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  1. #1
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    Default VFD and 3 phase conversion of my 45 size gear head mill

    Hello all,

    Well after procuring a suitable 3 phase motor and re-wiring it to delta (see http://www.woodworkforums.com/f65/co...-delta-160387/) and testing with the VFD, I have made a start on the conversion.

    The single biggest issue (as I discussed in another thread) was the incompatibility of the motor shaft with the take-up on the mill. The original motor had a 19mm shaft which mated with a keyed female. The replacement motor has (had) a 28mm shaft and an M8 threaded hole. I decided to have a bet each way and I bored the hole on the mill shaft to 22mm and machine the motor shaft down to 22mm to fit. This left what I considered sufficient "meat" left on both mating pieces even after deepening the existing keyways.

    I thought this process would be fairly straight forward, machine the motor shaft down and bore out the mill female, the only difficult part being the keyway in the mill female......

    Well, as it turns out I made a meal of the easiest part! In a moment of distraction I turned down the motor shaft just that little bit too much . It still would have been OK but I didn't like the slop on the mating parts and felt that it may be a source of noise in the operation of the mill. Noise that (if anything) I am trying to reduce, loose fitting parts will not help! So I bit the bullet and built up the shaft again with weld , making a sure as possible that the bearing seat stayed cool. I also took the opportunity to fill in the original keyway as it was larger than the key on the mill. I then turned it back down to what I considered a reasonable sliding fit.

    Now for the keyway on the motor shaft. In what should have been an easy 10 minute job on the mill became a PITA since my mill was already in bits! The the thread on Precision chucks a few of us talked about planning a job, well here's a classic example of a poorly planned job! I should have made all the mods on the motor BEFORE pulling the mill apart..... Oh well I live and sometimes learn.

    So anyway I ended up doing the keyway on the male and female parts in the same way, I ground a tool in HSS to the required dimensions and used the lathe as a hand operated shaper. The results were pretty good. The only real issue I had was running the tool into a blind end, the shavings tended to collect at the end and reduce the initial tool stroke. The feedrate was incredibly small, about 0.01mm per stroke (0.1mm on the compound set at 6 Deg) so it took a bloody long time. Lubrication was my best friend.

    The two pics show the finished bored hole and keyway on the mill part (female) and the part fitting on the modified motor shaft. You can see the botched job on the motor shaft, not one of my best pieces of work but I learnt many things just with this little exercise which makes little mistakes worth it (as long as it still works!).

    Now for the mounting (adapter) plate for the motor to fit to the mill head.......

    Cheers,


    Simon2012-10-27_12-14-40_263.jpg2012-10-27_12-15-40_575.jpg

  2. #2
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    Simon, having been caught out more than once in a similar way I now have a policy of boring the hole first, then finishing the shaft to suit. I find it easier to control the final size that way, sometimes with abrasives. You can't safely stick your finger with emery paper in a spinning bore.

  3. #3
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    There are two different standards for TEFC motors. The north American NEMA is all imperial. The rest of the world uses a metric ISO standard. Motors of same power differ in all important sizes between these two standards. For a VFD upgrade, I always recommend to replace the existing single phase motor with a 3 phase motor of exactly same standard and frame size. That way everything is an easy drop-in replacement. The motor mount fits, the pulley fits etc. 3 phase motors are the simplest and cheapest motors there are, no reason not to buy new exactly wahat you need. It is usually not worth the time and hassles to convert the machine tool mount, pulley and belt length to adapt to another motor frame, even if a near new motor was available for free.

    In your case, it looks like you replaced an existing metric 1ph motor with a larger, more powerful 3ph motor. Sometimes it is possible to find a motor one power size larger, but in the same frame size. This is done by using a wire with higher temperature rating insulation - this is why such motors cost a little more, and these motors also run hotter. However, it is often worth it as one can get more power in a small frame size, that still is an easy drop-in replacement. Once you want to get more than one power step larger, the motor frame will get larger too, and as you found out one has to modify and often to redesign the interface between motor and machine.

