3-D printing inquiry for 1935 Chrysler Airflow part

[Pete Phillips]

I need to get a reproduction of this parking light grille made for a 1935 Chrysler Airflow. It is pot metal and cannot be welded back nor epoxied back together. The contact areas of the  two when put together are so small that nothing will hold it. Size is about 7 x 7 x 1 inch. Can anyone suggest someone who offers this service? My thought is to get it reproduced/printed in plastic, which I can then get chrome-plated.

Pete Phillips

Bonham, TX

[61polara]

Pete,

I can't help you on that, but I will be reproducing the parking light lens soon and have the mold made for the tail light lens as well.

[edinmass]

That’s a difficult part to make. You could 3D print it, and it would work out fine. Cost of labor for computer is probably more expensive than you would think. Printing them out has become more affordable........but not cheap. I would guess a grand on computer time, and 750-1000 dollars each to print.(metal) Lost wax is probably your least expensive route.......but that is not an easy piece to make. 

Edited January 5, 2022 by edinmass (see edit history)

[bryankazmer]

The type of plastic used matters.  ABS should be capable of being "plated" afterwards, but verify that the specific grade you use is.

[Gary_Ash]

I got a 3D model created of the Airflow light grille.  It wasn't easy as the part is fairly complex, had to figure out how to make a triaxial ellipsoid - look it up!

 

Here are some renderings from the CAD software.  I just put the data in the printer, will be 25 hours to print it.  My fingers are crossed that it's a printable model.

 

A light grille on a 1935 Airflow.

 

CAD model front view.

 

 

CAD model tilted.

CAD model rear.

 

CAD model top view.

 

[edinmass]

 

Gary.......I’m guessing it’s too cold to drive the Indy car today? 😏

 

The grill looks great. 
 

Triaxial ellipsoid........and I thought covid gave me a bad headache!

 

Edited January 15, 2022 by edinmass (see edit history)

[Bhigdog]

1 hour ago, Gary_Ash said:

I got a 3D model created of the Airflow light grille.  It wasn't easy as the part is fairly complex, had to figure out how to make a triaxial ellipsoid - look it up!

 

Here are some renderings from the CAD software.  I just put the data in the printer, will be 25 hours to print it.  My fingers are crossed that it's a printable model.

 

A light grille on a 1935 Airflow.

 

CAD model front view.

 

 

CAD model tilted.

CAD model rear.

 

CAD model top view.

 

The most amazing part of the whole thing is that back then  someone made a die cast mould for that part using manual machines. No NC machines back then. That's when tool and die making was as much art as skill..................Bob

[edinmass]

45 minutes ago, Bhigdog said:

The most amazing part of the whole thing is that back then  someone made a die cast mould for that part using manual machines. No NC machines back then. That's when tool and die making was as much art as skill..................Bob

 

The term is master craftsman. Casting and pattern making is a long lost art now. Not more than fifty years ago, it was taught in high school.

[Gary_Ash]

As it happens, I did take a semester of wood pattern making in high school, a semester of foundry and forge, and four years of drafting.  I had another year or two of drafting college, but the CAD stuff was on my own in much later years.

 

Looking at the back of the original part, I can see the imprints of the ejection pins on the casting plus the draft to enable getting the part out of the mold.  I didn't put draft into the CAD model.  

 

Unfortunately, because the grille is about 6.5" x 6.5", it's too big to get printed direct-to-metal and polished at either Shapeways.com or I.materialise.com, my two favorite 3D printing sites. I.materialise.com will 3D print the part direct-to-metal in steel/bronze but the cost is nearly $600 each without polish.  The foundry in Providence, RI can investment cast in bronze much cheaper, but I'll have to print one 3D print for each casting needed, polishing and plating extra.  It's not expensive to print one out, just takes a day for each.  The bronze castings will still need to be polished and electroless nickel or chrome plated.  Here's how it might look in chrome.

