Recommendation? Motor for 2x72 belt grinder?

Discussion in 'Shop Talk - BladeSmith Questions and Answers' started by Arran Gneist, Dec 10, 2017.

  1. Arran Gneist

    Arran Gneist

    Dec 10, 2017
    so for a few months I've been planning and designing a simple 2x72 grinder as an upgrade to that 1x30 that doesn't even turn on half the time. Obviously the first step was to find a motor to run it all with and I was looking in the 1-1.5hp range, my confusion comes from two motors I've found from the same seller which appear to be the exact same except that one is 1.5hp as opposed to just 1, only the 1hp motor is about $100 more. So since I don't know much about electronics, I was just wondering what the difference is between these motors or if they're good at all. If someone could explain this to me or maybe even find a better motor for the same price it would be amazing. I am in australia btw.
    My plan is to mount the drive wheel directly onto the motor and I'm just running it off of household power so single phase is the only option to keep lower costs
    Last edited: Dec 10, 2017
  2. Britt_Askew

    Britt_Askew Dealer / Materials Provider Knifemaker / Craftsman / Service Provider Dealer / Materials Provider

    Dec 9, 2010
    You will need to give more info for an answer. as it is now the only thing I can tell you is one motor is 1hp and one is 1.5hp and one motor cost more. Are the motors single phase or 3 phase? what rpm ? what size is the shaft? tefc or open? etc.. There should be a plate on the motor with that info,posting a picture of the plate will help. Do you want your grinder to have variable speed?
    Justin Schmidt likes this.
  3. Justin Schmidt

    Justin Schmidt

    Feb 18, 2016
    You need a 1.5hp 3phase 56c faced, tefc (totally enclosed fan cooled) motor. But you should post a pic of the name plate to get more info
  4. JTknives

    JTknives Blade Heat Treating Knifemaker / Craftsman / Service Provider

    Jun 11, 2006
    Not necessarily. He did not say if he was going to use a VFD or not. If your not going to use a VFD then you need a single phase motor.
    Nick Dunham and Justin Schmidt like this.
  5. bmilleker

    bmilleker Gold Member Gold Member

    Nov 26, 2012
    Depending on your grinder design, 56C is also not 100% required.
  6. Drew Riley

    Drew Riley Riley Knife and Tool Knifemaker / Craftsman / Service Provider

    Oct 17, 2007
    Gonna need a bit more info to give any reasonable recommendations. Do you have a link to the two motors you're looking at?

    Are you looking for variable speed? Using a step pulley? What kind of grinder are you putting it on? Is it going to be direct drive or belt driven? What kind of power source do you have?
    Justin Schmidt likes this.
  7. Justin Schmidt

    Justin Schmidt

    Feb 18, 2016
    True was just figuring that's the route he was going.
  8. timgunn1962


    Apr 1, 2009
    In Oz, you'll probably be looking at Metric IEC-frame motors. The US uses NEMA-frame motors and restricting yourself to these in a Metric country is likely to make life unnecessarily difficult/expensive.

    IEC motor frame sizes have numbers which are the mounting surface-to-shaft centreline measurement in mm for foot-mounted motors. 90-frame motors are what most of the 2 x 72 (ish) grinders built by guys in the UK use. There are short (90S), medium (90M) and long (90L) versions. The mounting hole centres differ slightly with length on the foot-mount versions, but this is not usually a problem if building from scratch.

    The Drive-End casing is usually exchangeable for either a face-mount (tapped holes in the motor end casing) or flange-mount (clearance holes in a larger-diameter flange on the motor) version. As a rule, you specify what you want and the motor supplier fits the appropriate part.

    I think Oz uses 50 Hz mains (the US uses 60 Hz). 50 cycles/sec times 60 seconds gives 3000 cycles/min. Under load, there will be "slip" and the motor will run at a little under the synchronous speed.

    Motors can have different pole counts. Each pair of poles requires one cycle per revolution.

    A 2-pole motor at 50 Hz (3000 cycles/min) will run at a synchronous speed of 3000 RPM and a rated speed of "around" 2900 RPM.

    A 4-pole motor at 50 Hz (3000 cycles/min) will run at a synchronous speed of 1500 RPM and a rated speed of "around" 1450 RPM.

    A 6-pole motor at 50 Hz (3000 cycles/min) will run at a synchronous speed of 1000 RPM and a rated speed of "around" 960 RPM.

