Questions from GF Skeptics on FB


#1

Here is a list of questions pulled from a geekwire article debate that I didnt have all the answers to. Maybe @Dan or other glowforge staff can clear some of these up?

  1. Custom Tube: Designed by who? to what criteria? Resonator Physics is an applied science and not just a case of making a glass pipe with a couple of mirrors in it, to design a new tube takes a LOT of money and time.
    OR
    Is it just another buzzword to market a batch order of tubes from TongLi with a glowforge sticker on them then charge propriety prices for replacements because nothing else will fit. (something like a 75mm diameter body or such like)
  1. How long will the machine run for before it’s too hot to use? what cooling is possible to get rid of the 90% latent heat produced by a DC tube?
  1. How long is that TINY filter going to last when it’s used to cut MDF? are replacement filters expensive? if so,how much?
  1. What’s the fire resistance rating of that plastic case? how easy will it be to get a tube if one fails? what model do they have for shipping fragile glass tubes round the world?
  1. How many lens’s do they have available as replacements? How do you go about cleaning the thing when it’s covered in crap? where is the raised emergency stop that is required by law on Laser Cutters (see the above about UIN numbers)
  1. When an HT arc has nowhere to go it can jump a good distance, what earthing is there?
  1. Are things like optics and tubes user serviceable?

#2

Also unable to answer any of those, though for a few I don’t know what they are asking (what precisely would user service on a laser tube mean? Just replacing it, or full recharge? And while I thought I knew a ton about electronics and distribution, I have no clue what an HT arc is).

But, chiming in to inquire what the FB source is, a GF usergroup, or the Geekwire article itself? The later makes sense, I should go look for where their page is. But if the former, I am curious to have an ear on all of the various communities, and that discussion isn’t in the one FB GF page I am aware of so far.


#3

This is from the laser engraving and cutting group on facebook: https://www.facebook.com/groups/441613082637047/
as a response to someone who posted the geekwire article, which caused quite a stir.

I think the tube service question was more about replacement. Either way, I wouldnt mind knowing the answers to most of these out of personal interest, and to also be able to respond to those who ask. They seem to be reasonable questions, and I would probably ask the same if I were a more seasoned laser user.


#4

I guess the venom is to be expected when major innovations tend to make existing machines look inferior.
from that perspective, the condescension could be seen as flattery.
Glowforge isn’t even in production (as far as we know) and features are already being emulated.


#5

Some of that is definitely shining through. The title was enough for a fair number of people to start trash talking, as was rather misleading. However I know there are a lot of people on that board who are considering purchasing a glowforge and I would rather supply them with correct information than them only seeing misinformation posted by naysayers.

There also seem to be a number of people who are a bit more skeptical and just need some more solid information before purchasing which is completely understandable. Its a big risk to trust someone with $4-5k knowing as little as we do.


#6

An HT arc is a high tension (voltage) spark. I think CO2 lasers run at about 10kV, which would jump about 10mm in air. They need about 20kV to strike though and I think if the PSU is open circuit it can generate a lot more than that. I heard this: “The arc we were drawing from the live end of the tube was aprox 3 inches long, very fat and quite angry” from a local hacker space that have a cheap Chinese laser, so that would be about 75kV.

At the currents involved contact with an arc like that would be lethal. Normally laser cutters have a metal box that can be earthed. I wonder how GF make it safe in plastic. Presumably with very thick insulation. There would also be a fire risk as an arc is very hot.


#7

Some of these questions are not answerable, some just being negative about the concept of a low cost laser cutter, some are legit. My thoughts.

Guessing that the engineers that have designed and manufactured the tubes know a lot more about resonator physics than the person asking the question. GF has already received and is testing custom tubes. Initial reaction was that they were pleased. Only time will tell.

There has been a lot of info from the company about why they went the custom tube route. You can think of it as just a marketing scheme or take the answers at face value. Not going to worry about motivations, just results.

The system has internal cooling and is set up to operate within the cooling plan. They had a plan. Don’t know how well that is working and not going to second guess the design without data.

How long is the filter going to last? It depends and no production data exists. I couldn’t justify the cost of the filter unit, so don’t care.

Fire resistance? There is a topic titled “Fire Risk”. Read it.

How easy to get a new tube? Same as getting any other part. You order it from the company and if they have done their job it ships. If they are asking whether a custom tube will be available outside of the company logistics stream. Maybe eventually, probably not soon.

Shipping of glass laser tubes? Done every day from China. Not hard.

How many lens do they have for replacement? Today, zero. When the unit starts shipping, and if they have done their job right, enough. It’s called logistics. BTW: the lens are fully enclosed and out of the smoke stream. The windows might have to be replaced someday but cleaning is recommended and as of a month ago GF has not had to do even that.

HT Arc? Not even sure how this question relates. It’s not a Plasma Cutter or a super high power laser. Don’t see that type of arc occurring. And it’s a plastic case.

The tubes are user replaceable, as are the window. Easy replacement of other optics, maybe not on anything other than at the module level because they are enclosed. Might not ever need replacing.


