Looking for feedback on plan for CNC router out of welded steel tubing

[Ign]

Hi there,

I'm currently in the process of planing & building a budget table-top CNC router and came across this amazingly useful forum. Short introduction of myself: I live in Germany and have experience with all kind of DIY stuff, including welding (MIG, MMA), brazing, building cargo bikes, sewing, electronics, etc. :)

I'm building a budget machine from MIG welded steel tubing around one of the cheap kits that include supported SB20 rails and 1605 ball screws. I would like to get some feedback to my current plans.

I would like to process any type of wood and maybe aluminium.

As a spindle I will start with a 600 Watt router with a 43 mm Euro mount.

x axis: 1000 mm
y axis: 600 mm
z axis: 300 mm

All steel tubing is rectangular hot rolled 50x30x3. Z-axis plates are Aluminium, 15mm thick.

X axis will be driven on both sides. The gantry is hanging, as it seems to me that this way it is easier to make everything sturdy.

The y axis has both linear rails on the front, as I then will be able to use epoxy to level the two surfaces (at the same time) where the linear rails will be mounted.

I'm missing motor mounts and want to use steel tubing for x and y similar to this machine: http://www.mycncuk.com/threads/1541-My-steel-framed-router?p=10158#post10158
For the z axis I'm not sure but something like Aluminium plate bolted to the back plate.

I'm also missing mounts for the ball screw. Can I make them from steel, similar to the motor mount? How to make them adjustable?

After reading through this forum I've come to the conclusion that levelling is necessary. Is it? Am I missing any budget options for levelling? Did this build
skip levelling: http://www.mycncuk.com/threads/1541-My-steel-framed-router?p=10158 Can I use any low viscosity slow curing epoxy?

I'm looking for feedback particularly on my plan for bed and y axis gantry.


Best regards
Daniel

[Kitwn]

Daniel,
Welcome to the forum. The only problem you will have with MYCNCUK is making a choice between all the different options you will find for doing almost every part of your project.

My build experience is limited but my machine is similar to yours in having the rails mounted onto the face of the gantry. This is not the generally preferred method but does make the Z axis assembly simpler and, if you use epoxy on the face as you suggest, one aspect of the alignment is removed. Don't try to use cheap epoxy, it may well be too viscous and wil cure too quickly for an accurately flat surface. I speak from experience! West System 105 resin with the very slow 209 hardener is what those in the know recommend. Cleaning up the mess I made last time and starting agin is on my To-Do list.

I used two pieces of 50 x 100 stell box welded together to give a 200mm high flat face to take the eopxy and SBR16 rails with a 1610 ballscrew. By good luck rather than good judgement the spacing required between the gantry and the backplate of the Z axis turns out to be almost exactly the same for the rails and the ballscrew which makes this construction very simple to implement.

Your Z axis design has the same problem I faced: The linear bearings on each side of the back-plate overlap meaning you cannot fix all of them in place. I decided to have two plates, each of which has bearings, brackets etc. mounted onto one side only. This also means the whole Z axis assembly becomes a single removable unit. You also get the ability to slightly rotate the plates relative to one another for alignment purposes. Obviously the two plates need to be bolted together in as many places as possible for maximum rigidity. One of the rear plates needs to extend upward to include the motor mount.

The pictures show my machine in it's current plywood mock-up but shows the idea. It actually works surprisingly well in this state!

Kit

26799
26800

[Ign]

Kit, thank you very much for you reply!

I actually have the same idea that instead of ruining the aluminium plates directly, I'll first build a mockup from plywood. My idea to fix the overlapping problem is to just use counter bored holes, so the bolt heads of the bearings are below the surface. Is this bad idea? I'm not sure how to drill counter bored holes, maybe with a router?

