[Rezort]

Gday all,
I have been reading these forums for over a year now and have recently decided to stop dicking around and build my own cnc machine.

My aims:
300x300x50 work area
Moving table design
As accurate as possible (without blowing my budget out of the water)
Able to mill wood aacrylic and thin alumnium sheets (1-3mm)

My current plans are built around:
60x30mm alu extrusion from Profilium - Aluminium profile | Aluminium extrusion | Framing Systems | Machine Guards (half the price of other retailers I could find).
12mm aluminium plate for the z carriage and spindle mount plate.
20mm fully supported linear rail for all 3 axis. link.
SBR20UU 20mm slotted linear bearings. link.
16 X 4 Acme Trapezoidal Screw. link.
Nema 23 Stepper Motor. link.
400w Chinese Spindle. link.

Now some questions..
Are the nema 23's suitable for this project?
I also found some Nema 23's with dual shaft link, what is the difference and is it worth the extra 20 buks per unit?
Is that little 400w spindle going to cut it? short of buying a 1-2 kw spindle should i perhaps be looking at mounting a hand router? (to do thin alu)
With such a short z axis (50mm movement) is there a better option over the stepper and screw (linear actuator)?
Can anyone recommend a decent stepper controller (prefer 4 axis for future mods)?
I am having trouble envisioning my z axis set up, Im guessing (unlike my linked plans) I need double the clearance (100mm) required under the gantry bottom support to achieve my 50mm workable z axis to allow the spindle plate not to interfear with the movement.
Lastly looking at my sketchup screen grab is there anything that needs changing/is not going to work? (not all gantry brackets drawn in).

I know thats a fair few questions but I would love some advice on my plans.

- Chris

[Rezort]

So after several painful hours last night TRYING to find a source for 16x4 anti backlash nuts in australia.. I have decided to downgrade to 12x3 acme screws since I did manage to find a supplier for anti backlash nuts in that size.

I also stumbled across this.
Stepper Driver Full Kit
I haven't been able to find any reviews on this stuff so does anyone know if it will be suitable for what I have planned?

[zolpix]

Hello Chris,

I would recommend Homann Designs for your electronics, which is in Australia. I brought stepper motors without dual shaft which i now regret because with the dual shaft motors you have the option to fit encoders for position feedback later on. How do you plan to mount the z axis motor, i cant see enough clearance for it in your drawing and the brace for the gantry looks a bit weak but it is hard to picture without the dimensions i assume it is about 700mm. You did not mention your budget, but have you considered using the Chinese c7 grade ballscrews? if carefully designed the screws will only need to be a big as their travel not the whole length like you have drawn which will cut down the cost.

[Rezort]

Thanks for the reply Zol,
I really did rush into this post so Im stepping it back and starting to all from scratch (taking your advice on board).

Aim: Milling Acrylic Sheets, ABS, Hardwood and some light aluminium sheets (3mm max).
Cutting Area: MIN 300x300x50mm

Frame: 30x60 Aluminium Profile (filled with a sand/epoxy mix where I can)
Controller Kit: Homann Designs (inc 3x 387 steppers)
Rails and Bearings: SBR16-300mm Linear slide rails and Ballscrew RM1204-350mm- c7 (end machined) (might be a gamble in quality but the price is soooo much cheaper than anything else I have found)
Spindle: Probably just an ozito palm router for my first job or 2 (cutting room plaques from the ABS product above)
Budget: ~$1200

Here is the sketch up of the table design (very simple) green is where I hope to fill the extrusion with the sand/epoxy mix to dampen vibrations.
One questionn here, the red areas where the ballscrew feeds through the front and back of the table, can I just over size drill them out (20mm hole) or do I need to use some sort of bearing block in there?



Yes yes first one I attached had the rails not the slides attached to the table >

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Here is the Y axis minus the gantry and table (which needs to be slightly larger). I am worried about the 850mm ballscrew and the dimensions of the end supports (in red), I couldn't find the dimensions anywhere and i have no idea how much of the ballscrews are machined at the end.
I guess its no huge issue, I will just have to wait until parts arrive and make some minor adjustments.

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And here is my X axis design 100mm (probably over kill but rounded the supports out to 400mm) clearance from the table top (table top + sides of y axis = 76mm).
Around 119mm space between the 2 X axis rails. Again im not sure about the the ballscrew end supports but yeah we will see.

Any thoughts / comments so far?

[Rezort]

Next up the design for the X axis plate.
Sorry about the dimensions but basically its a 250x150x10mm plate with 2 sets of 10mm risers under the bearings.
The ballscrew nut is attached to a 50x30x2mm piece of aluminium tube. Is this going to be enough to secure the ballscrew nut?

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Here it is mounted on the X axis.

Oh also forgot to mention that the set of bearing blocks on the front are for the Z axis as I am planning on mounting the actual rails to the Z plate so the distance between the cutting tip and the bearing block is as close as possible when the Z axis is raised to its max height.

[Rezort]

Finally the Z axis..

Again im not 100% sure on the driven/non driven end support for the ballscrew, what im thinking is a simple diy pillow bearing (see pic 1) on the non driven end and probaby some sort of flanged bearing for the driven.

Obviously the stepper motor will have some sort of bracket or proper standoffs, it all depends on how much of the ballscrew is machined.
Also had to add a 5mm spacer ontop of the ballscrew nut so I could attach it to the X axis plate.

[Rezort]

X and Z put together.

Im not sure I like the distance between the X support rails and the front of the Z plate, its already 130mm and thats without the router/spindle and mounting plates. Is this too much?

My other option is to move the back Z support upright and place it infront of the first but im not sure this will help either.

