8020 (TSLOTS) Router Design

[derekbackus]

I'm designing a CNC router for my shop and wanted to get input on the design.

My specific needs are LOTS of Z travel with the ability to move the gantry to whatever Z height I want/need. I may put things in this router that are 30" tall but only need to machine the top 12". On the other hand, I didn't want to design in that much travel in Z.

So, I've come up with a table moving in 1 axis and a fixed gantry moving in 2. This allows me to move the Z up and down to suit the material height I'm working with.

The large square pieces are 3" square and the other is 1.5" x 3". All the plate on the gantry & Z axis are 1/2". The linear bearings are HIWIN 20mm and there are 4 on each axis (overkill??)

I would appreciate any feedback on this design. Any weaknesses, etc. I'd like to cut styrene foam, urethane foam, modeling board and aluminum.

I've attached pictures and here is a link to the 3D PDF file (it was too large to attach to a message). 3D PDF File Link

Thanks,

Derek

[CarveOne]

Three things jump out right away. These are not intended to be criticisms, just observations.

1 - Your table legs are too close together in the long dimension of your table top. (X axis) When the table is at either end of travel there is the potential for the machine to fall over backward or forward if the legs are not anchored to the floor. An MDF waste board on top of the extrusion table frame adds some weight.

2 - The table does not move full travel in both directions. The straight vertical gantry supports also prevent the router bit from cutting close to the rear end of the table also. Is there a reason to limit x axis travels?

3 - When the gantry is raised to clear a 30" object you will have a severe tendency for the cutter to chatter when cutting the object. Lots of angular bracing and a wide carriage will be needed to reduce this tendency to acceptable levels.

CarveOne

[derekbackus]

Three things jump out right away. These are not intended to be criticisms, just observations.

Thank you for your observations. I am looking for anything that might help meet my goals. I've designed and made lots of things, but nothing this substantial.

...for the machine to fall over backward or forward if the legs are not anchored to the floor.

Sorry, I should have mentioned this. I am going to attach the machine to the floor.

2 - The table does not move full travel in both directions. The straight vertical gantry supports also prevent the router bit from cutting close to the rear end of the table also. Is there a reason to limit x axis travels?

The table moves to the limits of the bearings. If I moved any further, the rail attached to the table would come out of the bearing blocks mounted to the frame. I'm definitely open to anything to increase travel -- The table is extended because I'm designing in 48" of travel.

3 - When the gantry is raised to clear a 30" object you will have a severe tendency for the cutter to chatter when cutting the object.

I was afraid of that. That seemed like the weak point to this design. The problem is that with any amount of cross bracing, I will limit the gantry positioning. Hmmm... more thought is required here.

Thank you for your comments! I really appreciate them.

[CarveOne]

My third comment is the one that will be the most difficult to deal with. If you have to reach down deep into the 30" high object, the problem is compounded by three things:

1. It's kinda hard to find cutters much longer than 4" to 6" at any price.

2. The Z axis can't cut the walls any deeper than the length of the cutter bit due to being physically larger than the bit. You just can't reach the walls with the cutter bit once the bottom of the Z axis reaches the top of the material.

3. Long bits introduce chatter even though the Z axis is lower on the gantry when in the bottom of the deep hole.

You have a challenge ahead of you but I'm not saying that it is impossible. Very light cuts at very low speeds on a very stiff machine may be the only way to get acceptable results.

CarveOne

[CarveOne]

Also, you'll notice that most gantries are "bent backward" to place the router behind the carriages. This is so that the router can get closer to the rear end of the table top and gain the otherwise lost cutting area.

Is there a reason to not anchor the lead screw at each end of the table frame? That's what most designs do to allow full travel. Take a look at the Rockcliff forum since that design uses a moving table similar to what you are planning.

CarveOne