PLEASE HELP! I am alone. CNC construction.

[esquema]

Good Afternoon. I am new to CNCZONE. Thanks for the people who created this site. I need help PLEASE!
Please forgive me for my bad English. I am making my own cnc machine for plasma and wood/aluminum milling. I will have an interchangeable work area on the table and a interchangeable plate on the Z axis. I have been surfing the net for materials for my Project, because where I live (São Jorge Island, Azores, Portugal. Population=9000) no one sells this type of materials and no one has a cnc machine on this Island. I have never seen a cnc machine, only by youtube. My Friends say am crazy for making something I have never seen. I am going to make my cnc 100cm by 130cm. I am going to use belt drive on both axis. I also want to use a ratio 6:1( 12 to 72 tooth) on my NEMA 23 stepper motors (x and y axis). The x axis going to be drive on both sides with belts. The Y axis gantry I am going to use a fixed belt. The Z axis I have a ball screw which will also have a 2:1 reduction.This will give me: X and Y step=0,05mm, Z step=0,0125mm (full step). I am thinking of using your HTD 5M-15mm belt and pulleys on all axis. I have the R-Tech P30C plasma cutter . I am thinking of buying a 2.2kw chinese water cooled spindle for milling.

Material I have bought by internet:
Fully supported 20mm rails and pillow blocks.( Marchante Dice)
300mm THK ball screw (jak8858 ebay)
400mm 20mm precision round rails (for Z axis) and pillow blocks ( Merchante Dice)
3 Axis TB6560 Driver Controller Board + 3 nema 23 (57BYGH56-401A) 263 oz.in. (first-supply ebay )

My questions are:

Would do you think of my configuration, what is bad?

What is better? 3mm or 5mm timing belts?

Should I use half steps? I heard that it is better? Less resonance?

Which is better steel or aluminum pulleys?


Thank you for your time. Please respond.

Paulo from Azores

[slowlearner]

Welcome to the Zone! There is alot of information on this site. I have been
visiting this site for years reading and learning how. My suggestion to you
would be to find a build that is using the same materials as you.
Read their build logs and then ask questions.

[esquema]

Thank you for your response.
Paulo

[awerby]

If I understand you correctly, you're talking about using a 6-1 gear (or pulley) reduction on your 23-frame stepper motors, presumably to increase torque. But this will also slow the speed of your machine to a crawl. Even if you don't care how long it takes to cut a part, wood will burn if you try cutting it too slowly. And plasma cutting takes a certain amount of speed as well. If your system isn't strong enough to push your gantry around reliably, I'd suggest getting something stronger, and not crippling your machine just to utilize some cheap Chinese parts you found on Ebay.

That controller, running on 24v, is already going to limit the speed of your motors substantially. You'd be a lot better off with a higher-quality controller that will handle more voltage, that will get much better performance out of your stepper motors.

Andrew Werby
ComputerSculpture.com — Home Page for Discount Hardware & Software

[esquema]

Thank you very much for your reply AWERBY. I am reducing because of precision, not because of torque. The motors are strong and the gantry moves well. Do you think it is not necessary such a reduction. Please not that this is my first cnc build. Once again thanks for your time.
Paulo

[esquema]

Correction: Please note this is my first cnc build.

[shey_med]

Hi.
I havent good experience with CNC but last 10 month im working on my own CNC machine.As my experience 6:1 reduction is too slow.As aweby reply, router bit would get too hot.Consider about 4:1 reduction.I am also searching about better timing belt for my CNC.But i couldnt find clear answer up to know.Any how i was able to get good knowlege about timing belt.Before you buy HTD timing belt u have to dive in cnczone.HTD has good tourque ability than trapezoidal (XL,T....etc) timing belt.But it has significant backlash than trapezoidal.

" HTD was developed for high torque drive applications, but is not acceptable for most precision indexing or registration applications. The HTD design requires substantial belt tooth to pulley groove clearance (backlash) to perform"

Please check following link for more details.

[shey_med]

here the link..........

Timing Belts and Pulleys - D265 Handbook of Timing Belts and Pulleys Introduction - Technical Section T-3

[awerby]

Lacking anything but your incomplete parts list to go on, it's hard to advise you, but are you really trying to drive this machine using belts alone? As was pointed out, that's not a great idea if you're concerned about accuracy. I thought you were using belts and pulleys to drive leadscrews, which is normal for machines like this. A leadscrew will typically give you some mechanical advantage, so you wouldn't have to gear down your motors but could drive them directly. This also helps you get the precision you need. A stepper typically has 200 steps per revolution. A screw pitch of 5mm would be reasonably fast if driven directly, and would give you 400 steps/cm or 800 half-steps. So half-stepping with a 5mm screw would give you a precision of .0125 mm, which should be more than adequate for any woodworking or plasma-cutting project. Even a screw with 10mm pitch, which would be twice as fast, would give you .025mm precision, and that's without micro-stepping.

