Conti Prestina Espresso Machine Restoration 101 (Completed and Indexed) - Page 19

Equipment doesn't work? Troubleshooting? If you're handy, members can help.
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drgary
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#181: Post by drgary »

I've confirmed Ray's belief that the texture will polish out. Here's where that happened on a slightly raised spot -- which "raises" another issue encountered. The polished spot here was a scratch deep enough to cause an indentation, so sanding wasn't reaching it. I turned the panel over and gently tapped it outward with the blunt end of a center punch so it was raised to the surface for sanding.

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At this point all panels have had the deep scratches removed with rough grit. I've polished them out with progressively finer grit up to 800. The polisher made quick work of that. Doing this gives a feel for the progression needed. I start with 100 and also have available 220, 400, 600. I found sometimes I could skip the coarser grits if only dealing with the fine scratches created by cleaning with abrasives, maybe starting at 400. Sometimes I went from 400 to 800, which saved time and didn't lose quality. The next step is buffing these panels to a bright shine.
Gary
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RayJohns

#182: Post by RayJohns »

Looking good. You'll be an old pro in no time :)

Ray

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drgary
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#183: Post by drgary »

RayJohns wrote:Looking good. You'll be an old pro in no time :)
Well, I am old. Halfway there. :? With a few weeks' more practice I may be good at this. It's a challenge to make sure I've got all the scratches out from the previous, coarser pass. The only way to find it is take it finer and see if scratches remain, and there they are! Using a heavy duty polisher like this is also tricky because it doesn't sand with the same pressure across the whole wheel but tilts here and there and this can be done to advantage or can grind some deeper scratches that then need to be taken out.
Gary
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drgary
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#184: Post by drgary »

A mirror polish is possible, but it's also possible to do a pilgrimage to a mountain hermitage doing prostrations all the way instead of walking. Here's how the back of my Amica turned out at the end of today's work session. There's a little metal polish on the surface and a couple of the deepest scratches didn't come all the way out, but it's a brighter shine than the original finish that remains on the sides. This is the result of fine-tuned work with the DeWalt hand polisher, buffing it on a bench grinder with buffing wheels dressed with emery and white rouge buffing compounds, and finishing it off by hand with Mother's metal polish. When I would bring it up to a mirror surface on the bench grinder, I would notice dull spots that needed addressing, and this happened about half a dozen times. :roll: Later add: Mounted on the Amica that polish is unsatisfactory as it still shows some ripples where the DeWalt cut some rotary patterns.

Image

I'm going to put in more time tomorrow on the Prestina panels now that I'm more familiar with my tools and will decide whether it's worth a mirror polish or whether I'll go with a brushed steel look. The key will be how efficient I can be sanding out the stippled texture shown above. I already tried buffing that texture with emery and white rouge, and these didn't touch it, so sanding will be necessary.
Gary
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drgary
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#185: Post by drgary »

I'm feeling more hopeful today after learning how to better use the polisher. It's variable rpm, so lower rpm's for coarser grit (about 1000) and higher rpm's for finer. The trick is to get enough speed so the sanding disk floats on the material. I'm also learning to move the polisher very gradually to avoid grind marks and to bear down a bit when I want to grind out scratches or create something close to a mirror finish. It makes quick work of the texture discussed earlier, although edges can still be challenging. What's still tricky is the transition point from DeWalt polisher to buffing wheels on the bench grinder. It's hard to find sanding disks above 800 grit and I haven't heard of buffing compound coarser than emery, so I went to an auto parts store and picked up some 1000 grit wet/dry sandpaper to use on a sanding block. This interim step is important in getting out the fine scratches that create a shadow or frost effect on an otherwise mirror finish that's very hard to take out with buffing compound. I also tried ultra fine steel wool (#0000) and fine (#00) and these don't seem to help much.
Gary
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RayJohns

#186: Post by RayJohns »

If it were me, I think I'd switch to block sanding by hand at 2000 grit. Then use a buffing wheel attachment on the DeWalt for the white rouge. Then use Blue Magic metal polish (I've never used mothers, but Blue Magic is fantastic) by hand.

