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Chemical Milling...
#1569479
01/27/14 03:21 PM
01/27/14 03:21 PM
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Joined: Jan 2003
Posts: 1,291
Tucson AZ,
MadMopars
OP
pro stock
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OP
pro stock
Joined: Jan 2003
Posts: 1,291
Tucson AZ,
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Before I begin, I just want to say this process can be dangerous if not done safely and responsibly. There's your warning.  Just curious as to who else is familiar with the process of chemical milling and what the results were. I dipped 3 items in a 70/30 mix of Muriatic Acid and Water over the last several days. I used a surface rusted razor blade, a new square Uni-strut washer, and a new 1/2" conduit strap. The razor blade had a pretty even removal of material overall. At this point it is very flexible and does have some small pin holes in it. It's starting weight was approximately 4 KG but my scale will no longer see a reading from it. The Uni-strut washer starting weight was approximately 2.5oz. It's now at 1.7. The majority of the material came from the 2 ends which look to have been sheared and thus fatigued. Material also disappeared from the hole drilled in the center of it. The faces and other two ends have very little surface change to speak of. Lastly, the conduit strap did nothing. The zinc coating disappeared and that was it. Although I was pleased to see results over the duration of several days, I did determine that control of where material is removed from is probably my main concern with the process. I believe tempering and fatigue are questionable areas that need to be considered prior to dipping. Cost and time considered, I was real impressed with the rate of deterioration for lack of a better word. I'm just not sure that continuation of attempting to lighten parts wouldn't come without a few hard lessons. That being said, has anyone else attempted this or familiar with the process? Any words of wisdom to offer?
Last edited by MadMopars; 01/27/14 03:23 PM.
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Re: Chemical Milling...
[Re: MadMopars]
#1569481
01/27/14 03:35 PM
01/27/14 03:35 PM
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Joined: Jan 2003
Posts: 7,489
Minnesota
Hemi_Joel
master
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master
Joined: Jan 2003
Posts: 7,489
Minnesota
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I did it with battery acid. It works pretty good. The acid got weaker as it was being used. It workEd faster if I heated it.
sometimes it cut the metal in strange patterns.
[img]http://i.imgur.com/boeexFms.jpg[/img]31 Plymouth Coupe, 392 Hemi, T56 magnum RS23J71 RS27J77 RP23J71 RO23J71 WM21J8A I don't regret the things I've done. I only regret the things I didn't do. "Wise men talk because they have something to say; fools because they have to say something. ~ Plato"
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Re: Chemical Milling...
[Re: MadMopars]
#1569482
01/27/14 04:07 PM
01/27/14 04:07 PM
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Joined: Apr 2008
Posts: 1,141
Phoenix,Az.
hemicop
super stock
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super stock
Joined: Apr 2008
Posts: 1,141
Phoenix,Az.
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Word of advice? Yeah, leave that to the pros. Chemical milling, aka "acid dipping" was popular in the early days of ProStock as many know but what some may not know is thatcontrolling the rate of milling is very tricky, the chemicals are dangerous & most likely doing it in your garage/backyard is illegal.
"Big Willie" Robinson lost a Daytona body, it was eaten so badly. There's plenty of stories where bodies-in-white were dipped only to have a roof panel come out of the tank---and these were done by pros!
A friend that worked for Penske in his Trans-Am days tells of cars being so thin they had to spray foam insulation on the panels so they wouldn't flex or cave-in at speed. He claimed without the foam you could shine a light behind a panel & see the glow from the flashlight. Look at some old P/S cars & you may find foam sprayed to the inside of doors, quarterpanels, roofs, etc. There's a reason for it! IIRC, the famous "wire car" of Don Carlton was "wired" just for this very reason.
The old S/S Darts & 'Cudas had their doors dipped & you'll find some weren't as cleaned up after dipping resulting in continued erosion from the acid.
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Re: Chemical Milling...