 

 

[edinmass]

Funny how someone taking shop class...........ends up as a very successful engineer. Pattern making, forge class, wood shop, metal shop, construction methods......... common high school classes back in the day. Today’s educational system says no shop class, no working with your hands, get a four year degree in basket weaving. 98 percent of the people with a four, five, or seven year degree are so helpless they can’t change a tire on their VW, and they making 17.50 an hour. Meanwhile, plumbers are billing at 150 an hour. The guy who pumps my septic tank is making six figures as an employee. My nephew graduated law school with 285k in debt. He’s working his ass off full time for seven years and still drives a twenty year old car and lives in an apartment. Real work is rewarding, pays well, and is ten times more satisfying than any code or programming. My high school did away 100 percent with the trades by 1990. No shop, no home economics, and the kids today are all helpless. Things are about to come full circle. Only difference is after high school, people are going to pay for the trade schools.........It also wouldn’t hurt to teach kids to get their ass out of bed before six AM. 
 

PS- most of the young engineers I know don’t have twenty percent of the talent or five percent of the experience that Gary has......... 

Edited January 15, 2022 by edinmass (see edit history)

[1912Staver]

I was briefly a HS shop teacher, 1989 / 90 time frame. The programs were still in pretty good shape, particularly woodworking. But the operating budgets were really starting to get thin , especially in the rural, remote locations where most of the jobs for new teachers were located. Most of the kids had quite a bit of interest , this was early in the video game era and before smart phones. But a fair number of difficult cases as well. They often took up a lot of my time with little to no good coming to anyone. 

 Even then the focus was shifting away from the traditional trades and toward what was at the time termed Technology Education. Lots of vague , well intended learning goals, but little most students were ever going to make a living at. Sort of a glorified sweat hog science class without the math and physics. 

 After a year of full time out in the boonies, and a term of teacher on call back in town I finally ended up back at my old Ship's Engineer job. 

 Both had their good and bad points , but I could make a decent living as an Engineer. Teacher on call was slow starvation and would have gone on for several years unless I was willing to accept a permanent posting in the outback.

Some of the automotive programs around me are still doing reasonably well , but it ends up being a ton of work for the teacher. The reality of underfunding makes everything 10 times harder. 

I always thought the Gov. agency in charge of the Shop curriculum was making a mistake shifting away from traditional skills. But at the time the thinking was that part was best taught in a Post Secondary setting. Expensive programs best targeted at people entering, and involved in the trades.

Edited January 15, 2022 by 1912Staver (see edit history)

[jpage]

How many platers did you check with? I've had some small pot metal pieces repaired with no issues, but maybe no one wants to touch them now. As far as shop classes, my son, a tradesman, sits on the board for the carpentry department for a local vo-tech school. They can't seem to find qualified teachers for one thing. Most of the teachers are retired from the trades, but have no teaching degree. They are required to go to school to get their degree, but the time and expense does not justify the pay scale for the positions, so most quit after a year. Also, the quality of the students has greatly changed in the last 50 years. Seems today, that many of the trade students are there for two reasons, they can't make it in the regular classroom or they are trouble makers. Maybe 1 out of 50 kids really wants to go into the trade! Who would want to teach if no one is interested. Even in the vocational college my son attended, few in his carpentry class really wanted to be carpenters. Besides, have you ever tried to find a young person who really wants to do manual labor, no matter how much they can make! Recently, a large, well known trade school has been closed for lack of interest!

Edited January 15, 2022 by jpage (see edit history)

[1912Staver]

I am glad you said it so I don't have to. But yes, the kids have changed. When I retired from my Ship job a few years ago I thought I would renew my teaching credentials and be a Teacher on Call a few days a week. But part way through the process I reflected on what I saw in my sons school, he was in grade 12 at the time, and asked myself if I really wanted to get involved in the school system again. After a lot of soul searching I finally decided the stress and aggravation really was not worth the return.

[edinmass]

When I was in mechanical drawing class.....which I took for five years, any of the kids that got out of line got the T Square treatment from the instructor. Get whacked with it a few times, and you kept your nose clean. Today, the teacher would be charged with assault and battery........and get fired and sued. We use to laugh hard at some of our instructors as they were all very unique characters. One was a fly weight golden gloves boxer with a short fuse. You would get a slap across the face if you spoke back..........many of us left the class bleeding at the lip. Old Harry had all the kids respect. Best thing is he would call you out and tell you to meet him at the gym. The old bastard was hard as nails.........a real old school gentleman who did 30 years in the Navy. He knew how to straighten out kids on the wrong path.......I’m certain he saved hundreds of kids from doing time. He would smack you one day, and let you borrow his Caddy for a date the next night. Wish we had more of him in the schools back then, and today. 

