Casting a windmill gear in grey iron

Yes, resin bound sand is very machinable.
You can drill it, cut it, etc. similar to what you can do with rigid foam board.
Many at the FIRE exhibit were using a rotary rasp mounted in a cordless drill, and other tools to shape/carve sculptures into the sand.

Here is today's work so far.
Still sort of a fluid thing, but I think I am closing in on it.
I am making this up as I go (seat of the pants type affair).

I forgot the shrink riser, so I will drill that in.
I will probably need sprue, spin riser and shrink riser extensions, or add a 4th piece to the mold.


Here is the cope.








and the drag.

 

I will drill two holes through all of it in opposing corners, for centering rods, prior to cementing it all together.

The grease could be a problem if it soaks into the sand.
The mold coat may help.

I think someone suggested putting the shrink riser over the gate.

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So you're dropping the iron into the top of the gear? I'm trying to follow, going back for extra butter.

 

The mold is complete.
I think I have it stacked correctly.
Maybe not.

Its rather confusing with all the pieces.
I guess I will be doing a waterfall (one of the big NO-NO's of metal casting).
Well, no time to back up now.

This is more or less proof of concept, ie: can I get the grease cleaned off sufficiently so that it does not cause massive gassing?

I can step back tomorrow and tweek the design.
The intent was a bottom fill, with the gate at the top of the runner.
I got the gate at the top of the runner, but failed on the bottom fill.

Damn the torpedoes.
If the grease screws it up, then no sense making it perfect right now.

Edit:
I should have mocked it up in 3D like I usually do.
No time for that.

 

I am going to call it like it is.
This is not going to work well.
I will go ahead and cast this mold, but it is not going to be high enough quality to consider a success.

These gears need to be made using David's lost PLA method, and I don't have that slurry, and don't plan on buying it.

Well, I learned a lot on this one, but at the end of the day, I have to chalk it up as a failure.

Sorry about that Ed.

Who wants to do some lost PLA castings in iron for Mr. Ed and his windmill project ?

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If Mr Ed were to supply me with a pattern that was drafted to be split at the gear tooth centerline, I could sand cast it in ten days. I’d do it this week, but have travel plans.

The resulting gear would have 2 degrees of slope up to the center from each edge of the gear. That probably would work as it is or could be quickly dressed off with a file.

Denis

 

Mr. Ed has it.
He has someone who can make 3D printed patterns too.

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The teeth are degraded pretty bad at this point.
It would be easier to cast a blank and machine it, and more accurate too.
Lost PLA is the way to go for casting them.

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Boy that's the truth!!

If it is a failure send it to me and I'll have a go at it. I think it can be done with plain old sand.

 

No need to fight and argue about who gets to cast a gear (or parts) ... here is a pic of the next mill on the list. Its still in Colorado, so I'm not fully sure what it needs yet. Will be picking it up in Nebraska in a couple weeks.

As far as the files for the gear, I have to get to my other computer and see what files I have. I made at least three versions in Fusion 360 (and I am no a pro at it).

I really need to finish up this mill and start getting some more casting practice under my belt. I need to get to a point that I can graduate to iron (I currently have a couple other parts at a foundry in Rice Lake, Wi).

 

Here is a shot of the rendering of the finished gear. If we can cast with the recess in place, that would be great. Let me know which process would work best ... I'd guess lost PLA (if David is game).

 

If the goal is to have an as-cast part work without any machining, lost PLA or sand casting using silicate (or other binder) and a two-part urethane positive might be best.

That said, if it were sand casted with silicate conventionally and 1.5 to 2 degrees draft used, the centerline of the teeth would be .013 to .017” higher than the outer edges if the face of the teeth is 1” wide. Considering the fact that it is to run (if I didn’t miss something in this 7 page thread) against an already worn gear, that degree of crown might be either insignificant or a bonus. If it actually caused a problem, 20 mins with a file would virtually clean it off.

Not arguing for any one method, but want to make sure the correct assumptions used in determining process selection.

Finally, it is likely this part, like any other casting will warp some. That warpage is likely to be greater than 60 thou. So, no matter what mold substrate is used, hoping for a tight tolerance part is optimistic. That warpage might be minimized by carefully maintaining symmetry in feeding the mold and riser placement. The symmetry considerations might argue for discarding the core idea and leaving the casting solid with a centered riser where a core print would be placed.

Drilling out and boring a solid-centered casting might take 1/2 hour or so.
FWIW

Denis

 

If you'd like to send me your Fusion360 file I can print my own gear. Recess should really be no problem, is it machined inside or just a spacer?

 

Are the teeth really going to pull better if you just add draft to the outside surface? That's probably only a 1/4 of the area for each tooth. Would be the easiest to remove and still maintain decent tooth profile though.

I just bought a hobart A-200 like yours. I was wondering what paddle to use but see you have the dough hook in.

 

What I wrote about the tooth part line may not have been clear. I would propose the gear be parted so that half of each gear tooth would be in the cope and the other half in the drag. Looking at the toothed portion of the gear only the partline would go right down the center of the gear teeth. This would make the teeth “humped up” symmetrically and would add slightly to their diameter. That might compensate for some wear on the mating used gear. At least it would not likely pose a problem.

 

My mixer came with a wire agitator, and that did not work, since it was too flexible.
I built my own dough hook, shaped to fit the curvature of the bowl.