Chriske

34 minutes ago, JamesF said:

So is it fair to say then, that when it comes to 3d printing, you're completely nuts?

James

Please do...

???

I hardly tap in my printed parts. Only when there's little or no force involved I use tapped holes.
Where there's a force involved I always use nuts to fasten the parts against each other.
In this part the upper-right hole I put a M3 bolt. About 15mm lower there's a 'square' hole. That's the hole were I insert a M3 nut. I use this system all the time. Makes mechanical connections even stronger. And what's more, when inserting a nut it never wears out if the bolt has to be removed from time to time. And second I don't worry at all destroying the thread when I firmly turn the bolt.
That square hole is a press-fit, so the nut will not revolve in it's hole.

If Table5.3 higher up in this thread will be redone using this technique, well,  it would look completely different.
I use this technique for many years now and it has never failed me once.
While drawing, It's a habit,  I even don't think about it anymore, it's  become standard to me to install that nut.

I'd use PETG instead if you still want to use even stronger stuff and filament that has a higher glas-temp.
It'll do for most of our projects imo

And If my information is correct ...hum...you did order 'one or two' reels of filament a few days back...?...?

1 minute ago, Gina said:

ASA filament is supposed to be UV resistant.

Common Gina, you don't mean this...
I will tell you a lie if I intend to sell you my product, in fact I tell any lie to reach my goal.
Maybe, just maybe, it'll resist  a bit longer compared to other plastics. Plastic UV-resistant..? that'll be the day...

And there's one other thing about PLA : Biodegradable ..?
Yes it is,  but takes YYYYYYears to do just that. But eventually it does.

The main reason I use PLA is because (in the end)it IS biodegradable(basic ingredients : corn  + printing ABS you need to suck these micro-particles (dust) out of the printer. And it smells awful...

10 minutes ago, upahill said:

 you only need to look at what UV exposure did to me to see the risks ?

Got a picture to verify this...?

Hold your horses guys...!

I ONLY tested whether white PLA would sag or deform under constant sunlight. Nope it doesn't, not at all. It does what it suppose to do, for me. It hold its shape.

What I did not test is whether PLA would degrade under sunlight. UV surely will degrade almost everything in sunlight..!  PLA or other filament is no exception to that.
Can someone name me one other plastic that does not degrade at all.
To prevent printed parts from degrading under UV you'll need to paint it. Using parts, say a telescope, most of the time during nightly observations don't bother, it'll hold for many years without painting.
As a matter of fact all things, except bricks a, concrete, we paint everything that needs protection, why would PLA be an exception...?

And btw, I only buy white PLA and PETG...

 2 years back I've tested different brands of PLA and also a few different types.
To make a long story short.
Hollow rings (150mm diameter) hanging in the burning sun all year long. Started with 0.5kg  weight and after a few days filled the bottles  to 1kg.
In the pictures were 2x PLA(black and white) another was nGEn and XT.
The absolute winner was PLA that had nearly no deformation after months in full sun.

The walls of the rings were only 0.8(!) mm thick.

Yep, black is not the best choice to make telescope-parts when observing(to long) the sun
That"s why I print all outdoor applications in 'pristine' white using PLA.
PETG is far better for outdoor applications.

5 minutes ago, Gina said:

I think most black filament will pass IR.  This makes it unsuitable for a lot of astro applications.

16 hours ago, Gina said:

I get worried when anyone starts mentioning telescopes and the sun particularly when it is suggested or hinted at of putting any sort of plastic within a telescope or at the eyepiece end.  This can be very dangerous. 

I made a (almost)fully printed 250mm f/6 Dob (Printsonian) I'm always careful working with it while observing the sun.

Hi,

Made a platform myself, and what I did was knurled the driving axis. It improves grip on the platform itself.
 

Chris

Dave,

Can we have peek how your CNC cutter looks like. Most curious, my pal Marc is busy building one.

Chris

If people would not buy that ultra cheap stuff this wouldn't happen in the first place.
A few days ago I found a 179€(!) printer on the net. Build volume 220x220x250 + heated bed.
In the add they even mention : all parts are precision made....!
This is a heap of nonsense..!
Oh, and they also mentioned : beside the manual(there's no support from the shop were it was bought)

On 10/11/2018 at 14:08, Dr_Ju_ju said:

Have a look at this

 

On hold...
We've decided to (maybe) install a cam combined with a zoom-lens to capture the focograms.
That zoomlens is needed to cover the entire area of the chip. The bigger the image the smaller details can be seen . An example of a very detailed focogram is posted higher up in this thread. Using a regular webcam(even with the lens)the image is WAY to small. So I need another solution.
A disadvantage of using my camera(as I always did in the past) is that I can not go 'live'. Meaning after the focogram is taken I need to connect my camera to the PC to have a look at the images on screen.

I have no experience with cams and other stuff. So my question : is there a good quality webcam(or other USB device) I can use to view 'live' images. I do not need the lens, I would use an old zoom-lens instead. Or maybe there is some other good device with a zoom-lens to do the job...?
Preferably not to expensive...
 