If you don't want to use leadscrews, then the best alternative is rack-and-pinion. That's usual in machines with long travels, where screw whipping becomes an issue. They typically have a bit more backlash than belt-driven screws, but that's not a big deal unless you're making machine parts.

Andrew Werby
ComputerSculpture.com — Home Page for Discount Hardware & Software

[esquema]

Thanks for your response AWERBY.
Today I hooked up the 3axis TB6560 Controller Board to my PC and with Mach3. Trying configuration of my step motors on the work bench. GOT REALLY F--King Mad. I did many configurations, almost all have step failures. So I went to the forums in this site and everyone says this controller isnt worth sh--. I am going to forget this controller.
Advise: DONT BUY CHINESE TB6560 CONTROLLERS!! I am thinking of buying a gecko g540. Is the g540 a good buy? Does the g540 work with my nema23 chinese motors (57BYGH76-401A), or should I also forget the motors also?
Thanks to all for your help.
Sorry for my bad English.

[bengineer]

check out probotix.com for stepper controllers - very affordable. I can't attest to the quality yet though, my 4 axis kit is still in the box, waiting on me to get my act together and finish my mechanical build.

If at all possible, I'd direct drive the ballscrew, it will be more accurate, and with a ballscrew, the power increase will usually be great enough to negate the need for a pulley: Ballscrew thrust = (Torque * 2 * pi * efficiency)/(screw lead). (efficiency should be around .9 to .95)

For half and micro stepping, in general, the more steps you have, the less torque you have (I've seen estimates say half step = about half the rated torque, quarter step = quarter torque, etc..., some estimates I've seen have it even less). However half, quarter and microstepping will reduce cogging, and give finer resolution (within reason, there are physical and manufacturing limitations to consider). I've also read of resonance concerns with full stepping that are abated by half/micro stepping, but I don't know enough to comment about that.

For belts, the bigger the better. Smaller profile belts will tend to stretch under load and you'll lose accuracy. Also, there are some belt tooth profiles designed specifically for positioning with reduced or (supposedly) no backlash. I get them from Misumi (MISUMI USA, Inc. here in the US), but they're just a reseller and the belts are made by many companies. I'd search for "high accuracy timing belt" or "low backlash timing belt" to see what's available to you.

I'd use an aluminum pulley with the stepper motors, just to reduce inertia. Steel will have a higher rotational inertia, and for quick starts/stops and direction reversals in higher inertia might cause your stepper to jump a step. Plus if you have to bore out the pulley yourself, aluminum will be easier to machine/broach.

good luck with your build! post pictures!

[awerby]

Thanks for your response AWERBY.
Today I hooked up the 3axis TB6560 Controller Board to my PC and with Mach3. Trying configuration of my step motors on the work bench. GOT REALLY F--King Mad. I did many configurations, almost all have step failures. So I went to the forums in this site and everyone says this controller isnt worth sh--. I am going to forget this controller.

[Before you forget it, try loading those motors a little, then testing them again. Steppers need something to push against; they don't bench-test well. So put a pulley on the end and attach a weighted string to it, and see if it behaves better. Start with a slow speed and low acceleration, and slowly increase it until you notice faulting.]

Advise: DONT BUY CHINESE TB6560 CONTROLLERS

[There's a rather lengthy thread on them here: http://www.cnczone.com/forums/genera...y_chinese.html ]

!! I am thinking of buying a gecko g540. Is the g540 a good buy? Does the g540 work with my nema23 chinese motors (57BYGH76-401A), or should I also forget the motors also?

[The motors are probably fine. The G-540 is a really nice controller board, which integrates the function of a breakout board and 4 drivers. It offers 10x microstepping, and can handle up to 50v from the power supply. I've set one up to run a Taig mill and have been quite pleased with its performance.

By the way, I don't believe that micro-stepping cuts torque much, if at all. It certainly doesn't do it in the linear progression that was claimed above, or these 10x microstepping drives would barely be able to move. Micro-steps don't really add to the accuracy of a system, but they do smooth out resonances that can cause lost step errors.]

Thanks to all for your help.
Sorry for my bad English.

[No need to apologize for that - you're doing better than many of the native English speakers here...]


Andrew Werby
ComputerSculpture.com — Home Page for Discount Hardware & Software