Ryobi BGH827 8" bench grinder vibration

If you recall, I had a struggle with a Ryobi bench grinder given to me
by a well-meaning relative. I first reported the saga in the thread
"Vibrating grinder returns" (21 April 2007). The then plan was to
machine new end washers to stabilize the stone wheels on the 5/8" arbor
shafts.
The Clausing 5914 is now up to the task, and so it was done. Actually,
I retained the pressed steel end washers, but used the lathe to face off
the center where the nut clamp on the washer. I also machined a pair of
1" OD, 5/8' ID by 1.35" long sleeves of mild steel, to adapt the Norton
wheels (1" diameter hole) to the 5/8" diameter arbor shafts.
So I put it all together today. The grinder still vibrates badly, with
wheels both wobbling side-to-side! But now the reason is obvious; it
was not obvious before (because the pressed steel washers were not
accurate). The two nuts that hold wheels onto the arbors are crooked,
very crooked. The thread axis is not perpendicular to the faces of the
nuts, so when one tightens down, the pressure is all on one side of the
washer, and so the wheel sways. The deviation is quite large, and
easily visible. The left-hand thread nut even looks wrong: the threaded
hole is noticeably eccentric in the hex nut outline.
What were they thinking? They have rendered the whole affair almost
useless by provision of cheaply made nuts. This has to have saved all
of ten cents.
Naturally, the nuts are actually metric, and appear to be M16-2.0, which
looks like 5/8-11, but is not. The 5914 lathe does not cut metric
threads. Closest it gets is 12 tpi, versus 25.4/2= 12.7 tpi. So I
can't just make a set of nuts, my first thought.
My second thought was to re-face the provided nuts. That didn't work
either, because the screwthread axis is not parallel to the hex facets
of the nuts. So, I gave up.
I will call Ryobi, in the hope that they now have better-made nuts. But
I'm close to junking this POS. It's been far too educational.
I was looking at the Delta 8" bench grinder. Amazon offers this unit.
Interestingly, there was exactly one customer comment, and that one
customer complained of excessive vibration caused by wobbling wheels.
Wonder if Delta buys its nuts the same place.
Joe Gwinn
Reply to
Joseph Gwinn
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you may consider machining the nuts in place - spin the grinder up to speed and hold a cutting tool against the exposed face of the nut
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Reply to
Bill Noble
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Well ... probably the nuts on the left-hand side of the grinder are left-hand thread -- but at least for the right-hand nut -- chuck an appropriate screw (you can get the M16x2.0 locally can't you), in the lathe with just enough sticking out the end and screw the nut onto it. Then face the nut in that position. If both sides use a right-hand nut you can do both sides easily. Otherwise, go to MSC (or some similar supplier) and look for LH bolts in the right thread. Or -- just look for good quality nuts in both hands.
I could probably make you a stud for facing the left-hand nut which you (presumably) already have -- using the Compact-5/CNC Emco Maier lathe. But I will have to trust measuring over wires, because I don't have a left hand thread sample to work from.
Enjoy, DoN.
Reply to
DoN. Nichols
a bit more on what I posted above - if you have a die grinder or dremel tool and can hold it still (perhaps with a clamp, or maybe by holding it in the lathe's tool rest) you can grind away at the outside face of the nut with the grinder running, it will take less time than ordering a replacement or making one or going to the store to buy one. You could also make a sleeve that fits the shaft accurately and is thick ehough that it won't wobble when the nut pushes on it off center
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Reply to
Bill Noble
Threads on import nuts and bolts I've seen bear little resemblance to any specification, so measuring over wires would be futile unless you had 3-wire measurements of the shaft on his grinder.
Better to have him send you the nut so you can make a stud to fit -- and then you may as well face the nut for him since you'd already have the stud in your lathe.
Reply to
Don Foreman
If the nut is drilled off center, will facing it do much good? It may make the wheel straighter, but the nut will still be off center.
The first thing I would do is run the grinder without wheels and see if it is smooth. If not, junk it unless you want to tear it apart. Next, check the shafts for trueness with a dial indicator. Then I'd add pieces one at a time to see what is vibrating.
Reply to
Ronald Thompson
I would indeed junk the grinder.
There is too much at stake with the fast spinning wheel.
i
Reply to
Ignoramus30238
The left arbor has a left-hand thread, the right arbor has a right-hand thread. Both are M16x2. (There is no rotor lock, so it can be hard to tighten and loosen the nuts.)
