Wobblycogs CNC Mk2

[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]

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?

Yes that's it. Just to help drop weight a bit and look a bit better then think about making the back plate thinner in middle but with ears at top and bottom.? Like this.

I've made a couple of Z axis for folks like this and works good and looks better.

[JAZZCNC]

Another thing.? . . Regards the spindle mount make it so can de fastened from front and not from behind front plate. May seem like a small detail but you'll thank me for it if did it other way round.!

[JAZZCNC]

Another thing I'd like to say is that 45x45 profile is weak so if that bed frame is all 45 then I'd invest in beefing up to 45x90 you'll get a much stronger machine for not much more money.! . . . No point going to all this trouble and spoil it for an extra £50.!

[Wobblycogs]

Thanks for the suggestions Jazz most are drawn up already. Anyway, here are some shots of the project so far.



I've added in a triangle brace for the gantry side plate but I rather like the one here so I might switch it for that. Depends on how much of an improvement it would make though.

As suggested the spindle mounts have been redesigned so that they fix from the front and the z-axis back plate now has a waist to reduce weight.

I initially had the z-axis stepper using stand-off legs like the x and y steppers but I felt this would weaken the top plate too much so it got a proper frame. The benefit of this is I can lock the z-axis back plate into the stepper support for additional rigidity. The stepper and pulleys will also be enclosed in a bent metal box.

The y-axis stepper has been mounted on an extension of the right hand gantry plate. Again this will be enclosed in a bent metal box to stop chips getting in. I've split the front chip guard in two so that the left section can be removed for accessing the belt and pulley for the y-axis without taking the machine completely apart (more cunning than a fox)!

I've had a think about where cables will run (very good suggestion). I think a cable drag on the right hand side and across the back should work fairly well. I've not even considered drawing it yet but I don't see anything obvious in the way to stop that idea.

I've not upgraded the bed to 45x90 yet because I wasn't sure if it should have the 90 edge vertical or horizontal. I assume vertical to provide resistance to twisting.

Now for the problems...

I've been reading loads of threads and I'm getting concerned that 45x60 profile in the gantry isn't strong enough and that I should probably go with 60x90. It's a damn sight more expensive and I don't want to upgrade if it won't help but I'd rather have a machine that was a bit over built than a bit under built.

The plan currently has SBR16 rail all over but I (and and a lot of other people it seems) have noticed there's not a lot of clearance (e.g. none) on the z-axis ballnut. The million dollar question is do I switch to SBR20 rail or try and rout out a pocket for the ballnut on the z-axis if needed?

And the big one... At the moment the rail is mounted straight onto the profile. Ooops, school boy error. I think I'd get away with it on the x-axis as there's a good 6mm of aluminium to bolt into. On the y-axis though it's clearly not enough as drawn. Presumably a 10mm plate bolted to the profile will fix this? Does it need to be toolplate?

Some other, probably stupid, ideas have come to mind though, would this machine be capable of engraving and or cutting brass? I've cut a couple of small bits of brass with a hacksaw and it seemed similar to aluminium in hardness. I've also considered making the x-axis significantly longer, say 1000mm of cutting length, I'm trying to resist that though as I still want to build my Mk1 machine which will be designed to handle large pieces.

EDIT: As well as considering using SBR20 rails what about moving to profiled rails instead? They would be a budget buster but I believe I could mount 15mm rails straight onto the extrusion and from what I've read they would lead to a better machine over all. A couple of lucky buys from the far east might make it possible.

[JAZZCNC]

Now for the problems...

I've been reading loads of threads and I'm getting concerned that 45x60 profile in the gantry isn't strong enough and that I should probably go with 60x90. It's a damn sight more expensive and I don't want to upgrade if it won't help but I'd rather have a machine that was a bit over built than a bit under built.

Absolutely would go bigger and even at 60x90 you won't be over building believe me.!! . . like the Famous film words.? "Don't under estimate the force" Wobbycogs.!!

The plan currently has SBR16 rail all over but I (and and a lot of other people it seems) have noticed there's not a lot of clearance (e.g. none) on the z-axis ballnut. The million dollar question is do I switch to SBR20 rail or try and rout out a pocket for the ballnut on the z-axis if needed?

Either has you can always pack for clearance and it keeps Z axis compact and light. Bigger will give clearance at the cost of weight and extra standoff.

And the big one... At the moment the rail is mounted straight onto the profile. Ooops, school boy error. I think I'd get away with it on the x-axis as there's a good 6mm of aluminium to bolt into. On the y-axis though it's clearly not enough as drawn. Presumably a 10mm plate bolted to the profile will fix this? Does it need to be toolplate?

Yes use a 10mm plate but wouldn't bother with tooling plate has the rail base will have more error than the standard plate so waste of money if your not going to skim the rail base.!

Some other, probably stupid, ideas have come to mind though, would this machine be capable of engraving and or cutting brass? I've cut a couple of small bits of brass with a hacksaw and it seemed similar to aluminium in hardness. I've also considered making the x-axis significantly longer, say 1000mm of cutting length, I'm trying to resist that though as I still want to build my Mk1 machine which will be designed to handle large pieces.

If it will cut Ali properly then it will cut brass Ok.

[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.!