[Over Engineered]

Hi all,

I am in the middle of designing a 3 axis CNC mill/router and eventually a 4th axis to make out of T-slot extrusions, 40x80, 80x80 etc plus partially encased in 16mm thick aluminium plate. I need the machinable bed to be 1400mmX x 620mmY x 250mmZ minimum and have designed the table/bench/stand to be 2000L x 860W x 950H + lockable castors and levelling foot pads which should give me more than enough space for the machine and a little bench for items and the ability to bolt it down to a concrete slab eventually. I'm going to be making the main frame of the "stand" using 50 x 50 x 2mm SHS which will be fully TIG welded. It will have a draw for the computer/touch screen, a slide out section for all the electronics for easy serviceability, coolant tank for when I need it, place for a vacuum, tooling draws etc etc...

I'm planing to machine timber (with a vac head on just the 3 axis), some composites, acrylics etc. but mainly I'll be working with aluminium (6061-T6/T651, 7050-T7651, 7075-T6 etc...) and some small parts I want to make out of mild steel, 4130, 4140, 4340 and G5 Ti (if it's possible with a coolant feed)... It'll only be a small bit of steel alloys until I can build a dedicated 5 axis machine that will be solely for these materials... (Baby steps lol )

I do have some drawings of what I am thinking but I think I'm on the wrong path with the linear bearings and rails of my first design. I initially designed it with those 25mm DIA fully supported rails and trucks from the CNC shop, but I am unsure they are going to be rigid enough for what I want to do with the machine.

I am now looking at THK bearings and rails for increased rigidity?
I'm thinking:

SR35W's for the top of the X axis rails (running 1800mm long) and for the top of the gantry's Y axis.

HRW60CA's for the 2 outer, lower X axis rails and the lower Y axis rail.

Then maybe 2 HRW27CA or CR rails/bearings for the z axis.

Does all that sound good and solid??

I'm thinking ballscrews for travel. 2 on the X axis and 1 for the Y and Z axis'.

Would it be better to use rack and pinion for this machine because I want to use a lot of aluminium and the occasional steel alloy? I know I need it to be as rigid as possible if I want to think about milling steel at all. (The steel will be 400mm x 400mm x 20mm max steel alloy at the moment... And some 125mm max OD on the 4th axis)

The gantry risers (sides) will be 25mm thick aluminium plate mounting off of 4 trucks (2 lower tucks on edge and 2 on the flat horizontal) with the rear of the gantry being 25mm thick aluminium plate. The main section of the gantry will be 2 lengths of 80x80 T-Slot stacked on top of each other and bolted to the rear 25mm plate then the rest is housed in 16mm aluminium plate (front, top and base).

The Z axis will be 25mm thick aluminium plates and will hold a single 2.2kw water cooled spindle to start off with, with the possibility of upgrading further down the track if it doesn't have enough grunt.

4th axis... Still searching...

Steppers I'm still thinking about what would be the best for it along with drivers etc...

Basically I'm wanting to build it right (solid, beefy, rigid etc...) from the start rather than spending even more money later on down the track trying to make it better or wishing I had done it differently from the get go. Please pick my plans (or lack of, I'll get actual plans up soon...) to pieces as in if this isn't going to work well for what I want to do with it. This is my first machine and first CNC build so all the help, advice and info is more than welcome and much appreciated! I hope to get some progress reports up soon!

Cheers

Steve

[ger21]

4 rails on the X axis are going to be nearly impossible to align, and will bind.

A 2.2Kw spindle is not suitable for cutting steel.

Basically, until I see someone actually build a "router style" machine that cuts steel well, I'll continue to say it won't work.

How do you plan on bolting all these parts together to form the gantry, and then make sure it's flat?

[Over Engineered]

Hi Gerry,

Thanks heaps for the info!

I'm planning to have all the aluminium plate cut out, drilled, chamfered and the surface skimmed by CNC at a local engineering shop that has the machines to be able to do it far more accurately than I could ever do it by hand. With that in mind all the bold holes for the linear railing should then be accurate which should allow me to use 4 rails on the X axis without binding I was hoping? I am still unsure though...

I have read that a 3kw water cooled spindle is capable of cutting steel. I'll start with one of them instead if you think that has the potential to cut steel? I know I will be going a lot slower cutting speeds with steel and I honestly don't plan to cut much steel alloys with it. I would like to build the 5 axis machine using this machine if it's at all possible.?

In my design, the machine is a lot longer in the X axis so I can spread the trucks out further to get the 250mm height rigid with the outer edges of the trucks being a 500mm apart to form a right triangle from the tooling's highest point. Is this just wasteful or will this give some benefit?

I'm still not sure what to use for the stands top, but I'm thinking either silestone or essastone in 40mm then have that CNC surfaced as well to ensure its flat. I will shim that off the stands frame so all is level and flat using machinist levels etc then fill any gaps with no shrink epoxy so it's solid all the way along... Then build the machine off of that and will shim and epoxy if necessary.