[Re: Hemi_Joel]
#1569483
01/27/14 05:46 PM
01/27/14 05:46 PM
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Joined: Jan 2003
Posts: 1,291
Tucson AZ,
MadMopars
OP
pro stock
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OP
pro stock
Joined: Jan 2003
Posts: 1,291
Tucson AZ,
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Quote:
I did it with battery acid. It works pretty good. The acid got weaker as it was being used. It workEd faster if I heated it.
sometimes it cut the metal in strange patterns.
The inconsistency of where the material is removed is what bothers me the most. It becomes a gamble at that point.
These chemicals are not strangers to me as we use them in the HVAC industry. While safety and proper handling is a concern anytime acid is used there are still many variables in this process that I'm not sure can be controlled. Horror stories as Hemicop pointed out do exist because of the variables.
I started this process and posted my findings because it's a cool concept and can be a neat way to lighten your car while maintaining a stock appearance as others have done in the past.
If I can do it myself, it looks like it would be a cost effective and viable option. If I can't control the material removal, I don't know that I want to play. My  .
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Re: Chemical Milling...
[Re: topside]
#1569486
01/27/14 11:27 PM
01/27/14 11:27 PM
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Joined: Feb 2003
Posts: 6,849
fullmetaljacket
master
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master
Joined: Feb 2003
Posts: 6,849
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Fellas, there are some different acids these days used and not as corrosive as yesteryear. I just had an extra dashboard dipped for my project and a Radiator support for my friends early Stingray and it was done in a way that took both time and experience to do correctly.
The process removed 7 Lbs and about 8 Lbs on the rad support respectably. Shortly after, while sitting in a basement garage, they both slightly oxidized. A little rust stop phosphoric acid sprayed on the surface and scuffed with a medium scuff pad and it was clean and spanking ready. An epoxy primer sealer was sprayed and now the topcoat is ready for application to bring back the stock look. Mind you, the gentleman that dipped them washed them thoroughly after the bath and warned me of some areas that would be a little flimsy, but you have to know what, when and how to mask the areas that are important to strength. Most importantly, you have to study the part, make a real world assessment of how much weight or percentage you (NEED) to remove from the part, as opposed to how much you (WANT) to remove. How much you (WANT) may lead you down the same fate as those 65' AFX'rs.
Out of respect to his way of business, I can't and won't discuss his process because it's his business to reveal that if he wants. I can just say that you get what you pay for and he delivered a sound item that is now feather weight. Last,but not least, this process is dangerous and not for the shade tree mechanic to attempt.
Gotta catch a plane. Later.
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Re: Chemical Milling...
[Re: MR_P_BODY]
#1569492
01/28/14 07:54 PM
01/28/14 07:54 PM
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Joined: Jan 2003
Posts: 1,291
Tucson AZ,
MadMopars
OP
pro stock
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OP
pro stock
Joined: Jan 2003
Posts: 1,291
Tucson AZ,
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Quote:
Why not use sand blasting it stops taking material
when you quit and is a TON safer
It was a thought that crossed my mind. I'm just not sure what the time standing there blasting, relative to material removed would be. Also, not sure that thinner items wouldn't deform first. It could probably be a more controlled process, just not quite as easy as dropping part in a bucket. 
I could take the easy way and drill holes which actually can look pretty cool when done right, but I am looking to maintain a factory appearance and finish on each item. Just looking for 1600 ounces to remove without the naked eye catching it. 
I'll give the blasting a shot this week and let you know how it goes.
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Re: Chemical Milling...
[Re: hemicop]
#1569493
01/28/14 07:57 PM
01/28/14 07:57 PM
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Joined: Jan 2003
Posts: 1,291
Tucson AZ,
MadMopars
OP
pro stock
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OP
pro stock
Joined: Jan 2003
Posts: 1,291
Tucson AZ,
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Quote:
If you can find a copy of "How to Build a SS/AA" car, there's a list of companies in the back that does acid dipping. Grant it, it's an old book now but maybe it'll give you some leads.......
