80mm long focal length refractor

[savarin]

Now working on the azimuth control.
I squared up a block of aluminium to hold a shaft with two bearings for an extension rod that links the flexible knob/shaft to the azimuth worm drive.
I was just going to drill through its length and counterbore for the bearings but the first drill bit snapped when it was almost through.
Hmm, no more ally to start again so I had a re think and re designed the block as shown in the drawing below in the hope a wood working solid carbide router bit would cut through the embedded drill bit and I could drive it out the remaining bits.
Heres the new design with the block and embedded drill bit.


Lets start milling and see


and finally, Yay! it worked

The angle milled to the face that has the bolt holes is so the shaft can angle out a bit for more clearance between it and the altitude control.
Have to counter bore the ends for the two bearings.
And of course more sanding and polishing.

 

[brino]

Yay! it worked

Hey Savarin,

Thanks for sharing even your little mistakes. Because this is not an uncommon occurrence in my shop, I wanted to take the opportunity to pick your brain about it.......

Was it a HSS drill bit?
If the drill was mostly thru, could you have started from the other end of the part and drilled thru and punched out the broken drill bit?
How did the milling cut go when you made it as far as the imbedded drill bit?
Did you mill clean thru the broken bit, or just open up a space to pull it out partially intact?
Also, why choose this method over EDM? was it strictly about the small diameter broken bit and access thru the recess?

Thanks!
-brino

 

[savarin]

Hey Savarin,

Thanks for sharing even your little mistakes. Because this is not an uncommon occurrence in my shop, I wanted to take the opportunity to pick your brain about it.......

Was it a HSS drill bit?

yes

If the drill was mostly thru, could you have started from the other end of the part and drilled thru and punched out the broken drill bit?

Hmm, never thought of that, what a dick. It was approx 1.5" in and I was unsure if it had wandered

How did the milling cut go when you made it as far as the imbedded drill bit?

I went clean through in the vertical direction, it made a fair bit of screeching as I went through but didnt seem to be a problem.
Then I milled along the the bit from the top not quite touching it then milled horizontally into it not quite touching it. This allowed me to pick it out and l drove the remaining bit into the gap.
Then some cleaning up but no dro fitted (dont have one so not perfect.)

Also, why choose this method over EDM? was it strictly about the small diameter broken bit and access thru the recess?

It was too thin and too deep so would have taken days I reackon.

Thanks!
-brino

no worries mate.

 

[Bill Gruby]

Charles, I have never seen anyone put the 9X20 lathe to work like you do. You are an inspiration to all. Kudos my friend.

"Billy G"

 

[savarin]

Thats very nice of you Bill, thank you.
Continuing with the azimuth bearing block.
I had a bit of a hard time deciding how to clamp this for boring it out for the stainless roller bearings.
After a couple of attempts to mount it on the face plate and being unable to get it centered to my satisfaction I had another idea.
I turned a mandrel to the inner dia 7mm to a tight slip fit in the holes and mounted it between centres in the 4 jaw chuck.
To get sufficient clearance I had to use a 3 to 2 mt adapter and a 2mt centre, gently tightening the jaws in the hope it would stay centred.
Then removed the mandrel and tail stock out the way and bored the hole for the bearing.



And it fits. I flipped it around and did the same for the other end.

Now I just have to hope they are parallel and the 6mm shaft will fit in them smoothly.
I have a bit of a problem with the altitude control cover plate as shown above.
When tightening the friction knob your knuckles now hit the two knurled screws removing a bit of skin. Answer - make a longer friction knob, that means another bit of brass casting.

 

[savarin]

The bearings work and the shaft fits nicely.
I had to use two universal joints to transfer the motion from the knob to the worm wheel.

but it rotates very smoothly. The new shield around the altitude gear is now aluminium as I had no brass wide enough.
Heres an overview of the how the controls hang.


I've made a new stainless washer to reduce the backlash in the azimuth clutch and that seems to be a lot better.
Now waiting for a short length of 100mm dia aluminium tube to make the dew shield.
Unlike a standard GEM mount the controls stay in the one place and never foul each other.

 

[savarin]

Whilst waiting for the 100mm dia tube I thought I may as well start on the fitting.
I turned a bit of 12mm plate to approx size and bored out the middle.
Bored this to the loose slip fit to the lens cell, then ground a grooving cutter and cut two "O" ring grooves, I did this with the lathe in reverse so it was easier to see paying a lot of attention to the screw on chuck to ensure it didnt un screw.


They fit just right with only a tiny bit proud


This is now a fairly tight push fit to the front of the lens cell

Now this ring has to be turned down to fit the inside dia of the 100mm tube, when ever that arrives.

 

[savarin]

turned the ring to a tight fit inside the tube and used high strength bearing lock to hold it in place.
Centered in the 4 jaw and cut a thread inside to act as an antireflection surface once coated in matt black.
Centering was a long job, every tiny adjustment of a jaw flexed it and sent the other three out of wack, it took forever but I got there.
Yes, thats a huge overhang and I was unsure if it would actually work but it did with no problems.
I really must make a carriage stop but the clamp worked perfectly.


I then turned down two mandrels for each end so I could clean them up and sand and polish the tube.
This shot is after using 800 grit followed by 1200 grit


Then it was of course polished.


Mounted in place

Very rigid, no chance of falling off or being knocked off.
Six more jobs left:-
1 make a solar filter holder (easy)
2 make a new end cap to fit in the dew shield (easy)
3 cut the central pier into two for ease of transport (easy)
4 cast a joiner for them (bit harder)
5 dismantle and re clean/polish everything (arghhhh)
6 powder coat all the black parts. (not my problem)
That should be the lot, I hope.

 

[ch2co]

Savarin
As usual good lookin' stuff. How do you plan to keep the polished finished polished and avoid scratches, oxidation etc?
I have always had most of my tubes powder coated with the exception of smaller stuff like finders, laser mounts etc.
The last two tubes that I made were a lens shade for my 105mm f15 and a main tube for a little 80mm f9.5. both those
tubes like most of my tubes are cheap welded irrigation tubing that always has a main seam that isn't very round.
I ground the seam mostly flat conforming to the rounded surface of the tube, then I turned
both these tubes on my lathe just like you did, but had a lot more oxidation. One tube was too long for my little lathe
and I had to improvise a bearing that pressed against the fully retracted and almost falling off the end of the lathe tail stock.
I tried to put a brushed finish on them, but it came out looking all wrong. Then I had the idea to use my angle grinder with a Scotch bright disk while the tubes were turning
slowly on the lathe for a finish that hides all the old scratches not already removed as well as the unevenness of the area around
the ground down weld. I am very pleased with the results and have gotten a lot of good comments on this finish from fellow
astronuts. So far after almost a year, this finish doesn't show scratches or oxidation that I have run into in the past.
Here's a couple of shots of it.

 

[savarin]

Savarin
As usual good lookin' stuff. How do you plan to keep the polished finished polished and avoid scratches, oxidation etc?

I've used an ultra clear lacquer for all the brass bits but am not worrying about the aluminium. I think the lacquer will get scratched eventually and have to be redone.
I'm hoping the dulling will occur slowly and I wont notice it until it really needs a clean up

Nice scopes, is the gem mount tracking? It looks a good one.