An equatorial platform (finally)

[Tim Armes]

Hi,

A couple of years ago I started work on an equatorial platform for my 8" Dobsonian, however the project got put on the back burner because I didn't have either the necessary tools nor the woodworking experience to do the job well.

This week, however, I started again. I now have a working platform 

(it just needs a coat of paint).

To design the table I made extensive use of the paper entitled "Geometric Method for Designing a Minimum Height, Vertical North Sector (VNS) Equatorial Platform" by Gene A Baraff. Those interested will find this paper in the "eqplatforms" Yahoo group, along with a Excel file to do the calculations.

Armed with all the information needed, I created a platform design using Adobe Illustrator and then printed the template to scale (tiling it across several pieces of A4 paper). This was used as the template for cutting the wood and positioning the sectors.

The jig is, without a doubt, the most awkward part of the build. I had a dismantled light table that I once built in a previous life, so I repurposed that in order to create a rotational axis on which I could attach the platform. During my first attempt (2 years ago) I tried to use a sander to for the sectors - however the result was very poor. This time round I used a router (since I have one now). You can see the platform clamped on here:

I built a mount to hold the router firmly at the right angle on the other side:

(Note that building the router holder was an interesting problem in its own right)

The Excel spreadsheet mentioned above generates a image of the theoretical curve that should be produced. By printing that to scale I was able to verify that my jig was performing correctly - and I was delighted when my sectors came out to be exactly the same as the printed ones 

Although the jig was the hardest part of the build, there was another part of the project which caused problems - the bearings and bearing holders. I scoured the internet for solutions, but it wasn't easy to find a product that would works well. In the end I discovered that I had a neighbour that worked in a machine shop turning metal (!), andhe was able to create the bearings and holders for me.

Anyhow, it ended up taking about 2 days to build, and I tested it last night to my great satisfaction 

[Joseki]

Congrats, that looks like a very neat job.

[Laurie61]

A nice looking job  I must admit to chickening out on building one of these and bought one, they are very useful. Mine came with a cut out switch which operates at full travel and a stop used to indicate the reset position. It stops the drive running the platform off the mount while you are not watching     I did a review and took some photo's of mine here, it shows the stop/limit switch.

http://stargazerslounge.com/topic/204807-the-watch-house-equatorial-platform/  

[Tim Armes]

A nice looking job  I must admit to chickening out on building one of these and bought one, they are very useful. Mine came with a cut out switch which operates at full travel and a stop used to indicate the reset position. It stops the drive running the platform off the mount while you are not watching     I did a review and took some photo's of mine here, it shows the stop/limit switch.

http://stargazerslounge.com/topic/204807-the-watch-house-equatorial-platform/

A cut out switch would be nice.

In my case there are screws at the end of each sector (holding down the metal strips) that should act as barriers to that problem. I should try it though

[astronymonkey]

Great project tim .... what thickness ply did you use and what motor have you gone for ?

it looks like a great end result.... but that jig looks like a 3d headache to put together !

cheers

[Tim Armes]

Great project tim .... what thickness ply did you use and what motor have you gone for ?

it looks like a great end result.... but that jig looks like a 3d headache to put together !

cheers

Hi,

I've used 18mm ply (which seems more than sufficient for my 8" Dob's weight), and the motor is a Celestron DC motor (sold for their equatorial mounts).

For the jig I had to be careful about the piece that holds the board to the rotating pole. I drew it out in Sketchup to make sure that I got the edge lengths perfectly correct in order to ensure that the center of rotation was about the polar axis.

Tim

[astronymonkey]

Thanks tim,

sorry about the questions ....

- does the motor rotate at the correct speed without any adjustment or is the platform built to the correct size to accomodate the motor speed.

- im also trying to work out which curve the router is cutting

ive considered making one of these for ages, hence my questions , as yours looks really neat.

cheers

[Tim Armes]

Thanks tim,

sorry about the questions ....

- does the motor rotate at the correct speed without any adjustment or is the platform built to the correct size to accomodate the motor speed.