    If you are running a single-phase motor, you are stuck with the plated speed of your motor.

    If you are running a 3-phase motor on 3-phase mains power, you are also stuck with the plated speed of your motor.

    If you are running a 3-phase motor on power provided by a Variable-Frequency Drive, you can vary the frequency and with it the motor speed.

    VFDs are readily available which take a single-phase supply and output 3-phase variable-frequency power to a motor.

    3-phase motors are usually able to be connected in Star (Wye) or in Delta. Below "about" 3 kW, most are able to be run on 230V Delta or 400V Star.

    If you have 230V single-phase mains and use a VFD, your motor will need to be connected in 230V Delta.

    Without considerably more information, it is difficult to make any firm recommendation. Some pointers:

    For different speeds, you can either go for a fixed-speed motor and a multi-step pulley system, or go for a motor and VFD.

    With step-pulleys, you need a shaft onto which the drive wheel is mounted, bearing for the shaft, a structure onto which to mount the bearings, a step-pulley on the shaft, a drive belt, a step-pulley on the motor shaft and a system for aligning the pulleys and tensioning the belt.

    With a motor and VFD, the drive wheel can be mounted directly onto the motor shaft (24mm diameter on a 90-frame motor). This saves the cost of the separate shaft, bearings, step-pulleys and drive belt. It also allows the use of a face- or flange-mount motor, which can greatly simplify the design by eliminating many of the potential alignment issues. The cost saving on all the avoided gubbins probably won't cover the cost of a VFD, but it'll go quite a long way towards doing so.

    I don't think there are many on here who would not regard the direct-drive with VFD as the better system, all else being equal.

    The IEC standards effectively give standard frame sizes for different motor power outputs and pole counts. It is worth noting that there are some "compact" motors appearing that are one size down from the "standard" frame for the power output & pole count. At present, I'd avoid these because they tend not to be recommended for use with VFDs because the smaller frame cannot get the heat away as well when run at low speeds and high torque/current.

    A standard 1.5 kW (2 HP), 4-pole motor or a 2.2 kW (3 HP) 2-pole motor will have a 90-frame. The rule-of-thumb for belt grinder motor power in industry is 1 HP per inch of belt width (750W per 25mm).

    Standard industrial motors tend to be designed for a maximum continuous mechanical speed of 3600 RPM to cover 2-pole motors running on 60 Hz mains in those parts of the world that use it. The actual plated speed of the motor will depend on the number of poles in the windings and the mains frequency of the country in which it is sold.

    Either a 2-pole motor or a 4-pole motor can therefore safely run up to 3600 RPM continuously when powered from a VFD with an output frequency of 60 Hz and 120 Hz respectively.

    Pretty much any VFD will run a motor down to 10 Hz. That's 600 RPM for the 2-pole and 300 RPM for the 4-pole.

    In my experience, it's nice to have the lower speed of the 4-pole available for sharpening.

    If you are on a really tight budget, a single-phase, 4-pole, 80-frame motor would get you started and it could be swapped for a 3-phase, 4-pole, 80-frame motor and VFD when funds allow.

    Before you design, check out belt availability. If you can easily get metric belts but not inch ones locally, it's worth making the tooling arm a little longer so that you can use 50 x 2000 belts as well. Just make sure the tooling arm doesn't hit the motor.
  9. Arran Gneist

    Arran Gneist

    Dec 10, 2017
    Im not too worried about having variable speed as I'm trying to keep the costs low.
  10. Arran Gneist

    Arran Gneist

    Dec 10, 2017
    Yeah sorry, I've now linked the two motors in the original post. I'm not looking for variable speed, it will be direct drive and it'll run off of household power so single phase
  11. Drew Riley

    Drew Riley Riley Knife and Tool Knifemaker / Craftsman / Service Provider

    Oct 17, 2007
    Not sure of the price discrepancy between the two motors, as they look to be identical other than the hp (unless I'm missing something).
    Given the two choices ONLY, I'd go with the 1.5hp for sure. That said...

    If it were ME, and I had a limited budget and motor selection, I'd probably try to find a 4 pole 1400RPM motor around 1.5-2hp instead of the 2800rpm, especially if you plan on a direct drive grinder with a 4" drive wheel or bigger. Once you start getting into finer belt grits, it becomes hard to keep up with a faster motor without burning blades, handle material, etc... If I could only pick fast or slow for a machine, I'd probably pick slow(er) 9x out of 10. You of course have the option of going the step pulley route, which will give you more versatility yet, but by the time you pay for bearings, shaft, bets, pulleys, etc... you might have just been better off paying a little bit more for a VFD and a 3 phase motor.

