cyclotron's cnc gantry

[cyclotron]

Hi all,

I'm a student in philadelphia, about to enter my senior year of college.
Our school shop has a vertical mill and a small roland cnc machine. The short of it is, I won't have the school shop forever, and there are 30 new sophmores entering my program next fall. You can bet that sharing the shop,
and trying to do any kind of precise work on an abused "Mighty Comet" mill
will be next to impossible. Thus, in january, I started thinking about making my own cnc mill. Since then I've been scanning the net, reading, and collecting anything that might contribute to this project. I Think I finally have enough parts to get this thing going.

I pretty much have one goal:
>>>>> I'm aiming to be able to cut aluminum... well.
My sub goals include making my machine faster and more powerful
than the roland desktop job. In addition, I"m thinking about making this all metric.

I have a bunch of material already to start with, but from here on out,
I think I could use the advice of any who are interested.

here's some stuff I already have:
-taig er collet spindle and upgraded motor (1000-10000rpm, 1/4hp)
-30" heavy duty iko linear slides (2 rails, 4 cars)
-21" iko lwl linear slides(2 rails, 4 cars)
-an ebayed thk assembly w/ ball screw. 6" of travel ( I'd like to use this for my z axis)
-various amounts and sizes of aluminum plate with thicknesses between
.75" and .125"
-a bit of heavy aluminum u channel
-a bit of that 80/20 extrusion.
- perhaps 25' of this weird i beam extrusion (its not what you might think, i'll post a picture. I think it might not be heavy duty enough, so this may be for making a cabinet or something...)


I'll post some pics of what i've got, in the next day or so. I'll also be posting
some sketches of some of my ideas about the design(I can model, but i'm no where near needing dimensioned shop drawings yet...)
stay tuned!
cheers!

[rustamd]

How big of work area are you thinking of? How well do you want to be able to cut aluminum? How much/how fast?

Just few question i'm wondering about

[rustamd]

Also what electronics are you thinking of? Servos? Steppers?

[cyclotron]

well, I'm hoping with the amount of rail I've got, that I can get an envelope of about 23"X18"X6," also I'm pretty sure I'm going with steppers. From what i can tell, the primary factor in how fast feed rates get is the power of the stepper motors being used. My big concern now is to have a really rock solid machine. I'll sort out the how far i'm going to go for steppers when I know exactly what they going to have to push around.For the time being, I would like this machine to cut faster than our roland machine at school. (I don't have the figures on me but i'll post them soon, I think it will be an easy goal...)

[cyclotron]

the feed rate of the roland descktop cnc that i want to beat is
1.2 m/min.

[cyclotron]

here is the general design of the machine, I still need to detail it tho.

[joecnc2006]

I would switch the Z-Axis to the otherside of the Y-Axis to gain more workable area on the table top.

Joe

[cyclotron]

I originally wanted to offset the spindle with the table as you suggest, by pushing the spindle back (I have seen many routers using this configuration)
My taig spindle's motor is hanging off the side of the spindle. If I flip the z around, the motor will bump into the gussets and severely limit the travel of the y axis. I 'm going to offset the table itself and the bottom most rails to compensate for the z axis' overhang. I think this will achieve the same goal.
I'll try and upload some orthgraphics to help with the visualization.

[cyclotron]

this is not orthographic, but it shows what i'm talking about by shifting the table one way and the rails the other. now the spindle has access to all reaches of the table.

[cyclotron]

I feel bad that I haven't been keeping this page up. Since school has started I have only been able to work Saturdays on the cnc project. Its been developing slowly but surely.

First off, I got some more parts.

1> gecko had a nice sale at the end of August so I took advantage and picked up 3 of their basic stepper drivers. I also picked up some solid copper heatsinks to match at a garage sale! I'm hoping those will will provide enough power to get things going.

second, I've made a number of changes to the design of the machine.
I've reduced the cutting envelope in both the x and z axis in the hopes of increasing rigidity. Also, the old design called for the spindle to be cantilevered out on this long plate. I figure that will be a big source of vibration so I deep sixed it. Now the spindle rides right over the linear bearing blocks.

Finally, I've been analyzing the design in terms of inertia and gravity. I've moved the I've tried to put the center of gravity of the zy assembly right in the middle of the x cars so their isn't torque on the rails from just the assembly wanting to fall over all the time. Also, Initially, I was going to use the taig 1/4 continuous duty motor to drive the spindle. that thing is just too heavy. I'll use it for something else (maybe a small cnc lathe? ) I'm hoping I can find a dc motor that is sufficiently small enough to not throw off the balance of the machine but still put out the power. This is an area that I actually need help with. How does one determine the appropriate torque and rpm for a spindle? I've seen numerous equations but I always get mixed up with the differences between feed rate and surface feet/ min and the like. I have redesigned the plate that the spindle attaches to with a matrix of tapped holes. hopefully this will provide enough versatility to accommodate putting off the motor decision till after the machine is made.

here is the first finished part. It is a riser block to accommodate the size of the cnc dumpster leadnut

I will also upload a pic of the updated machine design

[cyclotron]

ah

[cyclotron]

Today i busted out the Z platform. I'm attaching pics of the plate plus the spindle and the old motor.