Steel Tubing CNC Router

[thegimpster]

I have been working on building a CNC machine for a while now. I have my motors and plans, and have been soldering the electronics for the past few days now. But I think it is going to take a new direction. I was talking w/ my dad this past weekend about it and he got pretty interested in it. Strange for me b/c he never takes interest in most of the stuff I do. He has a good stick welder but wants a good reason to buy a mig so here it is.

We are planning on making most of it out of it. I have been searching for some square tubing plans, but I have been sketchin some of my own, nothing computer drawn, but give me some time. Does anybody have any plans out there or have built a machine mostly out of sq tubing?

I am thinking of making the Gantry like this (sorry for the ascii art

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where the bottom line is attached to the angle iron linear bearing and the middle upright supports the y axis also made from square tubing.

Will this be stable enough or not?

[mxtras]

Hard to tell from the drawing there.

The best advice I can offer is to look at the industrial machines available and mimic the basic design. There are some engineering rules that apply to stuctures and motion systems that are pretty basic - like bearing spread drastically improves stability.

Build a stable, rigid structure and you will be on the right path.

Scott

[andy_ck87028]

Hi

I've built out of square tubing and when I can get hold of a camera, I'll get some pictures up. I do have a user log but it has remained dormant for a couple of years.

I went 3mm and a stick welder but the frame could have been heavier (dollar cost) and the gantry could have been lighter (less weight but that might also have introduced unappreciated flex)..... Really depends on the span and span tables will help you there.

My machine is 4' by 3' by 6". I have used timing belt on x and y and acme on z.

I have used stainless steel tubing for rails and skate bearings.

Feel free to ask questions.

Manufacturing is now complete and I am now aligning everything. Have yet to start electronics.

I really love working with steel. Angle grinder, arc welder and drill press.

Because I do not have access to precision tools I have designed in heaps and heaps of fine adjustment. That has taken a huge amount of time.


Andy

[BobF]

Check out the mechmate. It is steel, but not square tubing. I think you could adapt some or most of the design to tubing.

[LeeWay]

I built my first cnc router using some steel tubing. Not soley though. I used stuff I mostly had on hand.
Here is the link to my build log. It may give you a few ideas.

http://www.cnczone.com/forums/showthread.php?t=8632

[wcarrothers1]

my cnc router was made mostly out of square welded tube. Well the gantry wasn't but the frame was.

Do a search on threads I've started and you will find pics. The machine was painted blue.

b.

[mxtras]

Originally Posted by andy_ck87028 Because I do not have access to precision tools I have designed in heaps and heaps of fine adjustment. Andy

Good advise.

Another rule of thumb - if the item has to move, weight is a concern. If not, make it heavy. In the case of a typical gantry based cutting machine, this equates to a heavy table base and a well designed gantry. Rigidity does not always come with a weight penalty if it is done correctly but weight is your friend in a machine tool. A super lightweight gantry can resonate and sing - adding mass is the cure. It's a balance. The use of triangulated geometry and material dispersion (spreading things out) can assist in getting rigidity without excessive weight.

As Andy said - the motion system needs to be (or should be) well aligned. If the base structures can not be made accurately, then provide for accuracy adjustments as he suggests. Jacking and clamping screws along with adjustable bolt patterns help with this. Some thought in advance is required. Provide for freedom of adjustment in all 3 directions.

If it's a welded structure, plan on making the critical surfaces in sets so they can be fixtured and welded as matched pairs, if possible. Make accurate cuts and good fit-ups. The welding alone can make or break a flat, straight and square assembly so measure often and compensate with opposing welds during construction. Straighten the individual parts as you go.

To help create a flat weldment, use three points of contact when you are welding things up and keep an eye on things with a straight edge. Use chalk to locate your reference points on the floor so that the three point plane stays constant - if you are working on the floor that is. Don't assume the floor is flat unless you check it. Out of flat weldments can many times be fixed with an appropriately positioned weld or with clamps and a bit of ingenuity.

Scott

[wcarrothers1]

Ya when welding heat is not your friend. All the things Mxtras says is important.

Keep weld beeds short and spaced appart to keep temps down. Then alow to cool and fill in more.

Anyone want to know what my first square tube linear rail looked like after welding it into the C channel for the first go around? tuned into a U shape due to over heating the metal welding to much to fast..

#2 and #3 rails came out streight going slower and spacing the welds.

b.

[andy_ck87028]

Originally Posted by wcarrothers1 Ya when welding heat is not your friend. All the things Mxtras says is important. Keep weld beeds short and spaced appart to keep temps down. Then alow to cool and fill in more. Anyone want to know what my first square tube linear rail looked like after welding it into the C channel for the first go around? tuned into a U shape due to over heating the metal welding to much to fast.. #2 and #3 rails came out streight going slower and spacing the welds. b.

I totally agree with where you are coming from and as construction advice it is good advice.

I wasn't aware of that at all when I built and so my tubing is probably as bent as a .....

However, it does not worry me as I know my rails are straight. I achieved that by a) through rigid bolt down and b) the bolt down arrangement I have used allows for fine adjustment for straightening......in all planes.

Consequently, I don't care if the floor is flat or otherwise or that the frame is warped.

What is important is that the rails (as distinct from the frame) are positioned horizontally, vertically and perpendicular to each other.

I believe that the concept of reference plane is very important in this area.

Ultimately, the whole machine depends upon the rails being true and the machine being rigid. Ignoring rigidity (separate subject), the need for true rails is one of reference planes.

With the help of a mate, I appreciated that the process of alignment is incremental and the first step is to get the first of the x rails (called x) true using whatever means are at your disposal. Then make the other x rail (x') true to x. Then get y true and at right angles to x. Then get y' true to y but also check it against x. Then get z true and at right angles to y but also check it against x. Then get z' true to z but also check it against x.

At each stage, ensure that x has not lost its original trueness.

Lock down occurs when x, y and z are all true which is where the rigidity aspect comes in. So far, I've used a mixture of bolts and will also judiciously use epoxy to achieve rigidity.

I have experimented with having x and y fixed and x', y' floating in my design but I've yet to implement it. I think it is achievable though. The reason I mention that is because it is another way of looking at solving CNC construction.

Andy

[degreaser]

Howdy - First post here. Been lurking for awhile. This is a design in progress. Second machine. First was an X2 conversion. The size of this router is 4.5' x 3' workable area. I'm aiming for 8" vertical travel. The frame is 2x2 steel tube, probably .1875 wall. As has been mentioned, the thinner stuff warps a lot when welding. The bearings and z-axis will be mostly Al. No metal parts yet as it will be 100% designed in Rhino before the first cut is made. Ballscrews and servos will form the driven part. I stole the linear bearing design from another post here on cnczone.


http://www.rawbw.com/~duncan/router53_assembly.jpg
http://www.rawbw.com/~duncan/bearing_truck.jpg

~Don

[jdell42]

degreaser

This a bolt together or you going to weld it up?

[degreaser]

A mixture of both. The x axis side rails will be welded along with the short pieces of 2x2 tubing which act as spacers and mounts to the crossmembers The crossmembers will be bolted to the x axis side rails and will allow some measure of adjustment. Hopefully I won't need too much. The "linear rail" (3x.25 hot rolled mild steel) will also be bolted on for alignment and replacement purposes.

~Don