26807

[AndyUK]

Hi IGN,

My first advice is to ensure you've read the gantry design threads:

http://www.mycncuk.com/threads/2023-Some-thoughts-on-cnc-machine-design-principles

http://www.mycncuk.com/threads/9082-Beginner-Moving-Gantry-Build-Read-This%21

I highly recommend using extruded aluminium profile where possible; because its heavy duty profile it can be just as stiff as steel, and you shouldn't need to use Epoxy to level it, which makes the Y axis a LOT easier. See my build thread to see what I've done with the Y axis; its a very common design on here, and the aluminium profile only cost £50, which is about what I'd need to spend on epoxy to level it if done in steel. It also meant that the rail bolted on in 10minutes after getting it - on my X axis I used steel and epoxy levelling - that took WEEKS of work. Grinding, Welding, Drilling, Painting, Epoxying... I wish I'd used Aluminium on X too. On your current design, I'd say the Y axis looks quite weak - you don't really want open area between the rails. Theres also a gantry stiffness calculator somewhere on the forum where you can put numbers to your design.

Your gantry sides should ideally be wide enough to have the router bit fall between the two bearings. It does reduce X axis travel however. Your rail also doesn't go to the back of the bed - how come? If I were to have that shorter rail, I'd put the gap at the front so I don't lose travel distance over the bed.

Get a quote from Fred for Profile rail - it might be cheaper than you're expecting, and is a significant upgrade over SBR.

[Kitwn]

Kit, thank you very much for you reply!

I actually have the same idea that instead of ruining the aluminium plates directly, I'll first build a mockup from plywood. My idea to fix the overlapping problem is to just use counter bored holes, so the bolt heads of the bearings are below the surface. Is this bad idea? I'm not sure how to drill counter bored holes, maybe with a router?


The problem is how do you get at the bolt heads which are underneath the bearing you've just fitted:upset:

You will need counterbores if using two plates as well since the plates must fit flush. But if you make the plywood mock-up first ( with badly drilled counterbores that will be adequate if not neat) you will then have a fully functioning CNC router to do the job for you. Yay!!

If you can find aluminium profile at the price Andy is quoting then that's the way to go. If any of our Australian readers know of a local source of profile at the 50 quid ($90 AUD) price point Andy mentioned I'd love to hear from you. Here in remote Western Australia I got a quote for 2 of 900mm pieces of 120 x 80 mm heavy duty profile which came to $638 AUD inc delivery. That's about 340 GBP or 390 EUR. Slightly more expensive than the steel I managed to scavenge off the local tip!

A quick look at Fred's website (BST Automation on AliExpres) for a price comparison on rails says that Chinese unbranded 15mm profile rails and bearings cost about 50% more than 16mm SBR and the preferred Hi-Win brand are about 150% more. You said this was a budget project but there's always the balance between saving money now against not having to spend yet more money in future to upgrade to something better. You can get SBR rails more cheaply on eBay but there's no guarantee of quality. Note that the profile rails are much less tolerant of uneven surfaces and other misalignments than SBR so the rest of the construction needs to be of a higher standard.

My machine is only intended for cutting wood and for reasons of cost and my uncertainty about accurate construction of the frame I went for cheap eBay SBR rails (20mm for the long X axis and 16mm for the Y) with the plan to upgrade to profile rails if the SBR proved inadequate for my future requirements.

[Ign]

My first advice is to ensure you've read the gantry design threads:

I started with the advice from these threads but somehow moved away from the L-shaped gantry. There is no reason to not connect the two horizontal parts...


But if you make the plywood mock-up first ( with badly drilled counterbores that will be adequate if not neat) you will then have a fully functioning CNC router to do the job for you. Yay!!

Oh! This is a very good point!

I think I will reconsider my plans as I went today to one of the local university's metal shops and there there is a Deckel FP2 mill that I could use to flatten the surfaces, so I can avoid both aluminium and epoxy! Does it make sense to first fully weld the bed and then flatten the x-axis surfaces? I don't know how to make sure that both sides are in the same plane, but maybe this is not necessary?