[Spk64]

Well I have been lurking for a while in the forums and have started to think seriously about building a CNC router. This will be a small machine aproximately 24"x24" x 5" travel. All aluminum 8020 extrusions. I am trying to get as rigid a machine as possible with the 8020 and aluminum. Being smaller in size this works in my favor.
Full Specifications are as follows:
Z Travel 4.9"
X Travel 22.25
Y Travel 25.5"

Hwin LG 20 Rails (2 per Axis)
Hwin LGH20 Cars (4 per Axis)
RM1610 Ball Screws each axis
2 Ball Screws and steppers Y Axis

8020 COnstruction
- 3030 Uprights and Main Base Sides
- 1530 Cross Bars
7075 Aluminum Mounts and slides
Gecko G540 Drive

I would like some feedback on my design to see if there is anything you guys would change. I do plan to cut aluminum, wood, plastic. May upgrade spindle down the road but for now going to throw my PC 690 on it.

Link to PDF with interactive 3d View of the machine.

[kevincnc]

Looks solid! I think your linear rails are bigger than necessary, but can't hurt. Nice work.
Kevin

[steve123]

I like it Steve (great name by the way). I think you can easily get by with 15mm rails. You could have some trouble getting enough room for the Y ballnut with smaller rails though.
I like the skin on the back of the gantry. That really takes care of vertical sag, and horizontal movement. I think the beams across the gantry are too small however. Those look like 2x3" or something. I would go with 3x3" at least. The extra weight won't matter. Also add more bolts to the back skin.
Also, take care how the skins on the sides bolt into the back plates that the fixed bearings are mounted on. Those fixed bearings will be taking a lot of load push/pulling the gantry. Those skins are what keeps the back plates from flexing. Have lots of bolts near the top or add some pins to be secure.
I see that you have cutouts on the sides of the bottom of the front Z plate. You actually could use more strength there. Consider adding that material back, and adding beam plates to the sides, right up against the router holders, with bolts through the Z plate into them. This would make the Z less prone to "nodding".
Consider widening the stance of the X cars. The router is hanging out in front of them.
Last of all, Consider filling the insides of ALL of the beams with an epoxy/sand mixture (EG). Aluminum doesn't dampen vibration, so EG would help a huge amount, IF you could get it in there. EG has 10x the damping as cast iron.

This is a very clean design. Good luck!
-Steve

[Spk64]

Thanks for the suggestions. I have taken your advice on most everything.
LG 20 Rails and Cars
I originally was going to build a larger machine but opted to start out a little smaller. Decided to keep the same rails and cars sized the same as I can reuse in the future if I decide to go larger.
1530 Extrusions on Gantry
Originally when I sized the 1530 (1.5x3") extrusions on the gantry I looked at the deflection and felt it was more than adequate. Then I went back and reviewed again with a point load (not even load across beam) a supported ends vs fixed. This did show more deflection than what I would like to see. Now just looking at a single extrusion of 36" .0014" deflection with 200 pound point load. Should not have any problems with that.
Epoxy Grouting Extrusions
I had never heard of the epoxy grouting to stiffen up a machine. Did a little quick research and yes, I will be doing that with all the 3030 extrusions. There is approximately a 2" square center section that should not be to difficult to fill.
X Axis wider Stance
Increased from 6 to 8"
More of my own changes
Increased stance on cars on Y axis 1".
Increased overall width to get a full 24" width, now ball screws and rails are same for both X&Y axis.


I also updated the interactive 3d PDF with all the changes.

[steve123]

I really like what you have done. This looks really solid. The EG will make it stiffer, but it's the vibration damping it provides that will really help. That's why you want EG everywhere you can. The recipe for grouting is 90% play sand, 10% epoxy by weight.
Three more things I can think of are:
1. You may have an issue with the aluminum extrusions not being strait enough for your very precise profile rails. There can be warp in extrusions. You may need to mill one face flat. Just something to be aware of.
2. The troughs that your x rails run in might want to fill up with chips/shavings. You need to think of ways of covering them, or having barriers attached to the sides of the gantry.
3. You haven't mentioned stepper motors yet. You need to be careful to get motors with low inductance. I think this one is good: 320 oz-in 2.8 mH Nema 23 Stepper Motor, 3/8" Shaft | CNCRouterParts

That's all I can think of. Very nice design.

