# Mike's Slow Speed Carbide Grinder



## macardoso (Feb 11, 2021)

As I start tooling up for hand scraping, I came to the realization that there was no good way to sharpen the carbide blade without a slow speed carbide grinder. Looking online, I liked the diamond lapping plate concept many are using. I have some components laying around the house which would be perfect for one so my design will be central around these components. I hope this will aid my scraping experience and perhaps allow me to resharpen my used carbide lathe inserts.

For the motor, I have a 25W (1/30HP) 3 phase induction motor from Oriental motor. It is pretty tiny but has surprising torque so I think it will be more than enough for this limited application. Rated speed is 1600 rpm and I have run it up to 3200 rpm no problem.




This motor will be driven by an Allen Bradley Powerflex 4 rated at 1/2HP. This is a super basic VFD with V/Hz control only. I wanted to use it because there is a built in keypad and potentiometer that will handle start, stop, reverse, and speed select.




I plan to use 6" diamond grit lapping discs. They can be had for about $12 each on amazon. So far I have purchased an 800 grit, 1500 grit, and 3000 grit. I bet these will cover the range of my needs.

I'll follow this post up with some CAD models as I am in the very early phases of my design. The key features are a 6" lapping disc retained with magnets, tilting table (tilt axis in plane with the front of the disc), dust/splash guard, and contemplating some kind of MQL drip lubrication to keep the carbide dust down. I am designing this based on stock I have on hand as well so that is determining the size.


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## jwmelvin (Feb 11, 2021)

Curious what sort of speeds you are targeting. I put one of those discs on my bench grinder (against the side of a stone disc) and it was great for a while (for TIG electrodes) but wore out pretty quickly. My grinder runs quite fast though (belt driven).


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## Braeden P (Feb 11, 2021)

if you got the same disks as me  the 800 grit wears to about 1500 so i only used the 800 and the 3000 grit ones.


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## macardoso (Feb 11, 2021)

jwmelvin said:


> Curious what sort of speeds you are targeting. I put one of those discs on my bench grinder (against the side of a stone disc) and it was great for a while (for TIG electrodes) but wore out pretty quickly. My grinder runs quite fast though (belt driven).



I expect to run in the 400-800 rpm range, but honestly I've never tried this so I have no clue. The grinder will be infinitely variable between 0 and 3200 rpm. I intend to use this for very delicate grinding.  The torque below 400rpm is not great, so it would only be good for polishing, not stock removal. Can always put a bigger motor on it, but this one is free and works perfectly with the VFD.


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## bakrch (Feb 11, 2021)

macardoso said:


> I expect to run in the 400-800 rpm range, but honestly I've never tried this so I have no clue. The grinder will be infinitely variable between 0 and 3200 rpm. I intend to use this for very delicate grinding.  The torque below 400rpm is not great, so it would only be good for polishing, not stock removal. Can always put a bigger motor on it, but this one is free and works perfectly with the VFD.


Accu-finish grinders spin at about 300 rpm I believe, and they are glorious.


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## macardoso (Feb 11, 2021)

Here is an early CAD model of the grinder. I have two 6" x 12" x 0.5" aluminum plates which I want to use for the backbone of this design. I will be boxing in the sides with 1/4" aluminum plate as well. Should be really stable.

I currently plan on using the motor bearings as the only support for the platter. They are spring loaded axially as many many small motor bearing arrangements are, so I am considering adding a single angular contact ball bearing in the front plate to take the thrust loads from the platter (otherwise the plate can traverse about 1/8" when a few pounds of force is applied.

The VFD is hanging off the back. Motor wires will pass through a hole in the real bulkhead. A tilting table will be added in front of the platter, roughly about centerline. I really want to design the hinges so the pivot axis is inline with the platter face and the top edge of the table.




And from the rear.


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## macardoso (Feb 11, 2021)

Here is it with the sides, top, and a mockup work table. I think I am aiming for a +45, -30 degree tilt range on the table.

There will be some sheet metal to cover the VFD (I am not concerned about heat since the motor is so undersized for the drive). That should also keep dust from settling inside. I unplugged the internal fan so it does not circulate. Again, I won't be running this anywhere near the rated load, so heating is not currently a concern.

There will also be a sheet metal plate below the table to help contain dust. The sides extend beyond the front of the wheel to catch spray or dust thrown by the wheel. The two holes in the side plate will be for the pivot for the table, and the locking screw to hold it in place. The work table is 5.88" x 3" currently, but it is up for changing. I might also add a shallow slot in the center for a fence. Table is 3/8" thick aluminum for rigidity (and I have some on hand).


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## homebrewed (Feb 11, 2021)

I used a stepper/driver combination along with a very simple 555 based timer (to generate the step pulses), to make my low speed grinder.  It runs about 120 RPMs and that seems to be plenty fast.  I set mine up so I can put a disposable aluminum bread tray underneath the disk.  I add water to the tray, enough to go about halfway up the disk.  This limits the RPMs you can use because higher RPMs start to sling the water off the disk, but it does a good job of lubricating the blade and capturing the nasty carbide/cobalt dust.

The 3000 grit disk produces a really nice edge on the carbide scrapers.


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## macardoso (Feb 11, 2021)

homebrewed said:


> I used a stepper/driver combination along with a very simple 555 based timer (to generate the step pulses), to make my low speed grinder.  It runs about 120 RPMs and that seems to be plenty fast.  I set mine up so I can put a disposable aluminum bread tray underneath the disk.  I add water to the tray, enough to go about halfway up the disk.  This limits the RPMs you can use because higher RPMs start to sling the water off the disk, but it does a good job of lubricating the blade and capturing the nasty carbide/cobalt dust.
> 
> The 3000 grit disk produces a really nice edge on the carbide scrapers.



Nice Idea! I left room to slide a pan under the disc to catch drippings, but not submerge the disc. I imagined a refillable tub on top with a needle valve to drip onto the disc. I like your idea though.


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## jwmelvin (Feb 11, 2021)

Designing the table motion to have a pivot axis at the wheel-table interface would be really nice. I'm imagining a four-bar linkage? I was playing around with this simulator.

I wanted the same action for my bench-grinder support, but no need for much precision, so I just used arc slots with a center at the support-wheel interface. It's a work in progress (slots here) but the prototype was good enough.


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## homebrewed (Feb 11, 2021)

macardoso said:


> Nice Idea! I left room to slide a pan under the disc to catch drippings, but not submerge the disc. I imagined a refillable tub on top with a needle valve to drip onto the disc. I like your idea though.


I stole the idea from the low-speed diamond saws we had at work, used for sectioning very hard materials.  We did a lot of cross sections and polishing.  With that setup, the (expensive) diamond saw blades lasted almost forever.  We did have to remember to remove the blades once we were done, though -- the disks are made of steel and would quickly rust.

Talking about diamond saws, I also got a lapidary-grade saw blade I can install on my grinder setup.  It makes it easy to nick a hunk of carbide or HSS to break it to a specific length.  Something else to think about...and they're not very expensive, either.  If you're sawing something by hand, don't twist the work piece -- the blade could catch and snatch the piece right out of your hand.


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## macardoso (Feb 11, 2021)

jwmelvin said:


> Designing the table motion to have a pivot axis at the wheel-table interface would be really nice. I'm imagining a four-bar linkage? I was playing around with this simulator.
> 
> I wanted the same action for my bench-grinder support, but no need for much precision, so I just used arc slots with a center at the support-wheel interface. It's a work in progress (slots here) but the prototype was good enough.



Yeah, That was a big deficiency I saw in the Youtube videos of these things. Mine isn't elegant, but by extending the walls past the face of the wheel, I could drill and tap the pivot hole in line with the wheel. The second hole will hold a bolt in a curved slot on the table arm for clamping. 

