Electronics > Mechanical & Automation Engineering

fascinating way to find center point of shaft

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coppercone2:


In this video, he finds the center point of a shaft by putting it into a drill press and pressing it into sand paper. Since this make concentric circles, I guess you can optically find the center point with good? accuracy.

It's not like a substitute for a lathe, but I can see this helping some people out a fair bit.

Gyro:
Isn't that going to give you the centre of rotation rather than the centre of the shaft? If the shaft is bent or there is runnout on the chuck then the centre of rotation wont match. Pressing the shaft into the sandpaper will probably exaggerate runnout and shaft flex because it doesn't have a centre point to locate it (as with a drill bit) so it will tend to 'shuffle'.

The best bet is to hold a small piece of sandpaper in your hand and bring it up to the end of the shaft so that the softness of your finger will cause it the wrap slightly up the sides. This, combined with the flexibility in your finger, will make it follow the end of the shaft. Note: Make sure that the end of the shaft isn't burred / sharp (and capable of cutting through the sandpaper into your finger) and that your finger will get hot!

jpanhalt:
What do you do if you want the center of 2" dowel and don't have a chuck that big?  That is, it's an obvious method but with very limited application.
 

Ian.M:
The guy is a hack! 

At 1:40 to 2:10 you can see him hammering on the output shaft to extract the bearing and to extract the shaft from the bearing.  No attempt was made to protect the bearing against brinelling so that bearing is definitely compromised. 

Also, I don't like the interference fit of the old shaft stub to the new motor shaft (8:44 to 8:54).  That should have been either bonded with Loctite 503 or similar, or a shrink fit or drilled and tapped for a grub screw and counterdrilled for balance.

thm_w:

--- Quote from: Ian.M on March 03, 2022, 11:00:11 am ---The guy is a hack! 

At 1:40 to 2:10 you can see him hammering on the output shaft to extract the bearing and to extract the shaft from the bearing.  No attempt was made to protect the bearing against brinelling so that bearing is definitely compromised. 

--- End quote ---

Hard to know if he replaced the bearings or not.
He did use a wooden mallet, if it were anything other than an old hand drill, maybe I'd be concerned.

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