- im also trying to work out which curve the router is cutting

ive considered making one of these for ages, hence my questions , as yours looks really neat.

cheers

The motor has a little speed knob on it which gives a fair bit of adjustment. In my case I did the following calculation:

North sector circumference: 3023mm

Minutes/revolution of Earth = 24 * 60 = 1440

mm/min for north sector  = 3023/1440 = 2.09

I needed to know how big my bearing diameter should be in order to work within the motor's speed range. Trying different values told me that a 16mm bearing would work:

Minutes/revolution for a bearing of 16mm diameter (50.24mm circumference) = 50.24/2.09 = 23 revs/minute (which is just above the motor's slowest speed).

Note that I bought the motor first in order to determine it's speed range.

---

With regards to the router, in the picture the router is cutting the north sectors. You're probably confused because I'm using the end of the router bit rather than its side. The reason for that is simply because with the overhang I have over the north sectors I couldn't get the router close enough to use the side of the bit. By using a 25mm bit I could just about cut the entire thickness of the sectors.

Some designs don't have this overhang, so that isn't an issue. I have it since, based on Geoff's design strategy, the Dob's feet sit directly on top of the north sectors for greatest strength and minimal flexing. Not wanting the Dob to be teetering on the edge of the platform I extended the platform over the sectors.

Tim

[Tim Armes]

Hi,

A couple of years ago I started work on an equatorial platform for my 8" Dobsonian, however the project got put on the back burner because I didn't have either the necessary tools nor the woodworking experience to do the job well.

This week, however, I started again. I now have a working platform 

(it just needs a coat of paint).

To design the table I made extensive use of the paper entitled "Geometric Method for Designing a Minimum Height, Vertical North Sector (VNS) Equatorial Platform" by Gene A Baraff. Those interested will find this paper in the "eqplatforms" Yahoo group, along with a Excel file to do the calculations.

Armed with all the information needed, I created a platform design using Adobe Illustrator and then printed the template to scale (tiling it across several pieces of A4 paper). This was used as the template for cutting the wood and positioning the sectors.

The jig is, without a doubt, the most awkward part of the build. I had a dismantled light table that I once built in a previous life, so I repurposed that in order to create a rotational axis on which I could attach the platform. During my first attempt (2 years ago) I tried to use a sander to for the sectors - however the result was very poor. This time round I used a router (since I have one now). You can see the platform clamped on here:

I built a mount to hold the router firmly at the right angle on the other side:

(Note that building the router holder was an interesting problem in its own right)

The Excel spreadsheet mentioned above generates a image of the theoretical curve that should be produced. By printing that to scale I was able to verify that my jig was performing correctly - and I was delighted when my sectors came out to be exactly the same as the printed ones 

Although the jig was the hardest part of the build, there was another part of the project which caused problems - the bearings and bearing holders. I scoured the internet for solutions, but it wasn't easy to find a product that would works well. In the end I discovered that I had a neighbour that worked in a machine shop turning metal (!), andhe was able to create the bearings and holders for me.

Anyhow, it ended up taking about 2 days to build, and I tested it last night to my great satisfaction 

My images have disappeared, and I've no idea why. I also can't find a way to edit my message to put them back. Help?

[Scott]

My images have disappeared, and I've no idea why. I also can't find a way to edit my message to put them back. Help?

Hi Tim, I've reported it to admin so someone may be able to help. Thank you astromonkey for bringing it to my attention

[Grant]

Hi Tim,

This is an odd one - it looks like the images were removed but I can't see when - they were present at 3am this morning and gone by about 11am.

I saw you uploaded images to a gallery - was this after you noticed your images missing or before? The other thing I noticed, the images weren't embedded in the regular way to begin with - had you posted them to another post before starting your own thread or something like that?

Thanks,

Grant

[Tim Armes]

Hi Tim,

This is an odd one - it looks like the images were removed but I can't see when - they were present at 3am this morning and gone by about 11am.

I saw you uploaded images to a gallery - was this after you noticed your images missing or before? The other thing I noticed, the images weren't embedded in the regular way to begin with - had you posted them to another post before starting your own thread or something like that?

Thanks,

Grant

Hi,

I created a gallery after I saw that they were gone, with the intention of editing my post. However, I can't edit my post.

I couldn't work out how to include the images inside the post without attaching them (but I wanted to embed them), so I attached them in order to upload them, then I referenced those attached files when inserting the images in the right place in my post. I assume that because they were really attached, the system deleted them during a cleanup.

How should I simply upload an image to embed it in a post (rather than attach it as a file)?

[Mickthedigger]

Upload it to http://imgur.com/ and just paste the folder link in here. Nice and easy.