Need help cutting Pyrex test tube

[vturbine]

Can someone help with instructions on cutting Pyrex test tubes. I've tried a couple methods I've seen elsewhere on the web without luck. These were for regular glass tube, not pyrex test tubes -- maybe that was the problem.

Thanks!

[Mike Everman]

I'd get out the dremel cut-off wheels. That'll work.

[vturbine]

Thanks Mike, I'll try it.

Would you fasten the Dremel down and rotate the tube to cut, or vice versa?
Gradually work around in several passes or cut through like a circular saw in one pass?
Tape over the area in advance?

[Mike Everman]

Yeah, I'd lock down the dremel tool, hold the tube against and end stop and spin the tube. I suppose you have extras; I'd push it for a deep cut and see what exactly the limits are, and how aggressive you can be, then back off. there's definitely a feed rate that maximizes life of the cutoff wheel. show us some photos of how it goes. You're making me think again about the wine bottle pulse-jet!

[Mark]

What are you making with the Pyrex tubes? I was thinking you might find some company that could do it for you. I have cut some quartz tubing using my diamond saw but it is a hassle because the motor/belt drive isn't mounted properly on some plywood and it wobbles because the screws aren't holding. I could fix it if I really wanted to. The saw even cuts thin stuff like those 4 foot fluorescent bulbs. My brother and I cut one one day. But ideally I would like an ultra-smooth polished end or at least sanded or frosted. My saw kind of looks like this link below only in a smaller unit with a 12 or 14 inch wheel. It uses oil to cool the work and it spins relatively slowly. The bottom of the wheel dips into an oil bath. So then you have to wash your piece off with soap and water too. My saw does a good job but it's a lot of work to set it up and then take care to do a perfect cut. You can tie a weight to the mechanism and let gravity slowly and evenly feed the piece into the blade, hands free. I've used a 5 ounce fishing weight with a string on a pulley to apply the force. But most times I just used my hand slowly advancing the tubing gently. The last bit is the tricky part, where you want to go slower, so the saw cuts a perfect edge and doesn't leave a lip.
I have also used a diamond band saw "wire" on my quartz tubing but the "blade" was rather coarse. It does an OK job and uses water for a coolant. The diamond wheel saw blade appears as if there is nothing that would cut anything, the diamonds are very small. It makes a smoother cut.
http://www.ecu.edu/glassblowing/glass-saw.htm

Maybe you could find something on eBay similar to these or find a place that sells small quantities in your size, if you want to retain the one closed end.
http://www.daigger.com/catalog/product/ ... Test+Tubes
http://bypharma.com/pyrexrimlesstesttubes.aspx
http://www.testtubesonline.com/Glass_Te ... s_s/31.htm
http://www.testtubesonline.com/product_p/206-0041w.htm

[vturbine]

Thanks Mike, I tried it briefly today with a broken remnant of a test tube I tried before. I taped it and fastened the Dremel in the vice. Unfortunately the little cutoff wheel I had wouldn't even scratch the glass. Wrong kind I guess. I went to the hardware store and picked up some non-Dremel brand wheels that specifically mention cutting glass on the package, so I'll try them next.

Mark, thanks for replying. A diamond wheel is out for me financially at this point.

It's also a little confusing not to say frustrating to see on you-tube 2 demos in cutting what looks like 1" glass tubing, where they make it look super simple and easy. In one a guy holds a glass cutter in one hand and the tube, and pressing his thumb against the tube, does a quick score for about an inch, then snaps the tube in his hands. No gloves on, either.

In the other video someone uses a triangular file to make a small score, then puts a singlre drop of water on the score, he lights a torch, puts a small glass rod in the flame until it's cherry red, then touches it to the water drop. Pop, a perfect cut.

I tried this last about ten times on the test tube. Nothing. I thought maybe it was because Pyrex doesn't expand and shatter like regular glass. Maybe?

Anyway, I'll try the Dremel again and let you know.