    Chris

  4. #4
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    Thanks Bryan & Chris,

    You are certainly right Chris, I am making things difficult for myself but the motor was cheap, is an extra 1 HP not that I was looking for extra HP but that extra 750W seems to somewhat compensate when using it at very low RPMs. I had been looking for a while on ebay, gumtree and graysonline and finding a 4 pole 1.5Kw, flange mount B5 motor in the same cage size seems to be remote.

    Also, measurements of the existing motor reveals that it is not a "standard size" according to the Baldor table I have. A 19mm shaft indicates a size 80 but some of the other geometries do not equate!

    I also didn't want to buy brand new "off the shelf" due to budget constraints. So this is where I find myself. In any case, the project has forced me to explore other machining options that I had not attempted before. This has provided me with a challenge that is still doable at my level. So far the only modification I have made has been to the input shaft of the mill, being from 19mm to 22mm. Not that big a deal as I could easily (there I go again getting ahead of myself!) make a new one to fit the existing motor, or make a sleeve for the old motor and revert back.
    2012-10-27_16-09-40_68.jpg

    Cheers,

    Simon
    Talking about mods, here's a pic of the flange plate of the motor after I faced off the protruding "locating ring" Since it's not needed and will sit flat on top of the mill head.

  5. #5
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    Ueee is offline Blacksmith, Cabinetmaker, Machinist, Messmaker
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    Good fix on the shaft Simon, i would never be game to weld on a motor shaft. As Bryan said, i do the bore first, for the reasons he said but also it is much easier to test fit a pulley on a motor shaft while the motor is bolted to the lathe, than try to hold the motor and test the fit on the pulley while it is in the lathe.....
    I'm with you on the budget thing, and anyway, if i could get either a: a new motor at $250 or b: a second hand motor at $50 and spend the rest on tools.......it would be option b every time
    1915 17"x50" LeBlond heavy duty Lathe, 24" Queen city shaper, 1970's G Vernier FV.3.TO Universal Mill, 1958 Blohm HFS 6 surface grinder, 1942 Rivett 715 Lathe, 14"x40" Antrac Lathe, Startrite H225 Bandsaw, 1949 Hercus Camelback Drill press, 1947 Holbrook C10 Lathe.

  6. #6
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    Quote Originally Posted by Ueee View Post
    Good fix on the shaft Simon, i would never be game to weld on a motor shaft. As Bryan said, i do the bore first, for the reasons he said but also it is much easier to test fit a pulley on a motor shaft while the motor is bolted to the lathe, than try to hold the motor and test the fit on the pulley while it is in the lathe.....
    I'm with you on the budget thing, and anyway, if i could get either a: a new motor at $250 or b: a second hand motor at $50 and spend the rest on tools.......it would be option b every time
    Thanks Ueee,

    I have been thinking more about the motor adaption and I've almost made up my mind to actually make a new bottom assembly (flange plate) for the motor rather than an adapter plate. The two main critical parts on this are the bearing housing and the lip that the motor cage locates onto. As long as I machine these both at the same time on the one piece, I can't see why I can't do it pretty accurately. I can then drill the same hole pattern that exists in the mill head.The original motor flange assembly will not allow this as there is not enough meat in the cast at the exact point where the holes would need to be drilled.

    It seems like a lot of mucking around, but I'm looking forward to the challenge and I have the steel laying around waiting for a project. Sadly, it will have to wait till after the Cup weekend as I''m off camping on Thursday for 6 days!

    Cheers,

    Simon

  7. #7
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    Well I have managed a small amount of progress on this project. I changed my mind (yet again) and I am making an adapter plate for the motor. Also my Hall effect switch arrived a few days ago. It seems to work a treat, toggles between 0V and 12V with and without a magnetic field and will sink up to 300mA so a direct couple to the LED tacho should work with no additional components. I may need either a pull up or pull down resistor but I will see. I also puchased a couple of rare earth magnets. They are sufficiently strong to switch the hall sensor from about 25mm away which should make mounting the setup quite straight forward.

