New to CNC design and need BIG HELP

[piashaw]

Hi

Quite a few questions as I am just starting out and getting VERY confused.

First i am trying to build a CNC machine, to start with 3 axis but maybe upgraded to 5 later to be able to Route and then drill out all the necessary fittings on the top (and sides - 5 axis) for general woodwork. Mainly routing MDF up to 25mm. Also soft wood, can't get hard wood easily in Greece. A 2m x 1m panel size would be nice.

1) What degree of accuracy does one actually need as I see such minute figures but what can one actually see?
2) What are the pros and cons of a movimng table system (except obviously you need a larger area if teh table moves)
3) I would also like to be abale to spray paint the MDF or put a varnish on the boards afterwards. Can one machine do both or is there some inherent conflict?
4) Many more questions once I've had your answers and hopefully will vaguely now in which direction I'm heading as opposed to in circles as at present!!!

Thanks for your time

Peter

[musicmkr]

Hi and welcome to "the zone". I'm pretty new here as well, but I'm sure you'll find this forum to be a great tool. You ask some very common questions, and often they can be answered by reading past posts. Let me try to give you some answers.

1-

Accuracy is great, and expensive. If you are making wood parts you will not be needing a .000x" level of accuracy. Most people build their machine as accurate as possible so that when they do want to cut a part to high tolerances, they don't have to build a new machine.

Accuracy and repeatabliity are not the same thing. You probably want to be able to make a number of identical parts. The smallest variation that the human eye can easily see is around .05mm. This sounds really small but it easy to get, and not too expensive. Some people here make machines that are only repeatable to .5mm, so its up to you.

2-
Like you said, with a moving table you need a lot more room, a machine that has a moving table in the x and y will take up around 3 to 4 times as much space. A big problem is in the design of the machine. When you are in the design phase you can calculate out how much your spindle and z axis weigh, and use that to calculate your motor size. The you can do the same for the entire gantry, and calculate your y motor requirements. With a moving table you don't know how much mass you'll have on it, so you need larger motors that are ideal.

3-
Using the machine to paint shouldn't be a problem as long as you're not using just a spray can. You will need a linear actuator to turn on the paint stream, but its not a big deal to do. Someone else here is building a painting gantry system, see if you can find the link.

Basically if you have a large budget for the project then do it right the first time. If the budget is tight then don't let that stop you. There are many ways to skin a cat, some are cheaper than others, and some are better than others, either way the cat still get's skined.

[turmite]

I don't think the paint on the same machine is a good idea unless you are planning on everything having a textured finish. I'm not saying it can't be done but that some things just should not be done. Unless you have the perfect dust collection system, and they don't exist, your mdf dust will always be in your paint.

Mike

[piashaw]

Thanks for the info. The tolerance aspect was very useful.

I was considering going for a raised gantry (hope that's the correct terminolgy) to avaoid teh problems of dust getting into the x- axis as well as spray paint. i know that putting the panels on would be harder but as they are generally not that huge I doubt it'll be a problem. As far as the MDF dust is concerned, I have the same problem in my work room now. So i need to give it a good dust off first and I clean all the panels before I paint them, hopefully this principle would work on a CNC machine

Peter