Checking for taper on a cylindrical grinder, what tool?

ballen · Feb 26, 2018

I am learning to use a cylindrical grinder. I want to measure the taper with micron accuracy at many points along a cylinder, so a micrometer is not so handy for this. What I need is a "C-shaped" tool which I can put a Millimess or other micron-scale indicator into, then slide onto the cylinder at various points along the length. The end away from the indicator should be a flat hardened landing surface, perhaps a centimeter or two in size. (Or a shallow V?) Sort of like a lightweight dial indicator stand, which I can easily lift up to the work.

Ideally this would be able to handle the range 0-100mm, with perhaps another to go 100-200mm.

Is there a standard tool for this? I don't need the absolute diameter (or I can put in gage blocks for that, if needed). I just want to easily measure/monitor how the diameter is changing along the cylinder, without removing the work from the machine.

Red James · Feb 26, 2018

One of the really nice things about grinding between centers is that the part can be removed from the machine, measured, then returned EXACTLY in the position it was originally in.

Now you can check the diameter using a surface plate and surface gage.

Oops! You want to check closer than surface plate flatness. Sorry for the post, it does not help you.

ballen · Feb 26, 2018

Red James said:
One of the really nice things about grinding between centers is that the part can be removed from the machine, measured, then returned EXACTLY in the position it was originally in.

At the micron level, it seems that removing and replacing the part on the centers can change things a bit. I don't understand why, and perhaps it's because I am doing some bad technique. So if possible I'd like to compare the diameter along the part without removing it.

RJT · Feb 26, 2018

Sounds like you want a snap gage. Grinding to those tolerances for a novice is going to be time consuming. Got anyone with experience to teach you? Make sure your centers in the part are round and dead centers are round and of appropriate size. make sure your drive dog is not pulling your part off center.Watch some you tube videos.

Gordon B. Clarke · Feb 26, 2018

ballen said:
I am learning to use a cylindrical grinder. I want to measure the taper with micron accuracy at many points along a cylinder, so a micrometer is not so handy for this. What I need is a "C-shaped" tool which I can put a Millimess or other micron-scale indicator into, then slide onto the cylinder at various points along the length. The end away from the indicator should be a flat hardened landing surface, perhaps a centimeter or two in size. (Or a shallow V?) Sort of like a lightweight dial indicator stand, which I can easily lift up to the work.

Ideally this would be able to handle the range 0-100mm, with perhaps another to go 100-200mm.

Is there a standard tool for this? I don't need the absolute diameter (or I can put in gage blocks for that, if needed). I just want to easily measure/monitor how the diameter is changing along the cylinder, without removing the work from the machine.

Why would you want to measure taper at several points? If you want to measure taper measure the difference at each end of the length and then use trigonometry.

Do you suspect your grinder of having a fault giving a taper or are you trying to measure a deliberate taper?

sfriedberg · Feb 26, 2018

I'll tweak RJT's reply slightly, look for "indicating snap gage" or "dial snap gage" which is a bit of a mongrel name. The snap gage gives you the C frame and a hard reference surface, the indicating/dial part gives you a indicator mount instead of a simple go/no-go comparison.

The Starret 1150Z is the sort of thing you want except that it's a bench tool where you bring the work to it, not it to the work. The Mahr Mahrmeter 300P or 840F, or Mitutoyo 201, are probably more appropriate to your intentions. Not cheap.

ballen · Feb 26, 2018

Hi Gordon,

Gordon B. Clarke said:
Why would you want to measure taper at several points?

I'm learning to use a cylindrical grinder. For example this bar (45mm diameter, 500mm long) is 2 microns larger in diameter at one end than at the other end. But it's 10 microns larger in diameter in the middle, tapering smoothly to both ends.

The experts tell me that this is because I ground it without using a "support finger" in the middle. The support finger has a spring that pushes the bar a bit towards the grinding wheel. You set the spring force by (you guessed it!) measuring the change in the diameter of the bar between the ends and the middle.

Hence the need for a simple and reliable way of measuring the diameter along this bar, and similar ones.

(PS: also, the way that you adjust the grinder table to "take out the taper" requires measuring the difference in diameter at the two ends of the bar.)

Cheers,
Bruce

Kaszub · Feb 26, 2018

Wheel is pushing material away from center. It is just like on a lathe same thing happens.

Gordon B. Clarke · Feb 27, 2018

Kaszub said:
Wheel is pushing material away from center. It is just like on a lathe same thing happens.

For Bruce:

What happens if you grind as little as possible on the final pass? Maybe take one more pass without any adjustment?

How often to you "clean" the grinding stone? It might be "rubbing" more than grinding.

ballen · Feb 27, 2018

Hi Gordon,

It might be that with more spark-out passes, this effect goes away. But the experts say I need the support finger to get the last microns out. Perhaps in a vacuum what you are suggesting would work. But the air and coolant near the wheel put pressure on the bar, even if the wheel is not touching/cutting.

The stone is freshly dressed. It is cutting, not rubbing.

Any further suggestions for a good tool to do what I have asked? The dial snap gauge (for example Mitutoyo Dial Snap Gages-Series 201) looks good to me. One flat anvil and one ball? Or two flats?