    Probably the most difficult part will be routing the wires out of the gear head given it's a sealed box with oil in it. I'll probably drill a small hole and have the wires exist in behind the front cover plate.

    2012-11-14_08-21-39_731.jpg

    Cheers,

    Simon

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    Hall sensors are low cost, but the disadvantage of hall sensors around machine tools, is that they need magnets which can attract metal chips. Capacitive sensors do not cost that much more, but these are capable to sense changes in matrial, things like holes or small screw heads in a pulley or flange - or even simply the tooth of a gear.

    If you install the sensor inside an oil filled gear box, make sure its seal and cable is compatible with the oil, as there could be some oil mist. Also consider it could be time consuming to adjust or replace a faulty sensor inside a gear box, especially if you were to feed the wires through a simple small hole sealed with epoxy.

  9. #9
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    Hi Chris,

    You have me thinking now. I have had a look on ebay, almost the same physical package, size and electrical characteristics can be had in a Capacitive sensor. It would certainly make life easier not having to mount a magnet on one of the gears as there is not a huge amount of room in there. My main concern is that in the description it says that just about any object in proximity can trigger it including oil, with hydraulic oil splashing around in the head during use, would it be inclined to false triggering and give erratic results?

    In regards to cabling, I had in mind to tap a 1/8 BSP hole and attach a 6mm push fit air connection (from the inside), then attach the 6mm flexible airline. I would then pass the cable through the airline. Either a cable tie at the end of the airline or a small amount of silicon in the end where the cable comes out should seal the system, essentially using a push fit connector as a cable gland. Removal at a later stage would be reasonably easy and if I wish to re-instate then a simple 1/8 BSP plug would fill the hole.

    Simon

  10. #10
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    Thinking along the same lines as cba, my Capacitive sensor arrived yesterday. eBay Australia: Buy new & used fashion, electronics & home d

    Although it was ordered 5 days after the LED tacho and Hall sensor they have yet to turn up. The plan is to use the drive dogs on the mill spindle it trigger it, that seems to be working "ok" judging by the LED in the back of the unit and the one I rigged up. It is much bigger than I was expecting, 18mmDia(yes is says that in the listing...... I just assumed). The ones I have used before were more like 10mm but didnt have sensitivity adjustment built in.

    Stuart

  11. #11
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    Quote Originally Posted by Stustoys View Post
    Thinking along the same lines as cba, my Capacitive sensor arrived yesterday. eBay Australia: Buy new & used fashion, electronics & home d

    Although it was ordered 5 days after the LED tacho and Hall sensor they have yet to turn up. The plan is to use the drive dogs on the mill spindle it trigger it, that seems to be working "ok" judging by the LED in the back of the unit and the one I rigged up. It is much bigger than I was expecting, 18mmDia(yes is says that in the listing...... I just assumed). The ones I have used before were more like 10mm but didnt have sensitivity adjustment built in.

    Stuart
    Hi Stuart,

    I did notice they were rather large in diameter although there are other ones listed that are smaller but they are about 65mm long. How close can the teeth on the gears be before the sensor cannot resolve the spacing at maximum RPM? Do you think oil splashing around will pose an issue? Perhaps if I install below the oil level and it is always immersed then it may be less an issue but then will air bubbles from agitation cause any issues? I don't know much about these sensors!

    Delivery times..... they are so so hit and miss! Half the time I order stuff and by the time it arrives I've forgotten what I ordered!

    Simon

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    Hi Simon,

    Oops I may have a problem, I was just checking the specs to answer your question....."response freq 100Hz"......Thats not likely to be enough........ I'd thought it said kHz I really must learn to read! I might be able to get it to read off one dog but you cant have a gear at a fixed ratio to the spindle going slow enough with few enough teeth to be less than 100Hz.