#8

Agreed.
My anxiety with the blind date is tempered by Dan’s track record, his ethics that have been on display and his availability to answer questions here - not to mention my clawing desire for a glowforge!
Even without the ability to pose questions here, anyone who really wanted more information could browse the forum, gain a little insight and know as much as we who actually have money in the game.
As for the rest, they will have to wait just like us. it is apparent to me that Dan has done his level best to keep us informed.
That said, I stand with you in my desire to have the answers.


#9

Actually when you are using a transformer to produce that high of voltage from 110v outlet it’s is static voltage. Yes it can be lethal if contacted by someone with heart condition, but being hit with 75kv static voltage is not lethal for anyone relatively healthy. I do hipot work and have been hit to 70 plus kv when a high voltage cable fails and bleeds back thru the shield. It will burn, blister and cause bad spasm if hit directly but no real current is present and that is what kills you not the voltage. Big misconception about arc is that it is high current only, the most lethal are low voltage high current arc but in this case you are talking high voltage extremely low current arc.

I cannot say what current they are inducing in this case but a point of reference is double the voltage half the current. An example is a 230 volt 3 phase electric motor that is 10 hp will draw around 30 amps and at 460 volts around 15. If you purchase a 10hp 575 volt motor you run 10 amps. So on and so on.


#10

…and piss you off at the speed of light!


#11

The current going into a laser tube is relatively high because they are very inefficient, 15-25% for CO2 so for 45W out it could be 200W in. That is 20mA at 10kV and that certainly isn’t static!


#12

Bleh. I hate when people make new terms for things. Granted, I assume HT has been a term for a long time. Just so pointless to call it tension >< How many people outside of the Navy would deal with high tension lines and high current power at the same time? Anyway… drop the analogies when you get out of the intro courses.

Personal rant aside… There are myriad ways to ground without having a full metal case. Like having the laser tube ride on a metal rail and having that grounded. I would assume they have done that much, and so unless you are closer to the malfunctioning tube than the rail it is riding on when it fails… no worries.

Anyway, lots of the list is questioning things which can only be known when units are in the field really. Though I did notice the filter one this time reading through and remember a topic long ago about the filters where it was stated you can quite easily put your own filter packing inside the filter case.


#13

Worked for the Navy my entire Electrical Engineering career. Never heard of the abbreviation HT. But then again 99% of my design work has been with computer level voltages and circuitry. Doesn’t count that I took power electronics in college if I’ve never used the theory.


#14

Very possible you are correct and I am very wrong, I know nothing about laser tubes just about testing height voltage cables and switchgear


#15

THAT will get your undivided attention!
Cool to watch the arc rise. I would expect the air around it is ionized so the hot plasma carries it up.


#16

Don’t think the innovations are the source of the venom. The innovations claimed (real time autofocus, camera detection of and alignment to material, etc…) are REALLY REALLY badass when compared to similar machines intended for similar use cases in this price range. There’s really nothing that anyone can say against GF if all those improvements work as claimed.

The issue is that these are super basic considerations for ANY laser cutter, and even the most crappy Chinese cutters more or less have this stuff covered (easy to service, required safety interlocks,** laserproof enclosre**, external water cooling for tube, high efficiency and suitably sized filters, etc…). In many cases, the basic features appear to be inferior to the most basic offerings currently on the market. Without info directly from GF it’s really impossible to tell either way.

But they are reasonable questions and should be relatively easy to get an answer from GF if you have access to the forums…folks on geekwire / FB / wherever maybe not so much.


#17

Not to mention the it would just be idiotic for glowforge to not do most/all of these things from a support/liability perspective. They would be shooting themselves in the foot. However the issue is that they arent 100% confirmed, so people will find any reason to nitpick. I tell myself it shouldnt matter to me what other people do with my money, but I feel personally invested in glowforge, and I like them as a company, so I feel a bit offended when people pass misinformation off as fact just because there isnt a solid quote from dan or staff to prove otherwise.


#18

when I was little, I asked my dad why they called the big power lines on the large transmission towers high tension lines. They looked kind of droopy to me, not at all tight. He never could come up with an answer. Went to Germany as an adult and saw a sign “hoch spanung”. Same question. In Italy, “Alta tensione”. Still droopy lines. In physics class it was always about voltage and amperage and power. Never did get an explanation about high tension other than still think it has to do with the stringing of the wires and not at all with the stuff that kills you.


#19

“Tension” is a French word for Voltage.


#20

Tension is a synonym for voltage. It was used before the term ‘voltage’ was introduced, when electrical concepts were still new and poorly understood.

See for example the following quote from this web page:

Volta defined electrical tension as the endeavour of the electrical fluid to escape from a body. Volta’s
tension was more akin to a force, unlike the modern definition of
electromotive force, which is a misnomer, being defined in terms of
energy.

I don’t know why people continue to use ‘tension’ today; it doesn’t accurately describe voltage and it doesn’t make sense to continue using it.

So ‘high tension’ is just a poor way of saying they are conductors with a high voltage between each conductor and to earth.