Center Funding With an Edge Finder

[RJSakowski]

Without a DRO, you can still find the center of the hole using an edge finder. Find the left edge first and note the dial reading. Then find the right edge and note that reading. The true center is the average of the two readings. The catch is that to position the hole concentric to the spindle axis, backlash comes into play. You need to know what that number is and add or subtract 1/2 of the backlash to your average, depending upon which direction you are traveling.

You don't have to be dead on a diameter to find the center along one axis. a visual is usually close enough as long as you don't change your position along the other axis. Once you center along one axis, you can position the table so you are an a diameter for the other axis and use the edge finder to center along that axis. If desired, you can redo the first axis but in most cases, you will find no change.

 

[CJ5Dave]

Guess I need to order that. Thanks.

 

[projectnut]

As lang as you're spending money you might as well get one of these.

Shars 0.20" Axis Offset Range Aluminum Body Co-Axial Center Indicator Set S} | eBay

The face of the indicator remains stationary with the help of the stopping rod while the machine spindle rotates in low RPM. Adjust the table position in both X and Y axis to reduce the travel of the dial indicator.

www.ebay.com

I bought one a few years ago thinking that although it was far from the top of the line it would be good enough for what I needed it for. I was pleasantly surprised when it was actually accurate to .0005". I don't use it often, but it has more than paid for itself given the number of times it has been used.

 

[woodchucker]

As lang as you're spending money you might as well get one of these.

Shars 0.20" Axis Offset Range Aluminum Body Co-Axial Center Indicator Set S} | eBay

The face of the indicator remains stationary with the help of the stopping rod while the machine spindle rotates in low RPM. Adjust the table position in both X and Y axis to reduce the travel of the dial indicator.

www.ebay.com

I bought one a few years ago thinking that although it was far from the top of the line it would be good enough for what I needed it for. I was pleasantly surprised when it was actually accurate to .0005". I don't use it often, but it has more than paid for itself given the number of times it has been used.

yea, not an area I would waste my money on. You have to raise and lower the table quite a bit to use it depending on what you are trying to do.
A DTI and some form of holder like an Indicol or similar is a useful setup. Co-AX is nice, but delicate as well.

 

[GeneT45]

yea, not an area I would waste my money on. You have to raise and lower the table quite a bit to use it depending on what you are trying to do.
A DTI and some form of holder like an Indicol or similar is a useful setup. Co-AX is nice, but delicate as well.

I was right with you until you said it was delicate. The Blake version certainly isn't. I bought one years ago (still have it). I like it for a number of things, and it's much more convenient than even my 2-faced Gem indicator, but you're right, they eat up Z height like nobodies business. As an added note I am not so impressed with the (not so) superlative quality of the Blake that I would steer anyone away from knockoffs.

GsT

 

[CJ5Dave]

I bought a bunch of odd tooling with the mill including a box of indicators and parts. Did not look too closely, most of the indicators were bad and the magnetic bases were good, but the parts to connect then to the indicators were missing. The dials themselves, if import, don't seem to hold up too well.

 

[woodchucker]

I was right with you until you said it was delicate. The Blake version certainly isn't. I bought one years ago (still have it). I like it for a number of things, and it's much more convenient than even my 2-faced Gem indicator, but you're right, they eat up Z height like nobodies business. As an added note I am not so impressed with the (not so) superlative quality of the Blake that I would steer anyone away from knockoffs.

GsT

I don't have one, but the imports are notorious for breaking the connection to the probes . That's why I said delicate.

 

[jcp]

I found out the hard way to spend the money on an actual Indicol rather than a Chinese knock off. No comparison in ease of use. YMMV.

 

[RaisedByWolves]

Backlash is messing you up. With a dro backlash is eliminated for measurements.

Using dials you move one way then the other. No way to eliminate the backlash unless you move in the same direction.

You can deal with backlash in a situation by knowing your machines amount of backlash and factoring it in to your math.

Amazon.com

For $15 . Edited for spending others money !

Ugh, most of the cheap ones are utter garbage.

I was given a cheap indicol and had to heavily modify it to make it work just OK. I thought I had it dialed until I bought a real deal unit and then realized how good these should be.

 

[mmcmdl]

Ugh, most of the cheap ones are utter garbage.

I agree . But for a hobby shop it'll work fine .