Edited January 15, 2022 by edinmass (see edit history)

[Terry Harper]

For the past 10 years I have taught Engineering Technology at a a high school Career & Technical Center. In fact my lab is  the same room I learned drafting in over 40 years ago. I feel fortunate that success in my previous professional career allowed me to be able to afford to take this position. If that sounds strange you need to realize that most technical school teaching positions are filled by people coming from industry. It's hard to draw quality people out of the workforce when all you can offer them is a teachers salary which is far less than what they earned out in industry.  For example, when I started this position my 30 year professional career was translated into a pay scale equal to that of a teacher with 15 years experience. I.E if you have 10 years in industry that translates to 5 years of teaching experience and so forth. It's hard to get good people to move from industry to teaching a trade. In addition, a trade program has a very, very high per student cost. My budget (maximum of 32 students but minimum of 13) is almost 12 times the budget for say a physics class in the local high school. Add to that the fact that since we are in a rural area, rarely are our classes filled to capacity. On top of this are the never ending costs in equipment and technology required to keep our programs current and abreast of the industries we represent. Needless to say the numbers never look good to the local community or state - thus we are costly programs serving a minority of the student body and are ripe for cutting.

 

Then there are the other issues. The decades long push for everyone to get a four year degree has greatly stigmatized tech programs and trade schools as the "lesser" path. The term "Vocational" is no longer used because of that. It became a slander. As a result our numbers are down. Our local community college which was in fact a very good technical school is now reduced to handing out mostly liberal arts degrees. I have had people who should know better advice my students that if they want to go into engineering or architecture they would be better off taking a foreign language rather than my class even though foreign language wasn't a requirement for college enrollment. Mind you these are the same people who graduate from high school, spend four or five years in college and upon graduation go to work back in a high school  - experiencing very little of the real world yet are expected to counsel students on career and educational choices when their experiences have been horribly limited.

 

As for the students... yes things are different than "when we were in school". Some for the better, many for decidedly worse.  However, we find in our trade programs that we tend for the most part to have good students that want to learn. This is in part because our classes are electives and they choose to be here. Many know what they want to do post graduation and for a career so they can be highly motivated. Likewise we often have students that were clueless about their future and our programs open up opportunities or at the very least they gain a valuable skill. However, some technical programs can easily become a dumping ground for students for various reasons - be they academic or behavioral. This in some part goes back to the use of the term "Vocational" as meaning lesser or easier and that of course can impact the classroom environment and every student in the program. On the other hand I have had students considered to be "a problem" in academic classes turn out to be excellent students.  I remember one such students who was late to class every day. Then, for a number of days, he showed up on time. When I thanked him for being on time he replied with a big grin: "Well Mr. Harper, to be honest your class is the only class I've been going too." sigh....

 

As for quality... its true that a lot of young people today tend to be passive. They watch Youtube rather than learning by doing and will quickly claim they know how to do something when in fact they have never done it themselves. When they do try it they often fail and simply give up. Society as whole views failure as something to be avoided always. When in fact we learn much more through failure than we would through success. "Embrace the suck" I believe would be an apt term. They feel that you have to be born with special skills to perform special tasks and why try and risk failure.

 

Students and youth are individuals - we can't simply write them off as a group. Last year I had a small group of second year students that were amazing! Their motivation was astounding. They would come into class all excited about ideas they had and work hard to take those abstract ideas and turn them into reality. Often - on their own initiative, they worked on projects at home. They produced a ton of work - prototyped an early magneto impulse coupling, a unique ice fishing rig, a piece of fitness equipment, a 3D filament recycler and extruder, designed a road and reverse engineered a bunch of stuff for various "clients". It was an amazing year. Of that group of five, three won four year, full tuition scholarships (two for mechanical engineering and the one for civil engineering). A 4th student is studying electrical engineer and the the 5th student earned quite a number of scholarships and is attending a trade school to become a licensed electrician. We joked that in two years he will be earning considerably more than the others by the time they completed college in four years.

 

Encourage, support and teach. 

