CNC Mill/Router Design Feedback

[PrestonH]

Hello everyone!

I am looking for some design feedback on my first CNC build. The footprint is 20" x 27" x 23.5" tall. I should have a cutting area of about 16" x 24" x7" if I were to clamp my work pieces directly to the table. I will mainly be machining aluminum, but may do some steel from time to time if I ever setup flood cooling (and want to deal with the mess associated with flood cooling). All structural parts are made from hot rolled steel, which will be milled flat and painted. I am thinking of using 15mm linear rails, simply because they are the cheapest I could find that still seem to have decent quality. I am planning on using 16mm ballscrews, with the Z-axis at 300mm, y axis at 550mm and x axis at 600mm. I am planning on using M8 bolts to bolt all the structural pieces together. The motors I am planning on using are leadshine 86CM45 due to their cost, power requirements, and reasonably large torque numbers.

What do you all think of this design? I am not necessarily chasing micrometers, but I would like something that is rigid and can make me some parts within a reasonable tolerance (maybe .005" or so).

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[ger21]

Add some 90° angles to the sides to stiffen it up, and shorten the sides if you can. If you only have 7" of cutting area, you shouldn't need it to be that high. And try to mount the bearings lower on the spindle. With the spindle attached at the top like that, you'll probably get quite a bit of flex when it's extended.

[peteeng]

Hi Preston - Your columns are going to wobble so as Gerry says they need stiffening. Especially with the "steel " comment your not near the ballpark for that yet. You had better look at some of the mill threads to see what they look like....Peter

[PrestonH]

Thanks for your feedback guys! I'll definately be working in some corner relief to stiffen it up! For some reason I was thinking that thicker steel and more bolts along the bottom would stop it from wobbling

[routalot]

Whenever I see a thread about somebody building a fairly tall machine I advise them to draw a tool in the collet and then to draw a line from the corner of the tool to the corner of the motor body.This shows the sort of slope you can work with and obviously,the distance vertically from the tool tip to the motor body shows the maximum depth from the top of the workpiece that you can reach.Rather than corner relief,GER21's suggestion of a stiffening angle section is good.A length of 3 inch X 3 inch angle on the outside of both gantry side plates would be a start.If steel is under consideration,buy a used Bridgeport and convert it.

[PrestonH]

Since this project is getting expensive, I would love to buy a bridgeport or another mill and convert it, I just dont have the space, which is why I wanted this machine which isn't 2000lbs and has a smaller footprint.

I guess the reason for the tallness is due to the large spindle motor I found. Ive been searching forums for days to try and find recommendations on good spindle motors that aren't super expensive and have decent quality and I found the one in my model on automationtechnologiesinc.com. I want something beefier and that can go to lower rpms, but it seems that those kind of motors are just massive.

[awerby]

The motors that power the spindles on a Bridgeport (as an example) aren't that massive; they're usually regular 3-phase motors about 2hp or so. It's the rest of the spindle assembly that starts getting heavy; the pulley cluster, quill, drawbar, etc. That's why they're set up so that the whole thing doesn't have to go up and down (as in your drawing) and just the quill moves.

[peteeng]

Hello Preston - Many people start these projects because they think a machine can be made cheaper then commercial machines. This generally is incorrect especially when it comes to cutting metals. I think you will find it easier and less expensive to contract your work to a machinist . In time if your volume gets up you then can look at correct machinery for your job. If your keen to make machines that's another matter. If your a Maker then start simple and learn about machines and their capabilities and costs. Study commercial machines and figure out why a mill is several tonnes of metal vs a router thats only a few 100kgs. There are many Makers on the forum that built MDF machines, used that to make an aluminium machine then used that to make a mill. Your first machine always has faults that you fix in No2 then you want to improve No2 so No3 happens and so on.... You may find an unfinished project or orphan machine if you look around, maybe a better starting point. Peter