Wobblycogs CNC Mk2

[JAZZCNC]

Ok it's getting there now.!! . . . Few more things I'll comment on.

I can see what you trying to achieve with Z axis but doing this your compromising it's strength where it will probably spend most of it's time cutting and that is Extended further out. Because the bearings are high up the extension distance is long when cutting thinner material and I'd estimate you'll rarely cut thicker than 50mm material.
Much better way would be to put bearings lower down but not flush with bottom, leave clearance for bolt access to Y axis bearing plate. Then make the spindle mount adjustable on front plate if you ever need to cut tall material.
Looks like your planning on using WC spindle so that alone can slide in the mount easy enough so you'll find a intermediate location for spindle mount that will allow you to adjust for all materials.


Next the material thickness of the Front and Rear Z plates are not thick enough and they could resonate and flex. Wouldn't go less than 20mm here.
The plate on the rear of moving Y axis carriage isn't needed or adding much strength so drop that It's only adding weight and cost. Good way to help gain strength in this area is to make a cover for the Z axis from folded 3mm ali plate and bolt into sides of Z rear plate and Y axis top bearing plate. This way it braces this area and protects the Z axis ballscrew belts etc see pic of cad 3d model and unfolded sheet, Next week I'll show real thing cause I've got to make one.


Also Got a way for you to increase cutting area and increase Y axis strength but will be hard to explain so may end up drawing it to best show.? I'll try explaining first.!

Drop the profile spacers on bearing plates this will allow you to use longer rails that extend right up to gantry sides. This will allow the Y axis bearings to travel over the X axis bearings. Now because you can still have the same Y axis bearing spacing(or more) you can drop the width of Z axis front plate and therefore gain some cutting width with no loss strength.
You'll need to brace the X axis bearing/gantry plate area but that's easy enough done with triangle plates.!

Hope this makes sense.??

[Robin Hewitt]

I can see what you trying to achieve with Z axis but doing this your compromising it's strength where it will probably spend most of it's time cutting and that is Extended further out.

What he said, plus, unless there is something in the way that I can't see, might you move that spindle motor backwards, sink it through it's mounting plate so it sits between the Z slides rather than way out in front of them?

[JAZZCNC]

What he said, plus, unless there is something in the way that I can't see, might you move that spindle motor backwards, sink it through it's mounting plate so it sits between the Z slides rather than way out in front of them?

Hey.??? . . .Even I'm not with you here Robin how's he going to do that without a completely different Z axis design.?

I know what you mean if re-design but to accomplish this he'd have to turn rails/bearings 90Deg and that causes other weakness and issues which IMO would be worse than spindle extending out.? . . . If you have another way on the same theme he's taking now that I'm not seeing then get doodling.!!

[Wobblycogs]

Really like the z-axis idea Jazz, thanks for that. As suggested I've...

• Moved the bearing z-axis blocks down to almost the bottom of the plate.
• Increased the spacing between the z-axis bearing blocks to 250mm.
• Beefed the z-axis up to 20mm plate all round (except the bottom spacer plate, will this be ok?).
• Upgraded the motor mounting brackets to 15mm as they looked a bit weedy up against the 20mm back plate.
• Put holes up the z-axis plate so the brackets can be adjusted up and down, in the lowest setting shown I have about 45mm of cutting depth with a 50mm bit. I'm sure this will be enough for the vast majority of the time.
• Added the chip plate for the y-axis ballscrew (still need to actually attach the z-axis to the screw)

I've got to get back to fixing the house (plastering, one of my least favourite jobs) but I'll try to draw up the other ideas tonight.

P.S. I was thinking the gantry back plate would have to stay because the screw is mounted to it but now I think about it I could mount the screw on one of the gantry beams. I'm tempted to still lock the two beams together vertically but with a small plate in the middle of the span. I'll have to have a think about the cover idea as I'm not clear how it would work (I think I've seen what you're talking about in another thread though).

Cheers.

[JAZZCNC]

P.S. I was thinking the gantry back plate would have to stay because the screw is mounted to it but now I think about it I could mount the screw on one of the gantry beams. I'm tempted to still lock the two beams together vertically but with a small plate in the middle of the span. I'll have to have a think about the cover idea as I'm not clear how it would work (I think I've seen what you're talking about in another thread though).

No you misunderstand here I think.? The plate on the Rear of the moving Y/Z axis carriage I meant. It does very little in adding strength, think of box with no sides.!!
Often this way causes more hassle than it's worth because if the edges are not machined perfectly 90deg then when tightened it twists the assembly on the bearings and locks up solid.!!

The slotted front way works great, you've probably seen I have design that uses it so know it works fine but it does cost more. It does offer some nice advantages thou like ball-screws are protected and every thing is neatly out the way. The way I do it the motor and belt are all inside the Gantry and covered up.

The other design which would suit your machine nice and is cheap and easy to build is the L shape gantry using 45x90. I've made few machines with this design and it's proven design which is very strong and reliable. Has some of the same benefits the Slotted design does in that the screw and motor is placed behind the Gantry out of the way. It does put the screw back a bit further than is considered ideal but again It's proven to be no issue in real world use.
If this design interests you then tomorrow I will have hopefully put the final touches to a gantry I'm building so can show the real thing with cable chain, Z axis covers etc instead of 3D model.

[Wobblycogs]

Ah, I see what you mean now and it makes perfect sense. I don't have an abundance of metal working tools (yet) so making two perfectly parallel faces would have been a challenge, presumably that would normally be done by milling them parallel?

I considered the L shaped gantry design but I'm hoping to mount this machine vertically at some point and it seemed simpler to just use a piece of plate at the back and benefit from a better / simpler connection with the ball screw.

Right, on with the design...

[Wobblycogs]

Jazz, was this what you meant when you were talking about having the y-axis bearings travel over the x-axis and make the front z-axis plate narrower? I like this design as I've gained about 30mm of cutting width and I've got a wider spacing on the y-axis bearings (in fact it looks like I could still go wider). The z-axis front plate is now just wide enough to take the rails and the ballscrew.



I wasn't happy with the x-axis cutting length after putting the thicker 20mm plates on the z-axis so the x-axis has grown 100mm :-). I've also been working on getting the stepper in for the y-axis. You can see the hole in the gantry back plate for the belt. The stepper will be mounted on a gantry side plate.

[JAZZCNC]

I considered the L shaped gantry design but I'm hoping to mount this machine vertically at some point and it seemed simpler to just use a piece of plate at the back and benefit from a better / simpler connection with the ball screw.

Both would work fine for your needs. The ball-screw connection is no more difficult or worse really and actually it's easier to align ballnut mount. The plus with this design is it's cheaper because you won't need the rear plate and the screw and motor belts etc are out of firing line of chips etc. . . It's neat and works well with cable management, which is something you should be aware of and design for has it's often overlooked and regretted when finished.!