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  #1  
Old Mon 18 December 2006, 15:12
Gerald_D
Just call me:
 
Setting the rails straight

Before checking the distance between the rails, there is also the very critical step of laying the first rail down perfectly straight. For this step I g-clamp short pieces of wood to the tips of the rails so that the wood protrudes out the side of the rail to form "shelf-brackets". Then lay a reference straight edge (extruded alu) on these "shelf-brackets" so the rail and the straight edge lie parallel and snug against each other. Then use feeler gauges to feel for gaps between the straight edge and the rail.
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  #2  
Old Mon 18 December 2006, 17:50
Brian_B
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I agree completely, Gerald. But I would consider a different method - somewhat akin to the "MadVac" strategy. The problem with using pieces of wood clamped to the rail is that there is no way to know that they are in alignment. I would go so far as to say that they will not be in alignment and any attempts at using a short reference straight edge will not help. 10'/3 m straight edges are available, but would cost more than the entire mechmate!!

I think my method would be more accurate over longer distances and would be orders of magnitude cheaper. It also will index to the milled point of the rail and not to the surface of the angle iron.

First, you need to have two gauge blocks milled our of 3/4" square stock as in the attached drawing:



The gauge has two opposing v-grooves with the depths of the grooves exactly 0.125" apart - the deeper fits over the top of the rail and the shallower carries and indexes a piece of highly tensioned piano wire. The gauge blocks have been drilled and tapped for set screws to hold them in position at the very ends of the rails.

In this way, you could use a piece of 0.125" thick material (aluminum, etc.) to act a gauge between the piano wire and the rail, shimming and bolting as you go down the rail.

If you wanted to get really clever, you could make the gauge blocks out of something non-conductive like UHMW poly or bakelite and energize the rail and wire with 6 or 12 volts DC and use a conductive gauge between them - wire a light or buzzer in series. In this setup, you would adjust the distance between the rail and wire until the light/buzzer just went out/off.

Brian
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  #3  
Old Tue 19 December 2006, 00:02
Gerald_D
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Brian, the wood I was talking about is purely to carry the weight of the straight edge. We typically use (borrow?) a length of extruded aluminum stock about 30mm high x 100mm wide.
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  #4  
Old Tue 19 December 2006, 05:58
Brian_B
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Sorry Gerald, I misunderstood and thought you were using the blocks of wood as spacers!

However, it got me to thinking that my little gauge blocks should be modified with another v-groove to allow for straightening the rail in both directions:



Using the single piano wire stretched above the point of the rail would only allow a visual "comparison" for straightening in the "y" direction. The addition of a second tensioned wire in the additional v groove would allow the use of a gauge block/feeler to set it more precisely. If you were to check the straightness/flatness of a 3m piece of aluminum bar stock, you would be amazed at how 'un'straight it is. A length of 0.020 piano wire, tensioned to 50 kg would be much more accurate - at least over such a short distance where gravity shouldn't be too much of a factor.

Brian
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  #5  
Old Tue 19 December 2006, 06:37
Gerald_D
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In the woodworking industry, extruded alu sections are the most common reference straight lines. The way to check the straightness is to turn it over (and end_for_end) and repeat the alignment procedure. If nothing changes after turning the extrusion around/over then it is a good reference.
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  #6  
Old Thu 23 August 2007, 19:52
Doug_Ford
Just call me: Doug #3
 
Conway (Arkansas)
United States of America
Straightening the Rails

I didn't have any extruded aluminum around the garage when it came time to bolt down my X rails and ensure they were straight so I came up with an alternative strategy.

I began by clamping a strip of metal to the vertical part of the end of one the main beams. Then I clamped one to the other end. Halfway up the strips, I added a small clamp. Then I stretched some .010" fishing line between the clamps immediately over the top of the center of the bevel. The threads of the small clamp are great for holding the line in place. If the threads are too coarse and the line needs to move slightly one way or another, you can simply bend the metal strip a little bit.

Once the line was in place over each end of the rail, I used a 5X jewellers loupe to look down on top of the line and was easily able to see where adjustments needed to be made.
Attached Images
File Type: jpg Straightening System.JPG (35.6 KB, 2600 views)
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  #7  
Old Thu 23 August 2007, 22:06
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
A lot of people use the line method, mostly with fine metal wire.
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  #8  
Old Tue 13 October 2009, 16:12
Allegheny
Just call me: Brian
 
Massachusetts
United States of America
For those that want to take the use of stretched wires to a high level of precision, consider that old-time millwrights set up massive machines using piano wire and a few precision tools (like precision gauge blocks and various styles of indicators). One of the important things to know is the effect of gravity on horizontally stretched wire. The link below has "sag" tables:

http://www.millwrightmasters.com/Sch...wire-sag_1.htm

Brian
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  #9  
Old Thu 24 June 2010, 05:50
rotorzoomer
Just call me: Account - DISABLED
 
Account - DISABLED
Australia
Rail Levels

My rails are perfectly parallel and level across the X axis but both rails on the X are tilted back outwards 0.9 degrees which makes the gantry v roller bearings not sit properly but only just!!

According to my calibrating methods, i can almost avoid all shimming of the X Rails if i can only tilt the V Roller bearing on the Y - Car to match the x rails angle offset.

Is this advisable?
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  #10  
Old Thu 24 June 2010, 07:49
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
If it is only 0.9 degrees I would leave it as it is.
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  #11  
Old Thu 24 June 2010, 08:19
Besser
Just call me: Besser
 
Vic
Australia
BFH + VSS = alignment

vss -> very small swing
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  #12  
Old Thu 24 June 2010, 08:40
rotorzoomer
Just call me: Account - DISABLED
 
Account - DISABLED
Australia
Besser, i am not sure how to follow that info?
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  #13  
Old Thu 24 June 2010, 14:20
smreish
Just call me: Sean - #5, 28, 58 and others
 
Orlando, Florida
United States of America
big fun hammer + very small swing = alignment.

I prefer bar clamps and shims:_)
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