[Spk64]

Yes, aware of the extrusion variations. Will just have to see how the parts look when I get them. Machining is no problem.
The chips in the "trough" area is my concern also. I have debated keeping the side shields in place or removing them. They are open on the sides for chips to fall through but can still gather on top the extrusion.
I had already changed my BOM to use motors and cables from CNC Router Parts.

Steve

[Spk64]

I have further refined the design. Ball Screws to the sides with covers to reduce chips. Overall Design simplified some and added additional strength. I have somewhat now committed to building a cnc as the ball screws are being ordered along with some of the other components. Looking forward to getting the build underway. Lots of machining on the manual mill first. Will put my old knee mill to work soon. All the detail drawings and assembly drawings have been completed.
Attachment 193990

Interactive PDF updated to latest rev.

[Spk64]

Should I do something like this to further protect the ball screws from chips?
These are Brush Seals from McMaster. 1 on each side with the ball nut attachment running between.
Attachment 194062

[pughdxk]

I think your linear rails are bigger than necessary

[aarggh]

Anything you can do to avoid getting dust buildup in bearings/rails is advisable. I use some long brush material for my machine to help deflect dust and keep the trucks clean.

Dust really clags things up.

cheers, Ian

[Spk64]

Yes, chips everywhere in the guides and screws are my fear looks like I will take as many steps as possible to keep them out.

On another note I have begun the process of sourcing my parts and material. Jumping in a little quicker than expected when I checked automation overstock on the cars again and they only had 1 left. Quick design change to the wide version and placed my order to insure no more design changes.
Ball screws are all ordered emailed Chai on the special lengths and his price was great so placed that order also.
While I was at it went ahead and ordered the Mic6 and CRS.

[Spk64]

Brought home the extrusions today. Purchased from my place of employment at a nicely discounted price over ebay 8020 garage.

[Spk64]

Started cutting some material. I had a 24" square piece of 1/2" Mic6 on hand. Rest of material should arrive next week. Bearings for the ball screws arrived, very quick from west coast and USPS.



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[Spk64]

Started building parts today. Fired up my trusty Millport that I have had for 30+ years.
Sorry for the terrible pictures, Need to start using my real camera for these pictures.

Now bringing all the parts to length.

Next up drill all the holes.

Adding the counterbores.

Need to bore out this hole.

Finishing the bore for the router mount.

Next up tap all the holes. Tapping head makes quick work of this. Seconds for each hole

All the 1/2" thick parts are machined except for some profiling.

Fedex made a saturday delivery with my materials. Cool.

Need to cut up the newly arrived materials next time.

[steve123]

Nice rapid progress! The pictures are OK. They could be better if you can hold the camera steadier (or have brighter light), and not have the light shining at you.

[Spk64]

That is what get for trying to take a picture with iPhone while cranking handles.


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[Spk64]

Ordered the rest of the supplies today.
Controller and motors from CNCRouterParts
Misc 8020 hardware
Motor couplings.
Rough cut all the stock that arrived yesterday. Now back to the shop to machine everything.
But may wait until some of the parts arrive to confirm my models match the parts.


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[Spk64]

Not much activity today. Did do a test fit of some the extrusions.
Gantry is going to be pretty heavy for a 2x2, but that is what I wanted.
1st ball screw arrived. I had ordered the Z axis screw to see how the quality was. Seems good. Bearings fit well and by hand it feels smooth. Need to check it closer for back lash later.

[Spk64]

Finished squaring up all the parts tonight. Ready to add all the holes now.
Expecting a large shipment of parts tomorrow, which I need to confirm the dimensions before machining.


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[Mason8DF]

All the detail drawings and assembly drawings have been completed.