I'm wanting to build a large cnc router, have a small one now but I'm kinda confused about what height to make the z-axis. I want something that can mill a large a depth as possible but it seems like you are limited to how deep by the cutting tool and the actual z-axis itself. Most 1/2" router bits are no longer than about 3" so it seem like that is you real limit without striking the workpiece with the z-axis. Can anyone give any suggestions on how to increase that figure or clear this up for me? I can see where I might want to mill about 6" depth.

Thanks

barkster, several things affect your Z axis cut depth.

1. Gantry height clearance over your table. If you have 6" clearance, you can only cut 6" thick parts.
I have seen some designs where the part is clamped to the side of the table and you can skirt this issue. Then its the height from the floor to the bottom of the gantry.

2. Z axis stroke. If you want to cut 6" deep, then you should have at least 7 or 8" of stroke, to compensate for various router bit lengths and some rapid travel clearance.

3. Part geometry. This is very important! If you want to cut a 1/4" wide, 6" deep slot in a part, you are out of luck with a CNC router, maybe a CNC wire machine, but router bits aren't made that long and that thin. But, if your part has a slope like the inside of a cereal bowl, you can cut very deep with a short cutter. The limit becomes your Z axis stroke and your gantry clearance.

Simply draw a side view of your cutter, collet, and router in CAD. Use this as an overlay over a cross section of your finished part and you can look for interferences.

Post a drawing of your part and you might get some good suggestions on creative ways to mill it.

T

Thanks, don't really have a particular part in mind just trying to figure out what I could do in the future.

I'd make sure the collet can go about 4" above the bottom of the gantry, and within about 1"-2" from the table, so that a long bit will clear the workpiece, and a short bit will reach the table. With 6" clearance you'd need 8"-9" of travel for this. Also make sure your router hangs down below the z-axis plate to give you a bit more clearance.

Gerry

I designed a new collet for my Hitachi 12 router which should add about a inch to the overall travel but didn't want to make it too long and have it wobbling around. The M12 collet is a bit different from the Porter Cable. What do you think?

Here is the orginal collet