GTA
All Springer/NP/PCP Air Gun Discussion General => Machine Shop Talk & AG Parts Machining => Topic started by: jackssmirkingrevenge on November 07, 2022, 06:23:48 AM
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https://youtu.be/SQBKHBAlLGM (https://youtu.be/SQBKHBAlLGM)
Lathe motor is turning very slowly even uncoupled from the belt and the lights dim when I turn it on, so it's obviously drawing a lot of current.
Any ideas what might be causing the issue? The lathe is a Craftex CX708 (https://www.busybeetools.com/products/lathe-metal-10in-x-18in-3-4-hp-cx-series.html) with a single phase double capacitor 110V motor with a fixed speed but can reverse direction, and the issue happens in both forward and reverse.
(https://i.imgur.com/xqHMCNp.jpg)
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Evidently bad dry bushings probably in need of cleaning up ??? Doubtful that regular roller/ball bearings are used in that motor. O lite bushings reamed to the right diameter would be your best bet ???
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Evidently bad dry bushings probably in need of cleaning up ???
Are you sure it's not more likely to be an electrical problem? It's done this intermittently a few times before. The shaft turns freely and there doesn't seem to be any play:
https://www.youtube.com/watch?v=51pNqvdw5Js (https://www.youtube.com/watch?v=51pNqvdw5Js)
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Dual capacitor, one starts, one runs
At low speeds, an internal switch turns on the start cap. Turns it off once up to speed.
Probably didn’t turn ON, the last time motor was shut off.
An old trick to check is to SPIN IT UP with a rope then turn it on.
The internal switch is just a large set of contact points on opposite end of shaft output. Cleaning those normally solves the issue but it could be a start cap.
Dave
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Thanks Dave!
The internal switch is just a large set of contact points on opposite end of shaft output.
Would that be under this rear cover?
(https://i.imgur.com/LA5vhYZ.jpg)
Edit: I assume it's the centrifugal switch that is described here (https://youtu.be/M-j6PhthXJY?t=205).
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That cover only covers a fan.
It would be under the end plate of the motor, normally. The plate that houses the bearing.
Dave
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Check out here https://www.quora.com/What-purpose-does-a-centrifugal-switch-have-on-a-motor (https://www.quora.com/What-purpose-does-a-centrifugal-switch-have-on-a-motor)
Dave
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I assume this is what I'm looking for:
https://www.youtube.com/watch?v=QUfLM4o2mDU (https://www.youtube.com/watch?v=QUfLM4o2mDU)
I'll check it out this evening, thanks for the tip!
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If it doesn't have start up torque (weak or none) I suspect the start capacitor. The value will be printed on the capacitor. Order one on eBay. They can be had very reasonably. The seller usually gives the capacitor dimensions in the description. You want to be sure it fits. Usually in a can on the side of the motor. I only worked on one split phase motor that had a bad centrifugal switch and it was a pretty old motor that had heavy use. I think a bad capacitor overloaded it. One of the contacts in the switch had fallen out.
I have repaired quite a few vintage capacitor start motors. I like to have period motors on my vintage machines because they look cool and run well. Certain vintage motors also bring good money. I've sold a few. Old Craftsman motors are desirable and run very quiet. They often have bad capacitors.
(http://)
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I suspect the start capacitor.
Looks like that's the issue, I took the motor apart to look at the centrifugal switch and nothing seems to be broken or dirty:
(https://i.imgur.com/Kr3p9NZ.jpg)
(https://i.imgur.com/nWkxZTf.jpg)
Of the two capacitors however, according to my multimeter the one on the left is faulty, as it's the one with larger capacitance I assume it's the start capacitor.
(https://i.imgur.com/nsxrg9W.jpg)
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Glad you found the issue! And caps are generally a cheap fix.
Dave
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Glad you found the issue! And caps are generally a cheap fix.
Cheers, and I appreciate the advice! I should be able to source a replacement capacitor locally without too much trouble.
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Good info on small motors, I have a 9x19 that has always been faithful.
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Yes, the 300mf would be the start capacitor.
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A good place to try is an appliance parts store or a Heating / Cooling Parts House.
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A good place to try is an appliance parts store or a Heating / Cooling Parts House.
You'll pay through the nose there. That's why I get them for cheap and delivered free on eBay. Lot's of sellers have a 300 mf. Check the dimensions! You'll find lot's of them
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A good place to try is an appliance parts store or a Heating / Cooling Parts House.
That's what I first tried (having already replaced some household heating capacitors from the same store) to give a local business a chance however no joy, they didn't have anything near the same capacitance, so I ordered one off Amazon instead, hopefully they should deliver today.
Since electronics are not my forte, here's an idle thought - would say 6 x 50μF wired in parallel had done an equivalent job to a single 300μF?
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Been awhile since I had the math on capacitance but there is a formula. Series is what you want to look at . https://kitronik.co.uk/blogs/resources/how-to-calculate-capacitors-in-series-and-parallel#:~:text=Capacitors%20in%20Parallel&text=This%20is%20show
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Parallel capacitors add. Series caps get smaller. They're the opposite of resistors.
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A good place to try is an appliance parts store or a Heating / Cooling Parts House.
That's what I first tried (having already replaced some household heating capacitors from the same store) to give a local business a chance however no joy, they didn't have anything near the same capacitance, so I ordered one off Amazon instead, hopefully they should deliver today.
Since electronics are not my forte, here's an idle thought - would say 6 x 50μF wired in parallel had done an equivalent job to a single 300μF?
Yes.
Dave
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Something to keep in mind for next time. I found this handy image here (https://hvacrschool.com/capacitors-series-and-parallel/):
(https://i.imgur.com/lrG2Spo.jpg)
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That might not fit into the can that the capacitor goes into on most split phase motors. However, I have done that to solve the problem of not being able to obtain the long obsolete "sardine can" capacitors in vintage Craftsman with the capacitor in the base. Excellent old motors that run very quiet. Definitely worth repairing. Put shrink tube over the crumbly wiring. The bearings they used were so good you just repack them and good to go another 50yrs. You might have to add a pig tail to allow hookup to a drum switch for reversing but well worth the effort. I put one on one of my South Bend lathes and it runs sooo quiet. Also adjusted the end gears for the quietest operation. Really nice.
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When my motor goes out, I'll be doing the VFD thing or perhaps BLDC route.
Either way, I want to automate the feed and crossfeed.
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I managed to source this capacitor locally, 270μF instead of the original 300μF but it seems to have done the trick ;D
(https://i.imgur.com/ThXUFgQ.jpg)
https://youtu.be/9LjxU5QbVtE
The capacitor came with a resistor between the terminals, which from what I've read is to bleed off residual voltage from the capacitor when disconnected, but I removed it as the original didn't have one.
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The tolerance for new electrolytic capacitors is usually +_ 10% (yours is +20 _ 0) so you are ok but it's so easy to obtain a 300 I don't know why you would sub.
Not going to hurt anything you're only spinning a chuck on start up. Only going to be on the start windings for a split second.
Glad you got your lathe going again!
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If you ever replace those twin belts make sure to get a matched set. +++