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How does someone gauge the power of a DC or AC motor?

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Ian P09/11/2019 14:59:38
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For a motor, mount, power supply, speed control pot, 13 ER collets and an adapter to hold them in I am sure its very good value. (they seem to be less then £50), however....

Whether its will do the job you want it to do is another matter. I would not expect any great accuracy from the collets and even less from the collet holder clamped to the motor shaft with grub screw. For the size of diamond wheels you showed earlier an ER11 collet adapter would not be an idea way of mounting them, the total overhang from the front motor bearings is far more than ideal.

You now mention that you want to use the diamond wheels for lapping, that is quite different from using them for grinding, what is your intended use of these wheels and with what materials?

Ian P

peak409/11/2019 15:00:01
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From the photos you posted of the diamond laps, 400rpm seems about right.
Sorry for using an ebay link, but how about something Like This ER16 spindle

A normal cheap 240v motor will run at 1425 rpm, so you need about 3.5/1 reduction.
Take the small pulley off the spindle, and re-use it as the motor pulley, procure a suitable belt and pulley 3.5 times the diameter of the one you already have, and fit it to the spindle.

Another ebay search for "NVR switch", will point you to one of the cheap black and yellow switches, so it all works safely. For the loads you're likely to be putting on the setup, I can't see the point of fancy overload/overheating protection for the motor.


Bill

 

 

Edited By peak4 on 09/11/2019 15:00:53

Ian P09/11/2019 15:14:59
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I left it too late to edit but I wanted to add that one should not take the sellers description too seriously.

The motor you showed purports to have a 'governor', which I assume refers to the speed potentiometer and I doubt there is much in the way of actual speed regulation.

The ER16 spindle Bill linked to is described as 'High precision', that too is in the eye of the beholder. No details of what bearings are used and whether it is capable of accepting axial loads.

Ian P

JasonB09/11/2019 16:23:39
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Posted by Chris TickTock on 09/11/2019 13:52:10:

My only hesitation is in not understanding what they mean by idle speed stated as 2000-12000. Baring in mind the DC input for this motor has a range of 12v to 100 are they talking about the no load speed?

Yes slowest no load speed will be 2000rpm and I doubt you will drop much more when running as you won't be putting much pressure on the wheels for lapping so too fast for what you want.

John Haine09/11/2019 17:23:14
2693 forum posts
138 photos

I can't understand why you don't just put it in the lathe. Normally that's frowned on because normal grinding wheels throw abrasive grit everywhere but used carefully diamond wheels shouldn't do that. Anyway you can cover the ways with paper to keep it off. Eternal actually say use them in the lathe.

JasonB09/11/2019 18:24:55
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I suppose the problem with that is you can't easily touch up a tool part way through a job unless you take it out of the lathe and possibly chuck too if you are using that to hold an arbor.

Chris TickTock09/11/2019 20:12:12
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Posted by John Haine on 09/11/2019 17:23:14:

I can't understand why you don't just put it in the lathe. Normally that's frowned on because normal grinding wheels throw abrasive grit everywhere but used carefully diamond wheels shouldn't do that. Anyway you can cover the ways with paper to keep it off. Eternal actually say use them in the lathe.

John , you may be right but I need to look first at the alternatives.

Chris

Chris TickTock10/11/2019 14:22:02
222 forum posts
8 photos

Hi Guys, I have finally gone for better or worse a 200w DC motor and speed controller / convertor. Reason being the motor is one used on a tread mill and has good reviews. Also the speed controller allows the speeds I wish for at around 400 rpm. This means I can directly attach the diamond wheels without complicating matters without additional gearing. The motors shaft is 10mm so the only question is whether to go with a 3 jaw chuck or ER16. I have looked into this and for the purpose of sharpening / grinding I would think a cheap 3 jaw chuck will do. As always time will reveal if my plans fail or otherwise. I am learning lots from this post including to match a chucks taper with the adapter. if anyone has thoughts on my best method of holding an 8mm arbor for my sharpening wheel to this 10mm motors shaft feel free to offer your opinion.

Chris

Chris TickTock11/11/2019 17:40:59
222 forum posts
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Hi, I ended up not going for the kit including the ER11 collets for several reasons but mostly the idle speed was far too high.

