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Posted by Joseph Gwinn on April 14, 2008, 9:27 pm
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> On Mon, 14 Apr 2008 06:37:19 -0400, Ronald Thompson
>
> >Don Foreman wrote:
> >> wrote:
> >>
> >>
> >>> 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.
> >>
> >> 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. <G>
> >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.
>
> I'd be suspicious that it was dropped and the shaft bent.
This was a common suspicion, but it turned out that the arbors are
straight, as measured with a dial indicator.
Joe Gwinn
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Posted by Don Foreman on April 15, 2008, 6:36 pm
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On Mon, 14 Apr 2008 06:37:19 -0400, Ronald Thompson
>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.
It would, but the mass imbalance of an offcenter nut would be trivial
compared to a wobbly wheel.
>
>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.
Good plan!
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Posted by Joseph Gwinn on April 14, 2008, 9:02 am
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> wrote:
>
>
> >
> > 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.
>
> 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. <G>
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
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Posted by Joseph Gwinn on April 14, 2008, 9:00 am
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> > 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.
>
> [ ... ]
>
> > 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.
>
> [ ... ]
>
> > 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.
>
> 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.
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 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.
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
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Posted by Ned Simmons on April 14, 2008, 9:41 am
Please log in for more thread options On Mon, 14 Apr 2008 09:00:29 -0400, Joseph Gwinn
>
>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.
>
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.
http://www.nolansupply.com/small_images/65332001.jpg
--
Ned Simmons
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