Help a noob plan a build please

[JAZZCNC]

I intend to upgrade it to a CNC without breaking the bank if possible. Instead of me researching for days upon days about the best systems to do this only to be told after I am wrong, I figured I would ask the experts here for very basic pointers.

1. Given its very long (3m) I am assuming

1. lead screws are a no go due to length?
2. Would there be a lot of slop/backlash using belts?
3. Am I correct in saying rack and pinion would be best?

2. What motor/driver combo would be suitable. I'm thinking its possible I may need a slave drive for the long run given the overall size? Presumably there are distance/proximity sensors that go along with this?

3. What do you see as the pitfalls at this stage (except me being an idiot at this stuff)?

4. Any suggestions for breakout boards and the go to software everyone uses?

If you have any links or websites to buy the parts that would be very much appreciated also. I'm based in Ireland so UK sites are good.

Thanks for any help.

Hi, well suppose I'm the man to answer these questions as I'm about the only person who builds vertical routers on this forum.!

First off to answer some of your questions.
#1 (a) As you'll see from the video ball screws can work perfectly fine at this length but there are certain things that need to be done for them to work correctly.
The pitch and screw size is critical and a little bit of trickery is required to get it correct. The secret is getting the screw speed down so to do this you use screws with a large pitch then apply a ratio which half's the screw rpm and brings the resolution back into line with what is ideal.
#1(b) No belts are very low backlash, much less than R&P, they are also much more efficient so require less power than R&P. However, they can be tricky to get right and keep tensioned, using the right system and tensioning is very important. If it's done correctly then belts can be very good and come much closer to ball screws in terms of backlash and efficiency than R&P.
#1(c) R&P is often used on large machines because it appears simpler than ball screws but it's not always, neither is it cheaper to do it correctly. It requires much more maintenance and it's clunky in comparison.

#2 You definitely need to have 2 motors slaved for the long axis, each with its own drive. The motors you require for a machine this size are Nema 34 and around 8Nm. Again it's critical you use the right motors and using the correct voltage and at this size, you need drives that use mains voltage. Using lower voltage drives cripples large motors and at this size, it's not something you want to get wrong.

#3 The Pitfalls are numerous but that shouldn't stop you and it's different for each builder based on their ability.

#4 I wouldn't worry about these things for now because your along way from them and I suggest you do lots more research to get a better understanding.
THE MOST IMPORTANT advice I can give is that you buy NOTHING until you FULLY UNDERSTAND what is required for the machine you are building.

When you are ready to build and fully understand what's needed then ask again and I will point you to where you can buy parts but to be honest I think you'll need to accept your going to have to buy most stuff from China as the prices in UK/EU range from expensive to ridiculous.

[nacimroc]

I had seen your video and think I hit the jackpot getting a reply from you. Those answers are exactly what I was looking for and give me a direction to start researching. I should have qualified my inital comment by saying I don't need accuracy down to the last micron and it'll be all wood.

Just on the ball screw pitch. Whats the purpose behind getting the screw speed down? Is it related to suiting the RPM of the stepper motor or could this not be corrected with gearing? Or is it related to accuracy of movement? Is there an ideal lead/pitch size for say a 25mm Dia ball screw? Or ratios to aim for with regards to stepper.

Sorry if they are stupid questions but your knowledge is invaluable and I'm trying to bleed you of everything I can .


Thanks

[AndyUK]

I had seen your video and think I hit the jackpot getting a reply from you. Those answers are exactly what I was looking for and give me a direction to start researching. I should have qualified my inital comment by saying I don't need accuracy down to the last micron and it'll be all wood.

Just on the ball screw pitch. Whats the purpose behind getting the screw speed down? Is it related to suiting the RPM of the stepper motor or could this not be corrected with gearing? Or is it related to accuracy of movement? Is there an ideal lead/pitch size for say a 25mm Dia ball screw? Or ratios to aim for with regards to stepper.

Sorry if they are stupid questions but your knowledge is invaluable and I'm trying to bleed you of everything I can .


Thanks

Research Ballscrew Critical Speed, and find a critical speed calculator to plug in some numbers.

In essance, the longer and thinner the screw is the lower its maximum RPM. By using a high pitch screw, you reduce the required RPM to reach a given machine movement speed.

If you're using quality components like ballscrews and linear rails, the additional cost of metal parts over wooden is minimal and will vastly improve the machine. Its like buying a Ferrari and running it on budget part-worn tires you got from your mate at the pub.