1/2 HP vfd conversion for 9x20


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Thread: 1/2 HP vfd conversion for 9x20

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    Default 1/2 HP vfd conversion for 9x20

    do you guys think that a 1/2 HP vfd with a 1/2 HP 3 phase motor will be enough power for the 9x20 lathe? i can get both fairly cheap and i think i would prefer this to the DC motor conversion. i know alot of guys buy 2hp dc motors to use but these are usually rated at peak power and its kinda hard to figure out how much power is actually available for turning and facing whatever else.

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    I recently installed a 1hp 3phase vfd setup on my 9x20. I have found there is no need for all 6 belt ratios and I need only 3 as it has plenty of power and it's a beast for such a little lathe.
    It easily has more metal cutting power than my x3 mill now.
    I would think 1/2hp and keeping all 6 speed ratios would work out pretty nice. It might be a bit under powered at very low rpms though.
    Steve



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    ideally, i want to get rid of the six gear ratios all together and go with a single pulley setup like steve bedair did. i really only need a peak RPM of about 1300 RPM and low for threading around 200. i know its a pretty wide sweep thats why i was thinking VFD with a 1725 RPM 3 phase motor. the only real question is how much HP will i need.

    i can currently take 1/8 cuts while turning in aluminum and would like to keep that. i can take .075 cuts in cold rolled steel and would like to keep that as well. i don't do much thread so thats not too much of a concern but i will do it every now and again, so i need enough power for this too.



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    Community Moderator Al_The_Man's Avatar
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    I converted a Lathemaster 9x30 for a friend of mine, but we used a AC PM motor I had on hand just over a 1HP, single pulley. The original was 3/4hp and that was a bit undersized when machining over 5" dia material.
    I would say go with the largest you can fit in the motor bay, within reason.
    Al.

    Last edited by Al_The_Man; 01-27-2007 at 06:08 PM.
    CNC, Mechatronics Integration and Custom Machine Design

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    Runner4404spd, Keep at least the direct drive 3 speeds and poly belt. A cog belt is bad for surface finish.If that does not matter then go for it like Steve did to keep things simple.
    You mention 1/8" DOC. Just to make sure ,are you talking about turning in the cross slide .125" deep which would be .250" diameter reduction on the part or are you talking about a .125" diameter reduction on the turned part?
    A 1/2 hp Motor is not going to rip off 1/8" deep cuts. 200 rpm for a low speed and 1300 high is a step backwards IMO.
    If you do this I would really consider keeping the 6 speed belt drive.

    Some of the DC treadmill motors are rated at 2.5 hp and will put out less than any true 1hp inverter rated 3 phase motor by the way.

    In any case, the limiting factor in power to the spindle is the belt drive not the motor.

    At 40 spindle rpm my motor spins at 200rpm. I have a spindle tach as well.
    I can stall the spindle to 0rpm and the belt will slip while the motor has not lost a single rpm and will still spin at 200 rpm with heavy tension on the belt.More gear reduction at the motor at that point is useless.
    In that case the motor is still supplying more power than the belt can transfer.
    That is what you need to check to set your true motor/spindle low speed set point. The faster the belt spins the more power it can transfer. Then at some point your motor can be the limiting factor as even a 5mm poly V belt can transfer near 5hp at extreme rpm levels near 15K.
    Steve



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    didn't think about the surface finish, but yes it is important. i was thinking of upgrading to wider v belt when i do the conversion. i was planning on using the segmented belts that the machinery place here sells. they are supposed to reduce vibration.

    i can take an 1/8 depth of cut to remove 1/4 in diameter in one pass. i would like to keep this as it makes turing to final size from large diameters very quick. a couple of rough passes then a final pass and its good to go.

    i guess i will stick with the 1hp setup, even though its a little more money upfront i'm sure it will be worth while in the long run.



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    Community Moderator Al_The_Man's Avatar
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    I used a 1" wide L style timing belt and pulleys, it gives him 0 to 2500rpm, of course using the AC PM servo motor gives superior results.
    Al.

    CNC, Mechatronics Integration and Custom Machine Design

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    Here is my to cents. Unfortunately this is based largely on my experience in industry on non metal machine applications. I haven't updated my 9x20 yet.

    First; is the issue of low speed stability. This varies a bit from drive and motor combo to other combos. Ideally you will still be gearing down the motor speed to drive the spindle. Not a huge problem as you seem to want to max out a 1300 RPM. Since it is a question of the motor and drive combo determining how fast above 60 Hz you can go you will need to do the math to find the optimal belt ratio. The good thing about the AC drives it that they will run reliably at high rotor speeds (up to the rating). Brushed DC motors on the other hand usually have very low top RPMs.

    Second; I really think that 1/2 horsepower is way to little for this machine. Realize that you have significant mechanical power losses in the drive train, so you will not likely see 1/2 horsepower a the spindle. In any event you should be able to look up horsepower requirements for the types of cuts you want to make. This might require a bit of math but is the best way to put to rest your concerns. You do have to take into account the power the motor is putting out at the speed it is being driven. Plots should be available from the drive manufacture showing power output.

