Need a new bit for Tal2M

[rawhead]

As mentioned in a previous thread the motor on my Tal is not working. I took it to bits (surprisingly easy) and found the problem…

I have posted two pics here: http://picasaweb.google.com/jonadambunting/BrokenScope

The second picture shows the cog no longer firmly secured to the inner bolt. Consequently as soon as there is any pressure on the motor it just spins on its axis. (Should stay fixed and drive the scope)

Where can I get a new bit? I will try the Talscopes forum over on yahoo. I have also got a phone no. for the guy who used to run Beacon Hill. (Thanks Steelrat)

Any further suggestions greatly received.

Thank you.

Jon

P.S. Tried super glue, instantly popped out

[Kaptain Klevtsov]

I had some success on a similar non-astro problem by popping the broken bit in place and fitting a cable tie round the damaged bit.

Kaptain Klevtsov

[rawhead]

I had some success on a similar non-astro problem by popping the broken bit in place and fitting a cable tie round the damaged bit.

Kaptain Klevtsov

Cheers. I'll give it a try...

[beamish]

what about a high end impact adhesive?

Karlo

[iancandler]

what about a high end impact adhesive?

Karlo

I've tried most on little plastic gears and other similar items and they dont want to know, as soon as theyre under stress they break again.

You could try the importers, other than that it might be worth contacting someone like arthur (ambermile) and seeing if they can knock up a replacement for you.

[rawhead]

It’s Fixed!

A friend of a friend with a shed full of lathes fashioned a replacement

Very happy :sunny:

Thanks for the suggestions

Cheers

[Frozentoes]

Hi.

I too have a problem with the motor drive on my TAL2M.

The very last cog in the drive's gear box has broken and no longer engages with the first drive shaft.

Everything else works fine but the gearbox just doesn't drive the worm gear shaft.

Does anyone supply spare parts for TAL motor drives ?

Any help gratefuly received, thanks.

[rawhead]

Exactly the problem I had.

I couldn’t find spares. I was advised they are not available.

You could keep an eye out for a second hand mount. They do appear from time to time.

I was about to email someone at a model engineering society. There are lots dotted about.

See here: http://www.modeleng.org/ukclubs.htm

I was amazed at what can be repaired.

I went from this:

(click to enlarge)

To this.

(click to enlarge)

(click to enlarge)

(click to enlarge)

Good luck.

[Frozentoes]

Hi, thanks for your help.

Your photos look exactly the same as my problem, even the profile of the break is the same.

Shame really that such a well engineered 'scope should be let down by such an under engineered component.

I suspected that spares would not be available, it is a 1996 vintage after all.

I tried the Novosibirsk site but Google gives a warning about the site being harmful and advises not to enter so no luck there.

I'll try our local model engineering society, see what they can offer.

One other question regarding the TAL mount, the declination axis on mine has a "positive stop" in it's rotation, should there be one or is it a flat spotted bearing ?

Thanks again.

[rawhead]

Mines also a 96

Not sure about your dec axis. Doesn’t sound right to me though.. (I’m only a noob)

With the mount, when you do get the cog fixed, make sure the clutch is not too tight (mine was well clamped down) this increases the strain on those flimsey plastic cogs…….

I found the following on the net (you might have come across it already) Some handy tips about the mount.

TALScopes GEM Mount FAQ

Getting the Best Out of Your Mount

By Bill Brady

And others

The TAL GEM mounts

The TAL GEMs are built in Novosibirsk Russia. The design is based on tried and true mounts of the 1950's and 1960's. All structural and drive components are metal, using tapered (stepped) steel shafts in both Right Ascension and Declination axes. The RA shaft is suspended in two ball bearings, the end taking the largest load being larger than the opposite end. The 4" mount has ball bearings in Declination, the smaller 3" mount uses sleeve bearings. All bearings are pre-loaded or constrained by compression nuts or other suspension components, which can be adjusted for, wear. The bearings are adjusted for zero play or runout of the shaft. Most mounts include a synchronous motor coupled to the RA shaft via a motor clutch, gear train, worm, worm (ring) gear and RA clutch. The worm gear provides the clutch bearing surface for the RA shaft and clutch plate. Thus there are two clutches in the RA drive where other mounts have one or none. To get the best service from these GEMs you must learn to make basic adjustments and take the time to do so. Given reasonable care these mounts will last for your lifetime and that of your children.

