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Gerhard Gerber

2x72 Belt Grinder plans

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The rule of thumb is ~1kW into the motor for every horsepower that comes out of it so your 1.5kW would probably be closer to 1.5hp, maybe a bit more on a good day.  More would be nice to have, but 1.5kW will make a lot of knives if the extra money just isn't there.

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That's what happens when I use an online conversion tool to translate Kw to HP...  :o  Is there a direct correlation, other than both being units of power?  I was thinking 1.5Kw output, but I can certainly see if that's the input power required instead the output is necessarily lower by quite a bit.  

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19 hours ago, Alan Longmire said:

That's what happens when I use an online conversion tool to translate Kw to HP...  :o  Is there a direct correlation, other than both being units of power?  I was thinking 1.5Kw output, but I can certainly see if that's the input power required instead the output is necessarily lower by quite a bit.  

Yeah, they rate the motor on what it draws electrically, not what it produces mechanically.  Induction motors in this size range are often around 75% efficient which means it takes 933W to produce the 746W out (1hp).  Hence the 1kW/hp rule of thumb.

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It doesn't look like that is not a TEFC (Totally Enclosed Fan Cooled) motor.  In a grinding environment it probably will not last long.

Check out the Motors and VFDs page on my web site.

Let me know if I can help you.  I prefer e-mail.

 

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my motor is open and right next to the contact wheel and lower than my platen which i use almost exclusively never had a problem also i am running a 1.5 which is fine for most things if i spent more time making knives i would upgrade to a 2 or even a 3 if i was doing a lot of stock removal haven't changed my belt speed in 14 years might save me some hand sanding if i did

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Strange question I guess.......

It seems I have a choice between profile cutting (with 0.5mm tolerance), or laser cutting which is supposedly very accurate and much neater but might be expensive....

I'm waiting for quotes.....

I've asked for either 5mm or 6mm mild steel plate, is that thick enough? 

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Laser cut if possible, and go for 9mm plate minimum.  13mm would be even better.  The 5mm will bend under the tension, and the 6mm might unless you weld gussets on it, which will then warp it.  

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Thanks Alan, acted on advice from my friend with the engineering shop.........should've asked here before I requested the quotes :wacko: 

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New problem, the drawings are not on scale, and no scale indicated.

Both companies I contacted got back to me on the matter.

You could guess, but then you might end up with a standard belt being too long  or too short.......?

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Did you send them the .dxf files, or the pdf's?  They should be able to read the .dxf's into just about any CAD software and they will come through in full scale.  They may just have to convert from imperial to metric or vice-versa.

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If someone only has access to single phase power, it it feasible to use a stepper motor with a high rpm and a pulse controller to control the speed of the grinder?

Edited by Wesley Alberson

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4 hours ago, Wesley Alberson said:

If someone only has access to single phase power, it it feasible to use a stepper motor with a high rpm and a pulse controller to control the speed of the grinder?

That seems a strange way to go about it to me.  Would that be smooth?

  VFDs are the way to go. Single phase input, three-phase output.

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9 hours ago, Alan Longmire said:

That seems a strange way to go about it to me.  Would that be smooth?

  VFDs are the way to go. Single phase input, three-phase output.

Ah, ok. I thought all this time that you need 3 phase input for a VFD, and the VFD simply changed the frequency. What is the most common VFD that people buy for this setup? After a quick search I found this: https://www.wolfautomation.com/index.php/catalog/product/view/id/8663/s/ac-drive-3hp-12a/?gclid=EAIaIQobChMIupfhm6LK2QIVjVcNCh0KsAZdEAYYASABEgJ6Q_D_BwE

I made my grinder with a variable pulley system, and I'm not really happy with it, everything is too fast. That being said, I am currently powering my shop with a drop cord and I can only run 120V power to my shop. As long as I use fresh belts, wood doesn't burn and steel doesn't overheat too fast. 

