Introduction
Some of my hot air and IC engines have glass cylinders. I cut them out of from standard (test)tubes or from other glass tubes. Especially for the hard glass types like heat resistant Pyrex and/or in case of a relative thick wall I had to use the galss cutting machine at my former employer Philips. But I don't like to be too dependent from that and it also is more convenient to be able to do that in my own workshop at the time that it occurs. That's why I conceived the plan to make my own and simple glass cutting equipment.
The design of this easy-to-make tube glass cutter
I know that cutting glass only goes well with a diamond disc. In fact this is a thin metal disc in what artificial diamond grains are impregnated.
I accidentally happened to have such a cutting disc but I also know that you can buy them everywhere for not more than some few Euro's/Dollars. Together with the fact that they have a very long lifetime this cannot be a cost problem. From experience with the Philips glass cutting machine I knew that the revolution speed of the disc must be rather high and that the pace where the glass is being cut must be cooled with water. I could make the high revolution speed of about 15.000 easily with my Dremel hand grinder tool. By making some additional parts it was not difficult anymore to make my own glass cutting equipment as shown on the picture below:
- I made the base plate and some other parts from plastic, mainly because some water is splashing around, although that turned out to be not that worse as I initially expected.
- The diamond disc is screwed in an axle that can turn on two little ball bearings in a brass support. The rubber drive belt is running over a small pulley on that axle and over a similar pulley in the head of the Dremel hand grinder tool so the transmission ratio is 1 to 1. This Dremel can turn with 30.000rpm, but I experienced that half the speed is sufficient in this case.
- The plastic V-block that is carrying the glass tube can move in the transverse direction and is pushed to the front with a spring on the central adjusting screw. To cut the glass tube the stroke of this V-block need not to be much more than the glass wall which in practice will be between 0.5 and 2 mm. But I made the maximum stroke about 20mm to be able to cut tubes with diameters between 4 and 35 mm on the same V-block. The cutting disc will touch the glass on different levels of course, but that appeared not to be a problem at all.
- The stop for the glass tube is made from an aluminum strip that can be fixed on the base plate in any position with a butterfly nut in a slot of the strip.
- I made the water tank from a tin can from out of what we ate brown bean soup the day before. At the bottom side a brass tube is soldered with a rubber hose on it. Over that there is a brass part in what an adjusting screw is made with what one can regulate the amount of droplets per second. Two to three droplets per second appeared to be enough for sufficient cooling while grinding so not more than an egg cup of water is needed for cutting one tube. So the water nuisance that I feared appeared to be unfounded; I made more serious mess in my workshop with other things. The little puddle of water is removed easily with a cloth or some paper and after that I spray some few WD40 on the parts that can possibly rust so everything keeps in good condition when the equipment is stored after use.
The incremental offset of the V-block is during the cutting of the glass tube is about 0.5mm or somewhat less with very hard glass types like heat resistant Pyrex. At each V-block adjustment the glass tube must be turned around gradually about 2 times after what you will hear that the disc is not touching the glass anymore. During the turning around the tube must be pushed constantly to the V-block and the aluminum stop which is not difficult after some practice.
During this grinding procedure you see the groove in the glass becoming deeper and deeper until the two parts fell from each other. The intersection face is already surprisingly nice and smooth most of the time. If one should not be quite satisfied with the result it is always possible to after-grind the intersection on a water proof grinding paper on a glass plate wetting with some turpentine.
The video below will probable more explanatory than the text above and it shows how well it works:
John Bonfoey made this nice replica:
