# How I made my cheap bench grinder useable.



## John Conroy (Mar 10, 2018)

A couple of years ago in a moment of mental weakness I bought a Craftex 8" bench grinder thinking "how bad can it be"? I turned out to be pretty bad. I mounted it on a stand made from a truck axle shaft, a large 13" brake drum and a 12" brake rotor together these 3 components weigh over 60 lbs. The grinder vibrated so bad it would walk across the floor by it self when running. I tried different stones thinking they were the problem, with no success. A total waste of money. For 2 years it sat un-used because I was so angry with myself. We have a 50 year old Snap-On bench grinder at work and it is smooth as glass, I wondered what makes this one so bad. Finally I decided to try and make it useable.
I removed the guards and stones and measured the run-out on the shaft at both ends. Where the shaft it stepped for the inside washer to register against both side have about .0015" run-out. Not great but not terrible either. I decided that the stamped washers that support the stones must be the problem so I made up some thicker  machined ones and still had a lot of lateral run-out at the outer edge of the stones so I decided to get serious and machine all the components to compensate for the shaft runout and build in a provision to balance the stones. Then build an adjustable set of tool rests.
I started by machining the center bushing for both stones from steel and long enough to protrude partway through the outer hub washer. Then I machined and thick inner washer/hub and mounted it to the shaft with no grinding wheel using the wheel center and nut to hold it in place. I made indexing marks so the center bushing and inner washer/hub an always be oriented to the shaft the same way, then measured the lateral run out on the inner washer/hub at the outer edge. The initial .0015" runout was amplified to .008" at the outer edge of the 4" washer/hub I had made. I marked the high spot and mounted it in my lathe chuck with the backing stands and a .008" feeler blade behind the high spot mark.









When I remounted the inner washer/hub with indexing marks aligned and measured the runout it is now .001". Close enough. I did this for both sides then machined 2 outer hubs. They are 4" OD and .5" thick, recessed in the center so the nuts will thread onto the shafts and they have eighteen 3/8" holes drilled and tapped around their outer edges. The holes are used to do the balancing. With all the parts assembled there is almost no lateral on the stones but the thing still vibrates like a paint shaker, it's not the shaft runout causing the vibration it's the stones. They are denser in some places . As I tired 2 different set of stones I have to assume this is a common problem.

It was easy to see where the heavy spot was on each stone when mounted separately. It would turn the shaft and go to the bottom. I marked the heavy spot on both stones then re-assembled one side and started with one 3/8" by 1/2" bolt and flat washer opposite the  heavy spot and noted and huge improvement. By trial and error, adding, reducing and re-locating weight. Once I had one side balanced as well as I could get it I did the same on the other side. I probably spent about 1/2 hour getting the balance tuned so achieve the lowest vibration level. The grinder is now super smooth so I moved onto building adjustable tool rests. I used some pieces of the same 4" square tube I used on my welding table with the top side being weld laminated to 1/2" thickness to allow a mitre groove 1/8" deep and 1/2" wide to be machined in each rest top. I also had to add spacers to be able to install the outside guards. With the heads of the bolts sticking out it would be easy to injure yourself there so the guards are a must. The bracket mounting bolt positions were all machined to be tightened with one hand, no back up wrench required. Here are a few pics, not fancy but it works.

































In the end this was a heck of a lot of work but it turned the Busy Bee grinder into something that actually can be used for grinding instead of a doorstop. I might even take it all apart and paint the stand now.


----------



## DPittman (Mar 10, 2018)

Good job on the fix!  It's a bloody shame the garbage that is sold nowadays.  Yes its cheap but a few more dollars spent at the time of manufacturing would have made many pieces of machinery much more valuable/useful.  
I remember watching a Keith Fenner video where he had a similar experience to yours with a cheap grinder and after a whack of work he ended up with something useable.