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16 hours ago, Alex Middleton said:

Did you send them the .dxf files, or the pdf's?  They should be able to read the .dxf's into just about any CAD software and they will come through in full scale.  They may just have to convert from imperial to metric or vice-versa.

 

16 hours ago, JJ Simon said:

I just had these cut.
They are on scale.
You need to use the CAD files.

Very strange, I did send them the CAD files because I assume that's the input of the cutter, both companies came back and told me the parts are very small, like the main horizontal part on their software is 8cm long.

Anyway, I found another supplier in South Africa that sells grinders in kit form, the frame in the kit even with transport is cheaper than I can have it cut locally.

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8 hours ago, Wesley Alberson said:

Ah, ok. I thought all this time that you need 3 phase input for a VFD, and the VFD simply changed the frequency. What is the most common VFD that people buy for this setup? After a quick search I found this: https://www.wolfautomation.com/index.php/catalog/product/view/id/8663/s/ac-drive-3hp-12a/?gclid=EAIaIQobChMIupfhm6LK2QIVjVcNCh0KsAZdEAYYASABEgJ6Q_D_BwE

I made my grinder with a variable pulley system, and I'm not really happy with it, everything is too fast. That being said, I am currently powering my shop with a drop cord and I can only run 120V power to my shop. As long as I use fresh belts, wood doesn't burn and steel doesn't overheat too fast. 

Look back in this thread to find a link to Wayne Coe's site.  He sells a couple of different models for different horsepower requirements.

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My one concern is I'm now buying a VSD instead of a VFD.........I'm hoping my purchase is just described with a less accurate acronym! 

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On 2/8/2018 at 10:34 AM, Alan Longmire said:

I'll just put them here on the forum as well. in all three configs, plus the assembly photo, so there!

assems.jpgassem11s.jpg

The drawings in one .zip file: drawings1a.zip

 

Individually: part1.DXF Part2.DXF Part3.DXF Part4.DXF Part5.DXF Part7.DXF Part8.DXF part9.DXF baseplate.DXF  NOTE: There is no part 6.  don't ask for it!

and finally, the drawing of all parts on a single sheet of steel: onepiece.zip

 

These are the plans I used to build my grinder but I welded my parts instead of bolts. I love this grinder! I also modified it to run with pillow blocks and a belt because I don’t have a vfd yet. I had my parts cut on a plasma table with no holes except the large one for the motor so I can add a direct drive at a later date. I absolutely love my grinder even though it only runs at one speed.

Edited by Aaron Money

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Now there is a DIY I could definitely consider.

I would  think about a solid bar bolted to the base plate at the bottom of the two panels with them bolted to it.

I also think it would need a spring on the moveable arm as a tensioner.

Edited by Vern Wimmer

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13 hours ago, Vern Wimmer said:

Now there is a DIY I could definitely consider.

I would  think about a solid bar bolted to the base plate at the bottom of the two panels with them bolted to it.

I also think it would need a spring on the moveable arm as a tensioner.

I tried using a spring but it seemed to develop a kind of bounce to it which was very irritating so I used a car boot gas lift from eBay 

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On 3/1/2018 at 3:47 PM, Gerhard said:

My one concern is I'm now buying a VSD instead of a VFD.........I'm hoping my purchase is just described with a less accurate acronym! 

hey Gerhard,

 

VFD, VSD, same thing. One stands for Variable Frequency Drive, the other is Variable Speed Drive. they both do the same thing in the same way, by varying the frequency out to the motor.

My day job is as an Electrical Technician, and i use these things every day. too bad that with what they cost landed here in Zim, i could never afford one. a 1.5kW single phase in costs over $1100 US. 

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Gerhard I have a complete set of plans in DXF format that are to scale designed to be either plasma or laser cut

The difference being I sized bolt holes for drilling and tapping to eliminate as many nuts and and bolts as possible

 

If you still need plans let me know and I can send them to you.

belt grinder-002.jpg

Edited by JeffM
add an image

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