New Member and New Build design check

[toomast]

Hello sir!

Gantry certainly looks beefy! What weight do you estimate for it?
It looks like it could handle steel...and little bit OTT for mostly wood? :)
Frame is simple and sturdy.
How will you solve the bed design and work-piece fixing?
I notice 4th axis?

[Boyan Silyavski]

I see a new contestant for the sturdiest build here

The only weak spot that i see at first glance are the corner table connectors. I would additionally brace then in the other direction / L. And this is additive :-)

[Procato]

Hello toomast

Many thanks for your reply.

Now you've got me worried, after some quick guestimation in CAD i think it's going to weight in at about 95+kg - is this too heavy?

Re; bed design -The lack of fixings and fixing holes is misleading - I hope to utilise the same method as Jonathon's, after the rest of the machine is built, I plan to attach a large 20mm-ish aluminium plate to the steel frame of the bed then mill it flat, then mill the slots and finally drill and tap it so that I can screw down aluminium strips to form the T-slots. I realise the t-slots on the outer edges won't be possible with this method so I will probably leave them unmachined.

I think I will be mainly routing highly detailed wooden figurines up to lifesize (in 2 parts) which will be held in the rotary axis on one end and free rotating tailstock at the other. both of these will be bolted down to the bed via the T-slots.

The 4th axis is a doughty drive which I bought a few years ago but I've also got a bargain harmonic drive off ebay the other week which is bigger and stronger and will turn that into the 4th axis. I hope then to mount the dougthy Drive onto the Z-axis to form a 5th axis when needed.

[Procato]

Hi Silyavski

Ha yes as you can probably see I'm hoping to use many of your ideas/designs in my build.

I'm also hoping to be able to mill aluminium moulds for resin infusion of carbon fibre hence the attempt at very rigid design.

Thanks for pointing out this weakness- do you mean something like this?

[Boyan Silyavski]

Yes, exactly that's what i meant.

It would be interesting to see the z axis. Where is the Z ball screw? I can not see it

[Procato]

The Z-axis has been causing me some concern. Do you think there could be a racking issue?
I had thought about putting the ballscrew in the centre of Z-axis pillar with a motor on top but that means either putting a slot nearly all the way down the z-axis pillar which I thought may weaken it too much?
Or making the z-axis twice as long, keep the same amount of travel and put the slot in the top half - this makes a ridiculously long axis.
Or I could add another ballscrew to the other side.
What are your thoughts?

[routercnc]

Hi Procato,

Interesting design. I drew something a bit like that a while back but didn't like the loss of X travel and obstructed access to the spindle for bit change. But I was working with upgrading an existing machine so if these factors are already considering in the geometry of your clean sheet design then it should be OK.

I should point out that the Z axis box 'front plate', i.e. one closest to the ballscrew needs to be lapped the other way to the side plate. You are trapping precision height linear rails against each other and they will want to be a certain distance from each other. Unless you can machine the Z axis side plates to very fine tolerance, then lapping them the other way is better as you can use slightly oversized bolt holes coming in from the sides and lightly clamp the assembly before nipping them up.

I can't see in any of the sketches but assume you have a third linear profile rail at the front for support? Should work very well for stiffness, but you also need to be careful on the order of assembly of the Z and Y. The front box section probably needs to be attached last once everything behind it is set. If this is your first build you need to think about the imperfections of machining and building and make sure things can be built in the right order with pre-loads or free running checks made as you progress. Try to build it in your mind.

As for Z axis racking I wouldn't be too concerned about it based on the design and what you want to do with it.

Looks like you've got twin Y axis drive with a twin pulley on the ballscrew nearest the stepper motor. So it looks like you want to link a short belt to the first ballscrew, and then have another belt between each ballscrew. That's no problem but make sure you can tension them. The stepper pulley belt is easy - just add slots which it looks like you have done. But the belt between the ballscrews will need an idler pulley and it looks like it's a tight fit between the side plates. Have you provisioned for one? If so make sure it can take up the required slack as belts come in fixed sizes (although I believe you can have custom ones made).

[Sven]

I've been told that the linear bearings and rails are stiffer than anything you could bolt them too.

If that is the case then you'd be better off combining all beams in the gantry in to one structure.
I think you now support the Z on two sides for stiffness, but you actually lose torsional stiffness this way.

Also, it will be extremely hard to line up all parts to run smoothly, with multiple carriages on multiple carriers.
All in all, though it looks very nice, I feel it is overly complex but will under perform.