I learn how to make glass button stems. F project | EP#8 

As always, your behind-the-scenes videos are fascinating. I also really liked the Midjourney images given to the client, and then a physical object made of their favorite. Such a cool process.

I will follow up with a more in depth email but you are going through the same process everybody goes through when developing a new stem. The biggest standouts I see are you are spinning the glass a little on the fast side. It should want to collapse in more. You are going to need to polish those molds. Also you will need a center ring with a stem diameter this large. The inner ring should be taller than the outer ring and you are going to want to heat the inner ring with the torch pointed down and on the inside of the ring to avoid overheating the pins and the outer ring being heated by a softer flame. 3 national N-1 size tips fed with propane and air only and 2 center OX-1 size tip fed with propane and oxygen pointed down at the inside. One of those tips was angled in a way to heat the flared exhaust tube as well. That is the setup that was used for a stems about this size about this when I visited the company who made them for us. They also found they had to pre bead the pins to prevent over oxidation and black seal color. Mullard was able to get away with making the 9 pin stems that fast because they were pretty small and they would introduce a toothed wheel to mash the glass in towards the center, but mostly because the lack of exhaust tube. Makes the thermal dynamics much easier. Sylvania had similar machines. At Toryonic in New Jersey they make a similar stem to the 9 pin noval and they sat me down to show me how they did them. They used a home made machine much like what you are envisioning. After the initial heat they would close the mold enough to hold the pins in place and then paddle in the soft glass with a small graphite rod to coax it towards the center and around the pins then close the mold the rest of the way, then open it back up to reheat to get the oxide on the pins to fuse then press again. Each one tool about 2 minutes, but only one outer ring and no exhaust tube. The larger stems like this were made on modified litton D type sealers with 6 surface mix torch tips and then the big big stuff was made with glass preforms with the beaded and flanged pins sealed individually afterwards or housekeeper type seals. Keep going.

We use graphite as a mold material and use a circular burner assembly to apply even heat all the way around and that way the glass melted more evenly than with two burners

This is one of those mad scientist development projects. You just gotta keep trying more and more creative silly things until it starts going right. I love that you are sticking with it and experimenting freely without getting desperate for trade knowledge. You can totally figure this out and you’re gonna get all the credit, one of the best feelings.

Another advantage to manufacture in-house, which I learned from you: if, later on, there turns out to be a quality issue, it'll be way easier to fix the production line if you control it. Not that I expect any quality issues from your operation -- you seem pretty careful in these videos -- but it happens to the best of us. Congrats on landing a prop job for a TV show! That's cool.

I love the iterative design process. Also called empirical design. The 3 clocks for the TV show are sensational as well. I'd never considered AI as a design tool!

Have you considered induction heating the dies? Might help with the pin overheating issue

Congratulations on the TV exposure! It's well-deserved 😎

Fascinatingly complex engineering. I love your work.

I absolutely love seeing these videos about the problem-solving process! If I lived in your part of the world, I’d volunteer to work for free (I’m semi-retired) just to be able to be a part of the process 😁

May I give you 2 maybe crazy ideas: 1. Make the mold up-side-down, it is easier to use it as a storage for the glass you are melting (to let it melt into a form) rather than flat table when it tries run away. 2. Have 1 or 2 adjustable induction heaters for the upper and lower molds, to adjust the temperature slightly less than glass melting point. It would help with controllable glass melt process and (if you use 2 levels) keep the molds hot enough for the easier extraction. I was in Czech once in my life, hope I can do it again :) Good luck!

This is awesome. I have done a lot of research into making tubes for ham radio mostly. Thanks for the insights

Thanks for sharing your progress Dalibor! The design of this manufacturing center is a good illustration that Simple and Easy are not the same thing; in fact they are often opposite: a _complicated_ machine is often *easier* to design than a _simple_ machine. In this case, I would find it easier to design the carousel type machine than a single station machine. With the carousel design, each stage only performs one action, e.g, First Stage Preheat. This makes each stage pretty easy to design. Because the single station design needs to perform every different action, it needs to be much more complex than any of the carousel stages while still fitting in the same size envelope, and thus it is more difficult to design. As a manufacturing engineer, I would much rather design the carousel machine than the single station machine 😀

Thank you for the gorgeous cinematography.

I think that this should be a two-step process. The first step is to mold a glass base blank preform that has the volume and piercings for the pins. This would go into the final press which forms the base to its final form which means the pins can be kept clean and you can control the final draft fit to the final mold tooling.

These videos are so interesting, love to see the progress!

I think one thing you haven't mentioned anywhere that I can see is controlling the mould temperature. Given that you are dealing with large metal pieces with equally huge thermal mass - consistent mould temp (of, let's say, 20c below glass melt temp) might help a lot.

You are a fine engineer and an artist, and I wish you every success.

Great work as usual! Congrats on the TV clocks. I really like the 1N-12 version too. You should sell it!

