Cutting gauge glass to length

I'm getting close to finishing my Polly Engineering O&K, and need to trim (~10mm) off the gauge glass provided for it to fit. Any suggestions on ways to perform this cut? I do have a lathe (Myford speed 10) and an old diamond scribe, also Minicvraft drill accesories.

Thanks

Mike

For a neat cut, wrap in paper and hold gently in 3-jaw chuck. Use a suitable tool to make a sound scratch around the glass. This is easier than trying to make an accurate circular scratch by eye.

Neil

I don't know whether the glass supplied is the soft soda glass or harder Pyrex borosilicate glas but whatever, keep it cool ie don't give it the opportunity to crack and chip due to overheating.

a nick with a triangular file then break in the fingers.

cheers,

julian

Thanks gentlemen. I will report back on the "outcome"!

Hi Mike . Never make the cut all way round ,only a third will be better. Put the mark on top,bend glass down and pull at same time. If you have a diamond tile cutter that will do it but more trouble.

I have broken many tubes the first way and no problem .Was a lab tech for many years

Good luck Maurice

If you only want to cut a small section off the end it is difficult to snap it after scoring. Never tried it myself but I have seen a professional glassblower cut tube by scoring it, wetting the scored line with saliva, and then just touching it with a red hot glass rod. The thermal shock does the work.

Russell.

I mark a line with pen then run round it on the bench grinder, light abrasion, then snap by hand. Never failed me yet.

If you have one of the DIY electric wet diamond tile cutters they will whizz through it

> If you only want to cut a small section off the end it is difficult to snap it after scoring.

Drill a close fitting hole in a wooden block, hold block in a vice insert the short end in the hole, and push free end down.

Neil

When breaking glass tubing or rod be sure to pull it apart as you snap it.

For flame-polishing, a laboratory Bunsen burner flame is about as large and as hot as you want to go because with more heat things will happen too quickly and over too large an area. The flame is soft and easily deflected by a draught eg if someone is walking about nearby. This would not be good for the glass or for your hand.

Rotate the tube end two or three inches above the top of the flame to warm it up slowly. There is a real possibility of a little bit of hot glass flying off, so wear eye protection. Make sure that you can see the end face that you want to melt.

Gradually lower the end - only the end - into the hot spot in the flame. As soon as you see the very end beginning to soften and smooth out return it to the hot air above the flame, still rotating, and let it sit there for half a minute or so then gradually lift it out of the hot air. The actual softening of the end will take only about 5seconds depending on the flame source. If you leave it 'cooking' for too long it will soften too much and melt back and develop a fat ring around the end, inside and out, which will somehow have to be ground off if you want a consistent o.d. Or perhaps you use forgiving O-rings?

Don't hurry the slow cooling: just letting it quench in air straight from the flame will introduce invisible strains in it and make it more sensitive to shock and liable to crack later.

This gentle heating and cooling are not quite so important if it is Pyrex-type glass, but then that wouldn't easily soften in a bunsen.

Quite a few years back on this forum their was a thread on this subject and one of the answers was to heat it up a bit of wire to cherry red and quickly wrap it around the glass let all cool and the glass will snap.

Bob

OK - I "measured twice and marked once" where the cut needed to come. I put the tube, wrapped in paper, in the chuck of my lathe. Tightened just enough to grip. I then set up a carbide tool tip in the tool post and VERY gently brought it in to contact with the rotating tube. Good clean line scored in the glass. Wet the line with saliva and tapped it with a light hammer. Not a perfectly clean break, with about an eigth of the circumference breaking beyond the line in to the work piece. No problem given the pipework configuration. Gauge glass now safely installed on the backhead!

RESULT! Thanks guys.