Another Intake Manifold Lid

Discussion in 'Lost foam casting' started by Al2O3, Apr 6, 2021.

  1. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    As many of you know, I have a number of motorsport and historical racing interests. I recently acquired this intake manifold.

    1 Prototype Intake.jpg

    It’s a Boss 302 development part that has some historical significance relative to the factory TransAm program, circa 1969/1970. It has a cast lower and lid machined from plate, which also may have been a development part but there was a cast version of the lid as well. I only know of one other to exist and the owner is an acquaintance. He supplied me with pictures, dimensions, and other details of the lid.

    2 Lid.jpg

    ……..and with that information and my lower intake I set out to make a reproduction of the cast lid, because even as a reproduction, it will significantly increase the utility and value of the part. It will be a very similar project to this thread:

    I thought I might try to make this the christening project for my cnc router but upon closer examination decided otherwise. The part may look symmetrical, but it is not and I couldn’t begin to decipher the curvatures ……so I resorted to my old school methods, and believe me, it took a lot of measuring and head scratching.

    3 Paper Template.JPG

    For shrink, location of the mounting bosses and alignment of the sealing surfaces is what counts so I laid them out by hand. It’s 22” long so there will be nearly ¼” shrink in that direction. I traced and sketched it all out on paper template then transferred onto MDF and the templates took shape.

    4 Template.JPG 5 Underside.JPG 6 Topside Template.JPG

    All the work in a project like this is in the layout and template building. Shortly after through various combinations of cutters and guide pin diameters on my pin router the pattern emerged.

    7 Pattern Profile.JPG 8 Pattern Underside.JPG

    I designed the templates to carve the pattern from a single piece of 1” foam plank except the bosses. To get good detail I bored the boss locations on a drill press jig, and used a tenon cutter to cut 5/8” diameter bosses.

    9 Pattern Topsdie Bosses.JPG

    So glad I decided to bore and fit the boss locations. I got the best pattern detail on a part like this I’ve managed to date.

    10 Tight Boss Work.JPG

    ….and at this point, after a little light sanding, I had a fairly detailed foam pattern with no wax…..100% machined……but, then there was the lettering.

    11 Pattern No Wax.JPG

    The original lettering was 1” tall and the line weight about 3/16” width and thickness. I deemed that to be too large for wax, so I scaled and printed the lettering from the pictures, fashioned the repeating letters by hand, and made a jig to cut them on the pin router. It worked well. I cut 1” thick letters.

    12 Letter Details.JPG 13 Letters Cut.JPG

    ….then sliced them to thickness on the hot wire.

    14 Letters Sliced.JPG

    And after I mounted them on the pattern, the pattern was beginning to look the part

    15 Detailed Top.JPG 16 Detailed Bottom.JPG

    ……now to sprue/gate it and get it to successfully cast!

  2. DavidF

    DavidF Administrator Staff Member Banner Member

    Gotta ask, how much time you have into the pattern??
  3. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    About 11 hrs so far.

    The vast majority of that time (6-7 hrs) was measuring feature locations, adding shrink, and applying those to the layout. There was a lot of head scratching because features I expected to be symmetric were not. So I took a paper rubbing of the web layout from the intake lower casting, cut it into smaller pieces, matched the critical features to the locations on the shrink compensated layout, and freehand blended the small differences between shrink compensated and actual size rubbings. I calculated shrink and stretched from the geometric center of the part. It's about 1/4" and 1/8" addition to overall length and width respectively (part is ~22" x 11")

    Once I had the outer perimeter, I cut one template from 1/2" MDF with band saw and spindle sander then used it to cut two more identical blanks. I transferred the web layout to one of those, blasted a bunch of holes in it that matched the tighter radii, jig sawed and spindle sanded the rest. The webbing was the majority of template fab time and I was able to use that template to cut the profiles for the features on the top template, except I had to make one carb pad and use it to pattern cut an identical second.

    I have about 1 1/2 hours in the letters but can make oodles of them in minutes now.

    Actually machining the foam pattern was only ~45 minutes total which was almost all set up which amounts to nothing more than installing a couple different diameter guide pins, cutters and setting depth of cut. The actual hand/pin guided cutting time of the foam was only a couple minutes on each side. I use two sided tape and packing tape around the perimeter to hold the pattern during machining; fast and effective. There is a .25" registration hole for each boss location on the template. I clamped a piece of plywood to the drill press table, drilled a .25" hole, stuck a dowel in the hole, then installed a 5/8" Forstner bit, then just proceeded to set the template on the dowel and drill all the boss locations.

    The bosses were cut with a tennon cutter. They took 2 minutes to whack out.

