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sonicwonder2000
02-22-2008, 01:39 PM
Hi gang. I'm getting ready to throw together a cnc router frame that needs to be perfectly square. I have done a little bit of mig welding with my crappy Harbor Freight flux-core welder, but never something so precise. I am very afraid that the frame will not be square - after a $250 investment in metal, that is NOT an option.

I am going to lay out a detailed plan here. The steel tube will be factory cut to +/-.005" so that should not be a source of error. The tools I have to work with are:

A) 30"x60" slab of granite that will serve as a reference plane. This will be lifted off the garage floor with cinderblocks to allow clamping steel beams to the slab.
B) Two right angle welding clamps and about 10 standard clamps.
C) Tape Measure.
D) Mig Welder.

Please refer to the attached pics and feel free to critique and tweak my methods.


PIC 1
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This is an overview of the CNC in question.


PIC2
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Here is a view of the frame only.


PIC 3
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This is the side frame assembly (there will be 2, one for each side). I plan to weld these together first. All tacks will be in the vertical seams of each beam, alternating left, then right seam.

Clamp the red beam down to the granite slab (purple). Tack the grey beams in place using the right angle clamps.

Shift the assembly so that the red and green beams are supported on the granite slab. Tack the green beam to the red using a right angle clamp.

Check to see the red beam is square to the green beams by checking diagonal length - Adjust if necessary.

Clamp the yellow beam to the green beams with two right angle clamps. Check for consistent spacing between the yellow and green beams. Clamp the red beam and yellow beam to the granite slab. Tack the yellow beam in place.

Check to see if structure is still square.

Clamp red and yellow beams to granite slab. Clamp the grey beams to the yellow beam using right angle clamps. Tack in place.

Check to see if structure is still square.

Clamp the yellow, green, and blue beams to the slab. Tack the blue angle supports in place.

Check for squareness.

Clamp all the beams to the slab. Put final welds on every vertical seam by alternating sides on each beam (ie. grey beam left vertical, grey beam right vertical, etc.)

Repeat for other sideframe, ensuring that they are identical.

QUESTION: Are welds necessary on the horizontal seams?? I am afraid of twisting the frame because I will have to flip the assembly every time I want to weld an opposite horizontal seam.


PIC 2
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This assembly is the bed of the cnc.

Clamp the brown beams to the slab. Clamp the white beam to two brown beams using the right angle clamps. Tack white beam to brown beams.

Clamp assembly to slab. Finish weld each seam.


PIC3
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Bottom support frame.

Clamp white beam to slab. Tack yellow beams to white beam using right angle clamps.

Check for squareness.

Clamp entire assembly to slab and finish weld.


PIC 4
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Attach bed to side frames.

Clamp the red side-frame assemblies to the slab. Use some scraps of metal to hold the green bed assembly elevated in place. Clamp each bed beam in place using two right angle clamps. Check for level and tack weld each green beam to the red sideframes.

Check squareness of structure, then lay final welds.


PIC 5
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Attach orange bottom leg supports.

Use same method as for the beds.

Check all diagonals for squareness.

Tack welds.

Check squareness again before laying final welds.



DONE! Hopefully a level cnc table will result.:banana:

millman52
02-22-2008, 05:27 PM
If you take proper care that everthing is square to begin with. Use the rule measure twice tack once remeasure. You should build a workable table. Still I wouldn't expect it to remain perfect after welding. Heat just simply does strange things to metal.

As long as it's true enough to be able to mount rails true & parallel using shims, slotted holes, or whatever is necessary after frame is built will be key to your success in an accurate table......


Neil.

cam1
02-22-2008, 07:13 PM
Hi:

Foret about trying to achieve perfection with welding.Take the time to do your weld prep, tack welds check, burn together, and so on.The reality is that a proper weldment design takes distortion into account. Make sure you have the ability to shim or adjust the guidways after assembly.

regards

LeeWay
02-22-2008, 07:47 PM
I don't know if you have seen it, but here is an interesting video on welding among other things.

YouTube - The Fabricator Enters the Twi1ight Zone! - Episode 7

sonicwonder2000
02-22-2008, 09:00 PM
I don't know if you have seen it, but here is an interesting video on welding among other things.

YouTube - The Fabricator Enters the Twi1ight Zone! - Episode 7 (http://youtube.com/watch?v=weloWIzurqU)

BRILLIANT - good info and great for a laugh!! :

Geof
02-22-2008, 10:30 PM
cam1 has it correct, you will never get a welded frame true enougfh and you always have to have provision for adjusting things afterwards.

If you have a good strong base to clamp your parts to, however, you can minimize distortion. To do this always clamp very firmly as close as possible to the weld area. When the parts are strongly restrained from moving close to the weld the shrinkage and distortion is forced into a small region and plastically deforms the metal so when the clamps are removed it does not move much further. When the clamps are a long way from the joint the distortion just springs the metal and once the clamps are removed the overall distortion can be much greater.

planekrazie
02-22-2008, 11:00 PM
Great Vid, Anyone know how to save? Sonic, Any Ideas on what you are gonna use for your Y axis. Thats where I am stuck at.
Looks great.
Steve

sonicwonder2000
02-23-2008, 01:31 AM
Great Vid, Anyone know how to save? Sonic, Any Ideas on what you are gonna use for your Y axis. Thats where I am stuck at.
Looks great.
Steve

The y axis will be belt driven; the guts of this table can be seen at www.solsylva.com. Your machine is beautiful; methinks you should name it the blue bomber :)

planekrazie
02-23-2008, 07:32 PM
blue Bomber is a great name hence the airplanes. LOL
I believe I am gonna order some xl belt this week.
Steve