My 2nd CNC machine design

[georgebarr]

Here is a picture of my second CNC design. I want to get some feedback so that I can make changes/additions to the CAD model before I start construction. It is a big router and I am trying to get as much precision as possible. The X and Y axis measure approx. 64" x 57" and the Z axis beam is 36". It will be made using mild steel. No welding will be used to eliminate the warping effects that MIG welding creates.

Any suggestions here?

[georgebarr]

Here is another attempt at posting the picture.

[Cold Fusion]

Picture is not showing up. Email it to webmaster@coldfusionracing.com and I will host it for you.

[DDM]

The design looks like a good start but you're going to need some cross bracing to keep the thing from folding on you. Think trianges instead of squares. I'd put some cross bracing on the X and the Y and you should be somewhat safe.

Carl

[ger21]

I'd run the vertical leg on the side of the gantry up to the top of the z-axis rails, and move the top bar of the gantry up higher. (much higher)It looks like you have about 4" between them. I'd have at least 2 feet. This should reduce the flex your getting on your current machine. Do you really need a 36" Z? How can you cut something that high without the z-axis or router motor interfering with it?

[InventIt]

George,
I have an idea what your dealing with. I made my router from steel tubing.

1, How are you attaching the cross beams to you uprights? Are you bolting through the tube? With thin walled tubing, 1/6 or 1/8", attaching or bolting to the sides will not work well. One wall is too flimsy to hold alot of force. You want to grab all 4 sides. Welding a thick plate to the end and bolting to the plate would be stronger then bolting through the side of the tube. Look at a light pole on the street, It will always have a thick plate where it's bolted to it's base.

2, Make the bottom frame into a shallow box with cross bracing to ensure it won't twist/flex.

3, Change the two rails running across the gantry to one larger rail/beam. OR-- Use three beams in a triangler arrangment with cross bracing in between.

Why do you need 36" Z?

[georgebarr]

InvestIt,

1. In my first router, the way I bolted the horizontal beams to the vertical beams in my gantry was to drill a hole on only one and sometimes two sides of a beam and bolt it. I am using 1/8" mild steel tubing. I am trying to avoid welding to eliminate warpage. However, I can weld a steel plate (say 3" x 8" x 1/4" or 1/8") to the vertical gantry beams and drill a hole through this plate so that I may bolt on the horizontal beams. Should I use 1 mild steel plate or two (one on each side)?

2. When you say "cross bracing" you mean to create a 4 sided rectangle with a diagnol beam, correct?

3. Are you referring to the two horizontal beams and hold the z axis? I do not think I can use 1 big rail instead of 2 smaller ones since mild steel sizes are limited. What do you mean by using 3 beams in a triangular arrangement? I can try using 2 beams and in between them I can add beams arranged diagnolly (is this the way to do it?).

Also, since I want to minimize the amount of welding, joining two pieces of mild steel tubing at odd angles (like the gantry triagular shape) has to be minimized since I use aluminum angles (90 degrees) to bolt two pieces together (unless there is another way to do it). I am considering changing the gantrys triangular shape into a rectangle for easier construction. What do you think?

The reason I need 36" is because I have limited space to store my cnc routers. I do not want to have a small router, then a mid size one, and finally a 3rd and bigger router. Also, I want to play with a lathe attachment and 5th axis (these two accessories needs a lot of z axis).

Thanks,



Thanks,

[georgebarr]

Here is another picture of a design that uses a rectangular gantry instead of a triangular shape. Since I want to reduce the amount of warpage, I need to minimize the amount of non-90 degree connections (any non-90 degree angle made by joining 2 pieces together). This is only a design consideration only. I have not started construction.

[georgebarr]

Here is a picture of the gantry part that uses mild steel plates at 1/4" thickness to join two pieces together. It was mentioned that drilling holes into the tubing will weaken the structure.

[georgebarr]

Forget about the other designs. I just learned that a moving gantry is not very stable. A stationary fixed gantry is more stable (similar to campbelldesigns.com as seen on the picture at bottom of his web page). I still need to add the sliding table, slide bearings, etc to the CAD picture and when I do, I will upload a new picture. Here is a picture. Any comments?

The mild steel tube is 3" x 3" x 0.12" (I might use 0.1875"). The gantry width is 62" and 55" for the sliding table.

I want to mill mild steel, aluminum, and wood projects so accuracy, stability, and rigidity is a must. Any way I can make it more rigid? Are there any improvements I can add? I mainly got the idea of welding a plate with holes to join two pieces together from looking at gym equipment (Hammer Strength gym equipment) at my health club and from advice. These gym equipment has to be rigid and strong since muscle guys use them to lift heavy weights. The only welding done is to attach the plates with holes to the mild steel square tube and I hope there will not be any warpage.

[wjbzone]

Your last design has a diagonal beam on the sides of the gantry. That will make it stable in the X direction. I would do something in the Y direction also. The channel beams across the gantry sides could be joined together to effectivly create a diagonal in the Y direction.

Also, I agree that a fixed gantry is more stable then a moving gantry. How much stability does a moving table loose compared to a fixed table. At least you know how much weight is going to be on the gantry. A large table could be loaded up with a workpiece and clamps that make it loose stability. Especially with the amount of Z clearance you have.

Bill

[georgebarr]

wjbzone,
I do plan on joining the horizontal beams on the gantry. Also, each horizontal beam is attached to the vertical beam by 4 bolts which will help prevent it from moving. All this is equivalent to using diagnol beams.

Thanks,