Damian

there's a never ending discussion here whether Ronchi or Foucault is best. As a matter of fact I never use Ronchi. Reason :  the only value is that Ronchi will give you only an estimate how the curve of your mirror looks like. In the end when that spherical mirror is ready to 'go' to a parabola you absolutely need a Foucaulttester.
What's more all de very small and 'delicate' roughness visible in a FT is not visible at all in the RT.
Look at the focogram higher up in this thread. That mirror has severe zones and on top of it it has scratches and microrippel. Again, there's no way you'll be able to see all that in a RT. And a another thing, when a mirror is not completely polished out, it'll be clearly visible in the FT, not in the RT.

kbrown,

Pinholes for testing optics should be as small as possible, but most of all it needs to be absolutely round. Another important point is using a thin object to allow light to pass through.
I always use a (very)thin sheet of brass and make a hole in it with a needle. Then I carefully sand it to remove all burrs that are made by the needle. Next I gently push the burrs that are forced into the hole(during sanding) outside and sand again. I repeat all this until the hole is completely clean and absolutely round.
During this operation I take care not to push the needle deeper every time the hole is 'cleaned up' by the needle.
Do not make that little hole to small of course.

Checking is done with a magnifying glass.
Lots of info is found on the net. This is one of the many. It does not tell how to make that hole, but gives lots of info about that hole and what to expect from it.
Info 'how to make' I got from Ingalls's books a very long time ago...

A printed pinhole is not a good idea. Because that hole is not 100% round and it is made out relative thick material it will result in extra and unnecessary diffraction.
 

One more thing : that 10" f/3.6 mirror(in that focogram) is completely polished out. There is that strange very fine pattern all over the mirror. That is caused by the polishing-pads. When the pads are replaced by pitch that pattern is  all gone in a matter of minutes. But before switching to pitch these rather huge zones must be removed of course.

Rough...?????
I call that VERY rough...!..
Like I said, this mirror is made while testing our M-o-m's.  In fact we were testing different strokes and also different positions of the tool. And this is the result, se-ve-re zone. But hey, with a MOM, removing these zones is a matter of minutes. In the old days (when we all made mirrors by hand) and would see this on our Foucault stand, the only solution to remove such a disaster is go back to grinding again. Polishing out zone like in that picture higher up would have taken us hours, even days.
My pal and myself have both one MOM btw. Mine is 'loaded' with a 20" mirror right now.

btw... Lucky we made these mistakes. It gives us an insight how such machines work, and most of all how to correct these errors.

This little camera is really superb indeed.
This is focogram taken with that little guy when we were testing our M-o-m's.  Incredible fine detail, ....and a few scratches...

Y-carriage was already printed, but I decided to add a compartment to hide all the electronics :
1- Switch
2- LM2596 'DC-DC stepdown' for the green laser.
3-Potentiometer for the LED. sometimes I need to check a coated mirror, so I need to dim the LED a fair amount.
4-Space for a small jack to connect to the power unit.

Left the old one, right the new one
All wiring will be hidden inside the unit. I made a few canals to lead the wires from the front to the back of the Y-carriage.

26 minutes ago, kbrown said:

Am I correct thinking that once everything is aligned properly, you only adjust the distance of the knife from the mirror? Does the light source and camera move with the knife?

When busy polishing you know the ROC of that mirror, so you first place the tester at the correct distance from the mirror indeed(does not have to be 100% perfect, but as accurate as you possibly can. I always use a tape measure) minor corrections are done afterwards. Then you point the laserbeam to the very centre of the mirror. Pointing that beam toward the mirror's centre is done by pushing and rotating the tester manually(there are also 3 set-screws at the bottom of the tester. These are for kinda 'levelling' the tester.
When that is done, the only thing left to do is 'levelling' and rotating the mirror on it's stand until the laserbeam hits a small plane(I explain about that later.
Needles to say this can only been done after that initial set-up I described higher up here is performed.

Yes, camera, knife and LED all move together on the Y-bed

There are a few holes in the camera'disk'. These holes you need to stick a pin in to fix that disk/camera in a certain position. Here too you need to set-up/adjust the camera only once. When that is done you need to remember what hole to put that pin in. When busy visual work, rotate away the camera. When taking a picture rotate the camera near the knife, put the pin in the correct hole and you're ready to make that next focogram. The reason for these many holes is to be  able to use any camera at all.

it all takes far less time to do all this then me typing this 'how to'. ..!!!

Steve,

All my designing is done in Autodesk Inventor. It is very powerful 3D-software. AI is not free, it is actually rather expensive. But I do have a license from my work in the past. It's already an old version but I can do everything I want to and more. It is in fact so powerful that I only use about (and I'm guessing here) 10% of it's features. But as I said before here on the forum. When you have a son/daughter still in school, you can download a student version for free. Maybe you're a student yourself...? If you download/install you need to give a name of a school.

All my printing is done with a printer I designed myself. UltiPrinter I call them. This very moment a few friends and myself are building five V3 of this printer.

Y-platform and X-platform-bearings already installed.
Printed with .7 nozzle

New laser-holder
printed with .4 mm nozzle

These parts from V1 will be reused