Retaining Screws for 31mm Filters for EFW-Mini

garyi

Sam,

I received my EFW-Mini today. I did not see any retaining screws for using 31mm filters. Do I need to purchase these separately? What size screw are they?

Thanks,

Gary

Sam@ZWO

sorry Gary

we will add them to the package in the future

robertm

I've just received the EFW mini as part of the ASI1600 bundle - excellent quality and amazingly quick shipping, thank you.

I've fitted my 31mm unmounted Astrodons to the mini and managed to hold them in with the screws and washers supplied but it isn't ideal. The washers need to be almost twice the diameter supplied to cover the edges of the filters securely. For now I've used the 'outlier' screws to stop the filters from moving sideways so they remain under the small washers between filters and in the recesses. I think this needs revisiting - bigger washers certainly.

The filter wheel itself is of very good quality and I'm impressed with the nice thick recessed metal construction without being heavy - a good job.

Best

Robert

Sam@ZWO

thanks very much Robert

we will try to use a larger washer

olav

Carefully tightening of one screw only, no washer, between Astronomik MOUNTED 31mm filters, seems to be just fine as far I can tell:

robertm

Hi Olav,

The plate and screws are made of different materials so expand and contract at different rates; this means means those screws will work loose over time and your filters may fall out (especially if using only two screws per filter). For that reason it's best to have washers to take up the differential expansion. The original washers were a little too small for my Astrodons but those provided with the 8 way FW are much better. You can of course tighten the screws directly down on the filter rims but that's not something I would recommend.

Hope that helps.

Note to Sam: Could you consider changing the screws to from cross head to Allen head as it's easy to slip off the cross head screws ! Also an extra mm or two on the screw length would be much appreciated.

Robert

olav

Thanks for warning me Robert!

The filter wheel body is definitely some high grade alu, but I'm actually not entirely sure about the carousel.

Anyway, will probably take out the screws one by one at next opportunity and put them back with a ultra-small drop of the mildest thread-lock.

And sorry for jumping in too quickly here. Just thought I'd say, because of the thread title, that there's another type of 31mm filters, with a tiny rim for easier mounting. Astronomik uses this version, guess the new ZWO ones are similar.

From a product page:

"Now Mounted in Low Profile Non-Threaded Cell.

Sometimes unmounted filters can be hard to handle. The smaller diameters, such as this 31 mm H-Alpha filter, can be especially difficult to pick up and insert or remove from the filter wheel, and that can lead to possible damage as well as unwanted reflections from incorrectly installed filters. Astronomik has solved this problem by mounting their 31 mm and 36 mm filters in a low profile (3 mm) non-threaded cell. O-rings, washers, or spacers are no longer required to hold the filter in place, and because the cell is only 3 mm thick, it works well in all appropriately sized filter wheels. Mounted 31 mm and 36 mm Astronomik filters will also play nice with unmounted versions in the same carousel."

So the filters actually slip a tiny bit into the filter hole, making it stable even with just one screw on each side. Would think that there's enough surface under the screw head so the filter can expand a little radially, relative to the carousel surface. Did not tighten the screws much, to specially allow for this movement. But again, thanks for reminding me on the threadlock - usually not forgotten!

Please have a closer look at the same picture in better resolution:

https://www.dropbox.com/s/oebm6zcwiu5ycru/EFWminiAndAstronomik31mmMountedFilters-big.jpg?dl=0

Maybe the "stand-alone screws" does not look so fragile after all.

And you can better see that Sam & Co is sending screws with Philips head. Can't comment on the washers as I don't which diameter they used to be. Anyway, they were not for my case - the screw head would have been left too high up.

The best would of course be if Sam updated the manual with complete mounting details for the most common filter versions/brands, like Astrodon and Astromomik. (And the ones from ZWO I'd guess. Wasn't an option for me at the time, as I needed several filters parfocal)

joeb

Sam, what is the size screw used for holding filters in the big EFW?

I need longer screws. I purchased Chroma 31mm filters that are 3mm thick. The filters have epoxy edges, not metal, so the soft washers are needed to avoid chipping the filters. With the washers the screws only have half a turn holding them in. I would prefer to have more threads holding the screws in.

Sam@ZWO

JoeB wrote:
Sam, what is the size screw used for holding filters in the big EFW?

I need longer screws. I purchased Chroma 31mm filters that are 3mm thick. The filters have epoxy edges, not metal, so the soft washers are needed to avoid chipping the filters. With the washers the screws only have half a turn holding them in. I would prefer to have more threads holding the screws in.

the size is M2 screws

current is 4mm long, I think you need longer M2 screws

joeb

Sam wrote:

the size is M2 screws

current is 4mm long, I think you need longer M2 screws

Thanks Sam, that's just what I was looking for.