Building an incredibly fast 4 axis machine

[Grego]

I was thinking about building a really fast 4 axis machine for the specific purpose of machining hard machinable foam. I have a MaxNC which works ok but is incredibly slow. It claims 50 in/min, seems slower. What is a "fast" speed on a commercial mill? I know I've seen some machining centers really fly when not cutting. That's what I want.

What it the difficult part of this? Controller? Motors? I don't have to worry about cutting force. Accuracy would be fairly important but in the +/-.005 range.

The 4th axis probably doesn't need to be too fast.

[SpeedsCustom]

It's going to be pricey. You will want Linear ways and ballscrews, controllers all depend on your size. What your working space?

An example Hass mills, 1000IPm rapids.


-Jason

[Starleper1]

I've ran the Haas Super Mini Mill and it is mind blowing how fast these machines can go. Very scary when running a program for the first time.

[LeeWay]

My mill, router table and lathe are all capable of 300 IPM. That's PDQ especially on the lathe and mill.
Just using Gecko 201's and 203V's with 72 VDC PS. Ground ball screws and linear ways on the mill. Rolled double ball nutted screws on the lathe and router. The router runs on skate bearings and the lathe linear ways.

Keling steppers. 495 oz on the mill and lathe. 425's on the router.
All direct drive except the Z axis on the mill.

All have better accuracy that what you are wanting. I can't measure any inaccuracy on my mill.
The router is better than .001" and the lathe is better than that.
At 300 IPM, it get where its going fast.

[Fixittt]

remember one thing, its a trade off. Resolution vs speed. I can make your maxnc haul balls, but you will loose the resolution (Like you need it with the maxnc anyways, they are to flimsy)

I have a machine I can run at 3000 IPM in full step mode. But I loose any type of precision. Get to a good fine resolution and the top speed goes way way way down.
So, what resolution are you wanting, and go from there.

[ger21]

You can build a router to get 1000 ipm without breaking the bank. Shopbot does it with V roller guides and rack and pinion. You could also use a belt drive, or very high lead acme screws.

As was mentioned, as speed increases, you usually have to sacrifice resolution. Going to servos will let you still get high resolutions and high speeds.

[Grego]

I'd guess 300 IPM would be fast when cutting. Whe I look at the MaxNC I can't imagine the ways lasting long at that speed. I was thinking of using linear bearings for everything. Cutting foam means I can suck up the chips pretty easily to keep things clean.

My work envelope would be something like 8" dia x 10" long x 8" y-axis (incase I wanted to cut in 3 axis). Most of my work is smaller.

This would be for concept work. So I think +/-.005 would be fine. I think if everything stayed tight I could slow the speeds down to get more accuracy if I wanted. I was also thinking stiff yet lightweight tables to decrease inertia. You're going to have to carry at least 1 motor, maybe make that in the direction you don't use for 4 axis milling. Oh, and the 4th axis and motor... Maybe you could remove the y-axis motor when not using it?

[escott76]

I was thinking about building a really fast 4 axis machine for the specific purpose of machining hard machinable foam. I have a MaxNC which works ok but is incredibly slow. It claims 50 in/min, seems slower. What is a "fast" speed on a commercial mill? I know I've seen some machining centers really fly when not cutting. That's what I want.

What it the difficult part of this? Controller? Motors? I don't have to worry about cutting force. Accuracy would be fairly important but in the +/-.005 range.

The 4th axis probably doesn't need to be too fast.

Additionally you will have to take into account the spindle requirements for such a machine. High feedrate is great and all that, but if your spindle isn't spinning fast enough you are simply going to tear stuff up instead of making clean cuts. As you have said your cuting forces are not super high, but it's still something to consider.

[HawkJET]

I was also thinking stiff yet lightweight tables to decrease inertia. You're going to have to carry at least 1 motor, maybe make that in the direction you don't use for 4 axis milling. Oh, and the 4th axis and motor... Maybe you could remove the y-axis motor when not using it?

If you do the calculations, you'll find that the lead screws are where the inertia is. You don't move the table very fast compared to the lead screws (especially if you want fast feedrates). There is no real point in worrying about removing motors to save the inertia. The lead screw inertia is probably an order of magnitude higher than the table.

[LeeWay]

I have about a 150 pound gantry on my router. It handles the change in direction gracefully at 300 IPM. I typically run it at 200 IPM though. That is plenty and farther from a stall point than 300 IPM is. I make some cuts in lexan at 150 IPM and 80 IPM for any small radius cuts. Inertia tends to overshoot and make a mal formed arc at anything higher.

[rocketers]

you guys rock wat an grt disscusion.......