Short strong springs

[morls]

I've decided to modify my Skywatcher 180 Mak, as I'm finding it very difficult to fine-tune the collimation with the stock configuration of screws. There are 3 points of adjustment, each with 2 screws.

One of each pair passes through an unthreaded hole in the visual back , connecting to a threaded hole in the plate holding the primary. Tightening this screw pulls the primary back towards the rear. The second screw of each pair is threaded into the visual back, passing through to push the primary cell away from the rear of the telescope.

I want to eliminate the need for adjusting the second of these screws when collimating, and use them only for locking the primary mirror cell in place once collimated. I'm looking for short strong springs to go between the visual back and primary cell, similar to setup for the primary mirror in a small dobsonian. These springs will keep forward pressure on the primary cell, greatly simplifying the collimation process.

I haven't removed the primary cell yet, but I imagine the spring would need to be somewhere around 8-10mm compressed and 20mm free-standing. There doesn't need to be a large range of movement, but needs enough force that 3 springs can hold the primary and cell securely.

Can anyone suggest a source for springs such as these? The screws that will pass through the springs have a 4mm hex head.

I've found a great post on another forum, in which a member Captain Scarlet documents the disassembly of the 180 Mak, and I'll post a link and an image that helps explain the setup. This image shows only the screws which pull the primary towards the rear, which are the ones I want to install springs onto:

https://stargazerslounge.com/topic/355495-reverse-engineering-the-skymax-180/


Cheers
Stephen

[Leo.G]

Most bolts and bearings places have good industrial grade springs and there's also companies who specialise in making custom springs from tiny things to coils suitable for freight trains.
I used to know a few companies but that was back in the early 90s but I'm sure a quick Google search will bring something up.


Are you after compression springs or extension springs?


Ah, this company is in Melbourne:


https://www.bellsprings.com.au/


They are numerous:


http://www.asisprings.com.au/default.aspx



There could be ready made springs cheaply available too in various hardware places but keep in mind there are good and bad quality spring steels (I have Chinese brass here which is extremely magnetic).

[glend]

Go to a large Bunnings store, they have an assortment of springs in the cabinet hardware section. I have used their springs a few times when building newts. Good range of lengths and diameters. They can be cut down to match what you need them to be. They are usually in a nice display area, in little bags with yellow labels.

[morls]

Thanks Leo and Glen,


I'm after compression springs. What I had in mind was chunky, high-tensile so I might start with this page:
https://www.bellsprings.com.au/category/compression-springs

[Startrek]

Stephen,
I replaced all my compression springs in all my newts with quality locally made custom springs from Better Springs P/L in Sydney about 2 years ago. They were fantastic to deal with and would make up a few springs to hundreds exactly to your spec , no issues
Just checked the supplier Better Springs and they are bloody shut down , damn !!!
I’m sure Bell will look after you

Cheers
Martin
PS: I tried Bunnings prior to finding Better Springs , and their “assorted springs pack” was rubbish , you could compress most of the compression springs with your thumb and forefinger. In fact they worse than the existing GSO springs

[morls]

Good to know, thanks Martin.

I think my first step will be to visit this store, I've been there a few times to get grub screws and thread-match the odd bolt.
If they don't have springs they have a good bargain bin which is always worth a look...

http://www.costlessboltsringwood.com.au/a/Products

[AstroViking]

You can always try the springs used in 3D printers for levelling the print bed. They're about 20mm long, 8mm in outer diameter and have a wire thickness of about 1mm.

I've had good results buying from the 'MakerStore' in Melbourne: https://www.makerstore.com.au/

Cheers,
V.

[morls]

I've bought a variety of springs, and cut one down to try out. I think with this setup the primary mounting cell now sits somewhere between 5mm and 10mm further forward in the OTA, but hopefully this won't have any detrimental effect. The mirror itself moves more than 50mm between all the way forward and all the way back when using the stock focuser.

I'll do a quick daytime collimation in a few days and then see how it all works when I fine-tune with a star.

[leon]

Hi Stephen, I am aware that these springs would probably be to large for your project, however when I built my 10" Reflector many years ago and to hold firm the main Mirror I used old car engine valve springs.

They are very high strength and are perfectly machined flat on either end to sit squarely on any surface.

They would be to large for your job I expect but there are millions of them of different sizes at any car wreckers, well they were when i needed them.:shrug:

Leon:thumbsup:

[morls]

That's a great solution, thanks Leon. As you say, I think they would be too large for this scope but definitely useful for larger projects.

[morls]

I had a brief session this evening before the full moon and clouds made star testing impossible. The collimation process was a lot easier, and I had much finer control of the adjustments. I'm not confident it'll be stable without the locking screws, but I got as close as I have ever been to getting multiple symmetrical rings around a central dot
Things changed a bit when I added the locking screws, but it's a huge improvement.

[Leo.G]

Motorbikes and 4 stroke mowers use smaller valve springs with the same functionality. An engineer friend was throwing boxes of them out recently when relocating and I grabbed just a couple, apparently they are very good for levelling stuff on a milling machine.

[leon]

That's right Leo, never thought of the smaller engines, they are brilliant to use.

Leon