Designing a Powerful Router

[atemylunch]

I have a 3axis Ahha system with #34 1535 oz/in stepper motors.
Right now the system is installed on my knee mill.
I have need to change it out, and I was thinking about building a router around the steppers.
I want as much precision/repeatability as I can resonably get.

So far I have a machine designed, but I wanted to put this out and get a reality check. Plus I have a few questions.

The design,
4'x4'x12"(12" for a 4th axis, thicker materials, etc) Gantry style. (I have limited space.)
The frame; aluminum tube 4x4 w/.5" walls. I will use tooling plate for mounts and etc.
For guides, Misumi linear rails. Sizes ? (Do I need to mill the surface the rails will be attached to?)
To drive the bridge, twin preloaded .75 or 1" acme screws, chain sync.
For the carriage the same size screws.
To move the spindle 3/4 or .5" screw.

I'm not sure what to use for a spindle(I'm leaning tward Porter Cable).
What is the best way(s) to connect the stepper motors to the screws?
I want to add a vacuum hold down system. What is the best way to do this?
Any sources fot t-slots out there?
I want to work aluminum, is building a machine structure out of aluminum a good idea?

Any input would be greatly appreciated.

Thanks

[ger21]

Originally Posted by atemylunch I want as much precision/repeatability as I can resonably get. To drive the bridge, twin preloaded .75 or 1" acme screws, chain sync. I'm not sure what to use for a spindle(I'm leaning tward Porter Cable). What is the best way(s) to connect the stepper motors to the screws? Thanks

I'd use GT2 timing belts instead of chain to sync the screws. I don't think chain can give quite the same accuracy.

The Porter Cable 7518 is probably the best Router to use, but if you have a big enough budget, a Columbo or Perske (or similar) would be a better option, if you want a lot of power.

I think the best way is helical couplers, or timing belts. The belts give you the option of changing gear ratios if you need to.

If you can, then I'd mill the mounting surfaces for the rails. It can't hurt.

[ynneb]

While You may have powerfull steppers, you may not be able to use then to your full potential, unless you get a substantial spindle. Its all very well to have speed and power but the feed rate your spindle can cope with, should be your main criteria. You will bog down the spindle if pushed too hard. You realise that you are probably looking in the 3phase specrum for a suitable spindle if you want to use those steppers to full potential.

[atemylunch]

Thanks for the replies guys.
Ger21 do you know of a good source for the GT2 timing belts?
Right now I don't have the budget for the larger spindles.
You never know, I will have to look into it further.

I've included a sketch of the machine.
Note: I left out the spindle.
Hope this works.

[dmoore764]

Have you been to McMaster-Carr's website? That place has just about anything you could ever want (including GT2 belts I'm pretty sure), but don't take my word for it.
Maybe the more experienced folk around here will have a "secret source" for cheap timing belts?

[ger21]

http://www.sdp-si.com for the belts.

[atemylunch]

Originally Posted by ynneb While You may have powerfull steppers, you may not be able to use then to your full potential, unless you get a substantial spindle. Its all very well to have speed and power but the feed rate your spindle can cope with, should be your main criteria. You will bog down the spindle if pushed too hard. You realise that you are probably looking in the 3phase specrum for a suitable spindle if you want to use those steppers to full potential.

If I went with a larger spindle. How big of a spindle do I need to match the steppers?
Formulas/ratios will do.

[ger21]

I think it really depends on what you're going to be cutting. I've never seen a formula to determine. It depends on how fast you are cutting, and how much material you are taking out per pass. Different types of router bits can also make a difference. Chipbreaker bits can cut faster than regular spiral bits, for example. If you find that the spindle can't keep up, you can always make multiple passes.

How fast did you plan on this machine cutting? I'd probably go with the PC, since it's about 1/10 the price of anything better, and see how it works out.

[atemylunch]

The worst I would throw at it would be aluminum(6061 T6),
up to .5" thick. If I take easy I could go a lot thicker.
My Bridgeport clone is 3 hp, and I've taken .5" cuts and better in steel.
It has a lot of low end power, and cast iron machine and an aluminum machine are very different beasts.

How well do do the PC routers hold up to working metals?

Do I have to do anything special to the machine, with the router running at such a high rpm? Vibration a problem?

Is machining aluminum with an aluminum machine a problem? Or is it more advantageous to build the machine out of steel?

[ger21]

Originally Posted by atemylunch The worst I would throw at it would be aluminum(6061 T6), up to .5" thick.

Unless what you build is extremely rigid, I would think you might have to do this in multiple passes.

How well do do the PC routers hold up to working metals?

Probably not very well. From what I've read, any handheld router used for CNC under continuous heavy loads, will need to have the bearings replaced somewhat frequently. Bearings are the weakest part of all routers, as they are designed mostly for handheld use, and nobody would buy them if they had $100 bearings in them and they doubled in price.

Do I have to do anything special to the machine, with the router running at such a high rpm? Vibration a problem?

Make sure you get a variable speed router, as the single speed 20K+ RPM routers are too fast. The PC's at 10K RPM are very smooth, and actually pretty quiet (until you start cutting). I think vibration depends on the machine.

Is machining aluminum with an aluminum machine a problem? Or is it more advantageous to build the machine out of steel?

Just build it as strong as possible. I don't think it matters which one you use, but stronger (stiffer?) is always better.

[Patrick2by4]

Just a side thought, from my personal experience, I've noticed that PC uses larger bearings that many of the other router manufactors in the 3hp catagory. This is one of the reasons this PC router outperform other routers in longevity and should last a bit longer before their bearing eventually fail and have to be replaced.

[duraflap]

I'm running a Porta Cable router on my cnc and have cut T-6 Alum very easily. The softer Alum is the problem. Wish I could figure that out.