[Mark]

I didn't think you would want to spring for a diamond saw but for me if I could find a place in town or artistic neighbor that could do it for me that would be the way to go. I guess if you have an extension cable for your dremel you could possibly use a coolant while sawing as the actual dremel would be away from the water or whatever you use. Here's some very meager thoughts I came across that may have a tidbit of useful information in your quest.
I have some little diamond wheels for my dremel and some diamond drill bits but have never used them. I imagine controlling vibration/wobble will be a factor, setting it up so the piece won't have too much play. I don't know how steady/true a tiny dremel diamond wheel spins if that would be a factor either. Seems if you went very slowly, sawing a test tube shouldn't be impossible. I'm sure there is a way. Are you making a Stirling engine or something? I think about my brother who used/cannibalized an old microscope to feed a part into the cutting tool. The coarse and fine knobs on a microscope are good for that. Figuring out how to hold the piece of work is often the hardest part. ha

"Dremel Tool Company says it does not make a tool that cuts glass, only tools that decorate glass. So can you adapt a Dremel tool to accomplish glass cutting? Dremel makes some great small-scale tools for the craftsperson. Dremel may have some tools worthy of considering for your next glass project."
What Dremel Tools Can Be Adapted To Cutting Glass?
"A diamond tipped Dremel tool such as the diamond cut-off wheel may be your best bet when cutting glass. Tungsten carbide bits or diamond-coated bits are great for drilling holes through glass. The use of water and oil during the cutting process will keep the bit and glass cool and help keep glass dust to a minimum. Remember to always wear safety goggles and take all safety precautions necessary for your particular project."
http://www.ehow.com/about_4779244_dreme ... tools.html
http://messageboard.dremel.com/Topic2122-28-1.aspx
http://www.ehow.com/video_4800305_dreme ... tools.html

[Mark]

"The regenerator tube is just a regular pyrex test tube I bought off Ebay. The tube needs to be filled with coarse steel wool. Size 18mm x 150mm long. I tried cutting one shorter and the engine did not run. I needed the full length tube. You can cut these tubes with a diamond wheel and a dremel if you have to. The diamond wheels are cheap and only cost a few dollars."
http://www.freemansgarage.com/lamina.html

[vturbine]

Thanks Mark, I didn't get a chance to try the Dremel on a test tube today because I ended up building a metal jar (my first pulsejet) and spent the afternoon getting it to run.

Yes, also, I did originally buy the test tubes for some "lamina" hot air engine experiments. I'm interested in oscillating/acoustic engines. To me there are some parallels between pulsejets and acoustic hot air engines. Kind of like the relationship of piston IC and piston Stirlings. That's an area of interest for me.

[Mark]

As with any fuel, there is an optimal fuel/air ratio, so that you may find denatured grain alcohol works better than methanol or wood alcohol if the hole size is more suited to favor the ethanol. But I have found, all things being equal, with a matched intake/exhaust port, methanol is less fussy and not as likely to flameout sporadically.
I really like jam jars, there are so many little things to think about, so many variables. One thing you will notice is how much difference it makes if a jam jar runs outside in hot humid weather compared to starting it indoors in an air conditioned room. Summer heat and humidity really affects performance here in Florida.

[Mark]

Vturbine I don't know since you are new here if you have read Reynst's book Pulsating Combustion. If you haven't it's got plenty of pulsating combustion topics to consider, including solid fuels and devices other than pulsejets. I have a copy in three languages. All German and French texts were translated in English upon the request and with the assistance of Project SQUID of Princeton University, (it says at the beginning of my book). ha

[vturbine]

Vturbine I don't know since you are new here if you have read Reynst's book Pulsating Combustion. If you haven't it's got plenty of pulsating combustion topics to consider, including solid fuels and devices other than pulsejets. I have a copy in three languages. All German and French texts were translated in English upon the request and with the assistance of Project SQUID of Princeton University, (it says at the beginning of my book). ha

No I haven't, but I sure would like to, from the sound of it. Where is it available?

(maybe we should continue this away from the test tube question -- I've been having so much fun with the jar today, that I forgot to try the test tube cut again! But anyway, will do it maybe tomorrow and report back here in case anyone else has a similar problem.

Anyway, to continue on the solid fuel pulse stuff, it's located here --

viewtopic.php?f=3&t=5423)

[Mike Everman]

Links to the only copy of Reynst's book I have:
viewtopic.php?t=2256#p39501

[vturbine]

Ten pages into it. Amazing. Thanks so much!

[copperchic]

I have cut pyrex test tubes without any difficulty. I use special equipment that you would not have. I would be glad to cut tubes for you.