[mforbes6186]

Hi All,

First time poster, long time lurker here!

So i've finally decided to press ahead with my CNC build after spending approx 6 months on and off researching designs etc. I was hoping I could post my ideas here and ask a few questions that i've been unable to find full answers for? (Apologies if this is the wrong forum!)

Background - I run a small local pet shop and was hoping to start selling pet ID tags but don't really have the capital for a commercial machine at the level i'm likely to sell at so I thought 'what the hell', why not try and make one?! So the main uses will be engraving pet ID tags and maybe branch out to small name plates etc at a later date. Part of the project is to keep the budget as low as possible but still have a reliable unit.

So the design i'm hoping to go with is the following -



My logic behind this design is that it will take the least volume of components to create a sturdy design and because I will be engraving relatively small items, I don't need an overly large range of movement in the X axis so it would be more beneficial to move that axis independently.

The letters on that image where just so that I can clarify my understanding of the components technical names, please correct me if i'm wrong, thanks -

A - Solid metal shaft
B - Threaded rod (lead screw?)
C - I figured it's a type of Flange Nut but I can't find a flange nut with screw holes to attach to the moveable worksurface like in the image
D - Linear bearings?
E - I'm guessing this is a bolt through the structure in to the centre of the solid metal shaft, am I correct? Or is there a component to grip the shaft?
F - Another type of bearing, but again I can't find a suitable bearing with screw hole to attach to the structure. Any ideas?

In regards to the stepper motor, i'm intending on going with something relatively lightweight due to the minimal load requirements -
1pcs NEMA17 78 Oz-in CNC stepper motor stepping motor/1.8A | eBay

Would this be a suitable unit or should I spend a bit more cash on them?

For the lead screw, I was thinking of going with a trapezoidal style as I believe these can reduce backlash? I worked out I would need lengths of 2 x 60cm and 1 x 30cm. I estimated 8mm diameter would be sufficient, would this seem suitable when considering the stepper motor choice? I have managed to source these at £25 per 1m delivered, does that sound a reasonable price? The spec is 8x1.5x1000mm (I believe 8mm diameter, 1.5mm revolution and 1m length)

I was intending to construct the unit from 12mm MDF, mainly due to cost savings against aluminium and perspex. Has anyone had experience of an MDF build and if so, what did you find the advantages/disadvantages to be?

I am intending on fitting home switches to each axis, would a standard TB6560 3 axis driver card and Mach 3 be compatible with home switches straight out the box or would I need to do any electronics/programming work? I do have experience in both but my knowledge is quite limited outside of HND level & Google.

Those are my main concerns pre-build but would really appreciate any other pointers on any issues that I may have overlooked for the design stage.

Thanks in advance!
Mark

[awerby]

Hi All,


Background - I run a small local pet shop and was hoping to start selling pet ID tags but don't really have the capital for a commercial machine at the level i'm likely to sell at so I thought 'what the hell', why not try and make one?! So the main uses will be engraving pet ID tags and maybe branch out to small name plates etc at a later date. Part of the project is to keep the budget as low as possible but still have a reliable unit.

[You seem to be concentrating on the former at the expense of the latter.]

So the design i'm hoping to go with is the following -



[That might be able to do some rough routing in wood, but it doesn't look like a metal engraving machine to me.]

My logic behind this design is that it will take the least volume of components to create a sturdy design and because I will be engraving relatively small items, I don't need an overly large range of movement in the X axis so it would be more beneficial to move that axis independently.

[This seems like a much larger machine than you'd need for pet tags. The bigger you make it, the less rigidity it will have, given the same components.]

The letters on that image where just so that I can clarify my understanding of the components technical names, please correct me if i'm wrong, thanks -

A - Solid metal shaft

[Those are unsupported rods, which will impart an interesting wobble effect into everything you try to cut.]

B - Threaded rod (lead screw?)

[That looks like hardware-store all-thread. It's cheap, but not very effective.]

C - I figured it's a type of Flange Nut but I can't find a flange nut with screw holes to attach to the moveable worksurface like in the image

[The guy who put this together may have made that himself.]

D - Linear bearings?

[They look like plastic bushings.]

E - I'm guessing this is a bolt through the structure in to the centre of the solid metal shaft, am I correct? Or is there a component to grip the shaft?

[It looks like he's grooved the shaft and used a wire clip to keep it from falling out.]

F - Another type of bearing, but again I can't find a suitable bearing with screw hole to attach to the structure. Any ideas?

[That looks home-made as well. You can't necessarily find all this stuff off the rack.]

In regards to the stepper motor, i'm intending on going with something relatively lightweight due to the minimal load requirements -
1pcs NEMA17 78 Oz-in CNC stepper motor stepping motor/1.8A | eBay

Would this be a suitable unit or should I spend a bit more cash on them?

[NEMA 17 motors are pretty weak. If you're replicating this design, I'd say NEMA 23 motors would be better. If you're making it a lot smaller, and using acme screws instead of the all-thread, you might get away with the 17s.]

For the lead screw, I was thinking of going with a trapezoidal style as I believe these can reduce backlash?

[That's the acme style thread I mentioned above. It doesn't reduce backlash, but it does work smoother, requiring less effort from the motor, and is more accurate.]

I worked out I would need lengths of 2 x 60cm and 1 x 30cm. I estimated 8mm diameter would be sufficient, would this seem suitable when considering the stepper motor choice?

[It would be better if they were fatter, like 12mm. You need to turn down the ends to get something to hold onto, and if you're starting with 8mm, there won't be much left.]

I have managed to source these at £25 per 1m delivered, does that sound a reasonable price? The spec is 8x1.5x1000mm (I believe 8mm diameter, 1.5mm revolution and 1m length)

I was intending to construct the unit from 12mm MDF, mainly due to cost savings against aluminium and perspex. Has anyone had experience of an MDF build and if so, what did you find the advantages/disadvantages to be?

[I'd say aluminum would be a better choice. The cost shouldn't be too much considering how small a machine you're building. MDF's only advantage is price, but it holds up poorly in moist environments (like the UK) and you might want to use coolants and lubricants on your cuts.]

I am intending on fitting home switches to each axis, would a standard TB6560 3 axis driver card and Mach 3 be compatible with home switches straight out the box or would I need to do any electronics/programming work? I do have experience in both but my knowledge is quite limited outside of HND level & Google.

[I don't think you really need home switches, and that driver card's well-known for problems. Here's a thread that discusses them: http://www.cnczone.com/forums/genera...y_chinese.html ]

Those are my main concerns pre-build but would really appreciate any other pointers on any issues that I may have overlooked for the design stage.

Thanks in advance!
Mark

[I'd say build it much smaller than the machine in the picture. For the things you're talking about, you don't need travels of more than about 50 mm in X or Y. Even at 100 x 100 mm it would be a lot stiffer. If it's small enough, those unsupported rods won't bounce as much (you could also use supported rods and open bearings). Make the Z-axis very short, since your material isn't thick. This will maximize rigidity. Get as good a driver card as you can afford, not some piece of junk from China. I like the Geckodrive G540, but there are others known for quality and not just low price. And find a spindle that will go fast enough for engraving but won't die after a few hours of use. You aren't saving anything if you go so cheap that you end up with a machine that doesn't really work.]

Andrew Werby
www.computersculpture.com