POSSIBLE CNC BUILD

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V8 BUG
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POSSIBLE CNC BUILD

Post by V8 BUG » Mon Nov 22, 2010 9:54 pm

This is my bridge mill design concept.
I already have the base plate which is a welded aluminum structure 28"x67" with a 1" top plate and 1/2" double "x" pattern for support. It has been stress relieved and blanchard ground top and bottom.
I have all of the linear rails which are thk hsr25's as shown.
I also have the x plate which is surface ground steel 1" thick and weighs approx 120 lbs.
I will need to fab the uprights(3"1/4 wall tube) and the "y" cross beam (6
" channel)
The y axis plate and z axis plates will be aluminum.
So I was thinking of ordering a ball screw package off ebay from linearmotionbearing which comes with 3 5mm lead screws nuts and bearing blocks with ends machined on the screws.
Gecko drives and stepper motors in the 640oz in range.
This is where I am not sure what to do. I plan to machine aluminum and softer materials like wood and foam. Do I need bigger motors to run cutting at 120ipm and rapids at around 400ipm? I may load the table with a bridgeport vice which is about 75lbs but am not sure. I really don't care if its not really fast as I am use to cutting with huge old duplicators that are maxed out at 60ipm cutting.
As for a spindle I am not sure if I will use a wood router or build my own spindle yet.
Any suggestions would be appreciated,
Thanks Kevin
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BUILDING IT IS MORE FUN THAN BUYING IT

TOTALLYRC
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Re: POSSIBLE CNC BUILD

Post by TOTALLYRC » Sat Dec 04, 2010 6:04 pm

Bigger steppers have more torque but the torque drops off faster with with speed than the smaller motors..
You need to not get into the bigger is better routine with steppers.
The nema 423 from keling work well and if you drive them with a G203v which morphs from micro to full steps you get the best of both worlds. High resolution at low speeds and high rapids because when it morphs from micro to full stepping you get your high speed torque back.
Running the motor at or near its mav voltage is the best way to get speed out of any stepper.

On my router I was playing with max speed rates and was able to get into the 700 ipm range but it was silly fast and scary. You also need a computer capable of generating the high step rates needed.

Mike

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JimGlass
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Re: POSSIBLE CNC BUILD

Post by JimGlass » Sat Dec 04, 2010 7:16 pm

Kevin;

I have concerns with how rigid your machine will be. Might be okay for milling foam and wood but not aluminum.

Below is my very first CNC project. The ways are all linear ball bearings
and Tompson shafting. It was smooth and fast but not at all rigid. Notice how far the spindle is from the column?? The "Z" axis was also on linear bearings. Seemed like a great idea at the time. :roll: I works okay for engraving wood but I wanted to mill steel.
Image

Below is my second CNC project. I used larger linear bearings and larger Tompson shafting. All I did repeated the same mistake only bigger. Although I did make square gibs for "Z" and that was an improvement.
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A friend wanted to buy the above machine mostly to play with so I sold it to him for what I had invested less my time. About $800.

However I leaned how to build a CNC controller using the Gecko driver boards from the second CNC project.

A year ago I aquired some cast iron dovetails and used my spare Gecko driver boards and other spare parts to build my third CNC mill.
Image

This has been a great little machine. I had to upgrade the spindle motor from a 1/4 hp to 1/2 hp for machining steel. I use Mach3 to run this machine.
Here is a link with pics showing how I built the milling machine.
http://smg.photobucket.com/albums/v30/j ... 0Mill%203/

With the knowledge aquired from CNC mill #2, I built an almost identical controller to retrofit this Bridgeport. I still use Turbocnc software on the Bridgeport because I like using a laptop to run the machine. I can take another computer loaded with Mach3 and run the Bridgeport without changing any wiring. Mach3 is great software but sometimes I like Turbocnc better so I use them both.
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Jim
Tool & Die Maker/Electrician, Retired 2007

So much to learn and so little time.

www.outbackmachineshop.com

V8 BUG
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Re: POSSIBLE CNC BUILD

