Thread: Anyone have any thoughts on the OBM grinder?

Originally Posted by Voidmonster

My local Lowes was impressively useless for that task. All the bins were horribly disorganized and they just don't carry any sort of bolt variety packs. I had it in my head that they carried assortment packs of bolts in a small organizer, so I didn't take measurements. Luckily, I guessed right, but the only ones I could find that were close to the right size were stainless, which was perhaps slightly overkill.

Most hardware shops don't. It's not worth the shelf space stocking them for someone who needs them. I think most people who use bolts have their own assortment of half filled boxes after a while. The big variation in length especially make assortment packs relatively difficult to put together well enough to sell enough of them.

Originally Posted by dinnermint

If the fan spins backwards, just install it backwards....

Doesn't work like that
If you flip it the other way around, the orientation of the blades is still exactly the same.

Originally Posted by Voidmonster

I haven’t done anything with ducting yet, and don’t really have anything invested in the idea — it just seemed like a decent step in controlling intake. Just having a filter over the intake simplifies things a lot, so I’ll give that a shot and see.

As for reversing the blade, I managed to design a fan that only really works in one direction. If its reversed, it pushes air sideways instead

I went back to the drawing board and started over from scratch, this time taking into account how it would be mounted and which direction it needed to turn. This is what I came up with:

(The weird treebranch stuff is supports for the printer, so it all remains appropriately attached to the build plate and the model).

It’s printing now.

Fun trivia: the filament based FDM print of the first model was done on a friend’s printer, and printed out fully in about 7 hours.

The SLA resin print I’m currently running, despite being exactly the same size model, will take ten minutes shy of 18 hours, which is why I had my friend print it! Flip side is my resin print will be much smoother. To flip to the third(?) side, my resin print will also not be anywhere nearly as tough.

Just a heads up as far as ducting goes, it's a problem I'm dealing with on a poorly cibbled together hvac system in my house.

Ahhhh, you designed a hydrofoil blade instead of flats, fancy! Double nut the end to be safe, hydrofoils are great for plane wings because of the lift generated but could cause loosening over time.

Originally Posted by Bruno

Doesn't work like that
If you flip it the other way around, the orientation of the blades is still exactly the same.

You're right, I'm an idiot.

Originally Posted by Bruno

Most hardware shops don't. It's not worth the shelf space stocking them for someone who needs them. I think most people who use bolts have their own assortment of half filled boxes after a while. The big variation in length especially make assortment packs relatively difficult to put together well enough to sell enough of them.

I have managed to find reasonable assorted nut & bolt kits in the past... And irritatingly, there was a great local hardware store called Orchard Supply Hardware. In business since the 1930’s.

They had a great selection of nuts & bolts, organized and kept organized, with some small assortment boxes. Well, Lowes bought them, ran them into the ground, then closed every store.

In any event: new fan blade printed!







The print didn’t come out as clean as I would have liked. It was a little bit lumpen, probably because I got impatient waiting for a new batch of resin to come in and decided to just try and use the batch that got degreaser in it (and then stored in a bottle that still had a little coffee in it). Well, it worked a LOT better than I thought it would, but I wouldn’t quite go so far as to say it worked fine despite the contamination.

The nut that’s on the arbor is a locking nut, but I’ll definitely be getting a second one to go on there.

I plan to use use enough ducting to have space for a heavy-duty filter, then a second bit on the other end where the air exhausts, which I’ll build out to house the controls and seal it all up with caulking or something.

All that said, it’s now working excellently!

How’s the balance? That’s pretty cool, if I was better at cad I would definitely look into a 3D printer.

If you have a shop vac that will allow you to pipe into the exhaust side that could work. Built in filter, positive air pressure, or just use it passively for its filter with your motors fan pulling air.

Are you going to shroud the fan to keep any debris from sneaking in the gap?

Originally Posted by jfk742

How’s the balance? That’s pretty cool, if I was better at cad I would definitely look into a 3D printer.

If you have a shop vac that will allow you to pipe into the exhaust side that could work. Built in filter, positive air pressure, or just use it passively for its filter with your motors fan pulling air.

Are you going to shroud the fan to keep any debris from sneaking in the gap?

The balance is good! When I designed the center part, I added a little mass around the keyway cutout to make sure things were as even as possible, and that seems to have pretty much done the trick. It’s probably helped by the drive wheel having significantly more mass on the other end of the arbor.

I’ve got a small shopvac, but space doesn’t really permit me to use it here.

My plan is to rivet together some sheet metal with a gasket between the rivets to make a shroud that has enough stickout to put some sort of filter over the end. Maybe an automotive filter. I’ll definitely be making certain there are no ways for dust to get in at any point on the motor or the electronics.

I figure running the exhaust over the electronics should let me keep dust out of them. The fan seems to be generating actively good flow.

Okay, this is hilarious.

File under “Off the shelf solution”:



It’s just the filter for a shopvac. It perfectly fits with a snug, air-tight seal, right onto the motor housing. There’s plenty of room around the fan blade.

I’m still probably going to need to make a short shroud for aerodynamic reasons with the fan — the end of the motor it’s blowing into is large open, but has enough flat spaces that there’s a lot of turbulence in the airflow and it doesn’t really push all the way through the motor that well unless the fan is inside of some kind of tube.

That's awesome!