Great work

❤a great throwback to my 1980’ies childhood, watching both Arabela and Návštěvníci on german tv broadcast. I am surely going to eatch this new tv series on ZDF in september! Greetings from Denmark

You gonna end up making CRTs :)

Perfect 👌

I wonder if the bottom half of the stem mould could be raised up and heated inductively. It could serve as a decent preheating option and it could prevent sticking and as an induction coil is both heating evenly and relatively low profile it could easily fit there in my opinion. It can also be water cooled and it is relatively insensitive to open flames

I would consult with a university scientific glass blower. Most have at least one of them, and they tend to be extraordinary problem analyzers and solvers.

Nice progress! One thought about the pins melting sooner than glass. How about the pins being on the one side of mold slightly preheated with the form. On the other side you would melt the glass with more powerful burner. And when they are both on the correct temperatures press it together? Problem is that the technical solution would be a pita to make work correctly in vertical position. Also on the problem of glass sticking to the mold. Use brass for molds, polish them and put bees wax on them before pressing. Or graphite. With the graphite you wouldnt have a problems with tighter tolerances after heating (and glass flowing where it shouldnt) and removing of cold finished stem. Also graphite doesnt need bees wax. Proper preheating of the molds before pressing might be critical for smother finish on the glass without wrinkles. Each mold material would have different temperatures for this, choose one with similar temp as ideal sealing temp for the pins. You cant polish the glass with flame or do a second pressing, because you risk melting the pins again. Last thing, with current setup, try higher rpms for glass tube collapsing further from the pins when melting it, centrifugal force is your friend in this case. When you decide to build the carousel machine, that document is a Holy grail!

woah I love the AI generated clock! such a cool idea!

That tv series sold itself to me with the chicken more or less escaping the oven 😅

I think you need a n ejector mechanism, where each pin has an ejector pin pushing up from below. The same way injection molding often works.

You in fact have 2 problems with this glass base and I'm relying on some anicdotes from when my father worked in these factories back in the 50s. The trick to glass is keeping everything hot and lots of pressure. You're press is ambient temp and do not have enough pressure which leads to rge glass cooling before it's properly formed

What about a 2 step molding process? A first mold that melts a glass tube into a thick ring with holes for pins, then the second mold stamps this thick ring into its final shape with the pins installed? It would let you heat the tube without the worry of melting the pins. This would also allow the batch production of "stem blanks" on the same molding equipment, and then resetting the machine for molding in the pins.

Good vid! Now do one on evap systems haha

Hi Dalibor, I think that you don't need a full 24 head carousel production tool. You just need one working position with two or three separately controlled burners, carousel of tooling heads and good automation. In the production carousel, there are positions for pre-heating, re-heating, controlled cooling, that don't require additional tool so your tooling carousel will be much smaller. Though you will be running at 1/24th production rate. It is very interesting project and I might be able to help a little 🙂(I am located in Bratislava). Good job.

Cool

Is it possible to retain the pins in the top part of the mold? Then melt the glass in the bottom part and press the pins in? That would give advantage of being able to heat the pins independent of the glass and possibly controlling how much glass adheres to them.

I feel like solid-state electronically-controlled heating would give you greater temperature regulation, so you would not overheat the metal, and being able to apply a heating and cooling profile would carefully control the process for annealing as well. Gas torches seem like a really difficult way to control heat for this process.

Have you thought about using an insulative material, like ceramic, to heat the glass on? I don't know how glass works, but metals tend to be very good at wicking away heat, so maybe that's why the bottom doesn't heat up as well? I don't know if glass would stick to the ceramic, though.

Zdravím Dalibore, ta pauza mezi #7 a #8 byla pro mě "nekonečná" 🙂 ale chápu že toho máte na vývoj až až. Moc držím palce abyste všechny problémy vyřešil co nejdříve. Můj obdiv k tomu co děláte neopadá. Mějte se moc fajn a nezapomínejte že je třeba i odpočívat.

I feel like separating the heating of the glass and the heating of the fixture would help a lot. Is it possible that you could drop a small slug of molten glass with high thermal capacity into the center of the mold while using torches to keep the mold and pins at a consistent pre-heat temperature?

One step seemed to be a roller that squeezes the glass into the gaps between the pins. Perhaps that is important?

Invert the mold such the bottom is larger diameter cup and top is smaller diameter insert; this prevents glass overflow beyond bottom cup diameter. Control hot gas temperature to well above glass melt point and well below pin melt point; glass will melt slowly but pins won't melt ever. Consider heating bottom cup such that glass flows which may remove need to spin the mold. Think glass casting. Think temperature controlled hot gas source (flame used now mixed with the right amount of ambient air). Think inductive heating the metal mold parts.

I wonder if you need a reverse draft angle on the top die? So it's almost like a blade then the surface area is small so it shouldn't stick but you can have tight tolerance to keep the glass clear, also maybe adding a mm of movement to one on the dies so they can get themselves concentric with each other during the press?

I think if the pins were pressed in from the top (press) mold you won't have the issue with glass on the pin contact area. Maybe see if you can find some old videos of vacuum tube construction. or see if you can find an old vaccum tube base press (or dies) as a starting point. Considering CRT tubes were still getting produced in the 1990s, I presume there has to some equipment available somewhere.

