Thread: Small 2-axis CNC machine plans?

Shouldn't that be a 3-axis router?

X and Y for horizontal movement, Z axis for vertical movement on the spindle.

Hi,

OK, I stand corrected. I assumed the z axis was for relief / variable depth cutting. But I guess the bit needs to go up and down

See, I really don't know much yet!

Thanks,
Darren

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I spent a couple of years driving a 2400 x 1800 14 tool CNC cutting kitchens etc so have some background. Taking the parts in your pic I think you will have problems with internal corners etc, unless you are willing to rework them or spend an inordinate amout of time cutting them.

A router (manual or CNC) can get nice crisp external corners because they can change feed direction to achieve them. But when it comes to internal corners etc, the best they can generally do is a radius equal to the bit radius. You cannot reduce the bit radius to negligible size to reduce the corner radius, because you rapidly move into an area where the bit is too small to withstand the feed forces imposed.

On the commercial machine I operated, we had 14 tools loaded and set up and tool changing was an automated 5 second process. On a single tool machine, you dismantle the spindle collet, manually change bits in the collet, and possibly the collet itself, reasemble on the spindle and then reset the z zero for the tool. Tool changing during jobs quickly becomes a hassle.

On the commercial machine, we used a 3/8inch compression bit for general cutting, but had access to 3mm, 5mm and 8mm spiral bits as well. If we needed a fairly tight internal corner for a job, we would 'peck' short line segments with the 3mm bit to create the corner, then let one of the larger bits remove the bulk of the material, leaving a 1.5mm radius at the corner which could be touched up later if required. Looking at the photo supplied, you need crisp corners, and 3mm bits won't give them to you, and smaller bits really are getting too fragile for any sort of cutting out.

A similar situation applies with cutting components for model aircraft and the prefered machine is often a small laser cutter, leaves a slight discolouration at the cut edge but it makes very crisp cuts and and tight corners without the sheet having to handle the feed forces from a bit.

Hi malb
Not sure that I agree with all that you have said.

If he uses say a 4mm cutter to cut out the parts then it would be a very small radius on the internal corners. So small, that it can even be ignored as the plywood parts slotting together would just crush into place anyway.

Hi Darren
Good to know that you are not seriously thinking of buying the Shark. It would be a waste of your money. Ask saisay what she has had to do to her Shark to make it even remotely usable.

If you are an experienced fabricator then you should have no trouble building a CNC machine assuming that you have a bunch of basic tools such as a welder, band saw, pedestal drill and table saw.
The welder is for making the sub structure, but it isn't really necessary.
The bandsaw is for cutting the aluminium sides to shape, but again, it isn't really necessary.
I do think that the table saw and the pedestal drill are necessary, just to ensure accuracy for the drilling and cutting.
China is the place to get most of your components from if you have the time. You will need ball screws, stepper motors, stepper motor drivers, drag chain (for the wiring), lots of wire and lots of holes to be drilled and tapped and then filled with bolts and nuts.
None of it is very hard, just time consuming to understand what it is that you are making and how it all works together.
When you have made the basic maching, you will need to work out a suitable way to stick either a router or spindle on the machine so that it can do the actual cutting work.
Check out some of the builds here on this BB.