Automotive Oval Air Filter

Discussion in 'Lost foam casting' started by Al2O3, Oct 27, 2019.

  1. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Years ago I started restoring these old Inline Autolite carbs.

    1 Inilne Carb.JPG

    I have offered these cnc billet aluminum filters for them which are very nice, but perhaps a bit too nice for the tastes of some who prefer a more period correct (the carbs are 50 years old) appearing filter like the cast aluminum oval air cleaners of the era.

    2 CNC Filter on CBs.JPG

    So I figured I’d have a go at making a cast version.

    You guys know my usual schtick. I made a few templates for my pin router to make the foam patterns for the base and the lid.

    3 Filter Templates.JPG 4 Cutting Pattern.JPG 5 Cutting Pattern.JPG

    Here are the first patterns. The typical wall thickness is 1/4”. They are just under 20” overall length, 6” wide, and 5/8” tall.

    6 Patterns Top.JPG 7 Patterns Bottom.JPG

    Next I’ll need to do a little light finish work, gate, and sprue them. -More to come.

    Tony, 509Maker and Tobho Mott like this.
  2. DavidF

    DavidF Administrator Staff Member Banner Member

    Ok, hold on! Here we go!! :D
  3. You could just about coat those MDF templates with epoxy, sand smooth and pull a resin sand mould off them even with minimal relief.
  4. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    ....or I could use the same templates to cut either a loose pattern from urethane modeling board or for match plate.......but, the foam patterns have no draft, so it would take a little more doing. The LF castings should be very near net shape.

    Yah, it's been a while David.......I need to get on the ball.

  5. Come to think of it, you can get ball nose tapered end mills that would give you the needed draft when you route the modelling board.
  6. DavidF

    DavidF Administrator Staff Member Banner Member

    Well, I'm pretty much moved into the new shops now. Have to build some shelves and get things organized, but I'm feeling a huge burden lifted.
    Wont be long and I'll be back at it...
    Al2O3, Tobho Mott and joe yard like this.
  7. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I do have a few 3 degree tapered router bits. I bid on a hole box of tapered end mills once at a surplus auction. There must have been 50-75 of them in all sizes......but didn't win them. They can of course be bought but can be pricey buggers. I like pattern making but it probably doesn't matter for me because the only reason for me to make a drafted hard pattern would be production work and I just don't have any interest in operating a production foundry. I don't consider my lost foam stuff to be production even though for some parts I will occasionally make a handful of copies at a time.

    I know folks are skeptical of this claim but I can make, prep, and cast a handful of foam patterns like this in less total invested time than I could in green catalyzed sand. If I had production molding equipment set up and continuous flow of molding material that of course wouldn't be the case. But I'd have to have a muller or mixer for green or bound sand, flasks, and a whole bunch of sand to prep five molds. The set up and conditioning time for the mold media would time very consuming compared to my current process..........and I have complete design freedom with lost foam without being constrained by draft, parting lines, or core work. If it were production work with production equipment......totally different story. - But that's why I do what I do.

  8. garyhlucas

    garyhlucas Silver

    My CNC mill, 3D model to foam part in minutes, no fixtures or patterns. Dry the mud over dehumifier and pour the same day. That’s what attracted me to lost foam.
  9. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    One of the challenges with a lost foam part like this is keeping the pattern from deforming while packing the mold. So I decided to gate down the outer edges of the filter gland and cast the base and lid together in pairs. I also put support posts in the central part of the pattern. I think this gating approach not only provides good support to the patterns, it also provides a lot of contact area to feed the parts along the 3/16” wide edge, and gates two castings at a time. They should also be easy to de-gate on the table saw and the gland edge is an easily machined surface. So here’s how we roll:

    8 Gated Halves.jpg 9 Sprue.JPG 10 End.JPG 11 Joined Pattern Bottom.JPG 12 Joined Pattern Top.JPG

    Once you stick a pair of patterns together like this it makes brush coating the interior difficult. Good thing I know someone with a dip coating rig. :D After a good dip and dry it should be ready to cast.

    Tony, Mach, Mark's castings and 4 others like this.
  10. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Gotter whipped…..or I mean dipped.