 

 

 

 

 

 

 

 

 

 

[edinmass]

My issue with kids today.......money doesn’t motivate them. They all want huge dollars, and can’t produce. Incentive based pay doesn’t work with them. They all want huge money, and can’t stick a stamp on an envelope. Ask one to meet you at 6am at the office or shop......they will pass out. I’m 55 and at 7am I am under cars in the bay. Just proves what a dinosaur I am. 

[jpage]

Great discussion; this should be a whole new thread, we're not getting Pete's parts fixed!

[Gary_Ash]

The first 3D print got finished after 24 hours in the printer.  It's pretty good, just a couple small spots need a little adjustment plus a reprint, but not a big deal.  I'll send the first one to Pete so he can check the fit on the car to see if any other adjustments are needed.  The original part in die-cast zinc alloy is just about 1 lb; a cast silicon bronze part will be closer to 1.2 lb, the plastic part is only 86 grams/3 ounces, mostly because it's a hollow shell in lightweight plastic.  The parts will need to get polished and plated; electroless nickel may be good enough, chrome will be more costly.  So who else wants one or more of these 1935 Chrysler Airflow parts?  I don't expect there will be many takers, but this is likely to be a one-time deal.

 

The bulge at the bottom is the tri-axial ellipsoid of the equation

     x²/1.75²+y²/1+z²/.583²=1

I can't imagine how the die was machined for 1935 production in the time before numerical-controlled milling machines.  

 

It would be possible to get the part printed in ABS plastic at a commercial 3D printer like Shapeways or i.materialise.com for about $91 and have it electroless nickel  plated by Sharretts Plating.  In principle, I could do a print in ABS on my printer, but I don't have a lot of experience with ABS, which takes different printing conditions.

 

Original die cast zinc part on the left, 3D printed part in silver PLA plastic on the right.

 

 

[edinmass]

Looks great.......and from the little research I have done, a real challenge to do on the computer. Gary, just curious.......how much screen time to get it to this point? I couldn’t hazard a guess. Thanks, Ed.

[hidden_hunter]

On 1/15/2022 at 1:48 PM, edinmass said:

98 percent of the people with a four, five, or seven year degree are so helpless they can’t change a tire on their VW

Woohoo 2%

 

15 hours ago, edinmass said:

They all want huge dollars, and can’t produce

Policy failures in most western countries has driven property prices to stupidly high amounts so it has distorted things and what people expect. The stupidest thing they did here was close our tech schools which provided viable pathways for people for the last couple of years of school and then combined with selling off of all the public owned utilities that used to train up apprentices, I hardly blame people for not taking up trades

 

9 hours ago, Gary_Ash said:

I don't expect there will be many takers, but this is likely to be a one-time deal.

Looks great, do you open source or license your models so that others could benefit from them in the future? I don’t have an airflow but wonder if people would be more willing to chip in to design work if they knew it was “preserved”

[jpage]

The part looks great, but I have a question. If the part was to be cast in a metal, wouldn't the pattern  have to be made a certain percentage oversize to allow for shrinkage, depending on the type of metal being cast?

Edited January 16, 2022 by jpage (see edit history)

[Terry Harper]

11 hours ago, Gary_Ash said:

I could do a print in ABS on my printer, but I don't have a lot of experience with ABS, which takes different printing conditions.

Hello Gary,

Looks great! I try to avoid ABS. Unless its a very small part we always have issues with warping and lifting from the build plate even with Kapton tape etc. and that is with a printer with a heated build plate and enclosure. We try to stick with PLA though PET, PVA & PETG we have had good luck with. 

 

At the moment we have a couple of patterns for Hele-Shaw clutch components printing off - Got to love a 48 hour print!

 

 

Edited January 16, 2022 by Terry Harper (see edit history)

[Terry Harper]

5 minutes ago, jpage said:

The part looks great, but I have a question. If the part was to be cast in a metal, wouldn't the pattern  have to be made a certain percentage oversize to allow for shrinkage, depending on the type of metal being cast?

Yes, but its a simple matter to scale up the 3D model. Also, if its being traditional sand cast as opposed to investment cast or lost PLA you need to add draft. In addition, often machining allowance as to be added as well. 

[jpage]

This 3d printing is really amazing!

[Gary_Ash]

3 hours ago, Terry Harper said:

Hello Gary,

Looks great! I try to avoid ABS. Unless its a very small part we always have issues with warping and lifting from the build plate even with Kapton tape etc. and that is with a printer with a heated build plate and enclosure. We try to stick with PLA though PET, PVA & PETG we have had good luck with. 