Don


----------



## PeterT (Mar 10, 2018)

Great work & very interesting! 
- where you used the feeler gauge, are you saying the washer thickness was a bit of wedge so you shimmed it to make both faces parallel?
- re the counterbalancing bolt, you found the right hole clock position that needed mass, threaded that hole & inserted?
- whats the bearing situation in that model?

I just have a little 7" dual wheel Delta, but it actually runs pretty smooth. I did have one brand new wheel that gave me grief right out of the box, I could feel a new vibration that wasn't there before. I figured the plastic inserts were off, or the center hole was off, or wheel OD was off, which is kind of the same net result. I say this because I played around with different inserts from the ones that came with, found ones that were looser that allowed the wheel to be shifted a bit & locked in that position. It improved it but still not smooth. Unlike your situation, because I wasn't second guessing the grinder itself, I knew something was amiss with the wheel.

Finally I took the wheel off, put it on a nice shaft with stock insert & onto my RC prop balance thingy. Sure enough, same heavy side always went down. Bad news. So I machined a slightly undersize sleeve & glued it into the hole with epoxy. It was slightly off original center but statically balanced. I noticed slightly interrupted grinding now so OD was re-dressed. I never thought to put it back on the balance, maybe these go hand in hand convergently, or it just gets close enough. Finally it ran smooth. I never thought about density variation, that's a good point.


----------



## John Conroy (Mar 10, 2018)

The inside washer/hub was prefectly true after i first machined it but the runout in the grinder shaft was making the face of the washer run out of true. I marked the washer and shaft so they can always be assembled the same relative to each other then measured the lateral run out and marked the "high" spot. The place where the outside edge of the washer tips away from the grinder body the  furthest. I had the three pads on my chuck all machined to the same distance away from the face of the chuck so i inserted an .008" feeler blade between 1 pad and the washer to duplicate the run out when mounted on the grinder shaft and turned the outside edge flat so it now has a .008" low spot where the .008" high spot is when mounted on the grinder. This procedure is often used to make an automotive brake lathe with a slight run out in its shaft machine rotors with no run out, as long as the shaft and backing washer are always oriented the same way.

All 18 holes around the perimeter of each outer hub are threaded so  i can install a bolt in any of the holes without disturbing  the assembled shaft, stone and washer assemblies. I had to use 2 bolts side by side to balance one of the stones. After determining approximately where the light spot was I started by installing 1 bolt and running the grinder to determine the level of vibration. Then I added a washer to the bolt to see if more weight made it better or worse. If it was better I added another washer and tried again. If it was worse I tried moving the bolt 1 hole left then right to see which was best. I  ended up with 1 bolt and washer on one side and 2 bolts and 1 washer on the other. I have not trued the outside of the stones yet and they both have a little run out so it may take a little fine tuning when that is done. I'm working on a diamond tipped stone truing tool that will slide side to side in the mitre slots and make the face of the stones true to the slot. I'll post more about that when it's finished. I hope that clears up any of the stuff I explained poorly.


----------



## PeterT (Mar 10, 2018)

Gotcha.

You probably seen Keith Fenners tear down of a Chinese grinder (different model) but interesting nonetheless. The series is called _There must be a lesson in here somewhere!_ There is another vid or post I came across that had the shaft out but I cant recall where I saw it. I think the conclusion was distortion across the threaded section.

Anyway, congrats, looks like you have it tuned up


----------



## Tom O (Mar 10, 2018)

I have the same thing I just bought 3 rubber pucks from  Princess Auto  in the boat section  they are  drilled and recessed for a 1/2 " bolt  that fits in the stand perfect!


----------



## buckbrush (Apr 11, 2018)

I like your grinding tables. Very robust.


----------



## Janger (Apr 15, 2018)

I have the newer 8” and 6” craftex grinders.

https://www.busybeetools.com/products/bench-grinder-8in-w-light-csa-craftex-cx-cx906.html

They both work fine. I think they must have addressed the issues with these newer models. The 8” does take 10-15 seconds to get up to speed which I find slow. Minor annoyance.

I like your tool rests John and how they are so adjustable and beefy.


----------

