John's Alu Profile build

[JAZZCNC]

I think the Z axis I have is pretty solid though, it's foundation is milled from stainless. I know the opposite arrangement than most recommend, with the rails on the z plate which seems to be preferred, but it was a simple solution for me. I've tried to keep everything as close to moving bearings and having as little overhang as possible. The Z only has 100mm of travel but after using my other machine for a few years I realised I've never needed to mill anything over a couple of inches thick so the z overhang was really compromising the strength.

There's nothing wrong with rails on the rear plate, I've built dozens of machines using both methods and neither is better than the other because the difference between them is hardly anything and any advantage one as over the other is mostly dependant on machine design and user needs.
In your case with a short Z-axis, it's the best method because it allows you to make the most out of a short-stroke while allowing you to keep the gantry low and squat giving the best strength.

Edit:

Don't worry about the profile it will be fine. If you using my "L" Gantry design just make sure you bolt it together well.

[Evengravy]

There's nothing wrong with rails on the rear plate, I've built dozens of machines using both methods and neither is better than the other because the difference between them is hardly anything and any advantage one as over the other is mostly dependant on machine design and user needs.
In your case with a short Z-axis, it's the best method because it allows you to make the most out of a short-stroke while allowing you to keep the gantry low and squat giving the best strength.

Don't worry about the profile it will be fine.

Ah that's good to hear, I didn't go for the L design you have no, I wish I had of kicked around here before but that does look like a better solution than mine, unfortunately I'm quite a way through the build so at this point I'm just looking to get her done and running. I don't know if you would have any comments on the design as it stands? There's a few places I could reinforce around the gantry connection to the Y axis plates etc. I'm sure I can figure something out there.

I could always beef up the gantry with some steel plate on the back-side too, if that would help. I might just get the base/table done next and see how she does though.

[JAZZCNC]

I could always beef up the gantry with some steel plate on the back-side too, if that would help. I might just get the base/table done next and see how she does though.

I would look to beef up and brace the gantry ends but other than that it's nice and stiff looking.

That Z-axis is spot on for the size and you have half-decent material size. You won't get a much stiffer setup.

NOW just turn it on its side, or stand on its end and bolt to that wall.!!! . . . . You'll love it.

[Evengravy]

Thanks mate I'll do that,

Once the steel shops open again I'll have a crack with the MIG and see how I get on.

[Evengravy]

So,

New ballscrews have arrived, TBI motion ground 2005 with double nuts. These ballscrews have BK15 mounts at both ends rather than a floating end and each BK15 holder, four in total, has a pair of Japanese 7002 angular contact bearings. These parts were bought lightly used from the same seller that I bought a lot of the other parts from in South Korea, but are clearly much better than the Chinese ones that I'm going to pull off the Y axis. One of these screws will be on each side of the Y axis as before so it should improve the smoothness of motion and the extra thickness of the screw (going from 16mm to 20mm) should enable me to increase the speed of the rapid movements a little without encountering whipping.



The only downside of the change so far is that I've lost a bit of travel on the Y axis, down from just over 1100mm to just over 1000mm. I'd rather have the piece of mind of these motion parts than the extra cutting envelope so I'm okay with it.

As a result I've needed to redesign a few parts though. As per Jazz suggestion I've added a new bracing for the gantry which will tie in to the Y axis linear bearing plates. This part only braces towards the back side of the gantry, as the new ball-screw connection will be made to the front side via a plate as shown below. I might figure out something for the front too at a later date.



I've designed some new shoes for the ballscrews to fix to to mate them with the Y axis profiles.



I've also rethought the design for connecting the ballscrew to the Gantry. I was never too happy with the previous welded solution, they were a mess.



Lastly, since I've moved up to a larger screw my motor mounts have to change too. These attach to the end of the Y profile on each side and carry the Y motors.



Since I can't buy materials at the minute I've decided to try to get all of these laser cut in the UK and shipped over. The company are running but with minimal staff so it might take a while to organise.

