First post - linear drive systems costs

[rdcd]

Hello everyone, this is my first post on this forum. I am very interested in building my own cnc router and i have being doing some research through the internet lately.

I would like to build a cnc router with a cutting area of x=4' and y=3', which linear drive system would be more suitable for this router in terms of cost (as of nov-09), considering that i am not cutting parts for a space telescope :
1) chain drive
2) belt drive
3) rack and pinion
4) ball screw
5) lead screw

regards

[wildwestpat]

Hi

You still need to think about the need for precision - precision costs money - and this should be your starting point. Like most engineering design a machine build pulls all the parameters in different directions and reaching a satisfactory - for you - compromise is what it is all about.

Precission has two main factors that impact on the choice of axis drive and these are loosley connected but need to be thought about. First is the repeatability of positioning - this is needed to cut complex curves and multiple cuts. Secondly is the need for absolute positioning of the tool so that parts can be made that will mate with other parts possibly bought in or made elsewhere.

What I am saying is that unless the sole object is to build the machine (and this is a worth while as a fun exercise) OR if you are serious about making stuff sort ot the accuracy requirements first in terms of tolerance and possitional repeatability of the stuff you want to make before even thinking about axis drives.

I wait with interest to see what you decide and others comments.

Regards

Pat

[rdcd]

Hi Pat, thanks for your reply.

I think i should then have posted 'which slide system do i need?'. Let's say that i want to take CNC routing seriously and in a near future i would like to be doing some jobs in CNC routing such as:
-cutting 2.5D letters and shapes y foam, wood and other soft material
-doing engravings in wood
-fabricating parts for simple 'toys', etc

Before taking it seriously and being more specific, i want to build a hobby cnc router, maybe 4'x3', with a linear motion system with enough accuracy and repetition for what i plan to do in a near future, taking into consideration the cost.

cheers
Rolando

[ger21]

The majority of the homebuilt machines you'll see here were built using acme leadscrews, and perform fine. The current trend is to use 1/2-10 5 start screws, which give good precision with high speeds. More recently, members building larger machines are moving to rack and pinion, which can give even higher speeds, and doesn't suffer from screw whip at higher speeds like acme can.

Both are similar in price, and both would work fine for a 3' x 4' machine.

[rdcd]

Ok, i like acme's.
I have another question about driving the gantry, but that should be a new thread.

Thanks
Rolando

[wildwestpat]

To get an idea of what is involved take a look at http://cncrouterparts.com/index.php?cPath=21. This company has been kind enough to give sketch drawings of a popular skate type of gantry trolley and will surely get your creative juices flowing. From what you have said about the work you intend doing start with acme screws and plastic nuts prefferably with some form of anit backlash wear compensation. You can progress from there with little loss on the financial side and gain a lot of experience which will enable you to build biger and better should you out grow your first venture. As you want to make stuff on the machine this is probably the very best way to go untill you hit a machining need that your DIY mill can't achieve.

Regards

Pat