First time building CNC Router. Would love some feedback on my design.

[itsenzothebaker]

Hi all,

This is my first time designing a CNC router and I would love to get some feedback from experienced builders so that I can avoid some common pitfalls. I tried to minimize machined parts as much as possible.

Here are the components that I have purchased so far:

Rail & ball screw set from AliExpress:
https://www.aliexpress.com/item/3-ba...608.0.0.si2sZi

NEMA23 Stepper motor, driver, controller set from AliExpress:
https://www.aliexpress.com/item/CNC-...608.0.0.si2sZi
(I heard some horror stories about this set but I tested them and they seem to be working fine)

Ballscrew housing from Ebay:
Ballscrew Nut Housing Seat Mount Bracket Holder 28mm Dia For SFU1604 1605 1610

Motor mount housing from Ebay:
New Nema23 Stepper Motor Aluminum Mount Bracket Clamp+4pcs Screws for CNC Router | eBay

I went with 8020 aluminum extrusions so that I can just install the linear rails on T-nuts instead of drilling & tapping million holes.


Side View:


Isometric View



Top View


Bottom View


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[wizard]

Not bad at all for a first attempt!!!

You didn't mention the machines size which is always a factor. In that regard im somewhat concerned about the gantry construction. You may need larger beam extrusions depending upon the span and your expectations. Also the uprights supporting the gantry beams might need better support or bracing.

As for avoiding drilling and tapping you still do a lot of that with extrusions especially the tapping. Of course if you buy a kit that would be done for you. Also to achieve your ladder frame you will need to drill a lot of holes for access to screw heads in the T-slotted extrusions or go with alternative mounting methods. You really don't want to rely upon just the gusset blocks.

You might want to consider that mounting two gantry beams in parallel will make life more difficult for you. It will be more difficult to get the beams in the same plane and parallel to each other thus making it more difficult to mount your linear bearings properly. How much you need this approach depends a lot on how much Z you really need.

In any event mentions of probable usage and work space size is a big help.

[awerby]

How big is it? It looks like there's very little clearance between the gantry and the table, which might just be an illusion of scale. But if you plan to use it for anything but cutting things out from sheets, you might think about boosting that bottom rail up a bit.

[1Jumper10]

Looks pretty good. If you are ordering the extrusion from 8020, instead of using gussets to join them, use their double anchor counterbore. Its stronger than the gusset and will form a perfect 90 degree joint (assuming the factory cut the ends squarely).

[NIC 77]

I'm not a fan of the tall gantry risers. I realize that you gain some advantage from having the bearings supporting your Z as far apart as you can have them, but you pay for it with the tall gantry sides which I think you will find are not very stiff if you build it like this.

IMO, all things considered, you are far better off to use a single larger tube for your gantry than two smaller tubes. You can put the ball screw on top or use spacers between your bearing blocks and your Z to mount the ball screw between the blocks (probably what I would do if using T slot and ball screws).

I would also increase the stance of your gantry bearings so that the front of the first bearing sits just under your cutting bit if you can, and get rid of the T-slot gantry risers all together. Make them out of something else, steel or aluminum, it doesn't matter. Even solid wood blocks temporarily if you will need the machine to make the new ones

I'm not a fan of the 5mm lead ballscrews. Without doing a complete analysis on the motors, weights, acceleration settings, and what top speed you want, I can't really comment more. You've already bought them, so, give it a go, you may or may not upgrade in the future if things are too slow for what you want....they should get the job done at any rate. Actually, looking at the motors, they're not the most powerful, so 5mm pitch may be all you want. I have no idea what speeds you want to push this too, so it may be just fine for what you want to do.

That's just my humble opinion, and I have no real claims to fame.

Enough with the negative. Good on you for designing your own machine. I can see you've put some real thought into it. I do think you should spend a little more time on the design before buying more stuff. I also think it's a great start.

[wizard]

One thing I missed is that you need to look at the length of your linear rails. As shown in the picture the rails look very short and may not give you the travel you might expect from the size of the base.

[A_Camera]

I think your gantry is going to be too weak and the tall design will result in a lot of flexing. I also think that the gantry fix to Y axis motors is also too weak, will not give you the rigidity needed and you will have problems with accuracy. The Z is pretty similar to mine, and assuming the plates you are planning on using is thick enough, that is OK, but it is a pretty large machine, so you need to make sure to make it very rigid, and the beam carrying the Z is just not going to give you what I guess you expect.

[itsenzothebaker]

Hi, thanks for the input! I worked out the spacing on the rails so that the holes on the rails (not shown in the model) will align with the grooves in the extrusions. I'm definitely going to beef up my support for Z in addition to the gusset blocks. Here are the rough dimensions:

[itsenzothebaker]

Got it. I think I'm underestimating how much this machine will flex. I will redesign this to attain more rigidity. Thanks for you input!

[fretman_2]

Yes...you're right in underestimating how much that tall gantry riser will flex. Since you may not have access to the software that measures flex based on your design, just way overbuild it and you'll come out ahead!

[louieatienza]

While that tall gantry riser may flex, the majority of the forces are on the lower beam of the gantry. Since the lower beam of the gantry is pretty far down to begin with I personally don't see it a major issue, unless you're taking some extreme cuts.