Been with my homemade rotating-drum muller for about a year now. It works just fine, and I've probably put an average of about 100lbs of petrobond through it per week with little issue, aside from having to continually add tape to the drive pulley to account for the axle slowly shifting under pressure. Here's some images of how she's looking these days. Most of the parts here are prototypes that I never got around to re-making since the thing just continues to work for me. I am reaching a point, however, where it is just becoming a hassle to scoop loads of sand in and out after every session. The drum can only process 20 - 25lbs at a time, and I don't love having to reach in with a scoop while it's running. I've been pondering various upgrade paths for my existing build, but I realized that a simple tumbler muller might check all of the boxes for me. I could easily spend more rebuilding this one than it would cost to get a Harbor Freight concrete mixer, and from what I've read they can do 50lbs+ per load, and have a dumping mechanism built right in. My question then is, what are the downsides of those tumbler mullers that I'm not seeing? Is there any major difference in mulling capability between the wheel and plow style mullers like mine and a concrete mixer with a heavy agitator? I know there's been mention of petrobond struggling to stick to the walls of those mixers. I wouldn't be opposed to grinding off paint and scuffing the surface in that case. Hoping someone who has experience with both styles can chime in. Also curious if there is a consensus on the best option for the agitator, ie size, weight, shape etc. I've seen one user recommend a large stone for a more erratic motion than a purely round ball. Being in coastal FL that might be a tough one to source, I was thinking maybe a cast iron kettlebell would provide a good mix of rolling and sliding actions.
Easy enough to turn a cement mixer into a wheel and plows muller. Tack in a wear plate for the wheel to roll on and suspend the wheel and plows from a crossbar attached to the mixer's yoke. I did have to scuff the wear plate all along the track the wheel rolls on when the petrobond sanded it so smooth and oiled it so slick that the sand would just pile up and slide instead of getting rolled over. It dumps out the same way cement would, as you mentioned. One of the short Rubbermaid plastic garbage cans fits under mine pretty good, I use the cut off piece from the top of the mixing drum as a sort of funnel to catch any stray bits of sand that take a funny bounce on the way out to keep from losing any more sand than I have to. I had to cut the top of the drum down to just below where it starts to taper in so that the opening is wide enough for the hanging bits to fit anyway. But mine only likes to process about half a 5 gallon bucket of sand at a time, it would choke on 50#. Might be able to tweak its capacity a bit by changing the arrangement of the wheel and plows I suppose... A few people here just took the paddles out of their cement mixers and throw in some heavy rocks, chains, cannon balls, whatever. Seems to work well for them from what's been posted here. Maybe that style can process bigger batches? Very happy with mine anyhow. I have a build thread for mine around here somewhere, got the idea from seeing HT1's. I've also used it to make some small batches of K-bond sand that seems to work about as well as petrobond from the foundry supply. Jeff
I've been using the small HF mixer with a rock for years. It might hold 30 pounds. Don't worry about the paint, it will soon get polished off. There is a learning curve to get it tumbling at first. Not enough sand just lets it slide, too much and it spills out the front. It's not a true muller but works good for reconditioning the sand before returning to the heap.
I am also using a small Harbor Freight mixer with the internal paddle removed and a selection of various round rocks. Sometimes I wish it had one scraper as the mix can ball up against the drum sometimes. While we're here, let's take a moment to review muller safety...
Yea I'm talking about switching to just a plain cement mixer (paddles removed) with some sort of agitator floating in the drum. That's a good point though that if I don't end up liking that setup I would have a good platform to build out an improved wheel and plow style with a dump mechanism. Your build looks really nice and would definitely be an upgrade from mine, the question to me is just whether fabricating something like that is truly necessary.
I saw your previous posts on the topic, certainly got me thinking. My current muller also likes a pretty specific amount of sand, so that's not a hurdle I'm too worried about overcoming. If I could ask, have you ever wished you had a "proper" muller? In other words, have you ever thought that a more traditional style might give you a better quality of sand post-processing?
This is the sort of thing I was wondering about, but maybe something that could be avoided by dialing in the amount of sand/agitator selection? Still seems less annoying that my current state of perpetual sand scooping anyway. I will say that the double v-belt reduction on my muller has just enough tension that it would slip before it mangled me. Of course it's a tradeoff for torque, but nice to know I won't be losing any fingers to it.
No, I’m quite happy with how it works. And it’s convenient for where I store it. I’m not making PB from scratch, just reconditioning.
https://drive.google.com/file/d/1VZCnBWLcZUhN1DepZBBUu8t7Bppt90sD/view?usp=drive_link Video of my new cement mixer putting in work. The mixer drum is 4 cu ft and seems to take about 50lb of PB to really getting tumbling (as opposed to sliding) with a 25lb iron kettlebell for agitation, though it seems like it could handle a good bit more. Maybe a bit large for my needs, but I wanted a wide mouth on the drum so I could dump in a full load of used sand straight from my shakeout bin. I wasn't expecting this to work so well right out of the gate, but my mold quality has not suffered and my mulling time has been significantly reduced compared to my original muller.
