<glowplug>
Agreed this is not easy stuff. It will be very painful and slow.
<glowplug>
The only way to know if 1um is possible with this design is to try it. =)
<Sync_>
I'll see tomorrow if it is feasable
<Sync_>
I have no small angular contact bearings but that should be no problem
<glowplug>
You have some way of making them?
<Sync_>
I'll just order some
<Sync_>
making bearings is no fun
<Sync_>
and 7200 angular contact bearings are like $4 each
<glowplug>
Is that like a rollerscate bearing?
<Sync_>
no
<Sync_>
a rollerskate bearing has no angular contact
<Sync_>
which is important here :D
<glowplug>
Back!
<glowplug>
I did not know about these. They are just more robust in radial and axial directions.
<glowplug>
Do you plan on trying to copy the design I linked earlier (the aluminum one)?
<Sync_>
it's not about being more robust
<Sync_>
you can preload them in O or X configuration to get a precise spindle constraint
<glowplug>
So this bearing is going to hold the end of the threaded rod.
<glowplug>
I was going to buy a rollerscate bearing. Good thing you said something. Haha
<glowplug>
I've never done preloading so I have to figure all of that out. The design says "anti backlash nut" I'm assuming thats where I put my normal m3 hex nut?
<Sync_>
yes
<Sync_>
the problem is with a regular bearing that while it supports your piece radially and axially it does so with play
<glowplug>
Alright. I'm not sure that m3 antibacklash nuts exist.
<glowplug>
Which is insanely important. So preloading it keeps everything level.
<Sync_>
huh. there seems to be standards which specify m8x0.25
<Sync_>
well the preload forces the assembly in a certain position
<glowplug>
.25mm pitch????
<Sync_>
yes
<glowplug>
I wonder how expensive that is per meter. o.O
<Sync_>
I guess you are not going to get threaded rod in that size
<glowplug>
Alright so the "Remote Detector and Interferometer" boxes.
<Sync_>
yes
<glowplug>
They take in one beam, offset it, and read the reflection with some optics?
<Sync_>
yes
<Sync_>
you get a fringe pattern
<Sync_>
and the intensity varies
<Sync_>
which you can read with a photodiode
<glowplug>
I know how interferometers work. =)
<glowplug>
I figured out what those mysterious boxes are. They are "linear interferometers".
<glowplug>
A system like that might be more difficult and expensive (due to need for increased optics quality) than just having two seperate interferometers.
<glowplug>
Which this really is two seperate interferometers operating off of a single beam source.
<glowplug>
Yeah I'm going to try it the other way. Lasers are cheap optics are expensive. Screw that. Haha
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<Sync_>
well you are only going to save one beamsplitter
<B0101>
yikes... chlorine gas is never fun to play with, more so when you have a gas leak in your test chamber
<glowplug>
You save all of the internal components that comprise a "linear interferometer" which is tons of mirrors, a beam splitter, and a retroreflector. The system is also very very sensitive.
<glowplug>
You have to be careful dawg. O_O
<Sync_>
huh how are you going to make a interferometer with just a laser?
<glowplug>
They are called "linear interferometers" but its confusing.
<glowplug>
They are really black boxes with tons of integrated components. Two of those are added to the configuration to make it work.
<glowplug>
So you have all of the necessary components of a single interferometer. Plus the two black boxes which are extremely complex. Plus massively increased system sensitivity.
<glowplug>
It's getting late though going to bed. 8)
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<Sync_>
glowplug: the integrated linear ones seem to be just michelsons with retroreflectors
<Sync_>
yeah two prisms and a beamsplitter will do
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<nmz787>
there's a video online of a $20 interferometer
<nmz787>
using a CD case, laser pointer, mirrors and a cheap lens
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<Sync_>
I just ordered some stuff from EO
<Sync_>
you can make one for under $200, that's not too bad
<nmz787>
if you just need micron-ish resolution, you probably just need something like the $20 one and a photodiode and comparator or schmitt trigger
<Sync_>
prisms are cheap and beamsplitter glass too
<nmz787>
if you want better res then you need to keep the sinosoid pretty noise-free, and get an ADC instead of the comparator/schmitt
<Sync_>
well, if it only has to have micron resolution I'd use glass scales all day long
<nmz787>
that's not consistent as interference though, so I guess it depends on your goal
<nmz787>
heh, I don't like suppliers that don't list prices
<Sync_>
I don't care, I pay what they want
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<Sync_>
but actually it is not that bad nmz787, if you get chinese ones with 500nm resolution they are like 200$ for 70mm length
<Sync_>
and not much more for longer ones
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<glowplug>
Good morning. 8)
<glowplug>
I agree with the glass scales being very accurate but we already have *some* amount of mechanical accuracy built into the system via the leadscrew assembly. The interferometers will be a reliable way to know if something else in our system is broken instead of guessing all day.
<glowplug>
nmz I agree they can be built for very cheaply. My current plan (need to update the wiki) is to buy a giant piece of 50/50 glass and CNC hundreds of tiny 10x10mm squares out of it. That gives you $1 beamsplitters with extremely good optical quality.
<glowplug>
In terms of replicating the linear box units lets call them. As you increase the amount of sensor positions in the beam network you multiply the system sensitivity by many times.
<glowplug>
I still think that two beam sources will give the best price/performance/reliability ratio.
<Sync_>
well if you have alot of 50/50 splitters a second source is a waste
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<glowplug>
That is technically correct. But aligning the system with a second beam is many many times more difficult.
<glowplug>
The alignment instruments need to be many times more precise. And I'm not sure if the quality of the optics I mentioned is high enough for a setup like that.
