Roller bearings on a Dob

I noticed that the Hardin Dobs advertise roller bearings on the base,
between the fixed part of the base that sits on the ground and the
movable part of the base on which the OTA rides.

Are roller bearings as smooth as Teflon and Formica or Teflon and
whatever other slick stuff is used on the Orion, Meade, and other Dobs?
I suspect they need lubricating now and then with something like
silicon spray or white lithium grease ???

Thanks.


SPQR

Are roller bearings as smooth as Teflon and Formica or Teflon and
whatever other slick stuff is used on the Orion, Meade, and other Dobs?

Good bearings have 1) enough friction so that the scope doesn't move when
you don't want it to, and 2) low stiction so that you can move it by small
amounts. Quality roller bearings can have low stiction, but typically have
too little friction. For small dobs, Ebony Star and Teflon is hard to beat.

Dennis

wrote in message
ps.com...
I noticed that the Hardin Dobs advertise roller bearings on the base,
between the fixed part of the base that sits on the ground and the
movable part of the base on which the OTA rides.

Are roller bearings as smooth as Teflon and Formica or Teflon and
whatever other slick stuff is used on the Orion, Meade, and other Dobs?
I suspect they need lubricating now and then with something like
silicon spray or white lithium grease ???

I've not noticed any problems with the bearings on my 8''


--
BV
Webporgmaster of iheartmypond.com
Check out the IHMP forums, ihmp.net/phpbb
I'll be leaning on the bus stop post.

On 20 Dec 2004 11:55:29 -0800, wrote:

I noticed that the Hardin Dobs advertise roller bearings on the base,
between the fixed part of the base that sits on the ground and the
movable part of the base on which the OTA rides.

Are roller bearings as smooth as Teflon and Formica or Teflon and
whatever other slick stuff is used on the Orion, Meade, and other Dobs?
I suspect they need lubricating now and then with something like
silicon spray or white lithium grease ???

Good roller bearings are smoother than static bearings. The problem with Dobs is
that roller bearings are usually _too_ good, and you need to add some sort of
clutch or tensioner to get the right feel. What I did was to put a roller thrust
bearing underneath the center of my Dob platform, which lifts it just enough
that the existing teflon bearings around the outside have a good load on them.

IMO, if you are really interested in making a first rate Dob, you would go with
roller bearings and strap tensioners on both axes. That would give you very fine
control.

At the low speeds such bearings are used, there is no need for more lubrication
than a drop or two of fine machine oil from time to time. You don't want to use
grease.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

wrote

Are roller bearings as smooth as Teflon and Formica or Teflon and
whatever other slick stuff is used on the Orion, Meade, and other Dobs?
I suspect they need lubricating now and then with something like
silicon spray or white lithium grease ???

No lubrication is necessary unless, I guess, you squirt dirt between the
base's discs. I have an e2 dob base, and my roller bearings work perfectly.
The difference between the e2 and other bases is that the e2 has a nylon
friction screw to control movement in azimuth, and it's very smooth and
precise.

In article om,
says...
Are roller bearings as smooth as Teflon and Formica or Teflon and
whatever other slick stuff is used on the Orion, Meade, and other Dobs?
I suspect they need lubricating now and then with something like
silicon spray or white lithium grease ???

While not exactly like the scopes you mentioned, my TeleKit has
roller bearings on the azimuth axis, with an adjustable brake. The
brake is a block of dense, heavy plastic (?) topped with a stiff felt
pad that can be adjusted along a threaded rod in a slot, riding on a
slightly ramped bottom under the rocker box bottom. The pad's tension
against the bottom can therefore be adjusted.

The altitude bearings are a combination of Teflon in the reat and
roller bearings at the front. In both cases, they roll against a
relatively smooth laminate surface. It's just slightly textured, FAR
less than Ebony Star and the like.

Are they better, worse or even with a purely Teflon/laminate
solution? I haven't decided yet, so they must be pretty close.

Pros:
Smooth, predictable (in terms of design and scope size/weight), when
properly adjusted and balanced they have a delighfully light touch,
adjustable

Cons: Too easy to move at times, less "friction margin" means less
margin for error when slightly impacting balance, slightly noisier,
adjustable

....you'll notice I put 'adjustable' in both categories... I've yet to
decide if it's an advantage or just something I needlessly end up
fiddling with.