The Other Mounts

This is the age where people expect instant gratification. The newer design Polaris type mounts work smoothly right out of the box. They require no adjustment, or very little adjustment. In fact most cannot be adjusted. Slack is taken up by the use of plastic thrust washers, gears are smooth because they are made from soft aluminum. When these parts wear out, the mount becomes useless.

The Warts

The TALScope mounts are not perfect.

1. They require adjustment and maintenance, you must learn how to adjust the main and motor clutch tension

2. The RA circle is labeled backwards, according to sun time rather than celestial coordinates.

3. The RA Slow Motion knobs are harder to turn than other mounts because of the second clutch

The Pluses

1. They can be adjusted and maintained. With a TAL GEM, a tear down and re-lube with careful reassembly is all that is required to restore the mount to top performance. Wear is compensated for by an increase in the bearing pre-loaders.

2. The RA circle can be used as is or re-labeled. If you happen to live in the Southern Hemisphere will be useable as is.

3. The Slow Motion knobs will always be harder to turn than other mounts because the drive has two clutches. You must overcome the motor clutch in order to turn the knob. This results in a tremendous benefit, however, in that manual slew of the OTA in RA is accomplished by just pushing on the tube. If you have a mount that does not have this feature and you wish to move to a new target you must unlock both axes, slew to and aquire the new target then attempt to re-lock both axes without the scope moving off the target. With some mounts, like the Sky View Deluxe, you also have to uncouple the motor drive shaft. With a TAL GEM, you loosen the DEC lock, move the scope in RA and DEC with the other hand and retighten the DEC. I often do this without even taking my hand off of the DEC lock knob.

4. Synchronous motors are very long lived.

Balancing

Learn how to balance the mount. It's a bit of a pain to balance the scope in RA. You have to loosen the 3 screws of the main clutch so the RA Axis is more or less freely turning. Then you can slide the weight(s) up and down the weight shaft until the mount is balanced with the weight shaft in a more or less horizontal position. But don't stop there; check to see if it's balanced in an operating position; with the business end pointed at the stars.

Get an extra weight or two

TAL mounts have rather long weight shafts and small weights. This is likely done in order to save on shipping; Siberia is a long ways from everywhere. With an extra weight or two, you can move the weights much closer to the OTA, eliminating bounciness in the long weight shaft. If all else fails, get some inexpensive barbell weights. They don't have a screw to secure them but your TAL weight can be put on last and used to hold them all on.

Remove the Plastic Feet

The plastic feet supplied with the TAL mount don't work in all situations. You can remove them completely, fill them with expanding foam that is used to seal air leaks in homes, or replace/line them with cut to fit mouse pad material.

Adjust the Worm Backlash

This is a very simple adjustment to make. The procedure is found in the section entitled "Operations" or "Preparations for Operations" in your manual for most scopes. There are some photos in the FILES area, which illustrate making this adjustment. When done, you should have no backlash (a delay when you reverse directions with the handwheels) or play when you move the weight shaft gently back and fro as noted on the RA setting circle. The 4" mount can be expected to have almost zero play, the 3" mount may have play amounting to slightly more that the width of a mark.

Raise the Pedestal

Get yourself some blocks of wood. You want some rather massive sizes like 2x10". Pressure treated is good because it's heavy and won't rot. Also collect some of those CDROMs that AOL, MSN and Earthlink keep sending you. Put down at least one block under each foot and use the CDROMs to level the column.