I'll take a look.
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Re: Chemical Milling...
[Re: MadMopars]
#1569494
01/28/14 08:21 PM
01/28/14 08:21 PM
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Joined: Jun 2003
Posts: 52,972
Romeo MI
MR_P_BODY
Master
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Master
Joined: Jun 2003
Posts: 52,972
Romeo MI
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Quote:
Quote:
Why not use sand blasting it stops taking material
when you quit and is a TON safer
It was a thought that crossed my mind. I'm just not sure what the time standing there blasting, relative to material removed would be. Also, not sure that thinner items wouldn't deform first. It could probably be a more controlled process, just not quite as easy as dropping part in a bucket.
I could take the easy way and drill holes which actually can look pretty cool when done right, but I am looking to maintain a factory appearance and finish on each item. Just looking for 1600 ounces to remove without the naked eye catching it.
I'll give the blasting a shot this week and let you know how it goes.
Different grades of sand take off more or less...
I would use a heavy (course sand) but do ONLY heavy/
thick parts.... if you try blasting on sheet metal
you will trash it or end up with worped parts quickly...
being your looking to dump 100# that shouldnt be
real hard if you look at EVERYTHING... cutting down
any extra length on bolts all under coating and many
more things
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Re: Chemical Milling...
[Re: clonestocker]
#1569496
01/28/14 11:46 PM
01/28/14 11:46 PM
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Joined: Jan 2003
Posts: 1,291
Tucson AZ,
MadMopars
OP
pro stock
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OP
pro stock
Joined: Jan 2003
Posts: 1,291
Tucson AZ,
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Quote:
Trent,
Cut your door braces out. They were big in the Aspen Wagon. Got to be big in your car. 
The GTX didn't get the bracing in 73, just the Satellites. Even without them my car is heavy.
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Re: Chemical Milling...
[Re: MadMopars]
#1569497
01/29/14 04:34 AM
01/29/14 04:34 AM
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Joined: Oct 2007
Posts: 4,206
New York
polyspheric
master
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master
Joined: Oct 2007
Posts: 4,206
New York
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Acid attacks steel just like electro-plating - the material is deposited disproportionate to the surface area. It removes the most material from edges, corners and the ID of holes.
It removes the least from flat surfaces, like all panels.
This is the very worst thing from a structural standpoint, since the weight loss is minimal until the corners and seams fall apart.
The entire panel must also be neutralized (baking soda, dilute lye) after thorough rinsing with water, or the remaining acid will completely destroy the panel. Submerging absolutely won't do it. Even cars carefully washed sometimes don't completely flush out (direct path from the acid to the exterior). For the final rinse, boiling water from a pressure washer is best.
Sandblasting works OK until your operator forgets to angle the nozzle or turn the regulator down, then you have a washboard instead of a hood. The bondo weighs much more than the weight saved.
There is also no such thing as "effectively masking the area" to allow blasting on assembled pieces. It never, ever works, and you can get sand out of it 5 years later.
Boffin Emeritus
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Re: Chemical Milling...
[Re: Cab_Burge]
#1569498
01/29/14 05:05 AM
01/29/14 05:05 AM
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Joined: Jan 2003
Posts: 27,468
So Cal
autoxcuda
Too Many Posts
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Too Many Posts
Joined: Jan 2003
Posts: 27,468
So Cal
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Quote:
Back in the day a company called Aero Chem in SO CA used Hydrofloric(not hydrochloric) acid to chemically mill steel for a lot of SO CA racers, the air quality enviormentalist got that banned in the L.A. basin years ago   They bought a plant up (in El Mirage) in the high desert later, if you knew someone that worked thier you could get them to still do it back in the late 1980 and early 1990s that company did a lot of the aerospace milling back in the day, the racer stuff was secondary only
There was someone around here in So Cal only around 5 years ago that had a vat big enough to do a front subframe. I don't know the name of it. 3rd hand info, but worked on the racecar.
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