    I poked around your Australian eBay a bit, and it looks like you've got to spend some real money to get more than a 1hp 3 phase motor, but given the prices and options, you MIGHT consider just puttin a 1hp motor with a VFD, direct drive on your grinder, and seeing how that works for you. Obviously 1.5-2hp is preferred, but if I had the choice between a 1hp variable speed set up and a 2hp fixed at 2800 rpm, I'd get the 1hp for sure, with maybe a 2hp VFD to run it (these can be had relatively cheap from china), and then maybe keep an eye out for a bigger 3 phase motor in the future.

    Whatever you end up with, just keep in mind that your drive wheels (or pulleys) will have to fit on the shaft, so make sure you have those bore sizes available, or the capability to ream the holes if necessary.
    Arran Gneist likes this.
  12. Jesenius


    Feb 16, 2016
    He can use 3 phase motor with 1 phase grid by using simple solution with capacitors.
    Here is schematic and here is capacitors calculate. I think motors You are using in USA with grinders are 3 phase motor modified by this way. From diagram You can calculate for 2 HP motor it is cca 210 uF (need few tests around this capacity). This is useful when he think about VFD in near (or not so near) future.

    EDIT: here is something about it in english
    olymon likes this.
  13. txhobby


    Aug 1, 2019
    I am wanting to make a 2x72 grinder as well and I have a DC treadmill motor that is 90 volts, 30 amps, 4000 rpm, 4.0 hp. Can I use this for a grinder or is it to big of a motor?
  14. Stacy E. Apelt - Bladesmith

    Stacy E. Apelt - Bladesmith ilmarinen - MODERATOR Moderator Knifemaker / Craftsman / Service Provider

    Aug 20, 2004
    Jesenius - It isn't all that simple. A static phase converter is probably more cost (and less effective) than a Chinese VFD.

    txhobby - That will not really make a good grinder.

    Arrran - I only see a $13 difference between the motors, with the 1HP being cheaper. The difference may be merely the demand, or he got a better deal on a palate of 1.5HP motors.

    That said, I would go with the 1.5HP motor.

    Personally, I prefer a 4 pole motor, but there are many grinders made with a lower cost 2 pole motor.

    EVERYBODY - This is a two year old thread.
    Last edited: Aug 13, 2019
  15. Britt_Askew

    Britt_Askew Dealer / Materials Provider Knifemaker / Craftsman / Service Provider Dealer / Materials Provider

    Dec 9, 2010
    Problem with treadmill motors is they are not sealed from dust and chances are they wont last long at all because metal dust causing a short. You would be better to find a TEFC motor
  16. Rsq

    Rsq Basic Member Basic Member

    Aug 7, 2011
    I have had great luck with grizzly motors. I have a few for different purposes, and find them to be a very good value with respect to simple, trouble free operation and long service life. I have a G2532 on my belt grinder, and while I'm not yet great at using the machine I made (I'm going to reconfigure it into a surface grinder anyway. I suck and grinding by hand), it's definitely not the motor holding me back. It may just be that I use a light touch because I mostly use it for regrinding finished knives and focus on keeping things cool, but I have found 1hp to be plenty. I'm sure more is better, but 1hp isn't that easy to stall, especially when you step it down to grind slower than 1000 sfpm.

    I use mine with stepped pulleys for speed control, and it does what it's supposed to do without complaint. I like a belt drive because I can isolate the motor from the belts, which means I can be a little sloppy with water spraying from the belts without worrying about rusting my drive shaft or bearings. I like grinding wet for respiratory safety, and even if it says TEFC, it's obviously not a great idea to get any motor wet. If you wanted to drive your belts directly from the motor, it would be easy enough to control the speed by having a few different diameter drive wheels.

    It's not exactly the answer you were looking for, but I've had baaaad luck with cheap tools, and every time I try to save money by buying something Chinese or off-label on ebay, I end up re-proving that only a rich man can afford cheap tools. A reliable, variable speed motor that has that much power for $100 just sounds too good to be true. Start with best tools you can afford that you are already sure can do the job and you'll save yourself a lot of trouble and money in the long run.

    I just noticed how old this post is. I'm leaving my response anyway.
    Fodderwing likes this.

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