Can this old, terrible focuser be replaced with a better one or motorised

[Cake]

I have an old (not NG) Meade StarNavigator 102. The focuser on it is rubbish even by my complete newbie standards, as it's plastic-on-plastic, rough sliding (no space for teflon skids or such) rack-and-pinion. Shakes the entire telescope when used. I have taken it apart, cleaned it up and lubed it up. I know I can attach some extensions to the wheels to improve it somewhat, but that's a half-measure that I want to only leave as a last-ditch option if nothing else is worth the expense.

The problem is, I don't know whether I can get a better focuser which would fit instead of it, as this one slides over the tube and none I've seen online do.

To make things a bit easier, I'm attaching some photos and here's some dimesions:

Outer tube - outer diameter 94mm, inner 90mm, 2mm wall

4mm gap

Inner insert - outer 82mm, inner 70mm, 6mm wall

All screw holes 12mm form the end of the tube

For good measure, the inner side of the focuser collar is 93-4mm (duh), and the actual tube is 55mm.

If there is no easy replacement, would I at all be able to mount an affordable motor (because I won't spend a lot of money on THIS focuser) like the Skywatcher one on the underside, as per photos?

Edited September 9, 2020 by Cake

[banjaxed]

Not sure of the size but the Skywatcher focuser upgrade fits the same way as yours and it fits the 102, 120 and the 150 models. If you get in touch with FLO I’m sure they will help.

[Cake]

2 hours ago, banjaxed said:

Not sure of the size but the Skywatcher focuser upgrade fits the same way as yours and it fits the 102, 120 and the 150 models. If you get in touch with FLO I’m sure they will help.

Is this what you mean? https://www.firstlightoptics.com/skywatcher-focusers/dual-speed-2-crayford-focuser-for-sky-watcher-refractors.htm

Because that's the problem, it seems to go inside the tube, mine slides over it. But if FLO offers advice, that's great to hear.

EDIT:

Looked it up, this website actually provides dimensions https://www.365astronomy.com/dual-speed-2-inch-crayford-focuser-for-skywatcher-refractor-telescopes.html

This focuser cannot be mounted on my telescope without extensive modification.

Edited September 9, 2020 by Cake

[Geoff Barnes]

9 hours ago, Cake said:

This focuser cannot be mounted on my telescope without extensive modification

Hmm, sounds like a wonderful opportunity to treat yourself to a nice shiny new telescope @Cake

(Hope you can afford one!) 😁

[Ricochet]

14 hours ago, Cake said:

as this one slides over the tube and none I've seen online do.

So? There is no need for a new focuser to fit in the same way as the current focuser, all it has to do is fit and provide the correct amount of extension to allow you to focus. If all other focusers fit into the tube then you need to measure the inside diameter of the telescope tube and find a focuser that fits that diameter. 

Teleskop Service are probably your best bet in terms of the number of different focusers that they stock. However, focusers are reasonably expensive and if your telescope has a plastic focuser perhaps it has other parts that are of similar quality in which case it might be more worthwhile changing to one of the 102mm Bresser achromats, which are available from FLO for £219, if you have a mount that is suitable (and if a 102mm achromat is the type of telescope you want).

[Cake]

9 hours ago, Geoff Barnes said:

Hmm, sounds like a wonderful opportunity to treat yourself to a nice shiny new telescope @Cake

(Hope you can afford one!) 😁

That's a backup plan, yeah. I'm just still hoping to be able to get full mileage out of this one, though.

8 hours ago, Ricochet said:

So? There is no need for a new focuser to fit in the same way as the current focuser, all it has to do is fit and provide the correct amount of extension to allow you to focus. If all other focusers fit into the tube then you need to measure the inside diameter of the telescope tube and find a focuser that fits that diameter.

Note that's that exactly what I did, I posted all the dimensions in the OP. The problem is that so far finding the focuser flange dimensions is exeedingly difficult and this telescope won't just take them as standard, hence this thread.

8 hours ago, Ricochet said:

Teleskop Service are probably your best bet in terms of the number of different focusers that they stock. However, focusers are reasonably expensive and if your telescope has a plastic focuser perhaps it has other parts that are of similar quality in which case it might be more worthwhile changing to one of the 102mm Bresser achromats, which are available from FLO for £219, if you have a mount that is suitable (and if a 102mm achromat is the type of telescope you want).

You are absolutely right that the focusers are expensive. Most cost more than I paid for the telescope in the first place, goto mount included. As for the OTA, the rest of it is reasonably decent and they just seem to have really cheaped out on the focuser (and the red dot which mounts to it). That seems to be the main thing Meade went on to improve in the NG models because from reviews in seems that those focusers are pretty much the same as skywatcher ones, the rest of the OTA and the goto stand are fairly similar to mine.

I guess I'll just try to improve this focuser as much as possible and maybe diy motorise it, and save the money for a 10" dob.

Edited September 10, 2020 by Cake

[Alan64]

I'm in the same boat, and with this Celestron 70mm f/13 achromat...

It came with a focusser from Hades...

I'm always on the hunt for a conventional focusser for that one, either of metal or plastic, no matter.  Metal is preferable, of course.

Best wishes in sorting your own out.

[JamesF]

My gut feeling is that the simplest solution would be to make an adapter to fit the OTA and accept a new focuser of a common size.  In some cases they may be readily available, but otherwise it might mean looking around to see if you can find someone who can machine one from aluminium or delrin or something like that.

I actually did just that some years back to allow me to fit an aftermarket SCT-style focuser to the back of a PST:

I chose the thickness of the adapter to make sure the image would come to focus somewhere useful.

James

[Cake]

On 11/09/2020 at 00:01, JamesF said:

My gut feeling is that the simplest solution would be to make an adapter to fit the OTA and accept a new focuser of a common size.  In some cases they may be readily available, but otherwise it might mean looking around to see if you can find someone who can machine one from aluminium or delrin or something like that.

I actually did just that some years back to allow me to fit an aftermarket SCT-style focuser to the back of a PST:

I chose the thickness of the adapter to make sure the image would come to focus somewhere useful.

James

Now that is a really interesting idea. I wasn't too keen on any attempt to modify the tube itself, as it's my only telescope at the moment and I don't want to do silly things to it, but aside from having it manufactured this has no downsides. Considering the OTA does have decent 4" lens, retrofitting it with a decent focuser would still be cheaper that getting a new 4" goto refractor, even if it's after getting a big newtonian dob.