    Third; V-Belts suck for driving spindles in my opinion. My goal is to replace the cheesy belts on the 9x20 with something different. I know some have expressed concern about the use of timing belts, but now a days there are many designs to choose from. The other option I've looked at is the multi-V belts like are common on cars and many machines. These are a lot like a flat belt but have tiny "V's" that mate with the pulleys. either way we are talking new pulleys all around.

    Fourth; Unless you invest in a real fancy motor/drive combo it would be best to assume that you need at least a couple of belt ratio options. Obviously the ratios can be much wider than without a variable speed drive. One ratio should be suitable for threading but I'm of the opinion that you would want to get your stable speeds down to couple of RPMs, a minimal speed of 200 RPM is high for my tastes. There is a lot to be said for creeping up on threads and adjusting spindle speeds as warranted. So maybe three belt ratio steps are in order.

    Fifth; If you have variable speed you really need to consider an RPM readout.

    Dave



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    Community Moderator Al_The_Man's Avatar
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    I don't understand the reluctance to use timing belt for drives, they have been used for many years for servo reduction, which obviously operate down to very low speeds, and cogging or uneveness would not be tolerated.
    Also, if the lowest speed is 200rpm, I don't see why there should be a problem.
    You also have to calculate wether you need reduction by looking at the torque curve figure, for e.g. a DC motor or PM AC motor would have a max. torque at 0 rpm and be fairly flat or decrease slightly at max, rpm.
    Check with the VFD manufacturer to obtain typical torque curve if you go this route.
    Al.

    CNC, Mechatronics Integration and Custom Machine Design

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    Quote Originally Posted by Al_The_Man View Post
    I don't understand the reluctance to use timing belt for drives, they have been used for many years for servo reduction, which obviously operate down to very low speeds, and cogging or uneveness would not be tolerated.
    High Al

    I'm not sure if you are responding to my post or not, it doesn't matter because I think I failed to communicate well. The cogging and low speed performance I was talking about in the post above is that coming from lower cost drives and motors. Some motor & drive combos don't do very well when the rotor speed slows dramatically. This is not a huge problem if the motor speed is stepped down a bit via belt reduction. In the original posters message the indicated operating speeds would be very doable on most drives. Of course newer, more advanced, matched drive and motor combos can deliver torque at very low speeds smoothly.

    As to timing belts I don't have a big problem with them and have seen such on every thing from diamond turning machines to old lathes. These all being axis drives. As to spindle drives I'm a little mixed on that as I haven't had personal experience where a timing belt caused surface finish problems. The problem is that nothing I've worked on has had timing belts in the final drive to the lathe spindle.

    I have had experience on other machinery that I can't go into detail where timing belts did impact performance of the machine. It was not a case where they could be disposed of either so great lengths where taken to make sure that the problems where minimized. This included monitoring the condition of the belt.

    So in the end I have no personal experience with the impact of a timing belt in the lathes final drive. What I do know it that the condition of the belt is a likely issue with respect to problems that have been mentioned. Along with the quality of the pulleys which can be a big issue with timing belt pulleys. In one case I dealt with the pulleys where all re manufactured for OD tolerance, run out and the like. IS it fair that timing belts are dismissed, probably not.

    In my case though it is more of a question of resources. When I make the new pulley for the spindle drive it will be much easier to fab a multi-V or flat belt pulley than it will be to make a timing belt pulley. Especially with multiple steps and a modest machine shop.

    Also, if the lowest speed is 200rpm, I don't see why there should be a problem.
    I would tend to agree with this. The trouble is if you have variable speed you may very well want to operate below 200 RPM. If you are down to 25 or 50 RPM you still want smooth torque flow from the motor. In my case this is what I was concerned about, that is the ability of the motor and drive to operate smoothly at very low RPMs.

    Since the original poster isn't demanding all that wide of a range of RPMs I think it would be advantageous for him to come up with a motor - spindle ratio that covers the low end well. It may be easier just to aim for at least two steps on the drive pulleys.

    I'm certain that, with no holds barred on the wallet, a drive can be found that will cover his speed range entirely. That without step pulleys. It may be far more economical to simply buy the cheaper drives.motors and add a step pulley.
    You also have to calculate wether you need reduction by looking at the torque curve figure, for e.g. a DC motor or PM AC motor would have a max. torque at 0 rpm and be fairly flat or decrease slightly at max, rpm.
    Check with the VFD manufacturer to obtain typical torque curve if you go this route.
    Al.
    If you are buying new it is very important to check into the details and to do the math. Can't argue with that. The problem is that on this forum many of us do not buy new.

