# Variable speed 9" disc grinder build



## melsdad (Aug 21, 2014)

Not exactly project of the day. I have been working on this for about a month off and on. This will be a 2 h.p. 3 phase  powered machine run off of a VFD.


I will be using the drive that powers my 2x72" belt grinder. I will simply plug in the machine I want to run into the drive.


The hub of the machine will be aluminum  with neodynium magnets pressed in to hold steel plates for quick change out of paper grits.





Stay tunned I will be adding pictures and get this caught up to were the project is now. This machine will also have a quick detach tilting work rest.


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## melsdad (Aug 21, 2014)

The magnets are ordered so I will get to that shortly.

Lets start with the clamp arm posts. These Will be attached to the base plate and support the work rest. They are made of 2"x2" 1018 cold roll. I am machining them in pairs so they match each other perfectly.



Here I am tapping the holes for the table arm clamps



Here they are complete.  I didn't get pictures of making the caps for the posts but you get the idea.


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## melsdad (Aug 21, 2014)

The arms for the table were also machined inpairs and surface ground so they are identical. The holes you see are reamed for a slip fit for a .500 dowel pin to locate on the rotary table. 



I reamed a . 500 hole in a piece of scrap aluminum to use as a fixture plate on the rotary table. There is also a hole for a s.h.c.s to hold it down to the table




Now I can place the arms on the plate and they will repeat easily.

Roughed in.



Finish pass



Radius complete


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## mattthemuppet2 (Aug 21, 2014)

that is some beautiful machining work Brian, looking forward to the rest!


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## melsdad (Aug 21, 2014)

The axle on the table will be a 1" dia.  Shaft. So those .500 holes need opened up to fit the axle. I removed most of the material with a 31/32 drill. Again doing these as a group so they are identical.



Then bored the hole to size .001 oversize of the axle.



Here is a cut off of the bar the axle is made of to check for fit. Just what I was shooting for...a good slip fit.


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## melsdad (Aug 21, 2014)

These need the slot cut in them  yet so they will clamp the axle in place. Here is a picture of the print.


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## Andre (Aug 21, 2014)

Looking real good, Bryan! I like the fast grit interchangeability system. 
Only have a 2hp motor? Might not be enough :rofl:


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## melsdad (Aug 21, 2014)

Andre said:


> Looking real good, Bryan! I like the fast grit interchangeability system.
> Only have a 2hp motor? Might not be enough :rofl:




Thanks Andre. Craigs list can be your friend if you keep looking for what you are after. I won't even upset anyone by telling them what I paid for the motor:whistle:

When I get her running I will try to bog her down....2 h.p. should be plenty though.

Drives start to get expensive over 2h.p. and that is the max capability of the drive I have.


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## melsdad (Aug 21, 2014)

Slots are cut. I have adjustable handles that will clamp the axle in position


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## melsdad (Aug 21, 2014)

I decided to surface grind the table clamp arm posts. My original thoughts were to black oxide the steel parts and anodize the aluminium parts. What do you guys think?


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## rmack898 (Aug 22, 2014)

Nice work. 
Having just finished a batch of parts with black oxide for the first time and being very pleased with the results, I highly recommend it for your steel parts. 
Anodized aluminum always looks great.


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## melsdad (Aug 22, 2014)

Things are coming together now! Got the base plate and motor riser block complete.


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## melsdad (Aug 22, 2014)

I was able to assemble most of the parts today. The last part is the table and to get the magnets installed in the hub.


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## mzayd3 (Aug 23, 2014)

how did you machine the slot for the table pivot clamps?  looks terrific!  nice work:goodjob:


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## melsdad (Aug 23, 2014)

I had the slots cut on a wire E.D.M machine. That's not cheating is it....lol

I would have needed a slitting saw about 6" in dia. To clear the arbor and get the depth I needed. I didn't have that and i didn't want to bandsaw the slots and risk messing them up at this point.


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## melsdad (Aug 23, 2014)

Got the table finished this morning.  Except for the slot for the bevel gage. That will be later.

Cutting the recess in the table





Releaving the underside of the table so it can be tilted to 45 deg. And be close to the disc.





