V4 350cc 2 Stroke

Very sensible.

Good luck with that. Here in the US, lost foam casting is very thinly practiced. If they aren't a lost foam foundry, chance of success or even interest are even less. Most foundries here want recurring production work and wouldn't consider doing a one-off casting for a privateer, especially if I showed up with a foam pattern in a bucket full of sand and asked them to pour metal on it........no way unless they are a personal friend or take an active interest in your project. -So thus my videos and here I am

With care, there should be no reason you can't produce a quality melt yourself. If your kiln has temp control, you can easily heat treat 300 series alloys to T5. In fact that can be done in a kitchen oven (but very dangerous if you if have a wife). T6 is more of a challenge because it requires heating so close to melt temps it can cause casting damage or distortion.....even when left to professionals. T5 achieves a high percentage of T6 improvement. I rarely go for T6.

I prefer to cut the fillets directly into the foam. I do have some radiussed flat bottom cutters but almost always just machine the pocket with a roughing clearance equal to the fillet radius and then chase the pocket perimeter with a ball nose profile cut to add the fillet. I do still occassionally use wax fillet, but usually at junctions where I have glued parts together and/or where it causes an excessive amount of programming to model and program the fillet. I rarely go to the effort of putting the internal fillets into the CAD model because they just complicate the model and they happen naturally when cutting the pattern with a ball nose cutter. External fillets I do model unless they are small, which can just quickly be done with abrasive paper after the pattern is cut.

A CNC Router is better suited to cutting the foam. Relatively small diameter bits on foam calls for very high (>20krpm) spindle speeds that are not typically available on a metal machine. Plus the foam clings to everything making an absolute mess on a lubricated metal mill. A dust shoe on the router eliminates most all of this. Even a cheap hobby CNC router will do a good job on foam. Their light weight construction is a liability for machining hard materials, but their low inertial mass allows high speed movement. Cutting foam is like cutting air.....almost no tool load. I just tape my machine stock to the spoil baord. But as you say, buying a machine for one use may not make sense, but I use mine for many things and since you already are knowledgable in CAM/CNC, all you need is a good post processor and you're good to go.

Yes, but I try to avoid it.

Gating and mold positioning is a more invloved subject and I can comment further on your specific parts, but since you have and are already expert at manipulating your own model, lets try this first. (Give a man a fish he eats for a day. Teach a man to fish and he eats for a lifetime )

You want to position the parts to avoid if not eliminate blind cavities (those that must fill from bottom up rather than top down), and horizontal overhangs. If you imagine your pattern placed in the flask, and then fill the flask slowly filled with water, anywhere that will create an air pocket will potentially produce a leaker. As opposed to creating a horizontal overhang, angle that surface in the mold. The incline allows the sand to be aided by gravity and more easily flow as opposed to having to flow horizontally. The fluid analogy is a good one, because vibration fluidizes the sand, but it behaves like a very viscous fluid, depending upon vibration energy level.

Lost foam gives you the freedom to positon the part in any orientation to do this. You also want to have the initial attach point of the feed system at the highest point of the part in the mold. I also have gone to what I call high contact area gating. If you review my timing cover or intake manifold posts here or YT videos, those have examples.

Complex parts require exceptionally good packing and high vibratory energy to do so. This is hard(er) to do with heavy molds. The prefered position/orientation of the part can often aggravate this by requiring a larger, heavier, flask. To minimize sand mass, you can build a flask from wood, or, you can place hollowlightweight objcts in the mold to take up space, but they must be heat resistant. They can be wood if you maintain a few inches of sand seperation for insulation.

You need to look into finding/making a high energy vibration source. Vibing in stages or continuously as you fill the mold will allow it to work on the mold as it gains mass. You also want very dry and graded sand (uniform mesh size/distribution). Wet sand will not fluidize under vibe. Sand of with large variationsin mesh size will not flow and pack as well. Washed and graded sands are common for use in mortars and abrasive blasting.

Also consider a making an offset pouring cup. You'll behappy you did.

The plastic barrels you've used are convenient but as you have experienced, a small spill will melt them and potentially cause disaster. As your parts get larger, they will bring a lot more heat to the mold after the pour and may soften and/compromise the flask. Steel barrels are much better. If you must use a plastic barrel, using thin sheet metal to form a ring dam an inch or so inside perimeter of the barrel will protect the plastic barrel from small spills.

I thought your introductory post looked familiar and had forgotten I had viewed your V Twin build and subscribed back then.



It's a long winded reply, but these are the nuance things that really matter when making engineered parts. -Good luck.

Best,
Kelly

 

Though likely good casting alloy I can't say for certain about the wheel alloy, but if you befriend someone in the scrap/salvage yard business they usually have handheld devices that can determine metal composition.

Best,
Kelly

 

Wow, that is great news. That's quite a valuable connection for you and within 10 minutes to boot. If it were me, I think I would do all I could to foster that relationship.......like a nice bottle of Scotch if he/they fancy such things.

