If only the flat burrs are to blame, then it sounds like a very easy solution.
Good for you and your customers if it can be sorted out so easily.

Good luck from my side and all the best for you.

I hope that I didn't say it was only the flat burrs. The larger exit channels that some have will be a problem.

I suggested that years ago we probably had some problems with inner conical alignment, there were several errors in our original concept of how to locate it (including the idea of the accuracy of the hole and its fit to the inner conical) that didn't work out with manufacturing possibilities. When this was improved I can't remember -- other than that it was quite a lot of years ago.

A replacement inner conical might make a lot of old grinders happier.

This morning I measured the axial run out of a grinder on our bench. I knew it would be good but... it was .0002" (.005mm) or less. I was using a Brown & Sharpe lever indicator - the smallest measurement on the dial is .00005". I don't guarantee that all will be that good, but it is quite possible.

I measured radial runout:
http://www.vimeo.com/267534053

Axial runout:
http://www.vimeo.com/267533402

And the static burr perpendicularity to the shaft:
http://www.vimeo.com/267533579

So to test the hypothesis of the parallelism of the conical burr I did the following. Mounted the conical burr (the right way), and mount the lower burr driver upside down. So the pointed end of the aluminum carrier pushed the conical flat against the shaft.
http://www.vimeo.com/267534137

The measurements you get are better - but I am less than +-0.05mm on all measurements (perhaps radially needs a better fix, my guess is that it required realignment between the top and middle plates to center it better.) It takes two notches (small notch) from the two burrs scraping to the burrs completely touching. Which is better than before.

But nowhere close to John's measurement (or Frank's).

Try this test. Take the bottom burr off the burr driver. Put the burr driver and inner conical back together. Of course make the mating surfaces extremely clean. Put the indicator on the bottom burr register surface (that face that the bottom burr is fastened to) on the burr driver. This will test how well the inner conical fixes the position of the burr driver and therefore the bottom burr.

If there is much error, which I suspect there will be from the extent of your problems, try to determine what is causing the error. A burr (not grinding burr) on a mating surface (shaft face, top and bottom inner conical, burr driver)? Rotate the top of the inner conical against the face (it is positioned against) to feel if they both smoothly rub against each other. Is there a radius where that face of the shaft transitions to the smaller diameter that goes inside the inner conical? And a matching countersink on the top of the inner conical?

John - it will take a few more days to run the test you suggest.

Meanwhile - I don't know if you noticed but I did something similar in one of the movies above. The configuration is as follows (the Brown & Sharpe Bestest lever indicator is seen on the bottom touching the conical burr)


And this is the movie:
http://www.vimeo.com/267534137

Once I do the test - what do I need to do to get the alignment back in order (other than rebuild again and again until I stumble upon perfection)?

Thank,

Assaf

BTW - The Brown & Sharpe I have is metric, hence the yellow dial. 0.01mm is the resolution.

Hi Assaf, I would like to make certain that we talk about exactly the same things. So I will be wordy.

The alignment of the bottom burr - let's call it a vertical wobble that once a revolution increases then decreases the gap between the flat burrs - is controlled in the following manner.

First the shaft needs to revolve in the bearings so that it has less than .003 radial run out - measured at the bottom end. The grinders that have been being shipped for some years (2013) are very precise and can't be adjusted as I will discuss here. If there is more than that run out, loosen the top pulley bolt, and by hand slowly move the shaft to run more true. Don't apply too much force, firm pressure is fine. Slowly tighten the pulley bolt while checking and readjusting if necessary. The bolt should be torqued to 150 inch pounds.

With the shaft running that true, the face of the shaft that the inner conical fits against should be equally running true since all those surfaces are machined together. The inner conical should show signs that both end faces were surface ground. So providing the shaft and top of the inner conical are clean and free of surface protrusions (burrs) the bottom of the inner conical should run as true as the face of the shaft.

There are things that can cause problems with this. It will be good if you can take a picture of the face on the shaft I have been talking about so I can see the transition from the face to the lower end of the shaft. Then also a picture of the top of the inner conical.

The inner conical is meant to sit flatly against the shaft face, with a few thousanths of an inch clearance to the lower shaft. Without this clearance the lower shaft will prevent the inner conical from sitting properly on that face.

Thank you for the details. I'll measure, photograph and get back to you.

versalab wrote:First the shaft needs to revolve in the bearings so that it has less than .003 radial run out - measured at the bottom end.

Hi John, at what point of the shaft, that you describe as "bottom end" do you make this run-out measurement?
Best regards, Bernhard

The very lowest end. As far from the bearings as possible.