Maybe if the pins were placed in the upper part of the mold. Then glass could be melted on the bottom piece, snd rhen jam the pins through the molten glass.

It seems that in the documentary they used much longer pins and much thicker glass tube.

Fascinating work. What metal are the pins made from?

Typicall the stems are pressed twice. The reason is to get better flow, not sure if it is possible to do it in just one press. Between the presses, the stem is lifed up from the lower mold by the pins. if you apply even pressure you can lift them up, and then you can heat both sides to get excellent flow for the final forming press. That is the problem you are having that the glass on the bottom will not flow because the mold will cool it to much and you can't get heat there. From what i know, it will be tremendous more difficult to do it in just one.

Would it help insulating the two cast iron pieces from the mould support structure so that the heat doesn’t just get sucked out of the mould by the surrounding cold mass? Great videos BTW love this channel.

Maybe a silly idea or question? Why not use a disc of glass, and make a series of small holes for the pins. Then when the disc is melted, the glass does not have to flow very far to seal against the pins. Two thoughts on how to make the holes: (1) Use something like a small diamond drill bit (if such a thing exists). (2) Or, melt the glass in a mold to pre-shape it. The mold would create holes. Then in a later step, the pins are put in the holes, and the glass is melted a second time. Maybe this wouldn't work, because: (A) If drilling, the process is too slow for production? Also, the drilling process might contaminate the surface of the glass, and cause a bad seal? (B) For various technical reasons, maybe the glass cannot be melted more than once without causing problems? Sorry if these are bad ideas or questions. I know almost nothing about glass work and manufacturing.

The RCA document could still be useful for a simpler machine: the document gives you a description of the process. Whether that process is carried out on a 24-step carousel or on a simpler machine with only one working position, the process could be very similar.

I might have suggested this before, but my gut instinct tells me to try making the mold from graphite.

May be a different mold could help.

have you considered making an die to form the glass prior to insert the pins, and then transfering to this machine?

Any chance starting with heating the glass part/shape first then pushing the pins through would be better?

I wonder if a thicker tubing wall would help with the lack of infill?

I wonder if you could heat up the bottom mold. Not hot enough to make the glass flow, but enough so that it won't cool down so quickly. The 3D printer folks do something similar.

Isn't it the issue with how glass curls after being heated? From the old clips it seems that one glass layer should be enough, provided it curls properly. Besides observation that gas torches seem to be crucial as well, I can't come with any smart solution. Actually, I'd enjoy joining your effort even for a while to play with this problem - sadly I can't.

have you considered using a different material for a mold? Maybe graphite?

Hey @Dalibor Farný, I have a question. Are there such a thing as other noble gas nixie tubes? Ones that glow different colors or something?

will it be possible to make a keyboard the font light with nixie lights

Have you tried to first make something like a small disc with holes where the pins need to go and in second phase put this disc together with pins in the mold and make final part?

Not hindered by any form of knowledge I would like to offer my 2 cents: How about to make the glass ring and drill the holes for the pins in the glass ring and then secure / seal them by melding the glass.?

I wonder if there's an old carousel machine sitting in someone's shed, waiting for you.

Maybe you came up with the solution yourself, but to counter the "overflow" just remake your molds, so that the bottom mold has the outer lip that stops the glass, or make a spring loaded two part top mould.

Вы не думали попробовать сделать форму из графита? Мне кажется, он лучше подходит для данной цели. Стеклодувы используют графитовую оснастку для производства сложных химических реакторов.

Uninformed comment from left field: is an epoxy base possible with an epoxy-based bond to the glass? Control of the epoxy would be much easier and more predictable.

Do you plan on making triodes in the future?

Just wondering if you are still using boro Schott, or trying any of their leaded stuff? My boro supplier is UST in America. They claim they are the only Schott importer in my country. I want a few cases of leaded crystal for it's acoustic properties, but they'll only supply it unless I buy the whole shipping container 🤦

A bit of 'Fringe' and a dash of 'X Files' maybe ?....cheers.

Maybe you could just use a lot more pressure? With a hydraulic press or something to force the glass to flow into the centre. A shallower draft angle and tighter clearances might be workable if you add ejection pins.

Dali can you share a link to that friend of yours who is trying to revive CRTs? Because I really wanted you or someone of your caliber to tackle that problem next! :D

No hlavně v tom videu z produkce je jeden hořák, co žhaví do skla a další tři, co žhaví formu ... pokud se dobře dívám.

jedine co ma napadlo bolo pouzitie elektro indukcie k ohrevu tej spodnej casti na zvolenu teplotu..nebolo by to jednoduche ale mozne

Can you really sell 20000 tubes/year? They seem like an extremely niche product.

It’s “a way to” or “how to.” It is grammatically awkward to say “a way how to.”

Amazing progress! Is preheating the glass in an oven to just below melting an option to make it melt better? Or making a preformed glass blank like @kentswan3230 mentioned.