Building a Slow Speed Grinder (Carbide)

  1. mm289 Member

    Messages:
    511
    Dover, Kent
    You know how you start one project and it just seems to spawn multiple others.......:whistle:

    So as part of rebuilding the Biax scrapers I need a way of sharpening the carbide blades. When we did the scraping course Pete brought along a lovely little grinder he had made from a Rexon disc sander which he could mount abrasive discs too.

    So the plan is too make something similar to that, and also along the lines of this one done by Build something cool.


    I have a selection of motors one of which is a lovely little 90w 3 phase unit complete with inverter that was used for opening security barriers. Have removed the reduction gearbox and with the VFD running at 20Hz the spindle speed is about 300rpm which is perfect for the grinder so that gets me away from having to fiddle with pulley sizes etc.

    Now the motor might not be man enough as its only 90w but it will be running at full torque and only spinning a 150mm disc so we will see.....:dontknow:

    The big design question for me is whether to mount the disc straight onto the motor in an arrangement like this
    upload_2020-1-1_12-44-5.png

    As I don't need pulleys for gearing or speed control I could do this. My concern is the motor shaft is only 4.5mm so potentially I could be putting a lot of load on the shaft and the spindle mount.

    The alternative is to use a layshaft? in pillow bearings run off drive belts like this.

    upload_2020-1-1_12-46-22.png

    Bit more complicated to set up and would need to source pillow bearings, pulleys and belt but takes a lot of load off the motor spindle and the pillow bearings would be much more able to support any axial load.

    So, any thoughts from the collective on which way you'd go?:waving:

    Also will need to turn the abrasive disc mounting plate down from some aluminium, so if anyone has any offcuts of ally maybe 10mm thick and big enough to turn a 150mm disc then give me a shout:clapping:

    Cheers,

    MM
     
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  2. gaz1

    gaz1 Forum Supporter

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  3. daleyd

    daleyd Member

    Messages:
    6,118
    Location:
    Wrexham, North Wales
    Interesting! I’ve got a couple of small 3 phase motors that have a reduction gearbox on which puts the speed down to about 400 rpm at 50 hz. I’ve been wondering what use to put them to, this might be an inspiration!
     
  4. pressbrake1

    pressbrake1 Member

    Messages:
    1,578
    essex england
    Op just wants a cbn wheel to get his 5deg neg rake
     
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  5. Shox Dr

    Shox Dr Chief Engineer to Carlos Fandango

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    14,057
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    East Yorkshire
    The motor might require force cooling running at less than 50% speed, at least another or bigger fan
     
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  6. brightspark

    brightspark Member

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    27,427
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    yarm
    4.5mm shaft not very substantial on a 6inch disk and would flex very easy. wont do the bearings on motor any good neither
     
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  7. Pete.

    Pete. Member

    Messages:
    8,589
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    Kent, UK
    My rexon grinder that everyone used at the class just has a single normal ball bearing held in a plastic housing. It uses a tiny open frame motor driving a big plastic pulley on the back of the wheel shaft and the drive belt is just a big o-ring.

    rexoninside.jpg
     
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  8. Spark plug

    Spark plug Member

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    3,403
    Location:
    Durham, England
    Here is a pic of the grinder I built, the pictures terrible I had to crop it out the background of another pic. It’s unfinished in this pic but you can see I have used the disc backing plate as the pulley to achieve the required gearing.
    5E42B006-591A-4ECD-95FC-D11625F2416B.jpeg
     
  9. mm289 Member

    Messages:
    511
    Dover, Kent
    Thanks for the input chaps.

    Will keep an eye on this, although the duty cycle will be quite low as it only takes a few minutes to sharpen a carbide so hopefully won't be an issue.

    Yep, thats was my concern, think I will go with a layshaft/seperate pulley approach to reduce this load.

    Thats interesting Pete, that motor is tiny:o - hopefully the one from the gate opener should be more than man enough then. I need to build a frame to hold it all together so am thinking I may as well look at the layshaft approach anyway.

    Thats a neat idea, not sure my machining skills are up to that:laughing: - I like how you've used the front plat to mount the motor and the backing plate:thumbup:

    So looks like the layshaft approach is the winner. Now just need to find some lumps of ally to make up the backing plate and pulley from.....

    Cheers,

    MM
     
  10. pressbrake1

    pressbrake1 Member

    Messages:
    1,578
    essex england
    Id go 25mm bore pillow bearings and get some mass in it.
    Heavier and more rigid better the finish
     
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  11. brightspark

    brightspark Member

    Messages:
    27,427
    Location:
    yarm
    made this one years ago brilliant for sharpening hss lathe tools etc. have 3 screw on plates for it using diffent abrasives
     
    • disk sander.JPG
  12. Pete.

    Pete. Member

    Messages:
    8,589
    Location:
    Kent, UK
    If it's solely for sharpening scrapers you need very little power. A 1500 grit diamond lapping disk at 3-400rpm is ideal.
     
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  13. mm289 Member

    Messages:
    511
    Dover, Kent
    Starting to collect all the bits for making this now, got the slug of 6" ally, just need to slice it down, will use pillow bearings with some of the bright steel rod I have as a shaft.

    Will probably make the mounting disc an interference fit onto the shaft up against a shoulder and then use a bolt/washer to hold on the lapping disk and act as a mechanical fix for the mouting disk as well.

    Also need to figure out if I can use a simple 2 pole on off switch with the VFD rather than a 3 wire design with seperate on and off switch's.....:whistle:
    upload_2020-1-22_10-50-33.jpeg

    Time to go off and update the drawings:D

    Cheers,

    MM
     
  14. Matthew Tinker Member

    Messages:
    18
    Location:
    93300 Aubervilliers France
    MM,
    Have you seen Stefan Gotteswinter's low speed grinder? He uses two locating dowels and magnets to hold the diamond wheels on!

    Regards, Matthew
     
  15. mm289 Member

    Messages:
    511
    Dover, Kent
    Hay Matthew how are you? Long time since a cold workshop in Sussex :clapping:

    I Haven't seen that one so will go and have a squint now,

    Cordialement

    Paul.:thumbup:
     
  16. Matthew Tinker Member

    Messages:
    18
    Location:
    93300 Aubervilliers France
    Hi Paul! Now I know what name your using on this forum! In all fairness to Andrew, his workshop wasn't cold, especially where we were! I'm getting used to being retired, which means I have less time than ever! I think Stephan's solution to swapping diamond disks is really ingenious, what say you?
    Cheers mate!
     
  17. gaz1

    gaz1 Forum Supporter

    Messages:
    8,954
    Location:
    westyorkshire
    i actually like it however is it a viable way to buy them than a longer lasting diamond disc instead
     
  18. Matthew Tinker Member

    Messages:
    18
    Location:
    93300 Aubervilliers France
    My personal experience of those disks is very positive, cheap too!. I have been using them for a couple of tears in a low speed bench grinder with what was meant to be a water bath. I've been running them in a Paraffin (US Kerosene) bath, keeps them nice and clean!

    Regards, Matthew
     
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  19. slim_boy_fat

    slim_boy_fat Forum Supporter

    Link, please?
     
  20. Matthew Tinker Member

    Messages:
    18
    Location:
    93300 Aubervilliers France
    To what?
     
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