obrentharris 

My next painting project is an Atala with nice chromed socks, crown, and lugs. The chrome extends several inches onto the tubing beyond the lugs and socks. I will mask the lugs, crown, and socks to retain the polished chrome but I'm concerned that a conventional primer may not adhere well to the unpolished chrome. Should I be using an acid etch primer on this? Are there particular contents or types of primer I should be looking for?




Thanks in advance,
Brent

Andrew R Stewart 

One way, the slow way, would be to lightly scratch/sand the chrome surfaces to be painted. Andy

obrentharris 

Thanks Andy.
A good excuse to use the ancient Dynafile I recently acquired!
Brent

bulgie 

Careful, a Dynafile will likely be too fast-cutting for that job. Maybe OK with Scotchbrite belts, but not with harder abrasive like AO, even in a fine grit.

Have you tried the Dynafile yet? it can kill a bike frame pretty quick.

More than once, seeing the frames built by "master" framebuilders, I could tell when they acquired a Dynafile, because their lugless frames started coming with deep trenches gouged into the tubing adjacent to the fillets. Seems to me that most people can't see those troughs as well as I can, because I've seen stuff that I would never have let out of the shop, even from some pretty big names. And if the FB couldn't see them, then the customer definitely won't. But if I can see it by eye from 3 feet away, then the amount of steel removed is substantial enough to reduce the strength or durability of the frame. I think it's something about the curves in the reflection lines that my eye is picking up. Calibrated by years of smoothing fillets, miles of them, starting in the '70s at Santana. I once saw a new custom tandem, the owners were very proud of it, but like a dick I pointed out where they should watch for a fatigue crack, TT and DT at the HT. They thought it was, I dunno, tactfless of me? Maybe! I wouldn't have said anything but they were friends/teammates, and they asked me what I thought. Expecting only praise, probably. But the frame didn't last more than a few months before it kinked right where I pointed, while JRA. So I guessed wrong, I predicted a crack, but fatigue takes time, and this frame wasn't strong enough to last that long! (Small, light riders too.) Previous frames from that builder hadn't had the troughs in them, before he got a Dynafile, then they all did. No I'm not going to name names. This was over 40 years ago.

I know you're not talking about smoothing fillets, you would be dynafiling on mostly safer surfaces, away from the joints. But I still think a dynafile cuts too fast for what you want, which is the shallowest of surface scratching. I recommend doing it by hand, perhaps "shoe-shining" with abrasive cloth strip in a fairly fine grit. I'm not a painter so I won't tell you what grit to use; someone here will have a better handle on that than I do. Doug Fattic ?

Mark B

obrentharris 

Thanks for the cautionary advice Mark.
I used my Dynafile for the first time last week on an off-topic welding project. It certainly commands respect. I nicknamed it "The Pneumatic Wolverine."
I shall refrain from scratching the itch to use the new tool, and go back to my abrasive strips for this project.
Any opinions on using a wire wheel to rough up the chrome?
Brent

Andrew R Stewart 

Mark's above post beat my "OMG, no!" thought just a few minutes ago reading the Op's last reply. If ever there was a time for actual hand work it is when paint prepping. Especially when close to masked or plated surfaces. 120 grit cloth folded around a half round file can do a fine job following lug edges. Remember the goal at this stage is etching the surface and not removing any real material. Power tools are best left to the fabrication stages. Andy

Doug Fattic 

Brent my recommendation is following the advice already given by Mark and Andy. I'd use 80 grit "emery cloth" (known strangely under different names like "shop cloth" when trying to find it from suppliers - emery is a British word). I buy it in 1" widths. Before scrubbing the surface so the paint can adhere better, I'd mask the lugs. Even when being careful, it is easy to mistakenly scratch the lug surface when roughing up the surrounding areas. I use an Exacto knife to cut the masking tape I've tried to stretch tight over the lug. I have to resharpen them all the time. I use many pieces to cover one lug. Just for reference I often sandblast the areas near the lug after coving the lugs with duct tape. It isn't necessary to get exactly up to the lug.

I use House of Kolor epoxy primers for several reasons. 1st of all they come in the 3 primary colors as well as black and white. By mixing them I can get almost any color. That way paint chips (often between the color and primer) are less noticeable. Furthermore it can double as a sealer (by adding more reducer) between sanded primer and color coats. In addition it is very sandable. A painting tip is that I always use the slowest reducer 312 (designed for the hottest conditions) when thinning the primer no matter what the air temperature is when I'm spraying. It flows out better.

Dynafiles should be used with the greatest caution. So much can go wrong so fast in unskilled untrained hands. I seldom use mine and I'm really good at knowing how to handle it. I never use it for any final work, just to get gross stuff off. I was chatting with my colleague Jeff Bock yesterday about Dynafiles and said I don't ever let students use them any more. My example was a frame building student back in the late 70's that I gave him one to thin his lugs. He was so delighted in how fast it took off metal until he noticed he had gone so far his silver brazing material was showing having completely gone through the lug. One safer method to tidy up fillets - after shaping them with hand files - is to wrap some emery around a steel shaft attached to a drill. I slot the shaft to insert the end of the emery. This technique works but not too quickly like an 1/8" Dynafile belt. The shape of the wrapped emery can be created by the size of the shaft and the amount of emery wrapped around. It is easy to get to new enemy by just tearing off the end. Even this more gentle method should be used with great care and only after practicing on practice fillets 1st. By the way it is also a good way to clean inside tubes or lugs before brazing.

unterhausen

I find it amazing that Paul Brodie can use a rotary tool to clean up fillets. Of course, he has a huge number of hours of experience doing that. His channel is great, but if newbies pick that up from him there are going to be some damaged frames. From what I see online, newbies do enough damage with files. I think a rotary tool probably works better on competently brazed fillets. I don't have a compressor big enough to power my dynafile. I just got an electric version. I really don't intend on using it for much finishing work.

obrentharris 

Thank you all for taking the time to provide me with such detailed advice!
Brent

unterhausen

Wasn't the frame previously painted? I have no experience, but I wonder how much prep it really needs. A good primer sticks pretty well.

obrentharris 

Good point! Sometimes I miss the most obvious things. The paint was pretty banged up and chipped but was holding on very well where it hadn't been leaned against lamp posts and scraped up by chain slap. Thanks for bringing me back to earth.
Brent