Get a good Level, Compass and a 4-foot stick

You can pick up one of those rotary dial levels for about $10. You can use it to level the column, it has a magnet and sticks to the side of the column or you can set it on top. Set the moveable pointer of the dial to your declination. You can then place the level on top of your Declination shaft where it will stick while you set your declination. Don't be afraid to put a lot of pressure on the lever. I use a box end wrench or the hole in the handle of an 8" crescent wrench; I stick it on the end of the lever to effectively make it longer. Eventually the lever won't move far enough to clamp real tight, but, like everything else, that's adjustable. See your manual. You can also use the level on top of your OTA as a final check/adjustment, but it won't stick to the non-ferric tube.

A Silva compass with straight sides and settable magnetic declination can also be has for about $10-$13. You can't use the compass close to the mount that's what the 4" stick is for. Most of the large lumber/hardware super stores have straight "hobby" 1x3's. Sight down the edge to get a straight one, or check it on a flat surface like the floor or a counter. When you get home, put some vegetable oil on it. Olive oil is good. I put a coat of shellac on first.

There are several web sites that will allow you to find your precise magnetic declination and latitude. Lay your stick along side of the motor housing and hold the Compass against the far edge. Don't try to use the retaining bolts that hold the head on the column to make a fine setting to north. Go ahead and tighten them. Use your screwdriver to nudge the feet around by using it as a pry bar. You can move a fully loaded mount this way.

Get a Motor Corrector

This is the single best accessory you can get for your scope. It allows you to run the scope at sidereal (star) rate, sun rate or moon rate. Otherwise you only get sun time. It also has a speedo button that lets you take up the slack in the synchronous motor gear train after you have used the handwheels (slo-motion knobs). It also lets you run your scope from a battery Pak or a car battery. The least expensive is the Vega. There is a review of 3 Motor Drive Corrector in the FILES area.

Learn how to adjust your clutches

If you find your handwheels difficult to turn you probably have your motor clutch too tight. On a cloudy night set your scope up indoors and slack off the three motor clutch screws. Set the RA pointer to the current time. Run your mount on wall power for 2-4 hours and see if it keeps proper time. If it "looses" tighten the clutch screws 1/8 turn and try again. If after you do this adjustment a few times and your handwheels are still really hard to turn, you may not have your scope balanced in RA.

The handwheels will never be as easy to turn as a mount that has no second clutch. But they can be made smooth and comfortable to turn.

Learn how to adjust your main clutch so that it is easily pushed with one hand. This requires some trial and error on your part.

The amount of pressure that each clutch requires will increase as the mount "breaks in".

Learn how to align your motor

First, I highly recommend that you replace the three slot head motor mounting screws with hex head type, and invest in a proper sized nut driver, likely a 7mm. If, when turning the handwheels you can feel the teeth of the motor gear meshing with the spur gear on the worm, you need to align the motor. Since the screws are underneath and cannot be seen, a nut driver can be used by feel. When properly aligned you won't feel the teeth meshing. This is not a critical adjustment.

Learn how to use the Setting Circles

The Setting Circles on TAL mounts work. If you can't afford digital setting circles, learn how to use the mechanical ones. It will increase your enjoyment immensely and make you fearless in seeking out objects. If you live in the Northern Hemisphere, you will want to relabel the hours so they run in the right direction. I highly recommend Edmunds Scientifics book All About Telescopes, it is useful for many other things as well. If you are using one of the sit down scopes, you may want to rig an extra Declination pointer on the side you sit on. The 4" mount has two pointers so this is not necessary.

Invest in an Observers Chair

Even if you stand while observing, you will find an observers chair will extend the time you can spend with your scope. These chairs have a sliding seat that adjusts from about 9" to 29" high.

[Frozentoes]

Hi, thanks for the data on the mount, no, I hadn't seen this before.

I will bear in mind your advice regarding the cluth adjustment.

The "stop" in the Dec axis rotation that I mentioned appears to coincide with 0 degrees so I had thought that it was perhaps a detent intended to help locate the 0 degrees position.

I guess I'm going to have to strip the bearings down and check it out.

Do you know if there is any data available for how to disassemble the mount ?

I have looked at it but apart from a couple of tiny screws I can't see any obvious way to take it apart and I don't want to mess with it until I know what I'm doing.