Having the azimuth axis on bearings /does/ tend to accentuate the
difference in friction between the OTA in the horizontal and vertical
orientations. IOW, set the azimuth brake properly for observing at
zenith and it's usually too free at the horizon, and vice-versa.
Having an all Teflon-laminate system /might/ make that a little more
even, but it's got to be calculated carefully.

I can't imagine having a roller system with no control over the
friction. I've thought about replacing the felt with a Teflon sheet,
but Randy (Cunningham) says they tried that and it wasn't as good.
--

-- Len Philpot - --
------ ----- http://philpot.org/ --

Sure they need lube, but so does your eyeball. Roller bearings work
well as base supports and anti friction especially if they are in a wide
circle distributed well. I havean old 14" dob, wont name the brand but its
a rare named brand, in its day - the base supports are stainless
steel with a molded ring and roller bearing. I never could find out where
the company got these bases but they were perfect as a heavy duty
dob base. The side wood that attaches to these bases are full 1-3/4
maple! The dob has always been smooth as silk. I lube it every now
and then with spray lithium, and I would be crazy to get rid of this
_______ Liner 14" f/5 dob. Full thickness mirror. Fibre glass tube.
80mm f/4 finder. Its not for sale.
Bondo




wrote:

I noticed that the Hardin Dobs advertise roller bearings on the base,
between the fixed part of the base that sits on the ground and the
movable part of the base on which the OTA rides.

Are roller bearings as smooth as Teflon and Formica or Teflon and
whatever other slick stuff is used on the Orion, Meade, and other Dobs?
I suspect they need lubricating now and then with something like
silicon spray or white lithium grease ???

Thanks.


SPQR

Chris L Peterson wrote:

On 20 Dec 2004 11:55:29 -0800, wrote:

I noticed that the Hardin Dobs advertise roller bearings on the base,
between the fixed part of the base that sits on the ground and the
movable part of the base on which the OTA rides.

Are roller bearings as smooth as Teflon and Formica or Teflon and
whatever other slick stuff is used on the Orion, Meade, and other Dobs?
I suspect they need lubricating now and then with something like
silicon spray or white lithium grease ???

Good roller bearings are smoother than static bearings. The problem with Dobs is
that roller bearings are usually _too_ good, and you need to add some sort of
clutch or tensioner to get the right feel. What I did was to put a roller thrust
bearing underneath the center of my Dob platform, which lifts it just enough
that the existing teflon bearings around the outside have a good load on them.

IMO, if you are really interested in making a first rate Dob, you would go with
roller bearings and strap tensioners on both axes. That would give you very fine
control.

At the low speeds such bearings are used, there is no need for more lubrication
than a drop or two of fine machine oil from time to time. You don't want to use
grease.

I beg to differ. It depends on the grease. Light lithium is just fine in
fact I wouldnt use anything else on mine. But the right smooth (pure) grease can add
just the amount of "drag" you were talking about -
Bondo





_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

The mind boggles at the concept of reducing friction via a roller
bearing and then adding extra friction via a seperate component to
increase the reduced friction of the roller bearing! ;-)

Larger & heavier dobs might well benefit from reduced friction in the
base bearing. But using roller bearings on smaller ones just smacks of
salesmanship.

The silky movement of Formica ( or Ebony Star) on Teflon is no
accident. The static and dynamic friction are closely matched. Start
pushing and the friction doesn't increase or reduce as it starts to
move and keeps on moving. See Dennis Woos' post above. :-)

Chris.B

On Tue, 21 Dec 2004 00:58:17 -0600, Bondo wrote:

I beg to differ. It depends on the grease. Light lithium is just fine in
fact I wouldnt use anything else on mine. But the right smooth (pure) grease can add
just the amount of "drag" you were talking about -

The problem is that you don't have good control over the drag this way. I was
speaking of what I consider the ideal design, with frictionless bearings and a
tensioner system to set the drag. With such a design, you don't want drag from
using a viscous grease in the bearings.

If you have a basic Dob that has been modified with roller bearings, sure,
grease is a simple way to add some drag.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com