Planned dust collection system

[retired2]

Dado is the word used in the USA. In England it is a groove if along the grain and a housing if across the grain. Then again a rabbet is a small furry animal that is very good to eat.

Sorry Bernard, rabbits are good eating, but rabbets are not!   ;)

[DennisCA]

I balanced the impeller last night and also mounted it on the shaft to test it out. This part is truly finnicky and making your own hub isn't as straight forward as it might seem. Here's where a custom metal part might have done good. There will be shimming, I can feel it.

[DennisCA]

Did some balancing today, put the impeller on a big ball bearing that's a big bigger than the diameter of the ebore, I added and removed weight until it laid flat


Towards the end I'd put it rocking a little bit and it would take 10 minutes for it to stop so I'd go away and do something else.

Eventually I got it to the point where the water level stopped at these readings, quite centered though perhaps not exactly, good enough?




Actually the reason I managed this was I removed the piece of metal I had between the piece of wood and the bearing, that allowed it to dimple the wood and that added friction so it was possible to balance it like this. The stiff and flat piece of metal was important to let the bearing move as freely as possible.

[DennisCA]

So much for balancing, the impeller blew up on the first test. The jolt of going from 0-2850rpm I think was too much for the design, without the supporting top as well as I figured I'd try without it.

I think this design isn't going to work, too much mass in the vanes. Perhaps only 5-6 vanes and less of a backwards curve, would work better, like this:
http://www.instructables.com/id/Insulation-Vacuum-Homemade-Commercial-Blower/step3/Impeller-part-1/

[jdon]

Sorry to hear about the results of the impeller's maiden voyage- I hope there wasn't any substantial damage or injury involved.

It does remind me of centrifuge calculations I did in my former life working in a hospital lab. I estimate from your pictures that your impeller diameter is about 20 inches (508 mm). The equation for relative centrifugal force is RCF (x g) = 1.12 x radius (mm) x rpm.

At 2850 rpm, your impeller was pulling more than 2300 g's. Just something to consider in deciding how sturdily you want to make your design- or whether you want to continue in that vein (or vane? :) ). Just saying, I think there's a reason most impellers are welded or cast metal. Also, precise balancing is critical.

[phil (admin)]

That is disappointing.

I had high hopes for this.  Any pics of the unit where things came apart?  It would be interesting to see how parts look after the spin.

[DennisCA]

No pics but I can see that the epoxy had let go, the bond wasn't very strong after all. So only the screws held it in place and they had been pulled straight through the the plywood bottom when things let go, one vane shot off into the ceiling and broke a fluorescent tube. These vanes are heavy and dangerous, I was lucky I put the circuit breaker on an extension cord and moved to the other side of the shop and stood crouched behind the jointer.

I'm remaking this but using plywood or MDF vanes like Marius hornberger used in his build- I think the lighter weight means there's less momentum to overcome as it starts up so less stress in that initial jolt, at least the vanes shold be light I now feel, the backing disc could probably be made heavier from 18mm plywood for deeper grooves.

Also I think the wood glue bond with wooden components will be a lot stronger than this failed epoxy joint, and safer if it blows up. Next time I'll be testing it with the top on too. I think I will follow Matthias wandels design closer in terms of vane layout for this new design, perhaps make it a little shorter, I had aimed for 10cm but perhaps 8cm will make for a stronger impeller.

[retired2]

No pics but I can see that the epoxy had let go, the bond wasn't very strong after all. So only the screws held it in place and they had been pulled straight through the the plywood bottom when things let go, one vane shot off into the ceiling and broke a fluorescent tube. These vanes are heavy and dangerous, I was lucky I put the circuit breaker on an extension cord and moved to the other side of the shop and stood crouched behind the jointer.

I'm remaking this but using plywood or MDF vanes like Marius hornberger used in his build- I think the lighter weight means there's less momentum to overcome as it starts up so less stress in that initial jolt, at least the vanes shold be light I now feel, the backing disc could probably be made heavier from 18mm plywood for deeper grooves.

Also I think the wood glue bond with wooden components will be a lot stronger than this failed epoxy joint, and safer if it blows up. Next time I'll be testing it with the top on too. I think I will follow Matthias wandels design closer in terms of vane layout for this new design, perhaps make it a little shorter, I had aimed for 10cm but perhaps 8cm will make for a stronger impeller.

Even with a successful build, I would always be worrying about when it was going to explode at full speed.  Home built blowers, especially large ones, should be isolated from the rest of the shop with a "blast barrier" - a very strong one to keep it from adding to the amount of shrapnel in an explosion.

[phil (admin)]

No pics but I can see that the epoxy had let go, the bond wasn't very strong after all. So only the screws held it in place and they had been pulled straight through the the plywood bottom when things let go, one vane shot off into the ceiling and broke a fluorescent tube. These vanes are heavy and dangerous, I was lucky I put the circuit breaker on an extension cord and moved to the other side of the shop and stood crouched behind the jointer.

I'm remaking this but using plywood or MDF vanes like Marius hornberger used in his build- I think the lighter weight means there's less momentum to overcome as it starts up so less stress in that initial jolt, at least the vanes shold be light I now feel, the backing disc could probably be made heavier from 18mm plywood for deeper grooves.