    While the torque should be max at zero RPM the unit is not getting any work done at zero RPM. I would want to know what that power delivery is like at zero plus RPMs. That is is it smooth and stable. Some of the newer drives on the market are almost servo like in their control over the rotor. Others remind me of old DC SCR type controllers.

    Dave



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    I don't think a timing belt can provide quite as "smooth" a transfer of power to a spindle as a flat or endless V belt. But It may be such a small difference that is of no concern to most users.I honestly don't know. The 5mm poly belts used on the 9x are a very good belt really. 60' high wedge angle not the usual 40' of a typical V belt. They are made of polyurethane and not rubber and have no seam. They provide very smooth power transfer. It is capable of transferring near 5hp at very high rpms. Where it lacks is at low rpm it can't transfer very much power. But this is just a 250lb lathe. On my lathe using a 1hp 3phase VFD at 40rpm ( about 200 motor rpm) it has as much or more power than my x3 mill even with the little 5mm poly belt.So do you really need much more cutting power on this lathe than that? I use just 3 speeds and really only need 2 for almost everything. I recently had no problem threading metric 39x4mm thread at 40rpm. That's pretty coarse so I don't see much need to go any slower. My range is 40-3500rpm. I limit the top rpm. It'll spin to 4600. I did away with the secondary pulley which was driven by a .5" wide XL timing belt. Removing this made for a smoother running machine most notable at higher motor rpms. I now direct drive using just the poly V belt. Very very smooth. I made a smaller low pulley for a 5:1 reduction. I have a tach as well. In any case the 3phase VFD is quite a worth while project for these lathes. Steve



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    Gold Member BobWarfield's Avatar
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    FWIW, I have a DC treadmill motor on my Lathemaster 9x30. I never bother changing pulleys. It's set to the mid-range. The factory Asian motor was rated at 3/4HP, while the treadmill motor claims 2.5HP. The overall impression is the treadmill delivers no more or less power than the old Asian motor did. Given that I never change the pulleys, that probably means it really does deliver more power.

    That sounds terrible, but I will tell you I never wish for more power from this lathe. I feel the rigidity gives out before I could use more power. A true 1HP to 1.5HP 3 phase with a VFD would be very nice, but is this lathe really worth the added expense? I'm not so sure. My rig cost right at $100 for motor and speed controller off eBay.

    I am using the timing belt, and I am also curious about the idea that finish can be improved from other kinds of belts. I have read in many places that running with the belt slightly loose on a v-belt system improves finish so maybe there is something to dropping the timing belt.

    I have also heard of another kind of belt that supposedly does wonders for finish and vibration. Its name escapes me, but the pictures make it look like it comes in segments. I'm sure Al or someone will know what I'm talking about.

    I will say the variable speed is absolutely a pleasure to use. I love being able to dial a bit more or less to tune to the specific situation at hand.

    Best,

    BW



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    Bob, the belts your descibing are fenner drive belts. i plan on using these. also, i already bought a 1hp vfd. i just need to get a motor now and mod some v belt pulleys to fit the lathe. i'll keep you posted.



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    Gold Member BobWarfield's Avatar
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    Runner, exact-a-mundo, Fenner belts are the ticket.

    Best,

    BW



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    Quote Originally Posted by BobWarfield View Post

    I have also heard of another kind of belt that supposedly does wonders for finish and vibration. Its name escapes me, but the pictures make it look like it comes in segments. I'm sure Al or someone will know what I'm talking about.
    Is this the one? http://www.goodyearindustrialproduct...lts/index.html
    Al.

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    Albert E.


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    Here's a little review on 2 link belt brands including the Fenner PowerTwist. http://www.paragoncode.com/shop/link_belts/ I don't think there is much to improve over the 5mm polyflex as far as vibration/smoothness goes. I have gt2, XL, MXL, HTD, some odd ball import timing belt, serpentines and the standard spliced V belts. IMHO the Gates 5mm polyflex belts are smoother than any of the other belt styles by a good margin. A tiny 5mm polyflex can spin to 15,000rpm smoothly according to the literature. I have thought many times of a geared or timing belt system just for low rpm cutting though. It's one thing to thread at 40-60rpm but another to cut a stainless 5" flywheel. Belt slippage becomes troublesome at such low speeds and then as the tool stops you get instant work hardening. That is really irritating. Heck I even thought of a chain drive. Just for low speed roughing cuts. But I never really pursued any low speed positive arrangement. Those Goodyear belts look interesting. Reminds me of Chevron treaded tires. Steve



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    It's all a question a of gearing. My Dad's 9 inch southbend pnly has a 1/3HP motor, but with its real back gear, the thing is unstoppable at low speeds.

    On the other hand I have a 3/4HP two pole (3000RPM) three phase motor with VFD set up driving my little 7x lathe through a 2.4:1 timing belt reduction, and this gives a fair bit more power than the crappy chinese DC motor did at the low end (about 200RPM at 10Hz) through to way more power than the machine needs at 3000RPM (100Hz).

    Regards,
    Mark


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