CNC Router - Medium Size with Focus on Aluminum Machining

[cyclestart]

Of course not - I appreciate your warning and it's a good reminder. I'm expecting this to be a month and a months-long project with many sleepless nights. Here I have all the standard tools (cordless drill, brushless jigsaw, circular saw (with alum cutting blade) grinder, taps etc), but I have a friend with a drill press (or I'll buy one) which I know I'll need!

(forum ate my earlier reply somehow)
A woodworker's router can cut aluminium, even pockets and slots with the help of a jig. Handy thing to have around the shop in any case.
If the decision has been made to go DIY enjoy the journey.

[redding]

Thanks Cyclestart - I have a router, but I'd certainly need to load some of the milling bits into it right?.. I'll looking how to do that before I hurt myself haha.

So I have taken everyone's advice. Keen for some feedback. See the attached images

Key Changes:

1. Will update Z-axis to include the bearings on the fixed side, and rails on the spindle side. This will help keep the bearings more separate and gives me now a z-axis range of 160-170mm. I'm happy with that.

2. Updated X-axis rails from 1 ballscrew underneath, to two on either side of the base. I will put some 110x16mm or 110x12mm flat plate on top of the 80x120 Alum T-Slot to mount everything to. This allows me to move the ballscrew closer to the gantry side so there is better clearance. Later I will also add some kind of protective case over the entire side like what is done in the "ripper" build. This was the best spot which allowed me to the fit the motor without hanging over the edge. Happy for any other ideas!

See pictures for the rough concept.

Notes about the rest of design:

I wanted to keep the Gantry as it is. It seems simple enough to build without over complicating things. I will put some reinforcing bracks between the two 80x80 on the rear side later.
I decided to keep the connecting 40x80 t-slot which runs underneath. Most of these designs have something like this, and will hope it keeps everything more stable. I may change this to either 40x120 T-slot OR 20mm thick plate (also 120mm wide).

What do you think? And yes, took everyones feedback and will certainly finish the design before ordering parts. I have already ordered the NEMA34 motors, DMA860H Controllers and 48V power supplies (4pcs of each) so going to make that work. For ball screws etc I will get new ones to suit the design.

EDIT: I noticed some of my models didn't update correctly - ignore some of the basic errors (like bearing locations, plate not going all way to the end etc).

[peteeng]

Hi Redding - If you are to have the bridge underneath you may as well have one drive underneath. This saves the cost of the "extra" drive and associated electronics. Agreed the lower bridge (or saddle) makes it stiffer laterally but usually the bridge width also restricts possible motion at the ends and it limits the thickness or ability to support the bed underneath the table. eg for heavy objects or heavy plunging loads you need a stiff machine base.

I think you have costed up and made it more complex with no real benefits. Cheers Peter

[Sterob]

Hi Reading,
Where are you going to get your Aluminium Extrusion from?

[redding]

I think you're right Peteeng - I'll remove it - What do you think about the positioning of the ball screws on top of the 80x120 T-Slot Frame? I will cover it with a channel or something similar.

[redding]

Hi Reading,
Where are you going to get your Aluminium Extrusion from?

I'm getting from a supplier in China
This one: https://detail.tmall.com/item.htm?sp...=4220935717296

[cyclestart]

The edit function was working weird last time I posted and ended up as 3 posts. Oh well.

Some options for frame design Link --->Build your own CNC router Step 2: The frame
I like the idea of fully supported frame. Of course it can't be fully supported while sitting on saw horses so there's more structure to consider.

The CAD stage is the time to think about the max Z clearance required. My router has 5.25" between spoil board and the bottom of the gantry and the fixed plate on the Z reduces the clearance to 4". I've never regretted it and could have gotten away with less. If building a new machine today I'd be tempted to build the frame deep enough to do away with the gantry side plates.

Ball screw blocks are made in BK and FK design. The FK types may be a better choice for the Y screw.

[NIC 77]

I took the liberty of drawing up a couple ideas real fast. Nothing polished about it, it's just easier to draw it than to try and explain it. Please use all, some, or none of the concepts here, it's up to you .

