Open Team Cheap DIY CNC Moving Gantry Router

[pminmo]

Project Objective - > To provide a basic set of public domain drawings to build a simple, cheap, functional DIY Moving Gantry CNC Router to be hosted here at the CNCzone. The build of the machine should be a learning experience, but techniques and materials to give the builder the potential to maximize accuracy and rigidity. The machine will be capable of cutting wood parts for hobbiest users. Accuracy goal .01 or better (if possible). Plan form to be no larger than 2' x 4'.

Goals -
1. Minimum Part count
2. COTS (Commercial Off The Shelf) as much as possible. Harware store, online stores also such as:
ENCO -> http://www.use-enco.com/CGI/INSRHM
McMasterCarr -> http://www.mcmaster.com/
MSC -> http://www.mscdirect.com/
(others as they become known)
3 Interchangability of accuracy determining components.
4. Fast to build
5. Repetative use of same size parts to minimize inventory and cut setup.
6. Usable design files that can be downloaded and updated.
7. Motor Mouting that allows easy modification for different types.
8. Spindle motor that can be used to help manufacture the chasis
9. Minimal tooling but at least a drill (and bits), square, rule, screwdrivers, and a method to cut wood or get it cut.
10. Techniques to aid in the assembly and accuracy
11. Design elements that aid in accurate assembly.
12. To be followed with stepper motor driver design and wiring planset.
13. To be followed with a metric conversion planset.
14. Pictures of assembly and techniques
15. 3/4" MDF will be used for many parts. MDF (not particle board or chip board) is rather dimensionally stable, flat and inexpensive. By using 3/4" MDF, use the 3/4" thickness a spacing component.
16. 5/16-18 Allthread for linear drive. (5/16 is very close to Metric 8mm, 1/4-20 was described by one who built a machine with it as too small) it is available in 3', 2' and 1' precut lengths. Brass inserts, Tnuts, couplers are easily available to make antibacklash nuts and drive plates. 5/16" tap and dies are inexpensive.

Cost goal - Less than $100 for the least expensive version just for the chassis. No spindle motor or electronics. (a Challenge)

Current Ideas ->
a) X rails 3/4" black gas pipe (1" OD), 1" Drill Rod, 1" plated rod, or 1" precision Ground Rod, all are available in 3' lengths.
-> make X length variable, i.e. a 2', 3' or 4' with intermediate simple supports for longer lengths that don't interfere with gantry movement.

b) Delrin/Acetel is inexpensive, slick and easy to machine if warrented. Easily available over the web.

Image available at http://webpages.charter.net/pminmo/DIY.pdf

>DXF and TCW desing files in work and can be downloaded here:
http://webpages.charter.net/pminmo/D...blyDrawing.zip

Free TurboCad (2D) Learning Edition Cad software downloadable at http://nct.digitalriver.com/fulfill/0002.16
(legit by the manufacturer)

Phil

[sol]

I have been watching in resigned bemusement as the Momma of this thread becomes a committee meeting; so I say "Thanks Phil!!!" for beginning this particular thread with a defined direction.

I like your ideas; begin cheap and simple; grow as time, money, need and ability allow.

Your list of current ideas sounds like a winner too... The only, yeah only, aspect I would change is the diameter of the all-thread from 1/4" to 5/16, and for the metrics among us 8 mm, so that it will fit reasonably well into a (gasp) skate bearing. These cheap bearings make passable lead-screw bearings as well as the ever so popular (and belittled) truck assemblies. The larger threaded rod can be used as bearing axles/mounts as well.

I have found that rod connector nuts (really long nuts) make decent anti-backlash nuts for a starter machine...upgrade later.

Rail supports...I made these and do not like them because the 120 degree angles make it hard to fine-tune the rail position. Somewhere here on the Zone I have seen a picture of a square 90 degree assembly that also is a simple unit made with wood, bolts and Tee-Nuts, and should resolve the problems I had with rail positioning.

Bearing truck assemblies can be a wide range of options. The image here shows one made of a sliced two by four that works well for what it is and it can be upgraded to steel or aluminum later.

Yeah, MDF Good...Plywood Bad...been there done that....


Okay, enough for now...am I on the same song sheet?

[pminmo]

I'm open to any suggestions, thanks. As simple as possible, I've got limited free time, so building has to go as quickly as possible. Maybe if some more people weigh in, we can get something going.

Phil

p.s. One of the time consumers is my driver experimentation:

http://webpages.charter.net/pminmo/board2.jpg
Built
http://webpages.charter.net/pminmo/proto3977.jpg

One of the cheap bearing ideas I saw someplace is attached.