Would that make it work better? Or is that still a far reach?

Thanks heaps for the help and info!

Steve

[Over Engineered]

I forgot mention... The top plates for the X axis rails that will be on top of the either 40x80 or 80x80 extrusions will be slotted for finer adjustments to hopefully eliminate any binding in those rails/bearings. Would this still be impossible to pull off? And if it is possible, would it give it any greater benefit over just running 2 rails for the X?

What is stopping a CNC router style machine from cutting steel alloys nicely?

Thanks for the info and help!

Steve

[bhurts]

Routers are to high speed for cutting steel. The lowest rpm of the router is about the max speed of a steel cutting spindle. They are also not designed with bearings and structure for cutting steel. Aluminum extrusion is not a good material to build a machine out of for cutting steel either. If your dead set on steel cutting then buy a milling head instead of a router. Also build the machine out of heavy walled steel tubing.

Ben

[Over Engineered]

Hmmm....

The 3kw spindle I'm looking at is capable of 0-24000 RPM and 0-400Hz? 3KW Water Cooled Spindle Motor 3KW Matching Inverter New 5 | eBay

I'm not using a router for this, it's a dedicated spindle, less runout better cooling etc... Or is what I'm looking at a router?


Thanks for the help!

[ger21]

It's still designed mainly for cutting wood. And the usable RPM range is more like 8000-24000. It will have very little torque below 8000 rpm. They typically don't have enough power to cut wood below 8000 rpm, let alone metals.

[Over Engineered]

Yeah I see what you mean now. 0 RPM meaning off and 8000-24000 being workable speeds... Chinese truth or Chinese whispers lol... :/

Can anyone recommend a decent, reasonably priced spindle motor that might have a chance? Ie reasonably being less than $1000 AUD for the spindle/head if that's possible? Might as well give it a chance all the way to the point. Or is there a kit for a geared head/spindle that I could buy/build as gearing it down should make it work at slower speeds and keep the torque maybe? Or is that just a stupid idea?

I might drop the Z axis to 210mm. That way I can still swing 200mm OD 6061 Aluminium nosecones on the 4th axis hopefully but the extra 40mm less will add to rigidity... It's mainly for aluminium but I would like to make a few guitars and amps with it also out of hardwood which is why it's a 1400mm X axis...

Thanks for the info and help!

Ps. The 5 axis mill CNC machine I'm planning is going to be heavy walled steel all the way and will be for alloys only.

This 4 axis machine is only going to be milling small parts for it out of steel. If I can get the cutting speeds down, do shallower cuts, fine final cuts and heaps of coolant it should be able to mill mild steel ok no? I'm talking 0.0003" cuts max?

[Over Engineered]

What about incorperating 2 x planetary gear boxs of say 20:1 and 32:1? This should give me 1200 rpm down to 37.5 rpm from running the spindle at 24,000 rpm. Then all the way down to 400 rpm and 12.5rpm. But that's just going off the motors rpm. Obviously I would work it off the rpm with the highest torque of the motor and gear down to suit. Would this still just be a complete waste of time and money?

I found this... http://m.youtube.com/watch?v=Z-_z0n1nRdk

But I can't find the build thread though? It is a aluminium framed CNC router cutting steel though but there is no mention of rpm, motor/spindle type etc. and it doesn't even look as though he was using coolant to cut it either. But it does make it look like it is possible. Granted you can't use 20mm + end mills but a 6-12mm 2-4 flute solid carbide Ti coated end mill which are designed to work at higher speeds should do the job ok though shouldn't it?

Are the THK bearings I'm looking at not suitable for this application? The HRW60CA's have a 120mm wide rail with a 200mm wide truck so the distances would make me assume that they would be the most rigid out of the THK's for sideways load (vertical load for how I will mount them) and due to their size I might get away with just running 2 of them and not the top HrW27CR's (the idea of them though was to increase rigidity for the Y axis for less slop givern the weight of the gantry, though I'm still unsure if it is possible to run the 4 rails even with CNC cut 16mm aluminium plates?).

What bearings would you run on a heavy walled steel tube CNC dedicated for milling alloys?

The parts that I want to make out of G5 Ti and 4130, 4140 and 4340 are only 200mm L x 60mm Od max and will be on the 4th axis and time is not an issue. The plates and brackets I want to make for the 5 axis will all be out of mild steel so it's heaps softer than others. Still dreaming?

[ger21]

I think that's this machine:
http://www.cnczone.com/forums/cnc-wo...minum-cnc.html

[Over Engineered]

Yep. That's the one! Thanks!

Thoughts on the THK bearings? And gearbox?

Thanks for the info!

[Over Engineered]

I should also mention that every fixing will have loctite on it be it blue or red depending on the parts that's being fixed... If that makes any difference to anything at all... :/

[ger21]

I forgot to mention that it looks like he's using a mist coolant in that video.