Axle mounted to the table



In position


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## Arkie (Aug 23, 2014)

That's pretty interesting how you built the table.  I guess trunnions would be the standard way, but they might be harder to machine.

Do you have any shots or a description about how you made the disc?  I'm thinking about building one of these grinders to complement my 2 X 72.


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## melsdad (Aug 23, 2014)

The discs took a good bit of time. I had them lazer cut out of 1/4" steel plate. They were not very flat so they needed to be surface ground.  To get something flat that is not flat takes planning. You can't just put a disc on the magnet and grind it. You need a surface plate and a variety of shim stock. With a dial indicator on the disc you need to shim the gaps under the plate all around till the needle is dead still. Then those shims need to be transferred to the magnet in the same location.  I ground the discs till they cleaned up. Now when flipped over and cleaned up both sides should be flat.

You can see the shims under the disc in these pictures.





Alll cleaned up


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## melsdad (Aug 23, 2014)

Once the discs were flat I trued them on lathe. I grabbed the o.d. in a 6 jaw chuck and bored the I.d. of the discs to a slip fit of the aluminium hub. The I made a fixture that mastered off of the I.d. and turned the o.d. of the discs to 8.875 dia. My thinking was that a standard sheet of sand paper can eeasily be applied and trimmed with a razor flush to the disc. 

I also turned a 30 deg. Relief bevel on the back side of the discs for clearance when grinding inside corners. 

The fixture






Disc held in place with a 4" washer.



Cutting the bevel



Fiinished product


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## pineyfolks (Aug 23, 2014)

Excellent build and very well documented.


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## melsdad (Aug 23, 2014)

pineyfolks said:


> Excellent build and very well documented.


Thank you very much!!


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## melsdad (Aug 23, 2014)

The last step was getting the magnets pressed into the hub. I used two staggered bolt patterns. Notice the jacks under the hub. On the first hole the hub rang like a bell so I needed to stiffen things up a bit. 

With the 12 magnets installed they have a combined force of 96#


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## melsdad (Aug 23, 2014)

Tomorrow I will post a video of the machine in action.


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## drs23 (Aug 24, 2014)

An absolute display of fine craftsmanship Brian. Great job. Are those pennies between your clamps and the workpiece to prevent them from being marred? A good thing for me to learn and remember.

Looking forward to the video.


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## melsdad (Aug 24, 2014)

drs23 said:


> An absolute display of fine craftsmanship Brian. Great job. Are those pennies between your clamps and the workpiece to prevent them from being marred? A good thing for me to learn and remember.
> 
> Looking forward to the video.


Yes those are penny's. And that is what they are for. I wondered if anyone would notice. Good eye! 

Thanks for the compliment! !!


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## melsdad (Aug 24, 2014)

Here is the video I promised with the help of my camera girl....my daughter Melanie.

http://youtu.be/0ZuI_-gOL4k


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## drs23 (Aug 24, 2014)

Absolutely a great job! Thanks for taking the time to document and share it.


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## Philco (Aug 24, 2014)

Brian, that is one fine job. The magnets & quick change plates are a really slick idea! Thanks for posting this build. I can imagine being able to change the grits that fast will make this machine a pleasure to use.
Phil


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## zmotorsports (Aug 25, 2014)

Very nice work.  Thanks for sharing with us.

Mike.


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## James Deprey (Sep 2, 2014)

Hi Brian

I really like your 9" disc grinder build,  I only have one question at this time.
Do you have a set of plans for this grinder, I would be interested in purchasing a 
set if available.

Thanks

Jim Deprey


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## melsdad (Sep 3, 2014)

James I do have plans. I need to revise them though. There were little tweaks here and there that I made along the way and all but a few of the prints need updated. 

Some parts would need to be different depending on the motor used also. Give me some time and I will post them up in the plans and drawing section for anyone to use.


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## James Deprey (Sep 5, 2014)

Thanks Brian, I'm glad to see that you are working on finalizing your plans
for the 9" grinder.  I'll be looking for them....

Again, thank you and great work

Jim Deprey


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