CNC conversion

[Zap]

I recently purchased one of these.

http://www.grizzly.com/products/item...emNumber=G0517

I'm almost ready to start buying parts to convert it to CNC. I'm interested in the FET3/Cruiser system at stepperworld.com. This is my first CNC project and I have a few questions.

1. Are 150 oz. steppers using a direct drive strong enough or should I multiply torque with a cog at 2:1 ratio? I will only be machining plastics and aluminum. Or should I just buy larger motors?

2. There seems to be a fair amount of backlash on the lead screws. Will I see much improvement if I convert to ball screws? I guess I'm trying to find out if it is worth the extra cost and time to do so.

3. I'm stuck on the Z axis. what would be the best way to set this up? I'm kind of leaning towards something like this.

http://www.homecnc.info/Pics/400z-axis-installed.jpg

[HomeCNC]

The 150 size stepper motors will not be strong enough for a Drill/Mill CNC conversion. You should look into at least 300-400 oz/in.

Glad you liked my Z axis design!

[cncmojo]

Hand wheels

I will caution you that if you use a Z design with out a hand wheel to use for small movements during setup, you may regret it. I have found that conversions without hand wheels are much more time consuming to use. Good luck with your conversion.

[ballendo]

Hello,

I guess I disagree with the previous replies...

150 0z. in, though a bit small, WILL work with this drill/mill. Set em up 2:1. (and do that even if you use bigger motors)

You didn't say if you were using the original leadscrews or not?
Using the smaller motor will limit your machining speed, but you WILL be CNC machining... And you can increase motor size later, if you wish.

Also, there is no inherent advantage to having handwheels on a CNC machine. The jog buttons on the control will do ANYTHING you might have used a handwheel for...

Perhaps the poorly implemented Jog functions of some of the PC-based controls are responsible for this continuing myth. I'd like to hear just why a computerised handwheel is "slower" than a manual one?

Against this, the handwheels can present a real danger as they spin, and if the handle is left on, can also increase vibration and chatter in the cut.

Finally a point of agreement, sort-of. Since this machine has no fine feed, a Z drive like Jeff uses would be a decent choice. BUT, it will be more work than necessary. You don't need to use a spinning nut...

Hope this helps,

Ballendo

[cncmojo]

Torque multiplication through belts and gears is a wonderful thing. Being able to use a smaller motor to perform a job that is way beyond practicality, is definitely possible. This process is nothing new, this guy was on to it …
“Give me a place to stand and a lever long enough and I will move the world”
Archimedes, 220 BC


The problem is after expending lots of money, and even more time you probably will not be satisfied with the end results. By spending a few more dollars, and purchasing adequate size motors, the machine has much more potential regardless of what you intend to do with it once finished.

Now as far as the handwheel issue is concerned.

” handwheels can present a real danger as they spin”

So does the cutter, the spindle, pinch points, high voltage, and just about every thing about these types of machines.
I suppose I could correctly say that even plugging the machine is a greater danger than three rotating handwheels.

” The jog buttons on the control will do ANYTHING you might have used a handwheel for... “

How about a fast manual cut?

Most home, or shop made CNC machines have poor, or no jog controls at all. With handwheels you can easily move the machine manually, just think about having to do this electrically ALL OF THE TIME, while building, servicing, setting up, and ANY time the machine has to move for any reason.

Have you ever need to do any thing manually on a machine with no hand wheels? Yes there are times when manually is the only practical way, do you really want to eliminate this option. When setting up nothing replaces the Feel you get with a hand wheel. You can feel the cutter making contact, and you know how much tension is on the cutter. If you do not understand this then you have not done much machine work, on these types of machines.
I would throw away a lot more metal with out handwheels.


Bottom line is do you want a slow machine that has to be jogged any time it is moved, I don’t think so. I have used them and they are a real PAIN.

[HomeCNC]

cncmojo: I must disagree with you. I have helped a few people make the addition of hand wheels on my CNC plans. After about 6 months of use I asked for feedback on the conversion. Every one of them said that they felt the extra work adding the hand wheels was a WASTE OF TIME! They now don't use them.

I too have found that I can use my controller software very easy. I get much better finishes on quick cuts because it's like having a power feed on the table.

I figured that professional CNC milling machines don't have hand wheels on the machine, there must be a reason for it.

[cncmojo]

Jeff

Well I will have to disagree with you , based on thousands of hours of experience operating CNC machines.

“I figured that professional CNC milling machines don't have hand wheels on the machine, there must be a reason for it.”