[vacpress]

phil - how much does that board cost to buy and build?!

looks good! cheaper xylotex for those able to assemble?

[pminmo]

I got 4 prototypes (1 panel) made out of country for less than $35 shipped. (Blank board's) When I say prototype, they were silkscreened, solder masked double sided boards. I'm pretty close to shipping them a revision to make. I had one land missing, a couple of components, physically wound up tight.

Schematic here:
http://webpages.charter.net/pminmo/3977.pdf

There is a companion board that takes the PC parrallel port, does the logic for +/- limit switches for each axsis, filtering and a kill switch. It has three mating 10 pin IDC connectors for each axsis. The intent is to have one of those and three of the 3977 boards for one setup. The companion board is a buddies design, I haven't asked him if he cares if it is realsed in the public domain. The schematic I posted, would need the 40106 IC replaced with a 74HC14 or 74HCT14 to run the logic levels straight from a brakeout board. But the main reason for the 40106 is noise immunity. One of the main reason's I didn't go with xylotec, plus electronics is my real education. Component costs would be roughly $15 a channel + board costs. Need to be able to do fine soldering. I don't have any intention on profiting, it wasn't a business venture. I've rolled it over in my mind to see if the board house was interested in selling them if there was interest.

Phil

[Rhodan]

Very interesting - I'm just in the process of designing and building my first CNC router/drill for PCBs. I say "my first" because I also expect it to be nearly useless 8)

One thing I might be able to contribute. I've been working on my own A3977 Stepper driver board as well - 3 Axis with spindle and auxiliary relays. Optoisolated inputs/outputs etc. Its about 99% done, still looking for improvement ideas from the CNC grognards. Got tons of help so far from the yahoo groups Electronics_101 and CAD_CAM_DRO_EDM.

Anyway, its described on my web page (sorry, no pictures - haven't built anything yet, still in design-mode.)

http://members.shaw.ca/pmeloy/a3977_3_axis_driver.htm

I could also alter this a bit to squeeze in a 4th axis (combine all enable lines into one and dump an auxiliary relay or two) but I'm really not planning on using a 4th axis.

Always happy to take suggestions on how to improve this design too!

[ESjaavik]

I would suggest that you use square tube. The rollers will wear a flat in the round tube in no time. The big problem is it will not do this evenly over the whole length, and you will have a bumpy ride. It will also bind when rolling over debris. Protect it by making a box around it with oiled felt wipers at both ends, that will pick up the dirt.

And I cannot see anything restricting the assembly from lifting. You need one bearing under the tube too.

[pminmo]

Rhodan,
There are some things about your design that might cause you problems. (i.e. maybe but maybe not) Remember that your talking a noisey electrical enviornment. The 3977's if running at full load will be switching 2.5 Amps per winding per axsis. That is 15Amps of async switching on the same physical board. A lot of noise potential. #2, using mechanical relay's to switch inductive motor loads is a second noise generator. Physical layout will be of utmost importance. I went with a single channel design for a couple of reasons. I felt I could use a double sided board verses a 4 layer board, so cost was one. While you maybe able to route everything, your going to have to pay close attention to physical land routing. Noise immunity, by physically seperating baords, and using seperate Voltage regulators I would decrease coupling. Flexible to do one thru as many axsis as I need simply. Easy troubleshooting, if one channel isn't working, just swap boards to aid in troubleshooting. Quick repair, if a board dies, you slip in a new one. One specific suggestion, seperate Vbb1 and Vbb2 with a 100uf cap close to each pin on the 3977, for an additional 25 cent component for each axsis, its good insurance. If I can be of any assistance write.

Phil

[pminmo]

ESjaavik
Thanks for the input. Has anybody that is running gas pipe with roller bearing run into the flattening? While I'm not a huge fan of this approach, it is not costly and can be migrated up easily. The lifting of the gantry would be an issue if the gantry weight is less than the down force of the cut. Could be an issue.

Phil

[ESjaavik]

pminmo: Not only the downforce. Also the side force will attempt to push the gantry over, lifting the bearings of one side off the track.

[pminmo]

My personal preference wouldn't be to use roller bearings at all. There is a post on linear slides Cheap Linear Bearing Holy Grail?
of a designer that use 1" cold rolled, polished it and using UMHW, has been for serveral years.
http://www.cnczone.com/forums/showth...1121#post31121

Phil

[pminmo]

one simple thing that can be done easily. post links to simple cheap machines that have impressed you.

Phil