I don't know how common left-hand metric bolts are round these parts.
MSC and Grainger have none. Nor do I really want to buy 100 of these nuts. At $20/100 times two, or $40, it's 2/3 what the grinder cost.
I'm not sure that the threaded stud to hold the nut to be faced will work, as both faces are crooked, so the nut will tilt to one side when tightened down to allow facing the free face. I think that the only solution is new nuts. I could make these nuts if I bought a set of taps, but even that is going to cost a major fraction of the cost of the grinder.
I'm going to call Roybi first. Maybe they have resolved their supply problem. Or gotten lucky.
Hmm. I wonder what thread Jet grinders use?
Joe Gwinn
Reply to
Joseph Gwinn
Or even better, make the correct nut. But I think it's a loose M16x2. great precision is not required. Only perpendicularity. In any event, if it comes to that, I can measure the arbor thread over three wires.
Joe Gwinn
Reply to
Joseph Gwinn
Compared to the wheel, the mass of the nut is trivial, and so some eccentricity is harmless in the nut. The issue is the degree of parallelism between thread axis and the hex flats, as it's to the flats that one clamps.
It appears that the thread was tapped at an angle to the body of the nut.
The grinder runs smoothly without wheels. The shaft runs true according to the dial indicator.
Joe Gwinn
Reply to
Joseph Gwinn
A lathe tool bit wouldn't work, as the motor is too fast and too weak to be a lathe motor.
The die grinder could work.
The hard part is holding the nut in place without tilting it, even though the nut's faces are tilted with respect to the arbor axis. I'm thinking a strong spring on the arbor will be strong enough for the die grinder.
Joe Gwinn
Reply to
Joseph Gwinn
I'd be suspicious that it was dropped and the shaft bent. Best regards, Spehro Pefhany
Reply to
Spehro Pefhany
It sounds like you know what you are doing and are on the right track. If you decide to use a grinder on the nuts while spinning on the arbor, You might have luck holding them with Loctite or something like it.
Reply to
Ronald Thompson
McMaster:
93695A210 Metric Class 8 Left-Hand Thread Hex Nut Zinc-Pltd, M16 Size, 2mm Pitch, 24mm W, 13mm H In stock at $11.20 per Pack This product is sold in Packs of 20
Or make some spherical washers.
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Reply to
Ned Simmons
or buy a single in stainless steel for $2.74
>Or make some spherical washers. >
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regards, Spehro Pefhany
Reply to
Spehro Pefhany
I found this today as well. They also have a stainless steel nut for a few dollars, sold in quantity 1.
I already have some spherical washers, but the stackup is too thick - there isn't enough arbor for this to fit.
Joe Gwinn
Reply to
Joseph Gwinn
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That is common with all bench grinders that I have used.
:-)
Understood.
How loose is the nut on the arbor?
:-)
A good question. I have an 8" Jet grinder -- and it has been an excellent one so far. I guess that I could try measuring the thread on the right-hand end with a thread checker or a thread pitch gauge. Even if it is the same thread size and pitch, I don't know how different the actual fit might be. :-)
Enjoy, DoN.
Reply to
DoN. Nichols
This was a common suspicion, but it turned out that the arbors are straight, as measured with a dial indicator.
Joe Gwinn
Reply to
Joseph Gwinn
As mentioned in another posting, it turns out that McMaster-Carr stocks left-hand M16x2 nuts.
I also talked to Ryobi yesterday, and will call their local distributor. The hope is that Ryobi has after two years already worked their way through that batch of bad nuts. And I know one of the local service centers - their people are able to use such products, and so should be able to understand the problem. And to tell a good nut from a bad nut.
You mean freedom to wobble when not tightened down? It's got to be a few degrees, by eye, though I never measured it. These are not precision instrument threads. But it's not loose enough for the nut to rest flat when tightened.
I'm betting that if it's a standard M16x2 nut, it will fit. I don't think Ryobi made the arbor threads wrong. I think they bought some bad nuts.
If I replace the Ryobi, I'll look at Jet.
In retrospect, I should have boxed the Ryobi grinder up and dropped it right in Ryobi's lap, to fix or replace or refund, back when this saga began.
Joe Gwinn
Reply to
Joseph Gwinn
It would, but the mass imbalance of an offcenter nut would be trivial compared to a wobbly wheel.
Good plan!
Reply to
Don Foreman

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