There is a reason for it, an automated machine center does not, use, need, or have handwheels. The same goes for most production CNC mills. The reason is they are intended to be placed into production . This includes ten of thousands of dollars in jigs and supporting equipment for production. The machine will normally be set up to replicate part after part with some type of precision alignment fixture. After performing an automated function, the machine returns to home X 0, Y 0, Z 0, and the cycle repeats. Over and over again. On the same type and size of material, precisely aligned in the same manner every time. In this situation there is no great need for hand wheels, although the service personnel would love to see them, as well as who ever sets up the fixtures initially.


I cant even imagine a home cnc machine without hand wheels, these are not production machines. They rarely make the same two parts. Also why rob their ability to be operated manually? There is no need to remove this function from a home CNC machine unless you just like to play with controls. The wheels are irreplaceable in function for non production machines, you would only know this if you were an experienced machinist. I just stepped out in my shop and asked the 5 machinist that I have working for me, what would you say if I told you I was going to remove the hand wheels from your all of your CNC machines, because you do not need them. They thought I was nuts.


Have you ever seen a non CNC Bridgeport mill with a power feed on the X ,Y, & Z with no handwheels. NO, and do you know why? It would be a pig. Believe me if the “No Handwheel” with power feed was a good thing you would have seen it on a Bridgeport, they knew what they were doing.

[HomeCNC]

Well it's done without hand wheels in my Garage.

[buscht]

Zap,

1. I'd look at bigger motors. If you multiply the torque x2, you are also slowing down the speed x2.

2. I'd try tightening up the leadscrew nuts to remove the backlash before going to the expense of ballscrews. There are several threads on this site that discuss methods for this.

3. I think HOMECNC's Z axis if fine. I wouldn't have the handles on my machine either. I agree with Ballendo on this one.

I've run a Bridgeport with power feed and you do need the handles for fine adjustments, but with a CNC control its as simple as jogging .007", very easy for almost anyone to do correctly.

Maybe there is a way to make removable handles and everyone is happy.

[IndHobby]

I do this size mill for a living. here is a snip from my site:

Where are the hand wheels?
They had to go for a couple of reasons:
The increased diameter and mass of the hand wheels degrades CNC performance.
The side where the encoder is mounted, the shaft it thinned quite a bit, adding a hand wheel is a bad idea.
Ballscrew speed can be as high as 900 RPM, handles are attached the the table which moves. Put that all together you have a 900 RPM wheel traveling at 180 IPM which means - accident waiting to happen. Although it's listed last, safety was the number one concern when the hand wheel was left off. Too many times you'll find yourself leaning up close to take a peak, or put something on the bench within the "reach" of the handle. Now some folks might be saying I'm a little overly cautious, but I'll bet that a spinner-handle on an hand wheel can snap your wrist or a bone in your fore arm like a twig. (NO BULL)


If you want to move the table, just run MACH 2 and get a $5 joystick, or use the keyboard.

Next point, if you reduce the drive ratio and you use a handle it will work against you when your doing it manually. Make it easy for the stepper, make it hard for you.

If this is your first CNC project you might want to put some sort of small knob or thumb wheel on the screw, this way if you hit a limit it's easier to back off. Once you get the hang of it you'll never use them.

If you tighten up the "anti-backlash" brass nut tight enough to prevent lash you'll do one of two things:

The increased drag and friction will cause you to loose steps or move so slow as to make CNC a joke.

The brass nut will wear faster than normal and you will always find a lash issue when you need it the least.

For a mill of that size look at 400+ in/oz steppers. Bank for buck ratio I would go with 640's and a 65VDC 20 Amp PS with G201's and ballscrew.

It's one thing to ask the little woman for money to do the project right, and another to ask her the second time for money to fix the mistakes you made in the first place.

Do it right and never look back.

Just my two cents.

Thanks
Aaron Moss
www.IndustrialHobbies.com

[lsfoils]

Cha ya Aaron,

The Mach series controller software make it easy to jog any where your machine can go. Ta hell with the hand wheels. Can't control 'em as well as the software, myself. Just figure, you can control your feed rate, the amount of movement and direction. A good machinist will find out the proper feed rates for the material he's removing and plug it in.

Ball screws, man! Roton! Spent a whole $30 an axis. No contest. Get an extra nut if you don't want to have the software deal with the back lash.

Good luck with your Grizzly. I'm not sure you need all that power for such a short stroke. By the time you accelerate to your max speed you've shot the table onto the floor. If yer cuttin' steel you won't need that much speed, anyway. By the by. is there enough room in the head stock for Jeff's marvelous Z trick? Roton does sell 1/2" ball screws. Post pictures when you get there, ok?

Doug

proly to much suds to make much sense tonite, folks

[lsfoils]

Oh yeah, the wiff. Don't tell her nothin and have all the bills sent to a freinds house...(dark)