[WilliamD]

While considering cost and available resources, I'm wondering if it'd be better to put two motors on the x-axis, rather than getting a bigger one. I'm getting the 276 oz/in motors from automationdirect. I'm sure they'll be powerfull enough to power the y and z axis's, but I might want more for the x. I know that there can be binding issues, but is there any real advantage? I figure that it would help more the weight more, so you could increase the RPM's a bit without losing as much torque. I'm running 1/2" - 10 ACME rod, as I'm sure that matters. For anyone with the classic 2'x4' JRGO router tables, is 276 oz motors enough? I would like to machine at around 150" per minute. I'll be putting a PC 7518 in it, so the router should be powerfull enough. Just wanted to get some thoughts and ideas! Hoping to post pictures soon!

[ger21]

I'm guessing you'll be lucky to get 100ipm. First, you'll need to run very high voltages to go that fast, at least 50V or more. Then, 1/2-10 at 150ipm is 1500rpm. Look at the torque curve for that motor at Automation Direct. At 450rpm, it only has 100 oz-in of torque. At 600rpm, it's down to about 50 oz-in. Go to www.nookind.com, and look at their technical data for acme rod.The critical speed (where whipping can occur) for 1/2-10 is around 50ipm. This can vary greatly due to different mounting techniques. Lastly, a 7518 is really heavy. Heavier than I'd put in that design. jmo, though.

As for two motors, it seems that you'll hear a ratio of at least 2:1 against them. But I'm not too sure that most of those against have ever tried it. Shopbots and many other commercial machines use dual motors just fine. A lot of people use the slaving function in Mach3 just fine. I've never heard one person say it didn't work with Mach3. I'm using 2 X-axis motors on my router, if I ever get it finished. I don't see any problems with it. One advantage is the gantry will be a lot stiffer when loaded from either side.

If you want to cut at 150ipm, you have a few options. Rack and pinion. Belt drive (like a rack and pinion). Bigger motors and higher lead screws. You may even need bigger motors with rack and pinion, too.

You didn't mention what drives you'll be using, but that can make a big difference as well. There are a lot of factors involved, and they can all influence each other. If you read through all the threads here, you'll find very few if any people cutting at 100ipm or more with a JGRO type or any other MDF machine. Speed costs money, sometimes lots of it, and these are usually entry level machines. Also keep in mind that the faster you go (and the bigger the router motor you use ), the stronger the machine needs to be. What may be perfectly fine at 60ipm may be way too flimsy at 120ipm. Sorry for rambling.

[dfro]

I am thinking about the design of a first router mill. I also am interested in using two motors on the x axis. How is that handled in the software and the drivers, ect,? How does Mach3's slave function work?

Thanks

[ger21]

How is that handled in the software and the drivers, ect,? How does Mach3's slave function work?

Thanks

Im Mach3, you set up two identical axis, one is X, the other usually A (or B or C). Then there is a Slave axis window where you assign the slaved axis to the master. If you set up seperate homing switches for each side, Mach3 will home each side independantly. By adjusting the switch locations, this will insure the gantry is square. That's really all there is to it.

[dfro]

Thanks for the info ger21. What, may I ask, is a homing switch? Is it different than a limit switch, which limits the gantry's travel?

[ViperTX]

dfro....yep, homing and limit switches are similar...homing refers to getting back to "home base" the zero, zero, zero location.

[dfro]

ViperTX,
Thanks for the reply. My experience is very limited on all of this. Am I correct in saying that the limit switches are at the ends of all the rods and tracks to make sure the machine does not try to advance itself out of its range of motion? And is the homing switch a button in the software that you press when you have determined where you want 0,0,0 to be? Is this set after manually advancing the axis' to where you want them (the starting point for the toolpath) through some kind of joystick in the software? I am trying to understand how all of this is used in action.

Can the motors be turned easily when they are not powered up? Is this how people reset the position of both x-axis motors, by manually turning one or the other motor when the machine is turned off?

[ger21]

The homing switch is the sam as a limit switch. You can even use you're limit switch as home switches. In Mach3, you click the home button, and the machine moves toward the switch. When it activates the switch, it then backs up until it's off the switch. This is your home position. In Mach 3 you can set this home position to be any coordinate you like. It can be X=0, X=-3, X=2. Whatever you want. So when you home the dual axis, each side moves until it hits it's switch. If it's not square, you adjust the switch position to make it square.

You can also zero your axis (set them to X=0) anywhere on the table with the push of a button. You can zero them individually, or all together. The Z axis is usually set this way. Jog the tool down to the top of the workpiece, and hit the Z zero button. Then the top of your workpiece will be at Z=0.

You can also set softlimits in Mach3, which are basically software limit switches. They'll stop the machine when it gets to your specifies "limit" coordinate.

