LightBridge azimuth bearing.

[richardda1st]

Can any owners of 12" or 16" Lightbridges give me the overall diameter of the lazy susan bearing on their scope.

I have the 10" LB which has a 12.5" diameter bearing. I would like to replace the 12.5" bearing with a larger diameter bearing. I want to improve the stability of the scope. If the 12" or 16" LB use a larger bearing (I would think so) I may be able to order one from Mead or one of the dealers.

Is anyone aware of a supplier of this type of lazy susan bearing, I haven't had any luck in my search. I prefer to use the same type as it works well.

Thanks
Richard

[Barrykgerdes]

I havn't looked at mine for some time but I think it is about 18".
However if you are suffering from instability with your current bearing size I don't think you will get any improvement with a larger bearing.

What you need to do is increase the thickness of the base with some 1/2" ply. Also do the same with the rocker box.

Next use a better pivot bolt that is firmly attached to the base and has a thrust race attached to the the rocker box to hold it to the base.

I have made new pivot bolts of different custom designs for a few DOB mounts that do just this and it makes the azimuth bearing very rigid.

Barry

[BEVAN5433]

Hi RICHARD
The base of the scope is 31" the bearing about 12" could be 10"
but cannot tell without dismantling my scope the guess is 12". Mitre 10 have
a lazy susan bearing for $32.00 it is a ball race 12" BUT requires 3/8' TEFLON
bearings for clearance. check out Scopestuff for the bearings.they also have
ebony black circles.I have purchased the larger ring to go with the lazy susan for a 12' mirror Dob Iam building
BEVAN

[cfranks]

http://www.minibearings.com.au/store/partslist/lazysusanbearings/bearingsthrust/wide/1/ Not sure of available sizes though!

Charles

[BEVAN5433]

Hi RICHARD
The LSB-300 is the bearing Im talking about see link provided by
others. The bearing on the L.B.16 cannot be 18". THIS IS OVER 2/3 of the base size .I AT FIRST THOUGHT IT was larger than 12'' BUT ON MEASURINGTHE BASE 12" was about the size provided.They probably use the
same bearing.They use a packer on the16" so the Teflon bearings are perhaps higher than on the 12'
BEVAN

[richardda1st]

Yes Barry I agree, replacing the chipboard with ply will greatly improve stability, and if I was going to make a new dob that is the way to go.

The axle bearing on my LB 10" is the same as your detail but without the recess for the thrust bearing (ie thrust bearing presses directily on upper face of base).

I still think that the larger the diameter of the lazy susan bearing the better, ideal would be to have the bearing as large as possible right up to the full diameter of the base. I have found some lazy susan bearings that come in large sizes, but at this stage I want to use the same design as the original.
The original bearing uses very thin needle rollers and two steel plates which results in a combined thickness of 3 to 4mm. I want to keep this thickness as it suits my new azimuth calibrations with added vernier setup.

You seem to think that the bearing on your dob is 18", that would be ideal for my simple modification. Can you give me the total thickness of the lazy susan bearing on your scope. Barry is your scope a Lightbridge and what size is it?

Hi Bevan, what size Lightbridge do you have? So you think that the LB 10" 12" & 16" all use the same 320mm diameter bearing, and using the three teflon pads for stability.

I should add that I had to remove the teflon pads as they interferred with my azimuth calibrations setup. Note that I compared the stability with the pads on and off and found no discernible difference.

I must mention that the stability I'm trying to minimise is only an issue at high magnifications of 300x plus.

Hi charles, thanks for that but at this stage I just want to use the same design as explained above.

Thanks all
Richard

[Barrykgerdes]

Hi Richard

I have a 16" lightbridge. However I can't see it for a couple of weeks as it is still at Wiruna. The bearing assembly is about 18" for memory but I haven't looked at it since last July.

It occupies a space of about 5 mm. I had it out last July because I had dirty/sandy water flow over the base in a rain storm and it was full of grit. It still is not right.

That drawing was lifted from a drawing of another dobsonian I modified years ago and edited slightly and I would probably make a special bearing housing for the rocker box rather than recess it. That drawing is for 1" thick ply. At the moment I just use a thrust washer and pull the bolt down with the underneath retainer assembly.

My lightbridge also has a different centre bolt. I have an old Magellan 1 and its replacement centre bolt with the encoder was an exact replacement except I had to make a new sleeve to remove the slop in the base. I also modified the altitude bearing to take the other encoder. These encoders are now used with an Argo Navis. Making specialised centre bolts is no problem on the lathe.

I have only used the lightbridge on DSO's at around 70 Mag. I did manage to see the flame nebula clearly but have not got the horsehead yet. To get 300 mag I would certainly need to beef up the base and azimuth pivot.

Barry

[hickny]

I built my own scope 13.1" mirror and used a lazy susan bearing from http://www.carbatec.com.au/lazy-susan-bearings_c15410
had it mailed out in a couple of days.

[BEVAN5433]

HI RICHARD
I have scaled out the bearing size from the assembly photos of the 16" L.B. AND IT DOES COME TO 18" given the base size is 31" in dia. this is suprising to me I would have guessed smaller.I have a 16" scope fitted with Jims TNT tracking.
BEVAN