[Rezort]

And lastly but not leastly the whole lot together.

I added some 2mm aluminium supports to the gantry uprights which may end up being 3mm depending on how rigid the whole thing is.
Also added 30mm length of extrusion between the bottom of the uprights.

[zolpix]

If it was me i would use at least 16mm screws for x and z axis and 20mm for the y. I have a 20mm on my x axis at 1200mm and it is a bit flimsy. Just some notes on your cad drawings:
the bearing blocks are drawn backwards, motor attaches to floating bearing block. You will want to make a decision on what spindle you are going to use, will save alot of design time. Box section for mounting the ballnut not the best idea imo, i would use plate at least 10mm thick, with a press fit hole to locate the ballnut and then drill the holes around that to mount the flange. I think that the extra upright for the gantry is not adding strength, if you put an piece of the ali extrusion at 90 degrees between the one upright and the frame you would get much more strength and save on material. both sides would be even better. An alternative way to mount the rails for your x axis is turn then 90 degrees, this will bring the z axis mounting plate much closer to the gantry.

[Rezort]

Thanks for the comments Zol, I did think 16mm might be a bit light for the Y axis, I will look into getting a 20mm instead.
Hmm I thought I had the bearing blocks the right way round but I guess not.
I was originally going to use a piece of angle steel (or aluminum) for the ball nuts, but thought it might be better to support the entire length of the nut.

Yeah the spindle is a pain, Im pretty certain I will grab a cheap Ozito for a while then probably upgrade a bit.
If you think I can get away with cutting out the second gantry upright it would be great, when you say 90 degrees between the frame and the up right do you mean on the inside of the upright or the side?
Hmm thats a good point about the X axsis rails, mounting them on the top and bottom of the extrusion would bring my Z in, but the extrusion is only 30mm wide and im pretty sure the rails are 45mm.

[zolpix]

Hi Rezort,
Bearing blocks go like in this picture: https://d2t1xqejof9utc.cloudfront.ne...cd6/medium.png
I think the steel angle would work well for the ballnuts, i plan to use 10mm angle for my machine. With the angle being anything but flat though milling it flat or filling with epoxy would be a good idea if you can. I don't have any experience with the epoxy but have read some great results on a few forums.

For the uprights, i meant the side kinda like this: http://www.exhibitanddisplaytruss.co...fl-6_large.jpg

Im just pulling images off google, i don't have cad on the computer im using right now. Here is a picture of the standard (im 99% sure) dimensions for the rm1605 screw:
http://i01.i.aliimg.com/img/pb/441/5...555441_165.jpg

If you also turn the two 540mm extrusions for the gantry 90 degrees you will have 60mm for mounting the rails.

[Rezort]

Cheers again zol. Not long ago I got some 10mm angle steel for a retain wall it was a pain and a half to drill but it is crazy strong.
Ahh right I see what you mean about the supports not sure how I would bolt them on(without buying an over priced joiner) is the only thing but there must be a secret with the extrusion.
Yeah I finally twigged on about rolling the entire rail and support my only concern was the extrusion flexing under the weight of the z axis if I rolled it.

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So i sketched up an alternate X axis, but i do have a few concearns..

Attachment 209526

I used 2 pieces of 10mm angle steel to attach the now rotated X bearings to the Z axis plate, 10mm is probably over board and if I could cut that back a bit it would make a few line up a bit nicer.

I dont like that the ballscrew is no longer centered on the uprights, thats going to make cutting the holes and mounting the blocks and motor more difficult. I am also worried that the weight of the Z axis and router/spindle is going to cause the Z axis to flex in the middle. Additionally Im not even sure that the linear rails are going to cope with weight pulling from the side like that.

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And another idea.

Attachment 209570

Support rails are another 20mm taller but I think the mounting for the whole X bearings and Z plate looks alot better.

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Ok so I am now trying to fix up my driven/non driven support bearing thingys, quick question.. Generally if you order 300m rail and 350mm ballscrew it should fit together like draw below? I see to have about 2mm of clipping when trying to go off the supplied measurements. It just seems a bit silly if they dont fit properly.

Attachment 209586

Noob question I know but im a bit confused.

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SO ran into a pretty major issue.. Iain over on another section of this forum pointed out that the profile I have listed is pretty light weight compares to the 8020 branded stuff many of the folks in the US use.

A comparison
My proposed material:
60mm x 30mm (2.36" x 1.18")
weight: 1.4kg/m (3.15261lb /m = 0.96lb/f)
Moment of Inertia
X:19.08 cm4 (0.46"^4)
Y:4.65 cm4 (0.11"^4)

8020 Stats (1530-LS):
1.5" x 3" (38mm x 76mm)
weight: 2.034lb/f
Moment of Inertia
X: 1.39"^4
Y: 0.31"^4

Now profile is hard to get a hold of over here so I am a bit stumped, I did ring 8020inc Australia and the quoted me something in the region of $250 for 4m of the stuff, which is just straight up too much money for the 6 odd meters I am going to need.

I just dont know if I should gamble with the profile I linked and hope its strong enough or look for other options...

[Rezort]

Just for reference AME systems equally priced and they sell per meter (vs 6m only from profilium).
80x80 $83pm
40x80 $51pm
40x40 $26pm

60x60 $38pm
30x60 $25pm
30x30 $15pm
(all excluding gst)

Mate on the phone who was super helpful said that he knows 3 or 4 people who have made smaller cnc machines from their 30x60 stock so maybe its worth the gamble after all.
Since I can get it per meter means I can make the X axis rails (and maybe the uprights) out of the 60x60 which was my big concern in regards to flex.