For R & P you gain speed (and give up resolution/accuracy and torque) based in the Diametric Pitch of the pinion times PI. So a 1" DP pinion gives you more than 3X the base RPM of the motor. That gives you speeds of up to 2400IPM. So you get speeds you can't use and give up acceleration and accuracy you can use.
Transmissions do not create power (work) they just change what is on each side of the equation. On one side you have SPEED on the other TORQUE (acceleration) and RESOLUTION. Resolution is defined as the smallest distance you can move in one step. Resolution is not accuracy but is a component of it. Your accuracy is resolution times any other mechanical errors (backlash, flex, thermal expansion, etc).
Rack and pinion for plasma is a valid choice. You have to deal with a lot of abrasive grit and precision screws don't fair well on the dirty environment of plasma. (neither do Laptops but that is another story!)
The big problem with single motor drive shaft gantry designs is getting a consistent and good gear mesh with the rack. You have to fixed gears (pinion and rack) so the only way to adjust mesh it to move the rack into the fixed pinion. That requires you painstakingly go along the entire length of the rack and adjust it carefully into the fixed pinion.
The design that solves both problems (driving each side and adjustable mesh) is the dual motor system with suspended type drive mounting. Each motor runs independently (but at exactly the same speed and distance) but having the pinion/belt transmission/motor assembly mounted on a pivot and pulled up into a firm mesh by a spring or cylinder. You no longer have to set each section of the rack for optimum mesh.
When you look at a "kit" or package make sure it can be configured to meet the type cutting you intend to do. What kind of support will you get for your application (not just how to hook up the motors and make them spin). If your choice of control software is MACH do they have the in depth knowledge of that package to make their hardware work for plasma and or routing? Look at their manuals. Does it cover using the "kit" in your type cutting? How much hard wiring are you going to have to do? Will you have components others can help you with. A kit should be more than a bunch of parts thrown in a box. It's often a shock that doing plasma cutting correctly, is more complex and technical than most routing.
The drive drive ballscrew for Z has some limitations. If you use too fine a thread you risk having a Z that will not function well as a THC. A 10 TPI leadscrew limits you to less than 100 IPM speeds on Z and under THC control that could fall to 30 IPM or less. That is fine for gently rising warps or on thicker material but if you have to cut a sharper rise you won't have the vertical speeds to do that and your THC response will be sluggish. If you use a two start leadscrew and get you actual TPI down to 5 or 4 then your speeds go up at least double.
You need more torque at lower speeds (and a heavier stiffer gantry) for router. Accuracy is more important since you may have to make several passes and any offset or error becomes visible on straight edges.
Unless you are looking for a pure learning experience (i.e you don't care how long it takes or how many "surprises" you get along the way) a package that is more completely engineered and integrated allows you to focus on the mechanical aspects of your build.
Then there is the software side......
07-25-2009, 10:52 AM
Similar Threads 
Linear Mode