 The reason for printing in ABS is that places like Sharretts Plating can cover it with electroless nickel, not quite the color of chrome, but not bad.  Also, I think PLA parts couldn't take the temperature that would happen for a car parked in the sunshine.  For some interesting thermal reasons, chromed parts get hotter than painted parts. In the end, I think the parts will have to get made by investment casting in brass or bronze to be on the safe side for durability.

 

I haven't put any CAD files in the public domain, don't plan to.  I still like to control, at least a little bit, how things get used.  Some years ago, I sent a file to a supplier to have a part laser cut for one of my projects.  Not long after, he was offering the parts for sale on his web site - but he wasn't sending any commissions to me, didn't even say thanks.  As it stands, I have way more hours in this project than I planned, but it's been fun and educational for me, so no complaints.  As Edinmass remarked earlier, if you really had to pay me at real, commercial rates, none of this would ever happen.  It isn't the 3D printing or investment casting that limits the use of parts replicated this way, it's the CAD time.  And, as Terry Harper well knows, it takes a long time to get good at CAD for complex objects and you have to be able to think 3D in your head. 

 

As for scaling, I usually design at 100% size, then compensate for casting shrinkage by entering a value for scaling in the "slicing" software that generates the data to make the 3D print from the CAD file.  When I had wood pattern making shop in high school, we used special rulers that had the shrinkage amount built in, say 1/4" per foot, plus we had to add draft to the pattern in the correct direction.  I thought i had saved one of those patterns from high school days, but couldn't find it when I went looking last year.  

[Terry Harper]

1 hour ago, Gary_Ash said:

I haven't put any CAD files in the public domain, don't plan to.

 

Gary, I feel the same way. I enjoy working on challenging projects. I love those "YES!!" moments when a difficult problem is solved and of course helping people - it never gets old. Like you, I don't share files on public domain for several reasons - the first is they are often the property of the client. Second: My time is worth something. If I do a project pro bono that is my choice as opposed to a third party profiting from my work without my consent. 

 

On the flip side I would recommend caution in regards to using work that is in the public domain. Usually its simply the 3D model in STL format with no supporting documentation or reference material to verify if it is indeed accurate. Seldom are there accompanying shop drawings or reference material. Creating a design package (3D model and shop drawings) that accurately captures and communicates geometry, design intent, tolerances and manufacturing processes is far, far different than a simple 3D representation. While many people can crank out a 3D model few have the skills, knowledge & background as Gary has to create true quality work.

 

Again, great work Gary! 

 

 

[Gary_Ash]

I fixed the flaws in the CAD model, now need to have a good print to test fit on Pete's car.  A challenge in this part is that there is a hook or beak shape at the bottom that sticks out about 3/4 inch behind the rest of the part.  It comes to a sharp point.  On the first test print, the tip broke off when I separated the print from the printing bed.  When I started another print, I noticed that in the first minutes of printing, the nozzle on the print head knocked over the beginnings of the beak, so I stopped the print. 

 

Because of the beak, the entire part has to be raised up by some disposable support material so that the top surfaces are horizontal in order to get a smooth finish.  I did a little Googling to find out what other people had done when confronted with things that start small on the print bed.  The best advice was to build a "raft" on the build plate before the actual part is printed.  This is to give more material to grip and support the small pieces.  So, without further changes to the CAD file, I ran the file through the Ultimaker Cura 4.11 slicer software again to put a raft of about 1/16 inch thickness down first.  I also added instructions for "Z hop" so that when the print head moved to a different location not directly connected to where it was printing, it would raise up slightly to prevent collisions with previously printed areas, then come down to the next surface to be printed.  While I was at it, I finally installed a previously-purchased special 6 mm thick glass build plate with a polyetherimide (PEI) coating to provide an extremely flat, stiff build surface with good adhesion properties. 

 

Wow, what a difference!  With the bed leveled, the PLA plastic went down in uniform thickness lines to make the raft.  The beak started to grow and was well-attached to the raft.  So, there is art and technique to using the machines, all to be learned by experience.  With luck, there will be a good part waiting for me in another 22 hours.  I just learned that one of my grandsons has started to use the 3D printer I gave to his family last year, good to start them early!  He's taking a robotics course at his high school in the Netherlands, may have to make some parts for a robot project.

