Hi, I'm Andy. I'm creating the world's most affordable desktop CNC machines

[Robin Hewitt]

lol, when a 5mm bent screw causes the whole axis to wobble then there is something wrong with the design. Most 3d printers i have seen are more rigid than this.

What you are seeing is a motor bolted rigidly to the end of a shaft and being allowed to wobble. Much easier than messing with universal joints or isolating it with toothed belts. I have been suggesting it for years so it must be clever

[magicniner]

What you are seeing is a motor bolted rigidly to the end of a shaft and being allowed to wobble. Much easier than messing with universal joints or isolating it with toothed belts. I have been suggesting it for years so it must be clever

See what a formal engineering education and Finite Element Analysis can do for you?
Sweet Felicity Arkwright it would seem!
There but for the grace of god.............

[Robin Hewitt]

See what a formal engineering education and Finite Element Analysis can do for you?
Sweet Felicity Arkwright it would seem!

Note to self: Takka takka takka

[JAZZCNC]

What you are seeing is a motor bolted rigidly to the end of a shaft and being allowed to wobble. Much easier than messing with universal joints or isolating it with toothed belts. I have been suggesting it for years so it must be clever

Ye real cleaver.!!! . . The Drives will love dealing with all the resonance banging thru that motor...

[cropwell]

Here's one from a few years ago - at a Pneumatics Suppliers Counter in Nottingham.

Me: Can I have one of those XYZ-123/B, like the one that's on the shelf over there.
Jobsworth: I'll just look it up on the computer. Sorry mate we haven't got any, computer says zero stock.
Me: What about that one there!
Jobsworth: If the computer says we 'aven't got any, we aven't got any.

Cheers,
Rob

[magicniner]

Jobsworth: If the computer says we 'aven't got any, we aven't got any

I bet he was an engineering graduate just waiting for that big design contract to drop in his lap ;-)

[komatias]

I bet he was an engineering graduate just waiting for that big design contract to drop in his lap ;-)

Not all of us graduates are waiting for contracts whatever the sun and mirror lead you to beleive

[Robin Hewitt]

Ye real cleaver.!!! . . The Drives will love dealing with all the resonance banging thru that motor...

Oooh! I love it when you get cross, can I call you Mr Spanky?

[JAZZCNC]

Oooh! I love it when you get cross, can I call you Mr Spanky?

Robin you can call me Miss Piggy if it makes you feel better and I could never be cross with you sweet heart. .

[routercnc]

This thread has gone a bit weird!

Back to the OP post#1 If you set yourself a design brief to 'Develop and then market a very affordable CNC machine' then I do think it has some merits. High performance CNC machines (DIY and industrial) have 2 vital characteristics. They are very stiff, and they have precision mechanical and electrical components. Together this allows them to cut harder materials properly, and with good levels of accuracy.

However, to fulfill your brief you must wind back the budget and therefore these 2 vital characteristics must suffer. You are therefore left with no option but to build a machine which can only cut soft things, and with a modest level of accuracy. But this is not the end of the project as I would say there is a huge market for craft work, balsa cutting, maybe drag knife vinyl cutting.

The challenge is to come up with something cheap, robust, does not need constant maintenance, and delivers. I'm not sure this has been done for the price you are aiming for, but that should not stop you trying. Some aspects of your current design are interesting, but some need more work.

For info the FEA analysis looks like you clamped each end of the beam then loaded the rail normal to the surface with 30 N. You got 0.03mm deflection on the rail which is reasonable for that beam on it's own - but remember your beam end conditions are not infinitely rigid, the V-bearings and brackets and gantry will flex, as will the Z axis, and the tool (dremel type I assume?) will along with the cutting bit which will have to be small. Backlash in the threaded rod will allow the tool to vibrate as so on. Push the Z axis with a set of scales and measure the deflection with a DTI. This will give you the true machine stiffness and it will be quite low. This is where the challenge lies to come up with something simple and cheap that still works.