Tobho's HT1-Inspired Cement Mixer Muller Build

Discussion in 'Sand Mullers' started by Tobho Mott, Mar 22, 2018.

  1. Tobho Mott

    Tobho Mott Silver Banner Member

    There would be a gap between the wheels because their hubs stick out a bit farther than the wheel is wide. I don't have a lathe to turn them down... maybe I could do something with a saw but not sure... I'd love to to cast a big wide wheel, but once again - no lathe. Maybe I could cast one directly around an axle instead of using a sand core... Don't think I'm not thinking about it! :D

  2. Melterskelter

    Melterskelter Silver Banner Member

    You have an angle grinder with a cutoff wheel, right? Just zip off the offending portion of one or both hubs til they butt together. :)
  3. Tobho Mott

    Tobho Mott Silver Banner Member

    I guess that could work too...

    Edit - added some still pix the the last update post.

    Last edited: Jun 4, 2018
  4. Petee716

    Petee716 Silver Banner Member

    Looking great Jeff!
  5. Tobho Mott

    Tobho Mott Silver Banner Member

    Thanks Pete. I think the muller also looks quite nice. :cool:

  6. Petee716

    Petee716 Silver Banner Member

    Lol. Ill leave it alone.
  7. Tobho Mott

    Tobho Mott Silver Banner Member

    So. I made some new greensand!

    The whole idea of moving the wheel inwards turned out to be unnecessary; because Olfoundryman's (video comment) suggestion to ease up on the spring tension in order to allow the wheel to ride over the sand rather than push it aside was much easier to implement than repositioning the wheel, I tried that first and it seemed to work really well.


    Then I started mixing up batches of sand.


    Since 14kg of the 75 mesh silica...


    ...was a little under half a bucket full, and because I knew from reconditioning my Smelko sand that the muller can handle a half bucket at a time, I went with 15kg batches containing 4.5% sodium bentonite.


    I ran the dry ingredients through the muller for 11 minutes, clearly losing a little bit of that bentonite in the process (cue "dust in the wind")


    Then I added water and mulled for another 11 minutes. Well, I must have seriously miscalculated how much water to add to the first batch. 750ml is enough to make 15kg of dry ingredients absolutely soggy!


    The next 3 batches got got far less, more like 250ml, and came out much nicer.


    But an odd thing happened that had not happened in the first soggy batch: The sand fluffed up so much it began to back up on the outer scraper after about 7 minutes of mulling, and I had to tilt the drum a bit in order to let gravity help keep the sand moving along and getting underneath the wheel. This is hard to show in a still pic, and it is even a little hard to notice in the video.



    I also noticed that just before this backing-up occurred, the sand would become sticky enough that the scrapers would peel it up off the floor, revealing the wear plate, rather than allowing the sand to pass beneath them. I think the backing up was caused by putting oversized batches into the muller - I had based the measurements on a half bucket of dried out greensand not being too much, but a half bucket of dry ingredients becomes a half bucket of greensand rammed up hard once you mull it...

    I gave the 4th batch a bit less water still, and the backing up never happened, nor did the scrapers ever peel sand up off the floor. I added a little more and let it mull for a few more minutes just to be sure, and it did back up as I had come to expect from these 15kg batches. Once dumped out, that batch felt great, so I used it to ram up a test drag just to see if it would hold together, which it absolutely did. The test mold-half looked pretty good actually, I kind of wish I'd had time to pour it.


    The latest video covers it up to this point:

    After all that, I let the new sand sit in my bench stewing for a couple days (Smelko sand went into buckets, for now). At the end of that, the whole 60kg + water heap now just feels soaked and sticks to my hands like the pic above from batch 1. So I riddled the lot of it back into the bench to aerate it a bit and hopefully speed that drying up as much as I can (a first). I guess it is gonna need a few days (or another trip through the muller with a heat gun trained on the sand) to dry out before I can really put it through its paces to see how strong a 4.5% clay batch will be, and therefore whether or not I might want to add a little more bentonite.

    Any of you guys with more muller experience than me see anything I misinterpreted or missed? Thoughts? Anything? I'm pretty stoked to pour something in this sand once it's dry enough!

    Got my microwave timer ready to install in some kind of yet-to be devised enclosure so that I can just punch in (ie.) 11 minutes and not have to listed for the alarm beeper over the muller noise because it will just stop when it is supposed to.

    Thinking about casting a wider wheel... What do you guys think the odds are of me making one that will spin well without having access and knowhow to run a lathe?

  8. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    For a one-off, I think it could be made net shape in lost foam. You'd need to decide how fancy you wanted it but if you stuck a hub and outer ring to each side of a disc, drilled a nice hole in your hub so you could spin it on a pin with the outer edge touching your belt sander, I bet it'd be close enough for a muller wheel. After casting it, if you drilled and bushed the hub, you could tune up the OD of the wheel on the belt sander the same way. How many pounds of aluminum can your pour?

  9. Tobho Mott

    Tobho Mott Silver Banner Member

    I never weighed a casting with its gating and leftover ingots, but I have a #12 crucible. If you think I can make it work by just drilling out the hub, maybe it will work. I've never "bushed" anything before (hence the wheels on my first muller were walmart barbell weights simply spinning free on some pipe...), but I figure I can teach myself to figure that part out, I guess. I will take a closer look at how the existing wheel is made for starters... Lost foam could work but part of me wants to use the new greensand for that project! :D would mean having draft on the wheel surface I guess, but it seems like it could be a fun project.


