Calculate Error from uneven rail and reference

[mekanik]

Hi John
Do you have a link to a cheap digital microscope, we used to use the Taylor Hobson kit @ work but there are no cheap options that i know of.
Regards
Mike

[John McNamara]

Hi mike

I also have a Taylor Hobson alignment telescope, not the digital just the older optical model, It is quite a fiddle to set it up and once set if it is knocked it will go out of alignment, having to set the targets and keep checking is slow.

I restored a lathe a while back and used wire, it was a Heidenreich and Harbeck 20 Ro 2.4 metres between centres. to check the straightness of the bed I attached the wire along the side of the bed level with the top of the V's and used an optical microscope. not fancy just a student microscope. the wire was firmly attached and did not need to be constantly checked it never went out of alignment being firmly bolted in position. The microscope was attached to a stage that was guided by the V ways was fixed over the wire and positioned with a Mitutoyo micrometer stem (They are available to be built into an instrument). error readings were taken with the micrometer after positioning the microscope over the wire. it worked very well.

I later purchased a cheap USB microscope About 40AUD it came with software. regrettably I lent it out and it never returned! Hmmm.

So I also need to buy a new one too with cross hair measurement software.
The trouble is there are hundreds of models available for a few quid.

Maybe someone in here has purchased one and can report on it?

Regards
john

[mekanik]

Hi John
Thanks for your reply, since i have been thinking about the rail alignment issue i have wanted to go with optical alignment as this seems the best way to do it, but the cost of a Scope/targets ect makes it a none starter. if i had still been working i could have borrowed the kit from work. will look into USB microscope idea.
Regards
Mike

[John McNamara]

Found a photo of the setup I mentioned, it was just a lashup for a one off, it worked well. Note the bolted on wire support and adjustment unit

[feldah]

Found a photo of the setup I mentioned, it was just a lashup for a one off, it worked well. Note the bolted on wire support and adjustment unit

I was digging a bit deeper in the wire alignment. It sounds quite interesting as I said. previous. I am considering that in our days even a smartphone camera should do the trick. In my case I can go as close as 7cm without loosing focus. one pixel takes then the picture of a 0,015 mm square. One thing I would be interested in if you could explain the construction for the support of the wire. More in detail. As I see it as difficult to keep it in place.

Further I was reading an article where they recommended to use "stainless steel “down rigger” (fishing line) wire, rated at 150 lb" as this would be better then piano wire.
http://fwrc.msstate.edu/southernsaw/alignment1.pdf

But to pull it that hard with 75% force I would need a very rigid support.

[mekanik]

Johns post gives the weight for the required tensioning of the wire, ie 75% of breaking strain. wire is fixed solid @ one end and run via a pulley @ the other with the weight attached. Had a look on ebay and the USB microscopes are as cheap as chips.
Regards
Mike

[feldah]

Johns post gives the weight for the required tensioning of the wire, ie 75% of breaking strain. wire is fixed solid @ one end and run via a pulley @ the other with the weight attached. Had a look on ebay and the USB microscopes are as cheap as chips.
Regards
Mike

But in the article I am referring to they recommend to use sloted adjustment nuts. And a winch instead of weights. I mean from this 150lb wire 75% is a lot of force pulling on the pulley. Also I would expect that a pulley has a lot of play.

Sure for the usb microscope I am not arguing because of the price but the quality. As I am expecting it to have a really bad image sensor for that price.

But I am still trying to fully understand the method they are using in the article.
http://fwrc.msstate.edu/southernsaw/alignment1.pdf