A big jar of nothing.

 

 There it is with the view ports welded in. I went for one to view filament and on to view object being coated. (I didn't do the welding, I thought, as it was critical I leave it to the expert!)

 There was some distortion when the welding happened so I had to sand the flanges flat again. I made that little sanding thing to help. It took a while but I got then flat enough for the o-rings to take up any of the remaining irregularity.

 

 The strangest thing was the bottom of the jar was no longer flat after the welding process. It shrank upwards towards the welded pipe. I was very surprised. It was across a section of at least 50mm. I spotted it when I did a test pump down and the bottom gasket was buzzing as air rushed in through the gap! Back to the counter top with sand paper as described before.

 Above is a view of the o-ring seal on view port. The o-ring are viton(€16 each woops). 6mm cross section. The glass is a square in 12mm, normal type. I just got a glazier to cut it for me.

So the tube sits proud of the flange by about 3mm. This keeps the o-ring in place. I cut the clamping rings from 3mm aluminium. Drilled the top one tapped the underside one. It is split as you can see from the side view.
Oh and I pumped it down today, its tight! Yipee!

Cheapo (metal) Bell Jar the beginnings...

After a long stretch of solid work I got a chance to get back to vacuum for a while.

I was getting a bit nervous of my glass belljar imploding so I decided to go for a metal one instead.

After seeing a guy on youtube who built a mildsteel box to coat telescope mirrors in I decided to give the gas cylinder a second try.

I bought a used gas cylinder 380mm diameter just right for my base plate at 400mm.

I let the remaining gas out and unscrewed the valve. Don't forget to fill it with water to displace the remaining gas before you go a cuttin'

 

I marked the line by wrapping a yoga at around the cylinder to get a parallel line. That wasnt a good idea... you need to use some thing not so stretchy, that defeats the purpose! I marked away and used the bottom end with the complete dome.

I put the cylinder on it side and cut it with the water still inside. It was pouring out all over the place. I trimmed much of the foot ring off too. I wanted to get rid of excess weight. It is heavy.

Once it was cut I dried it straight away. We don't want any rust forming, very bad for outgassing.
Then on to leveling. Even though I paid great attention to the cutting I still spent 3 hours leveling the cut to get it nice ond flat. For this process I spray glued strips of al'oxide paper to a scrap of countertop. Its nice and flat and very ridged. I did a couple of hours of 80grit and an hour with 120...

Very tiring on the arms! During the sanding I regularly ran a black marker along the edge so I could see my progress clearly. I would watch the colour sand off, and the black patches get smaller and smaller. Eventually I got down to a consistant edge. I went then, by hand with a finer sand paper to get rid of the 120 scratches. I rubbed along the edge insted of across it. If there are scratches left they are better not to be radial across the edge as it is more likely to leak in that case.

The whole interior had a dark crust on it. I don't know what it is, possibly passivated with phosphate? I diligentlly sanded this away. There was still a bad smell coming from the tank. This got less and less as the crustyness came off.
I cut a new flat rubber gasket and greased up and sure enough it pumped down to 40micron the limit of my pump....

A Little Closer!

This is the casating I wanted to try a bit of evaporation on to. Its made of fastcast polyurethane and then spray-painted with gloss black.As the Al coating has no filling qualities the gloss of the coating is a result of the texture of the base.

 

I picked up a few aluminium prefused tungesten filiments from a company called Midwest Tungsten in the US of A. This is a bit overkill for a DIYer but the were cheap, from their surplus bin!

 

So I hung the plastic part from a wire inside the bell and began to pump down...

When I got to 40micron or so I turned on the MOT power supply.(I wrote this up in the blog a good while ago)

After 20 seconds I got this! I was delighted! Just mechanical pump, no diff. Now, its not up to scratch yet but these little victories help me keep the faith.(Ignore the electrodes poking through, they are just sealing the holes here)

A strange thing at this vacuum is the fact that the back of the part got a covering of Al. as well. It must fly around in the belljar at these crappy vacuum levels.

 There is the front. Opaque but not bright. It has greyness in person. Getting there...

I found a leak!

After a long absence from my metalisation project I decided to get back to it. I was having a real nightmare with my belljar not getting the vacuum level I was expecting. Or that I needed to even start a diff pump. There were so may potential leaks I was overwhelmed for a while. So I decided to go step by step and eliminate the possibilities starting at the pump.
Flexible pipe tested fine, under water with compressed air. The second section however had a f**king leak. Right there, bubble, bubble, bubble. I couldn't believe it. The solder joint looked fine but it was leaking.
So I Glyptaled it under a vacuum and I was all fixed up!
More to follow...

