Bench-top or welded frame

[driftspin]

Dean,

I've been thinking about this a bit, and been through different iterations of a design for the gantry, as always trying to work out the best compromise. Most recently I've been measuring the width of the shed door opening - I don't want a machine that I have to dismantle to get in/out of the shed.

Can I pick your brains on the following - it does, I think, have problems but I simply don't know if they are problems that I need to be worried about.



My concern is the projection of the spindle substantially away from the rails.

For info: Y-Axis beam is 80x120x5 box steel. Uprights are 100x100x5. Braces and bottom skids 100x50x4 . Sizes chosen on the "big is good" rule of thumb but also with a mind towards availability and ease of mounting stuff. Shiny stuff is 15mm alu tool plate. There's imaginary bracketry involved tbd. Of course there'd be a brace across the top, made from similar big-steel.

The obvious solution for the projection is to place the spindle assembly on the other side of the Y-gantry (this was my previous design), but I have a real-life constraint (the shed door width, and sensibly the amount of real-estate that this can take up) that means I'd seriously compromise the available space in the Y-plane (this current design obviously impacts the X-axis a bit - but I can tolerate that more than the Y).



Kind of shows the impact having the ball screws on the inner face gives me. There's also another issue that the (invisible) top-brace then impacts the available Z-height with the spindle impacting the brace (something I can bodge around somewhat inelegantly by offsetting the brace).

I have looked at replacing the Y-Axis with just a big block of tool plate (20mm), but the deflection calculators suggested a pretty terrible performance by comparison to box section.

My real question is one of opinion - of whether the spindle offset will impact the performance enough to make this design impractical - if you have any thoughts I'd appreciate them.

Hi doddy,

What work area are you aiming for?

Did you concidder going vertical?
This might solve some of your space problems.
And you could move through doors more easy.

After reading a lot of the comments on peoples 1st designs, i basicly wanted 3 things.

-A simple and heavy bed/frame
- A simple and rigid gantry.
- The spindle within the boundaries of the gantry x axis bearings.

Will there be a rigid fixed connection between your gantry sides?
How do you prevent gantry going out of square?

Your design does not look like it has a rigid gantry now.
Is it made out of 3 separate moving parts?
I think it will be very hard to get a rigid end result that way.

Also the spindle is not in between the linear bearings, this also does not help for rigidity.

Now for me i am no expert.
So please have the more experienced guys here point you in the right direction.

I started my cnc design reading at cncroutersource then came here :-)
Still on a steep learning curve.


My 2cts worth,


Grtz. Bert.






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