Ballscrew Thickness!

[Ross77]

I have seen this done before, but this normally involves more money and because the motor/gearing that is associated to this type is moving with the ball nut, the moving mass is higher.

Didnt think of that . Ist the main problem in this case the actual torque needed to spin the screw? Although the extra weight wouldnt be ideal surley it is a lesser evil ? wouldnt it be possilble to also use a smaller screw which would make it cheaper?

Sorry to hijack your tread :naughty:

options options options, think im going be scratching my head till ive build my machine and ready for the motion! and thats not to far away!

Isnt that all part of the fun.....:heehee:

[Gary]

I have customers who uses this method to get faster motion, but normally would use a servo motor and specific gearing that is only for this type of application.
Unless you get the parts on ebay, it will cost a few hundred just for the gearing.
Also fixing both ends of the ball screw offer similar results (Within about 25%)

Didnt think of that . Ist the main problem in this case the actual torque needed to spin the screw? Although the extra weight wouldnt be ideal surley it is a lesser evil ? wouldnt it be possilble to also use a smaller screw which would make it cheaper?

Sorry to hijack your tread :naughty:



Isnt that all part of the fun.....:heehee:

[AdCNC]

haha yeh but its not fun anymore my wallets burnt out!

[Ross77]

Tell me about it, this definetly isnt a cheap hobby....:nope:

I would love to throw 5K at a scratch built machine, with everything designed for its purpose....as opposed to buying S/H parts and making the machine fit them :whistling:

Thank god for Ebay tho.

[irving2008]

a 16mm dia screw with support both ends would work fine over that distance (~1.8m) up to 700rpm approx, you don't need a 25mm screw...

[tribbles]

Well, according to the calculator:

- 14mm root diameter (subtract 2mm due to thread size)
- 1800mm length between bearings
- B-style end fixing (one fixed, one floating)

Maximum speed is 522RPM.

Even with a 16mm root diameter, it's 597RPM.

(But I know engineers like to put some extra for safety, so it probably would work up to 700RPM).

Or do you have another way of calculating it?

[irving2008]

Well, according to the calculator:

- 14mm root diameter (subtract 2mm due to thread size)
- 1800mm length between bearings
- B-style end fixing (one fixed, one floating)

Maximum speed is 522RPM.

Even with a 16mm root diameter, it's 597RPM.

(But I know engineers like to put some extra for safety, so it probably would work up to 700RPM).

Or do you have another way of calculating it?

14mm root, C style fixing, 1850 long, 727rpm

[tribbles]

14mm root, C style fixing, 1850 long, 727rpm

Yeah, having two fixed ends does improve things - although on my machine it's one fixed (BK), and one floating (BF), and I would guess that's what the standard machining on Gary's ballscrews would provide.

I suppose you could use BK on both ends, but you'd need to make the ends with a lot of precision (or have a number of different size shims to pad out the end with the screw-thread).

[Gary]

You would need to have the fixed end machining done at both ends and the fixed end machining is were all the money is so it would be more expensive.
I dont do the machining, this is done at a local engineering company so i would need to get a quote.

Yeah, having two fixed ends does improve things - although on my machine it's one fixed (BK), and one floating (BF), and I would guess that's what the standard machining on Gary's ballscrews would provide.

I suppose you could use BK on both ends, but you'd need to make the ends with a lot of precision (or have a number of different size shims to pad out the end with the screw-thread).

[John S]

Waste of time on something like a router. You fit double thrusts on both ends, adjust to get a preload, and all that happens is the end frames deflect inwards so the screw is still whipping even with double bearings.

The design has to take this into account.
Bystronics have realised this on their new range of lasers, they have massive end castings and tension the ball screw to something like 70 tonnes tension [ no typo ] to stop it whipping.

Mind you they are using twin drives with 15 HP servo motors on each drive :whistling:

I feel the OP needs to sit down, count his pennies then come up with something that's workable instead of throwing down pie in the sky figures for his first build.

Why the insane rapids anyway ? The whole idea is to bury the tool and work at feed rate.

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