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  1. #21
    Instead of heating and quenching why don't you chemically black the steel? It doesn't add any hardening but does add a bit of rustproofing, not much but some!


  2. #22
    Quote Originally Posted by njhussey View Post
    Instead of heating and quenching why don't you chemically black the steel? It doesn't add any hardening but does add a bit of rustproofing, not much but some!

    Cause it seems a bit expensive to buy the kit for blackening at the moment. The torch is easy,cheap and toughens the material. No quenching, air cooling. But that would be the next logical step

    Now about Power.
    Motor power. I was lead to believe / from forums/ that you need at least 1hp per inch belt, so i decided the machine to have 1.5kw motor. Mean while i had
    made my self a 12" sander. 3 phase 0.75kw motor that run on 230VAC using capacitor, no VFD. The disc was easy to stop. See video below. So i decided to invest in a VFd cause i wanted to run it from 0-3000RPM depends what i am doing. I connected it yesterday. Man, i could not stop it in any way, its brutally strong combo. And only 0.75kw.

    So i am starting to believe there is some misconception here. Cause belt is not wider than portion of disc i used for grinding yesterday.And as i said, i couldnt stop it pushing hard using steel bar. So i started to think thats the pulley mass is to blame. while all pulleys i designed are very much big bored and so they are light, the motor wheel is a whopping 1.6kg at 120mm. I started redrawing it recessed in the middle but could not lower the mass less than 1.1kg. So i went further and made all walls 8mm only. Weight dropped to 680g.

    So in short i start to think that this could be driven using 0.75kw motor combined with VFD instead of the over sized 1.5kw, when pulleys weight is made minimum. yet to prove on next machine. of course i will see how much i need that low revs where is a small loss of power

    Below video of the 0.75kw motor when runs on capacitor on 2 phase line

    And video of same motor that runs on VFD again 2 phase line. I could not stop it pushing very hard against it a 40x10mm steel bar.Trying seriously to abuse it . The disc itself is a very thick diamond cut disc and the blue sanding disc thats glued, is a 60 grit zirconia. So you judge what a beast it is now with the VFD connected.

    Its very interesting to me if sb has a similar machine, 12" disc sander using 1400RPM mono phase motor, no VFD and if it could be stopped pushing hard against it?????

    PS. Black lines on disc are from sharpening my pencils. Disc is new otherwise. First i run it at half speed and then at full speed at 100hz. It was scary to hold thebar with only one hand.

    project 1 , 2, Dust Shoe ...

  3. #23
    Boyan I think you have answered your own question you can't compare using a 3 phase motor on single phase with caps against the VFD. You won't get the torque with the caps especially if they are not big enough.
    The more you know, The better you know, How little you know

  4. #24
    Have almost finished the 3 grinders. There were some details that slowed the process, now more or less everything is clear.

    Welding the motor mounts, trying to keep things on one same plane:
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    Grinding away the spot welds, drilling holes, making stronger weld...only on one of them. Too much works and then i had to make it flat. So i decided to stop there and the other 2 only were reinforced where necessary.
    Next time as i know now which weld first where and how, i will just do all pproperly.
    Click image for larger version. 

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    Then some painting:
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    Too much paint mixed at once? No problem some but not all that was upgraded at home:
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    Now the blackening, heating the steel at around 300C. Then brushed in olive oil when cooled down. The oil made them even darker after some time. Very happy with the result, last 2 pictures.
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    Now why its called prototype, and why as Dean said it is good to be done one by one. I knew it could happen and was sure that i have avoided it i have not designed the future 2 attachments, it happens that belt would interfere with one of them
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    This is what took me most time. Deciding on the spring, finding the proper spring, tension, length and how to fit it on the machine correctly so it willnot mess with the belt and the future attachments. Main problem being is- this is the shortest spring i was able to find at that rating.
    I finally was happy with the result, so version .01 was born On right picture is Jeffs grinder, we left his motor as he does not need it for making knifes so no future attachments.
    Click image for larger version. 

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    Finally mounted the handle, at the end it happens upper side of the arm is best and easiest. Then the VFD and motor. Cut some scrap belt and started the machine to program the VFD. Boom. The fuse goes down at home. Again, and again. Half day later after some research i went to the conclusion -"leak current" from input capacitor filter. Bloody hell, so i started reading the manual. Good old Toshiba. have made a switch on the VFD that can deal with that changing the capacitance. clicked the switch and all is working.

    No vibrations. Super quiet. Not so when i mounted the old belt which is quite bumpy, the connection where is spliced. The belt tracked easily though but makes some noise.But as machine is heavy even that introduces no vibrations.

    I am quite happy. Worked from first time. Tracking is perfect, speed is right. I dont see that machine without speed control though, i can not stress enough on that. Did some test grinding today and is super important to control exact speed at every moment.

    The other important detail is that the 2 rollers at the front are fixed by spacers and shoulder bolts. So these 2 holes were drilled on the mill and hand tapped. That could not be. The must be machine tapped. hand tapping M10 is you could make it straight or not. Had to redo them a couple of times. As i have no M10 machine tap i bought yesterday. Next time will make tapping fixture similar to drilling holder, where shaft passes through a bearing and use driver to spin the shaft, so its clutch does the job of releasing when too much resistance.Though if needed, may be its the time for tapping head.

    The video is a bit shaky but you could get idea what happens
    project 1 , 2, Dust Shoe ...

  5. The Following 2 Users Say Thank You to Boyan Silyavski For This Useful Post:

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