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Thread: Power tool and cutter grinder
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20th Jul 2020, 02:31 AM #46Golden Member
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20th Jul 2020, 07:30 PM #47Most Valued Member
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I think the original motor might have made a habit of chewing on its own power cable. There’s at least 4 repairs amongst this lot.
There’s continuity between all the windings internally.
Steve
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20th Jul 2020, 08:24 PM #48
Hi Steve, Guys,
Argh suicide cords
A rewiring job if ever I saw one. Someone failed to dress the cables properly there !Best Regards:
Baron J.
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20th Jul 2020, 11:02 PM #49Golden Member
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20th Jul 2020, 11:03 PM #50Most Valued Member
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Yeah, the danger of having a motor on the end of a column that can rotate. It really needs a guard around the pulley.
Steve
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22nd Jul 2020, 06:55 AM #51Most Valued Member
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My bridge rectifiers arrived in the post yesterday, so I can have a go at getting this treadmill motor running.
Following a bit of combined info from online, I've got a SCR based speed controller/dimmer which will supply the AC to the bridge rectifier, which then goes to the motor.
In regards to filtering the DC what is the recommendation from those of you that have played with these motors?
Also is a flyback diode necessary in this application?
Steve
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22nd Jul 2020, 04:11 PM #52Most Valued Member
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emmmm machines been following you home to mate.
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22nd Jul 2020, 06:29 PM #53
Hi Steve,
Yes you have got it right ! It might just pay you to check the motor runs in the direction you want ! Some of these motors have angled brushes and prefer to run in one direction, usually into the angled face. They will run in either direction though, just a few more sparks at the comm if the wrong way. Use a couple of 0.1 uf 1Kv from the brushes to the motor case for interference suppression and make sure the motor case is well grounded.
A flyback diode could be used but will only let you run the motor in one direction, so I wouldn't bother. As far as smoothing caps are concerned, as big as you can, but beware of inrush currents. C = I / 2 x f x Vpp will get you in the ballpark.
"C" = capacitance in farads, "I" = current in amps, "f" = frequency in Hz, "V" peak to peak ripple voltage.
I personally wouldn't worry to much about ripple, any capacitance will reduce it, and the motor won't care ! So 2000 to 20,000 uf at the peak DC voltage. It will be a physically big cap.Best Regards:
Baron J.
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29th Jul 2020, 01:40 PM #54Most Valued Member
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Power tool and cutter grinder
Been busy with (too many) other projects, but got a chance yesterday to play with the treadmill motor.
Couldn't find any decent size capacitors of suitable voltage, but found a 200uF 400v electrolytic to connect.
There's a bit of vibration and some noticeable brush sparking on acceleration, but once its up to steady speed its really smooth. I'm guessing there's very little power required to keep it in that state - hence the reduced sparking.
With the help of the in-house fabric expert I did a bit of prototyping for the new column bellows. Had a couple of false starts until we worked out a sequence for sewing it up so that there's inverted seams where we wanted them on the outside. I ordered a small PVC tarp online so have some material to make the real one out of, and will drag out the old sewing machine in the shed - definitely not risking the good lady's new machine (she still hasn't forgotten when I used the previous one for sewing up trapeze harnesses for sailing. It was never the same afterwards...)
Trying to work out how to get a one-piece bellows onto the column. I thought it would be simple to pull the head off the column but turns out to not be the case.
The spindle head won't come off, and the column won't just wind up out of the base.
I unbolted the base flange, but that won't lift out as the rack and shaft for raising the column is connected underneath.
It wasn't intended to be a complete disassembly job, but that's pretty much where its headed!
The V's that the table runs on are in good condition, a slight rub line where the balls have been but can't feel any wear with your fingernail.
I'll just clean them up and put a bit of graphite powder on them when they go back together.
Also interesting that the ways are in separate sections, matched together. I expected them to be just one larger piece.
Steve
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30th Jul 2020, 07:38 PM #55
Hi Steve,
Couldn't find any decent size capacitors of suitable voltage, but found a 200uF 400v electrolytic to connect. There's a bit of vibration and some noticeable brush sparking on acceleration, but once its up to steady speed its really smooth. I'm guessing there's very little power required to keep it in that state - hence the reduced sparking.
The DC will become more smooth as the voltage and hence motor speed increases, reducing the start up vibration you are experiencing. The motor current will increase with load. A pair of 10Kpf 1Kv ceramic capacitors, one from each motor brush terminal to the earthed motor case will reduce the sparking and any RF interference that may be generated.
Easier to understand graphically, unfortunately I no longer have my University notes, or I could have scanned them and posted them. Ignoring the maths, there was only two pages with the right illustrations. I'll have a look on the net for the right pictures for you.Best Regards:
Baron J.
