First Build 5 x 12 Steel Frame CNC router

**Scott Damman** · 05-03-2016

Originally Posted by Boyan Silyavski

Ok, lets start from the beginning. I will try to resume some things, you just need to further research the topics:

1. You should absolutely know what weight your gantry is with all things mounted. Knowing the mass of the gantry will be decisive on what motors, what size ball screw, rotating nut, Rack and pinion, etc..

2. Be realistic about the feeds and speeds. And what you really need the machine for. All in one would be usually a disaster in some area.

3. Motor sizing. People drive 3nm nema 23 motors at 70VDC. And we are talking low inductance motors. Expected reliable performance from such motors coupled with xx10 ball screws is 10000mm/min. The motors you have are high inductance motors. I am not a specialist here but there are a lot of knowledgeable people here that will tell you at what voltage, but i am sure that it must be more than 110VDC. Do your research and find at what voltage these motors perform well. And if these drives will be ok.

4.Without knowing the total weight of the gantry... but i see you start ambitious, so yes, you will need servos to drive the gantry reliably fast if you aim at 25000mm/min. And you will need rotating ball nut or rack and pinion

5. There is a very well made calculator at the forum here, search for it, and i am sure that the gantry legs deflection will not be as you say...but may be i am wrong

I dont want to discourage you, but i am having the feeling that if you continue without thinking it too much, there will be disappointments on the way. WHY JUST DONT YOU SLOW A BIT AND READ MORE BUILD LOGS. All the info is there.

And by the way it seems the american thing is to desire rapids of 1000ipm. And make rack and pinion machines. We here in EU prefer precise ball screw machines and rotating ball nuts for big machines and heavy gantries.

The gantry will weight around 550lbs, this number comes from the 3d drawing which worked out to 494 (this included the Z axis and the spindle) and I added 50 lbs for cables and cable routing. This was my bassis for sizing the motors. Sorry I thought I had been clear on it earlier in my thread about the weight.

Feeds I am happy to be realistic and dont care much about super fast rapids but I want to be able to drive the machine at proper cutting speeds.

Im sorry I came across as I jumped into this without any research when the opposite is true, I have done lots and lots of research both on forums and by inspecting commercial machines. I would not have been able to get to the point I am without lots of learning from all sources. I find there a very different views on most subjects associated with the gantry style cnc router so its hard to nail down whats the best design. And thats where some of my questions came from. The stepper route was more of a cost thing and I should have done more research on servos before going down that road.

I will find the calculator you speak of and give it a try. I just started out by doing the math, the hard part was actually finding out how much force would be applied at the tool so I could back calculate the flex at the gantry.

**I want to say machining Aluminum is a bonus for this machine as it will mainly be used for wood**

Hi Scott,

Just to scale point #3 from Boyan - 3Nm Nema 23 at 70VDC could be used up to gantry weight of 50-70kg tops. As yours is 5 times this weight the stepper / driver combo needs careful thought.

I can sort of see the machine you are trying to make by piecing all the photo together - and it looks like a commercial wood router with raised gantry.

If you want to cut aluminium as well I would suggest you chop the legs off the gantry, and go for a raised X axis instead. Lift the X axis members up on supports away from the bed until they meet the bottom of the gantry. This makes a much stiffer machine for little effort. Your span is quite wide so you will need all the help you can get for aluminium.

Can you post up a picture of the overall machine design?

I looked carefully at doing a bridge style machine with high sides, the problem that kept running into this design was not easily being able to side load the machine. I do alot of work with large wood slabs which this machine will be used to flatten and I need to be able to side loads these as I dont have an overhead crane. (they weigh in excess of 1200 lbs)

Here is the Frame starting, I have blocked up the frame to level and used the gantry to set the exact distance.