jamespels

Ah, didn't realise you already had a tripod! Sometimes it is very hard to beat a good bit of basic engineering and this is a great example. As Dave says, excellent reuse of materials.

Btw, do you find the OTA is stable on the plank? If not, a strip of wood down either side should keep it lined up.

The design itself is not too bad from a vibration point of view - it is essentially the same layout as the Tal mounts which are excellent.

That said, 2" may be a little light and I think glowjet is right - you would be better off making a tripod. However, if you take yourself off down to a decent plumber's merchant and use a length of cast iron sewer pipe (110mm iirc), you could be on to a winner.

Neither design is going to fall into the "lightweight" category, however!

Ordered a pair of bins (one of the few places to have Revelation 15x70s back in stock) and a couple of L adapters around lunchtime on Wednesday last week; had dispatch confirmation by end of the day and the bins arrived on Thursday.

Slight problem in that the order only contained one L adapter (bins and one were a gift, the other adapter was for me) so I dropped them an e-mail; had an apology same day and the other adapter arrived on Saturday.

Excellent service that held up when something went a bit wrong - full credit to them and will definitely use them again.

J.

On mine, both the smaller and larger RA bearings were a bit rough - I could have lived with them if necessary but not worth it foe £10 worth of bearings. The Upper dec bering was fine; the lower one was extremely rough and would frequently catch as it turned. Muct admit, I didn't even bother cleaning it and went straight to swapping it for a shielded one.

Right, going to have to tune my mount up a bit now!!! I ned to sort out a nick in the work drive so I can tighten up the meshing a bit better - the slack is really annoying me. I missed that guide first time round, AndyH, so thanks for posting a link to it.

Anybody have any objections to me bringing this lot together into a single article on the new Peak District Dark Skies website when I get it built? All usual credits, etc.

Will have to sort out a special discount for TAL owners at PSP2012 (good luck with me pushing that past the committe!) so we can all gather in a corner and "oo" and "ahh" over how smooth we've got them

Thanks,

J.

I'm now wondering is a tapered roller bearing might be a viable upgrade.

I wouldn't bother - the bearing isn't taking any thrust as such (rotational load only - not axial) so this will detract rather than add to the performance.

Off to find a bearing pullers now.

Take one wooden spoon, feed the handle from the back and knock out the knackered bearing(s). Both came out easily in mine and it was years old with some dreadful set ex-grease. If either of the bearings are OK, just leave them, through it might be worth taking them out anyway to a soak in de-greaser and re grease them.

J.

Thanks Andy, and I really should have credited you with a lot of this - thanks for the help previously!

I should have said - those bearing sizes are inner diameter x outer diameter x width. The original are all open; I am not sure if there is a benefit to geatting shielded bearings for the RA axis but it is definitely beneficial for the lower bearing on the dec axis. AndyH (I think) points out elsewhere (possibly on the defunct TAL owners club fourm - not sure if it is still accessible) that the swarf and other muck produced as the dec axis turns all falls down onto this bearing so it will probably be the one in the worst condition. Another solution posted by somebody else on the the owners club (sorry, not sure who) was to put a split fabric washer above the bearing to protect it.

J.

meant to say, the bearings are as follows. One of these is the lower dec axis bearing - I think it is the smallest one but am not sure - it will be obvious when you look at them. I got the cheap ones from Simply Bearings Ltd ~ Oil Seals SKF FAG TIMKEN KOYO NTN NKE TRULOC Needle Rollers Taper Rollers Rod Ends Oilite Bushes Loose Balls O Rings Grease Plain Thrust and had great service.

1 x 60052RS Budget Rubber Sealed Deep Groove Ball Bearing 25x47x12mm (6005.2RS.EU) = £2.99

1 x 69042RS Budget Rubber Sealed Thin Section Deep Groove Ball Bearing 20x37x9mm (6904.2RS.EU) = £5.84

1 x 6006 Budget Open Type Deep Groove Ball Bearing 30x55x13mm (6006.EU) = £2.83

I also replaced the dreadful slotted machine screws holding the mount head together:

M3 x 12 Black Countersunk Allen Key Screws x 20PK

M3 x 12 Black Countersun

M3 x 6 Black Countersunk Allen Key Screws x 20PK

M3 x 6 Black Countersunk

These came from needabolt (High Tensile Socket Cap Screws, Allen Key Screws, Machine Screws, Nylon Nuts, Washers,button,countersunk,). Quck service again, and very cheap.

J.

AndyH, can you check this over please?

Will sort out something a bit better with pics later on. For now, start by taking the motor drive out. The motor is held in place with three large screws you will see on the underside of the mount body. It is soldered into the switch, red light and power socket which can all be easily removed using the obvious screws around them - be careful to keep all the nuts, bolts and spacers - I reassembled them once the bits were removed from the mount head. The switch is held in place with a collar nut - I used a pair of pliers to undo this, with a bit of cloth to protect the nut. You will now be able to remove the motor and gearbox and all the electronics. Having done that, remove the three bolts that hold the RA clutch plate in place and take off the clutch plate itself (leave the large brass drive gear for now).

Next, you will need to remove the worm drive. The plastic knobs that you can use to manually drive the RA axis can bre removed by holding them while you undo the central bolts with a large screwdriver. Pop the knobs off afterwards by prising them off the axle with a screwdriver against the mount head if they don't come off easily. You will now see four small bolts around the worm drive on each side of the mount. Undo these to release the round securing plates on each side. Note which is which - the full circle goes on the right as you look in; the "C" shaped on goes on the left, on the same side as the motor. You should be able to "jiggle" the axle out now; if not, release the large gear on the motor (left as you look in) side - there are two grub screws locking it in place, 90 degrees apart. Whatever you do, take great care not to damage the worm drive or the large brass gear around the RA axis.

Once the worm drive is out, carefully remove the brass drive gear. Probably worth giving all this lot a good soak in de-greaser, then re-greasing it before reassembly.

Now you will need to take the dec arm off. From here on, all the screws may be sealed in palce (like loctite, you will see a hard red film left on the bolts). To remove the dec arm, locate the two grub screws (about 6 mm) in the body, on the RA axis near the RA indicator wheel. These are simply covers and can be removed. If you look through the resulting holes, you will see two more grub screws. Undo both of these by about three turns (much more than that and you risk losing them inside the dec axis body).

To remove the dec axis body, insert a large screwdriver into one of the three holes you can see in the RA drive plate back in the mount head. Rotate the dec axis counterclockwise until the screwdriver catches against the body. Now force the dec arm counterclockwise (as you look at it from the front of the mount, so that the head is behind the dec axis body). I had to belt mine several times with a rubber mallet to get it to move (be careful the screwdiver in the back doesn't let go!).

With the dec axis body removed, you will see what appears to be a large washer with two holes in it around the RA axis: this is a locknut. Carefully knock it loose - I used a small screwdriver in the hole and tapped in with a small hammer- but be gentle as it is quite delicate. Now remove the remaining washers, etc. (get the order right when you put them back). One of the plates is held on with three screws, when you have removed this you will be able to remove the RA setting wheel if you want to.

At this stage, you should have exposed the smaller front bearing. All that remains is to knock the RA axis back into the mount - again, a rubber mallet or a metal hammer with a bit of wood between it and the threaded end of the axis.

You will now be able to pop both the bearings out.

To put it back together, to the above backwards!

Hope this helps, if you need a pic from any stage, drop me a line.

J.

Oh yes

Just done exaclty the same thing, except I want on to take the dec apart too

PM on its way.

Thanks Mark - really helpful!

Your title sums up my approach a little to closely, though - point the scope about right and hope!

J