I had to design a connection between the top canister and the bottom screw cap with its bottle. Since the wall thickness of the top canister was very thin, I fabricated a flange out of 11 mm plywood and glued a short length of PVC pipe vertically inside it so that the latter would poke through to the bottom screw cap.

Unfortunately, the PET bottle that I had available was not very strong, so I had to add in some other internal supporting frames to make it strong enough to withstand the vacuum pressure. I did this by gluing a cd with some spacer wedges so that the face of the bottle would be in contact with the wedges, all glued fast by epoxy resins. In another place, I placed some steel wires on the internal surfaces of the bottle and then glued them in place. Upon testing, they seemed to be able to withstand the vacuum pressure without collapsing.

The push-button switch for the vacuum cleaner was situated quite high up when the assembly was mounted on the wall. I used a few pieces of wooden strips to create a lever mechanism so that I could touch the switch from an accessible place.

Now, the vacuum cleaner does not choke up as I could very easily remove any dust collected by just unscrewing the bottom bottle.



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