Autocollimator

[pressbrake1]

I’m Pretty sure he did.
prior to him coming up with scraping with blue, they used to use a polishing compound on the three plates. The results were no where near as good. By scraping he could quickly knock down the high spots, then lap the three plates together when they were already quite flat. Joseph Whitworth literally came up with a ‘thou. The accuracy in machine tools and more importantly metrology equipment all followed on from his incredibly (for the time) flat planes.

I’ve originated with three plates
Two identical concave can be scraped off each other to make straight
The third convex is to create identical concave standards

 

[pressbrake1]

Better explanation than my simplified version. Carpenter and stone masons had done it for centuries or millennia

 

[Seadog]

Extracts from your course work in 1850 Clive?

 

[pressbrake1]

Extracts from your course work in 1850 Clive?
Hey you’re the old timer!

 

[Wedg1e]

If only pensions were that simple

 

[Pete.]

3-plate rotation is for serious masochists and apprentices only. These days you can buy a standard which you would struggle to replicate with scraping. Or use equipment capable of measuring several orders of magnitude finer than your desired result.

I've got a 12x18" iron plate on which my 1um repeat-o-meter doesn't waver. Scraped by a master who added his nameplate to the hardwood protection cover. I use that as my standard and I'll cherish it just as much as the creator obviously did. It's as good as I can measure with my modest equipment and easily meets AA standard.

 

[Pete.]

I've just bought another Hilger & Watts autocollimator, a slightly later TA1-5 model. It has a slightly different layout and increased resolution, also has a larger eyepiece. It came out of a college so had very little use, as seen by the great condition paintwork. It was however very grubby and the box needs re-finishing where it's been damp.

Still, it's a very nice instrument so I'll be keeping this one and selling the first to cover the cost.

 

[Pete.]

Nice! That’s very clean. If you see any decent granite plates let me know.

Thanks, I will Brad

I refurbished the box on the weekend. It had been damp and the finish had suffered, plus the lid was badly gouged from aving other things stacked on it. I wtried to revive the old shellac finish with meths but that didn't work so I sanded off the whole of the outside and oiled it. Came out nice, I also claeaned up all the brass fittings.



The leather handle was perished so I used a piece of handbag strap I got off one of the ladies of the hosehold.





New box compared to old box

 

[Pete.]

I also made a mount for my mobile phone just like I did for the first one. This instrument had a removable eyepiece with a 40tpi thread so I turned up a screw-on collar





Then I turned another collar to fit inside the first and glued that onto the phone case. This time I made the hole for the camera just a bit bigger than the camera eye to aid alignment.



Now with the phone attached I get a cracking good zoom-able image which means I don't have to keep stooping down to look in the eyepiece.