Bench grinder spindle thread

snipped-for-privacy@gmail.com wrote:
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I've had a 'Newsgroups' folder for over ten years, with sub folders, with sub folders. I also have an archive of tens of thousands of messages in a separate set of folders on my news client. Since the files are stored as text, I can search for what I remember about a subject and find the information.

I dunno the reason for the dies not starting, but there are some really poor quality die sets on the market and for China/India standards, the products just looky-like dies but are barely sitable as thread chasers for cleaning up a slightly damaged good thread. Almost always, the side of the die that's marked with the size is the starting side and the exit side doesn't have the widened opening for starting onto the workpiece.
Also, the end of the workpiece should have a fairly uniform chamfer which aids in starting the cutting action.
If no cutting action can be felt in the first 1/4 to 1/2 turn, it's likely that something is wrong.. either the quality of the die is very bad/damaged, or the workpiece is excessively oversize (assuming that the workpiece isn't hardened steel).

On Fri, 16 Dec 2011 17:45:43 -0800, snipped-for-privacy@gmail.com wrote:
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You may also find 1/2 24, RH or LH Gerry :-)} London, Canada

On Mon, 19 Dec 2011 01:28:48 -0500, Gerald Miller
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Right. But so far I have not been able to ascertain why a common or garden 1/2-13 thread would not do just as well in this application (L or RH).
Michael Koblic, Campbell River, BC

Arbor nuts for securing grinding wheels aren't torqued like some fasteners in other applications, but being able to attain a specific torque value is easy with a fine thread, and mating contact areas are of benefit to holding a position. All bets are off when considering low-grade hardware.
A factor someone mentioned is the deeper the thread, the weaker the arbor (or bolt/stud) for a given size.
With blotters on each side of a grinding wheel and the appropriate cupped plates, (typical bench grinder) arbor nuts generally only need to be snug, and a fine thread is beneficial for achieving snug.. not even close to a grunt.
The blotters become slightly compressed, making good/excellent overall contact between the abrasive and the plates.

On Tue, 20 Dec 2011 01:31:45 -0500, "Wild_Bill"
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OK. That makes sense. SOunds like it comes under the category of "beneficial" but not "essential".
Michael Koblic, Campbell River, BC

I believe there would be reasons for using fine threads from an engineering standpoint.. but if I did know, it's been forgotten.
In pondering my own experiences with a lot of mechanical assemblies, I'm certain that fine threads are most often chosen for fasteners associated with moving parts in power transmission components.
In automotive applications, items bolted to the engine block are often coarse threads.. but wheel studs, connecting rod caps, crankshaft end parts, etc.. have generally always had fine threads IME.
In many applications the thread choice is related to the metal/material types which have threaded holes.

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My understanding is that coarse threads were intended for steel screws in cast iron assemblies, and the fine threads came about for steel into steel.
Joe Gwinn

On Wed, 21 Dec 2011 13:12:41 -0500, Joseph Gwinn
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Yes, and the reason for the move to finer threads in steel is twofold: Fine threaded *screws and bolts* are stronger in both tension and shear (counterintuitive, perhaps, but check it out) and they are better at self-locking: they're less likely to loosen from vibration.
In favor of coarse threads, aside from some installation issues, such as less likelihood of cross-threading, they are less likely to strip out of a soft or fragile material. And it is easier to make a strong threaded hole in brittle material (cast iron) with a coarser pitch.
As for total strength, then, it's a matter of the relationship between bolt strength and thread strength in the hole. In hard, strong materials, fine is better. In softer, weak, or brittle materials, coarse is better. In the latter cases, bolt strength is much greater than the hole strength either way.

On Wed, 21 Dec 2011 13:28:50 -0500, Ed Huntress
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I can see how a coarse thread may be less likely to strip in a very brittle material, or perhaps in a coarse grained material where the size of the grains is large relative to the threads. But a properly cut (or formed) fine thread should be somewhat more resistant to stripping than a coarse thread in a reasonably ductile material, regardless of the strength of the material. I'm using "stripping" here to mean shearing of the threads as a result of tension on the screw.

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Apparently this is generally true. The older theories that I learned are based on the fact that the stress on the first couple of threads results in failure of those threads before there is significant stress on subsequent threads, and shear strength was dependent on some product of thread contact area and the pyramidal strength of the thread form -- coarser threads producing stronger pyramids.
I haven't looked at any of this for 30 years, except in passing. From what I've seen, the current thinking is that shear strength is almost exclusively a product of shear area (divided by a factor for helix angle) and that this says finer threads are always stronger in shear, except, perhaps, in brittle materials.
Somewhere there must be some good engineering test results to clear this up, but I haven't looked for them.

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The explanation I remember from college is that the first few threads are overloaded and fail sequentially because the bolt elongates more than the female threaded element, if it is a solid block. If the female threaded element has the same cross-sectional area and elongation as the male thread, as in a turnbuckle, the bolt is more likely to snap at a thread root as long as at least [3 to 5??] threads engage.
When a turnbuckle made personally by the great yacht designer L. F. Herreshoff was tested to destruction every part of it deformed, showing he had balanced the strengths all over without wasting material.
http://en.wikipedia.org/wiki/Hyatt_Regency_walkway_collapse
jsw

Try a bench grinder ;
https://reviewscube.com/best-bench-grinder/

On Fri, 12 May 2017 10:28:06 -0700 (PDT), snipped-for-privacy@gmail.com wrote:
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spam spam spam spam spam. Don't bother. 6-inchers, including Wen. ;)