Author Topic: Ground glass joints from stems  (Read 1478 times)

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ApprenticeCook

  • Guest
Ground glass joints from stems
« on: March 13, 2004, 01:05:00 AM »
Swim was asked by another person a few days ago of some way to adapt a ground glass cone onto a piece of equipments plain stem, thought it would bee of use to share it with the hive. The example problem which was solved by this method was a separating funnel, plain one, turning it into a dropping funnel. Rubbers stoppers with a hole are ok but under really high vacuum they just dont cut it in swims experience.

Figure out the size you want to make the cone and get a stopper that size. Use the handle of the stopper and put it into a vice held by the handle.
Use a PROPER glass drill bit, dont try and use normal drill bit, swim destroyed a stopper seeing if it would work, all it does is digs in and shatters the glass in one easy step. The proper glass bits are cheap anyway, well find dead center and drill a hole the diameter of the stem + ~0.5mm so you can slide the stem in easy without having a huge space around it. This hole should go all the way through the stopper cone and a little of the way into the handle, this makes it easier to snap off the handle without breaking the cone.

Flip around the cone into the vice, be careful not to snap it in the vice grip, put some cloth around it works ok. Using a hobby hammer (little tiny one) slowly tap around the handle starting off light and getting harder little bit by little bit. It will eventually snap off, you may have left over glass on the top, that’s fine. If your hole is not all the way through, re do the previous step to make the drilled hole end to end.

Use a small metal dowel wrapped in very fine glass abrasive paper and run it up and down the hole  ;)  to sand off the side walls. Flatten off the top if you want but it does not really matter, as long as the hole is all the way through.

Slide in the stem very carefully, may take some Vaseline to let it slide in easier.
Slide the stem until it protrudes about 3-4mm past the cone.

Now this is the part swim was unhappy with, securing it in there, using epoxy resin (glass repair glue crap) run glue into the drilled hole if you can otherwise just seal the ends. What type of glue (glue?) should swim have used to remain vacuum, temperature and chemical safe?

Unfortunately swim did this without taking pictures so cannot offer it, but a repeat with swims own funnel and stopper is coming so photos will come.

The only problem is you cannot put weight on this joint, the entire funnel needs to be supported once the seal is made by the joint.
Thoughts on improvements for swims funnel?

moo

  • Guest
How about using a thermometer adapter of ...
« Reply #1 on: March 14, 2004, 02:52:00 AM »
How about using a thermometer adapter of suitable diameter? It is used for other equipment than thermometers too.


ApprenticeCook

  • Guest
Thought of that, as a method which is not...
« Reply #2 on: March 14, 2004, 04:26:00 AM »
Thought of that, as a method which is not permanently attached to the sep funnel, using an O-ring in the adaptor to secure the stem.

bio

  • Guest
Chem Rated Epoxy
« Reply #3 on: March 14, 2004, 08:53:00 PM »
"What type of glue (glue?) should swim have used to remain vacuum, temperature and chemical safe?"

Epoxy is good for many chems and new versions are good to 600F. Look for Novolac type Here are a couple links if I did it right. You won't find this stuff in the hardware store and it ain't cheap. For coating parts use the no filler or solvent Novolac. Also PTFE tape used to mold the glue provides a temporary virtually impervious barrier.

http://www.graphitestore.com/itemDetails.asp?item_id=246&prd_id=51&cat_id=4&curPage=1



http://www.graphitestore.com/itemDetails.asp?item_id=236&prd_id=50&cat_id=4&curPage=1



Make sure you sand the surface for adherance and don't put on any thicker than the spec.



http://


livid

  • Guest
re: glue
« Reply #4 on: March 14, 2004, 11:08:00 PM »
a chem resistant bonding agent that can handle high temps is jb-weld. the only problem with it is, it is not flexable. but as long as you bond to a solid surface, works great.