Conti Prestina Espresso Machine Restoration 101 (Completed and Indexed) - Page 17

Equipment doesn't work? Troubleshooting? If you're handy, members can help.
Warrior372

#161: Post by Warrior372 »

Obviously use whatever you guys want. It may very well be more efficient, but I have never used it on an espresso machine.

I was simply stating, for those who happen to be reading this thread in hopes of restoring their own machines, that citric acid at a concentration of 4 tablespoons per gallon of water will remove anything you run into on even the oldest, most corroded machines perfectly well and it is much safer than oxalic and muriatic / hydrochloric acid.

The oldest machine I have restored was a '52 and when I got the boiler open it was still half full of water with a thick black and red coating. I had to soak it longer than any of the other machine I have restored, but within a two to three days it had all flaked off.

All highly concentrated acids are dangerous to different degrees . . . . I try to avoid using acids that can dissolve glass as much as possible, with a personal preference leaning toward ones commonly found in food products :) .

If the crud is giving you a real problem you can always take a steel or copper wheel brush to it on the end of your drill too.

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drgary
Team HB

#162: Post by drgary »

Warrior372 wrote:Obviously use whatever you guys want.
Not fighting you on this, Mike. I had already started the more intensive acid treatment -- the parts were in the acid baths -- when I saw your warning it may be unneeded, so no disrespect intended. If memory serves, I'd also seen muriatic acid mentioned by Jim Schulman for cleaning old boilers in a thread cited above.

Since I've already started, I'm hoping this approach will save some work. I appreciate all the help you've given and hope those reading this thread will try the citric acid approach first.

BTW, when I wrote I'm taking precautions, I wasn't gratuitously saying I'd jump in a pool if needed. That literally was my Plan B! My pool is 15 feet from the bucket, and I made sure there was nothing in my pockets that would suffer if drenched! :lol:
Gary
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drgary
Team HB

#163: Post by drgary »

Hi Folks,

A quick update on the restoration -- all of the parts are safely out of the acid baths, mostly cleaned up, no damage to machine or person or even environment. I do want to issue a warning, however, and I'll post it earlier in the thread too. If you seek to neutralize the acid bath by adding a solution of baking soda, add it slowly, outside, while wearing protective gear. The acid bath intensely foamed up when I added the baking soda solution, so I was glad I did that carefully and in isolation.

Here are the boiler and face plate. Even after a week in muriatic acid, I'll need to scrub off the loosened crud with steel wool.

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Gary
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drgary
Team HB

#164: Post by drgary »

Update

I'm writing this post to gather my thoughts on next steps as well as update you on progress behind the scenes.

Case parts have returned powder coated, and I'm now awaiting piston gaskets and an assembly that includes a Sirai PSTAT and an extra valve that will release false pressure so I can start up the machine on an appliance timer. One of our members has offered to help me fabricate a drip tray grate, and I'm leaning toward one that spells "Prestina" in a nice typeface in the grille since I won't be able to get the drip tray grate exactly duplicated anyway. I'll also finish cleaning parts that have been descaled, will rinse them carefully, and will inventory the seals, gaskets and stainless steel bolts and fasteners I'll use. I'll also seek your collective advice on how to deal with a pitted cylindrical part that sits atop the actual piston cylinder. And I've acquired a bench grinder and polishing wheels and buffing compound to bring the stainless steel plates back to life. I've obtained a breathing filter and face mask but still wonder how much debris the polishing work is going to spread around my work area and whether this is something that must be done in the driveway for that reason. How have others who've done metal buffing and polishing contained the dust?

The epic saga continues ...
Gary
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What I WOULD do for a good cup of coffee!

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Clint Orchuk

#165: Post by Clint Orchuk »

Hey Doc,

The boiler and plate cleaned up really nicely. They look great. I didn't put the baking soda directly into the acid bath when I did it. I made a separate solution and dunked the parts in it to neutralize the acid that was left on the parts.

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drgary
Team HB

#166: Post by drgary »

I did both: neutralized the acid bath (be careful, see caution above) so I could more safely move it and pour it down the drain, and soaked the parts in baking soda solution, then rinsed them. A final baking soda treatment and rinse is just to be extra careful.
Gary
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What I WOULD do for a good cup of coffee!