    Couple little details, I made a wood button and hot glued it on the sprue. After the patterns get dipped the weight increases and you can pull a drywall screw out of the foam sprue. I’ll just hotwire off the button when dry. I also spritzed down the pattern with a dilute Dawn dishwashing soap and water as a surfactant and blew of the excess with compressed air.


    Wow, am I glad I invested the time into making the dip coating rig…..The Big Dipper! Very fast and very consistent coating.–-the-big-dipper.776/

    On my last couple patterns the slurry seemed a little thicker than I preferred so I added about a half-gallon of water to the 25 gallons of slurry to thin it just a bit and mixed it up with a cordless drill and the mixing paddle hanging on the rig. After fifteen minutes or so of fussing around with that, it took about 15 seconds to dip coat it. I let it hang there and drip back into the barrel for another fifteen minutes or so while I cleaned up a little in the shop then capped the Big Dipper back up and placed a piece of plastic on the lid to catch any late drips.

    14.JPG 15.JPG

    You fellas know what comes next……annihilate the pattern with molten metal!

    Mark's castings and Tony like this.
  11. ESC

    ESC Silver Banner Member

    Looking good Kelly.
  12. Tony

    Tony Copper

    Awesome cant wait to see how they turn out.
  13. Tobho Mott

    Tobho Mott Silver Banner Member

    That's gonna look great, good luck with the pour!

  14. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Thanks Fellas. I think it's similar to my automotive intake manifold lid pour like the pattern at the bottom of this post.

    So I used a lot of the learnings from that project for the first go here. Longer lost foam castings like this one do have greater risk of pouring short.......but the risk of failure is also part of the thrill of success. I'm vacillating a bit about whether to use any vacuum with the pour but given the lid's I successfully poured without, I don't think it should be necessary.

    -Now just some time to pour it.

  15. oldironfarmer

    oldironfarmer Silver

    You just make be sick because you're so good and I'm so bad.:p

    Great work as usual!!:D
  16. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Now anyone that's seen your posts here and Youtube channel knows that's not true but thanks OIF. I'm happy with the pattern but a bit apprehensive about the pour. Maybe as Tobho Mott has suggested about lost foam pours, I should further shift my insecurity to sincere doubt to improve the chances of lost foam success. LoL!

    Tobho Mott likes this.
  17. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    The Jury is back. We have a verdict. I’m going to test the picture limit.

    Here’s the dried pattern.

    16 Dried Pattern.JPG

    Vibed, packed, and prepped in the flask

    17 Mold Prep.jpg

    As usual, the scene of the crime

    18 Staging.JPG

    I did video the pour. It was very tranquil and uneventful. Typical lost foam pause and then it steadily took metal for 24 seconds. I had a nearly full A10. Good thing, it took it all. This was a very good sign. I think the slight thinning of the coating helped permeability. It poured very well.

    19 Raw Casting Top.JPG 20 Raw Casting Bottom.JPG 21 Weight.JPG

    De-gated on the table saw.

    22 Degate.JPG

    Introduced the castings to my mill.

    23 Mill Top.JPG 24 Mill Bottom.JPG

    I’ll have to media blast them at work Monday to color them up uniformly but am pleased with how it turned out, especially for a first attempt.

    25 Finished Casting.JPG 26 Finished Casting Bottom.JPG 27 With Clear Filter.JPG

    Shrink was as expected and fit the carb well.

    28 Fit.JPG 29 Fit on Carb.JPG

    I still can’t believe this lost foam stuff works;)………I need to make more!

    Tobho Mott and Mach like this.
  18. Tobho Mott

    Tobho Mott Silver Banner Member


  19. ESC

    ESC Silver Banner Member

    Way to go Kelly. Refresh my memory, do you lift off the pouring basin while it is still molten? I seem to remember that you were able to reuse them.
  20. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Thanks ESC. Yes I do reuse the pouring cups and I do pull the cup while the metal is molten. That's why there's that big lump on top of the sprue. The sheet metal saddle is there so I can grab it with plyers after the pour. If you extract it slowly, the metal just replaces the volume where the cup resided. The moldable fiber material is a good insulator and handles metal contact well. I have about twenty pours on this one. So far so good. Here is the before:

    30 Cup.JPG

    ....and after the pour. It's a thick foil. The cup has a little draft so I fold the foil in with needle nose plyers until I get near the bottom and the skin easily pulls out.

    31 Cup after pour.JPG

    The pouring basin thread is here.


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