Offset Gantry

[jcdammeyer]

Hi,

I'm slowly starting to put together a JGRO router. Measuring where the router bit will be relative to how far the gantry will move leaves a lot of unreachable space underneath the gantry.

Based on the measurements the centerline of the router is 10.75" away from the centerline of the horizontal gantry rails. Was this perhaps done so the centre of mass of the router and Z mechanism was roughly over the front Y axis bearings?

I've attached two pdf's that with the right add on allow 3D rotating of the parts in the documents. (Drawn and exported with Alibre CAD).

The one shows the Grantry as designed in the JGRO documents. The Offset document shows a method of shifting the X axis horizontal rails and lead screw back so the router centre line is in the middle of the Y Axis Linear bearing. The router now gets closer to the end of the Y Axis travel.

Any reason why I shouldn't build it this way?

Thanks
John

[TommieK]

Hi John, I don't have any pictures of my machine, but what you have drawn is almost exactly what I have done with my JGRO. I say almost as my legs only adjust 3 1/2 inches back. I also mounted my trucks directly on the outside of my legs and made the inside pieces of the gantry 1 1/2 inches wider than the plans called for. I did not lengthen my machine, yet, but when I bought the gas pipe it was 5 1/2 ft. long, and when i bought the 1/2" 8-2 Acme threaded rod, it was 6' long. If I would have bought that stuff before I built the base and table boxes, I would have made the boxes to fit the pipes or screws. Good luck with your build, and don't forget; this stuff is just MDF so have as much creative fun with it as you want to. Tom

[u77171]

Sometimes I can be a little thick :-) Wouldn't that just leave more unreachable space behind the gantry? I think if you add to one side you will be taking away from the other.

[sonex128]

The sides offset to the outside of the router. That allows the cutter to travel closer to the edge.

Brian Bland
Claremore, OK

[TommieK]

I originally got my inspiration to change my gantry sides from Grunblau's machine. His machine looks like MDF art. Mine, not so much. This upgrade or change (whatever you would like to call it) puts a little bit of YOU into the mix. Even with the change, though, there is still about a foot of unused table.

[dustin1706]

I finally got my machine put together and I finally see what you mean about getting more space with the offset gantry.

It seems that you will only gain about 3" of Y. Would it maybe just be easier to build a vertical gantry and let your cutting table overhang those 3 inches?

[jcdammeyer]

You'd still have to support the cutting table so the frame would have to be changed. All that's probably more complicated.

Another thing I'm considering is how to expand the X in a way so the router can get closer to the edges while still leaving the rails where they are. I'll post a drawing when I figure it out.

John

[dustin1706]

Yeah, a bit bigger would be nice. Not sure how you'll do ti unless you make the X/Z unit narrower.

The first thing to hit on the X is the lower Z adjustment screws. Drilling a hole for them in the gantry sides would give you 1/2' to 1".

[snmartin]

I'm currently building a JGRO cnc router and I had planned on offsetting my gantry back only ( about ) 4 inches. I wanted the router bit to extend just a little past the linear bearing rail. I also didn't want to torque the bearing rails too much with an extreme weight shift.

[jcdammeyer]

Originally Posted by snmartin I'm currently building a JGRO cnc router and I had planned on offsetting my gantry back only ( about ) 4 inches. I wanted the router bit to extend just a little past the linear bearing rail. I also didn't want to torque the bearing rails too much with an extreme weight shift.

I finally got the table saw cleaned up this weekend so if all goes well over the next few days I can do some MDF cutting. My plan was to set the router center line over the middle of the carriage. That would allow maximum travel. Can't be any worse than the stock design that has the router hung way over the end of the carriage bearings.

John

[TommieK]

Hi John, How is your build coming along? When I first answered you I did not have any new pictures of my machine, well now I do. The first is my machine right after I built it and the second is my machine in its upgraded version. We sure would like to see how your machine is progressing!

[jcdammeyer]

I'm sitting in the Trolley Cafe in southern Greece drinkink ouzo. I'll get back to it in about two weeks when I return to Canada. Nice weather here.
John