Also I think the wood glue bond with wooden components will be a lot stronger than this failed epoxy joint, and safer if it blows up. Next time I'll be testing it with the top on too. I think I will follow Matthias wandels design closer in terms of vane layout for this new design, perhaps make it a little shorter, I had aimed for 10cm but perhaps 8cm will make for a stronger impeller.

Even with a successful build, I would always be worrying about when it was going to explode at full speed.  Home built blowers, especially large ones, should be isolated from the rest of the shop with a "blast barrier" - a very strong one to keep it from adding to the amount of shrapnel in an explosion.

I imagine a sufficiently strong wood housing would absorb most of the damage, no?

I think one important factor demonstrated here is to never spin-up a partial blower, one that doesn't have both the top and bottom glued on.  Having the top in place would have made the entire wheel exponentially stronger.

[DennisCA]

No pics but I can see that the epoxy had let go, the bond wasn't very strong after all. So only the screws held it in place and they had been pulled straight through the the plywood bottom when things let go, one vane shot off into the ceiling and broke a fluorescent tube. These vanes are heavy and dangerous, I was lucky I put the circuit breaker on an extension cord and moved to the other side of the shop and stood crouched behind the jointer.

I'm remaking this but using plywood or MDF vanes like Marius hornberger used in his build- I think the lighter weight means there's less momentum to overcome as it starts up so less stress in that initial jolt, at least the vanes shold be light I now feel, the backing disc could probably be made heavier from 18mm plywood for deeper grooves.

Also I think the wood glue bond with wooden components will be a lot stronger than this failed epoxy joint, and safer if it blows up. Next time I'll be testing it with the top on too. I think I will follow Matthias wandels design closer in terms of vane layout for this new design, perhaps make it a little shorter, I had aimed for 10cm but perhaps 8cm will make for a stronger impeller.

Even with a successful build, I would always be worrying about when it was going to explode at full speed.  Home built blowers, especially large ones, should be isolated from the rest of the shop with a "blast barrier" - a very strong one to keep it from adding to the amount of shrapnel in an explosion.

My solution to this is to put it in a separate storeroom that nobody is in. This will also save space in the shop.

[DennisCA]

No pics but I can see that the epoxy had let go, the bond wasn't very strong after all. So only the screws held it in place and they had been pulled straight through the the plywood bottom when things let go, one vane shot off into the ceiling and broke a fluorescent tube. These vanes are heavy and dangerous, I was lucky I put the circuit breaker on an extension cord and moved to the other side of the shop and stood crouched behind the jointer.

I'm remaking this but using plywood or MDF vanes like Marius hornberger used in his build- I think the lighter weight means there's less momentum to overcome as it starts up so less stress in that initial jolt, at least the vanes shold be light I now feel, the backing disc could probably be made heavier from 18mm plywood for deeper grooves.

Also I think the wood glue bond with wooden components will be a lot stronger than this failed epoxy joint, and safer if it blows up. Next time I'll be testing it with the top on too. I think I will follow Matthias wandels design closer in terms of vane layout for this new design, perhaps make it a little shorter, I had aimed for 10cm but perhaps 8cm will make for a stronger impeller.

Even with a successful build, I would always be worrying about when it was going to explode at full speed.  Home built blowers, especially large ones, should be isolated from the rest of the shop with a "blast barrier" - a very strong one to keep it from adding to the amount of shrapnel in an explosion.

I imagine a sufficiently strong wood housing would absorb most of the damage, no?

I think one important factor demonstrated here is to never spin-up a partial blower, one that doesn't have both the top and bottom glued on.  Having the top in place would have made the entire wheel exponentially stronger.

I think it as as well that I tested it without, the epoxy bonding had clear flaws I would not have been privy to knowing about without this test.

I think if I had used screws with large flat heads or washers, those could have held the impeller together, perhaps. And perhaps some other glue, like polyurethane construction adhesive.

Still now I think making the vanes as light as possible is the best way to go, that way the explosion when/if it happens won't be as catastrophic. I think the plastic vanes would work if you used large bolts all the way through, and a steel disc backer instead of wood, that might be strong enough to handle material.

I also remember reading on Bill Pentz site something a bout how a wooden cage stood up to abuse better than a sheet metal one did.

[DennisCA]

A soft starting unit was cheaper than i had expected, I could get a new one from germany for 140-150 euros shipped. That might be worth it considering the long run.

I cut out a new impeller disc last night at 45cm, I am scaling it down a bit. Partly because I also have plans printed for this impeller to 1:1 so it'll make things easier to visualize. There will be changes though to the vanes I think, slightly curvature and I will make them longer so they go all the way into the hub and cut the vanes at an angle so they don't protrude from the top lid. Much like a commercial impeller.

[DennisCA]

Well it's going to be a little while now I think. I've had to order new router bits so I can route grooves that will fit my vanes, and bending and laminating those will take a while as well. I've also ordered a 28mm brad point bit because the drill bit I used to make the holes earler was less than optimal.

[DennisCA]

Going slow, laminating the vanes still, here's a picture:


It actually worked better to just stand the jig up and use clamps.

Also yardworking, prepping & sowing a lawn, casting concrete slabs, stuff like that.

[DennisCA]

Been on a break, but I've glued and assembled the impeller vanes & hub now, top plate still needed, and then balancing. I will try static balancing this time using bearings on a threaded rod, but I need to wait for the bearings I've ordered. So much waiting.

Spun up the impeller plate only though to test it and thought, damn, this is scary, this is really ****** scary. Definitely don't want to be in the same room.