Bench-top or welded frame

[Doddy]

Yes that's the idea thou wouldn't fasten between those two gantry uprights as it will make setting up difficult with little room for error.
Fasten rails on front, ballscrews on side and put brace between gantry uprights at top. Connect two ballscrews with belt and single motor running along top of brace.
Put rails on front of gantry and ballscrew on top.

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.

[JAZZCNC]

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.

Well think you could afford to go with something like this setup with you having ball screws on inside and not lose to much travel.
On original design with 100mm wide bearing plates and the gantry going to outside edge the spindle centre line will actually be over the linear bearings or very close. So if you used say 80x40 for the diagonal you would still have room for railbearings and only lose probably 40mm or so of travel.

To be honest I don't think the over hang is massive anyway and provided you build it strong then won't have massive affect. End of the day the extension is still less than most Milling machines.

Personally I'd build a wider door in my shed than compromise the machine.

[Doddy]

Much appreciated - I needed a fresh perspective - 40mm loss of travel is affordable (and should save a reasonable chunk on the X axis in the process).

(I'm avoiding going wider on the machine - yes, it's a compromise, but I am somewhat space-limited - too wide a machine is simply impractical for me)

[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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[Doddy]

Hi doddy,

What work area are you aiming for?

Bigger than my StarMill (160x100!). Height isn't a massive issue for me (at least not as yet), but 200mm would be an aim. X/Y = around 600x400 was my goal.

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

Only the crazy people go vertical! Actually, it's something I had just started to think about - I know Dean here has done this in the past. That might be the next machine.

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.

(assuming you mean square across the Y-Axis) Yes, a beam across the top, with gusset plates to hold square (sorry, the design is obviously incomplete - more to get the concept right in my mind before burning hours on Fusion 360).

Is it made out of 3 separate moving parts?
I think it will be very hard to get a rigid end result that way.

Yes, more steel to be added yet. As above, this is just a basic geometry sanity check.

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,
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That's exactly why I posted this. Placing the spindle where I did I'm very conscious that it's putting a large force on the rails. Having said that, better and brighter people than me have suggested that the rails are more than strong enough for anything a small machine like this is likely to throw at them, and Dean's earlier comment re. most mills - yeah - they'll place a similar cantilever load on the rails as well.

[driftspin]

Bigger than my StarMill (160x100!). Height isn't a massive issue for me (at least not as yet), but 200mm would be an aim. X/Y = around 600x400 was my goal.




Only the crazy people go vertical! Actually, it's something I had just started to think about - I know Dean here has done this in the past. That might be the next machine.



(assuming you mean square across the Y-Axis) Yes, a beam across the top, with gusset plates to hold square (sorry, the design is obviously incomplete - more to get the concept right in my mind before burning hours on Fusion 360).



Yes, more steel to be added yet. As above, this is just a basic geometry sanity check.



That's exactly why I posted this. Placing the spindle where I did I'm very conscious that it's putting a large force on the rails. Having said that, better and brighter people than me have suggested that the rails are more than strong enough for anything a small machine like this is likely to throw at them, and Dean's earlier comment re. most mills - yeah - they'll place a similar cantilever load on the rails as well.

Hi doddy,

What is your main problem with exiting 6040 designs?

I feel like the " lean back " gantry design is most space saving.

Do you think 20 mm alu gantry sides will cover your rigidity needs?

http://www.mycncuk.com/showthread.php?t=11610

like that one... but a bit smaller.


Grtz Bert.


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[Doddy]

Hi doddy,
What is your main problem with exiting 6040 designs?

Significantly - I want to do as much of the build myself, and (to an extent) I can work with steel. Having said that there's a recent threads that show some very enterprising use of hand tools (though throwing a woodworking hand held router through 20mm of alu would certainly be different to what I'd normally use it for). The design (once I understand it!) is something that I can build with the equipment that I have. To some extent there's a certain curiosity value as well.

[driftspin]

Significantly - I want to do as much of the build myself, and (to an extent) I can work with steel. Having said that there's a recent threads that show some very enterprising use of hand tools (though throwing a woodworking hand held router through 20mm of alu would certainly be different to what I'd normally use it for). The design (once I understand it!) is something that I can build with the equipment that I have. To some extent there's a certain curiosity value as well.

For cost... steel is the cheaper way to build.. there is a catch though.. steel is not easy to get straight/flat enough to mount linear rail directly.

Did you decide on square or supported rail?


Do you have access to tools to get the steel flat level and straight ?

If not.. epoxy is a solution... but not very easy to do.. and not cheap.



Grtz Bert.

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[driftspin]

For cost... steel is the cheaper way to build.. there is a catch though.. steel is not easy to get straight/flat enough to mount linear rail directly.

Did you decide on square or supported rail?


Do you have access to tools to get the steel flat level and straight ?

If not.. epoxy is a solution... but not very easy to do.. and not cheap.



Grtz Bert.

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what about this one?

http://www.mycncuk.com/showthread.php?t=11152

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