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drgary
Team HB

#167: Post by drgary »

Hi Folks,

This project is starting to come back to life, if slowly. There have been lots of distractions, you know, life and all...

Anyway, I've set up the 6 inch bench grinder and polishing wheels and protected my makeshift workbench with a cut-out cardboard box so I don't get lots of polishing detritus on the plywood. Here's that setup with uncomfortable breathing filter and all. In addition I use a full face mask and leather gloves and am doing this in the driveway. I'm thinking of going to a paper paint dust filter because these particles don't seem very fine and that mask is really uncomfortable. I sound like Darth Vader when I'm wearing it too. The grinder's action seems pretty steady and it's not high RPM, so the gloves may be overkill.

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I have three machines with scratches in stainless steel, including the Prestina. I also want to polish the aluminum on my otherwise restored Microcimbali. Here's one of the Prestina panels to show you what I'm facing. As so often happens, a previous owner scrubbed the steel with abrasive. It's hard to photograph how extensively its scratched. Let's just say I would like a mirror finish and this ain't it!

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My first attempt used this Dico Emery buffing compound as the most aggressive, and after maybe 15 minutes of application it still didn't buff out those scratches.

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The wheels I'm using at the moment are stitched cloth and I've since obtained solid felt, but I don't think that's the issue. I need something with more bite.

Is there something else that can be applied with that bench grinder?

For the moment, I'm left with one of the panels covered with buffing compound and still in need of a good polish. BTW, does anyone know how to remove that greasy compound? What dissolves that stuff?

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But then maybe the collective wisdom on this forum will come to the rescue. Here's a great thread by Mark Hoy restoring an Elektra T1 that suggested the same thing in some detail. This is where the relevant part begins: Elektra T1 - #771 built in 2000 is now mine, and some quotes from that thread:
SL wrote:... if it is a stainless steel then all you need is a sandpaper and a lot of time. I do not know about Elektra but many machines are made of 304 steel which is very easy to work with. You can start with 220 or 320 grit paper (depending on how deep the initial scratches are) then continue with 400, 600, 1000 (it will start to shine at this point) and finish with 2000. The idea is to move from coarser to finer sandpaper, on every step the current grit will remove the scratches made by previous one and leave finer scratches instead. When you are at 2000 grit the steel will shine like a mirror. You can find all grits of paper on ebay or check your local Home Depot or other similar store for coarse paper (up to 600) and auto parts store (PepBoys, Kragen, etc) for 1000-3000 paper. You can also buy a small buffing wheel that can be mounted on the electric drill and polishing compound at Sears or Home Depot. In this case you can skip 1000 and 2000 paper, but if you have visible scratches you will have to start with coarse sandpaper anyway, because most of the polishing compounds are too fine to remove those scratches.
shadowfax wrote:2 words: orbital sander.... or alternately, belt sander. I like the orbitals best. They will save you a lot of time, but I think that, from what I have read about polishing stainless (never done that, only rough-sanded aluminum), you may want to use an orbital sander up to 1000 grit and then buff it the rest of the way. Of course, that is only if you have bad scratches. They are a serious pain to get out, I can imagine.
Mark Hoy suggests using a Festool Rotex 150, but that's almost $500! That's a random orbit sander with adjustable speeds. Maybe I can rent one ...

I do have a cheap Craftsman random orbit sander that takes stick-on pads. I wonder if that would do the job? Here's what that looks like:

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I would love any suggestions about how to do this relatively quickly without spending more on tools or subbing out the work than it cost for the Prestina itself.
Gary
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RayJohns

#168: Post by RayJohns »

Hi Gary,

You might want to consider getting something more along these lines:

http://www.amazon.com/DeWALT-DWP849X-7- ... 185&sr=8-3

That's what I use when I have a big grinder or polishing job. Also, don't under estimate the effectiveness of hand polishing. A bench grinder is okay also, but usually doesn't work all that well for large flat surfaces.

As far as removing that polishing compound build up, you can try carb cleaner (such as Berryman B12 chemtool).

For most polishing jobs, I finished with a product called Blue Magic. It's a cream for polishing. It works amazing on everything and leaves a great finish. If you want even a slightly more amazing finish, you can use a polish designed for plexiglass after it (such as Plastic X).

