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Thread: Motor stalling on jet midi lathe

  1. #1

    Motor stalling on jet midi lathe

    After many years of flat wood woodworking I decided last year to take up turning. Bought a Jet 1221VS midi lathe and started developing my skills turning small to midsize bowls (6-8" diameter); exclusively working with green wood from the neighborhood. All was well until I decided my abilities had progressed to the point where I could take on bigger projects and I started mounting 12 inch blanks, mostly around 4" thick; maple, oak, ash, etc. When turning around the perimeter of these pieces (where obviously the force exerted on the tool is greatest) the motor constantly bogs down and sometimes stalls. This is a problem even when taking very light cuts, and it makes it impossible to make the continuous sweeping movement along the piece that yields clean curves, as I need to keep backing off to allow the motor to recover its speed. (I typically turn between 400 and 500 RPM - wouldn't want to go higher on these heavy pieces.) The problem disappears as I move toward the center of the piece, where the load on the tool is lighter.
    Can anyone tell me if this is normal or if I have a defective motor? It seems odd that Jet would put a motor on their machine that isn't capable of handling the biggest pieces that will fit. (And by the way the lathe is plugged directly into the wall outlet and the belt tension is a high as I can make it, so I don't think I'm experiencing a voltage drop or slipping belt.) Not much point in making a lathe with a 12 inch swing if you can't turn a 12 inch blank on it. Advice/others' experience much appreciated.

  2. #2
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    The little dc variable speed lathes chop the voltage to reduce speed. So much lower torque at low rpm. Move the belt to the smallest pulley on the motor and get the motor rpm up to turn the bigger pieces. But with the pulley change the wood speed will still be lower.

  3. #3
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    In addition to the pulley, be sure the gouge is sharp, sharp, sharp. I didn't see where you said - are you using a traditional gouge? What kind of grind? I'm not familiar with that lathe model but I've turned pieces on some pretty wimpy lathes and even from dry oak - if the tool is sharp and the technique is good it seems you should be able to make continuous cuts with a razor sharp gouge once the piece is roughly shaped, even at the largest diameter.

    BTW, having the belt as tight as you can get it may not be a good idea. That can put extra stress on the belt and bearings. Maybe loosen it a bit to where it still turns but doesn't slip. That shouldn't affect the motor strength or lack of strength.

    Are you a member of a turning club? If so, you might have someone willing to come to your shop and try the lathe, ideally an experienced turner who is familiar with that model of lathe. If they have the same problem with the same blank you are turning it might rule out a problem with your technique. They may have a feel for what that lathe motor is capable of. Maybe someone reading this who lives near you would be willing to visit. (Unless you are in the witness protection program, perhaps put your location in your profile.)

    If you like turning that much you may suffer the fate of many turners, me included. I started with one of the worst lathes in the world and very quickly decided to get a better lathe. I gave the other one away.

    JKJ

  4. #4
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    De tension the belt Bill, it isnít necessary and can be detrimental to the lathe.

    Then next and it is more a question, but what kind of tool are you using to rough turn the blank, and also where are you attacking the wood ??.

    Here I added 3 pictures, as pictures do help more than mere words.

    Here is a piece of hickory and not nicely round yet (wormy and they do not taste good DAMHIKT) yuck. (Donít Ask Me How I Know That)

    See it is better to start at the face and remove wood, layer after layer, it will get the piece round and is much easier on the latheís motor, I have a Delta Midi very much like the JET.
    turning from center outward.jpg

    As I continue shaping the blank it gets rounder and more into the shape Iím after, (more guts)
    Keep on rounding the blank.jpg

    Rounded and ready to flip it to start the hollowing.
    rounded and ready to hollow.jpg

    I used a ľĒ Sorby bowl gouge for this, and of course you might be doing all this already, but I figure it would not hurt to bring this up, lowest speed pulley and at least a 50% of the power, more if the lathe is not dancing around 1thumb.gif
    Last edited by Leo Van Der Loo; 04-12-2019 at 12:06 AM.
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    Have fun and take care

  5. #5
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    I've turned on the Jet Midi. I own Jet minis. Also a Jet 16". The midi isn't exactly a powerhouse. I can stall my 2hp Jet with my bowl gouge, so maybe you're asking the lathe to do too much.........
    You can try using the next step up from the lowest speed. I know this is counter intuitive, but that helps me when using the minis and turning something "large". I don't know why, can't explain, but give it a try. I also have a Rikon midi, and can stall that no problem. As mentioned sharp tools matter when using the small lathes.......

