First Build-Steel Gantry CNC - Comments on design wanted

[olaff]

Hi everybody.
Im new on the forum and have decided to jump into the world of CNC building. I originally was thinking about buying a ready built CNC router, but the quality of the ones with a reasonable price made me change my mind.

I have been lurking around in the shadows for a few months reading build logs, trying to suck in as much info as possible from the various builds in here. Im impressed with the quality and the amount of work you guys put into the projects, and it’s a lot of knowledge in here.

So now is the time for me to kick off my own build, inspired from quite a few different builds in here and other forums. I have an engineering background, and have a workshop with a manual mill, lathe machine, saw etc. so I have some equipment to help me out at least.

I have quite a few of the parts collected already so the size is fixed and Rail size will be 1300x950x500 (I want to get approx. 1000x700x220 travel out of it)

Im planning to mill wood plastics and aluminum. I want the travel on the Z axis to be around 22 cm as im toying around with a bit of electronic enclosures and other things that can be this high.

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This is the parts already collected and taken into the design: (most of it from BST automation)

Steel tubing 80x80x3mm
Various 10mm steel

X axis: (Gantry will ride on this)
Ballscrews: 2 x RM1610 L-1200mm with BF12/BK12 angular contact bearings
Rails: 2 x HIWIN HGR20 1300mm with HGW20HA blocks

Y axis:
Ballscrews: 1 x RM1610 L-900mm with BF12/BK12 angular contact bearings
Rails: 2 x HIWIN HGR20 950mm with HGH20HA blocks

Z axis:
Ballscrews: 1 x RM1605 L-400mm with BF12/BK12 angular contact bearings
Rails: 2 x HIWIN HGR20 500mm with HGH20HA blocks

Motors:
All axis will be driven with Leadshine NEMA24-3NM Easy servo (closed loop steppers) 60HS30-EC-1000 with HBS86 drivers.
(This should be approx. the same as the ES-M22430 motors with ES-D808 drivers I believe?)

Spindle: Watercooled 2,2kW with VFD from BST

Limit switches: NC inductive proximity sensors. I have not decided on how many an where to place them yet.

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I have not purchased belts and pulleys for the ballscrews/motors yet, but it will be 1/1 ratio, and I guess 20T pulleys.
I am also missing the powersupply and the other electronics still. I Want to get the build started before I look into that
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Over to the design: I have been playing around with Sketchup for a few months and this is the design I have landed on in the end after a lot of scrapped ideas.. Im quite sure its overbuild, but thats better that the opposite…I was hoping to mill aluminum with a good result.

As earlier mentioned I want a travel on the z axis on about 22-23 cm. This have caused me some headache in the design, trying to limit the cost. Ideally I would like to have a aluminum plate on the bed, but that have to wait for a later upgrade….So for now I will try out with a torsion box made from plywood for use when milling plates/sheets and remove it when I need the full height.
I also extended the rails outside the bed and made a removable last section of the bed for milling end of plates or for fixing a 4^th axis.

The main construction is made from 80x80x3mm steel tubing, and all the other part is 10mm thick steel plate. As Its not so easy to get parts laser cutted around here, Im trying to keep the construction simple and easy to fabricate. Im thinking to use epoxy to level the rails, or I might use shim if its not too bad out of level

My biggest concern is the weight of the gantry at the moment. Its all build from steel, and is currently calculated to 90 kg. Im not sure if that will be a bit too heavy?
Im considering to redesign the Z axis for 20mm Aluminum to reduce the weight, but its not so easy to get aluminum in small quantity around here..

Here are some pictures. I was hoping to get some comments and hopefully someone can steer me away from some possible pitfalls and bad ideas…:)

[Clive S]

Welcome to the forum Olaff Its nice to see that you have taken the time and read a few of the build logs. To my eyes its looking good I think you might have to beef the Z plate up a little to be able to have 220mm under the tool but the guys on here will chime in as usual.
Also don't buy any electronics until the frame is finished as a lot can change over time.

[Boyan Silyavski]

-Clive is right. Additional braces are needed at Z. Take a look of build n1 in my signature, i am sure you have seen it but look again at the Z. Its just a 1-2kg more

-I would not bother so much for the 90kg.
First of all the so called speed you need at home is a fiction, so i would happily make a reduction if i am concerned with gantry weight.
I would suggest also for the price you are to spend on the closed loop servos to take a look also some servos. Just wrote about that in my build log #182
Just have in mind they are not tested yet. The Chinese i mean. Price is great though and it took me a lot of time to find them, not to speak about the emails.

-i like your gantry sides. I had to cut a windows on mine and decided exactly the same as you have drawn it will be better. Good that my girfriend tightened the bolts as i could not fit my hand

I just love this trend of "real" DIY machines. God, how i hated the crap especially in forums.

[njhussey]

Welcome to the forum Olaff!! This is one of the most thought out researched and designed starts to a build log I've seen for a while.

Looking good, as Clive and Boyan said the Z looks a little flimsy and could do with some bracing/stiffening if you're going to use steel. I can't help thinking that a couple of lumps of 20mm Aluminium tooling plate with milled (you say you have a manual mill) recesses for the ballscrew and carriages would be a simpler option and you wouldn't have to worry about distorting the front plate welding the rail supports on....just a thought.

[olaff]

Hi all and thanks for your comments.

I suspected as much that the Z axis was the weak link.
I have had quite a few variations of the design that whas more stiff, but got to concerned about weight and scrapped the ideas. Then I started to think about Aluminium instead...

When it comes to the motors, I choose the closed loop steppers mainly to prevent racking on the X axis. (since im a beginner at this, its one of the main concerns)... It was not so much info to find on the net, but found some people that was very satisfied with this type of motors. I negotiated quite a good price for the set of motors and drivers, so I decided to just go for it. I understand that this still is just a stepper, but hope it will work good on this type of machine.

A few more questions as im not so familiar with aluminium
-Do I have to use Aluminium Tooling plate, or would 20mm 5083 Aluminium be OK? (Plate used in ship building industry)
-Does using Alu plate still require additional bracing of the Z axis, or is this much stiffer in it self?

I will have to work a bit more on the design of the Z axis, and I guess finally make a descision on Steel or Alu.

[njhussey]

A few more questions as im not so familiar with aluminium
-Do I have to use Aluminium Tooling plate, or would 20mm 5083 Aluminium be OK? (Plate used in ship building industry)
-Does using Alu plate still require additional bracing of the Z axis, or is this much stiffer in it self?

Tooling plate is best as it is ground flat so you don't have to do as much machining. With standard Aluminium plate it's not quite flat so wound need machining so the rails were exactly level with eachother. No Aluminium plate if it's 20mm thick wouldn't need additional bracing, there are loads of examples on this forum of machines with exactly this. I wouldn't get hung up on weight as I've got a 40mm thick front plate hanging off my Z axis and it's no bother at all. As I said somewhere else when I was putting my 20mm thick aluminium plate on the base I had my machine vertical and just for a laugh stood on the gantry and turned the X axis ballscrew (both linked with a belt) pulley with a thumb and two fingers and easily lifted my weight (19.5 stone) so don't get too hung up on weight, there's a huge mechanical advantage when using ballscrews!!

I will have to work a bit more on the design of the Z axis, and I guess finally make a descision on Steel or Alu.

Looking forward to seeing your new design....