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Message |
    
fabrica
Registered
Username: Daya
Post Number: 126
Registered: 10-2006
| | Posted on Monday, December 18, 2006 - 08:54 am: | 
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To get the exact parallel distances between the Y Rails correct don't you think that a Guage rod similar to what was used for the table should be used.
If so what should be the lenth of the Guage rod. |
Gerald_D
Registered
Username: Gerald_d
Post Number: 642
Registered: 11-2005
| | Posted on Monday, December 18, 2006 - 09:30 am: |
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549 or 555mm ??? I get conflicting info between two drawings I have here. Let me check that later today.... |
fabrica
Registered
Username: Daya
Post Number: 127
Registered: 10-2006
| | Posted on Monday, December 18, 2006 - 09:56 am: |
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Ok, I will await your reply. No hurry. |
Alan Conolly
Registered
Username: Alan_c
Post Number: 11
Registered: 07-2006
| | Posted on Monday, December 18, 2006 - 10:22 am: |
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I get 554 from the drawings and 554.9 from the sketchup model.
424(width of carrier plate) + 2x25 (to centre of cross member tubes) + 2x46-6 (centre of fixing hole to outside edge of rail minus rail thickness) = 554. |
Gerald_D
Registered
Username: Gerald_d
Post Number: 643
Registered: 11-2005
| | Posted on Monday, December 18, 2006 - 11:09 am: |
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Havn't done a detail check yet, but 555 sounds like the right one. Alan, that 424 of the carrier plate ends in the real world as 425 between the cross-tubes.
The actual dimension is not critical because the spacers behind the v-wheels get adjusted at the end. |
Gerald_D
Registered
Username: Gerald_d
Post Number: 644
Registered: 11-2005
| | Posted on Monday, December 18, 2006 - 02:33 pm: |
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Yes, 555mm is the right length for a gauge rod for the rails on the y-gantry. |
Brian_B
Registered
Username: Allegheny
Post Number: 8
Registered: 07-2006
| | Posted on Monday, December 18, 2006 - 07:41 pm: |
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Rather than use a gauge rod, I'd suggest having a gauge machined out of square steel stock (either 3/4" solid, or 1"/greater tubing with heavy walls.
Have the machine shop machine two parallel V grooves exactly 555 mm (or whatever distance) apart. These grooves should be perpendicular to the long axis of the steel.
By setting directly on top of the bearing surface for the the V rollers, this arrangement has several advantages: 1) it will index the actual bearing surfaces, and not simply the inner face of the rail's vertical portion - this is important as the unmilled surface of the angle may not be regular, and the milled V point may not be exactly centered as well; and, 2) it's a lot easier. By resting on the top of the rail, it's self supporting - a gauge rod has to be held in place somehow. The inverted V slots would be self locating and would allow the gauge and the two rails to be clamped together. I would suggest straightening and bolting one rail into position and then using the gauge to clamp/bolt the second.
If you opt to go this route, don't forget to have a second set of grooves machined for the y-rails at the same time!
Brian |
Gerald_D
Registered
Username: Gerald_d
Post Number: 646
Registered: 11-2005
| | Posted on Monday, December 18, 2006 - 11:12 pm: |
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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. |
Brian_B
Registered
Username: Allegheny
Post Number: 9
Registered: 07-2006
| | Posted on Tuesday, December 19, 2006 - 01:50 am: |
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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 |
Gerald_D
Registered
Username: Gerald_d
Post Number: 648
Registered: 11-2005
| | Posted on Tuesday, December 19, 2006 - 08:02 am: |
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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. |
Brian_B
Registered
Username: Allegheny
Post Number: 10
Registered: 07-2006
| | Posted on Tuesday, December 19, 2006 - 01:58 pm: |
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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 |
Gerald_D
Registered
Username: Gerald_d
Post Number: 650
Registered: 11-2005
| | Posted on Tuesday, December 19, 2006 - 02:37 pm: |
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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. |
20. Gantry