General pointers for a CNC router

Hi everyone, I'm looking to start a build soon so I'm after the help of you clever lot please.

I like the style of Toomast's machine, and I'd be able to manage this sort of welded frame etc.

Attachment 28369
The beast built by Toomast


The machine will be used mainly to cut sheets of MDF, Plywood etc, so needs to be an 8x4' beast. And I do love to tinker, so cutting aluminium and steel is also on the wish list.


My rough plans so far are to basically use the style of Toomast's for the frame, rails and gantry. Do you think 75x75x3mm MS box section is sufficient for the rails and frame? And 200x100x5 for the gantry?

I'll use 25mm square rails and carriages.

I'm not sure on the drive system yet, I like the idea of using ballscrews but at this size I'll either need thick screws or possibly a driven nut (which I won't be able to machine myself)

I was going to go for NEMA34 12kN motors on each axis, as once it's up and running it will be used for extended periods each day.

I plan to level critical surfaces with epoxy, as it seems to work well for most who've tried it. Although I have inquired about having the surfaces milled, but I imagine that will be a costly job.

Any pointers you can give me is greatly appreciated, I am doing drawings in scketchup currently so I'll post some when done.

TIA

Unless you have extensive experience in high speed machining of steel,you would do yourself a favour if you found a mill to do a conversion on.The spindle speed of a router is extremely high for the activity.How do you intend to attach the rails to the box section?

Cutting steel would just be a bonus, not really essential.

I plan to use 5mm box for the rail members and bolt them on.

3mm wall is too thin use 5mm on all steel sections.

Only use 12Nm Nema 34's if your using Mains voltage drives. If you don't use high voltage they will be slow.

Thanks for the info.

I must admit the electronics part is what worries me most about the project, I keep putting off the research :untroubled:

What's the reason for 5mm, extra rigidity or resonance?

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Originally Posted by scott88

Thanks for the info.

I must admit the electronics part is what worries me most about the project, I keep putting off the research :untroubled:

What's the reason for 5mm, extra rigidity or resonance?

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Resonance mainly, rigidity comes from frame design mostly but there are other advantages like more material for threads.

Yeah, I was thinking of at least 5-6mm for anything that will hold a rail and 3mm for the rest, mainly for budget. I've seen people filling with sand, so maybe I could do that for dampening the high frequencies?

Have you considered bracing the top rail of the lattice laterally?The triangulation within the lattice does they job longitudinally,but with those hefty steppers moving the column across the machine,what is there to prevent flexing?It could be more significant than high frequency resonance.

Interesting point. It seems to work well for Toomast but he did use 100mm box for the frame.

Possibly a tweak on this design could reduced the rail height and slightly increase the gantry height, that should potentially reduce any lateral racking.

I don't fancy bracing the front of the machine as it would make loading awkward.

Quote:

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Originally Posted by scott88

Interesting point. It seems to work well for Toomast but he did use 100mm box for the frame.

Possibly a tweak on this design could reduced the rail height and slightly increase the gantry height, that should potentially reduce any lateral racking.

I don't fancy bracing the front of the machine as it would make loading awkward.

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Don't over think it because it's not required for the use your wanting it for, infact, for a sheet material machine you'd be better without the high sides to make loading and access easy, just build a strong gantry with stiff sides will easily do what you need. Over engineering might appear good at first until the real world issues stick there heads up because Accessing cut parts on a 8x4 with high sides is a pain in the arse unless your 7ft tall.!

I'm not far off 7ft tall but I get your point :D

I guess I was wanting it to do everything, but that's obviously not going to happen.

I've just been looking at your vertical machine on YT Jazz, it's a beast. I'm just looking through the options for dealing with whip on the long axis, so will probably go with thick ballscrews. I think the step up in price will still be cheaper/easier than a rotating ball nut.

Quote:

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Originally Posted by scott88

I'm not far off 7ft tall but I get your point :D

I guess I was wanting it to do everything, but that's obviously not going to happen.

I've just been looking at your vertical machine on YT Jazz, it's a beast. I'm just looking through the options for dealing with whip on the long axis, so will probably go with thick ballscrews. I think the step up in price will still be cheaper/easier than a rotating ball nut.

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Being thicker doesn't mean they won't whip, it's the rotation speed you need to think about if your rotating the screw. Going with a larger pitch and using ratio to decrease the screw RPM is what you need to look at.

If you want to see 10x5 vertical then I'm just up the M62 at Goole.!

Thanks Jazz, I'm actually just reading about different pitches etc. My head is about to explode!

Thanks for the invite, I'd definitely like to see it and pick your brain :D