How's the crankcase design and pattern coming along?

Best,
Kelly

 

I use to pour at 1450F but these days 1350-1375F. Like conventional casting, it can depend upon the nature of the parts. Small and thicker parts can be poured cooler. Thinner walled parts with high surface area/volume and long metal travel distances from the feed system would be the higher end of the range. Since I have taken to using more generous feed systems with high pattern contact area and larger runner cross sections, I can pour toward the cooler end of that range. This approach works very well but can accentuate the variation in pouring rate. Once the metal consumes the sprue and engages a lot of contact area with the pattern, the metal velocity increases significantly......be ready!

Might be worth a little further discussion about how you intend to position and feed the parts. It can have a large bearing on probability of success and quality of the casting. The upper casing/cylinder pattern in the picture should be fairly easy. The crankcase requires a little more thought, but in addition to my earlier remarks, I'd position it angled with the open cavity partly/mostly exposed upward, feed in the top bulkier sections, and also down edge of what will become the gasket sealing surface of the case. It will require a little extra degating effort, but it's a good trade for first pass yield versus having to remake the pattern and doing it second time.

I just gated up this intake manifold pattern. I'll take a picture and add it to this post later today.

Boss 302 Inline Autolite Carb Intake Manifold | The Home Foundry

Do you intend to pack the mold at home or the foundry? Remember....good vibration! Also a good pouring cup with at least 6" of sprue height before the pattern is important. This is true any time but especially for any first time lost foam casters, who tend to get fooled by the "lost foam pause" (very unequal rate at which the mold takes metal from the ladle). That or any flinch/pause in the pouring stream as a reaction to flame/smoke that causes the sprue to become uncovered and a gap in the pour will most likely result in a fail. A pouring cup >25% of the part volume is very helpful in avoiding such. You want the cup to be low mass so it doesnt rob heat from your melt lowering the effective pour temp. The sprue height usually helps to reduce flame and initial cup turbulence as the pour commences. When I have a pour where the metal just tranquilly fills the cup and then the mold with no flame or smoke, I know it was a good feed system design.

Best,
Kelly

 

That's what I do. Just to clarify, PVA = PolyVinyl Acetate or water based wite glue. It can also mean Poly Vinyl Alcohol, which can also work, but the former gives you plenty of working time. Use it very sparingly. You dont even necessarily need to coat the whole joint width because all you want is bonding not necessarily sealing. It's also helpful if you cut yourself some 1/4" wide strips of packing tape, compress the joint with your hands, and apply the tape every few inches as needed to hold things in place. Then if you can, apply weight to keep the joint compressed and let it dry overnight. You can achieve some nice tight, strong, gapless joints, but an occassional wax patch in localized places is nothing to hang your head about. There's an example and good result of a complex parting line joint in that intake thread I linked earlier.

You dont have to go crazy with sprue length. 6" above the pattern seems to let the melt settle in nicely and continue in an orderly filling progression. The extra height will also make the mold get much heavier so helps to vibrate as you fill in stages.

A pneumatic rammer might be a little aggressive. Generally you'd like higher frequency than that. Another vibrator commonly found in foundries is the one they attach to match plates to help free them from the mold. If they had a larger or a couple of these, thay can usaully just be bolted to the flask.

I think the best thing might be for you just to make a simple mold and mold one from bonded sand. I'm sure the foundry has sodium silicate or other catalyzed binder systems. It would be expendable but simple and effective. Remind me, what to you expect the weight of the casting and feed system to be? How big will the mold be? Dry silca sand is ~90lbs/ft3.

I'd really like to see you succeed because I want to hear a 4cyl, 350cc, 2-stroke come on the pipe at full song! I presume you'll make your own expansion chambers...? Also, I presume you will brush coat the pattern. You can do it in stages if convenient.

Best,
Kelly

 

You'll need to remind of the estimated weight of the casting. The feed system seems a little larger than needed, but there is little downside to it being larger.

By comparison, I'm pouring up to 30lbs through a 1.5 inch square sprue. I think traditional sand casting foundies are fond of round sprues because tubular of sprue cutters, and in theory it minimizes surface area/volume (heat loss, which I think inpractice is negligible by comparison). But I think square spues are preferred because they reduce/inhibit aspiration caused by coriolis affect.....and as a bonus are easier to make. Same reason for rectangular as opposed to round pouring cups. I do add some slight taper of say 1/8" total.

Yes, like shown. As just a general rule, I'd keep the cross section of the sprue, combined cross section of both runners, and pattern contact area comparable in area. If I were to stray, I'd make the area slightly decrease from sprue to contact area. In lost foam, none of this matters much initially as the feed system is filling, but as the pattern starts to be consumed, it can take metal much more quickly, and the feed system must be able to keep up and maintain a slightly pressurized system for good mold support and to keep the metal front in good contact with pattern. Most of my patterns are 1/4" wall typical. Yours looks to be more like 1/2".

