Gantry Aluminium thickness guidance

[JAZZCNC]

I've decided to go the other route and mount the rail on the sides of the plate pictured, and just have the cart on the back of the spindle.

If you don't have need for tall material or long tools then wouldn't go that route as your losing stiffness for no reason. It's not more difficult building it the other way around.

Also have you realised that you'll need to space the rails off the plate or machine channel down centre to allow clearence for the ballscrew/bearings.?
Best if you take little from each plate depending on the ball nut mount the total need machining off is the distance from bearing face to ballscrew flat which is 45mm. Profiled rail and bearings total aprox 30mm depending on make, (Hi-Win HGH-20CA are 30mm) so I'll let you do the math.?
How you devide it upto you, I just split it in half.

[dachopper]

If you don't have need for tall material or long tools then wouldn't go that route as your losing stiffness for no reason. It's not more difficult building it the other way around.

Also have you realised that you'll need to space the rails off the plate or machine channel down centre to allow clearence for the ballscrew/bearings.?
Best if you take little from each plate depending on the ball nut mount the total need machining off is the distance from bearing face to ballscrew flat which is 45mm. Profiled rail and bearings total aprox 30mm depending on make, (Hi-Win HGH-20CA are 30mm) so I'll let you do the math.?
How you devide it upto you, I just split it in half.

I'm planning on using up to 200 mm z height, so really needed a design that maximizes this, when I put the first plate with back to back bearing blocks, it becomes hard to do them up ( I have to offset them , in gives less stiffness, down I loose z clearance, and up I have a greater z overhang for the same clearance. I can always bolt angle onto the spindle plate sides if on the future there is some play going on.

My plan is for the rails to be mounted flat on the back plate, I will add 15 mm spacers between the bearing block and the spindle plate to get the extra clearance as at the moment making a rail spacer, or counter sinking is far more work.

[JAZZCNC]

If you rush and make bodge of the Z axis you'll regret it. Z axis is THE most important part of machine get this wrong and you'll always have poor finish and excess tool wear.

The extra time taken to Mill slot, even with hand router will be worth it. It's the little details that are easy to skip that bite you in the arse later.!!

[Robin Hewitt]

I'm planning on using up to 200 mm z height

Is that scratching the top of something 200mm tall, or 200mm long cutters?

There is a big difference in the designs

[dachopper]

If you rush and make bodge of the Z axis you'll regret it. Z axis is THE most important part of machine get this wrong and you'll always have poor finish and excess tool wear.

The extra time taken to Mill slot, even with hand router will be worth it. It's the little details that are easy to skip that bite you in the arse later.!!

If I mill out 15mm ( 7.5mm from each plate ) that's almost half the thickness of the plate. Surely that is going to weaken the plate sufficiently to cause me more grief, than keeping the plate stiffer and using a spacer to create the clearance.

What is the draw back of using spacers?

Yeah - we need to fit in work pieces up to 200mm high - that is not aluminium, that would be softer material like surfboard or denser foam for shaping.

Making a 1 machine fits all - because my work pieces are generally long, it's the most economical approach and I don't have room for 3 different machines when the mahority of the cutting is foam / fiberglass/carbon/ wood, 3d Printing and the odd smaller aluminium job possibly.


Regarding the z height , I have an area 80mm high to insert a bed, and fit the spindle, and then 200mm of clearance to the bottom of the gantry. I wasn't sure about the spindle overhang, so I assumed it was going to be 40-60mm, but I also made the spindle mount adjustable so If the bed takes up more room, I can raise the spindle by up to another 8 cm if I have some crazy length tool on the end. It will only be a factor for the foam jobs If I have a 200mm thick slab that needs shaping. for the most part, when working on the smaller pieces, I can attach something on the bed to raise the workpiece so the spindle is level X axis, and therefore less tourqe and vibration.

[Neale]

If I mill out 15mm ( 7.5mm from each plate ) that's almost half the thickness of the plate. Surely that is going to weaken the plate sufficiently to cause me more grief, than keeping the plate stiffer and using a spacer to create the clearance.

It's a well-established technique, though! Look at it another way, it's less than half plate thickness and along an axis where there is little bending load, and where at least part of the channel is spanned and reinforced by the spindle mount. It keeps the spindle axis as close as possible to the Y rails to reduce leverage compared to using spacers. Probably won't matter too much for light cutting loads like foam but it seems like a good idea if you have the facilities to do it (and plenty of people have ploughed this kind of channel with a portable router, well-clamped guides, and a bit of care).

[dachopper]

It's a well-established technique, though! Look at it another way, it's less than half plate thickness and along an axis where there is little bending load, and where at least part of the channel is spanned and reinforced by the spindle mount. It keeps the spindle axis as close as possible to the Y rails to reduce leverage compared to using spacers. Probably won't matter too much for light cutting loads like foam but it seems like a good idea if you have the facilities to do it (and plenty of people have ploughed this kind of channel with a portable router, well-clamped guides, and a bit of care).

I see your point, it doesn't really need to be exact, just enough to avoid screw contact.

[Tom J]

Nick
I would not use anything less than 20mm, 25mm for Z plate and at least 20mm for spindle if braced by spindle bracket or other form.
If you are not limited with machining process and time than do not cut the corners - do it properly.
See how I keep changing design




after 2 days of scratching my head - still not happpy
All those changes were made to short the overhang by less than 50mm - is it worth it?

[dachopper]

Lots of drilling and tapping yesterday,

And I had an accident and slid a bearing cart off the linear rail - then 10 bearings fell out..took ages to pack them back in there, but much easier than repacking ballscrews !

Slides well, next to attach the Y axis ballscrews, and machine the Z axis plate :)

Nick

[dachopper]

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