Belt Grinder 2x72" and 50x2000 mm

[Boyan Silyavski]

Surprised you have made 3 identical when it's still in prototype. I Prototype lots of stuff and first version nearly always gets changed or improved in some way. Hell with my little router design I see ways to improve or make building easier just about every time I make one.

Surely would have made more sense to build one and test then improve second and test again etc.?

I make one small wooden musical instrument as a side hobby and every now and then i have a whole day or 2 day, when i do sanding all day long. So the faster the better.

I needed a serious sander also for all the steel projects. I have a nice DIY 12" sander but what i am making here is a "grinder" not "sander" meanung it will have very serious surface speed with 120mm OD wheel at he motor spinning at 300rpm / 4 pole 3 phase 1420 rpm motor with VFD/

The other thing is that i have a knife project where i am at the stage of needing the grinder. I made the prototypes using small bench sander but as i am using one of the bad ass tool steels its very difficult to grind with belt sander to shape.

Plus as i found the typical paradox- " To make a grinder you need a grinder"


The design is more or less clear, a lot of DIY copies of the KMG grinder with plans in internet. The KMG is also a copy of an older machine, so i understood while looking at the plans that these are not just copies, but a concept proven through the years of abuse, that works. So i directly started building on it knowing that it will work.

Jeff needed a grinder, all of the above+ that they sell material in 6m, packets of 10, etc., so doing 3 machines at once made sense to me.


The next step from here is next week machine is ready, i continue my knife project and while having actual experience using it for knifes, i will meditate upon a much more brave design.


In fact Dean next step would be directly producing them by the 10, cause of the fixtures on the mill and the lathe is makes sense to make 10 pieces at once.

Needless to say that the experience from building CNCs till the moment helped in in such way that the only error till now was just 1 spot weld not at the right place.

[JAZZCNC]

Needless to say that the experience from building CNCs till the moment helped in in such way that the only error till now was just 1 spot weld not at the right place.

Erm I'd say the error was the spot welding.! . . . Doesn't look good or strong. Great for proto typing but not for real thing. It needs proper welds to give it credabilty as industrial strength tool.!

[Boyan Silyavski]

Erm I'd say the error was the spot welding.! . . . Doesn't look good or strong. Great for proto typing but not for real thing. It needs proper welds to give it credabilty as industrial strength tool.!

I feel that too. Nothing will go out from here that could be broken by hand and a hammer. And you are absolutely right, now i could take the hammer and certain pieces could be broken apart for seconds. When all belts are spinning and i see everything is working correctly there would be proper welds where necessary. The other thing i will do is blacken all bare steel heating it with the gas torch to 315C.

[toomast]

...The other thing i will do is blacken all bare steel heating it with the gas torch to 315C.

What do you mean by that?

[Boyan Silyavski]

What do you mean by that?

There is a way to treat low carb steel / mild steel/ . You heat it at 315C, keep it there a couple of minutes, thin oxide layer forms in black, then you brush it with some oil and it goes even blacker. Result is much tougher part, even if not a high carbon steel. Black oxide layer is not real anti rust though it gives some protection


bellow you could compare bare cold drawn steel bar and treated.

[toomast]

There is a way to treat low carb steel / mild steel/ . You heat it at 315C, keep it there a couple of minutes, thin oxide layer forms in black, then you brush it with some oil and it goes even blacker. Result is much tougher part, even if not a high carbon steel. Black oxide layer is not real anti rust though it gives some protection


bellow you could compare bare cold drawn steel bar and treated.

Interesting. What is the "official" name of this process?

[JAZZCNC]

When all belts are spinning and i see everything is working correctly there would be proper welds where necessary.

Well next time do your self a favor and grind Chamfers on the edges will give stronger nicer welds. Created your self lot of grinding now or ugly proud welds.

[Boyan Silyavski]

Well next time do your self a favor and grind Chamfers on the edges will give stronger nicer welds. Created your self lot of grinding now or ugly proud welds.

Where was important and i was sure that will not need to break it apart its done like you say. The machine is still not finished.

[njhussey]

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!

[Boyan Silyavski]

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.