Gina's Observatory

[Freff]

Gina,

The bottom threaded hole I guess takes a standard bolt - the top looks as if it takes a bolt with the thread removed near the bolt's head to form a captured bolt so it doesn't fall out as you struggle with the mount and try to do up a bolt from underneath...

Once you've screwed the bolt through the threaded hole, the bolt's plain shank will allow the bolt to be easily handled to 'find' the thread in the mounts base and will then tighten as a normal bolt...

Just a thought - Francis

I think francis is right that the threads are only for retaining.

I don't think there is enough 'meat' on the bottom of the extension for holding. (I'm not sure of the specs)

Either as Gina suggests drilling out the threads in the extension or a purpose made bolt.

[Gina]

The original Tripod bolt is used to attach the Base of the extension to the tripod, inside at the top there is a smaller version which you have to attach to the mount. that's the bit i used to attach my mount to my pillar.

Ah yes, I see.

Thinking about it I would recomend you use two bolts.

One to attach the top base of the pillar to the underside of the mount, as you can see from the 3 hex bolts its easy to take off the ends, and then attach the bottom plate in the same way.

Yes, I agree, top and bottom would be best attached separately. I guess I could tighten the top bolt so as to allow movement for polar alignment and not really tight.

Gina,

The bottom threaded hole I guess takes a standard bolt - the top looks as if it takes a bolt with the thread removed near the bolt's head to form a captured bolt so it doesn't fall out as you struggle with the mount and try to do up a bolt from underneath...

Once you've screwed the bolt through the threaded hole, the bolt's plain shank will allow the bolt to be easily handled to 'find' the thread in the mounts base and will then tighten as a normal bolt...

Just a thought - Francis

Yes, you're right the thread and reduced shank provides a captured bolt.

Maybe the idea is to take the tube apart to tighten up the top bolt after polar alignment. I think the parts would go back together exactly the same as they came apart.

I had thought of using the tripod bolt as shown in the attached sketch. This would just mean drilling out the bottom plate thread and leaving the thread in the top plate. But I'm thinking now that two bolts would be better. I could use the tripod bolt cut off below the knob for the top bolt and an ordinary threaded bolt for the bottom.

[Freff]

The original Tripod bolt is used to attach the Base of the extension to the tripod, inside at the top there is a smaller version which you have to attach to the mount. that's the bit i used to attach my mount to my pillar.

Ah!! I see how it works now.

[Gina]

I don't really want to cut my tripod bolt in case I should ever want to use the tripod or maybe sell the mount at a later date (eg. upgrading). So I've been trying to find reduced shank bolts but without any luck so far. Nothing on eBay, Screwfix or Amazon and Google wasn't helpful either.

If I can't find a reduced shank M12 bolt I think it's back to drilling out the thread (on the top plate).

[Freff]

I could turn the threads off on the lathe for you.

[fwm891]

Like Tony I have a small lathe and can turn a reduced shaft on a bolt for you - provided your not looking at stainless steel...

Francis

[Gina]

Thank you both I have yet to get a bolt the right length. There are a couple of shops that sell tractor and farm implement parts and such in our local town, they have all sorts of bolts and suchlike. I'll pop in next week and see what I can get.

[Gina]

Just thought... I have a couple of spare M12 SS bolt from the 10 I bought for my nylon wheels. Having 8 wheels (for roll off) I only want 8 bolts so have 2 spare. They're a bit long but I also have plenty of SS M12 washers spare. Wanted 48 (or so) and got a packet of 100. So I can pad out the bolt with washers until I get the right length (if I bother).

The thread in the aluminium top plate is only 5mm long (3 threads) so would be very easy to remove. I don't need the bolt to be captive anyway - no use in this application.

[Freff]

The top threads in the adapter are 5mm so are of no use other than captive. How much thread is on the base of the adapter.

I would be inclined to go for a full lenght bolt, not knowing the depth of thread at the base or the overall lenght of the adapter.

Unless there is a lot of thread at the base, using it as the main holding point is questionable with the amount of torsion that comes into play could strip the threads.

[Gina]

Well, I've done that. Cleared the threads to leave a clearance hole with a small hand reamer. Easy It's now all put together on top of the pier, mount included! Getting the mount all the way up that high up was a struggle but I managed it

Photos attached :-

1. Extension tube attached to pier adapter.

2. Close up view from the north.

3. Mount on top of extension tube.

4. Close up of above.

[Freff]

So how did you finally do it, what method.

[Earl]

Sorted !

[Gina]

The top threads in the adapter are 5mm so are of no use other than captive. How much thread is on the base of the adapter.

I would be inclined to go for a full lenght bolt, not knowing the depth of thread at the base or the overall lenght of the adapter.

Unless there is a lot of thread at the base, using it as the main holding point is questionable with the amount of torsion that comes into play could strip the threads.

The threaded section at the base is 20mm or more. A 25mm bolt with a large washer and about a 1mm gap between that and the bottom plate spigot just reaches the top of the threaded hole. The bottom plate is steel I think so there is plenty of thread and I was able to do the bolt up really tight. That's not gonna move If anything it's stronger than the mount thread.

Sketch attached showing the two fastening bolts. Note the long thread in the bottom extension plate :-

[Gina]

Pre-empting the next question... I unscrewed the polar alignment post from the tripod and screwed it into the extension tube top plate. And I tightened the top bolt so that the mount was secure but could still be turned with the adjuster knobs. It feels quite solid

[Freff]

Looks good and solid, glad it's all worked out for you.

[Gina]

Looks good and solid, glad it's all worked out for you.

Thanks I'll put the scope on next and see just how solid it is

[Freff]

Be careful, it looks iffy there.

[Gina]

Be careful, it looks iffy there.

Thanks - I certainly try to be

[Gina]

Sorted !

It would certainly seem so

Now have the scope on the mount and aligned with my favourite test tree. Slightly less rigid than without the extension tube but I think it should be alright. With the mount directly on the pier adapter I tried thumping the mount with my hand and nothing moved at all - with the tube on there is a slight visible vibration at higher magnification. But I can still focus even with my 4mm Plossl EP without shaking the image noticeably.

The focuser on this scope is somewhat sloppy and coarse. I was thinking of using a motor drive on the focuser both to avoid the shake and provide slow motion. The shake problem seems to be cured but the focussing is still very coarse with manual adjustment. With any future scopes I intend to have two speed focussers.

I think imaging should be fine (though the proof of the pudding ... etc.). I intend to do white solar, lunar, planetary and wider DSO. DSO will use lower magnification and the others are bright enough to use shorter exposures I gather, so I may not want to do high magnification and long exposure at the same time.

[Gina]

Photo attached - scope on mount, on extension tube, on pier adapter, on pier :-

[Astrokev]

Looking good Gina. All you need to do now is put a shed on the top. Simple!

[Gina]

Looking good Gina.

Thanks

All you need to do now is put a shed on the top. Simple!

Yeah!!

[yesyes]

Gina, the background image on your webcam page doesn't load. Therefore the page never finished loading and therefore it does not auto-refresh... ;-)

[Gina]

Gina, the background image on your webcam page doesn't load. Therefore the page never finished loading and therefore it does not auto-refresh... ;-)

Just noticed and fixed it - been out this morning so unable to keep an eye on it. Just got back and had lunch. Thanks for telling me though At least it seems alright now. I'm using the latest version of Yawcam which has an FTP bug. I have the previous version on the box that went wrong - I'll be sorting it out soon and will then copy the older version to the currently working box.

[yesyes]

It's still not loading the background here...