Something similar was discussed back in 2015:

**LINK**

Regards

David

Perhaps something like this **LINK**

Rod

.

A 'Digital Read-Out' system.

But having been now seen the link kindly provided by Rod it may seem that I was wrong about the costing.

But you would of course then have to make the optical device linked. And it's accuracy for ever more would depend on how accurate you made it in the first place.

Nick

I used to deal with an old time toolmaker who used something like you describe, don’t know what it was called but it was basically a clear plastic block with a hole in it. Across the underneath face it had two lines engraved/scribed, these lines were lined up vidually on your marked out work and a close fitting centre punch dropped into the hole and tapped.
This guy could work to close tolerances using it!

Alan

The very first issue of MEW carried just such a device – home brewed, of course and very simple – it must have been 'cos I made one and it worked! It may still be lurking in the chaotic shambles of my workshop but more likely went to the skip with the other debris from the 'surge'. I also had a much rarer beast – a drill chuck on a 2MT taper which had a built-in centring viewer!! Clever idea but a bit short on practicality, as you had to place your eye against the chuck body to view the centre! If not available elsewhere, I may be able to send you a copy of the MEW article, assuming Neil and his paymasters don't object.

rgds

Bill

Tell you what, send me a scan of it and I'll put it up on the website

Hawkeye you are not mad they were in regular use in the 60's bothe before and after that time they were called Optical Centre finders as far as I recall, used them many times.
Both Roderik and Steve M are spot on but the ones I used the eye piece was at 45 deg so easier to view than the 90 deg ones shown but you would need a prism for this. Never seen a S/H one for sale but guess they must come up now and then.

This is a very good place to buy prisms: **LINK**

http://surplusshed.com/search.cfm

Just put prism in the search box and have a browse.

Postal charges a very honest too [although USPS costs increased quite dramatically last year]

MichaelG.

I use a laser edge / centre finder.

http://littlemachineshop.com/products/product_view.php?ProductID=2604

Reg

Or look at something like an App similar to Camerfi that works on a mobile phone but you will need a USB to Micro USB converter for the cable.