Still working on the CAD for that.


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## jmkasunich (Feb 11, 2021)

Feel free to make it as complex as you want if that's your thing, but a perfectly adequate "MQL" system for this is that bottle of windex that you use to wash the windows.  Give the disk a squirt when you start grinding and whenever it seems to be getting too dry.  Done.  Not sure who originally came up with windex - I heard about it from Richard King at his scraping class.  Seems to work better than plain water.


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## homebrewed (Feb 11, 2021)

I'm looking forward to stealing, er, seeing, your grinder setup .


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## jmkasunich (Feb 11, 2021)

I assume you've seen Stefan's version?  



I wound up mostly copying that, using a small gearmotor that I found at HGR.
So far I've only used it for scraper blades, and my rest is literally a chunk of wood cut at an 8 degree angle with a miter saw and screwed to the base with drywall screws.  Works great, but I plan to eventually add a tilting table.


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## macardoso (Feb 11, 2021)

jmkasunich said:


> I assume you've seen Stefan's version?
> 
> 
> 
> ...


Hey, you're 10 minutes down the road from me, we should do an HM meetup at HGR  

I actually think I might get more use out of this for doing inserts, so I want the added capability to add cutting relief, hence the tilting table.

Looking to make this as easy as possible to build. Plates and screws pretty much. Maybe one CNC part for the pivot arms.

EDIT: I have seen his video. Like his setup a lot minus the big gap between the table and blade. Stealing his magnet and pin idea for sure.

EDIT #2: Don't have a welder so my construction will be different.


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## macardoso (Feb 11, 2021)

homebrewed said:


> I'm looking forward to stealing, er, seeing, your grinder setup .



I'll throw up a PDF with the drawings if you'd like when I'm done. Then you can mod to your desire.


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## macardoso (Feb 11, 2021)

OK, Table is designed. It uses two 3/16" shoulder bolts as pivots and has a large swept arc at a 1.75" radius. A 1/4-20 screw on each side clamps the table in the tilted position. There is a sharp V in the middle of the arc which will act as a pointed to a graduated scale to be engraved in the side of the walls. I ended up with a +/- 45 degree angle for the table (not the easiest to achieve).




Here is the table from below. It uses socket head cap screws as fasteners. The table itself is blind tapped from the bottom and screws on the top of the support bar. Slotted clearance holes allow +/- 1/8" of travel on the table to set the gap between the edge and the platter.




I still need to model the graduated scale for the tilt angle, add fasteners to the walls, top, and base, add wire holes in the rear, add sheet metal around the drive and bottom of the platter, and add a provision for an angular contact ball bearing behind the platter.

Trying out Solidworks for the first time in 5 years. I usually use Inventor but they cut me off of student licenses. It is sorta like driving a car in a country that drives on the other side of the road. It all works the same but everything is in the wrong place.


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## macardoso (Feb 11, 2021)

Updated shot with thumbwheel locking screws and a slot for a fence. Down the road I could make a set of fixed angle fences to sharpen carbide inserts to exact geometry.


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## macardoso (Feb 11, 2021)

Had just enough room to sneak a 15x35x11mm 72xx series angular contact ball bearing into the design. This will add about $10 to the cost, but make it so that pushing on the platter does not cause the motor shaft to slide inward against the spring preload. I would have liked to fully enclose the OD of the bearing, but this will be fine (I don't have stock thicker than the 1/2" stuff I will be using).

This section view shows the motor (left), the front bulkhead with partially pressed in angular contact bearing, the shaft adapter with 8-32 setscrew bore just barely snuck in there, the platter, and finally the tilting work table with knife edge bevel.


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## macardoso (Feb 11, 2021)

Getting close...

Added fasteners (and related holes) and mounting feet. All that is left is some sheet metal covers for the VFD and lower platter, add mounting holes for the VFD, cable pass thru holes, and drill the pin holes in the lapping disc. 

