24 X 72 X 5 Aluminum Router Build - Need Advice

[BigSmith]

Hello everyone. New guy here.

In the planning stages for a router that will have a specific purpose. 95% of the cutting will be on 1/16" thick aircraft grade plywood. 5% 1/2" ply. 5% .020 aluminum. Router will be Bosch Colt PR20. Cutting area 24" X 72". The parts I'm cutting are very small and I'll need a very powerful vacuum hold down system. I have well equipped machine/welding shop. 30 years experience. Fabricating the unit won't be a big deal. I just need a few tips on sizing some of the components.

I really like the simple design of the new Probotix FireBall Comet. It is a 25" wide unit, so I should be OK copying the gantry design. My unit will be 3 times longer, so the supported linear shafts and lead screws will need to be larger.

Will 25mm Supported Linear Shaft be ample? What size lead screw? Motor size?

I welcome your recommendations.

[ahren]

Craig,

The supported linear rails are fine for this length, but using a screw for a 72" axis is asking for trouble. You will need a large screw to avoid whip, and at anything over 1/2", multiple start anti-backlash ACME nuts are not readily available at affordable prices. You could go ballscrew, but this is also going to be quite expensive.

I would highly recommend going with rack and pinion drive for the long axis -- lots of others have done this with great success. Here's an article in our FAQ about R&P vs. ACME that might be of interest to you:

CNCRouterParts

Ahren
CNCRouterParts

[ger21]

95% of the cutting will be on 1/16" thick aircraft grade plywood.

I would think a laser would be a far better tool for this.

Since vacuum holding strength is proportional to part size, small parts are very difficult to hold. You may find that you'll need to add tabs to keep the parts from moving, even with a very good vacuum.

Exactly how small are the parts?

[DIYaholic]

Originally Posted by BigSmith 95% of the cutting will be on 1/16" thick aircraft grade plywood. 5% 1/2" ply. 5% .020 aluminum.

95% + 5% + 5% = 105%

If you are only willing to give 105%, then those people out there giving 110% will out perform you!

Just busting your (FIRE)balls.

Randy

[cabnet636]

why not consider dual drive R&P for the long axis, this will give you a clear space under for the vac and the long axis accuracy, have you looked at joes cnc?

[ger21]

Originally Posted by cabnet636 why not consider dual drive R&P for the long axis, this will give you a clear space under for the vac and the long axis accuracy, have you looked at joes cnc?

With a screw on each side, you still have the same clear space under the table.

[BigSmith]

Originally Posted by cabnet636 why not consider dual drive R&P for the long axis, this will give you a clear space under for the vac and the long axis accuracy, have you looked at joes cnc?

After talking with Ahren, I decided to go that route. Going with his Nema 34 R&P mount. Here is my preliminary welded steel frame design. 2" square and 2"X3" steel tubing structure. 3030 aluminum extrusions and 1/4" 1018 cold finished steel for side rails sitting on six 1/2" thick mounting/leveling pads. 1530 aluminum extrusions for bed cross members.

[BigSmith]

Originally Posted by ger21 I would think a laser would be a far better tool for this. Since vacuum holding strength is proportional to part size, small parts are very difficult to hold. You may find that you'll need to add tabs to keep the parts from moving, even with a very good vacuum. Exactly how small are the parts?

The edges absorb glue better when routed. These are aircraft parts and many don't like the burnished, sealed up edges the laser leaves. Smallest part is roughly 2" X 4". As you say tabbing and or onion skinning is necessary. But, I want pretty good vacuum system to keep the whole mass flat and in place.

Here is example of smallest part:

[BigSmith]

Originally Posted by DIYaholic 95% + 5% + 5% = 105% If you are only willing to give 105%, then those people out there giving 110% will out perform you! Just busting your (FIRE)balls. Randy

Hi Randy

It was late. I was tired. I'll try to give a little more in the future.

[brtech]

Most designs look like yours. The rails are about the same height as the work surface, and the gantry is projected up from the rails, so the Z can project down from the gantry and reach the work.

An alternative, which is how the FineLine Automation larger designs (FLA-300 for example) work is that the rails are just below the gantry, such that the bearing carriages bolt directly to the gantry beam and the work surface is suspended below the rails. This makes the gantry is much stiffer, because there are no vertical supports between the gantry and the rails.

[BigSmith]

Originally Posted by brtech Most designs look like yours. The rails are about the same height as the work surface, and the gantry is projected up from the rails, so the Z can project down from the gantry and reach the work. An alternative, which is how the FineLine Automation larger designs (FLA-300 for example) work is that the rails are just below the gantry, such that the bearing carriages bolt directly to the gantry beam and the work surface is suspended below the rails. This makes the gantry is much stiffer, because there are no vertical supports between the gantry and the rails.

Hi brtech

I like the alternative method you describe better. Thanks.

Here is where I'm at so far:

Green frame - 1 1/2" square and 1 1/2" X 3" steel tubing.
Purple members - 2" X 6" steel tubing (bolted to frame)
Gantry - 2 pieces 3/4" X 8" aluminum
Gantry sides - 7/8" aluminum plate
Long axis rails - 1/4" X 2 1/2" 1018 cold finish steel
Long axis carriages - CNC Router Parts
Long axis R&P drive - CNC Router Parts
Short axis rails - 1" linear shafts
Short axis drive - 1/2" 5 start ACME
Z axis rails - 5/8" linear shafts
Z axis drive - 1/2" ACME
Nema 34 steppers