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  #1  
Old Sat 21 May 2011, 13:01
JamesJ
Just call me: Jim #104 (retired)
 
Kansas
United States of America
Once again I have been away for some time. Fortunately not having posted does not mean that no mechmate work is getting done. Even when circumstances don't allow me to post I am always watching the forum so I can learn from the other builders. I had progressed to the point of needing to setup my rails and I did manage to take some photos the process. I started with the x-axis with the idea of using the same methods on the y-axis. Lacking any accurate 10' long straight edge I settled on the wire method. This method involves supporting a wire of known diameter at two distances of known separation while having the wire under a known tension. Since my rails are of a uniform height, the wire can be used as an accurate reference when setting the x-axis installed rail height provided that I compensate for the wire sag. Suitable wire sag tables can be found on the Internet.

This photo shows the overall setup in place on the x-axis.


Here are several photos of the setup I used to support and tension the wire.




By slotting the wire support bars where the bolts pass through, I can set the wire to the correct height above the top surface of the x-axis rail at each end. I started with the bar too high and by leaving the bolts snug but not too tight I was able to tap the bar downward while checking the distance above the x-rail top. Since I did not want the wire to touch the rail due to sag I chose to set the wire .025 " above the rail tops at both ends. When using a wire as a reference it is important to avoid touching the wire as doing so will displace the wire and result in inaccurate results. I also took the time to align the wire laterally to each end of the rail. This was accomplished by bending the support bar to one side or the other slightly until the wire was positioned in the center of the flat area of the top of the rail. I then proceeded to use feeler gauges to determine the distance below the wire of the rail top at each location where the rail is bolted to the table beam. I used a .025" feeler gauge that I mounted on a fixture to account for the initial wire distance above the rail top.

Here are a couple of photos of the fixture in use.


I then added feeler gauges by slipping them under the .025" feeler gage until I could add no more without touching the wire. This gave me a initial measurement of how thick the shims beneath the x-rail needed to be. The next step is to account for the wire sag by adding the wire sag value to the initial measurement in order to arrive at the correct shim height needed. In my case the wire sag was approximately .006" at the mid-point of the wire. Example: If I had to insert .020" of feeler gauges at the mid-point I would need to add .006" to this to account for wire sag which would then require .026" of shims be placed under the rail to bring that point to the correct height. Once a shim was put in place I then re-checked the distance and, if necessary, made additional adjustments. I followed this procedure for each bolt location by interpolating wire sag charts to come up with wire sag values for each location.
Once I had shimmed each bolt location to the correct height I then used the wire to do my lateral rail alignment to insure that the rail is straight. I found that by using a magnifying glass it was easy to get the rail aligned and straight.
I hope you will find explanation this useful. I have received so much assistance from the mechmate community I wanted to add to the community for a change.
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  #2  
Old Sun 10 July 2011, 20:12
MetalHead
Just call me: Mike
 
Columbiana AL
United States of America
Here is the SAG Chart
Attached Files
File Type: pdf GE Tight-Wire SAG Chart.pdf (69.5 KB, 545 views)
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  #3  
Old Mon 07 October 2013, 16:57
Mrayhursh
Just call me: Hurshy
 
Riverview, Florida
United States of America
Awesome

I was wondering how I was going to do this. I was thinking laser. Wire is cheap and easy. Thanks.

Mike do you run...own..Mechmate Forum.

I was wondering, CNC is projected to become the centralized foundation for home grown businesses in the next ten years. This is similar to what happened in Japan after WWII. Where machine shops moved from factories into homes. Companies are looking for local sources for manufactured parts. China is only interested in orders of 100K or greater. Does the forum have any ideas of expanding beyond the CNC table concept.

If you think of the MM table in a componentized manner it has a CNC control center, and machining surface, and a cutting head. These are the same items needed to build a slant lathe(which are starting to become more popular), or a vertical mill.

Is MM interested in expanding beyond the table and building a slant Lathe?
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  #4  
Old Mon 07 October 2013, 21:01
MetalHead
Just call me: Mike
 
Columbiana AL
United States of America
We let the zone cover these other areas. I do have thoughts around a table top version but have not really decided on how to move that forward. I do not want to split the focus of this forum and the content it holds.

If you have ever noodled around on other CNC related sites, you know how hard it is to stay on your topic. Not an issue here. It is ALL MechMate ALL the time !!!

But I will leave a small crack in the door for a desktop version using the same control box.
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