Copper bellows again

I decided I wasn't going to let the peskey bellows defeat me, so I went for it again. My copper bellows MkII are a success! Here's what I did...

As before, I made a wax model on the lathe. This time I stuck to the rules I mentioned in my other copper bellows effort above.

So my recesses are tapered and wider than they are deep.

 

Wired, dipped in white/mineral spirits, covered with graphite powder. After a bit, burnished with a Qtip with more graphite on it.

 

Copper plated at very low current.

Below is the bellows just out of the plating solution.
It had two sessions in the plating solution. One to get the form strong enought to survive a bit of handeling and the burn-out. And another to build up a decent thickness of metal. 

Another warning note here: I was calculating on the assumption that the solution was putting down 1 micron every 2.5mins, as I read in the literature.

But even after 6/7 hours I only ended up with 150 microns or so. Measured from the waste I cut out of the top of the form. I'm sure the vertical parts of the cylinder are thicker but the important flexing parts are only that thick, if not less. I would like to have gotten .3mm or even more. As there is serious strength,brittleness and porosity issues with simple electroforming like this.

I realised later that the problem was that even though I had calculated my current density ok, I was using voltage control to achieve it. So my overall power/wattage was less than it should be. Hence the thin deposit.

Very Expencive Beer Mat

I know this is off topic again but...

Just a quick post of a couple of pictures of a thing I cut with my homemade CNC today. This started life as a drawing which I photographed and vectorized. Then CAMed and routed. I'm very happy with the results. Size 120mm dia.

The reason for this piece is partly promotional and also I'm tring to see what my machiene can do!

I'm delighted with how this turned out.

Copper Bellows. A lesson for me.

I'm trying to eliminate leaks in my(still not working) laser so I decided to go for copper bellows instead of my current O-ring seal for mirror adjustment.

But I couldn't find any copper bellows, so I decided to give it a shot and see if I could make a pair.
After first considering soldering them up from parts, I decided to electroform.

Here is a picture of my wax mandrel. It is made from injection moulding wax. It turns ok if you don't try to take too much off in one go.

I then cut the recesses or corrugations or what ever you would call it. With the piece still spinning, I hit it with a touch of a gas flame to soften the corners and give me a nice smooth finish.

 

I parted off and heated a bit of copper wire and stuck it in to the end. Then I was ready for conductive coating.
There are a few options here. Sputter, chemical silver, electroless copper, conductive paint, graphite.
I decided to go with graphite because it was the simplest and I had it at hand.

 So I dipped the wax in "white spirit" for 20 seconds and drained it. Then the surface of the wax was slightly sticky.
Then I bunged it in graphite powder. I made sure it was all covered before the white spirit flashed off.
After a minute I brushed the excess powder off with a makeup brush.
A very important note here is that burnished graphite powder is significantly more conductive than non burnished.
Just rubbing with the bristles of an artist paint brush is enough to burnish it.
I need to reach into the interior ring to burnish the graphite there before it would plate properly.

 Here it is beginning to get its initial copper coating. Nice!

I electroformed for 8 hours giving me 8*24microns so 0.2mm in theory!

 

 Measuring the bare wire versus the electroformed part confirmed the thickness.

 I drilled and melted out the wax.

I then very carefully annealed the tube, in the process evaporating the remaining carbon. I pickled
and ultrasoniced the remaining crud off.

And then disaster!! The inner rings were so thin that they cracked in the ultrasonic. They came out with some small holes and
crack lines.
I had always planned on re electroforming inside the tube as I thought they would be a little thinner. But they are significantly thinner and quite brittle.

So I placed a copper pipe electrode into my copper plating solution and began plating from the inside.

After another 4 hours...

 I ran the ends on the belt sander to clean them up...

 And tin/lead soldered it together. Ta da, one flexible mirror mount!

In retrospect I would do this differently. I had a huge problem with the shape of the mandrel causing different plating thickness
I bet anyone with plating experience could have seen that coming. So for the next electroformed copper bellows I will follow these guides:

• Interior corrugations must be wider than they are deep.

• Returns must be angled to face the electrode for copper plating reasons.