Thread: Wobblycogs CNC Mk2
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).
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.
Last edited by JAZZCNC; 17-08-2013 at 02:58 PM.
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...
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.
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.!
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.!
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.
Last edited by Wobblycogs; 20-08-2013 at 09:22 PM.
BUILD LOG: Wobblycogs CNC Mk1By Wobblycogs in forum DIY Router Build LogsReplies: 91Last Post: 02-01-2013, 06:38 PM