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  #41  
Old 10-23-2009, 08:45 PM
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Originally Posted by allessence View Post

If someone knows of a good site for beginners on rotary phase converts or if someone knows how to build one of these things and can point me in the right direction that would be great.
Well for openers, have you looked here?
Dan's 30hp might interest you.
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  #42  
Old 10-23-2009, 09:51 PM
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You'd tighten the belt between the 2, start the 1/2 hp 1phase then once up to speed, you'd put juice to the 3ph and then you'd loosen the belt and the 3 phase would spin away.
As Cutter said, that is a pony motor started RPC. If you are really cheap and really strong, you can rope start the idler (just like a weed eater) but hardly anyone does that now.

The purpose of the pony motor (which is sized 1 hp for every 10 hp on the idler) is to spin the idler to full no-load speed, which is always higher than rated nameplate speed. For instance, the Baldor M3611T is nameplate rated at 1750 rpm at 100% load. At 25% of full load, it spins at 1789 rpm. At zero load (which is what you have when bringing the idler on line) it is turning around 1800 rpm. That means you want to adjust the pulley on the pony motor & the pulley on the idler so that the pony is driving the idler at 1800 rpm. With the idler at full no-load speed, you can start a 50 hp motor from a 100 amp panel, since no electrical energy is needed to spin a heavy rotor from standstill to full speed.

A lot of people build the auto start RPC, but the pony start removes all the complexity and mystery. First photo is the ugliest & most simple RPC that you'll ever see

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Here's a snapshot of my phase converter setup. It's made from a 5 hp motor that I got for free, mounted on a wooden platform. There's a 1/4 hp repulsion-induction start motor mounted on another hinged platform with the belt tension set by the motor. The idler motor is powered thru a fused knife switch which is fed from a 240 volt, 15 amp breaker.

The converter runs my milling machine and lathe, each of which have about 1 hp motors in them. There are no power factor correction capacitors, no balancing capacitors, and no starting capacitors. It's manual start, by powering the kicker motor which is plugged into a switched outlet just ouside the view of the picture. Once the idler comes up
to speed the knife switch applies the excitation. Then the kicker is switched off. Lifting up the hinged platform allows the belt to fly off.

This setup is sort of stone-age because there are no bells or whistles at all, but it was built for free and it has been running my machines for about 10 years now. The only fancy bit is that the wooden framework is resting on some large rubber stoppers to provide vibration isolation. It's pretty quiet while running. Jim Rozen, PM Forum
In a perfect world, each of the three phases should be the same voltage. In reality, two will be close & one will be higher. Most three phase machines could care less and run fine with an unbalanced output. It's easy enough to add capacitors to the output & play with the values until the voltage is balanced under full load. It will continue to be unbalanced at anything less than full load, but again it may not matter.
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  #43  
Old 10-24-2009, 10:53 AM
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I will be experimenting with the 3 phase convert. I have several around it is seems the way to go for some things.


My main question is now, What kind of bandsaw blade stock should I buy? Supposedly the unit will to High carbon and bi-metal blade stock.

Does anybody on here have any experience with either?

I also posted the Blade welder manual back at beginning of thread.
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  #44  
Old 10-24-2009, 12:48 PM
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What kind of bandsaw blade stock should I buy?
It's all weldable with your blade welder. A decent bimetal blade from MKMorse or Lennox would be my first choice - you may want to again phone Stacey at DCT and check pricing on both coil stock as well as finished blades.

The real advantage to a blade welder is to be able to take a finished blade, break it so that the broken end can be threaded through an internal hole in a part, weld it back & make the internal cut, break it and remove from the part, weld it back again ...

If you aren't planning to do lots of internal cuts, you're probably better off buying finished blades. DCT (and most every distributor) guarantees that their blades will not break at the factory weld or they will reweld the blade at no charge ... learning to weld your own blade takes a combination or art, science and practice - about 5% art, 5% science & 90% practice. If cutting metal is the goal, buying finished blades is the way to go.
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  #45  
Old 10-24-2009, 01:03 PM
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It's all weldable with your blade welder. A decent bimetal blade from MKMorse or Lennox would be my first choice - you may want to again phone Stacey at DCT and check pricing on both coil stock as well as finished blades.

I agree with Barry, in both cases, first a good bi-metal blade is important, and secondly both Morse and Lennox offer great blades, with good performance and good pricing.

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  #46  
Old 10-24-2009, 05:20 PM
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I have had good luck with the Ellis house brand in a variable pitch. You will need a differen blade for aluminum.
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  #47  
Old 10-26-2009, 07:41 AM
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well, I've bought some blade material off Ebay. I'm going to experiment and see what I come up with. I mean to say, I've ordered some 3/4" blades to long and will cut down. (cheap money) Some 1/2X0.25 X 24T. and I'll have to get some smaller size for radius cutting. I have some 2" holes to cut out of some 1/2" alum plate. What size should I get? Some of the radius are in the 3/8th range.

The blade welder is supposed to be able to weld Carbon or bi-metal blades. The only info I'm lacking is to what size I can actually get away with. It says with the 220V unit 1/16-3/4" I will try some 1" to see if it is even possible.

What about TIG welding the blades then annealing in the welder? Which rod should I use?

I have checked several different bandsaw welder MFG's and if looks like for the most part the machines are the same for basic units.
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  #48  
Old 10-26-2009, 07:46 AM
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On another note. I started to make the machine mobile last night. Took and old moving dolly and cut the welds off and center bars and will be adding a drop down and correct length bars.
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  #49  
Old 10-26-2009, 07:46 AM
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few more
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  #50  
Old 10-26-2009, 07:55 AM
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Warning.....make sure your footprint is large enough to hold it up, they are very top heavy.

I think 24Teeth will be OK for some very light material but I expect you will need to get into 8 or 10 for structural steel.

You are just starting with the saw, why not buy a couple of ready made blades and have something to use while you are learning the blade welder?
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