CNC 3018 Pro - Z Axis Stability improvement idea..

[richardsenior]

Hello I'm Richard.

Like a lot of people during coronavirus lockdown.. I decided to buy something to make myself feel better.
So I bought a cheap chinese CNC router (it actually came from Czechia).
It's a CNC 3018 Pro. And it cost me 140 quid on EBay.
I don't know what I was expecting... I knew I wasn't going to be sending sheets of white hot steel 30 yards down the shop floor with a huge carbide face mill.
I knew it was probably a bit of a gimmick, but all I wanted to do was engrave a small aluminium box with a logo about an inch square.

The way I saw it.. it's a 3 axis cnc for 140 quid. I mean.. it's rude not to buy it!
Anyway... the machine has both amazed me and disappointed me in equal measure.

For example... I put a dremel 2 flute router bit in it, and it happily ran a pass 8" long 15mm deep and 2mm wide on a chunk of plywood without any complaint.
It's accuracy is flabbergasting. I can run the same grbl file from the same zero point over and over, and it's bang on.. Easily to 0.1mm

But when engraving aluminium, there is just enough play in the axes to cause the outline of the engraving to be fuzzy due to machine vibration.

If you get hold of the router bit and yank it about a bit, you can cause a good 2mm movement.
When you examine where that movement is coming from, at least 50% of it is due to the Y Axis rails actually bending. (they're about 300mm long and 10mm diameter).

Some people have cured the other 50% by fitting longer linear bearings in the z axis, and bushing the z axis lead screw.
But they're still going to get y axis torsion.

So I had an idea.
There's a gap of about 5mm between the back of the z axis and the two extruded aluminium struts (on which the control board mounts).
What if I just shim that gap with some PTFE?
That way, we're still using the guide rails for accuracy, but you can't bend the guide rails because the PTFE will touch on the extruded bars.

I note that those extruded aluminium bars are used by the openbuild machines.. And you can actually buy bearings that run in the slots.
That was another thought I had.. just to attach some nylon bearing wheels to the z axis, that would run in the openbuilds backing bars.

Has anyone tried any of this?

Before anyone goes down this route.. Yes.. I know I could buy a better machine.
I could also just send off my parts for professional engraving, and let them worry about things like z axis stability.
Or I could just lay on my bed all day and do nothing at all... You get the idea... Please don't evangelise, it's tedious.

Anyway..

Hello :)

EDIT :

I bothered to create this page on my modifications (http://www.richardsenior.net/cnc3018pro/)

[Doddy]

Not tried, but when I had something similar to a 3020, though UK sourced, I found chasing stiffening and accuracy when engraving (which is no easy thing to do well unless your machine is stiff!) long winded and ultimately futile. But!, walk that path. Try it (why PTFE?, out of interest?) and report back. Keep an eye on Z deflection across X/Y travel as well as being aware of possible XY deflection. Turning your conversation around you have a perfect opportunity during lockdown exploring the limits of your machine.

[JAZZCNC]

Lifes too short to waste time trying to make a Silk purse out of a sows ear.!!. . . Don't take that path build or buy a better machine and live life la Vida loca

[richardsenior]

why PTFE?, out of interest?.

It's just what springs to mind when I think of plastic bushing materials.
I know Nylon is used a lot, but I think PTFE is just a little softer and more appropriate for aluminium.
It's an engineering sensibilities thing.

I've ordered a bit of PTFE and some nylon roller bearings.. I'll post something when I've done it and
see how much of an improvement it makes.. if any.

I also got a sprung diamond drag engraver for about 30 quid.. Which is actually very very good.
It cuts vinyl really nicely. I'm hoping it'll make some nice drag engraving work on aluminium too.
We'll see.

[RogerH58]

Hi Richard - I'd be interested in a link to your machine - the best I can find is about £170 unless it comes from China?

Also interested in how you get on - I'm planning on engraving perspex - which may or may not be easier than ali.

Thanks,

Roger.

[Adrian_S]

So I had an idea.
There's a gap of about 5mm between the back of the z axis and the two extruded aluminium struts (on which the control board mounts).
What if I just shim that gap with some PTFE?
That way, we're still using the guide rails for accuracy, but you can't bend the guide rails because the PTFE will touch on the extruded bars.



Hello :)

I bought myself a much smaller version, the 1610, in January to learn about CNC. I too am impressed with the accuracy and repeatability, I set up a DTI and checked all 3 axes one by one and found less than 0.02mm backlash, the sprung brass leadscrew nuts obviously do a good job.

I don't see as much movement in the Z-axis as you do, maybe the increased Y-axis allows more flex in the linear guides and/or the horizontal 2020 sections you are talking about using as auxiliary bearings. Also, on my machine I changed the verticals to gain increased height so I could mount MDF waste-boards on the table and still get the full travel of the Z-axis. In the process I added corner blocks to every junction I could.

The only problem I forsee is that the increase in friction might cause skipping in the stepper.

There are two other paths you could consider:

1) with extra 2020 material, double up the verticals and the horizontals on the Y axis, as the increased rigidity might prevent so much twisting force being transmitted to the Y-axis linear rods from actually bending the frame. In the process, add extra corner blocks wherever you can.

2) replace the Y-axis linear guide rods with fully-supported linear rails. The extra material forming the support with also help with beefing up the horizontal 2020 sections mentioned in 1)



Despite the advice to go no further with this and buy a better machine, I think it worth persevering, 2020 section is cheap, fully-supported rails likewise, and the main thing is, if everytime you discover some shortcomings in a machine you go out and buy a "better" one you are going to amass a collection of machines.

[richardsenior]

Roger,

Sorry for the slow reply..
Firstly I created this, which you might find interesting (http://www.richardsenior.net/cnc3018pro/)
I got mine from ebay from this user (https://www.ebay.co.uk/usr/listarcy?_trksid=p2047675.l2559)
Maybe you can see the auction here (https://tinyurl.com/y7ccpr49)
You might want to try BangGood (a chinese online shop).

Advice.. You WILL need a sprung 'drag' engraving tool.
Don't try and engrave perspex with a rotating router bit, it will make a mess.
If you buy a diamond drag tool (see my page on this above) it will work perfectly.

[richardsenior]

Here's where I'm at so far (http://www.richardsenior.net/cnc3018pro/)

[Hevda]

Here's where I'm at so far (http://www.richardsenior.net/cnc3018pro/)

Thanks Richard. Very helpful blog post ��