  6. #6
    Thanks to all for advice. To answer the queries, I'm using a 3/8 inch bowl gouge with a fingernail type grind. I think I keep it nice and sharp ]- sharpen every 5-10 mins while turning, but maybe could do better. Per Leo's suggestion, I've tired both starting and the face and moving around to the perimeter as I round the blank and turning the whole blank to round at the beginning. Same problem both ways, except with the latter the motor starts bogging down immediately; with the former only as I move towards the perimeter of the bowl. I'm a little confused by Richard's suggestion to move the belt to the smallest pulley and then crank up the RPM. IF the RPM reading is, say, 500 when the belt is on the smallest pulley wouldn't the wood be turning at the same speed as happens when the read-out shows 500 when the belt is on the medium pulley? Is there more torque in the former situation? If I'm using the smallest pulley what would be the max safe speed to rough turn a 12 inch, 4 inch think blank oak?

  7. #7
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    You get the most torque and the slowest speed with the smallest drive pulley (on the motor) and the largest pulley on the lathe spindle. The actual torque and speed at the various pulley locations would depend on how the variable speed works with the motor on that lathe, of which I am clueless. I'm making the assumption that lathe has a step pulley. My lathes with VFD speed controls have pulleys with two steps - I generally use the step that gives me the higher speed since I like to turn small things, but when turning bowls and platters I generally use the one that gives the lower speed.

    I do like the 3/8" bowl gouge for this. Some people try to use a big honkin' gouge and make it take too big a bite. If I'm not using a smaller bowl gouge I reach for a Hunter carbide tool like the Hercules. (Actually, I think I use the Hunters more than the traditional gouges these days.)

    It's not the frequency of sharping but the sharpness. If it will shave arm hair it's probably sharp enough. I sharpen gouges on fine wheels with a jig then hone a bit on a leather wheel or MDF plate embedded with polishing compound. I general touch up between sharpenings with an extra fine diamond hone and a lick or two with the MDF or leather. I don't usually go back to the grinder as often as you mentioned, but I know some people do.

    Not everyone agrees on the speeds to use, even the experts. A speed low enough to avoid a lot of vibration with an out-of-balance blank is always recommended and that speed can usually be turned up a bit after turning round. If the piece has any defects or if the holding method is not the best (improper tenon, recess, etc) or if you still get an occasional catch then a lower speed is better since when the thing flies off the lathe it will have less kinetic energy and there may be less pain and suffering. Many people err on the the side of caution, ESPECIALLY when recommending speeds to someone with an unknown level of experience. There are some who tout formulas but to me there are too many variables to put absolute numbers on diameters. Here is one web page with some guidelines: http://blog.woodturnerscatalog.com/2...-lathe-speeds/

    I personally keep the speeds fairly low when roughing, but "fairly low" is defined by feel and experience - I rarely look at my speed display. I won't recommend my particular speeds to anyone except when turning thin spindles (I turn those wide open, over 3000 rpm). For a 10-12" diameter shallow bowl/platter from 2-3" thick dry stock already shaped to final size on the bandsaw and held by a perfect recess with a good chuck tightened properly I might turn at 800 at first then increase to [higher - I won't say what] after most is cut away, especially if the piece has "wings" which are best turned a bit faster. However, I'm sure the holding method, use wood without defects, and ALWAYS stay out of the line of fire. What ever you do, wear a face shield and safety glasses! A very experienced friend of mine was injured enough recently to require stitches in his arm when a large green blank came off the lathe. Perhaps he forgot for a second to stay out of the line of fire. Fortunately his face is OK.

    Again, a great way to see if the problem is with your technique, the tool, the wood, or the lathe is to get someone else to come take a look and a try. Where do you live?

