Shopsmith Forums

How flat is a typical steel sanding disk?

How does one analyze a sanding disk to determine how flat it is?

beeg wrote:Use a dial indicator?

OKAY That's the tool and I have one. How do I employ this dial indicator to answer my questions.

Use the dial indicator in the same manner as you use it to check saw blade alignment. I would mount the indicator in a fixed position and slowly rotate the disc and measure the runout.
Is this a test?:D
Bill V

Was just reviewing an old 1983 revision of PTWFE. The section that caught my interest was about aligning the saw table of a 500. It said to find the "high" point of the sanding disk, using the hex wrench through the miter gauge. Evidently all sanding disks are not quite perfectly flat.

After determining that location and marking it - rotate the disk 90 degrees and draw a line across the diameter. Keeping this line parallel to the table set the table mounting screws so the table is parallel to the disk. Rotating the disk 90 degrees (so the line is vertical) use a square to set the table top to an angle 90 degrees from the disk.

Remember that old school trick of mounting the long hex wrench in the miter gauge? We sometimes wonder how things were done before digital technology. Do we ever wonder how accurate digital tools are?:eek:

OKAY. I'll try this differently. I did not get the feedback that I was hoping for. Maybe I'll do better by requesting specific comment.

I have mounted a sanding disk on the left side of the headstock and a very old plywood blade on the other side. The sanding disk is nothing more than a wheel with which I will rotate the drive shaft. The saw blade, for the moment, is the item under test.

I have set a dial indicator on the main table with the table lowered to the position where the dial indicator contacts the blade just above the arbor. I then moved the dial indicator to a position where it contacts the blade just inside the gullets and on the infeed side of the blade.

When I slowly rotate the sanding disc (the shaft), the dial indicator swings about .006". I positioned the disk so that the dial indicator reads the lowest reading and then zeroed the dial indicator. (I think I have located what I will call the low spot). Without moving the dial indicator, I rotate the disk, looking for a "high spot". I found two and they both measure .006". I marked one with a magic marker (I will call that the "high spot").

At this point, I would say that I have .006" runout (attributable to the blade and arbor). Is that a correct analysis? Or am I incorrectly labeling this test result? I have, by virtue of another test not described here, declared that I have .002" runout on the main drive shaft. Therefore, .004" of this variation I would attribute to the arbor and blade.

Now, having found and quantified that high spot, I set the dial indicator to .000" and rotated the high spot to the other side of the blade (outfeed side). At this point, I measure .008". I would, at this point, say that my table is not parallel to the blade and that it is off by .008". Is that a correct analysis?

BTW The old plywood blade looks to be quite flat for a saw blade. Maybe it should be my alignment tool (reference plane).

dusty wrote:At this point, I would say that I have .006" runout. Is that a correct analysis? Or am I incorrectly labeling this test result? I have, by virtue of another test not described here, declared that I have .002" runout on the main drive shaft. Therefore, .004" of this variation I would attribute to the arbor and blade.

Were both tests - the one showing .002" runout and the new one showing .006" runout - tested at the same distance from the arbor?

heathicus wrote:Were both tests - the one showing .002" runout and the new one showing .006" runout - tested at the same distance from the arbor?

To answer your question directly - No. All measurements were made at the same point on the saw blade except the drive shaft runout measurement.

That test was run with no saw blade attached to the headstock. The dial indicator was mounted firmly on the way tubes and positioned such that the sensor was riding on the main drive shaft.

The farther away you are from the arbor, the larger your runout measurement is going to be. The distance will amplify that number. So a .002" runout on the arbor could translate to .006" runout a few inches away. Or am I not understanding your tests?

heathicus wrote:The farther away you are from the arbor, the larger your runout measurement is going to be. The distance will amplify that number. So a .002" runout on the arbor could translate to .006" runout a few inches away. Or am I not understanding your tests?

I think you probably understand the tests but I have to think about your approach to evaluating the result.