Calculate Error from uneven rail and reference

**John McNamara** · 03-02-2019

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

Click image for larger version.

Name: 4-02-2019 1-01-41 AM.jpg
Views: 263
Size: 218.1 KB
ID: 25421

**feldah** · 03-02-2019

Hey love the idea simple and good.

Sent from my MI 6X using Tapatalk

**feldah** · 09-02-2019

Originally Posted by 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

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** · 09-02-2019

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** · 09-02-2019

Originally Posted by 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

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

**magicniner** · 09-02-2019

This is starting to sound all "Model Engineer" where they can achieve "almost acceptable" (but not near industry standard) results from the input of unacceptable amounts of time and effort!
:D

**John McNamara** · 10-02-2019

Hi All

Below is two images of the wire supports I made, As you can see made from scraps of mild steel rough machined to size. The dovetails (SIC) are just groves cut with a standard end mill with the parts held at 45 deg in the mill. I also machined the clamp to fit the bed of the lathe the clamps were set about 3800mm apart.

The long dovetail rail has two carriages one fixed one movable by a simple screw, that provides a simple Y axis, the slide clamps were set very tight for lateral adjustment the stack of washers on a grade 8 bolt worked fine, the wire does not run on the threads just the smooth section on the bolt For scale the large fastenings are M8. While he setup was crude it got the job done, once tightened the setup rigid and .0001" setting accuracy was easily obtained.

My objective was to get the job done fast a few hours making the jig. They are not pretty. certainly not up to the standard of a model makers work.

Stainless steel has a lower tensile strength than carbon steel.

You need the lightest weight, and that will be the the thinnest material with the highest tensile strength to resist the pull of gravity. I double checked the number on my roll of Roslau wire and it is marked #2 it measures about .008"
I remember at the time there was a finer one but it was not in stock.

The only real alternative to high carbon steel is a synthetic material like carbon fiber, Aramid etc. I have read university papers where these materials have been tried. They were more difficult to read because of uneven the surface finish on the material. They are also non conductive, one very popular method to sense the wire is by a simple electrical contact. (Actually the point where contact is lost, that guarantees you are not deflecting the wire.)

Regards
John

**magicniner** · 10-02-2019

Very impressive, how does the machine run?

**feldah** · 10-02-2019

Haha great that sounds perfect. Especially the stack of washers. Thank you for the inside information. I know a bit of computer vision so I think I will go with the optical approach instead of the electrical contact. With an automatic edge recognition I could easily read out the error. Only downside now for me with the Röslau wire seems to be that it is transparent but it should be fine. Do you remember the pulling force/weight? If not I will find out.

Sent from my MI 6X using Tapatalk

**John McNamara** · 10-02-2019

The weight was a 4140? 200mm dia gear blank 35mm thick I never did weigh it by calc about 11kg

Roslau blue label carbon steel wire is not transparent?

The lathe if you are referring to that works fine I use it every day. Not perfect but near.

There is a picture of Heidi in this old paper I wrote when she got her referb.

http://www.mediafire.com/file/b0rxnx...mpact.ppt/file

Regards
John