I have decided and bought a treadmill DC motor with pulse width control this gives speed control with one really good bonus.....maximum torque at all speeds. Reason: max torque is when max current and pulse width is either on or off (max).

I am thinking of just using a 1.5 to 10mm drill chuck to mount the 50mm grinding wheels and other related small disks.

Chris

JasonB11/11/2019 18:18:21
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By the time you have modified the motor shaft to take a chuck or made an adaptor for the chuck as  well as an arbor for the disc to be held in teh chuck you may as well eliminate one or two sources of run out and simply modify the motor shaft so you can fit the disc direct to that or make an adaptor/arbor to fit the shaft and hold the disc on the other end

Edited By JasonB on 11/11/2019 18:19:26

PekkaNF12/11/2019 11:12:12
94 forum posts
9 photos

Or you might get something out of this vid.

https://youtu.be/GOBtH4m2TYo

 

Edited By PekkaNF on 12/11/2019 11:16:13

Edited By JasonB on 12/11/2019 11:19:37

Ian P12/11/2019 11:46:28
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2246 forum posts
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Thats one of the better produced YouTube videos and I learnt two useful things from it, one that he describes it use as lapping as well as grinding, secondly, I want one!

The diamond disks that he uses are much cheaper than I thought they would be and two from different sellers are on their way to me now.

Ian P

PekkaNF12/11/2019 17:27:25
94 forum posts
9 photos

Build something like that 2017 to lap carbide scraper blades. I used 90W 2800 rpm furnace blower motor geared dow with round belt pulleys.

I used scraped aluminium profile for frame and build very simple spindle with two ball bearings that acsept 12 mm shaft. i glued one bearing (fixed bearing) and left another easy fit. All parts and materials from scrap box.

Work table is mild steel to allow fixing jigs there with magnets.

Different holes for different r (on scraper blade radius).

Plinth made of C-section mild steel is milled to proper angle (scraping blade needs small negative angle).

Slow speed works fine and even blade change is not too hard with knurled knob.

 

p2124324c.jpg

p5284921c.jpg

p5284922c.jpg

 

 

Edited By PekkaNF on 12/11/2019 17:31:09

Edited By PekkaNF on 12/11/2019 17:32:50

Chris TickTock16/11/2019 12:40:45
222 forum posts
8 photos

Adapter now made not 100% happy with as blind hole face could be better but on whole acceptable and should do the jobadaptermk1.jpg

Thanks for all help and posts which are appreciated.

chris

Howard Lewis16/11/2019 16:32:01
2440 forum posts
2 photos

Commercial Plummer Blocks are OK for shafts, but not for precision grinding. There will be chatter!

BEWARE!

One of our bearing suppliers made up a broach grinder using commercial plummer blocks. The chatter ground into the broach was small, circa 0.00001" and was reproduced in the bearings. It caused the white metal bearings to fail. The chatter marks acted as drains for the oil, despite being pressure fed.

Howard

Ian P16/11/2019 16:48:43
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2246 forum posts
90 photos

Whoa!

Is there some danger to life or limb that warrants an all capital beware warning?devil

I doubt it myself, and dont see the connection with where an imperfect surface (less than a quarter of a micron) causes loss of oil pressure. I think there was more wrong with the design of the 'broach grinder' than the plummer blocks.

Ian P

Ian P16/11/2019 22:05:10
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2246 forum posts
90 photos
Posted by Chris TickTock on 16/11/2019 12:40:45:

Adapter now made not 100% happy with as blind hole face could be better but on whole acceptable and should do the jobadaptermk1.jpg

Thanks for all help and posts which are appreciated.

chris

I would not be in the slightest concerned with the state of the face at the bottom of a blind holes, its not like anyone will ever see it and its serves no functional purpose whatsoever. As long as the shaft enters far enough its done its job.

One observation I would make is to say that ideally the grubscrew should make contact with the shaft about half way along their engagement length. It helps to increase the chance that the axis of the two parts are parallel with each other.

Out of interest, how did you ensure the concentricity of the bore relative to the threaded shank?

Ian P

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