Polish using a micro fiber cloth and/or bounty paper towels. The blue magic should turn black in the final stages of polishing. Then wash the residue off using either B-12 chemtool or soap/water. Finish using Plastx.

I'm using the same basic polishing routine for my motorcycle forks (on hard chrome). The surface of the hard chrome is malleable to a certain degree under polishing. With proper polishing, you can reduce the friction coefficient down below that of a DLC coating.

Anyway, I would do the finish work by hand, not machine. The DeWalt is good for doing the heavy lifting (i.e. running through the lower grits of sand paper when you need to remove a lot of material). Once you get to a certain point though, try to phase into sanding by hand if you can. Then use the DeWalt with a soft buffing wheel (instead of the bench grinder) to polish (or by hand).

Looks like you are doing a great job though. Getting a perfect (i.e. flawless) mirror finish on a panel is tricky :-). Even the slightest hair line scratch stands out quite a bit.

Either way, nice job polishing that panel!! It looks good.

Ray

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drgary
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#187: Post by drgary »

Thanks, Ray. I've tried the 2000 grit on a sanding block and the shadowing is a bit rougher than that, so I picked up 1000 grit yesterday for hand sanding and will go to 1500 maybe before more 2000. I also picked up some Blue Magic polishing cream at the same time. I'm staying with the flannel buffing wheel on a bench grinder because I tried a polishing bonnet on the DeWalt and it didn't easily take the buffing compound. I stopped short of spending $23 for a lambswool polishing pad since I already have the buffing wheel, although I'll bet your suggestion of using the DeWalt must work faster. I'm checking on eBay to see if I can get that more affordably.
Gary
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RayJohns

#188: Post by RayJohns »

You might consider something like this:

http://www.amazon.com/Pack-Cobra-Microf ... 542&sr=8-6

It's a microfiber bonnet that you put over the buffing pad on your DeWalt.

Usually, however, the final stages of polishing can be done by hand without a lot of problem. Try that Blue Magic stuff and see how you like it.

Ray

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drgary
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#189: Post by drgary »

For a Great Mirror Polish, Use Chrome Plating

That's what I decided after working on a panel for three hours today. Instead, I want to do the turned finish that Adam (aka ANeat) suggested on page 12 of this thread here with this image he grabbed off the web. I'll skip the decal, though. But I believe that finish will be very decorative on this machine with all of its square and boxy angles.

Image

Here's another example I grabbed off the web, where the swirl pattern is a bit more symmetrical and overlapping for an aligned look that gives an appearance of depth.

Image

It's just very difficult to work steel that has a little give to it, and I don't have the right tool. The local specialty tool retailer, Tooland, says those machines cost about $700.

Here are the images from today's work so you can see the difficulty I ran into:

In this first image, I sanded with 220, 320, 400, 600 and 800 grit by machine. Then I sanded by hand with 1000 and 2000 grit. I buffed it out with emery compound and white rouge and used Blue Magic polish machine buffed with a wool pad mounted on the DeWalt polisher to get what you see, which still showed some sanding marks in the steel. To get to this point took about two hours.

Image

Just to see if I could achieve a mirror finish I went at it again, attempting to polish out the defects using emery buffing compound and white rouge at high speed, about 3000 rpm, on the DeWalt polisher. It came out brighter but still had shadowing, as you can see here:

Image

In one of his threads Cannonfodder said that using power tools to polish steel can leave you with a worse mess than you started with. In a way his advice held up because I was stuck with swirls and shadowing from the DeWalt polisher. At least the rough sanding did get out any heavy, random scratches, so maybe that's a necessary first step. I hope to achieve the turned finish by the time my long Thanksgiving weekend is over and will post pictures. I think it will actually look better than the mirror finish I'd planned. To achieve a symmetrical turned finish, I'll pull some strings across the panel and will use temporary markers to make sure I achieve a straight line of swirls.
Gary
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RayJohns

#190: Post by RayJohns »

Gary, you might try a final polishing with corn starch. I've never tried it myself, but I have heard it works pretty well.

Like I say, no first hand experience.

Ray