Ray

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drgary
Team HB

#169: Post by drgary »

Hi Ray,

Thanks for offering this information. Trying to keep this project within a budget and document how others might do that, might my humble Craftsman orbital sander do the job? The one you're suggesting costs $180. If there are important advantages to a sander like the DeWalt, what are they? If necessary I can rent one.

Added later: I just found this on the forum too: Scratch Removal from Stainless Steel

One site I've just found advises to do each level of finer polishing at 90 degrees to the prior polish. The idea is to see the scratches from a rougher polish when taking it one step finer. Here's that link: http://www.englishcustompolishing.com/u ... nless.html. This would apply to a belt sander or a buffing wheel, not the orbital sander I'm thinking of using.

My online research also shows that buffing stainless steel with intensity may make it lose its stainless property so it's prone to rust and that there's something called "burn compound" to restore the stainless. Any comments about that are welcome.
Gary
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What I WOULD do for a good cup of coffee!

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drgary
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#170: Post by drgary »

Test Polishing Begins

RayJohns gave me some tips offline to try polishing by hand, starting with 600 wet/dry sandpaper and wetting it to clean and lubricate, then going to 1500, then 2000 grit before trying Blue Magic metal polishing cream. He says if I use a buffing wheel with buffing compound, go easy on the compound, and don't underestimate the potential of hand polishing, which may give better results.

For this first step, I tried sanding on the inside of a Prestina panel and am off to a good start. I didn't use water for these tests but simply knocked the dust off the sandpaper and cleaned the inside of the panel after each polishing step with a damp rag.

It seems the key is using coarse enough sandpaper to get out the deep scratches, then backing out from there. If there are nasty scratches one needs to scratch it just as badly to bottom them out but do this in neater fashion so the finer passes take that initial roughness out. Really it's not that bad, just learning how to take it down to brushed steel and then shining that up. I'm not finding it very time consuming, maybe 30 passes per grit level. Doing this gives a feel for it.

Ray suggested staying in the same direction. An online source suggested going across the grain with each finer grit, which I tried because it seemed if I could eliminate the cross pattern underneath I would have bottomed out to the deepest level reached. As usual, Ray's approach is better because I can still see some subtle cross grain lines. Getting those out becomes increasingly difficult with finer grit.

When shopped for fine wet/dry sandpaper, the smallest grit they carried at Ace Hardware was 1500. They also were a bit pricey on the sanding blocks. The cheapest was $9. I had to go to Kragen to get the 2000 grit sandpaper and they sell this nice weighted sanding block for $4. That's more like it! Each sandpaper sheet, about a foot square, or the equivalent in cut strips runs about $1.69 to $2. Not bad. I got four sheets at each grit level Ray recommended because I have three machines to polish.

Here are some iPhone pix of the results so far.

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It grips the sandpaper with teeth and then the rubber snaps back into place. I use a home scissors to cut the sandpaper to size. Whoever designed this cared about making it work well and feel right. I appreciate that. :)

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Here is a "before" shot showing deep, fine and erratic scratches on a mirror finish.

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I attacked this with 600 grit, but it wasn't doing anything to bottom out the deep scratches. You can see the deepest scratch curving in from the right. I needed to go coarser.

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So I went down to 200 grit and that started removing those scratches. That still took too much elbow grease. Next time I'll go down to 100. Since this is a test patch, I left the end of a deep scratch in place to the right so you can see how taking this down to a brushed look actually eliminates the scratch that went into the center of the piece.

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Now I started polishing out, going to 600 grit again. This stage was surprising. Even though you're going to finer grit, the first few passes show that you're putting new scratches into the steel. After a number of passes these finer cuts predominate and the steel starts to look more polished, not more scratched. This happens with each finer stage. This shot and the next one show some cross grains that aren't entirely coming out at this point.

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Now I went to 1500 and the steel started becoming reflective again.

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Here's what it's looking like after 2000.

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Next I'll try buffing wheels with polishing compound and also metal polishing cream to see what works best at which stage. After finishing this test run, when I go after the outside of this panel, which has a pretty deep scratch, I'll probably start coarser and will try Ray's suggestion of using water for lubrication during the sanding.

What I like about this first sanding stage is it's not difficult, slow or expensive, and it doesn't even require power tools. The good news is it looks like these machines are easy to polish, eliminating the high cost of chrome plating large panels.
Gary
LMWDP#308

What I WOULD do for a good cup of coffee!