[ger21]

If you have any thought toward cabinetmaking, even if only for your shop, you will want the capability to cut dovetails. That will mean being able to cut off the front of your machine. I'm not sure how far the cutter in a spindle overhangs the frame on a CNCRP/Avid pro machine, but you will need a few inches clearance. If the pro machine doesn't provide that "out of the box," you will need to set the front crossmember back sufficient to give you room to cut dovetails. There are alternatives, but they usually involve making removeable sections of spoilboard. The loss of a few inches of table length made the most sense to me.

My preference wold be to add some length to the side extrusions. The downside is that you need longer gear racks and linear bearings as well. But you don't give up any length.

Or, you can just assemble it with the end crossmember set back, can't you?

 

[RainMan 2.0]

You got me thinking guys, I’ll order one with a 5’ Y axis and a 4’ X . That would fit perfect and give me real estate for tenons etc. The idea of a 5’ X axis concerns me ,as the gantry wouldn’t be as stiff.
And a 4X5 would still fit very well in my shop as well

 

[gmedwards]

My preference wold be to add some length to the side extrusions. The downside is that you need longer gear racks and linear bearings as well. But you don't give up any length.

Or, you can just assemble it with the end crossmember set back, can't you?

I set my front crossmember back a couple of inches on the CNC I'm building. That's where I lost the spoilboard length. On the plus side, I have more than 48" of Y-axis travel, so even with the setback, I have about 48" of cutable spoilboard left on Y. My custom CNC started out with more cut area than the CNCRP/Avid 4 x 4s. That came from longer side extrusions, which meshes with your preference. My racks are 54" on X and Y. I adjusted them so I use most of the length.

Gary.

 

[gmedwards]

You got me thinking guys, I’ll order one with a 5’ Y axis and a 4’ X . That would fit perfect and give me real estate for tenons etc. The idea of a 5’ X axis concerns me ,as the gantry wouldn’t be as stiff.
And a 4X5 would still fit very well in my shop as well

My Y side rails are 60". My X axis is also wider than the CNCRP. My crossbeams are 68" and my gantry is 74". If you are concerned about gantry stiffness, I suggest you go to the 80/20 website and download the Tech Toolkit. You can select the extrusion and play with various configurations to see what deflection you can expect. Yes, I use a lot of 80/20 and have for years.

Here's an example. My gantry is metric 80mm x 160mm x 74" long. Adjusting the length to remove the length that sits on the interface plates, the length adjusts to 65". If I apply 50 pounds of force to the face (as mounted) at the center of the extrusion, I get .0013" of deflection front to back. In the up/down direction, 50# applied weight yields .0006" of deflection. Given the way I have the extrusion mounted, my front to back deflection should be lower than the Tech Toolkit indicates. The way CNCRP/Avid mounts their gantry, the Tech Toolkit should be pretty close to what you can expect. Anyway, you can play with it and satisfy your concern about gantry stiffness.

Gary

Edit: I can't get the link to work right, so I took it out. Just go to the 80/20 site and search for Tech Toolkit. It's a free download. GME