It is held together with #6 flat head cap screws, except for the front bulkhead which uses 1/4" fasteners for stability. The #6 overhang the edge, but I didn't want to go down to #4 screws. The right thing would have been to use thicker side walls, but I have a bunch of 1/4" plate so that is what it is. I'll file the edge of the screw head into a chamfer once it is assembled.

With a bit of planning, I definitely think I could build a drill sharpening jig that mounts onto the fence slot. TBD...


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## jwmelvin (Feb 11, 2021)

Thanks for posting all the updates. It’s looking pretty good. I sometimes design things and then realize the scale for certain features is smaller than I realized. The area around your coupler and bearing seems like it could be like that. But clearance is clearance.


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## jwmelvin (Feb 11, 2021)

I liked the idea of a removable water tray that allowed for submerging part of the wheel (though the rusting potential seems undesirable). I’d maybe think a bit about getting whatever tray you plan in and out if it overlaps the the wheel. And a mount for a drip system. And maybe a light under the top front edge.


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## macardoso (Feb 12, 2021)

Here is the back of the unit with a simple sheet metal guard. Really brings the look together.

Still need fasteners and other odds and ends but it is getting close.


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## Janderso (Feb 12, 2021)

I've been struggling with the same concept.
Looking forward to your build. The design and compact structure is awesome.
Meanwhile, I've discovered my Baldor tool room grinder with a diamond wheel does a decent job of sharpening/lapping the Sandvik hand scraping tool carbide.
Please continue to post your progress!!


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## macardoso (Feb 12, 2021)

jwmelvin said:


> Thanks for posting all the updates. It’s looking pretty good. I sometimes design things and then realize the scale for certain features is smaller than I realized. The area around your coupler and bearing seems like it could be like that. But clearance is clearance.



Yeah, that is going to be tight. Just need enough room to sneak a long T handle allen wrench in so I can tighten that 8-32 setscrew. I wish I had built the AC bearing in from the beginning, but it works nicely. I really wanted to stick with 1/2" plate so I didn't need to go buy something else.


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## macardoso (Feb 12, 2021)

After much frustration, I added a graduated scale to the side of the grinder graduated in 1 degree increments with a major tick every 5 degrees. 

I have some super sharp engraving cutters that should have no issue making these features.


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## Janderso (Feb 12, 2021)

macardoso said:


> After much frustration, I added a graduated scale to the side of the grinder graduated in 1 degree increments with a major tick every 5 degrees.
> 
> I have some super sharp engraving cutters that should have no issue making these features.
> 
> View attachment 355229


I sure admire you guys that can draw these things up = clueless here.


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## macardoso (Feb 13, 2021)

All done!

Added a few fasteners I forgot and the drip plate below the table. I'm going to hate myself for the number of tapped holes on the edges of the plates, but I can build this whole thing with scrap I have on hand.




Next step is to figure out how Solidworks drawings work so I can make some prints to build from.

The one deficiency I am questioning myself on is the inability to grind off the side of the wheel (since it is recessed behind the walls). This is perfectly acceptable for the purposes for which it was built (scraper blade sharpening and insert grinding) but it will be a bit limited for other uses.


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## macardoso (Feb 13, 2021)

Got one drawing done. Don't know any of the tricks, but the interface is pretty intuitive. For home use, I make simple drawings like this and put each piece of stock I need to use on top. Keeps me efficient and I like having the drawing to reference. This is not the "professional" kind of drawings we make at work - just enough notes so I know what I am doing.

I had some sweet border templates in Inventor that I miss. I'll have to recreate them in SW.


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## macardoso (Feb 13, 2021)

Here is a rough draft of the drawings in case anyone wants to follow along at home


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## brino (Feb 13, 2021)

macardoso said:


> All done!



Virtually, it's all done!


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## macardoso (Feb 13, 2021)

brino said:


> Virtually, it's all done!



Yeah, No joke, this is going to be a bit of work to build. Just went through all my stock and picked out what I needed to do this job.


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