[Plan_B]

Hello everyone! I will start by thanking everyone on the forums for posting such a wealth of information here. There are very few questions out there that haven't been answered in these discussions.

My build is nearly done. I'm just waiting on the router fixture I thought I would post some info on the machine here because I am beta testing Ahren's new Gantry Risers from CNCRouterparts and I thought y'all would like to see them. I designed this machine using only off-the-shelf parts - many from CNCRouterParts. It was just a matter of assembly as the parts started rolling in. It's a 12 ft by 6 ft table.

There is a 3D CAD drawing attached and a couple photos. You'll see the design has changed a little since the CAD picture was rendered. The machine uses rack and pinion to drive X', X and Y Axes, and a 5 start ACME screw for the Z. The linear motion carriages are from CNCRouterParts and they ride on 1/4" cold rolled flatbar. The motion is very smooth once a few adjustments were made. The Motors are NEMA 34 900 oz-in steppers.

I used a drive on both ends of the gantry to keep it from racking. The gantry is very stiff using 8020 3060 extrusions. They are attached by Ahren's Risers. This definitely makes for a very rigid gantry - and simple, too! There isn't very much to say about the risers - other than that they are perfect. One suggestion would be perhaps to offer a shorter version.

My favorite part though is the Rack and Pinion drive system. Talk about turn-key... I bought the kits from CNCRouterParts. Using the extrusions, the R/P kits just bolt together and bolt on, mating perfectly with the racks.

I'm interested in your questions/comments. I have the machine moving now but haven't taken any videos yet. I'll try to get some soon.

Cheers!

[zool]

Great conceptualization and execution.

Not reinventing the wheel has grand benefits.

[Mountaincraft]

When are those risers to be available I wonder? I may hold off on remaking mine from aluminum and go that route...

How tall are they? Ideally, I'd like them to set the 3060 4-6 inches above the Bearing carriages.. 5" would be just about perfect...

[Mountaincraft]

Also, are you running the machine yet?

[Mountaincraft]

Shouldn't the High Z plate be attached to the carriages on the gantry rails?

[Plan_B]

The risers place the bottom of the 3060, I believe, exactly 5" off of the carriages. I think you are right about Ahren's intent for the high Z set up. That would put the motor onto the moving axis. I am waiting for the router fixture to arrive. I may reconfigure that then but I'm not sure I understand the benefit.

I have run the machine using a pencil for a router to check squareness accuracy and repeatability. It may not be perfect but the error is too small to measure with my tools so I'm happy!

[bobmagnuson]

This looks really good!

Couple questions...

How's the stability of the machine when doing rapids? Any lateral movement of the base?

Is the base 6' x 12' and if so, what's your max cut size?

Thanks...

Bob

[Plan_B]

Ya, the base is built like a back yard deck. It does move a bit during rapids but once I properly triangulate the legs it will be rigid enough, I think. The platform itself is very sturdy.

The x travel is about 135"
The Y is about 63" but that limitation is strictly due to the length of rails. The Gantry risers allow the R/P system to traverse them. So if I had longer flat bars on there then the travel could be about 70"

I can't wait to get a router on there. I have lots of roadrunner pictures on my table! - from the Mach3 G code folder

[CarveOne]

Crossed 2x4 boards do much better stiffening than a single diagonal 2x4. Notch the boards where they cross at mid span, 3/4" deep on both boards so they interlock, and put a single bolt and nut through the middle of the joint. Do this on all four sides.

Looks good so far.

CarveOne

[Mountaincraft]

Plan B said:
" I think you are right about Ahren's intent for the high Z set up. That would put the motor onto the moving axis. I am waiting for the router fixture to arrive. I may reconfigure that then but I'm not sure I understand the benefit."

If you want to see exactly how Ahren's Z axis goes together, take a look at my build thread.. (URL in signature).. Currently, you have it mounted backwards.. The High Z plate attaches to the carriages on the gantry rails, and the another set of carriages attaches to the Hi Z plate with long 5/16" bolts..

The 4" CRS Z rail rides in those carriages, and the 1530 is bolted to that, with your motor mount hanging towards the back.. Your screw goes between the Z carriage 4" CRS rail and the High Z plate.. the lead nut is bolted to the Hi Z plate...

The only connections between the Z carriage and the High Z plate, is the bearings on the CRS rail, and the lead nut.. all the rest of the Z carriage hangs off of that... Then you attach your router to the front of the 1520 extrusion...

[Mountaincraft]

There's some pretty good pictures on page 8 of my build thread...

[Plan_B]

Hi Mountain, thanks for the insight.
What's the benefit of doing it that way? It seems the same - just flipped 180. I have the plate to attach the router and vacuum and the 1530 connects directly to the y axis carriages.
What do you think?

[Mountaincraft]

Not real sure except that's the way it was designed to be done.. Seems like I tired it your way at first, but ran into a problem...

You'd have to make an 'additional' plate, and you'd loose the ability no mount your router to the 1530 (the tee slots are handy for mounting all sorts of stuff that you'll be wanting to down the line).. but other than that, I'm not sure.. maybe alignment of the motor shaft and acme screw?

I'd run this past Ahren...

[Mountaincraft]

Is your 4" CRS stationary? It looks like your extrusion is bolted to the carriages that move on the Gantry, and that your 4" CRS is is bolted to that in a stationary position... then your Z carriage made of two standard bearing carriages and a high Z plate move up and down on that..

Have I got it right?

If so, you've lost all your Z travel.. You won't be able to get hardly any clearance under that fixed CRS rail...

You need to not only allow for various thickness materials, but vacuum system, and hold down fixtures..

If you really plan on building a machine with only 1" or so of available travel in the Z direction, then I would shorten everything up and move that gantry right down on top of the X rail carriages.. thus reducing the twisting forces on the gantry... If you're not gonna use the extra travel of your Z fixture, why introduce extra force?

[Mountaincraft]

By doing it the way Ahren designed it, you will be able to move the entire Z carriage almost all the way up to the bottom of the gantry... thus using the entire range of your available Z travel...

[Plan_B]

You do have it right - except there is no need for an extra plate. I'll post a photo of the z later.

Actually I have 5.5" of z travel with the present configuration. I can't use it all now the way it is assembled because of the vertical position of the 1530 (It's too low). I could slide it up about 3 1/2 " higher and I would have the 5.5" travel. Right now I have about 2". The Z is kind of just roughed in though. Once the router bracket is here I'll decide on a final configuration.

One other disadvantage I see with my present set up is that vibration and cutting forces will exert higher loads on the 4 bolts holding the extrusion to the extended carriages. Could this result in racking my z by overcoming the clamping forces? My guess is no but I'll be watching for that none-the-less. Your configuration is better in that respect.