  10. Melterskelter

    Melterskelter Silver Banner Member

    Jeff, I am assuming you have some as-yet-unmixed sand. If so, I would suggest measuring and adding 3.5% water to a new mix to see what that looks and feels like. You are looking for some sort of reference to get a feeling for correct moisture content. Most likely that mix will be just a tad on the dry side. Compare that to what you have. I think 3.5 to 4% should get you very workable sand.

    Just putting a heap of sand on the swept floor and putting a fan on it will dry it post-haste. Let the fan run for half an hour and then shovel the sand around and hit it again. It won't take that long to dry it out as green sand seems to dry very (too) quickly.

    Mulled sand does fluff up a lot. Riddled green sand fluffs to a remarkable degree.

    You are making great progress is an otherwise murky area endeavor. Good for you.

    With respect to needed draft on a cast wheel: 1/8" per foot of run should be adequate draft and will be barely noticeable on the part.
  11. Tobho Mott

    Tobho Mott Silver Banner Member

    Funny thing, I was aiming for 4% water when I made the first batch and totally soaked it... Have checked my math, it still seems correct... not sure why or how that went so wrong... I thought about spreading it out in the sun for a bit on a tarp or something to dry it out (floors in the sheds I work in are gravel/dirt, so sweeping is not really an option). Maybe I'll do that, but they're calling for thunderstorms later today... I've never had a problem with my sand drying out too slow... :D

  12. oldironfarmer

    oldironfarmer Silver Banner Member

    Great progress on the muller!

    You didn't show your math, but if you have 15,000 grams of sand, 4% of that is 600 grams of water, or 600 ml. But that assumes bone dry sand.
  13. Tobho Mott

    Tobho Mott Silver Banner Member

    Yeah that's close to what I did, but I gave the first batch a little more than that, just to be safe, more like appx. 750ml (a 500ml bottle and a half, roughly). It was absolutely soaking by the time the 11 minutes of mulling was over. Batches 2 and 3 got closer to 250ml (1/2 bottle) and came out feeling pretty good. By the end batch 4 got close to the same. I can't explain it. All the new sand is way too wet now that it has had a couple days to percolate in my bench, maybe it just needs time and use? Or perhaps more clay? 4.5% bentonite was the low end of what Tim Smelko told me his company puts in their aluminum sand blends, which use sand that is AFS GFN 115-130 (as opposed to my 75 mesh).

    I'm not gonna add anything until it dries out a fair bit so I can get a better feel for what I have created...

  14. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Jeff, Ya-might have two things working wrt to the amount of water required. The total surface area of sand in a given volume decreases as the grain size increases. There is some grain shape dependence but If you double the mesh size you could be reducing the surface area 4x-10x. The amount of water it takes to wet everything will probably be a very strong function of surface area. The bentonite clay may carry more water too and may also depend on how much water hangs on the sand instead of on or into the clay. So if you were larger on mesh size and lighter on clay content it could potentially reduce the required amount of water a bunch. In reality the sand is a distribution of grain sizes averaging to the mesh range but assuming similar distributions, same goes. -May explain why you see widely varying amounts of water required from one persons sand to another.

    Last edited: Jun 13, 2018
  15. Tobho Mott

    Tobho Mott Silver Banner Member

    Yeah, I wasn't sure whether coarser sand than Smelko's would mean I needed less clay or more, same goes for water, so I figured it would be easier to add more clay later than to take some out (I did save half a bag of silica though, for just in case, and also for making cores later on) and went with the lowest number Tim S had mentioned. The sand will dry out eventually, then we'll see what we see, I guess...

  16. _Jason

    _Jason Copper

    One thing I've thought about as a wheel for a muller - I wonder if you could use a 2.5lb or 5lb steel weight (or two, welded together) as the muller wheel? These are about 5 1/2" in diameter and 3/4" wide. I used to have a complete set when I owned a home and practically gave all them away when I moved just to be rid of them. They're made out of pretty crappy steel so I'm not sure how well they'd weld but I'm sure you could stick them together somehow.

    I would suspect you might be able to find them on the used market pretty inexpensively. Most people who buy a weight set end up growing tired of hanging laundry up on the weight bench and get rid of their weights.

    Just thinking out loud.
  17. Tobho Mott

    Tobho Mott Silver Banner Member

    I have a couple ten pounders left from the first "muller" I built, which I gave up on before I got it working anything close to properly. I got the idea from a guy on AA, can't recall who, but they got it to work better than I ever did or I would not have tried to copy it...

    There's also a shorter part 1 video that is even more hilarious if you are in need of a good laugh... :D

    But the idea could work. Just not as fun as trying to cast a nice big 4" wide one, I'm thinking...

  18. _Jason

    _Jason Copper

    Jeff what did you power youe first muller with? Interesting pulsing action.
  19. Tobho Mott

    Tobho Mott Silver Banner Member

    It was the motor and controls from a very small washing machine, part of an apartment sized 2-in-1 washer dryer combo. I never figured out how to stop the pulsing, just how to stop every second pulse from spinning the motor in the wrong direction...

  20. _Jason

    _Jason Copper

    Ah! That makes sense.

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