Thanks

[rawhead]

Do you know if there is any data available for how to disassemble the mount ?

Sorry no. I mostly got mine apart but still can't work out one bit. Have you joined Talscopes on Yahoo?

Might be worth asking over there. (It took several weeks before they 'approved' my first post)

Jon

[AndyH]

Hi.

Some good Tal 2M mount info on Jan Timmerman's (sp?) site. He used to be a regular on the Yahoo forum.

http://www.thefirmament.nl/astro/main_screen.html

It's not the easiest site to navigate. Click on some of the obvious tal mount images and look in the 'tutorials' and under 'equipment'.

I've done a complete strip down of the RA arm, replacing the tal bearings with modern equivalents. It was much smoother once complete. I didn't touch the dec arm. It was okay on mine.

If you want I'll venture into the loft, trying to avoid Shelob, and have a squint at the mount up there. I swear that spider is the size of a small dog :shock:

I do recommend joining the yahoo group. Lots of interesting stuff in the files section.

Cheers,

Andy.

[Frozentoes]

Hi

Many thanks to Rawhead and Andy H for your advice, I will have a look at the sites mentioned.

Andy, thanks for your offer to do battle with Shelob but don't worry for now, I'll do a bit more research myself first.

I have cats so spiders don't last long in my house !

I would be interested to know more about the replacement bearings that you fitted, specification, where from, cost etc.

Just taken delivery of an Orion collimating eyepiece so while the TAL is out of service I'll have a go at tweaking the mirrors.

Having said that, a quick check yesterday showed it to still be pretty much in collimation, since new.

Not bad eh ?

Russian Engineering - a bit agricultural perhaps but it lasts.

Guess I'm going to have to get to grips with polar aligning my ETX125 for a while.

Clear skies to all (fat chance this weekend !)

Frozentoes

[AndyH]

Hi again.

The original intention when I stripped the mount down, was just to re-grease the front and rear bearings and generally get an idea how the mount worked. I'm a terrible meddler with stuff ! I once took my 1300cc Triumph Dolomite engine to bits, even although it just needed a new oil pump. Brilliant engine, brilliant car, horrible bodywork Back to the Tal. Well, once it was stripped, and the bearings out, (I think they were relatively straight forward to force out?) I cleaned the Tal bearings out, by immersing and rotating them in cleaning fluid( I may have just used white spirit) to get rid of the Russian gunk. Once clean, noticed how rough they were by rotating them. This is when I noticed tiny metal cuttings at the bottom of the cleaning tub. I did try repacking them with bearing grease, but to no avail. Knackered. I took them down the road to BSL Ltd, a bearing stockist amongst other stuff. Branches country wide. I'm sure any bearing stockist will be fine. They measured the o/d, i/d, and width as well as noting the ruski code number on the bearing itself. I was told it was a standard, off the shelf item. Cost? Can't remember, which makes me think they weren't extortionate. Reassembly after packing with bearing grease again, was a skoosh, knocking them in with a piece of wood, to avoid harming the bearing facings and which seats them true and flat.

I too have a cat. Ben. Sadly he is rubbish at being a cat. Enjoys sleeping like Bagpuss. His brother, Pete, (sadly gone to Cat Valhalla ) was the killer in the family.

Cheers,

Andy.

PS: I'll be venturing into the loft this evening, so I'll retrieve the mount. I need to check that it and the tal vega variable-frequency drive corrector is working okay anyway, cause this is going to carry my Tal 200K. I've got a longer tube made up for the mount to sit on, cause it's way too short for anything other than a Newt.

[rawhead]

Hi Frozentoes :wave:

Don't know whether you are still looking for a fix?

I received an email from Optical Vision yesterday. Have PMd you the details...

[Frozentoes]

Hi Andy, Rawhead :wave:

Once again, many thanks for all your help and feedback.

I have now made contact with Optical Vision regarding the complete gearbox replacement - I await their response.

I'm going to have a go at the bearings this weekend so your advice is much appreciated Andy, thanks.

[chrisp]

Did you find the new part?

I have the same problem but with a TAL 1 M.