Cheers,
Bruce

CarbideBob · Feb 27, 2018

ballen said:
......

Is there a standard tool for this....?

Of course there is an Adcole or even a Jenoptick hommel that would do this.
Got the 1/4-1/2 million ante?
Mits has some new but high priced mics which are friggren great at a much lower price level. (one would want to do a R&R here and operator training counts big)
With some thinking old school LVDTs and difference units get you into a cheaper way.
C-frame setups at this tolerance have a R&R problem no matter how good the indicator due to user variation.

When you get into the small world people lie to themselves about what they can do or measure....A human nature "gut feel" thing.

The "spring" in the center of your part is natural. The how to kill is wheel loading and even with a thousand passes part sag (catenary curve) so a mid rest is sort of needed and the push force varies.

Or you could just buy a decent sized though feed centerless and whip it out in no time.
Bob

Street · Feb 27, 2018

The Mic can go to 0.001mm increments on a special we'll moderately special one the feel however is very important at that level as you can measure incorrectly- Still a mechanical micrometer.
Lower than that its a digital micrometer or a snap gauge with a special dial attached.
Small deviations the surface are still relatively flat in effect to the anvil faces of a micrometer.
The snap gauge may get what your looking for in regard to elimination of feel errors but absolute size i think you will fall back to a micrometer as snap gauges need calibration for a standard size.

You can grind such a range of sizes i think snap gauges are going to get expensive to cover all.

So digital micrometer with a keen sense of feel is needed, if the sizes your chasing are below 0.001mm

I have had great difficulty getting repeatable results on measuring bearing balls at that level my feel effected the measured size a lot i have found.

That just my take on it.

RC99 · Feb 27, 2018

If I got that level of straightness over 500mm with my grinder I would be over the moon.

Are you sure you are not over estimating the ability of the machine in a non temperature controlled room.

bebop · Feb 27, 2018

Having done a fair bit of match fit grinding for hydraulic servo valves. I can say that its very challenging to hit sub micron tolerances in a non temp controlled environment. Everything becomes a detail that must be addressed , the wheel, the diamond, what kind of coolant, it might work great for one kind of material but not for another , oil in the wheel head, the bearings in the wheel head , is a truck going to drive by as your making your finish pass and cause a change in your finish, and on and on. As for what to use for use for checking the part for taper I have a couple of Mahr Marameter pick what resolution of Millimess works best for your application and your on your way .... but not for sub micron, then you need something in the line of heavy comparator stand and I prefer CEJ Mikrokator's .
as always YMMV
Cheers Don

ballen · Feb 27, 2018

RC99 said:
Are you sure you are not over estimating the ability of the machine in a non temperature controlled room.

The machine is "new" to me, so I am trying to see how good I can get. But I don't know how much is me, how much is the grinder, and how much is the room.

Since the diameter is 45mm and the expansion coefficient of steel is about 10^-5 per Celsius, a 10 Celsius temperature change (18 Farenheit) will change the diameter by 4.5 microns. I think when I am doing these measurements the different ends of the bar are within 2 Celsius in temperature, so I suspect that it's not an issue.

ballen · Feb 27, 2018

Hi Don,

bebop said:
As for what to use for use for checking the part for taper I have a couple of Mahr Marameter pick what resolution of Millimess works best for your application and your on your way .... but not for sub micron, then you need something in the line of heavy comparator stand and I prefer CEJ Mikrokator's .

Thanks for the comments. I own four different devices that read at the micron level:

- Mahr Millmess indicators 1 and 0.5 micron divisions
- Mahr Millimar electronic LVT which is 3 microns full scale
- A Mikrokator with 1 micron divisions
- A Heidenhain MT-30 linear optical indicator and digital display with 1 micron resolution

But I need something to hold these devices in, so that I can carry them to the work, zero them at one end of the bar, and then move along the bar to different points to see the deltas. So the question is: what can hold these?

So far the "snap gauge" C-frames look like the right way to go. Is there one where I can insert one of the devices above? All but the Microkator have European standard 8mm stems.

Cheers,
Bruce

bebop · Mar 1, 2018

Yes Bruce, the Marameter link I posted is a Mahr "C" frame for holding a millimess quite handy, but ... nothing hand held is really suitable for sub micron gaging, these "handy" things at the end of our arms should be 98.6 F (37c) locally heating any and everything the come close to. But for checking taper a Marameter frame with a Millimess indicator should work quite well.
Cheers Don

ballen said:
Hi Don,

Thanks for the comments. I own four different devices that read at the micron level:

- Mahr Millmess indicators 1 and 0.5 micron divisions
- Mahr Millimar electronic LVT which is 3 microns full scale
- A Mikrokator with 1 micron divisions
- A Heidenhain MT-30 linear optical indicator and digital display with 1 micron resolution

But I need something to hold these devices in, so that I can carry them to the work, zero them at one end of the bar, and then move along the bar to different points to see the deltas. So the question is: what can hold these?

So far the "snap gauge" C-frames look like the right way to go. Is there one where I can insert one of the devices above? All but the Microkator have European standard 8mm stems.

Cheers,
Bruce

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Checking for taper on a cylindrical grinder, what tool?

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