Gantry to ballscrew mating part will be made of 15mm mild steel laser cut and I'll paint that later. The rest will be laser cut from 10mm stainless steel. That's the plan at the moment, it's hard to get companies to do much at the moment so we'll have to see.

[JAZZCNC]

Don't understand why you are making the Y ball screw plate and the brace plate separate.? This could be made as one piece and will be stiffer and easier to fit.!

[Evengravy]

Don't understand why you are making the Y ball screw plate and the brace plate separate.? This could be made as one piece and will be stiffer and easier to fit.!

Hey,

I designed it this way just to give me scope for adjustments in each degree of freedom. I couldn't think of a better way of doing it to be honest, open to suggestions though.

I could get both parts made up from mild/bright steel and once everything is lined up get the joints welded. I picked up my MIG today and dusted it off, maybe I can get good enough with some practice to get it done myself.



Also there's scope to brace between the front and side section with some triangulated pieces.



Honestly not too clear how I could make it in one piece, but I'm probably being blonde...it's been known to happen.

[JAZZCNC]

Hey,

I designed it this way just to give me scope for adjustments in each degree of freedom. I couldn't think of a better way of doing it to be honest, open to suggestions though.

Ah makes a bit more sense now. I was working on your old setup and seeing all those holes which matched the profile ends I thought was fastening into ends.

Carry on.!! . . Lol

Edit: The drop bracket still needs some bracing thou.!! or a redesign of the whole thing.!.

[Evengravy]

Edit: The drop bracket still needs some bracing thou.!! or a redesign of the whole thing.!.

Yea, I was planning some welded triangulation braces between the two parts once it's all aligned properly, the overhanging section that mates with the ballscrew is annoying me but I'll come up with something to strengthen it up. Front plate will be heavy (15mm) but I know that will be a weak spot for flex. I'll play around with the design a bit more in CAD.

[Evengravy]

Edit: The drop bracket still needs some bracing thou.!! or a redesign of the whole thing.!.

Hey, so I've decided to go back to my existing design of the gantry to Y ballscrew connection which was 10mm steel plate welded and braced with 10mm triangular plate sections. After testing this arrangement on the Chinese screws for play, measured at the tool with my dial indicators I'm quite happy with it strength wise so I have redesigned the same arrangement to fit the new ball-screws. The current layout has between 0.02mm and 0.03mm of play which is largely coming from the ballscrew nuts themselves, you can feel a good bit of play by hand in the ball nuts when these are off the machine which does tighten up significantly when both screws are in the machine (weirdly), but I definitely got unlucky with these Chinese ball-screws compared to what others seem to get. There's noticeable bends in them too so out they go. Bare in mind the current ballscrews are running with angular contact bearings in the BK12 holders, which I bought after the fact, so those bearings tighten up the play in the Y. Initially play was in the order of 0.1mm+ in my measurements before and fitting angular contact bearings. I can't feel any play at all by hand in the new ground ball-screws so I'm confident they'll be a big improvement.

One catch with the new design is that I'll need to machine a ball-screw nut mount for the new ball-screw, one each side. Would anyone here be able to machine this part for me (x2) out of Aluminium for payment? I'd rather spread work here than a bureau service if anyone is free/able/willing.

I don't think my Momus will be accurate enough to do it to this depth to be honest, there's just too much play in the Z (part is roughly 57mm x 65mm x 70mm from Ali (6061/6082 etc))

Failing that I'll have to consider milling it in thinner 25mm sections bolted together until I can machine it myself from a single piece when the machine is in situ, but I'd rather get it done right the first time if possible.

I still need to consider the bracing of the gantry to the Y bearing block plates, but I'm happy enough I can do that after the fact pretty simply and am considering an adjustable design there.

I'm leaning towards setting this up in the standard horizontal arrangement atm, reason being I'm thinking of running high flow flood coolant on it and it's easier to manage that way.