Using belts for large format machines

[scott88]

Evening all,

I'm currently planning a 4x8 router build. I'm not sure which drive type to go with yet.

My other post http://www.mycncuk.com/threads/13764-General-pointers-for-a-CNC-router

My thinking was to use ballscrews on each axis as in my mind they seem to be the easiest option (apart from the Y axis).

I have no experience with belts, do they stretch out and need adjusting? If so, how often?

P.S. Does anyone else find no matter what you search for, you get the same results in the forum search? :tennis:

[JAZZCNC]

Ballscrews are by far the better choice but they need careful selection and fitting. Rack & pinion is often used on large machines but there is quite a bit more work involved because it needs a gearbox or ratio applied using timing belts n pulleys, also more maintenance required.
Belts work well for lightweight machines but not so good for heavy gantry machines, they also require correct type and size plus tensioning system. I wouldn't use it for an 8x4 machine but I would on a smaller machine.

However, If you have never built a CNC machine before then I strongly suggest you re-think the size and build something smaller to learn on before attempting an 8x4 machine.!! . . . It's a mistake to think it's the same only on a bigger scale. Many builders have done this and failed or at best they build a machine that sadly leaves them disappointed. Then they try to correct the errors which end up costing them more money, but often they would have been better scrapping it and starting again because can't make a silk purse out of sows ear.!

[scott88]

Thanks Jazz, I think ballscrews is the answer then.

This might give me a reason to buy a lathe, so I can machine some driven ballnut housings 😁

I understand what you're saying about building a smaller one first, but I'd have no use for it, so to me it'd be a costly affair. I'm going to get my design fully planned out before I even consider buying anything.

[Mister Mills]

Hi Scott.. Belts are a no no for a machine that size. I tried a few years back and failed miserably. Fine for a plasma with a light gantry but a definite no go for anything to do with machining timber or aluminum. Rack and pinion has some merit for a machine that size but it really depends on what you want to cut and the tolerance you wish to achieve.

As Jazz said Ball screws are the better option but budget often dictates.

[JAZZCNC]

I understand what you're saying about building a smaller one first, but I'd have no use for it, so to me it'd be a costly affair. I'm going to get my design fully planned out before I even consider buying anything.

Build it right and you'll make money when you sell it. What you learn will be priceless for building a large machine and you'll also learn how to actually use the control etc so when you do build a larger machine your cutting meaningful parts straight from the get -go.

The scale up in Size really does need more attention to detail and techniques which you need to learn before attempting to build if you want a good machine. ie: Mister Mills failing with belts on a large machine.!!. . . Building a smaller machine with them first might have shown him some of the pitfalls and hopefully tipped him off it wasn't the best choice for a large build.

Yes, you are doing the correct thing by doing the research for whats required but you can read as many threads as you like none of them can prepare you fully for the build process and what's required and that's on a small/med size, large machines magnify what's required and throws in a few curve balls of its own which can be disastrous if you don't catch them first.! . . . Which you probably won't because your experience level is Zero and often these things are not realized until well into the build anyway, by which time you have sunk plenty of money into it. This is why you don't see so many complete large build threads, plenty of new builders try but often fail.

So building a smaller machine will actually save you money long term and if done right you'll sell it for more money than it took to build which you can put into a better large machine.
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