Looks to me like you need to narrow the contact area on your runners (like shown in the attached) to achieve the above. It will have the side benefit of making it easier to degate by cutting with a slitting saw through the thinner cross section. If the contact area gets large in comparison to the feed system, it can be harder to keep the cup full at peak pattern consumption, and keep the entire system slightly pressurized.

Agreed. On that part, what helps in this regard on one side, hurts on the other. As long as you have good dry, well packed sand, it probably wont matter. If you are to bias the position from vertical, I'd do so on the side where a leaker would be least impactful to the casting function.

As mentioned before, I've been pouring at 1350-13750F. I used to pour slightly hotter but since I've gone to high contact area feed systems like this, I've reduced to these temps and could probably back off another 25F. These are on 1/4" wall castings. Yours look somewhat thicker wall. Thicker castings can generally be poured cooler but higher temp will significantly increase the odds of a completely formed casting.....pouring short by small amount after all the pattern work can be a real drag.

Have you decided what you will do for a pouring cup? Out of curiosity, how much machine stock did you leave yourself on the casting? Are you going to pour this one before the crankcase or at the same time?

Best,
Kelly

 

The challenge is usually having enough Z axis travel, and (low) speed control for long small diameter bits.

Wow, that's a lot thicker than I thought. Looking at the pattern I can see where certain areas would be that thick just becuase of design constraints to accomodate bolt bosses etc, but doesn't look like the majority of it is that thick. As always it can be a matter of design constraints and practicality in being able to model and machine away the additional stock, but believe it or not, besides being lighter, thinner (than 1") walled castings can be stronger because in general they are more defect free than thick castings, and this can be especially true in lost foam.

I wouldn't worry too much about it on this go, but don't be afraid to machine away more pattern stock if needed. Light = fast, especially on 2-wheels.

Comparable to your sprue and runner area. So if you have a 1.5" square sprue (2.25 in^2 of area), and you have two 1" x 1" Runners (2 in^2 combined area, but if you add the reduced contact area extension probably right around ~2.25"), the width of the contact times the total linear distance everywhere those two runners touch the pattern should be around the same area........but not less than .188"-.25" width ever.

So if the width of the contact was .25", it would call for about 9" of total linear contact length with the pattern. The reason I say not less than .188"-.25" is because of strength and the fact that there is resistance to flow because of surface tension and head loss since molten aluminum is viscous. As a practcial matter, for long patterns .25" width contact can easily exceed the cross sprue and runner area. Sometimes I dont continue contact all the way to the lower last length of the pattern, sometimes I just except in knowing it may really rapidly suck metal from the cup when the feed system full pattern become fully active.

Keep in mind, the real goal here is to have a thicker more massive runner that will deliver hot metal to the majority of the pattern. I also like to use lower denisty white EPS foam for my feed systems because that stuff evpoartes very quickly and causes the runner and feed system to fill more quickly than the pattern, which is exactlt what you want to happen.......plus I have an inexhaustable supply of free scrap EPS.

For your pattern, I might hedge a little wider (but not more than .375") if it really is mostly 1" wall thickness. But just be advised, when the total contact area gets large, it will rapdily take metal from the cup after the initial phase of the pour, so be ready with the ladle tipped! Foundry guys that pour open cavity casting get taken off guard by this.

I'm sure you will have at least 2kg in your feed system plus whatever additinal volume you may have in, which could easily be another 2kg. I'd have at least 10kg in the ladle.

That's about what I typically provision. It's rarely all needed but better to be material rich and tolerate minor surface flaws. As long as the pattern doesn't distort when you pack it you should be fine. Fill the flask evenly in stages keeping the sand depth (pressure) equal on each side of the pattern. If there is some distortion, just straighten it before heat treating. The green/untempered casting are quite easy to move in a press....at least small amounts.

Best,
Kelly

 

I use a wax fillet profile specially formulated for lost wax casting that melts at the same temp as the foam. That stuff is great. But I used other waxes before I started with this product and got good results for the most part. My advice would be to use it as needed but very sparingly. In lost foam casting you wan't the lowest pattern mass possible and wax is still much more dense than XPS foam. Even a 1/8"R fillet is an enormous relief to stress compared to a sharp corner so you don't need to get carried away.

When it comes to the pour, you want a nice tranquil pour with no smoke or flame but because you have much thicker cross sections, the chance that you may have some gas escaping back through your sprue is much higher and that can cause more cup turbulence and obscuring of your visibilty of the cup.

That means there's the potential for flame and smoke that you will need to pour through. Dont flinch, anticipate such, and keep the cup full. Hopefully, it will be relatively uneventful in this regard. Most of time I get nothing or just a small flash before things settle down. A little more sprue heigh can help in this regard.

Good luck......wishing you the best of success.

Best,
Kelly