Surface Grinding

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Harold_V
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Re: Surface Grinding

Post by Harold_V »

John Hasler wrote: Where did I suggest varying the speed? I suggested making it impossible to do so.
Didn't say you did, but reality dictates that the average user wouldn't make it impossible to vary the speed, thinking it a good and clever feature, one that is generally a part of using VFD's, in fact.

If one is to use a VFD expressly for a way to produce three phase, yeah, it's a great idea, but most folks think themselves clever and wouldn't disable, or otherwise make speed change difficult, and that's the reality I spoke of. In time, they would do something stupid-----and it could cost them their life. I don't, and won't, endorse anything that offers that kind of risk.

Make it impossible, or VERY difficult to alter frequency? Yeah, good idea.

Harold
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BadDog
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Re: Surface Grinding

Post by BadDog »

That's good to know (that the CBN and diamond not being so sensitive to speed).

And I very much understand and share the concern, but how would that be different than other machines with variable speeds. If you left them at too high a speed for the tooling, disaster and death can be found there as well.

But along those lines, I wonder if VFDs (or any VFD) can be programmed to reset to 60hz each time the power is reset. That way there is no risk of starting it up with a different wheel and a dangerous speed. Though I think that knowing it's been setup for variable speed, the action of changing a wheel would make me think to adjust it appropriately just as I do on mill or lathe. As with any of them, it only takes one mistake to hurt you badly or even take your life.
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Harold_V
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Re: Surface Grinding

Post by Harold_V »

BadDog wrote:That's good to know (that the CBN and diamond not being so sensitive to speed).
Aluminum oxide and silicon carbide aren't really speed sensitive, but the bonding of each is, and that's the problem.
I'm a bit of a cheapskate, and use wheels until they are literally useless. As they diminish in size, it becomes perfectly obvious that they behave softer, as they slough away faster and faster. And---armed with that idea, it's easy to see why a guy would enjoy a variable speed grinder, as original performance can be easily restored. It's just dangerous, because of the things we've talked about already. I admit, it's a good idea, but the safety factor, for me, overrides any possible gain.

Many have suggested that the smaller wheel won't do much work, as it has lost a lot of surface, but the fact is, it will. If you have any doubt, think of the wheels used for internal grinding, where a wheel may be only 3/4" diameter (or even smaller). They crank up the speed, generally by changing grinding heads (that's how Heald did it), although some machines (like a tool post grinder) offer pulley changes.
And I very much understand and share the concern, but how would that be different than other machines with variable speeds. If you left them at too high a speed for the tooling, disaster and death can be found there as well.
Well, yeah, it can, but it takes a lot more to explode metallic objects, so even if you start a spindle with the wrong speed, it likely will give you plenty of time to shut down. Wheels don't do that. They let go fast and violently. It's not something you need to see to gain respect. But, if you've ever seen what an exploding wheel can do (I have), you don't really want to go there.

Harold
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GlennW
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Re: Surface Grinding

Post by GlennW »

My grinder is six speed to accommodate a number of wheel sizes and is equipped with a sign, which I use when switching between 7" and 8" wheels...

So it can be a bit dangerous without VFD assistance!
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There is also another spindle speeder attachment for running mounted stones (think Jig Grinder) that brings it up to 20k I believe, but I don't have that attachment.
Glenn

Operating machines is perfectly safe......until you forget how dangerous it really is!
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Harold_V
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Re: Surface Grinding

Post by Harold_V »

Thanks, Glenn. That's a first for me, as I'd not seen a surface grinder with variable speeds. I have also taken note that they have gone far out of their way to ensure that one does NOT use the wrong speed.

Harold
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gcarsen
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Re: Surface Grinding

Post by gcarsen »

A lot of the late model Brown and Sharpes, as well as Parker Majestic's have electronic vari drives on the spindles. very handy for dressing resinoid bonded wheels. and for making up lost surface sped as the wheel wears down. most top end grinders that are not vari drives, if you open the back covers have different pulleys to allow for changing rpms. you need to take not of the rpms and be very careful as others have stated!!
just bought and brought in this small grinder, got a smoking deal on it!! my boy Lucas is "checking" it out for me!
its a 1962 Thompson, 12 by 40, walker electronic chuck. was rebuilt and new electronics by Boeing before they surplused it. sat for last 10 years with no usage. cleaning up very nicely. 3k delivered!
Grant
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GlennW
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Re: Surface Grinding

Post by GlennW »

gcarsen wrote: most top end grinders that are not vari drives, if you open the back covers have different pulleys to allow for changing rpms. you need to take not of the rpms and be very careful as others have stated!!
Yep, mine is a Parker majestic.
Glenn

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GlennW
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Re: Surface Grinding

Post by GlennW »

I damn near bought a Thompson just like that about five years ago, but not in that condition. The 14x1x5 wheel size was the same as my Universal O.D. grinder, so that would have worked out OK.

The same guy had a P&W rotary surface grinder (surface grinder with a powered rotary table instead of a traversing table)that really had my interest, but I passed on that one as well as it was definitely old.
Glenn

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ctwo
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Re: Surface Grinding

Post by ctwo »

The Chevalier 618 surface grinder is still sitting on craigslist. It's a bit gritty, but reasonably priced with a mag chuck and spindex.

I might be able to borrow a Titan pickup, and I think it could handle the weight, but not up so high. It's at least a couple hour drive to take a peek.

How hard would it be to break it down some? At least I read that the table should be removed to protect the bearings from banging and flattening or dimpling the way. I'm not sure how accommodating the seller would be either, or if they have a fork to load it. Not much detail in the ad, but for the price and if I had an easy to get it home, I'd be a couple weeks into grinding by now.

Howard would love the fact that I would install it with a VFD, since I'm sure it has a 3 phase motor...
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GlennW
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Re: Surface Grinding

Post by GlennW »

ctwo wrote:Howard would love the fact that I would install it with a VFD, since I'm sure it has a 3 phase motor...
So will Harold!
Glenn

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ctwo
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Re: Surface Grinding

Post by ctwo »

Howard is my late grandfather's name. One of those things, although I'm sure Harold would be a great grandpa too :D
Standards are so important that everyone must have their own...
To measure is to know - Lord Kelvin
Disclaimer: I'm just a guy with a few machines...
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ctwo
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Re: Surface Grinding

Post by ctwo »

So, that Chevalier was burning away and I was deciding what was going to be more painful. I think it sold, or my search at work does not give me the same result.

I see this one close by... five bills

And there is a fork there... can the table simply be blocked up to protect the bearings?
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Standards are so important that everyone must have their own...
To measure is to know - Lord Kelvin
Disclaimer: I'm just a guy with a few machines...
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