Small but strong cnc machine

**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.

**Clive S** · 09-07-2015

I did not understand this the first time round but now I do. Thanks for the clear explanation I will have check mine out now.
Edit I appear to get 0.01 at 5Kg pull from just below the collet with a dowel in it on X and Y

**Alexandre** · 12-07-2015

Hello.
routercnc, thank you for the explanation. This seems to me a good way to get an idea. I will try this method and post the results here.

Alex..