Steel frame cnc router design/build

[CraftyGeek]

If you can get over the annoying accent there is a guy on YouTube called chucke2009 I think who does some handy trouble shooting videos on stick welding. I found them useful anyhow. Practice is key though I think...

I found his trouble shooting vid at the weekend - that has helped me loads...need to have another quick go, I think I should be sorted after the next practice.
For anyone needing welding help have a look at this...
How To Weld: Stick Weld Troubleshooting - YouTube

I've got a fan set up blowing 'most' of the black crap away from my nose - still got a bit of filth working its way through :-p

Progress report...
Design is still progressing, well on the way now - I should have a more advanced version to show soon.
As the design for the main base frame is finalized, I've bought the steel for the sides & rear brace so at least I can start making some progress on the build. First pieces were cut & drilled over the weekend.

[CraftyGeek]

Ok - design progress time

The overall machine...base frame is mostly the same as before except for a few minor tweaks - I'll probably add more cross bracing when its built if I feel it needs it (there's plenty of room)


Moving on to the gantry - i've lost count of how many times i've altered the way this fits together...i'm now pretty happy with it - there's nothing offending me there now
The upper & lower front plates are 5mm aluminium...all other plates/braces are either 15mm or 20mm (ecocast where appropriate).


Back of the gantry is also skinned with 5mm aluminium - 2 sections to allow easier removal around the Y-axis motor mount block. I did try to fit the motor inside the gantry, but there just wasn't quite enough space...by the time limit/home switches are in place I really don't think it'd fit.


Back of the gantry with the rear plates removed for a peek internally. There are a couple of 5mm aluminium plates at either end on the rear of the front faces to help tie them in at the sides (they will bolt to the back of the vertical piece between the main gantry side braces).
The main gantry frame as such is now 75 x 50 x 3 steel box (top, bottom & vertical side blocks)


Z-axis - 20mm plate with rails & leadscrew mounted on the back.


An attempt at a cutaway to show how the whole of the gantry/Y/Z fits together - its tight in there, but everything has at least 2mm clearance except for the Z anti-backlash nut housing which only has 1mm clearance on the back of the Z plate.


X-axis:
2x 1610 leadscrew (1400mm thread length)
SB20 rails - 1500mm
linear bearing spacing - 200mm (outer faces)

Y-axis:
1610 leadscrew (800mm thread length)
SB20 rails - 900mm
linear bearing spacing - 170mm (outer faces)

Z-axis:
1605 leadscrew (350mm thread length)
SB20 rails - 400mm
linear bearing spacing - 170mm (outer faces)

X-axis movement is roughly 1200mm - a smidge under what I was originally aiming for, but acceptable
Y-axis movement is roughly 750mm - a little more than I was aiming for, happy
Z-axis movement is roughly 180mm - could probably tweak this to gain another 10-20mm.

How does all this look/sound?

Looking for some sort of approval (hopefully :-p) before covering all the parts in holes etc

[JAZZCNC]

Looking for some sort of approval (hopefully :-p) before covering all the parts in holes etc

Couple things I see and sure I mentioned this one before.? The Rear plate on the Y axis.? . . . It's not required and adds very little strength and actually can cause you problems with binding the bearings if not perfectly flat and edges of mating plates perfectly 90deg. . . . Drop it and save some money and weight.!!

Next is the Z axis motor arrangement.!! Why have you got the motor fastened to the front plate and sticking out the front.?
It looks to me like you have enough length to the Y axis front plate to mount ball-screw on this and fasten motor other way round. Your rails look shorter than the movement range your ball-screw will allow.
If so and it's longer than your Y axis front plate then just do away with the bottom bearing and shorten screw provided it gives enough screw range to use all rail length. On a short Z axis screw you can easily get away with this and it also makes aligning screw/nut that bit easier.!!

Other way is to have longer Y axis front plate and do it this way, both work.!! . . . Either way Your better off with screw and motor has I've described because it will allow higher acceleration from the Z axis which helps if your planning on 2.5/3D work.!!. . . .No point making the motor/drive work harder than needed.!!


Rest looks ok except that I'm not too keen on the low base frame due to large adjustable bed range.!!. . . .Do you really need that much adjustable range because it's compromising the strength quite a bit.?

[CraftyGeek]

Y-axis rear plate...partly to help keep crap out of the leadscrew etc Thought it would add some extra sideways/diagonal rigidity...can easily drop it.

Z motor - probably didn't think it through quite correctly...with that arrangement, the y axis front plate is considerable shorter than it would need to be to have the leadscrew & motor attached.
The rail lengths are pretty much spot on compared to the screw length - maybe i've got the Z axis linear bearings spaced further apart than needed? (170mm outer face to outer face along the axis). I'll look at swapping the leadscrew & motor to the Y front plate.

Base frame - do you mean raise the lower shelf/surface, or reduce the overall height?
I don't really want to lose much overall height if possible as it will be at a good height for me to work with it at...rather than being low down on the floor like my last mdf machine which was a major pain in the back.
I don't necessarily need all that adjustment - I could raise the lower surface & add more cross bracing to the outer frame?

[masinecc]

What is the vertical distance between the linear rails on ur y-axis?

[D-man]

Personally with you just starting to weld I would urge you to chamfer the two parts to create a 'V'.

Welding can be a tedious venture and without, lots of practise it can take some time to master. So I would not have a gap as you mentioned in image two (I think) as filling gaps with weld is another learning process.

[CraftyGeek]

Personally with you just starting to weld I would urge you to chamfer the two parts to create a 'V'.

Welding can be a tedious venture and without, lots of practise it can take some time to master. So I would not have a gap as you mentioned in image two (I think) as filling gaps with weld is another learning process.

Thanks - think i've got it covered now....been practising a bit on scrap. I'm now at the point where I'm happy to start some of the basic less important pieces to get a bit more experience before getting stuck into anything tricky.

[mart154]

As I understand you are not too far from me. If you like, I could come and give you some welding tips / help over the weekend.

[CraftyGeek]

As I understand you are not too far from me. If you like, I could come and give you some welding tips / help over the weekend.

Thanks for the offer - no i'm not far from you. To be honest, I think i'm ok now - after watching more videos over the weekend & working out what I thought I was doing wrong...I tried again very quickly last night - the result is a presentable weld that i'm happy with. If I get find that I run into problems, I may well take you up on that offer - but for now, I think i'm ok

[CraftyGeek]

Right given the lack of negative comments on the last revision of my design, i'm starting to move on to the next stage which brings me onto another set of questions...

Gear ratios & microstepping.

After reading around, it seems that the general consensus is that less microsteps are better ie, either use full steps or at most, half steps.
My understanding is that the accuracy of the stepper motor gets lower when the number of microsteps is increased...I think this also has an effect on the torque?

Couple this with the gear ratio from the stepper to the leadscrew makes the choices a little open ended as far as I can tell.
The general flat answer for the ratio that I seem to see is to use 2:1.

I'm only thinking about the X & Y axis at the moment which are both going to use 1610 screws. Belts/pulleys will be 5mm HTD 15mm wide.
Full step geared 2:1 gives a resolution of 0.1mm
Half step geared 2:1 gives 0.05mm
Full step geared 1:1 also gives 0.05mm

0.1mm sounds quite a coarse resolution to me - 0.05mm sounds more like it. So why gear 2:1 & use half step when the same resolution can be had with full steps & 1:1?

or perhaps go for a somewhere inbetween like 1.4:1 (eg 28/20) full stepped = 0.07mm ??

Am I missing something here?