Want to build stout gantry CNC router

[Jr's Farm]

Hey guys,

I’m looking to build a fairly stout moving gantry CNC in the 24”x 36”x 6” +/- range. I basically just started my research but I know (or at least think I know) that I want it to have rigid rails and ballscrews. I’m looking for pretty high accuracy/ repeatability, .001” or better, so I want to use sound techniques and hardware. I want it to be made from aluminum and steel; no wood or plastic. I’m willing to spend somewhere around $3-4k or so building the machine, motors and controller. I have access to heavy duty lathes and milling machines, as well as a pretty well stocked tool shop and welders.

The general design would be something similar to the Ironman by Blurry Customs utilizing some 8020 and steel/aluminum plate.

http://www.blurrycustoms.com/Images/IronMan%201.jpg


The purpose of this machine will be primarily for small inlays, such as you’d find in pool cues and jewelry boxes, tooling diameters would be down to .020" and smaller. I will eventually add a 4th axis attachment, mainly for indexing but also for rotational carving. I’m not concerned with spindles just yet, as I’ll likely use the Kress motor I’m currently using for live tooling on my lathe. Right now my primary goal is the frame and controls.

Currently I have a very limited knowledge of what is required regarding motors, drives, gear reductions and what it takes to figure out what size motors to use, as well as what size and thread ballscrews I’ll need.

I’ve tried to find some build threads for something similar but I find it hard to locate that kind of info here. This site has far too much info to weed through and I can’t seem to be specific enough to fine-tune my searches, so I’m hoping someone here can point me to a thread or two that could get me started or maybe even some plans I can use, if something like that is available.

Anybody here care to help a newbie out?

Regards,
Frank

[ger21]

Originally Posted by Jr's Farm I’m looking for pretty high accuracy/ repeatability, .001” or better

Accuracy and repeatability are two different things. Most inexpensive ballscrews are only accurate to around ±.004/ft.

Can you fabricate a machine that is straight to .001"?

How fast do you want to cut? How fast do you want to rapid? How much mass do you have to move? How fast do you want to accelerate?

These are questions that you need to answer to properly choose motors. Or, you can just by 5/8" ballscrews with 2-5 turns per inch. The higher the turns per inch, the faster you go, at the expense of resolution. If you want speed and resolution, you may want to use servos.

This may be the closest thing to what you want that I'm aware of.

http://www.cnczone.com/forums/showthread.php?t=30751

[Jr's Farm]

As far as .001" accuracy goes, I don't need to hold that particular number from one end to the other, just in the general area of operation. When doing cue inlays most of the work takes place in an area no bigger than 3/4" wide by 4" to 12" long.

As for speed and rapids, I guess I'd rather have better resolution than speed.

In my mind, I've already come to the conclusion that I'll want to spend good money on rails and ballscrews, as I know that there is no cheap substitute for accuracy (or is that repeatability?) Can someone explain the difference for me and how it applies?

Bare with me, I'm a little new to this but I'm a quick study

Frank

[Jr's Farm]

Educated myself on these terms:

- Accuracy = The ability to machine a part to a specified size. The closer the part is to the program design the better the accuracy.

- Repeatability = The ability to return the machine to an exact location, after moving off axis. Not to be confused with accuracy

- Resolution = The way to measure the smallest movement the machine can make.

That sound about right?

[ger21]

Yep.

[FandZ]

That Iron man cnc machine is right around your budget. K2 cnc's at that size are also right around that budget, and so are pncnc (I think that is the name) machines. My point is, why build one with your budget when you could buy one?

If you want to build one to build it, you could buy the fineline autoamtion 80/20 kit without linear parts and score better rails and ballscrews off of ebay and build it that way. K2 cnc sells a nice Z axis for somewhere around 400 to 600.
http://www.finelineautomation.com/store/show/PB-0005

But really since you plan to use yours to make money and you have the budget, I'd just buy one already built.

[Jr's Farm]

I haven't ruled out a ready-built one yet. I was under the impression that I'd be able to build one with better components for the same money, or the same quality for less (not including my time of course). And of course I was looking forward to the challenge of building my own from scratch.

Thanks for the link to fineline. That may be something to consider. I'll have to d/l the plans and go over them I guess.

Frank

[leggazoid]

Pilot Pro has Blueprints for a reasonable price and sell parts and complete machines.

http://www.pdjinc.com/pilot%20cd.html