simple motor sizing

[smoker]

Hi, I use simple because calculating all the stuff is out of my league. I tried learning from a lot of post before me and trying the free programs for motor sizing suggested in other threads, but I still fail to make it happen.

I plan of building a moving gantry for woodworking with rack & pinnion, dual drive for the X (sive of machine 5' x 10') I have already the thk rails
Max design speeds: 200 IPM (400 IPM rapids)
I will first have a porter cable 3HP router (so will be cutting at only 50 IPM at first)

Taken from peolple already suggested on the forum I have the folowing:
Rack 20 angle
Pinion 12DP/18T
With a 10:1 reduction this would give me a cutting motor speed of 424RPM (for 200IPM) and an accuracy of .002. I attached an excel file where I have done the calculation and the parameters in blue are changeable.

First, is this calculation correct? Does anybody have better suggestions for the rack and pinion? Arent't those motor speeds low for steppers? (http://www.cnczone.com/forums/attach...chmentid=20569)

Second, and now not simple (impossible for me), what kind of steppers do I need?
a/ force needed to cut wood and move gantry
b/ dual drive x
c/ inertia (gantry weight)

So, here we go with my questions
a/ I learned that the equipment you use for cutting makes a huge difference and the type of wood. Does anybody have an idea what it takes to cut MDF with a PC and with a 10HP spindle with a regular bit)
b/ if using 2 drives for X, can I devide the needed oz-in by 2?
c/ no idea what this is; but my gantry will weigh about 200lbs

There are also the velocity etc that I have no idea of how to calculate and incorporate.

I have looked at stepper motors on the net (homeshopcnc, camtronics) but they do not list their motor specification, so I am totally in the dark there.

If somebody can point me in the right direction please? (if not you may also tell me what motor I need directly ;-)

David

[MrBean]

I plugged your numbers into my calculator. I hope I got it right.

Just substitute the words "Belt Drive" for "Rack and Pinion".

These are the results I got....

[smoker]

Nice! so I guess I got the first part right.
Now the more difficult motor sizing part....

[juanca]

Too... How can I calculate Thust/cutting Force ???
and Friction FORCE?

[Sheldon]

My friend is building a router apeoximately the same size. if you use dual motors for x axis I reccomend 600oz-in (Bigger is always better), y-axis, assuming it is single drive can use 1200oz-in and the z-axis can use a 600oz-in. Another place to look for motors is ebay. I bought mine for alot cheaper than from a dealer.

[Zumba]

Bigger is not always better when it comes to stepper motors. A big motor has more holding torque.... not necessarily higher torque at max speed. One thing is for certain though.... they always have higher rotor inertia and in all likelihood, higher inductance, which means lower max speeds.

I can't tell what size motors you need without seeing your machine. It will depend on how well your THKs are aligned and how much friction there is in your R&P drive system.

However, despite Sheldon's logic, his recommendation for two 640 oz-in motors is probably pretty good. Take advantage of the internet... buy yourself a pair of motors from Homeshopcnc or Keling and worst case, you sell them on ebay for 90% of what you paid and buy a pair of different sized motors.