Questions for first cnc built

[leen1985]

Hi,

I want to begin working on a 3-axis cnc router in a short while. Only I have some questions:

I mainly see spindle mechanisms or belt mechanisms on designs on the internet. Is there a price difference or tolerance issue why people choose for one of these solutions?

Is a working area of 1 X 1m possible if i still want the machine to be quite precise?

[acondit]

Originally Posted by leen1985 Hi, I want to begin working on a 3-axis cnc router in a short while. Only I have some questions: I mainly see spindle mechanisms or belt mechanisms on designs on the internet. Is there a price difference or tolerance issue why people choose for one of these solutions? Is a working area of 1 X 1m possible if i still want the machine to be quite precise?

It depends on what you mean by quite precise, but generally yes, if you are willing to spend enough money to do it right.

Alan

[leen1985]

Ok,

And between belts and spindle. I could imagine that a spindle has less tolerance issues than a belt. But is far slower than a belt. But i Think a spindle is also more expensive. Is that right?

Does somebody know an indication of prices for these solutions?, what is cheaper?

Is a spindle also not more vulnerable for dust. I could imagine that dust can get between the motor and the spindle, is that right? And can there be a same problem with lineair bearings?

[acondit]

Originally Posted by leen1985 Ok, And between belts and spindle. I could imagine that a spindle has less tolerance issues than a belt. But is far slower than a belt. But i Think a spindle is also more expensive. Is that right? Does somebody know an indication of prices for these solutions?, what is cheaper? Is a spindle also not more vulnerable for dust. I could imagine that dust can get between the motor and the spindle, is that right? And can there be a same problem with lineair bearings?

When you talk about a spindle, do you mean a screw?

Assuming for the moment that you are talking belt drive vs screw drive. I have only used belt drives for printers and scanners and driving the spindle or screw. Some people whose opinion I generally trust have indicated the capability of very good precision from belt drives. However, I still tend to think that it depends on the amount of force required. I wouldn't hesitate to use a belt drive for cutting wood, but I wouldn't be likely to choose a belt drive mechanism to move for a mill table for cutting steel. I used a belt as part of the gear down mechanism on the cross slide of my lathe. The belt and pulleys provide a 4:1 gear down between the motor and the leadscrew. Generally the forces working on the belt are relatively small and it provides very good accuracy.

For any given drive and motor combination the trade off is resolution vs speed. The faster you design it to go, the poorer your resolution will be. It doesn't really matter whether you are talking belt drive or screw drive, the same is true. You can gear a belt drive down to increase the resolution or gear it up to increase the speed. The same is true for screws. A finer pitch screw will give you better resolution than a coarser pitch screw but the finer pitch screw will generally result in slower motion than the coarser pitch screw (assuming that you have adequate power for either). The limits of your accuracy are probably the stretch in the belt or the error in the cutting or rolling of the screw. Depending on your choice of software, it may be possible to map out the screw error.

Your ultimate accuracy depends on the accuracy of all of the parts, the engineering and implementation of the design, and the ability to control the movement accurately.

Dust is always the enemy of machine tools and precision (motors, rotary bearings, spindles, screws, ways and linear bearings).

Alan

[leen1985]

Ok, I see now. In the end I want a machine that is very accurate. Waiting isn't such a problem. Thanks for the answer.

Im going to start with searching out the materials and prices. And then start building asap

[leen1985]

I'm thinking about making a similair design as this. (http://www.infinigral.com/melder/cnc...1/DSCF0036.JPG)

I presume that the person used a spindle and servo on one side of the router. Could that give difficulties with operating? Because I would think that one spindle in the middel is the most optimal solution isn't it?

[ger21]

That looks like it's based on these.
http://solsylva.com/cnc/cnc_plans_home.shtml

It's driven on both sides, with a screw on each side.

[davidrussell74]

I'm curious at this rail design I see. Is it worth it to experiement with this design if you're looking to build your first CNC?

[jzurek]

My dad has one of these builds. It is very accurate however now that it is starting to age needs some attention. I am in the process of designing my own CNC and I will use linear bearing rail for mine. In the end he has decided to build an almost identical machine to the one I am designing.

For the first CNC this is an affordable way to start. I can't say for sure how accurate his is (how many thousands of an inch) but we are using it to cut my machine parts. When I cut wood inlays I have to undersize the inlay by 0.007 or more to even begin to get them to fit inside the pockets and there is no visible gap between the wood parts. It makes nice parts.

As with anything the more you spend on quality components, the better accuracy and quality you will get. If you want really tight tolerances you might consider using THK linear bearings on all axes. That can get quite expensive. I myself will be using a mixture of linear bearings on mine, THK for the Z axis and supported rail style linear bearings on X and Y from glacern.

Many people seems to be using these parts from CNCROUTERPARTS.com CNCRouterParts
They seem like a good compromise between cost and high tolerance. I thought about using them for mine but in the end decided to use linear rail from glacern. If you're interested to see what I've played around with in my design you can check out my build thread. There is some discussion about tolerances with the CNCROUTERPARTS components. Ahern chimes in around here too. His products will be more accurate than the pipe rail and skate bearing design. My thread is here: http://www.cnczone.com/forums/diy-cn...ign_model.html I still have to upload the new screen shots.

Good luck with whatever you decide to go with. Any machine is better than no machine. After playing with my dad's machine for a few months I just had to build one.

Jeremy