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30th Jul 2020, 10:21 PM #56Most Valued Member
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Power tool and cutter grinder
Thanks John - I've got a reasonable idea what you're saying.
The original treadmill power supply board has a slightly larger 400v electrolytic on it, so I can salvage that to increase the capacitance. I should have some small ceramics around somewhere to put across the brushes.
Been continuing with the mission of freeing the column from the base.
Off with the table support casting:
Nice scraped surface under the feet of the casting (and many years of dead millipedes etc):
These 2 rusty plugs seemed to be out of place, until I realised that they were about the right spacing for the Y axis leadscrew nut.
Removed the plugs, removed the 2 socket head bolts in the nut, but the nut still wouldn't release from the base......until I realised there are 4 bolts....
With the saddle now free from the base its obvious what was stopping the inner column coming out - the elevating rack:
Finally got the column out:
The assembly that came out consists of an inner and an outer. The inner is attached to the spindle head casting but is free to rotate inside the outer. The outer is the one which the elevation rack attaches to, to set the spindle height. There are a couple of small locking levers to lock the rotation, and 3 small socket head bolts that appear to lock the graduated collar containing the locks, to the top of the outer sleeve. Even with the bolts removed and the locks released the inner sleeve doesn't want to separate from the outer. It moves up about 0.5mm then stops. I don't actually need to remove it to fit a new bellows, but feels like one of those things that if I don't work it out now it will bite me in the bum later.....
Steve
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30th Jul 2020, 11:06 PM #57
Hi Steve,
The original treadmill power supply board has a slightly larger 400v electrolytic on it, so I can salvage that to increase the capacitance. I should have some small ceramics around somewhere to put across the brushes.
Those capacitors don't have to cope with the sort of pulse voltage that you are getting with the Thyristor/Triac inside the bridge rectifier scheme.
The treadmill PSU is what they call a PWM drive to the motor. The rectified AC is well smoothed by those one or two large capacitors, providing a stable 330 ish volts DC. This DC voltage is applied to the motor in very rapid narrow pulses that vary in frequency thus controlling the average voltage applied to the motor. Exactly similar to the way a VFD drives a 3 phase induction motor.
Nice scraped surface under the feet of the casting (and many years of dead millipedes etc)
They don't like degreaser spray at all. Spraying some on the wood caused some to emerge from holes in the wood. I complained to the supplier, who burnt the lot, after reporting it to his supplier I assume. Unfortunately in my case I had already started to use the wood, but I did give it a good dosing with the spray.
You know looking at your pictures, I would be surprised if that lump on the top where you have it suspended doesn't come off somehow.Best Regards:
Baron J.
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30th Jul 2020, 11:08 PM #58Most Valued Member
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Power tool and cutter grinder
Here's the part that has me perplexed.
Spindle casting with the dovetail rotates compared to the slightly rusty collar below it, which contains the 3 small bolts (hole is where one of them has been removed) and the 2 locking levers.
There's no visible way of removing the locking levers, and they feel like they have a cam style action. Free in the middle, and lock up when turned either way from center.
You can see in the photo that there is a slight gap between the spindle head and that collar where the collar and outer sleeve has dropped down slightly. That's as far as it drops, then one of the locking levers goes really tight in its normally loose central position.
Any ideas on how this style of lock might be constructed would be appreciated. Perhaps its just an accumulation of grease and crud that is locking them up?
Steve
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31st Jul 2020, 03:23 AM #59
Hi Steve,
Just a wild stab in the dark ! If you set the locking levers so that they are loose, then rotate the head all the way round will it come loose. My thoughts are that there is a ring that has one or more slots machined in it that the locking levers will pass through, so that the head can be lifted off. A bit like a bayonet fitting.
In the picture the locking lever looks to be tapered, suggesting that it can only have been inserted from the inside !
Have you removed that cover where the belt is and had a look inside ?Best Regards:
Baron J.
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31st Jul 2020, 04:37 PM #60Most Valued Member
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Power tool and cutter grinder
Thanks John. I did think about something like an entry slot for the locks, but since the outer with the locking ring needs to slide down relative to the inner/head then I thought it would need to have slots all the way down the inner to be possible.
Nothing obvious inside the cover/head, but I gave it a better clean and could just make out the ends of a series of fasteners coming from the outside. So the head must be fastened into the tube from the outside, and the tubes have to come apart before the head can come off.
Took a closer look at the locking shafts, and they are parallel where they go into the collar.
More cleaning and found these small holes in the bottom of the tee slots. Rotated to above the locking levers and bingo - there's tiny screws to retain them.
Removed the screws, the shafts come out, and the outer sleeve slides down showing the clamping bolts for the locks.
Steve
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