    I still need to gate/sprue it. Still pondering some aspects of that but it will be similar to the other intake lid thread. Like here.

    Then dip coat it and obliterate it with molten metal and hope I have a piece of aluminum that looks like the pattern :)

    Now I know what you're think David, Kelly, you big pussy, why didn't you use your cnc router? The layout time would be the same but without a scan, I wouldn't know how to layout and blend all the curvature. Maybe try importing a top view picture of the lower casting? I am curious how a program would handle the fillets at the boss intersections.

    Not a big market for this casting. It's about!

    Clay, Tobho Mott and Billy Elmore like this.
  4. dennis

    dennis Silver Banner Member

    Wonders aloud, "how hard would it be to make a (much?) smaller version of that router setup?"

    Was thinking to use a laminate trimmer, e.g. Bosch "colt" or similar, and chiefly palm/saucer-sized pieces.
  5. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Very easy. You just need to mount the router on a small linear actuator and a fairly rigid over arm, which could be wood. There inverted arms that can be bought for use with a conventional router table,

    Daisy Pin Router Attachment, Router Jigs: Eagle America

    ......but you can't see the cutting being performed on interior features and the chips tend to wad up.

  6. Billy Elmore

    Billy Elmore Silver

    Wish I could find cool but useful shit to make for myself. I obviously do not have enough hobbies. Nice work Kelly! Having played around with foamy airplanes and hot wire cutters I like the idea of casting with lost foam more everyday. I also highly respect your ability to do something with the degree of difficulty this non symmetrical nightmare had.LOL
    dennis likes this.
  7. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Thanks Billy. LF has it's place. I've gotten a lot more out of it than I ever dreamed......still can't believe it actually works LoL!

    When I first started making those tubular castings, I invited a couple of my old foundry mentors over to see the process, and when I told them what I was going to do, and what was going to happen, they just looked at me like they wasted all the time they spent with me. Then when I poured the part, dumped it on the ground, quenched it, and handed the casting to them, there was a long period of silence..........

    If you can machine and work foam, it's the easiest route into casting IMO. Most woodworkers have the equipment to take right to it. You literally don't need anything special other than the ability to melt and handle molten metal.

    Next for me is probably LF iron. I do some machine restoration and like old iron. Most of the online sources I learned/borrowed process from were in fact iron foundries. Mercury Marine in Fondulac Wisconsin uses a pressure/vacuum version to cast the aluminum Marine engine blocks. I was trying to get a tour and was almost there, then the pandemic hit and quashed that. Still on my to-do list.

    Billy Elmore likes this.
  8. Billy Elmore

    Billy Elmore Silver

    I have seen the videos on their process. Pretty damn cool. Not extremely fast but very controlled and consistent. I think I would enjoy designing and casting combustible engine upgrades but am positive I would enjoy testing them even more.LOL
  9. dennis

    dennis Silver Banner Member

    You need gubbins, don't you? Those little brackets, collars, handles, Knobs, etc?

    Tobho used lost foam to make his for his Muller...

    I've used green-sand for mine, though I'm not knocking foam at all.
    Billy Elmore likes this.
  10. Tobho Mott

    Tobho Mott Gold Banner Member

    I go to foam when I just want a quick and dirty casting ready an hour or two after I think of it. Like those muller parts, they ugly but they work. That or when I just want to make some goofy shit like using those premade foam easter bunny and halloween skull "patterns" you can sometimes buy as an excuse to indulge my inner pyro.

    So I'm always amazed how nice Kelly's lost foam stuff is. Well worth taking the time to make and dip such nice patterns!

    Good luck and remember to say the magic words after the pour is complete!

    "There's no way in hell that filled"

    Works every time... if you really believed it.

    Billy Elmore likes this.
  11. Billy Elmore

    Billy Elmore Silver

    I knew I forgot something on that last misrun casting! LMAO Never say "that looked like it poured good" either! LOL
  12. Billy Elmore

    Billy Elmore Silver

    I actually was about to look into making some brass handles the other day and then found a bunch I had forgotten I bought a while back...I hate it when I already have something that I was wanting to make.LOL
  13. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Had to attend to other duties for most of the day but did get a little shop time this afternoon. I was staring at the bottom side of the pattern and all the webbing snaking around. I didn’t want to invest a lot of time but also wanted highest probability of success. So then I looked at the guide template and decided to just stick some EPS to it with two-sided tape and use a dovetail cutter to make a high contact area gate (or is it a runner?).

    17 Gates.JPG

    The dovetail angle increases the cross section while maintaining the ¼” contact width.

    18 Gate Cross Section.JPG

    Using low density foam, I think I get the runner full pretty quickly and with the bigger cross section, so I should be able to get hot metal everywhere needed. A bit more work to degate, but I have a good slitting saw for the mill.

