ZWO EAF on SW Esprit 100 focuser

[Barns]

Hi, picked up a ZWO EAF focus unit recently (in fact, the one advertised here as customer return - thanks FLO!) and I've fitted it to my SW Esprit 100 scope using the "Takahashi Adapter kit" (which advertises as also being suitable for the Esprit 100). However it wasn't a smooth fitting; the bracket will only bolt into one bolt hole under the focus tube, not a pair of two as I'd have thought required for a nice firm non-slipping fit, plus it's at a (slight) angle since the holes don't line up nicely. The holes I'm attempting to bolt into are the OUTER pair of holes as you look under the focus tube; these are apparently the ones designed to have things bolted into them.

Has anyone else fitted this focus unit to this scope successfully? It does seem to function like I have it - focus moves in and out ok even when pointing at zenith which I assume strains the focuser the most. But it doesn't feel correct and it worries me maybe it'll be straining something more than it should, being "forced" a little like it is.

The bracket would have fitted nicely into two other bolt holes under the focuser (two of the inner set of 4 holes), but I'm 99.9% sure those holes are for adjusting the focus drawtube tension etc, NOT for bolting brackets into underneath. So I'm very loathe to touch those.

[Barns]

Adding a link to a pic of the bracket fixed to the Esprit 100 focuser with annotations to show the issue I'm having :

https://imgur.com/a/SDn2QOO

 

[rogmet]

That doesn't look right. I was going to take apart my 120 focuser to see what the 4 inner screws do but it's got my own DIY focus unit firmly attached to it.

This page shows a guy fitting a autofocuser to a 120 and it's fitted to the inner screws. It's got to be worth a try - it can't be any other way if the fairly pricey additional mounting plate is specifically said to fit the Esprit. I'd pull off the focuser by removing the 4 outer screws and have a look inside (I've done it before but I can't remember how it looks). If it looks like snugging up 2 of the inner 4 screws isn't going to unnecessarily stress the mechanism, I'd go with that.

If you haven't already, a quick mail to FLO may help.

Let us know how you go, it's got to be useful to someone in the future - maybe even me....

[Barns]

Hmm ok I'll need to do some more investigating. I've already emailed FLO and they've contacted ZWO about how the adapter is supposed to fit. I'm just wary about unscrewing the inner 4 if there's any chance I'll muck up the focuser mechanism, it's my brand new shiny and I'm hesitant to break it!

[rogmet]

Yeah, don't break it, it's an awesome bit of kit!

I took apart my focuser; the 4 inner screws are grub screws that set the separation of the pinion from the rack. I wouldn't use these to mount the EAF, the chances of getting the correct separation and sufficient tension on the mounting plate are driven mainly by luck I would have thought. I'd bet it's what you're supposed to do though. Maybe I'm not giving them enough credit.

Let us know what happens, I was tempted by the EAF to replace my DIY stepper motor thing that drives the fine focus knob through a "slack as I dare" belt. It works but I don't really like driving the fine focus knob with all its delicate internals

[Barns]

To bring up to date, FLO got advice from ZWO that apparently I should use the standard adaptor bracket that comes with the EAF to fix to the Esprit 100 focuser, NOT the Takahashi one. However I do think I need to be using the flexible coupler that came with the Takahashi bracket as this has a different inner diameter to fix to the Esprit focus "rod" from the 4 couplers that come standard with the EAF, none of which fitted snugly. So it's quite a lot of money for one coupler but that's astro gear for you! I've changed the mounting over and it does seem much more secure and lined-up now, even though it's still by a single bolt.

I'm still having issues with the EAF however, some largish backlash that I think is internal to the EAF itself, but that's the subject of another thread.

[Stub Mandrel]

I've just fitted the EAF to a 130P-DS which I think has a very similar focuser.

I had to mill 3mm off the end of the long part of the bracket and re-tap (they were already deep enough) the M2.5 holes for the screws that fix the angled bit on the end.

This allowed me to use the M5 screws through the bracket into the hole for the lock screw and the one opposite it which was closed by a set screw.

Without this the only option was to use long M3 screws centrally which would have meant the focuser was pivoting on the pad which sets the  focus rod tension which would not have been good (plus M3 screws don't really have large enough heads for the central slot in the bracket.