13 replies to this topic

[daviddecristoforo]

I've had little time to work on the telescope project but I did manage to get the mount design refined a bit. I also managed to make a wooden bearing, just to see if it would be sufficiently functional. It did work OK but I realized that wooden bearings were not going top provide the kind of smooth, quiet action I want for this mount. I started looking at steel bearings and found what I would need was going to cost around thirty bucks each making the total cost of the just the bearings around $250 plus shipping (ouch!) Then I discovered AliExpress, kind of a Chinese version of Amazon and found the exact same bearings for a total cost of seventy bucks including shipping!

 

 

The only issue was the interminable shipping time.

I redesigned the mount around the steel bearings, a radial needle roller bearing and a flat thrust bearing at each end of the two shafts. There are also numerous small changes in the design which simplify the construction. I will add some locking screws and setting circles before I'm done with this!

 

The jpeg is too small to see the details as the original drawing is done full scale. If you are interested, a full sized PDF version can be seen here:

 

http://www.daviddecr...isc/mount_2.pdf

 

Would be most interested is any comments or advice and I will be posting progress shots as I go.

[555aaa]

Is this linked to another post?
Is this wood?
My only feedback is that needle bearings are very thin and rely on a stiff and precise bore to stay in round. A conventional deep groove ball bearing is inherently stiff. Good luck, it looks nice.

[daviddecristoforo]

Is this linked to another post?
Is this wood?
My only feedback is that needle bearings are very thin and rely on a stiff and precise bore to stay in round. A conventional deep groove ball bearing is inherently stiff. Good luck, it looks nice.

All wood except for the bearings and a couple of lag screws. Precise boring not a problem. I am figuring that these shafts are not going to be moved much. It's not like they are rotating at 1500 RPM! I just want a smooth action and these bearings are load rated at far beyond what they will actually be subjected to in actual use.

[Pierre Lemay]

I like it. Building a GEM is a bit of a step back in time (most build dobsonians now) but it's refreshing to see someone working on making an equatorial mounting like we used to make them. I will be following with interest. Are you going to add a drive?

[daviddecristoforo]

...Are you going to add a drive?...

The idea is to make a mount that could be motorized at some point. I'm building the scope for my grandson. Maybe he will take enough interest in astronomy to talk his dad into it! Never know. I had originally planned on a Dobsonian type mount but this just idea just popped into my head one day and got stuck there!

[daviddecristoforo]

So I have the two tubes ready. Right now, they are longer than they need to be and I need to determine the lengths. Since there are no dimensions on this drawing, I'm really looking for general advice. It seems to me that the length of the DEC axis would not be critical. But the length of the RA shaft has me wondering. It would seem logical to assume that the tilt requirement would affect the tube length. As I have it drawn the polar tube will hit the base at some point, limiting the tilt range. But again, it would seem logical to assume that as long as the correct angle can be set, it would not be necessary for the polar tube to be able to be tilted to vertical. For reference, the tube diameters are 6". Any advice on this? 

 

Thanx

DD

 

PS

Here is a link to the pics of the bearing blocks that have already been made...

https://www.cloudyni...venture-begins/

Edited by daviddecristoforo, 22 June 2017 - 01:19 PM.

[macdonjh]

The only time the polar axis has to be horizontal is if you're tracking the stars at the equator.  Seems unlikely you'd need to design for that.

[daviddecristoforo]

The only time the polar axis has to be horizontal is if you're tracking the stars at the equator.  Seems unlikely you'd need to design for that.

Unlikely the scope would ever be used at the equator. So what  would be a good range of movement for anywhere in the continental US?

Edited by daviddecristoforo, 23 June 2017 - 12:17 PM.

[JimC2]

How far north and south in the US do you plan to set the scope up?  That defines the Polar Axis range.

[daviddecristoforo]

How far north and south in the US do you plan to set the scope up?  That defines the Polar Axis range.

I live in the Sacramento, Ca area. Let's suppose I wanted to be able to use the scope at both the Canadian and Mexican borders. What would be the range of movement needed?

Edited by daviddecristoforo, 23 June 2017 - 03:14 PM.

[GShaffer]

How far north and south in the US do you plan to set the scope up?  That defines the Polar Axis range.

I live in the Sacramento, Ca area. Let's suppose I wanted to be able to use the scope at both the Canadian and Mexican borders. What would be the range of movement needed?

Have a look at the latitudes on this map....

http://www.enchanted...tivity/latlong/

[daviddecristoforo]

So a tilt range between 25 and 50 degrees would be Ok?

[JimC2]

Yes

[daviddecristoforo]

Sweet...

Thanx