[stevensturgis]

I have designed a new cnc for my shelf and would like feed back before I start the build. all support is welcome.. what do you think. any design changes i should make?

[stevensturgis]

Carriage design steel or alum.

[awerby]

The Y axis gantry beam needs to be a lot thicker in the vertical dimension. All the strength it has is in the horizontal, but the tendency to sag and vibrate is nearly all in the vertical. Make it 4 times as thick, and it will work 4 times better.

[stevensturgis]

I was concerned about the weight. Do you think the nema 23 450 oz steppers will work well? i can only find steel square tube in 2 x 5 .25 thick wall if it needs more i will have to re engineer the gantry. I only have room for two 2.5 in tubes and the ball screw on the axis. do you think that would work well? I don't want to under size that axis.

[SteveWill]

I like it. Also if you put in a 2 inch long bit, Do you have enough height/travel room, the Z rails will hit the Z axis stepper motor plate as a limit.

[stevensturgis]

new thoughts Make a square beam two pieces 2 x 5 ,24 tubes steel and plate top and bottom with 1/8 " plates

[stevensturgis]

the rails are 500mm. 19" the suppoat bearings are 8" apart I should get 11" travel - 2" bit total 9" I don't know if thats good or not. the new design would put the spindle collet at the bottom of the gantry.

[greggv]

Myself, I'd like to see the X axis bearings futher apart, more rigidity, and less rock.

[stevensturgis]

greggv
I thought about that too. how much would you suggest?
the more i move them apart the less traveled i get im also limited to 8" plate alum. do you mean wider gantry or wider z carriage to increase the bearing separation.

[awerby]

I was concerned about the weight. Do you think the nema 23 450 oz steppers will work well?

[It's hard to say without knowing more about your system: how much voltage you're supplying, the inductance of the motors, the pitch of the screws, stuff like that.]

i can only find steel square tube in 2 x 5 .25 thick wall if it needs more i will have to re engineer the gantry.

[That would be a good idea, since it won't work too well as it is. Turning it 90 degrees so the long side is vertical would help. You can put the rails on the front instead of on the top.]

I only have room for two 2.5 in tubes and the ball screw on the axis. do you think that would work well?

[No.]

I don't want to under size that axis.

[Then use one 5" tube instead of two half that size, and run it vertically.]

[stevensturgis]

I think i have the x and y axis mixed up

------------- this is y i guess along gantry

my old cnc has it backwards x is along the gantry ill have to fix it on this one.

[stevensturgis]

I thought the force would be in the x axis. front to back not sagging glade you caught that

[stevensturgis]

The 'System Kit' Includes:
(4) TB6600 Single Axis Stepper Motor Drives
(4) 425 oz.in. Bipolar Stepper Motors with 1/4 Inch shafts on both ends, nema23 mounting holes
(1) 40V 400W Power Supply
(1) DB25 Male Breakout Board (BOB)
(2) 24VDC Fans with finger guards
(1) DC-DC Converter
(1) AC Power Switch
(1) IEC AC Power Inlet connector
(1) IEC AC Power Cord
(1) 3' 25 Conductor Parallel Port Cable
(1) Rubber Grommet

i think pitch is 5mm not sure

1 set RM1605--500mm anti-backlashed ballscrew

3 set RM1605--1500mm anti-backlashed ballscrew

4 pcs RM1605 ball nut

4 pcs DSG16H ball nut housing

4 set BF12/BK12 with nuts &crips

4 pcs 6.35*10mm coupling

2 set SBR20--500mm linear rail

4 set SBR20--1500mm linear rail

12 pcs SBR20UU

[stevensturgis]

do you mean like this . will this be a strong gantry? I can get different materials i what it to be firm.

[stevensturgis]

This is the new gantry design. I have moved the x axes to a vertical plate. I also changed the gantry beam to a 3" x 8" 3/16 wall steel tube as per comments by awerby on strength. I have also spaced the berrings further apart for the z axes. This still gives me 11" travel on z axis. I also spaced the y axis bearing 2" further apart.

please advise if these improvements would work well. greggv,SteveWill,awerby

[awerby]

That looks a lot stronger to me. There is a certain amount of back-and-forth moment on the gantry as well, but the vertical moment is worse. And having more distance between the trucks on the Z axis rails helps with the back-and-forth.