Tasco 4.5" Dob

Tasco 4.5" Dob

Bonjour, mon ami! I put this together through the week for you. It was just easier than sending a PM with an album full of pictures...
This way it's also a little more permanent. It might save you some time with measurements; at least it's a starting point, and I took some "detail" shots to highlight certain things.

The measurements for the wood are at the bottom of this page.

If you click on the image it'll open up in a new window/tab as full size. This is very Web 1.0 here; I'm actually writing this in Notepad...!

In the Beginning...

I bought one of these a few years ago, a Tasco 4.5" at f/7.9. Bone stock, Apollo-era Tasco 'Lunagrosso'. It comes complete with a spherical mirror, yet it puts up really stunning views, especially with a 1.25" focuser and some good Plossls.

The problem with it was the mount. Not that it wasn't any good, it was just overloaded.
The clamshell holding the scope onto the mount weighs almost what the scope does.

Well, that had to be fixed, so therefore the Dob base.


These pictures were taken a while back, after I had a very nice first light with it.

A few items, like the handles, I added later. One thing I still have to add is an eyepiece tray!

I keep forgetting about it until I'm outside with the scope, then I bring everything back inside and forget about it again...

As for the original mount, it's in really good shape. It made a nice home for my 60mm Sears 6331, and it's from the same time period; late '60's/early '70's.

I made a clamshell for the 60mm that weighs about a fifth of what the Tasco one does. Complete with that, the 60mm f/11 is very solid on this mount.

Too bad they weren't sold like this originally!

So that's the history behind my 4.5", whether you care or not... 😄

The Rocker Box

Now on the rocker box itself, I cut out a V-shape for the telescope to sit in. I don't have a router, otherwise I would have cut a semi-circle. There would be more surface contact between the scope and base, which is probably a good thing. Still, I have had a DSLR on it and it's been fine. Your call.

Below are four pictures of the inside of the base to highlight a couple of things I did.

That piece of black stretching across the front part of the base is actually an inner tube. I used some pieces of aluminum from an old window frame to screw it in. Why? Well, this keeps the scope from banging against the wood on the front of the base. The base would've been a bit narrower, but I figured it was worth the extra inch. And really, it is. After the first time I collimated it, I've had to collimate this thing once in two years. The inner tube is stretched enough so that there is some "give", but the tube can't hit the wood. Saves jarring the mirror.
I figure I may even trim the ends off the tube one day too...😉


The 2" X 2"'s on the inside at the bottom are what holds the three sides together.

Then there's the handles. The one on the left is towards the back; the one the right is toward the front. I found staggering them like that made it very easy to pick the scope up while still seated, and put it wherever I want. I even did the same thing to my 10"; much easier to lift, though not while seated!


I put some adhesive backed black felt along the inside of the rocker box where the tube box rubs against it. Barely touches it, but adds to the smoothness.
The pieces of material in the V-groove are furniture sliders from the Dollar store.

And the ground, or base, board. This is the part I really wish I had a router for. It doesn't even have to be a circle; in hindsight I should have just cut a square instead of trying to follow a line with my jigsaw. It is what it is.
The board I used had some laminate on it, and I initially tried that with the furniture sliders I used as contact points. It was OK, but I found it a bit "sticky" on the movement. Using an old 33 RPM record was the way to go, at least for me. The laminate on the board I had was somewhat rough in texture, so that probably didn't help. You can also see where I screwed the 2" X 2"'s in.

The feet are old bicycle brake shoes bolted onto some 3/4" wide X 1/8" thick flat bar, and screwed into the base. I butted the nuts hold the brake shoes on up against the base, so there's no sideways motion. They work very well, no scratches on tile and no slippage either...

BTW, the record is Danny Boy sung by Ray Price; thrift store for a buck 😁


The OTA Box

And finally the tube box. I thought about this for a bit, and this was the second build of that... On the inside, I used furniture sliders to go against the top and bottom of the tube. For the sides of the tube, I used some of that black plastic you find at the bottom of some cloth grocery bags. Also, the top piece of wood on the tube box is bolted in at the sides.
I used four 'L' brackets, screwed them to the top piece of wood, and drilled holes and used bolts in the sides. This way I can get the tube out if I have to, without worrying about screws not holding when I put it back together. I've never had any reason to take the tube out yet, though...!