[dfro]

Gerry,

That makes a lot more sense. Mach3 sounds like a great program.
So, please tell me if I am right:

If the two x axis motors get out of alignment, you just have the software move the ganrty to the home switches on the x axis rails, which were carefully set in the beginning (so that the x and y axis' are as square as possible). When one of the motors hits its switch first and stops, the other will keep moving until it hits its switch and then it will stop. This will return both x axis motors back to the original adjustment.

Is this correct? I am sure using the software makes this all obvious. I will also try to read the Mach 2 manual to get a better sense of how the controls work. Is the master/slave function new to Mach3?

Thanks.

[ger21]

You've got it right. I think slaving may have even been in Mach1.

[dfro]

Gerry,

The Mach2 manual is really well written. I got a lot more info about the homing and limiting switches in section 4.6 (pg. 34) and info about the master/slave option in 5.7.4 (pg. 62) of the Mach2 .pdf manual. It offers a great overview of cnc setup.

I definitely want to try directly attaching two x axis motors to their respective leadscrews and master/slaving them together. If you do a simple homing operation at the beginning of each machining job, your machine is good to go. To me it seems the danger of the gantry wobbling and belts flexing outways the danger of lost steps, as long as the motors are powerful enough, imno (in my newbie opinion). It also seems that with two leadscrews the danger of whipping is reduced.

[ger21]

If you do a simple homing operation at the beginning of each machining job, your machine is good to go. To me it seems the danger of the gantry wobbling and belts flexing outways the danger of lost steps, as long as the motors are powerful enough, imno (in my newbie opinion). It also seems that with two leadscrews the danger of whipping is reduced.

You would home the machine every time you turn it on. Imo, if your losing steps, fix the machine. Either get bigger motors, slow down, or fix what's causing it.

As for whipping, two screws vs one shouldn't make any difference. If a single screw would whip, then both probably will. But if you're using two motors, then the extra power may let you use screws with a higher lead, which would let the screws spin slower, reducing tendencies to whip.

[JerryFlyGuy]

To run two steppers on the same axis could you not just double wire your stepper drives off the same leads off your break-out board [ in parrellel] and each stepper would see the same # of steps from their respective drives? This would save you slaving the axis so you could use it for something else later?

Sorry if this is a dumb question... there could be other things which make this impossible ie; vdc or something..

JerryFlyGuy

[ger21]

Yes, you can run two drives from the same step and direction pins, but it may not work with all breakout boards or parallel ports, if there isn't enough voltage or current.

[dfro]

Gerry,
Another basic question. What do you mean by a higher lead? I have not heard that term used before. Do you mean fewer threads per inch? For example, 10 tpi is a higher lead than 16 tpi?

But if you're using two motors, then the extra power may let you use screws with a higher lead, which would let the screws spin slower, reducing tendencies to whip.

[ger21]

Gerry,
Another basic question. What do you mean by a higher lead? I have not heard that term used before. Do you mean fewer threads per inch? For example, 10 tpi is a higher lead than 16 tpi?

Correct. The screw lead is (# of starts)/tpi, or how far the nut will travel per turn. A 10 tpi single start screw is .1 lead. Multiple start acme screws can have very high leads. You can get 5 start 1/2-10 acme, which is .5 lead, or 2 turns per inch. The best bang for the buck is 1/2-8 2 start acme at www.mscdirect.com, around $30 for 6ft. I bought some 2 years ago for $22, but the price has gone up quite a bit recently.

[energyforce]

Is anyone here running a large gantry ontop a x axis with only one motor on one side and how is it working for you and what type of setup are you using (shaft and pillow blocks? ballscrew? rack and pinion? etc) Thanks.

[dgolka]

I have run 2 motors off the same drive ( both wired to the same terminals) it works fine as long as the motors are identical ( same deg of step & reistance per wining) otherwise you get all kinds of neat stuff happening.

[energyforce]

I have run 2 motors off the same drive ( both wired to the same terminals) it works fine as long as the motors are identical ( same deg of step & reistance per wining) otherwise you get all kinds of neat stuff happening.

Sweet. Thanks!

[efiniracer]

I belong to another forum as well, and over there my Avatar is "The guy who reads....", But I just felt inclined to comment on this one. I am building my own router as well, and this was a question that I have had for awhile now. I just didn't want to ask a question that may have been written about before.

Thank you all so much for sharing this info with us, as I think it helps everyone who passes by.

Now...On to my question. Can you run 2 servos in the same manner that GER21 described? I also wondered about running 2 servos in the manner that was described by DGOLKA. As was stated earlier in the thread. I think that this would be easier and more intuitive if I had something in front of me, as in limit, home and other miscellaneous bits. I'll read up on MACH2 to see if that helps, but mostly, thanks to all of you.

PS-I don't know how "dangerous" this is, but I'm doing a router that is of my own design. I'll share pictures when I get a little furhter along.