Gantry advice please

[Clive S]

I was going to order from Fred at BST
He has offered machining the ends for pulleys.
He also offered better bk/bf bearings.
Is this the bearings you are talking about?

Thanks for advice

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Yes those are correct bearings. Just tell Fred the f length you require but as I have said the ball screw length includes the f length . Its an easy mistake to make.

So just order say ball screw machined both ends 1610 x 1200 with f length of 30mm

(where 1200 is the total length)

For the avoidance of doubt my router has twin screws twin motors and the screws are 1450mm overall. Motors nema 23 . without any problems.

[Crunch]

Yes those are correct bearings. Just tell Fred the f length you require but as I have said the ball screw length includes the f length . Its an easy mistake to make.

So just order say ball screw machined both ends 1610 x 1200 with f length of 30mm

(where 1200 is the total length)

For the avoidance of doubt my router has twin screws twin motors and the screws are 1450mm overall. Motors nema 23 . without any problems.

Are your ball screws 1610 or 2010 ??
How heavy is your gantry, roughly ??

[Clive S]

Are your ball screws 1610 or 2010 ??
How heavy is your gantry, roughly ??

1610 and about 70kg



there are two 1000x60x60 x5mm box section behind the front plate on the gantry.

Also you don't need the screw to be the full length of the machine

[Crunch]

I like the ajustable bed.

How wide are the plates top and bottom of your gantry. As you have slotted your gantry for ball screw.
I like the look of your gantry.

The slot in your gantry is what I had planned for my box steel,so I could fit the ball screw inside. But I didn't realise how much strength I was going to lose. I ordered 8 mm thick to allow for it. After posting here and getting the information realise it will weaken it to much.



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[Clive S]

If I was doing it again I probably would have used heavy duty ali profile formed in a L shape. But that was my first router.. Gantry front plate 1000x210mm
Some pics here:- https://photos.app.goo.gl/cfbXGLBdxYvB9s536

[mattnedgus]

Don't cut the tube. Add diagonal braces and end caps (welded, glued, or bolted).

Don't worry about weight. My dual drive 381 Oz in steppers will throw around my 100kg gantry system at 20metres/min.

Pippin88,

How do you get 20m/min out of those motors direct-driving your screws? Is it something to do with the quality of screws you're using?

I can only get 7m/min direct-driving 1530mm of 2010 which (I thought) agreed with the theoretical max speed of the calculations I did.

On a 16mm pitch that same calculation says I could maybe get 12144mm/min on the same motors but that still seems way off what you're managing (and my gantry is light - made-from-plywood-light!).

Matthew

[Max Maker]

Your X axis is quite long for 16mm - You'll get a 12mm root diameter on these, which means assuming you use a BK and a BF, you'll have a max speed of 1000rpm before whipping. With the 10mm pitch you're okay because it sets your max rapids of 10m/min - definitely wouldn't want to go 1605 though! A 20mm screw instead will give you a max rpm of 1260 which bumps your possible rapids up to 12.6m/min, but will take slightly more power from your motors.

The Y axis gives you a max rpm of 1800, which is fine.

Could you make that calculation for a 2.2m long ballscrew? I only have 2010 available so far.

[Neale]

Could you make that calculation for a 2.2m long ballscrew? I only have 2010 available so far.

If you Google for "critical speed calculator", you will find a number of sites where you can plug in your dimensions and check for max speed. They all give slightly different answers but you will get a good idea of what might be possible. Then you can play with different lengths, motor/screw gearing, etc, to meet your needs. For example, my machine is configured more for acceleration than speed as I do a lot of fine work where I seldom hit maximum speed anyway.

[Max Maker]

Thanks. Looks easy enough.