Small but strong cnc machine

**Alexandre** · 05-07-2015

Good evening.
I would like to present a project that I did recently for a friend of mine in order to serve as an inspiration to those who seek a small but robust machine. This machine despite being small would have to have sufficient strength to cut carbon aluminum and plastics mainly.
The overall size of the machine shall not exceed the 62cmx42cmx45cm
I will leave a description of the material used in construction.
Aluminum alloy chassis 5083 with 10mm thick.
Linear guides Ø20 with SC20UU bearings in the x and y axis.
Linear guides Ø16 with SC16UU bearings in Z.
1605 ballscrews in all axis.
Nema 23 size motors 2NM force in the x and y axis.
Motor Nema 23 1NM the axis Z.
TB6560 drivers in all axis.
15A 24V power supply.
Here I leave a few drawings of the project, and later I will take pictures of what is already done.
Any question just ask.

Best Regards
Alex

**Alexandre** · 06-07-2015

Hello
and this is what i had done so far....

any questions just let me know.

Cheers
Alex

**njhussey** · 06-07-2015

Looks good. ...though I'll quibble with you over it being robust as youre using unsupported rails all round with thin plate and none or very little in the way of bracing. As long as you're realistic with the speed you're going to cut at with the 24v and TB6560 controller and take light cuts I'm sure you'll be fine :)

**Alexandre** · 07-07-2015

Hello.
Thanks for repply.
Yes rails are unsuported but they measure only 60cm the biggest and i have 18cm from "top to top" of bearings, so i think they will not bend.
And yes, tb6560 with 24v is a litle bit light but i will change them soon for a system with feedback.
Machine is all most done and i will post a few picures more and videos.

Cheers
Alex

**Clive S** · 07-07-2015

Originally Posted by Alexandre

Yes rails are unsuported but they measure only 60cm the biggest and i have 18cm from "top to top" of bearings, so i think they will not bend.Alex

It would be interesting to put a DTI on it with some weight and see how much it bends.

**Alexandre** · 07-07-2015

Hello.
Thanks for comments.
Clive can you give me any suggestions on how to measure it. Where should I put the weight, and where should I measure for a more accurate value, to see what happens

Alex..

**routercnc** · 09-07-2015

Hi Alex,

This is how I did it . . . .
http://www.mycncuk.com/threads/7155-...ight=stiffness

Attach a DTI to the collet (mm) and push it with some scales (reads kg so *9.81 to give N). Divide one by the other to give N/mm. Repeat for vertical, fore/aft, and side to side directions. This gives a rough stiffness figure. You will see the sorts of figures achieved by the DIY machines in the post. They will all cut aluminium.

There are some guideline cutting force levels for different materials:
5N wood
50N alum
75N steel

This will of course vary in practice, and the steel force is probably on the low side, but I think it is enough to get a feel for things. You can then estimate the deflection due to the cutting force by inverting the stiffness (do 1 over the stiffness value to give mm/N) and multiplying this by the cutting force (N) for the material you want to cut. This will give (mm) of deflection during cutting. You will have to decide if you think this is acceptable based on the accuracy you want.

Your machine does look on the low stiffness side, but it is small so that will help. Plus it is beautifully made so well done on that front.

**njhussey** · 07-07-2015

I'm sure that they'll be fine for what you want to do, but they will bend and your gantry will bend from side to side as it's a bit like a cornflakes packet with an open top and bottom. If you get a bit of plate across the back that will help...