J. Phil Thien's Projects

Quote from: retired2 on June 03, 2015, 06:09:44 AM

Quote from: DennisCA on June 02, 2015, 09:45:51 PM
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.

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.

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/

I'd like to see some photos of the blower itself, if you have some.

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.

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.

Not really sure how to make such a thing, some kinda jig on the router table perhaps. Still I am not sure the payoff would be worth it compared to just the groove and screws.

But I've made such pocket already, the vanes sit in them and are also screwed, this has already been done. If you see my latest picture and look you can see how the vanes are recessed & epoxied into place. They are also screwed into place from the other side, but you cannot see that in the picture.

Yeah I knew what a dado was, but not a stooped dado? Or rather it was likely a stopped dado, I thought the grooves I made in the disc qualified as such, hence my confusion.

I don't understand your question, I had to look up what a stooped dado was (not familiar with the english terminology) and it looks like what I called a groove, which I did make for the dadoes? For a better glue/epoxy bond, and screws in addition.

Sounds good then! I had to cut a new disc, the smaller diameter of this pipe I went with was too different, so a new disc has been made and wider grooves, I epoxied them in place with slow setting epoxy, I also screwed them in with two screws per vane, then I trimmed the edges with my bandsaw circle cutting jig to make it proper round. I'm also considering putting construction adhesive around where the vanes meet the plywood and smear it out with a finger, to create a softer surface, fill in any gaps and to add even more strength.



There must be some trick of perspective because the inside looks off center, but looking above the individual vanes follow the interior guiding line, I've scaled it to work with an 8" main trunk, though I think I'll go for 6" all the way, maybe 8" after the separator as I understand it's helpful to increase the diameter afterwards for some reson.

I got a pretty serious angle on these vanes too... it sorta looks like an airfoil impeller...

Next step is to make a hole in the middle and try and balance it.

Well that motor sidetracked me a bit but I cut up the vanes today and boy the 12 of them turned out heavy, 3760 grams all of them, which is 8.3lbs, this is gonna be a heavy impeller. I wonder what the larger metal designs weigh...

Just the parts loosely together:

Got the pipe home but I went for a much thicker one instead:


It's a bit smaller diameter but I thought it was worth it for that thickness.

And the motor, incredibly heavy for a 2.2kw one:

Going to pick it up tonight and a 2.2kw electrical motor (to replace the 4kw one going to my DC, used to be on my jointer/planer, it was too big for that little machine though).

Won't have a lot of time this week to work on the DC though, have to do yard work:
https://farm6.staticflickr.com/5446/17642152710_3475d0db2c_k.jpg

ALso found a pipe of suitable size, 500mm diameter, 1 meter piece I could cut into vanes. 30 euros for a piece. It sounds very interesting.