Newbie- First Build

[finishlinewrx]

Hello Everyone

Thought i say hi first off. I am starting my first build with some reading/studing from here. And i love the site..

So far plans are still up in the air. I am shooting for somewhere in the 48x48 to 48x60 area. for work with mostly wood and plastics maybe some light aluminum depending on how ridged i can get it.

So far i have got enough box tube to build the frame and gantry.
I got the computer and software done. I am going to run Mach3 control.
And i have Solidworks and AutoCAD thanks to the programmer at work!!
And trying to get Mastercam out of them.

Here is the one i am pretty much going model with a few changes.



I do have a couple questions if someone could point me the right way or link me some good reads.

I was planing on using dual 1/2-10 acme on the x with a belt drive to sync them.
Would a R&P drive be better? (Its shown on some later pics of the posted machine.)

Im not really looking for alot of speed maybe 70-100ipm rapids.
Is that doable with a 10tpi acme?

I still have a alot of reading left on electronics. More i read the more lost i get

What i am thinking is the gecko g540 3 axis package from keling
http://www.kelinginc.net/CNCNEMA23G540Package.html
Second one listed.
Is that Ok?? Have enough Tq. to pull a 48" gantry?
I am sure there are better options but i am trying to keep the whole build under 1500$

[jsheerin]

By my calculations, if you run mach3 at a 45kHz kernel speed and use the G540 (1/10 micro stepping) with a 10tpi screw, you can get 135ipm max. If you run a 1/2-10 5 start, so a 2tpi screw, you can get 675ipm. With the 10tpi screw, you have lots of force to move things around and very fine resolution. With the 2tpi screw you have roughly 1/5 the force (actually more than that because the 2tpi screw has an efficiency of about 77% versus 43% for the 10tpi in the same conditions) and 1/5 the resolution, but these levels are typically still okay for a wood router consider the medium you're working with. With the 2tpi setup you also might need to evaluate if you have enough torque from the motor to accelerate your load to that max speed before you reach the end of your travel. I don't have personal experience with that bit of the equation yet.

[finishlinewrx]

Thanks for the info.. 130ipm is slow on a table this big isnt it? almost a 30sec. travel time full distance in x

[ger21]

1/2-10 5 start would be a much better choice. 70-100ipm rapids are way too slow. Ideally , in most situations, you want to cut faster than that. The 5 start should give you around 200ipm.

[CarveOne]

Just FYI, in the Joes 4x4 forum there is some work being done with 1/2-10 8 start screws.

CarveOne

[finishlinewrx]

Will the keling package i listed be ok to run a 5start lead? Are the 387oz-in motors enough to pull a 2tpi screw.

Where do you recomend buying the screws from?

[CarveOne]

Originally Posted by finishlinewrx Will the keling package i listed be ok to run a 5start lead? Are the 387oz-in motors enough to pull a 2tpi screw. Where do you recomend buying the screws from?

Yes, no problem with 387 oz/in motors.

The ones I bought for my second build is McMaster-Carr #99030A704
http://www.mcmaster.com/#99030a704/=mb9we The price each is currently $60.74 usd

CarveOne

[finishlinewrx]

How are you figuring ipm? do you have a calculation somewhere i havent found yet?

With the 1/2-10 5 how is this going to affect my accuracy. what is a holdable resolution with this? Post above said 1/5 of it?

What about 1/2-10 2?

And what is the average resolution of a home build machine? With round supported linear rails anyway.

im used to our stuff at work..Our new cnc grinder will hold .000040. But im hoping for maybe +/- .005

[jsheerin]

Resolution is different than precision. Resolution is the theoretical minimum distance the cutter (or whatever) can be moved by your system. So say you have a full step driver, a 200 step/rev motor, and a given lead screw. Then you can calculate what the minimum movement can be - your motor can turn 1 step which can move the cutter 1/200th of the pitch of the screw. So if you have a given screw and then compare that against the same screw but with 5 starts, the resolution of the 5 start screw will be 5 times worse - the minimum movement will be 5 times larger.

For speed, I figure it out this way:
linear speed=(kernel speed)*60/(microsteps per full step)/360*(deg/step of your motor)/(lead screw pitch)

So for the example above, 45000*60/10/360*1.8/2=675ipm for a 5 start 1/2-10 screw run at 45kHz kernel speed with a 1.8deg/step motor using a G540 with 1/10 microstepping. For a 1/2-10 single start, 45000*60/10/360*1.8/10=135ipm. I believe I checked the results of this against an example in the mach3 manual and playing around with my G540 and 1.8deg/step motor and 1/2-10 5 start lead screw - I was a bit unclear on the relationship between kernel speed and motor speed, but it seems to be linear from the example. Also, microstepping seems to reduce your speed by the ratio of micro steps to full steps. If any body thinks this is incorrect, please let me know.

[finishlinewrx]

Thank you for taking the time to help the rookie it is really appriciated
Use the formula above with a 1/2-10 2 start acme came out to 270ipm.
That should be a desent speed right?

Thanks agian and im sure ill have more questions as i get farther along.
I have desided on 48x60 with 12" on z.
I have got the almost everything to put the frame together and the gantry.
Linear rails for x are ordered. Got to love ebay!!

Machine repair guy at work got me. cycle start/stop buttons, home/limit switches, mpg jog wheel, couple e stops, and a small electric cabnet to build from.

Ill get pictures as the build go on.

And thank you again for the help so far..

[ger21]

Originally Posted by finishlinewrx Thank you for taking the time to help the rookie it is really appreciated Use the formula above with a 1/2-10 2 start acme came out to 270ipm. That should be a decent speed right?

Actually, that formula will not tell you the speed of your machine. All it tells you is how fast Mach3 is capable of spinning the motor.

trying to calculate how fast your machine will go is very complicated, and involves much more complex formulas. You need to account for friction, screw efficiencies, motor torque curves, mass of machine, acceleration rates, and on and on....

You also have to consider if the screw is capable of spinning 1350 rpm at the lengths you intend to use it at, without violently whipping around.

As for resolution, 1 full step with a 5 start screw will move the machine .0025. Microstepping may get you to .00025 per microstep.

[jsheerin]

Hi Gerry,
Yes, that formula does tell you the speed - it calculates how fast Mach can spin the motors and then divides by screw pitch to give how fast that will move your nut on your chosen screw. You're right, however, that it does assume proper engineering of the rest of your system. Such as that your motors have enough torque to accelerate your load to a constant speed within the travel of your machine and that the motors have enough torque to overcome dynamic friction to keep the load moving at that constant speed. It's a good tool to use to evaluate design changes. I actually did include all the other things you mention in my own calculations, but that's a bit more involved than I feel like typing out on a message board.

John