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Thread: Full kerf blades on 40's 1.5 hp unisaw

  1. #1
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    Full kerf blades on 40's 1.5 hp unisaw

    Hey y'all! I've searched around and haven't been satisfied with the relevance of information I have found pertaining to horsepower and thin or full kerf blades.

    I have an old unisaw (1946) that I picked up a couple months ago with a 3 phase 1.5 hp motor on it, put a VFD on it and have been using happily since with a cheap thin kerf 40 tooth blade from the Borg and a Freud dado stack. I've run some deep 1/2 x 1.875 notches for lap joints in cedar 4x4s for some posts with good luck and no bogging down, but I have seen people hesitant on whether the 1.5hp is enough to run a full kerf blade.

    Before I go out and spend a couple hundred on decent plywood and general purpose blades, does anyone have any experience with full kerf blades on similar saws? It seems that much of the information out there sends to be geared towards saws rated similar to my 6.5 hp shop vac so I'm not certain how big of a gain of salt to take the advice with.

    Thanks!

  2. #2
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    Full kerf blades should be no problem. I once owned a mid 60's Unisaw with the 1.5 horse motor and had no problems running full kerf blades and dado stacks. I could be wrong, but I think many of these older motors had more muscle/torque than newer motors. You should be fine with full kerf.
    Don't forget your splitter or riving knife.

  3. #3
    I used a full kerf blade on a 1.5HP saw successfully. You just need to go slow and listen to the sound of the blade.

    Regarding Mike W's comment that old motors had more torque or HP, I'm afraid that's not true. A HP has been a HP for quite a while and we've known how to accurately measure HP for a long time. HP is directly related to torque so if a motor had more torque (at the same RPM) it would have more HP.

    You can always check by looking at the input voltage and amps and guessing at the efficiency. A HP is a bit less than 750 watts, and taking efficiency into account, allocate about 1,000 VA per HP. Old motors were less efficient than modern motors.

    Mike
    Last edited by Mike Henderson; 09-21-2019 at 2:23 AM.
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  4. #4
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    I had a '70's vintage 1 1/2 HP Unisaw I bought new, and had never heard of thin kerf blades back then. I suspect thin kerf blades were not common when your saw was built, and that it was designed for full kerf blades.

    It will work fine.
    Rick Potter

    DIY journeyman,
    FWW wannabe.
    AKA Village Idiot.

  5. #5
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    I remember when there was no such thing as a thin kerf blade and it was a long time after the 1940's when your saw was designed. If full kerf blades worked well then, they should still work well. On the other hand, I owned a Ridgid 1.5 hp contractor saw for many years and initially thought it was under powered. After I started using thin kerf blades, it felt like I swapped out the motor for a 3 hp one. Thin kerf makes a difference cutting thick lumber. I have a more powerful saw now and prefer regular thickness blades. There is less vibration.

  6. #6
    I run full kerf blades on my 1-1/2 Hp craftsman all the time with no issues.
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  7. #7
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    I too run full-kerf blades on my 1978 1.5 hp Unisaw. No problem. But you don't have to believe us, you can run your own experiment at a lower price point than "a couple hundred on decent plywood and general purpose blades". Buy just one combo blade. That's what's on my Unisaw about 99% of the time. For instance, Freud makes a good one for $65 or so. See how that behaves on your saw, and then decide whether to buy specialty blades.

  8. #8
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    Quote Originally Posted by Mike Henderson View Post
    ...and listen to the sound of the blade...
    This ^^^

    Just my opinion, but thin-kerf blades are for jobsite tools. I would always go for the beefiest blade on a table saw. Like a shaper, more mass + smoother cut, better heat dissipation.

    Erik
    Felder USA Territory Representative: Central & South Texas

  9. #9
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    I'm with most answers here, it should be no problem. Although we love to think that older tools were "better", the laws of physics still apply. That being said, your motor should push a full kerf blade fine. Just do as Mike suggests and pay attention to your machine. It is obvious when a machine is laboring. You could try an inexpensive FK blade and prove things for yourself for not too much money. I run a FK flat top grind 24 tooth rip blade for doing things like grooves in small boxes, miter keys and the like. Although some folks prefer TK blades for ripping, a FK FTG rip blade would still be a benfit in a shop. Here's a good quality, inexpensive one to try if you are unsure. There are others in this price range as well. My rip was about $95 but, is of a type that can be re-sharpened a dozen times. My point being that I purchased it for a specific reason and many good rip blades are available for under $50.
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  10. #10
    I will agree with the other opinions. I've owned at least 5 table saws and all were 110V. My current main saw is a PCS with the 1.75hp motor. I've used full kerf blades in them but also sometimes use thin kerf. I don't think the kerf width is a overwhelming factor on the ease of making the cut. The only time I've tripped the overload on my PCS was in 1 inch oak that was bowing back into the blade. The thin 2.3 mm splitter on the PCS was a contributing factor but the main thing that would have prevented the overload is a wedge in the kerf to stop it from closing up. The blade was full kerf but I've had to stop the same thing from happening a time or two using a thin kerf. There is a cheap WEN thin kerf on it right now. I got it for free but had to write a review and I like the blade. It is almost as smooth cutting as the Infinity blades (full kerf) I bought new when I got the saw and it doesn't burn the kepper side of the wood like the Infinity seem to want to do. The smaller kerf was also handy when I was splitting some 4 quarter stock to make 3/8 slats for a crib I am working on.

    I think the reason it doesn't make a huge difference is the thinner blades are more prone to flexing which also is a power user. In any event, I do not see a big difference in the hp required to make the cut. I can cut to the full capability of the saw - 3 plus inches - in hardwood with either thin or thick blades. But not with a 50 tooth combination I use most of the time and not if the blade is dirty. With a clean rip blade, either will work. And either will have a problem if the wood starts warping.

  11. #11
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    I run nothing but full kerf blades on my 1 1/2HP table saw with no problems. As stated previously, listen to the saw. I have had issues with thin kerf blades in the past and quit using them.
    Ken

  12. #12
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    Quote Originally Posted by Ken Fitzgerald View Post
    I run nothing but full kerf blades on my 1 1/2HP table saw with no problems. As stated previously, listen to the saw. I have had issues with thin kerf blades in the past and quit using them.
    That sounds like my story. I only buy full kerf blades.
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  13. #13
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    Thanks everyone this is encouraging. I'll stay going the fk route and see how it goes!

    Your thoughts reflect how I assumed it would pan out but I didn't have the experience to say for sure.

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