[Rickylee53]

Hello,

Fairly new here, I'm just starting out to build a CNC plasma table. I say starting out, I've bought nothing yet.

My plan is to use a rack and pinion drive. I'm in the UK and currently struggling to get 2.5m racks. I've seen you can join them but wasn't that keen on the idea. My worry here is backlash. What do people do to stop this?

I have seen some Nema 34 motors that are approx 800oz, I was going to use these on a 3:1 reduction system by belt. I've not seen any belt/pulleys suitable yet though. I only planned to use 1 motor for each X and Y axis, using a through spindle to connect the 2 racks. I figured this would be less complicated than trying to run 2 motors for the Y axis.

I planned to use the actual table itself as the linear guide, with bearings running along the the outside/top of the table.

The Z axis is the bit i'm unsure about. I've seen some that are "prebuilt" which look ok, when I consider i'll spend hours designing/milling the parts to make it.
The other concern on the Z is the THC, I'm not sure which to use, exactly how they work etc etc. Could anybody give some advise here?

Thanks for your help/time.

[thefu]

use high quality racks from atlanta rack and pinion. i have used belt reduction in the past and its just not worth the hassles...planetary gears are the way to go.

[asuratman]

thefu,
Which type, size you use and cost approximately? It is very costly? Do you have problem when making up connection on rack?

[thefu]

well what are you planning to do with the table? I have built several tables for both myself and for friends/customers.







just made a batch of these.

[Rickylee53]

Hello,

It'll be to cut various parts for cars and size material for the milling machine. I will consider cutting some of the flanges out before they go on the milling machine as well.

well what are you planning to do with the table? I have built several tables for both myself and for friends/customers.



That looks good, what is the second holder for?





just made a batch of these.

The link didn't work, is there a direct website link for planetary gears? Could I use direct drive off the motors, maybe if I used more powerful motors. Or would accuracy struggle?

[thefu]

accuracy would struggle, not enough resolution.

High-Torque Stepper Motor, Stepper Motor, Driver, Stepper Motor kit, DC Servo Motor, DC Servo Motor kit, Stepper Motor Power Supply, CNC Router, Spindle, and other Components. Automation Technology Inc

2nd holder on there is to hold a spindle for milling/drilling holes

[Rickylee53]

I'm having a look for a UK or supplier that will send to the UK. Is joining the racks ok or does it cause problems?

Also what do you think of my idea for the linear guides. Using bearings running along the outside edges of the frame. Will this lead to problems?

On this picture, whats attached to the spindle? Looks like a face mill?

http://pictures.targetsfromus.com/va...G?m=1345009258

accuracy would struggle, not enough resolution.

High-Torque Stepper Motor, Stepper Motor, Driver, Stepper Motor kit, DC Servo Motor, DC Servo Motor kit, Stepper Motor Power Supply, CNC Router, Spindle, and other Components. Automation Technology Inc

2nd holder on there is to hold a spindle for milling/drilling holes

[thefu]

attaching 2 gear racks is perfectly normal and acceptable and is done very commonly.

linear bearings on the outside edge is also normal.

ignore the facemill. it was used to hold up the assembly. there is a helical cut pinion gear that mounts where that facemill is. that whole motor mount assembly has springs that push the pinion gear into the rack but its very rigid so it doesnt allow anything to rock up/down side/side