I used the same 80x80 and 80x120 extrusions. Those are Rexroth size 25 rails and a 25mm ballscrew....simply because that's what I had some drawings of to modify.

To assemble this there would be many countersunk socket head cap screws throughout.





Yellow: Countersunk socket head cap screws bolt this into the T-Slot, leaving the rest of the plate to be drilled and tapped as desired.

Blue: The 80x80 and 80x120 extrusions

Orange: Chip guard....the idea is that any flying chips that can get over this will most likely have enough energy to miss the linear rails and ballscrew....I would be more concerned about getting chips in the ballscrew as the wipers on the linear rails are usually pretty good.

Red: Rest for your Cat Track / Drag Chain....

Hope this helps with your concept design....I really like the concept from LinuxFan of bolting aluminum plate together and filling with epoxy concrete...but I tried to go with the same extrusions you want to use.

Like I said, not trying to steal your thunder, I won't be offended in the least if you go a different direction. Just some ideas.

How long are your ballscrews in your design?

[redding]

This is fantastic NIC77 - Thanks so much for your efforts. I think I will use most of this design. Going to work on it this weekend and will show how it's looking! One question: On the Gantry y-axis, why do you bolt the rails into flat bar before the T-slot, and not into the t-slot directly?

X-Axis = 700mm Ball Screw SFU2010 (to buy) x 2
Y-Axis = 600mm Ball screw SFU2005 (brought)
Z-Axis = 250mm Ball Screw SFU1605 (to buy)

[NIC 77]

redding,

I should have read your post more carefully before I made mine.

So you already bought your motors? The reason I asked what the lengths of your ballscrews are is because I was thinking of doing some math to show you some theoretical differences that gantry weight would have on your design using a few different motors.

So what motors did you buy? I would need a torque vs speed graph for them (preferably a table of RPM vs Torque in Nm with 14 points) and the rotor inertia in kg*m^2 as well as the ballscrew lengths if you want me to do this.

[NIC 77]

On the Gantry y-axis, why do you bolt the rails into flat bar before the T-slot, and not into the t-slot directly?

I didn't know how much of a lip you have on either side of the rail compared to the T-Slot Gap. Using the wider aluminum acts as a bit of a washer.

[peteeng]

Hi All - Now your getting serious with the design I think this element needs sorting a bit. The drive nut needs to be integrated with the column or the bearing plate so it is a more direct connection. It will wobble a bit as drawn. Perhaps the column plate can be extended so the nut bolts direct to it. More thought bubbles needed. Peter

[NIC 77]

Hi All - Now your getting serious with the design I think this element needs sorting a bit. The drive nut needs to be integrated with the column or the bearing plate so it is a more direct connection. It will wobble a bit as drawn. Perhaps the column plate can be extended so the nut bolts direct to it. More thought bubbles needed. Peter

Good point. It is simply a conceptual mock up. But it can be improved. The flatbar it bolts into is 1" thick as drawn. But yes, it can be improved .

[peteeng]

Hi Redding - for your X axis you have 2x20mm ball screws. !6mm will be fine saves you some $$$.. and less inertia now your getting down to numbers...Peter

[redding]

So you already bought your motors? The reason I asked what the lengths of your ballscrews are is because I was thinking of doing some math to show you some theoretical differences that gantry weight would have on your design using a few different motors.

So what motors did you buy? I would need a torque vs speed graph for them (preferably a table of RPM vs Torque in Nm with 14 points) and the rotor inertia in kg*m^2 as well as the ballscrew lengths if you want me to do this.

This would be very very useful - I'd love to learn how todo do this also. Yes I have got these NEMA34 Motors "86HS11860A4" driven by DMA860 controllers (same as MA860).

Ball Screw Length (between Floating/Fixed ends - inner distance):
Y: 628mm (700mm total length)
X: 528mm (600mm total length)
Z: 185mm (250mm total length)
Rotor Inertia: 1800g/cm^2 which I converted to 0.00000018 kg/m^2
RPM v Torque: Attached - Similar motor (in RPM vs Nm @ 48V), but also attached this motor PPS with 60VAC. I think just refer to the similar motor graph will be fine.

