Ze MK I Eyeball

[John S]

Do you ever doubt yourself when looking at a job?
WELL DON'T
The MK I eyeball is more accurate than you think.

Over the years I have bought no end of fancy gadgets to help me speed up what I do in the workshop.
Some have been a help but often I still fall back on old tried and trusted methods.

Take centering a shaft up in the mill for cutting a keyway or cross drilling. I have tried edge finders and split the difference, a dowel with marker blue on and touch each side till it rubs then split the difference, one of those upside down vee things with a pointer on and loads of others, only to go back to the time honoured method of dobbing the cutter down on the work and looking at the marks, a bit like reading tea leaves.

Well talking to someone the other day about this he reckoned that it wasn't accurate enough and had to be to within two tenths of a gnats left bollock etc

So I decided to do a mythbuster.
In the following pic the shaft has been centred up bang on using edge finders and the mills DRO and the spot on the left is a 6mm cutter just touched on the work, notice the overlap both sides as being equal as it should be.

Now the spot on the right is with the DRO moved off centre by 2 thou, no bullshit, just 2 thou, now note the uneven over lap.

So the MK I eyeball is good to at least 2 thou.

 

[BobWarfield]

Interestingly, I have heard that 2 thou figure in a couple of other places too.

First, in Machine Shop Trade Secrets, I believe he mentions that figure for tramming a vise with a straightedge. Not hard to do, place your long straightedge in the vise and line up the edge visually with the table edge or a T-slot. Works great with my 30" straightedge and I use the thing a lot more often. If I need better, I add a pass with the tenths indicator. Amazing how much easier that is when things are very nearly right to begin with.

Second, I can't remember where, but I seem to recall reading somewhere you can eyeball the point of a drill bit over to a mark with about that accuracy.

The Mk I eyeball is one of you most important tools--take good care of it as they're hard to find replacements for!

Best,

BW

 

[derekm]

I have Ze Mark 1 eyeballs but I cant find a manual anywhere

 

[ksouers]

I've got a pair of Mk 1s, but they are severely out of calibration due to age :

 

[Cedge]

Don't forget the mark 1 mod zero fingernail. The sensitivity of the average fingernail can detect as little as a half thousandth of variation in a flat surface. It's not much for centering, but it sure knows flat when it feels it.

Steve

 

[baldrocker]

My wife had the Mk2 Eyeballs.
You know the ones in the back of the head ;D
BR

 

[Dhow Nunda wallah]

I used to have a MK II eyeball or 2, they've since been downgraded cos they no longer meet ISO 9001
The Mk 57 fingernail and the less calloused parts of me pinky still work though.

For wot it's worth, have a shufti at this

http://woodgears.ca/eyeball/

 

[Jadecy]

That is a fun little game. I may play that some more to work callibrate my mk1 eye ;D

 

[tel]

Hmmm ... 4.41 Guess the ol' eyeball still retains something.