    19 Both Gates.JPG

    So I used some fast grab tacky glue, stuck it to the pattern, and weighted it to dry. Should also benefit pattern flatness. After it dries, I’ll machine away some of the unneeded excess.

    20 Weighted Gates.JPG

    I had a little time left so decided to fillet the letters. Probably not required but it does prevent trapping water when I apply soapy water and dip it in slurry. The slurry can penetrate very small cracks. So I extruded some small diameter wax from my lost foam wax.

    21 Syringe Wax Rope.JPG

    I didn’t need a lot so I just stuffed some wax in the syringe, heated it with the hot air gun, and squeezed out some small fillet stock…..~<1/16” diameter. It wipes in easily with 1/16R fillet tool.

    22 Small Fillet.JPG

    Tobho Mott likes this.
  14. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Finished the pattern today. With the roughed in gating glued in place, I taped it to an inclined board and planed away some height on the bottom end of the pattern.

    23 Planing.JPG

    Then I did some additional carving and patching the channels for preferential metal routing. I also added legs for the pattern to sit on when it dries. I turned the pattern over and used the pin router to level the legs to the same plane. I’ll probably cut the legs off after the coating dries before casting.

    24 Carved Away Runenrs.JPG 25 On Legs.JPG 26 On Legs.JPG

    Then dipped it in slurry. After it hanged and dripped for a while, I placed it on its legs to dry. The patterns get considerably stiffer after coating so having it well supported on a flat surface as it dries will help promote stiffness and flatness.

    27 Dipped.JPG

    There’s rain in the forecast for the next couple days :(. Maybe I’ll get a window of opportunity.

    Mark's castings and dennis like this.
  15. Gippeto

    Gippeto Silver

    Awesome project and incredible execution as always. :cool:

    oldironfarmer likes this.
  16. oldironfarmer

    oldironfarmer Silver Banner Member

    The sad thing about lost foam, you think "That didn't pour well" then you get a successful casting. Dang!
  17. oldironfarmer

    oldironfarmer Silver Banner Member

    I see you're struggling as usual, Kelly, but still manage to impress the rest of us.

    Well done!

    I do have a serious question. I see you've added shrinkage. I'm assuming you are doing that through experience since you've done a lot of large lost foam castings. I have yet to be able to measure shrinkage in my lost foam castings. I have been under the assumption that somehow the way the mold fills minimizing shrinkage. My longest casting was about 24" but I didn't think to measure the pattern accurately since dimensions on that casting didn't matter. I have done some shafts which seemed t come out full size, and the pipes I cast. Please elaborate on what you see in shrinkage.
  18. oldironfarmer

    oldironfarmer Silver Banner Member

    By the way, make two and post one for sale at an exorbitant price...
  19. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Thanks Andy, but it aint metal yet!

    Though I commented in my "Confessions" thread that I rarely if ever see shrink (defects), I do see normal dimensional shrinkage. Normal for me in aluminum is .013"/inch. That's about 1.3% which is exactly what you would expect to see due to the coefficient of linear thermal expansion with cooling from the melt point to room temperature. This is with A356 ingot as casting stock. I used this calculated shrinkage on the previous intake lid and it correlated very well. The part in this thread is a couple inches longer.

    I have seen references for shrinkage up to 3/16" per foot for aluminum, and 5/32" per foot (same as .013"/in) is a pretty popular aluminum shrink ruler. Opinions will vary.

    For this part I have built in ~.25" of shrink over the 22" length.

    Now I have seen remarks here that wrought aluminum stock (dimensionally) shrinks more than casting alloys, but other than having a modestly higher melting point, not sure I'd understand why. I do think I understand why it would be more prone to shrink defects.

    I don't think I'd have an explanation for why you wouldn't see something similar. Now I have heard that (higher) mold rigidity can affect (reduce) shrinkage. The highest rigidity would be permanent mold.

    For most of the parts and tolerances I work to, the dimensional shrinkage isn't much of an issue, but on a part this size, a .25" error in the location of a 5/8" diameter mounting boss would be. Even splitting the difference with 1/8" error on each end would still be objectionable. -We'll see how I do.

    oldironfarmer likes this.
  20. oldironfarmer

    oldironfarmer Silver Banner Member

    Thanks for the thoughtful reply.

    I see appropriate shrinkage with sand casting. I attribute it to some compressive forces going into the initial cooled skin of the casting as the liquid inside adheres and tries to suck it smaller.

    It seems like I need to do some careful measurements on my next lost foam casting and admit I may have missed the shrinkage. :rolleyes:

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