[redding]

Hi Redding - for your X axis you have 2x20mm ball screws. !6mm will be fine saves you some $$$.. and less inertia now your getting down to numbers...Peter

This is a good idea, but if the difference between 16 and 20mm is $5 USD for a 700mm length, which is why I was just going to upside if I was going to do it anyway.

[redding]

NIC - One disadvantage of this design is I'll likely lose maybe 50-100mm in x-direction. I guess that's just one disadvantage of this solid design?

[routalot]

Maybe while you are playing with the suggested design improvements over the weekend,you can find advantageous locations for some of the components within the overall footprint of the machine.It certainly costs a lot less to adjust things within a parametric design program than to toss actual metal into the scrap bin.I would suggest you model a cutting tool in the collet of the machine and then check to see which projections on the Z axis mounting plate will limit your access into corners and recesses when you are machining.there may be gains to be had.We will be eagerly anticipating a look at the revised design.

[NIC 77]

NIC - One disadvantage of this design is I'll likely lose maybe 50-100mm in x-direction. I guess that's just one disadvantage of this solid design?

That's true. But on the other side you have the motor sticking out, so it doesn't make as much of a difference to the overall size on that side.

If you look at what I drew up it's similar to ThomConcept but with the addition of the chip guard. I am more of a fan of the high rail design as opposed to tall gantry risers. ThomComcept's design looks like it has tall gantry risers, but it doesn't, it's a high rail design, he just spaced his gantry bearings very far apart.

I really think that it's a good idea to look at what has been proven to work, in particular because you said that you want to cut mostly aluminum. Can you find some examples of designs that cut aluminum well and have really tall gantry risers like yours where the ballscrew is under the machine? It's not a rhetorical question...I don't know, have you found any?

I personally don't like anything driven from under the sides of the machine because it prevents the machine from being bolted down along the sides, which increases the rigidity on the long axis.

Also there is nothing preventing you from doing a dual drive under the machine if that is what you want to do. It's not what I would do, but it's not my choice. Ultimately, all anyone here can do is offer an opinion. Sometimes those opinions are good, and sometimes they are not.

Since it is so important to you to keep the footprint as small as possible....I suggest starting to draw in things like your drag chains, etc to see how this effects the size of your machine.

Designing a machine from scratch takes so much work and rework in the CAD files to get it right. That's why I've been saying to hold off on buying any parts until everything is finalized the way you want it. It's not a time to rush things.

You should check out the Avid CNC benchtop PRO design. It looks like they have made it to take up as small of a footprint as possible for the amount of travel. Ballscrews driven on the sides, as opposed to from underneath, and that would be my choice. I will have more to say on this later.



I have a bunch more things to say, but that will come over a few more posts. Hopefully my comments are helpful, and not too annoying. I'm certainly not trying to come off as a know it all, because I certainly don't know it all.

CAD CAD and more CAD
Order material
Shop for parts
Wait for parts
Hmm... need more tools,,,shop for tools
Cut material
Oops didn't think of that.... back to CAD
Damn customs lost my parcel.... shop for parts
Don't have that tap....shop for tools
Can't find that fastener local....wait for fasteners in mail
What ? I need to understand electricity ? I'm doomed !

Or at least that describes my projects

That describes mine as well. So true. I added the bold to CAD.

This is an interesting build as well, but has a moving table design.

[peteeng]

Hi Redding - Good time spent is finding a commercial machine that does what you want. A considerable amount of time has gone into it to get it to that development point. So this gives you a real point of reference. If it does what you want then copy it saves 100's of hrs of work or buy it...

Designing from scratch there are two paths 1) Design from the envisaged footprint inward and you usual end up with less working envelope to what you wanted 2) Design from the Z axis out and you get the envelope you want and the minimum size footprint to achieve this. Footprint and envelope usually conflict. Spend lots of time in CAD at a "rough" level then jump to a detail level when all the stars line up. Maybe 400 hrs plus into the work...

High rail designs are considerably stiffer then column designs....Peter