    I couldnt find any smaller ones when I had a quick look last night..... might not be an issue it seems

    Does anyone have a spec for the hall senors freq response?

    Stuart

  13. #13
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    Great! turns out I must have had a man look with my specs too. I could swear I read it had a response up to the Khz range but now that I go have a look I can't see anything.

    I may still get away with it even with 2 magnets as I can't see my mill going much over 2000rpm and with 2 magnets that produces a 66hz signal. Surely it can handle that? Thats relay territory!

    Simon

  14. #14
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    Quote Originally Posted by cba_melbourne View Post
    Hall sensors are low cost, but the disadvantage of hall sensors around machine tools, is that they need magnets which can attract metal chips. Capacitive sensors do not cost that much more, but these are capable to sense changes in matrial, things like holes or small screw heads in a pulley or flange - or even simply the tooth of a gear.

    If you install the sensor inside an oil filled gear box, make sure its seal and cable is compatible with the oil, as there could be some oil mist. Also consider it could be time consuming to adjust or replace a faulty sensor inside a gear box, especially if you were to feed the wires through a simple small hole sealed with epoxy.
    Simon, there are many ways to skin a cat.

    I cannot tell you for sure if oil will cause a problem with a capacitive sensor. Probably yes, because even small quantities of water or oil causes capacitive tpe digital caliper scales to misread. But I just notice a blunder, I meant to say Inductive sensors in previous post, not capacitive - sorry for confusion.

    Inductive sensors are cheap, capacitive sensors are expensive. I use inductive sensors on my Hercus 260 lathe and on my X3 mill, and a lightbarrier in my smaller Emco lathe. I would look on ebay for an inductive sensor. There are very cheap ones from China in plastic housing, I use one of these in the Hercus, it senses the tooth of the main spindle mounted gear. For the X3 mill I use an Omron steel sensor (new old stock cheap from eBay), in a 6mm steel tube about 20mm long, it even has a LED inside to indicate reading. This sensor senses the heads of three small M3 screwheads I inserted into circumference of the spindle drive pulley. If you buy inductive sensors, these things mainly matter: the diameter or size of the sensor (where I think smaller in better for this purposes), the sensing distance (which can be anything from 0.5mm to 10mm, where for our purposes maybe 3 mm are ideal), the type of package (plastic is cheap, metal is much better), the type of mount, the output which can be PNP or NPN, the supply voltage (usually anything between 5 and 24V DC will have the sensor work, but check the data sheet). For brand name sensors like OMRON it is easy to download comprehensive data sheets, but you may have to search eBay for a while to find a cheap new old stock sensor.

    As for the mount to your mill, I personally would stay out of the oil filled gearbox. Have the sensor read somewhere accessible the main spindle itself. Much easier access if something is wrong, and no worries about the sensor or its wires or its feed-through being oil resistant/proof. If it is not feasible to stay out of the gearbox, there may be a possibility to put the sensor through a reamed hole in the side of the headstock casting , sealed with o-ring, to read some gear teeth. I am sure you find a way that is rigid, protects the sensor, and is easy to make. Chris

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    Hi Chris
    You owe me $10.34
    I believe it was you that said capacitive in an earlier post in another thread, I thought "oh thats what they are called" and ordered one. No wonder they were bigger than I expected........I was expecting something else lol..... a little knowledge.........
    Should make mounting them much easier, as if I want to use the dogs I either have to be fixed to the quill or move(on a spring maybe) out the way when the quill it down.

    Hi Simon
    Maybe we confused ourselves with the 100kHz measuring range of the tacho?
    Well you wouldnt need magnets with the capacitive, but yes that might be ok, if you can find somewhere to put it, but if you dont have one why buy one? The inductive senors seem to be about 600Hz.

    Stuart

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