<glowplug>
The optics they are using in the PDF you linked are probably $10,000+
<Sync_>
I just ordered stuff from EO to try that
<Sync_>
I like the idea of using prisms for the beam return
<Sync_>
that way you can shift the receiver diode a bit
<glowplug>
Good luck. Haha
<glowplug>
The prisms can be fashioned from multiple standard mirrors correct?
<Sync_>
yes but it'll be annoying to align that
<Sync_>
and they are only $29
<Sync_>
:D
<glowplug>
$29 each! Ouch..
<glowplug>
You can get another HeNe tube for $50.
<glowplug>
This is why I abandoned the single beam idea.
<Sync_>
wat, you need the prisms anyway
<glowplug>
For two standard michealsons you only need beamsplitters and mirrors.
<glowplug>
And two beam sources.
<Sync_>
yes but that is not as compact
<Sync_>
with two prisms and a beamsplitter you can move the receiver to the side of the input beam
<Sync_>
which is cool
<Sync_>
and $29 per piece, come on
<glowplug>
That is extremely cool. But I have plenty of desk space and not very much money. HAha
<Sync_>
that's not too bad
<glowplug>
I'm shooting for $29 for the entire assembly. 8)
<glowplug>
I wonder is it possible to put the entire thing under vacuum. That would make the lasers more accurate and reduce the chance of contamination.
<glowplug>
Everything is electronically controlled anyways.
<Sync_>
then you cannot make it out of acrylic
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<glowplug>
Why not?
<Sync_>
outgassing properties
<glowplug>
There are retail acrylic chambers that pull 30"
<Sync_>
yes, but 30" is not really a vacuum
<Sync_>
at least from my vacuum perspective
<glowplug>
I knew that was coming. Haha
<glowplug>
I agree that is not 0 torr but it would still greatly increase laser accuracy and greatly reduce contamination for a very low cost.
<diginet1>
the best way a DIYer can get a vacuum is a bell jar
<Sync_>
and then do what? suck on it?
<Sync_>
;)
<diginet1>
acrylic is just about the worst possible thing I can imagine for vacuum stuff
<diginet1>
Sync_: well you need a pump too :P
<diginet1>
but I more meant for the chamber
<glowplug>
I wonder why they sell $2000 acrylic vacuum chambers then.
<Sync_>
to outgas resin
<diginet1>
yeah, calling that a "vacuum" is a bit of a stretch
<glowplug>
So the acrylic chamber wont hold any amount of vacuum that is useful for increasing beam stability and reducing contamination.
<Sync_>
I mean, yeah it is lower than atmosphere but oh well
<glowplug>
That just doesn't seem realistic.
<glowplug>
Remember it's a $500 litho device. No need for a $1500 bell jar.
<Sync_>
I'd just put some shields
<glowplug>
It basically is a shield with a low vacuum.
<glowplug>
I mean... maybe its not worth the extra ~$50.
<glowplug>
But something that both improves beam stabilit and reduces contamination for such a low cost is at least worth examining
<glowplug>
*stability
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<Sync_>
nice
<Sync_>
that came out pretty well
<glowplug>
?
<Sync_>
just made a spindle
<Sync_>
rather amazed how backlash free it is
<Sync_>
only the material pairing isn't the best
<Sync_>
yeah I'll need oil but then it'll work fine
<Sync_>
pitch error is very low
<Sync_>
under 1/100mm in 5cm
<Sync_>
backlash when properly adjusted maybe 200nm
<Sync_>
but that is probably my setup
<Sync_>
because it cannot really have backlash
<Sync_>
the next one will have a brass nut and case hardened spindle
<Sync_>
yeah :) I like it
<glowplug>
Holy crap that is great!
<glowplug>
What material did you use for the stage?
<Sync_>
I did not build a stage yet, just the spindles
<Sync_>
I'll probably use aluminium
<glowplug>
How did you test the spindle accuracy?
<Sync_>
mahr extramess 2001 and gage blocks
<glowplug>
Aha! I see!
<glowplug>
And your leadscrew is standard .5 pitch stainless?
<Sync_>
no
<Sync_>
aluminium, cut it myself
<glowplug>
Your joking? That is seriously fantastic!
<glowplug>
I would buy that from you in a heartbeat! How much for 200mm? Haha
<Sync_>
I'll verify that next week but it looks quite acceptable
<glowplug>
I was actually going to look at alu I saw it mentioned. I would totally buy some as soon as you think they are ready. You made them from M8 rod?
<Sync_>
no, I took some stock, turned it to 7.90mm and cut a thread
<Sync_>
bb in 15
<glowplug>
So it is 7.9mm in diameter. That is A LOT better than the m3 rod from mcmaster.
<Sync_>
no shit
<Sync_>
that's why I wanted to do it that way
<glowplug>
Easy there! Haha
<glowplug>
I know it's better thats pretty obvious. I just didn't realize you had a precision lathe and mad skills. =)
<Sync_>
I'm more or less amazed that the pitch error is that good
<Sync_>
gotta verify that after my exams
<glowplug>
Me too thats awesome if it works. =)
<Sync_>
but in reality it does not matter
<Sync_>
:D
<glowplug>
Why is that?
<glowplug>
It matters for me I'm the first customer of Sync_'s Custom Aluminum Threaded Rods Inc.
<Sync_>
because if you use closed loop positioning with the interferometers only backlash will hurt you
<Sync_>
but for that to work you need a very rigidly coupled system
<Sync_>
and no backlash
<Sync_>
but the next ones will be made from c45 steel and brass nuts
<Sync_>
the Al-Al pairing likes to bind
<glowplug>
Ahh so you will be using steel. Can your lathe cut steel?
<glowplug>
I think we can get rid of backlash pretty easily using the DIY spring method.
<glowplug>
And I agree about positioning otherwise. As long as we have good absolute feedback the accuracy of the leadscrews is not super important.