There's absolutely no reason to use 4 rails/axis. And anything over 25mm is far more than you'd need.

As for the gearbox, I don't think they can handle that rpm. I just bought some 21:1 gearboxes, and they're rated at 3000 rpm input.

Your best option is probably a belt drive spindle, or a spindle designed for milling.

Belt Driven Spindles | Cartridge and Block Spindles | Gilman USA

[Over Engineered]

Awesome! Thanks! I just spotted the coolant tank in the build thread. Looks like a good feature.

I get what your saying about the 4 rails. I think I might downgrade/upgrade the X axis rails to THK HRW35CAM's instead. They're 107mm wide rails with 120mm wide trucks so that width will (should) help any side wobble from the Y axis movement on the gantry. Plus the CAM's are stainless which is an added bonus. So it'll be just 2 rails on the X and 2 either ballscrews or rack and pinions, 2 rails on the Y with 1 ballscrew and 2 on the Z with 1 ballscrew. That should cover that.

Hmmm... I didn't think about the max input rpm with the planetary gearboxes. What about incorporating a Sieg X2 or X3 geared head/spindle? They are cheap enough but the question is quality. I know a lot of people have used the for a convert CNC machine so they must fair ok. Plus getting one of these will leave enough change for a 2.2kw water cooled spindle for timber work which is a plus!

I couldn't find any prices on the Gilman USA site but it looks high quality (?) and is definitely an option if the price is right. I can always upgrade if it starts to make real money lol...

For steppers I'm thinking these (but probably not from this company...)... https://www.damencnc.com/nl/componen...er-motors#p784

2 x Nema 34 Closed Loop 8.0Nm High Voltage steppers for the X axis (16.0Nm on the X total), 1 x Nema 42 Closed Loop 20.0Nm High Voltage stepper for the Y axis and probably a Nema 34 Closed Loop 8.0Nm High Voltage stepper for the Z axis. Still thinking about the 4th axis but I can leave that until I get this thing up and going. This should be enough grunt for what I want to do with out bogging down too much if at all, hopefully??

Thanks for the help and info!

I'm hoping to get some build shots up soon!!!

[ger21]

Choosing the proper steppers requires knowing how much weight your moving, how fast you want to move it, and how quickly you want to accelerate it. You need to do the math to find out how much torque you need, and see if those motors will work. Steppers lose torque as rpm's increase, so you need to make sure you have enough torque at your max acceleration rate at the max velocity you want to have.

[Over Engineered]

Very true! I need to finish drawing up the design in sketchup to work out the weights though. Working on finishing the new rails/trucks drawings and the gantry at the moment... Slowly getting there... Looking at other peoples CNC's of this style they should be in the ball park, though I haven't seen anyone running the 20Nm Nema 42's? Only the Nema 23's and 34's. Will soon find out the weights etc.

I cut up most of the steel for the stand/trolly/table/etc... Just need to pick up some 75x50 or 100x50 x 2mm duragal for the top section on Wednesday so I can hopefully start welding it up next weekend it's begun! Need to get quotes on bench tops this week sometime too. I'm thinking of doing a skim coat of self levelling epoxy to ensure its flat if they are really that good though. Or just go with my original plan of shimming and no shrink epoxy in between... Either way it will be a solid and true foundation (hopefully lol)...

Thanks for the help!

[ger21]

20Nm = 2800oz-in.

Very few machine here use 960oz motors, and almost all others use smaller ones. If you really read that much power, I think you'd be much better off with smaller servos, which can use a belt reduction to achieve the same amount of power in a smaller package.

[Over Engineered]

Good point. I need to get this plan finished so I can work out the physics before ordering (hopefully by next week... There's a 3D printer show next week so might be able to get some good deals on stuff if I get my arse into gear! Ha ha). Just finishing up the gantry... Nearly there............

I was thinking of just going direct drive with the servos to ballscrews to eliminate human and material errors when using belts (eg wrong or uneven tensions, wear, slipping, etc which could/may cause binding in the x axis since there will be 2 ballscrews) still not sure though. Does anyone use oil soaked, greased or dry gear boxes instead of belts? It's pretty hard to mess up when setting the backlash with gears so I would prefer that if I have to "gear" down if possible to keep it simpler and ensure accuracy isn't lost with a simple mistake. Just trying to protect the machine from myself ha ha ha! Using belts or gear boxes will allow a slightly lower profile machine on the ends using my design though which would be good on that front. I hope to get some figures soon!

I haven't even scratched the surface of ballscrews yet either... :/

Thanks for the help and info!

[Over Engineered]

Picked up the rest of the steel for the bench today ready to start welding it up this weekend!

[ger21]

Does anyone use oil soaked, greased or dry gear boxes instead of belts.

Not with a screw drive. Some use planetary gearboxes with rack and pinion drive, but good, low backlash planetary gearboxes cost $500-$1000 each.

Belts are far easier to use, and shouldn't have any of the issues you're worried about.