Gantry advice please

[pippin88]

Thank you for advice,
how big is your machine ?
what size pitch and ball screws you using to move gantry, have you used pulleys, if so what ratio.?

Regards Paul

Gantry span 1300mm.
15mm pitch screws. 15mm diameter I think. They are secondhand ground screws.
I use 16mm pitch 16mm diameter screws on other axes (from BST automation).

No pulleys.

Steppers are best used with high pitch screws (10mm or more) not 5mm pitch screws. Steppers have max torque at 0rpm and it falls as rpm rise.

Servos are different. They are rated for torque at rated rpm (often 3000rpm).

[Crunch]

Thank you for all your information.

I think I will go with
1610 x 900mm x 2 for y axis
1610 x 1200 for x axis ( gantry )
1605 for z axis ( still sorting out the lenght )
Going to get ends machined to suit pulleys.

20mm square linear rails all round.

Does this sound ok ??

Thank you

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[Clive S]

Going to get ends machined to suit pulleys.

The bit where the pulley is fitted is called the f length 25-30mm is usually fine BUT remember that the f length is included in the total length of the screw.

Standard machining for the f length is about 15-20mm.

Make sure you get the better bearings AC type for the screw as some suppliers will just put in simple bearings in the blocks.

[Crunch]

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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[pippin88]

I've had very good experience buying from Fred.

Why 1605 on the Z?

[AndyUK]

Thank you for all your information.

I think I will go with
1610 x 900mm x 2 for y axis
1610 x 1200 for x axis ( gantry )
1605 for z axis ( still sorting out the lenght )
Going to get ends machined to suit pulleys.

20mm square linear rails all round.

Does this sound ok ??

Thank you

Sent from my SM-G900F using Tapatalk

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.

[Crunch]

Pippin88

Only because it only travels a short distance. So thought 5mm pitch was fine for that.

And I don't know . Lol

I've read loads of builds and most use 5mm pitch . But I'm open to advice.

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[Crunch]

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.

That is where I started with 2010 on x axis
To stop whip as I had read so much.
The more I read the harder the decisions.

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[AndyUK]

Only because it only travels a short distance. So thought 5mm pitch was fine for that.

And I don't know . Lol

I've read loads of builds and most use 5mm pitch . But I'm open to advice.

Sent from my SM-G900F using Tapatalk

I used 1605 on my Z. Thoughts were rapids are less of an issue as you're travelling the smaller distance, and theoretically the fine pitch gives you twice the height resolution.

At a stretch, maybe thats better for surface finishes?

[AndyUK]

That is where I started with 2010 on x axis
To stop whip as I had read so much.
The more I read the harder the decisions.

Well it was routercnc who said stick with the 16mm due to the added intertia of the 20mm. The man has built four of these things, he knows what hes doing.

I'm saying they'll work, but realise that they'll limit your rapids more than 20mm will. Personally I'd be more than happy with 10m/min rapids - You'd need some pretty strong motors to get up there anyway with a 100kg gantry.