Look At My Rack

[Misterg]

Was expecting cleavage shots.

Here you go:

 

[angellonewolf]

Here you go:

View attachment 419929

how does that count as cleavage its just a crack and not the one im thinking about being male

 

[Misterg]

Say I want to build a router rather than plasma table that would do 8'x4' (maybe even 10'x5') sheets

You would need to print at least 20' (or 25') of rack with good and repeatable dimensional accuracy. How does the cost of filament compare to using (say) 'belt and pinion' drive?

 

[iNf]

With regard to printing the rack ,would it be better to split the 2 parts horizontally rather than vertically so there's no problems with the teeth lining up? Would you even need the bottom half if you bolt it to the tube?
As you have plenty of square tube have you seen this guys printed cnc he uses it for his rails, he also does what looks like a well thought out controller
https://www.rootcnc.com/root-4/

 

[slim_boy_fat]

@Onoff From the title, I was expecting something along these lines.....

 

[angellonewolf]

@Onoff From the title, I was expecting something along these lines.....

View attachment 419946

well at least its fleshy

 

[Onoff]

'belt and pinion' drive?

Didn't realise it was a thing even!

 

[Onoff]

@Onoff From the title, I was expecting something along these lines.....

View attachment 419946

Given the title I can't complain about the ribbing.

 

[Onoff]

Seeing these motor/controller/PSU kits, some are termed "4-axis" and come with 4 motors, controllers and PSUs.

With a wide gantry am I correct it's usual to use 2 motors on the X axis? So for a big, 3-axis machine you'd need 4 motors?

 

[m_c]

In terms of the kits, 4-axis just means it comes with 4 motors and drives, however I would advise against buying one of those kits.

 

[Onoff]

I would advise against buying one of those kits.

Why can I ask?

 

[m_c]

The kits are generally compromised. Taking that one you linked to, 36VDC PSU isn't going to give you that great performance.
Even for the NEMA 23 motors in that kit, I'd be wanting 50-70VDC.

Also I wouldn't recommend a switched mode PSU, as during hard deceleration it's like to trip out due to overvoltage.
A conventional basic unregulated PSU (transformer+bridge rectifier+capacitor) is far better for most CNC applications.

For something with twin motors on a single axis, I'd also strongly recommend stepper drivers with stall detection, so if one motor does stall, the entire machine stops reducing the risk of damage due to the gantry twisting.

 

[DAPPH]

Excuse my mad musings, this could be a very short thread if I'm being silly.

I know very little about CNC table builds other than the theory and am as aforementioned, in awe of those who build them.

I'm also a cheapskate whilst at the sane time always thinking I can reinvent the wheel!

So.....what I have is masses of 25x25 steel box. 3m lengths. I got to thinking I could build the XY rails out of this. Then came the rack and pinion vs belt issue. What if I was to print the rack in two halves, in lengths, as big as the printer would let me, then screw it to the box section? The print could be done as a sort of diamond profile to suit a custom carriage.

View attachment 419897

How about a rack & rail for not a lot of money about 9 feet long
Two of the same model stair chair lift , they have a precision ish counter sunk screwed toothed rack in the rail and the rails are very very sturdy , . print the wheels so they are bearing on both sides and don't fully sit down in the teeth . Same principle of a change gear lathe compensating for wear .

Can get a photo of some of the rail I begged for free . They came from a disabled stair lift installing company removed because it is an insurance liability to sell second hand ones with no guarantee .

 

[DAPPH]

Who drew that?

The top and bottom rollers appear to do nothing, only redirect the rope.

If you turn the middle roller anti-clockwise, it unwinds to the left and winds up to the right. So the distance between the loops of rope never changes.

It's adjustable so you can break the spine slowly on the middle roller over a few days & dislocate upper body or lower body joints at differing times during the stretch .

 

[DAPPH]

Here you go:

View attachment 419929

Is that is known as cherry busting ?

 

[Onoff]

How about a rack & rail for not a lot of money about 9 feet long
Two of the same model stair chair lift , they have a precision ish counter sunk screwed toothed rack in the rail and the rails are very very sturdy , . print the wheels so they are bearing on both sides and don't fully sit down in the teeth . Same principle of a change gear lathe compensating for wear .

Can get a photo of some of the rail I begged for free . They came from a disabled stair lift installing company removed because it is an insurance liability to sell second hand ones with no guarantee .

Possibly, show me what you've got as they say! Cheers.

 

[Onoff]

I may be jumping the gun here as what I really should do is ensure I have the large, dry space to house such a build. I have the space in the form of a tumbledown old stable block I think around 7x6m but it's at the point of collapse with cracked walls, a leaking roof and running water down the sloping floor! So that's a whole other story for another time and a couple of years off at very best.

As much as anything this is for my lad, something for him to get his teeth into. I'm mulling then buying a single stepper motor, controller and PSU for him to maybe build a test bed on.

Any suggestions? Nema 23, 34 etc? Thanks.

 

[DAPPH]

Possibly, show me what you've got as they say! Cheers.

 

[DAPPH]

These four foot sections ( been out side five years or more came out his scrap bin , He said he would set aside two matching rails if I paid him .

 

[m_c]

As much as anything this is for my lad, something for him to get his teeth into. I'm mulling then buying a single stepper motor, controller and PSU for him to maybe build a test bed on.

Any suggestions? Nema 23, 34 etc? Thanks.

If it's just for testing, pick a stepper and drive from whatever source, and combine it with a basic bench PSU.

£60 will get you a 0-30V 0-5A bench PSU which will be good enough for testing, and be useful for other things.
For an actual machine, it all depends on budget.
I'd probably suggest a couple 4Nm Nema 23/23 closed loop steppers if you're running twin motors on the one axis, such as https://www.ebay.co.uk/itm/203449278205 although you'd have to budget in for extending the cables.
For the other axis, a motor stalling isn't likely to be as big a problem, so you could save money with an open loop setup.

Then there is also the controller options, which are very much dependant on budget, and how much frustration you're willing to risk.