Fettling and Flocking

As stated in an earlier post I have sent my mount off to be hypertuned.
There had been a number of things that I have thought about doing come next summer however with the mount being sent away I decided to bring the timeline forward and get them done.

One of the first things that I had wanted to do is flock the scope. As standard the scope is already pretty good and is lined with a matt finish paint.
I had on a number of occasions whilst collimating notice just how reflective this coating still was and even more so the focuser tube.
Knowing that I would have to strip the scope down to its bare compoinants I also decided to double check the focuser collimation and the centre spot on the primary mirror.

The first task was to strip down the scope. This actually turned out to be pretty easy and the only issue I had was getting the primary mirror cell out as it was wedged in fairly tight. Once everything was stripped down it became even more apparent just how reflective the standard coatings are on the tube and focuser.

img_20161020_2023461The first step once stripped was to wipe down the entire surface with Isopropyl Alcohol to remove any residue either from manufacturing or from dust from imaging.
You can see from the image just how reflective the coasting are and even more so the silver on the outside of the focuser tube.

Now there seems to be somewhat of a debate in regards to what you should use to flock the scope. The main goal is getting something that stays together so to not end up with tiny fragments of the material over time. One of the suppliers that I have come to trust recently is First Light Optics. I found that they also sell flocking material by the roll at a very reasonable price (See Here).
Given that the tube is not the largest I quickly opted to line it in strips. I cut the strips and lined the tube allowing a small gap between each section to allow for expansion and contraction. Once complete I set about cutting out all the holes with a scalpel blade and gave the tube a good hoover to get rid of any fragments that may have come loose during the cutting process.

 

There wimg_20161021_0157171as a  very viable difference once completed and I actually used less than a single roll doing the
entire tube. The next phase was to flock the focuser tube and black out everything else that mattered.

This took two different approaches. The focuser tube on the outiside a silver finish and a matt finish the same as the scope on the inside.
The focuser tube runs on runners and I did not want to impede these so opted to flock up to the runners and then black out the small remaining strip with a black sharpie.
After measuring the inside it was clear that there was also more than enough room to be able to flock the inside of the tube. Again this was done in strips up as far as the threads at the end.

This made a massive difference and I can see this really helping with stray reflections and brighter targets.

img_20161021_0156361

The next step was one of the parts that I was in two minds about doing, the primary and secondary mirror.
I opted to not flock the back and sides of the seconary but instead black them out again using a few coats with a black sharpie. Trying to get the flocking material at the right size and shapes was not something I wanted to tackle and the sharpie worked fine. The primary mirror once in the housing did not seem to have too many issues so I opted to leave this at least for now.

 

 

 

dscf1100The next step was to check the centre of the primary mirror spot and it also quickly become clear that I needed to do something that puts the fear of god into even some of the most experienced people, cleaning the primary mirror.
I had already done a bit of research on this and decided to use a combination of two different approaches to get a clearer picture of things.
The first was to draw around the primary mirror and then cut it out and make a small circle in the centre to give me the centre of the cell.
The second was using a photographic approach. Both came out with pretty near the same conclusion, the centre spot was out by around 2mm.
I had already worked this into the project and ordered a replacement centre spot at the same time as ordering the flocking material.
You can see from the state of the photo just how far out the centre spot is and the condition of the primary mirror.

I first marked the centre spot using the circular template I had made and then set about removing the original centre spot.img_20161021_0154321
The entire processed that I followed came from a popular you-tube video on the subject (see here).

I set about with some acetone (Nail varnish remover) and slowly worked at the centre spot to remove it. the standard centre spot came off pretty easy but being very careful not to remove the new centre mark I had made. Once this was done I then cleaned the surrounding area again with Acetone and applied the new and improved centre spot (more about this further down)
The next step was cleaning. I used to own a Marine aquarium and just happen have had an RODI machine setup. this is what I opted to use instead of the standard distilled water. The issue I have with any kind of water like this is that its very quick to take contaminant form the air around it and the container its held in. The RO water that I used came out with a 0 TDS and is about as pure as you can get (as used in labs).
After cleaning the mirror as described in the video and giving it a good rinse I allowed it to dry.
At this point the focuser was put back on and checked for correct collimation and the scope put back together.

I was lucky enough to have borrowed a laser collimator from a friend and I must admit it did make aligning the primary a lot easier.
The idea behind the new centre spot is that as well as giving a better contract for when you are collimating, it also is shaped in such a way that you are able to know instantly which of the primary bolts need adjusting. When putting the primary back into the housing its a simple case of making sure that each of the three point correspond to one of the collimation bolts on the rear to the primary mirror cell. This instantly made collimating a lot easier. With the scope back together I was over the moon with how everything looked and how much better I think it will be once out under some dark skies. I will give more of an update on this once I have had a chance to test it.

As far as doing this I would recommend flocking to anyone. As long as you have some good sharp cutting tools and patience there should be nothing stopping anyone with a basic knowledge from doing this.
On the flip side cleaning and re-spotting a primary mirror is not something I would say was for the faint hearted. Under normal conditions you should be able to go a number of years without needing to clean a primary. It is only down to the fact that my location has a lot more dust in the air that it got in the condition it did so quickly and re spotting the primary did make a few marks which needed additional cleaning as well.

1 Comment

  • Jason Colbeck

    November 5, 2016 at 8:32 pm Reply

    Good article.

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