[poopopo]

Im tryin to build a cnc plasma with a 4 x 4 table. I have a little of my plans drawn in autocad which i just recently started using. my axis are going to be with 20mm Linear Guideway off ebay. I haven't come up with plans for the gantry yet but im thinking aluminum. the table its self is very rigid. so my question is can i use stepper motors directly with rack and pinion? also what size steppers do you recommend? I would like to use geicko drivers. I appreciate any info and help. point me to the places you recommend getting them from also. thank you

[tleah]

i have been using these people and they are great for helpfull advice, they have a matched motor and drive that they say marry up perfect drop them an email


Shenzhen Yako Automation technology Co., Ltd
4/F,Keyan building,39Keji C.Rd.2nd,High-tech Industry Zone,Nanshan District,Shenzhen,P.R.of China
Tel : (86) 755 86142288 / 86142255 (ext.128)
Email:[email protected];[email protected]
Website :www.yankong.com

I used them as i am in Hong Kong at the moment but they will fedex world wide


Tony

[poopopo]

thank you

[stedgar]

Take a look at the offerings from Tormach.com. They sell Motors and drives too. As for your setup I would reccomend using the 34 series motors and the Gieco drives. Rack and Pinion will be fine as opposed to ball screws. Rack and pionion is use on most CNC routers and CNC Plasma tables. We do use a ball screw for the Z axis on ESAB tables. This accounts for the smooth movement the torch needs to maintain proper Arc Voltage Height Control.

Steve Edgar
FSE Esab

[Torchhead]

Do some math. Rack and pinion gives you a net gear INCREASE based on PI times the DP of the pinion gear. So a 1" dia pinion moves the gantry 3.14 inches per motor rev. Since stepper motor has a raw resolution of 200 steps per rev (.005) that drops your effective resolution to .015. It also has an inherent 5% positional (rotary) error so that error gets multiplied by the same ratio. It also means you lose 2/3"s of your torque. Torque gives you acceleration. acceleration gives you sharp corners at higher feedrates. What direct drive does give you is plenty of speed. A Stepper running with a Gecko and the proper DC volts will spin about 800 RPM. That gives you 2400 IPM!

As you can see direct coupled steppers (no gearbox or no belt reduction) have speed you can't use and poor resolution and accuracy.

It's like having a car that only has one gear and it's stuck in "high". Great for highway but a bad choice for stop and go city driving.

Any table design is a process of optimizing for the purpose. You trade speed for torque and resolution (or vice versa). Just buying bigger motors does not help the resolution and neither does microstepping. Bigger motors tend to have sharper torque dropoff with RPM so the primary benefit would be in the lower RPM part of the curve.

Tom Caudle
www.CandCNC.com

Good place to buy motors and drives: www.HomeShopCNC.com

Look at his new 570 oz-in 23 frame steppers. Wired in parallel mode (8 wire motors) they match up well with a Gecko drive. You need about 50VDC or more to drive most steppers to full RPM.

[Lukster]

Your rack and pinion will do fine with stepeprs... but i always worry about wear. What is going to be exposed and what can you do to protect it yet keep it clean.. Also Ramping up too fast will shorten your machine life so in toher words . Decide what you want : speed, accuracy, vib reduction, affordability, etc: If you want clean cuts and ability to cut faster.. most of that will lie with in your torch head and plasma machine itself.. A torch table regardless of that little bit of torque lost can still be configured to be consitent at the same quality , like torchhead stated . It counts but only for speed. its plasma you can only go so fast. The one thing i learned is that stepper motors are strong.. so no need to go all out and overboard on them . u will be surprised as to the ratio they can pull. If you weld your table... be patient.. one table we had welded to fast and had slight warping. Needles to say the table is no good for accuracy! Keep in mind your plan need to be as level as possible that your cutting and parallell to that your gantry needs to run the same.. This will eliminate dross by keeping your at a consistant hieght to your material and also width of the table.. if your tracks go in out or up down then that will be troublesome later when running the machine, U might get madd!! If at most i can tell you is try your best to make your table and gantry in sync and level.. all else is simple and variable.

What are you slats going to sit on? My experience use 1/8" slates, and use at least 1/4" to 1/2" material to rest slots in .. mine rest in a 3/16" i think yet still a couple have poped out from time to time, and also I have a support beam alond middle of them with slots to keep midle of slats straight.

What tpe of plasma cutter? My experience, going cheap isnt the way to go.. highdef is a real good choice, and a high amped capability will allow versatility with material thickness and cut down on bevelled cuts and give better accuracy.

Us stainless steel ( aluminum too soft) strips along the x-axis runways for your rolllers on both sides near the steppers and rack&pin. The mild steal tends to rust and when the rollers role over just a little bit it can be noticed. esp debree

What about exuast/ventalation? Side panels with an exhaust duct and drop trays that can be roolled out from under are greatly considered. Esy clean up and less smake and debree to tear up the machine, less cleanups. Water tables are good also, but pref exhuast.


What are you gonna use as your cable support? I made my own, use alluminum for the gantry axis and also for you cable support unless u use the plastic kind. Keep it from being top heavy.. the steeperscan take it, its just that you dont want to build something to high and have it tople any.


What size is your table? If a 4x4 then ask your self if you need any room for the gantry to be clear as you load material etc.. mine is a 5x10 so this may not matter to you!

Peace

[Brian2007]

When I program for the routers at work I can program the machine with the stationary gantry much "hotter" and it is more rigid and there is less vibration. The more rigid the smoother the cut. Period.