3D printed 130P focuser

[John78]

Having had my 130P sat in a corner for 2 years gathering dust after I took off the stock pathetic focuser with the intention of replacing it...  I've actually done it.

I had a couple of ultra high precision IKO linear slides the right sort of size in the bits box so I designed the focuser around those...

I need to reprint the draw tube as it was printed when my new printer wasn't quite working right - one of the corners of the spacer from the ota lifted slightly too when printing.

I need some M3 studding for the actuation which will run inside 4 623ZZ flanged bearings and then a 10mm brass insert pressed into the part sticking out of the tube - once I know its the right distance and travel to reach focus I'll swap the orange part to a motorised version yet to be designed.  It's been quite an experience that involved building a hypercube 3D printer as my eBay special finally bit the biscuit.

Its going to be a bit of a pain if I can't get close enough to focus, if I need to move out I can use extension tubes or print a thicker spacer - if I need to move closer its going to require a much more radical redesign - or much more limited travel which isn't necessarily a problem.

We shall see maybe tomorrow if the forecast proves accurate.

[Chriske]

Nice one...!!!!!

But there is a drawback using these linear slides. You loose lots of focusing travel. The concept of these slides limits you to use maximum travel of the focuserbody itself.  Therefore it would be better to use ball bearings to do the guiding work. You still loose travel but far less compared to these slides.
I was planning to do the same in the past, but a 50mm long (expensive!)slide only gave me 25mm travel.

[John78]

3 minutes ago, Chriske said:

Nice one...!!!!!

But there is a drawback using these linear slides. You loose lots of focusing travel. The concept of these slides limits you to use maximum travel of the focuserbody itself.  Therefore it would be better to use ball bearings to do the guiding work. You still loose travel but far less compared to these slides.
I was planning to do the same in the past, but a 50mm long (expensive!)slide only gave me 25mm travel.

I don't disagree - but when using a matched filter set for imaging only the focus travel could be like 5mm and it would be ok - as long as you get the 5mm in the right place by design!

The clear advantage of them when using a 3d printer means not having to find/fabricate something to run a crayford or ball race against, although I did consider using a piece of ground tool steel which is cheaply available but I had these in the bits box  

Looking on RS they're £120 per piece so I wouldn't be using them if I didn't already have them!!

[Chriske]

1 minute ago, John78 said:

The clear advantage of them when using a 3d printer means not having to find/fabricate something to run a crayford or ball race against,

Correct, that's why I use thin sheets of metal(or brass) to have planes to allow smooth action while focusing.
Tested it without these planes but that was 'No go..!' at all..!!
This is an example of these planes. Using these planes there is no difference compared with any other focuser at all. Perfect and very smooth action. The sheet brass parts are only 0.4 mm thick
This is a reversed Crayford btw.

[John78]

1 hour ago, Chriske said:

Correct, that's why I use thin sheets of metal(or brass) to have planes to allow smooth action while focusing.
Tested it without these planes but that was 'No go..!' at all..!!
This is an example of these planes. Using these planes there is no difference compared with any other focuser at all. Perfect and very smooth action. The sheet brass parts are only 0.4 mm thick
This is a reversed Crayford btw.

nice!

[John78]

So a brief field test last night - the forecast was for clear night, reality was cloudfest but managed to do a quick test.  Used a extension tube so the drawer tube doesn't need to be racked out quite so far - but it clearly reaches focus and I've motorised it...

The venerable 28byj-48 can actually source enough current from the USB cable to actuate the focuser with the image train attached - I'll design and print a case for it though and give it a proper amount of current @ 12v but I'm sure it will work.

Between the clouds I managed a poorly focused single 15s sub at M31 - so still to do is cleaning the primary and a proper go at collimation - and I guess a coma corrector - not sure how bad the coma will be if I get the image properly in focus.

 

[John78]

So in an effort of being a cheapskate imager - oxymoron much - I designed an optically correct combination sight tube and printed it.  Given how old the website is and how technical it is - I'm made the assumption its correct.

It printed like a champ, few strings to knock off but its a snug push into an eyepiece adaptor and appears to show the correct things nicely framed having matched the ID to the F number...

So now I just need a clear night to have another go at getting it in focus.

[Stub Mandrel]

Nice work John!