Post by V8 BUG » Mon Dec 06, 2010 10:15 am

Thanks for the feedback on the design. I will get back into Solidworks and try and make my Z more ridgid. I want to make aluminum symbols for vehicles and things like that.
I still need to sit down and go thru the math for the stepper requirements.
Jim, do you think the biggest problem is the lack of dovetail column? I would still like to build in the hsr 25's that I have.
BUILDING IT IS MORE FUN THAN BUYING IT

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FLSTEAM
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Re: POSSIBLE CNC BUILD

Post by FLSTEAM » Tue Dec 07, 2010 8:29 am

I can attest to the need for a ridgid Z axis. My table was built with two 1" SS rods 48" long. There is no problem when I am using the plasma since there is no load on the bearings. But when I use the router there is way to much flex and I need to cut at very slow speeds to get almost accurate work. I have new linear bearings to rebuild the gantry I just need to take the time to tear everything apart and do it. A PITA. Oh well.

Good luck.

John
http://www.ngshay.com/
Shay drawings and castings

V8 BUG
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Re: POSSIBLE CNC BUILD

Post by V8 BUG » Fri Jan 07, 2011 9:41 pm

Here is my updated version. I reinforced the gantry cross bar with another 6" channel in the back to create a box section. I improved the y axis carrage and added a plate for the z. I am thinking of creating a box section with 1/2" aluminum for the z axis and may be putting the router in the center.

Jim, I would like to stick with this style of machine as I have the aluminum fixture base weldment already and it is nice and flat (inspected on our cmm at work) . I do like your machines they are along the line of a real mill.
I realize this machine will not cut like my Bridgeport...but would like it to cut light cuts on aluminum, wood and plastic for casting patterns.
Below is the new picture of the machine and below that is a image of the stuff I would like to cut.

Any more input would be greatly appreciated as I would like to get this started this year.

Thanks Kevin
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Rick
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Re: POSSIBLE CNC BUILD

Post by Rick » Sat Jan 08, 2011 11:03 am

V8 Bug

Looks good, I have a similar machine but not as big as your. Mine ws an old Techo-ilse (not sure about the spelling) It is not near as rigid looking as your. The supports that hold the x and z axis are the weak link. One day maybe I will get around to stiffing them up. But for now I mainly machine plastic and alum (light cuts) and do engraving with it and it does just fine. Getting 400 ipm rapid depends on the pulse rate your control can do along with motor resolution and screw pitch, plus you have to figure in weight also what resoultion are you trying to achieve. Power wise your steppers look plenty big. My machine has 315 in-0z motors and it rapids about 120in/min. The only sugestion I would make is to put some sort of counter balance on you Z axis so as to even to load on the motor when the axis is retracting and extending. The different inertias of going up and down can cause some issues. I added one to my machine and it made a big difference as I would some times loose a few steps, never was sure which direction but thinking it was during decel going down to position. My counter balance is just an regulated air cylinder. One I put the counter balance on the problem went away.
Attachments
Picture 011.jpg
Old picture of machine without counter balance on z axis
DSCN0280.jpg
with counter balance
Rick

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V8 BUG
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Joined: Sun Jan 28, 2007 8:10 pm
Location: Great White North

Re: POSSIBLE CNC BUILD

Post by V8 BUG » Thu Aug 11, 2011 8:44 pm

Well, I have put this design on hold for a while as I found a TMC-1000 bench mill on sale from a local high school. I jumped at it as the deal was too good to be true. As these deals go, the unit didn't have all of the electronics that are required to run. So now goes the retrofit. I am thinking of a kit from Keling with some new steppers, Gecko G540 4 axis drive, new power supply and the latest version of Mach 3. I don't really want to make a career out of geting the mill running as there are projects that I would like to complete before I die.
Below is a picture of a machine exactly like the one I bought. It's a nice machine with a R8 spindle taper which is nice because all of my bridgeport stuff fits.
Spindle motor is 1hp 500-5000 rpm.
Step motors are 150 in oz on all 3 axis. (round motors which are from what I have read not as good as square ones)
Cast aluminum frame and cast iron table
Made in the USA
What do you guys think of my plan?
Any imput would be appreciated.

Thanks
Kevin
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BUILDING IT IS MORE FUN THAN BUYING IT

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