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Thread: Hello; this is my post here and its about giant RA saws and phase conversion

  1. #1
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    Hello; this is my post here and its about giant RA saws and phase conversion

    Hello;
    I have poked around the site from time to time and have been meaning to post a few things but never got around to it. Now I need some help and hope some one here knows the answers and will be willing to share them.


    Some one wants to give me an old dewalt radial arm saw. its pretty big and has a 7.5 hp motor. I am pretty certain its 3 phase. What size phase convertor would I need for this? Would a 3hp rotary convertor power this saw and not damage it (or the convertor) if I didn't care about achieving maximum horse power or is it going to burn up the motor on the saw or convertor if the phase convertor is to small?

    Its not a bad looking saw but takes up a lot of room. I would like to have it because it looks like it will have a wicked cross cut. Any info would be great. Thanks for the help in advance.

  2. #2
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    welcome to your first post,, keith, now for the RAS you can get single phaze saws real cheap these days so perhaps you should look at that option first unless this is a hugh one then thats another story..
    If in Doubt, Build it Stout!
    One hand washes the other!
    Don't put off today till tomorrow!

  3. #3
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    Keith welcome, and as for the RAS no a 3 hp would be way to small you will burn up the motor.
    "There’s a lot of work being done today that doesn’t have any soul in it. The technique may be the utmost perfection, yet it is lifeless. It doesn’t have a soul. I hope my furniture has a soul to it." - Sam Maloof
    The Pessimist complains about the wind; The Optimist expects it to change;The Realist adjusts the sails.~ William Arthur Ward

  4. #4
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    Quote Originally Posted by larry merlau View Post
    welcome to your first post,, keith, now for the RAS you can get single phaze saws real cheap these days so perhaps you should look at that option first unless this is a hugh one then thats another story..
    Yes its huge. its the only reason I would like to have it. It has a 20" blade and I think it will do over 30" cross cut. It would be really cool to have. I would like to use it for dados also if I ever could get a custom dado blade set for it.

    Quote Originally Posted by Don Baer View Post
    Keith welcome, and as for the RAS no a 3 hp would be way to small you will burn up the motor.
    Thanks Don. I kinda had a feeling it would work that way. I know someone who wants to sell a 3hp and he said it wouldn't matter what size the converter was as long as I was only running one machine but I didn't think that was correct.

  5. #5
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    I THINK, you will need about a 5hp convertor to get it started. Once it starts it won't pull near as many amps. Also, there are differences from one converter to another. I built mine and the fellow that designed mine cuts no corners and from what ever says, his work better than most commercial models.

    If I am not badly mistake that saw will have a 1" arbor and you can find 10" and maybe 12" dados sets with a 1" arbor.
    God grant me the senility to forget the people I never liked anyway,
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  6. #6
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    Quote Originally Posted by Jeff Horton View Post
    I THINK, you will need about a 5hp convertor to get it started. Once it starts it won't pull near as many amps. Also, there are differences from one converter to another. I built mine and the fellow that designed mine cuts no corners and from what ever says, his work better than most commercial models.

    If I am not badly mistake that saw will have a 1" arbor and you can find 10" and maybe 12" dados sets with a 1" arbor.
    How much would you say that it cost to build your converter? Did you make a rotary converter or a static one?

  7. #7
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    The general rule is that a rotary converter needs to be 1.5 times the hp of the motor being started, plus the running HP of all other connected (previously started) motors. Kay Industries (the leader in rotary converters) had so many people ignore the 1.5 times requirement, that the Kay Rotary Converters are specified based on running, not starting HP (i.e. they have about 50% more capacity than the rating says).

    Phase Perfect is the "go to" company in good static converters, and is what I would buy today.

    There are lots of vendors of cheap static converters that only apply running power to one of the phases of your motor, yielding a maximum of 70.7% of the rated HP. For light use, you won't miss the extra hp, but don't try to run anything with electronic controls on a cheap static converter - it can trick a 3 phase motor into working, but doesn't really supply 3 phase power.
    Charlie Plesums, Austin Texas
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  8. #8
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    I built mine 3 years ago and I spend $300 - $350 I think. It's a rotary, a static is just a starter really.

    I had to watch Ebay for a couple of months rounding up parts. Everything is fused and overload protected. I was building a 5 HP and I found a brand new 7.5 hp motor that was damaged in shipping. The motor company got it replaced free and then repaired this one but they had to return the motor plate to Baldor. so they couldn't sell it as a new one. Gave me a heck of a deal to just move it off the shelf. Bruce modified the plans slightly and so far it works flawless.
    God grant me the senility to forget the people I never liked anyway,
    the good fortune to run into the ones I do,
    and the eyesight to tell the difference.


    Kudzu Craft Lightweight Skin on frame Kayaks.
    Custom built boats and Kits

  9. #9
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    Thanks for the help so far. I am really nervouse about getting
    This saw now. The saw is Gonna cost me $350.

    I have some one who will sell me a used 10hp rotery converter
    For $200 that came out of a machine shop but he has never
    Used it. The guy he got it from says it worked.

    Is there anything I should look for when I go look at the
    Converter?

    I'm starting to wonder why I want such a large ras anyway.

  10. #10
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    Quote Originally Posted by keith Boutselis View Post
    Thanks for the help so far. I am really nervouse about getting
    This saw now. The saw is Gonna cost me $350.

    I have some one who will sell me a used 10hp rotery converter
    For $200 that came out of a machine shop but he has never
    Used it. The guy he got it from says it worked.

    Is there anything I should look for when I go look at the
    Converter?

    I'm starting to wonder why I want such a large ras anyway.

    what do you do in your shop? are you a pro and do this as a living or are you just a small hobbiest? you need to look at what you have made and where you want to be 5 yrs from now. then look at the costs and the needs.. not the wants or desires unless your financially set for the duration.. this can be like a iron horse and be a large space taker for what little you get back out of it..
    If in Doubt, Build it Stout!
    One hand washes the other!
    Don't put off today till tomorrow!

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