 

The "beak" on the rear side of the Airflow grille.

 

3D printing the grille on the new PEI-coated glass bed.  The tip of the beak is beginning just above the letter "A".  The long strips are the beginnings of the 

support material which will eventually be 3/4" high before the rear surface of the grille starts.  The supports separate fairly easily when printing is done.  The smears are some special adhesion-enhancing fluid applied before printing.  The thin raft can be seen around the outside edges of the print but extends under the whole of the printed area.

 

 

 

 

[BearsFan315]

looking good

 

i do 90% of my printing in PLA, I use a high grade that has properties like ABS but much easier to print. doing drafting and design for hte last 25+ years makes this hobby even more fun for me. cant find a part design, print, make it  

 

and depending on the material you try to cast in shrinkage is not that big of a deal we are using lost foam process for many casting now and print near net. reducing machining and finishing required. super clean nice parts, not as clean as lost wax but hard to beat

[Matt Harwood]

Well this is just impressive as hell. Amazing work, Gary! So many possibilities opened up with that kind of talent and technology--without you, could that Airflow part ever be replaced? Unlikely. Nice work!

[bryankazmer]

39 minutes ago, BearsFan315 said:

looking good

 

i do 90% of my printing in PLA, I use a high grade that has properties like ABS but much easier to print. doing drafting and design for hte last 25+ years makes this hobby even more fun for me. cant find a part design, print, make it  

 

 

PLA is fine for casting patterns, but what properties do you think are similar to ABS?  PLA has rather low heat deflection temp and low resistance to moisture.

[Gary_Ash]

As Robert Burns the poet once wrote, "The best-laid schemes o' mice an' men gang aft agley".  [Burns 263rd birthday is January 25, when we recite the "Address to a Haggis" and drink a dram or two to his memory.]  In this case, after about 3/8 inch of material height was deposited, the nozzle kicked over the beak and kept right on going.  Is wasn't tied as tightly as I had hoped to the raft, but it can't be "welded" to the raft or the part will never separate after printing.  After a few passes of depositing sagging filament across the gap, it eventually bridged the gap and continued printing smoothly.  Of course, the underside of the where the tip of the beak should be is stringy and rough, so I might not be able to glue the tip back on.  It appears that the failure of the tip on my first print was due to the same thing, not because I broke it off removing the print from the build plate. 

 

Plan B:  I went back to the CAD file, added a small block to the tip to provide more surface for an anchor.  It can be cut off either before the pattern goes to the foundry or after the casting is made.  I'll let this print continue to the end to check that the other fixes worked, then make another print tomorrow.  It's the waiting that really kills me!

 

The tip of the beak knocked off with the opening re-bridged.  The strings are the result of bridging a large gap unsupported.

 

 

Plan B:  A small tab about 3/8 x 3/8 x .090" added to the tip of the beak to provide enough adhesion to the build plate.

This CAD image shows the back side of the grille.

 

 

[Oldtech]

4 hours ago, Matt Harwood said:

Well this is just impressive as hell. Amazing work, Gary! So many possibilities opened up with that kind of talent and technology--without you, could that Airflow part ever be replaced? Unlikely. Nice work!

Agreed. 

[BearsFan315]

could the stringing be caused by oozing, too hot a tip for the material or not enough retraction ? 

those are the 2 places i start

[Terry Harper]

Nice work Gary!

That is a tough part to print. I see your using a Creality Ender? We have two of the Creality CR10's  - for fairly cheap printers they are reliable and do an excellent job.

On our older printer, which had a slight warp to the build plate, we now use a mirrored tile with blue painters tape for adhesion. On the newest printer the build plate is the coated glass and is nice and flat but we still use the painters tape which works excellent.

