Surface Grinding

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ctwo
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Re: Surface Grinding

Post by ctwo »

I will refer the concept of a Reuleaux triangle and the result of measuring that directly on a surface plate - you would not see the error.

So, it seems complicated. I tell you the v-block angle answer is, it depends. The meat here is in tables 2, 3, & 4.

https://www.matec-conferences.org/artic ... _08016.pdf
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Harold_V
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Re: Surface Grinding

Post by Harold_V »

That's what I was saying. With a V block of any given angle, error would be displayed, but it would not be representative of the amount of error, due in part to the relationship between the angle of the V block and the amount of error (and location on the part) of the less than round part.

H
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ctwo
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Re: Surface Grinding

Post by ctwo »

The point of the article seems to be that, for a particular out of round shape, there IS a v-block angle that accurately represents the amount of error, and other angles could be used to determine the same through additional calculation.

My point extends that to, for a particular out of round shape, there is a v-block angle that will show no deviation from roundness. But I do not know if that is true.

I was more savvy with math years ago and could plug in all the necessary formula and derive such a curve formula. I can't now, so it's just a hunch. I probably need to find some HS intern to do it now.
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ctwo
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Re: Surface Grinding

Post by ctwo »

Back to my square, I had not measured the side squareness, and it was out over half a thou. I set in my screw-less grinding vise with the outside edge against the fixed jaw, and I use a square to set the side-side lean. I haven't been able to get it square. The difference between sides is 5 tenths, so it's leaning 2.5 tenths.

Is there a better setup to consider?
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Harold_V
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Re: Surface Grinding

Post by Harold_V »

It has been my experience that getting things square (high precision) with a vise is difficult. When I hope to achieve true squareness, I use an angle plate of known quality.

H
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ctwo
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Re: Surface Grinding

Post by ctwo »

Now that you mention it, that seems obvious.
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Re: Surface Grinding

Post by ctwo »

For some reason I made five ~1/4" diameter x 1/10" thick steel discs to place at each corner and center of my mag chuck. I proceeded to grind each one to the same height and noticed some were skating on the chuck. I discovered strong magnetic fields are ~3/4" apart. What I mean by that is I can slide my little disc across the chuck and there are alternating strong/weak zones. The ad said Pole pitch: 1.5+0.5mm(2mm). Looks like they got the simple math right... Does this seem normal for a "fine pole" magnetic chuck?

I blocked the parts and that was fine but I was still concerned a part would jump up and explode the wheel.

I'm still thinking of getting an ebay Vevor 6x12. Mine is the Longbo version in 5x10. I suspect the two brands are identical, however.
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Harold_V
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Re: Surface Grinding

Post by Harold_V »

Hmmm. 3/4" is a lot larger than 2mm. What am I missing? If the pitch is as you said, I don't understand the relationship.

I can't address the "fine pole" question. Don't have a clue.

H
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mcostello
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Re: Surface Grinding

Post by mcostello »

Magnets placed closer togheter. Fine pitch vs coarse.
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Harold_V
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Re: Surface Grinding

Post by Harold_V »

mcostello wrote: Mon Jul 11, 2022 8:56 pm Magnets placed closer togheter. Fine pitch vs coarse.
Yeah, I get that, but what isn't clear is how that relates to the 3/4"/2mm mentioned.

H
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ctwo
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Re: Surface Grinding

Post by ctwo »

Harold_V wrote: Tue Jul 12, 2022 1:32 am
mcostello wrote: Mon Jul 11, 2022 8:56 pm Magnets placed closer togheter. Fine pitch vs coarse.
Yeah, I get that, but what isn't clear is how that relates to the 3/4"/2mm mentioned.

H
The chuck specification (lip service) is fine pole with pole pitch of 2mm. The top plate has alternating steel/brass (copper?) plates that are ~2mm thick. I do not know what is inside.

The ~3/4" is the stronger/weaker magnetic force spacing I feel when sliding my little 1/4" disc across the chuck when it is turned on. I am not expecting this and would expect a constant magnetic force since this part should span multiple magnetic poles (at least 3). But this is the only magnetic chuck I've experienced and maybe it's a normal field given the interaction of materials/forces. Maybe if I rolled a 1mm dowel across the surface I would feel strong/weak forces spaced 2mm? I tried that and could not feel enough of a different to tell if there were poles at all, it was a constant (and very weak) force to me.

The thought is that the Chinese are using the same magnet pack in both of their fine and coarse chucks because it's cheaper, or I just don't know what I'm talking about/doing.
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Harold_V
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Re: Surface Grinding

Post by Harold_V »

I was thinking along the same lines you presented, and I suspect that what they claim isn't truly representative of the magnet spacing. They interrupt the magnetic lines of force with the laminated construction, but that doesn't really change the spacing.

I've not ever concerned myself with that subject. I've operated a myriad of grinders, all with various chucks. Some are definitely better than others. My favorites are those with a release feature, whereby the chuck is energized with AC at a constantly diminishing voltage. That allows the part being ground to be removed from the chuck without effort and eliminates any potential scratching of the bottom face.

H
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