“DIY” Spectroscope – the next chapter…

[Tony Rodda]

It’s well seen that January has been a miserable month for observations.

So, having taken delivery of a large box of goodies from Ken Harrison (lenses, gratings, mirrors,splitters, prisms, etc) and a new Wanhao 3D i3Plus printer I’ve set to work on Paul Gerlach’s LOWRES spectroscope as a first instrument.

I un-boxed the printer today and set about printing the smallest components for an easy start.  After a few false starts I’ve printed the first four bits.  Not huge progress but gathering speed and I’m happy with the initial quality.  I reckon a few days and then I’ll have a platform for experimentation.  

I’ve set up a workbench and will start playing with various configs. Adopt and adapt.

As another example, I’ve seen a UVEX from Christian Buil that looks good and I’ll try anything else that pops up. 

I’ll have two or three “proof of concepts” to discuss at Newcastle (5th May) and Warwick (7th July) if anyone’s interested.

The pic shows lens holder, mirror holer, etc.  I’ll attempt the body/sides as soon as I can shake off my wife…

Regards

Tony

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[Dr Andrew Smith]

3D printing seems about to revolutionise DIY astronomy. I look forward to seeing your work in July.

I do wonder how stable the parts will be compared to say aluminium alloy?

Regards Andrew 

[Tony Rodda]

Yes Andrew, lots of questions about strength, stability, etc. but we have to start somewhere and even my little printer duplicates in about six different materials.  There’ll be one (or more) that proves suitable. 

Plus, as you say, it’s the manufacturing process that is revolutionary but if we need a part that needs high strength (and say “Carbon” won’t do) such as the ‘scope end plate that takes a lot of weight, then I can make specific/individual parts in metal or buy/adapt ready available screw adapters.  But that’s a bit of plate work – you don’t need an experienced lathe operator for the complex stuff. (McClaren are printing complex gas flowed inlet manifolds in titanium if you fancy a £500k printer but that defeats the object!).

My current ‘production run’ is only to construct test beds.  One to use and evaluate the actual practicality and accuracy of the spectra produced (and it’s resolution, etc.) in various materials and one to ‘hack about’ with different lenses/grating, etc.  I hope to do that for each design ‘out there’.

I produced three small ‘blocks’ of material with identical dimensions except for wall thickness and infill density.  Then carried out a very scientific test called ‘hitting it with a two pound hammer’.  (OK a bit more controlled – identical drop height, etc).  I increased the wall depth but kept the infill to 80% on one block as per PG’s instruction and had to physically pick up the hammer and belt it two or three times to destroy it.  I’m printing larger parts this week so I’ll begin testing rigidity, etc.  If, in the end, I have to brace the sides with one or two metal struts (Meccano style) or thicken sides/bases, etc I’ll do that.

As for the chemical /photo stability of PLA, ABS, etc I think a bit of practical use and testing will point the way.

I think a composite will be a short term reality and the dramatically cheaper cost will tempt more people into trying more serious spectroscopy before a large outlay is required.

Regards

Tony

[Dr Andrew Smith]

Tony I will follow your work and results with interest. Thanks for the detailed reply.

However there is no way I shall be hitting my spectrograph with a lump hammer!  

Regards Andrew 

[Robin Leadbeater]

Don’t forget thermal stability either. The coefficient of expansion of ABS is about 4x that of aluminium. 

I think 3D printing is a great prototyping tool but after using spectrographs with rather poor and excellent stability (LHIRES and ALPY respectively) I  look for the highest stability possible in the design and construction of a spectrograph.

Cheers

Robin

[Dominic Ford]

I too shall follow this with interest.

I built myself a ~ £300 3D printer a couple of years ago. One tricky issue I came across was the accuracy of the printing. I never really achieved better than 0.2mm accuracy. So, mechanical components generally needed a lot of cleaning up with a file before they were usable. I didn’t have much luck fine tuning the calibration, but perhaps I was just incompetent. 🙂

As regards mechanical strength, I think you almost certainly want to be using ABS. I found that my PLA prints couldn’t be left in tension for more than about a few weeks (depending on thickness) without snapping. This improved somewhat if I made the infill 100% solid, but at the expense of using lots of plastic and taking ages to print. I gather that PLA degrades and deforms particularly fast if exposed to moisture, so in a dew-laden observatory, I’d certainly favour ABS’s chances!

There even seemed to be differences between suppliers. The plastic I bought from RepRapPro (sadly now defunct) seemed noticeably stronger than what I got from various other suppliers.

While 3D printers are a lot of fun to play with and they’re great prototyping tools, I think making a precision spectrograph is quite ambitious!

[Robin Leadbeater]

Stability can be designed in though.  Looking at the ALPY for example, the design cleverly transfers the load of the camera round the key (very light weight) optical components, leaving them carrying no load which means no measurable flexure.

Robin

[Tony Rodda]

I agree entirely with the comments.

As Robin stated present this is a great prototyping tool but I’m looking forward to better materials and a composite metal/ABS design perhaps.  I’m keen to explore the possibilities. Certainly not suggesting it’s a replacement for existing kit at this stage.

Really keen to test though and hence the plan to print a number of designs/platforms.

Dominic, yes I think this will be finalised in ABS (at present).  I’ve left a couple of PLA ‘block’ prints in the obsy to test exposure. I’m printing at 0.1mm and Paul’s design is superb, everything fits with minimal finishing/adjustment.  May I ask what spectro design did you try?

I think with additional layers of paint may help IR/transparency in general.

With luck it’ll be fully assembled this weekend.  Hope ‘her indoors’ has no plans!

Regards

T

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