 

 

 

Edited January 18, 2022 by Terry Harper (see edit history)

[BearsFan315]

4 hours ago, bryankazmer said:

PLA is fine for casting patterns, but what properties do you think are similar to ABS?  PLA has rather low heat deflection temp and low resistance to moisture.

lol

 

they are not the same, totally different materials. was just a statement not a debate. I have been using a high temp PLA that has better properties that regular everyday PLA. the Black prints at 225C and i use a bed temp of 30C have had excellent prints, using them indoors and out. no issues with them to date, some 5+ years in the direct sun. i have been happy with it. when i need something stronger i change materials. 

pretty familiar with the materials, composition, and applications

[bryankazmer]

Please bag the condescending "lol" - I also am familiar with most plastics.  You rarely see PLA used outside of 3D manufacturing.  I'm interested in what material properties are enhanced in this grade - a question of neither statement nor debate, but one of data.

[Restorer32]

In my humble opinion it would have been way less complicated, and likely less expensive, to have this part lost wax cast.  Maybe $500 to have the rubber mold made and the mold is good for 100 pieces at least. Maybe $100 or less to have the part cast once you have the rubber mold.  We recently had a batch of small parts lost wax cast in bronze and the cost was $145 for 5 small but fairly complex parts.

[Gary_Ash]

There were a couple of issues that argued against just making a silicone rubber mold and wax copies.  First, the original is broken in half because the die casting was too thin in a number of places to begin with.  The two wings are not in the same plane as the center section, they are each angled back at about 2.5 degrees.  The car owner had tried to epoxy the parts back together, didn't work for him.  So, getting the broken parts exactly aligned and angled during gluing would be tough, though perhaps not impossible.  But, there is not much room for added epoxy volume around the breaks.

 

The second, and more important issue, is that a bronze casting made from a wax replica would be about 2% smaller in all dimensions.  That means the mounting holes would be a full 1/8 inch closer together on this part.  Additionally, the opening for the parking light lens would shrink enough that the glass wouldn't fit into the new part.  When the 3D printed part in PLA plastic is made for the "lost PLA" casting process, it will be printed 2% larger than the finished size.  There are times when one can get around the shrinkage issue for silicone molds by dipping the part in molten wax to get a thin, hopefully even coating of wax on the part before molding, but difficult on larger parts.

 

I have made a couple of subtle changes in copying the original part to add a little more metal thickness where the part broke.  The other wing of the grille has a break in one of the fins because the metal was also too thin in the casting.  There are advantages in being able to make adjustments from original parts.

 

I made the water pump impeller castings and new castings for the tire pump air compressor for Ed Minnie's 1917 White by CAD modeling and lost PLA casting in bronze at a local art foundry.  The compressor bodies weighed a few pounds. 

 

 

Water pump impeller for 1917 White.  Machined part at top, raw casting in middle, 

3D print at 100% size to finished dimensions at bottom (not used for casting pattern).

 

Bronze raw castings of tire pump air compressor bodies from "lost PLA" process.  Finish machining required.

 

[jdome]

6 hours ago, Restorer32 said:

In my humble opinion it would have been way less complicated, and likely less expensive, to have this part lost wax cast.  Maybe $500 to have the rubber mold made and the mold is good for 100 pieces at least. Maybe $100 or less to have the part cast once you have the rubber mold.  We recently had a batch of small parts lost wax cast in bronze and the cost was $145 for 5 small but fairly complex parts.

I agree with that. I have made a lot of parts by lost wax casting from silicone molds. I make my own molds and cast wax copies from the molds. You can get very detailed castings as long as you start with a good piece. I would have filed & sanded the pits flat on the original piece and filled imperfections with finish bondo and epoxy the broken parts together and finished all surfaces smooth. If I can't live with the shrinkage I cheat and figure out where to strategically add material (bondo) to allow shrinkage. Shrinkage occurs when the molten alloy cools, not during the mold & wax process.  In this case I would epoxy a 1/16th plastic strip around the outside perimeter and fill the seam. Fill the screw holes and redrill the holes after casting. The casting process I would use is the type where they dip the wax piece in ceramic slurry to build up a ceramic shell around the piece.

 

Since you did a great job with the 3D print. I suggest you make a part out of (whatever) plastic at +2% size and use it to make the silicone mold. 

[bryankazmer]

21 minutes ago, jdome said:

 

 

Since you did a great job with the 3D print. I suggest you make a part out of (whatever) plastic at +2% size and use it to make the silicone mold. 

This is a very interesting "hybrid process." 

I don't think there is one best way - it depends on the part function and what you gave to start from.

Gary, you are doing some fine work here