The altitude or elevation bearings are 5" drain caps I found in the plumbing section of Home Depot.
I think they were $6 each or so. They make for good carrying handles for the OTA, too.
They also have a "molding" point in the exact middle, so making measurements to get it all squared up is simple.

The Finderscope

And the finderscope, if you're interested. I used a 6 X 30 straight through from a Celestron, and shortened the front part of the tube by about half. I put a .965" diagonal in the middle with some plastic spacers (again!), a bit of glue, and it's been fine for two years. The pics do a better job explaining, probably...


As for attaching it to the scope, I used a piece of aluminum flatbar I bent and drilled holes in to match the finderscope mount holes already on the tube. The clamp is an aluminum handlebar clamp from an old scooter. You can also see I didn't use the original holes in the focuser, either. Only two holes from the tube lined up with the holes in the focuser, and it was skewed. Drilled three new ones...


Plans and Ponderings...😄

Well, there's actually not much else I can think of. Pretty straightforward; took me a weekend to put the whole base together. Or at least to the point where I knew it would all work.

As for the finish, I used Marine Spar varnish on each piece individually; two coats per piece, all sides. It's meant for the outside of boats, as they live in salt water, so this is probably overkill.

I cut all the wood, drilled the appropriate holes, and "lightly" put it all together to make sure everything fit.
Then I took it back apart, and did all the sides and edges of each piece. Between the two coats, drying time and having to flip all the pieces over to do the back side, it took four nights.
And if you use the Marine Spar varnish, be aware the fumes are pretty nasty; doing it outdoors with a bit of wind would be the idea!
I found the varnish at Canadian Tire in the paint/stain section. I bought the can that was $20, and there's still more than half left.

Most of the wood I used was 3/4" thick pine board shelving that I found at Lowes. The laminated piece I used for the base I found in my basement. I'm all over the map with my supplies, it seems...
The pine board shelving is light weight, easy to build with, and most importantly, straight!
But, maple or birch would be nice, too...

And please measure the width of your tube first! I'm sure you would, but just to be sure... My tube is 5-3/8" wide, yours was manufactured in a different decade, so I can't say for sure if your scope OTA is the same as mine. Not to come across as yelling, but that thought just hit me. If it's the same (and it probably is), my measurements will work; if not you can just adjust accordingly.

Now for the dimensions. Again, keep in mind I've made my rocker box a bit wider on the sides to account for the "inner tube" stopper. Eight inches across would have worked too, but the tube would be about 1/4" away from the front piece of wood when vertical.
And like I said also, you might want to go with a semi-circle instead of the V-groove that I did...

I didn't put in the dimensions for the 2" X 2"'s holding the rocker box together; I figure the angle and measurements are pretty obvious from the pics, and you may choose to do it another way.

So here they are. Not very artistic, or to scale even... 😁


When the tube box is assembled, the top and bottom piece at 5-3/8", plus the two 3/4 wide pieces bolted/screwed to the side, comes out to 6-7/8" wide (probably 7" with the varnish). The inside width of the box is 7-1/4", so that leaves 1/8" on each side for play. Seems to work.

The whole thing with a KK 18mm in it weighs 18 lbs (just over 8 kg).

For seating, I find a milk crate with a bar stool on top the perfect height for me to sit at and use the scope. However, I'm all of 5' 10", so I don't know how that would work for you. Might be an idea, too, to find what your comfortable with sitting on, and build the base to the appropriate height.
So many choices when it comes to personal preference!

Est voila, mon ami! Hope this is of some help to you. Any questions, just shoot me a PM on AF and I'll get back to you; they come to my email, too. I usually check email and AF daily.

Clear skies and good luck with the build! 🚀

Below, my 4.5" with (left to right):
Sears 6331 60mm, C80 by Vixen, Skywatcher 10" Dob