    JKJ


    Quote Originally Posted by Bill Bell View Post
    Thanks to all for advice. To answer the queries, I'm using a 3/8 inch bowl gouge with a fingernail type grind. I think I keep it nice and sharp ]- sharpen every 5-10 mins while turning, but maybe could do better. Per Leo's suggestion, I've tired both starting and the face and moving around to the perimeter as I round the blank and turning the whole blank to round at the beginning. Same problem both ways, except with the latter the motor starts bogging down immediately; with the former only as I move towards the perimeter of the bowl. I'm a little confused by Richard's suggestion to move the belt to the smallest pulley and then crank up the RPM. IF the RPM reading is, say, 500 when the belt is on the smallest pulley wouldn't the wood be turning at the same speed as happens when the read-out shows 500 when the belt is on the medium pulley? Is there more torque in the former situation? If I'm using the smallest pulley what would be the max safe speed to rough turn a 12 inch, 4 inch think blank oak?

  8. #8
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    Quote Originally Posted by Bill Bell View Post
    Thanks to all for advice. To answer the queries, I'm using a 3/8 inch bowl gouge with a fingernail type grind. I think I keep it nice and sharp ]- sharpen every 5-10 mins while turning, but maybe could do better. Per Leo's suggestion, I've tired both starting and the face and moving around to the perimeter as I round the blank and turning the whole blank to round at the beginning. Same problem both ways, except with the latter the motor starts bogging down immediately; with the former only as I move towards the perimeter of the bowl. I'm a little confused by Richard's suggestion to move the belt to the smallest pulley and then crank up the RPM. IF the RPM reading is, say, 500 when the belt is on the smallest pulley wouldn't the wood be turning at the same speed as happens when the read-out shows 500 when the belt is on the medium pulley? Is there more torque in the former situation? If I'm using the smallest pulley what would be the max safe speed to rough turn a 12 inch, 4 inch think blank oak?
    Bill yes using the smallest pulley on the motor and the largest on the spindle will give you the most power/torque on the spindle.

    To put this in a different way, if you have a car or truck with standard transmission, you would know that you start in first gear, and if trying to do that in high gear your engine would probably stall.

    Especially with variable speed DC motors, when you are basically giving less electricity to the motor to turn at a lower speed, you are having less torque at the spindle, the reason I suggested to turn at least at 50% of the speed, where the power of the motor is much higher than at lower speeds.

    here is a typical DC motor power curve, this will vary with different DC motors, but it is typical.

    typical DC motor.jpg
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    Have fun and take care

  9. #9
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    I'll agree that you must get more torque from the smallest/largest pulley arrangement. That said, give this try. When attempting coring on my Jet mini, I did start on the lowest speed. (Yes, I can core on the mini. It's really not worth the slowness unless you have a blank that is real nice.) This may not be the "best" arrangement. I found that coring requires more speed. I core on the second smallest drive. Yes, you must take smaller cuts, but you may find you can remove wood faster. Once balanced, I always step up the speed. For me, it works better. Take light cuts. The mini is way weaker than your midi.

  10. #10
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    Bill Bell,
    You've received a lot of good advice. I want to suggest something from another perspective for you to explore.

    See if you can find someone who has the same lathe and either have them try yours or see if they will let you try theirs using your own tools, techniques and wood. If they are the same, then you can rule out a problem with your lathe. But if your's seems to have substantially less power, you could have a problem with your motor or speed controller.

    If you have a clamp-on AC ammeter, you could measure the AC current draw when approaching a stall and see if the power is in the ball park. Power is measured as watts, which is the product of current and voltage. So, if at stall you were drawing 3 amps and your line voltage was 120 vac, then your power draw would be 3 * 120 = 360 watts. One horse-power is equivalent to (IIRC) 746 watts. So in this example, if you were drawing 3 amps, your input power would be roughly 1/2 of a HP. These will give you some rough data points.

    I had a Craftsman 9" lathe with a 1/2 HP AC motor. I could stall it if I was taking aggressive cuts but I learned to cut somewhat below that point. Also, the belt would squeal if it stalled.

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