Looks very rigid. Thanks for the pics.
What loads did you apply on the z-axis where the router mounts in your FEA simulation?
Before I started building anything I decided to put something down on paper about what I wanted, needed, and could afford. After a good bit of research I came up with this.
Criteria:
• Cutting speeds of 300+ in/min
• Over all rigidity of greater than 20,000 lbs. per inch of deflection
• Resolution of .0005” or better
• Fixturing systems for a 6” precision vise and sheet material
• 10” or better of z axis travel and clearance
Constraints:
• Budget of less than $2500 for complete machine.... haha
• Must fit through a 20” wide door
• Must fit in an area 6’ X 8’ with max overall height of 5’ with room to work around machine
• Must have the ability to be manufactured with manual mill, manual lathe, band saw, stomp sheer, hand brake, MIG welder, TIG welder, and hand tools
• Must run off of 110 volts
Features:
• 3.25 HP spindle with a 10,000-21,000 rpm range
• Precision grade collet with a TIR < .0002
• Anti-backlash rolled ball screws
• Supported shaft linear bearings
• Zero backlash flexible shaft couplings
• 270 oz.*in hybrid stepper motors
• Gecko G540 stepper motor drivers with 1/10th Micro stepping
• Full 3 axis control
• Resolution of .0002”
• Aluminum space frame chassis with stressed aluminum sheets for extra rigidity
I chose aluminum, because there was plenty of good aluminum pieces always coming though at the scrap yard. My design changed a lot due to what I could find that would work.
Lots of time at the drawing board eventually led me to this:
I ran FEA's on about every part of the machine to see what I needed to achieve my goal. Here are a few.
Then I started making stuff.
curved jaw couplings
WORD OF ADVICE:
For those of you with the Chinese supported shaft rails, CHECK YOUR SHAFT BOLTS. On mine, the holes were barely tapped and the bolts were all loose and partially stripped. Some of the holes were tapped so crooked, I had to make a new hole.
I have my eye on a set of beefy thk linear rails a friend has, but I will have to come up with money before I can get those.
First test of motion with a impact gun on the ball screw
For dampening I did a test with Right stuff foam, and it came out pretty good, so I will start with this and move up to more drastic measures if I feel the need.
The difference is clearer in real life but the video still gives you an idea.
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Looks very rigid. Thanks for the pics.
What loads did you apply on the z-axis where the router mounts in your FEA simulation?
If it were me, I'd spend an extra $30 for 380 oz motors.
Gerry
UCCNC 2017 Screenset
[URL]http://www.thecncwoodworker.com/2017.html[/URL]
Mach3 2010 Screenset
[URL]http://www.thecncwoodworker.com/2010.html[/URL]
JointCAM - CNC Dovetails & Box Joints
[URL]http://www.g-forcecnc.com/jointcam.html[/URL]
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)
50 lbs of force applied as a remote load from the cutter.
270 ounce*in steppers are plenty strong down low. my steppers will have to turn 750 rpm to make 300 IPM, a lot of places that sell steppers dont have torque graphs for them, so I had to look up a stepper with similar specs, and make an educated guess. It looks to me like larger stepper motors fall off quicker than smaller ones.
As an option, take a look at the AC servos from dmm-tech.com . I purchased the 900W, 7.2 Nm servos and drives as a package and don't regret the investment even a little bit. The owner and developer, Hui, is absolutely fantastic when it comes to customer service.
Keep up the good work! I'm looking forward to seeing the finished machine.
I hear ya! I thought that would be the easy part. Almost 9 months later I moved the gantry for the first time! The best part of the experience is knowing every single detail intimately! I've got a BIG 3-ring binder of every step. It's an awesome process and really rewarding when you move it for the first time. I'm getting ready for a size upgrade and getting just as excited as the first time. Best of luck to you and enjoy the process. The nice thing to know is you can screw up and then always do better on v2.0.
Awesome looking build! I'd definately like to know more about the simulation process and method.
cheers,
Ian
It's a state of mind!
I used solidworks fea simulation. You set up fixtures and loads as they would act on the real part and use the results to interpret how the deformations will affect the machine overall. Some simulations were simple just one part and simple forces and constraints, others were more complex with fea of an assembly and more complicated loads and fixtures.
I'm really trying for there to not have to be a V 2.0 lol
If you count the number of times the design has had a big change this would probably be V 10 or something.
I'm going to make an offer on those THK 30mm rails. If I get them these Chinese rails are up for grabs, I've got a few unused ball screws laying around too.
I think the thk rails would take the quality of the machine up a notch or two, they are defiantly more rigid.
I wish I had seen the 380 oz-in motors before I bought these, if I cant get the results I wanted out of these motors Ill switch them out.
I went ahead and fully mounted and preloaded the z axis rails and tested rigidity... These Chinese bearings are not that rigid, no big surprise. My z axis has about .002" deflection at around 40-50 lbs. That is about my deflection "budget" for the whole machine. I spent a lot of time making sure that all the parts of my machine were nice and rigid. Hell I even took into account the rigidity of the ball screws, and the mounts for them, and the shaft couplings. The cheap ass rails wont cut it. I WILL be getting my hands on a nice set of rails eventually.
The Anti backlash ball screws and love joy GS series knock off couplings are working out quite nice, There is less than half a thousandth either way when I push on the assembly with the steppers on holding torque, I think most of it is from the steppers.
Here's a quick video of testing the z axis.
http://www.youtube.com/watch?v=i-6XEdNCS-k]Sharp's Cnc z axis test - YouTube
When I brought this up before, you said you has plenty of power??I wish I had seen the 380 oz-in motors before I bought these,
Check out Automation Overstock for the best prices you'll find on linear bearings, other than buying used from Ebay.
Gerry
UCCNC 2017 Screenset
[URL]http://www.thecncwoodworker.com/2017.html[/URL]
Mach3 2010 Screenset
[URL]http://www.thecncwoodworker.com/2010.html[/URL]
JointCAM - CNC Dovetails & Box Joints
[URL]http://www.g-forcecnc.com/jointcam.html[/URL]
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)
I said they have plenty of power down low, and they do. I am able to jerk the motor assembly that weighs about 35 lbs around with it in the vertical position up to 270 in/ min. It used to be faster but I have the bearings and ball screws loaded with thick grease and it adds a good bit of drag to it. To cut at the speeds I want I might have to buy the stronger motors.
Here's an interesting read on stepper motors.
Stepper Motor Inductance / Torque
after looking at this, https://probotix.com/specs/HT23-280-8.pdf It looks like I need to hook up at the half winding point of my motors to get more torque at the higher speeds. The specs of the probotix motor are pretty close to the ones I have.
Edit*
After hooking up the motors through half of the winding, I am able to yank the router motor around at over 400 in/min. After a little trial and error and some math I figured that my motors are making at least 50 oz-in at 1000 rpm.
Last edited by dbsharp; 08-13-2012 at 02:28 AM.
Nice work so far! It won't be long for the chips to fly...
BTW, where did you get the mill vise from?
ebay
Cnc runs!
Now, I'm busy getting the electronics in order and getting all the accessories made.
Here is one of my first parts.
Wow! The machines come together really well, and the finish on the parts looks great! I had to zoom in to see the cutter marks as they were so smooth they looked like they'd been fine sanded!
cheers,
Ian
It's a state of mind!
Great work, as evidenced by the finish on your part! Hope to see more!
thanks. Still a lot of work to be done to the machine, first in line is a vacuum attachment. The piece I made is part of the vacuum system.
oh yea, this thing rips through aluminum (for a homebrew cnc router)! I was making some 200 ipm test passes with a .375 3 flute EM and it did quite well.