2x 2005 C7 Ballscrew 1450mm Length with Ballnuts + FK/FF mounts and motor coupler

[JAZZCNC]

You need to take everything though, I'm not pissing about wasting diesel to pick 10 bobs worth of gear up.

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Well Mr Stevenson I saw your Post before the SS jumped in and I must say I've never been so insulted in my life good Sir.

So on this matter request you meet me Sir in the Central reservation of the M1 for a dual at dawn. (Or when ya eventual fire the zimmer up.!!)

Bring the Axle grease because the loser gets Rm2005 inserted side ways and Z axis up his Pi$$~£.!! . . . . Now F@~% O%% You Old B%@~% and happy Xmas mate. . X X X
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Now I've got a important and just has relevant Calculation for Jonathan.?

Was in workshop Tuther day and waiting for Job to finish when I felt another Jobbie coming on and while there Nipping the Old vice Cheeks started to wonder just how many Nm of force could be applied thru Cheek power alone.? . . . . Obviously realise this will be a rising rate has desperation sets in so some parameters will be needed..?

So lets say when at the Turtle point of 15st Fat B@~&$ erds thrust curve when powered by a full Vidaloo madras.?

Oh and what will be the stall point time curve so know how many liner meters of paper for Clean up.?

[John S]

Well Mr Stevenson I saw your Post before the SS jumped in and I must say I've never been so insulted in my life good Sir.

You have obviously not been round much then.

If we are talking about the central reservation on the M1 than lets use the bit just below J27, the Mansfield turn.

Rather partial to that bit after having removed about 30 metres of it in a wrecker one day doing a slow spiral from slow lane to central reservation.

So after all the "Pi$$~£.!! . . . . Now F@~% O%% You Old B%@~% and happy Xmas mate. . X X X
X X X X X X X X X X X X X X X X X X"

Are you having them ?

[WandrinAndy]

.... started to wonder just how many Nm of force could be applied thru Cheek power alone.? . . . . Obviously realise this will be a rising rate has desperation sets in so some parameters will be needed..?

Afraid I don't have a formula at hand but would like to suggest that it include a parameter that caters for dwindling power over age, as I'm convinced I canna hold them in as well as I used to do!

[Shinobiwan]

It would just have been nice to have had the chance to buy some cheap replacement screws before being offered up to general public considering the involvement I've had with this machine.!! . . . ANT.

To be honest, when you mentioned this the other day, I thought you were going with 2010 if it came to replacing the screws and gearing down to 1:1. Didn't even enter my head that you might want them otherwise would have given you a shout of course.

Your in luck because John's a true gent and looks like he's willing to step aside so your welcome to them if your still interested by the time you read this. Let us both know ASAP and we can sort the details.

[Shinobiwan]

The only thing this size ballscrew is good for is maybe a big milling machine or lathe. For other machines, like CNC routers, the forces on the ballscrews are so low that you don't need the slight increase in stiffness gained from using a RM2005 screw

Its not slight when your spinning them at 1000rpm+ At 1.45m I've got a 1610 on the Y axis and it just starts to show whip at 10m/min, at 14m/min its like jelly! You won't run at these speeds of course but for cutting wood you want in the range of 4-7m/min depending on the cutter dia and flutes along with DOC. Unless of course your spinning the nut but I'd still go 2010 at those lengths anyway. The cost difference is minimal for the added peace of mind.

Presumably John S has a big machine to convert...

Or he's chopping them up into lots of little screws ;) More likely though is he'll put them in his cnc spares stash and leave them for a rainy day. The man has enough parts to set up a cnc factory.

[Jonathan]

Its not slight when your spinning them at 1000rpm+ At 1.45m I've got a 1610 on the Y axis and it just starts to show whip at 10m/min, at 14m/min its like jelly! You won't run at these speeds of course but for cutting wood you want in the range of 4-7m/min depending on the cutter dia and flutes along with DOC. Unless of course your spinning the nut but I'd still go 2010 at those lengths anyway. The cost difference is minimal for the added peace of mind.

The cutting force on a CNC router is a few tens of newtons, even when taking 'heavy' cuts in wood or aluminium. There's an additional force when acceleration so lets say 100N. The RM1610 ballscrews are rated for something like 7800N for one million revolutions, so operating at 100N they will last for a very long time. Hence you don't need a bigger screw unless critical speed is an issue, which according to your experiment and the calculation it isn't for this length (1450mm) and RM1610.

Got two RM2010 at 1450mm with end machining and ballnuts from chai for $218 including shipping. So 325 is very expensive where ever your buying those from.

I did not say that I had bought any at that, or any, price. That was the first seller I found on ali-express who has RM2010. Last time I checked Chai doesn't sell RM2010 and Jazz posted only a few days ago saying the same. So where did you get your RM2010, or are they actually RM1610?
Either way my point is valid - RM1610 or RM2010 is a much better choice for this length for the vast majority of machines built on this forum. If John S has got a use for them then good for him, since he's just got a good deal.

[Shinobiwan]

The cutting force on a CNC router is a few tens of newtons, even when taking 'heavy' cuts in wood or aluminium. There's an additional force when acceleration so lets say 100N. The RM1610 ballscrews are rated for something like 7800N for one million revolutions, so operating at 100N they will last for a very long time. Hence you don't need a bigger screw unless critical speed is an issue, which according to your experiment and the calculation it isn't for this length (1450mm) and RM1610.

Jonathan, your good with this maths stuff.

I have a gantry that weighs approximately 80kg with spindle. With a decent rate of acceleration let's assume its set to 1000 and 160 steps per in mach with dual RM2010 and 4Nm motors. How much kinetic energy is transferred to the motors when doing a direction change at say 1000rpm or 10m/min? You got to decelerate that 80kg in a very short space of time and I'd hate to think how big this number is going to be or if the motors can even handle that.

[Jonathan]

I have a gantry that weighs approximately 80kg with spindle. With a decent rate of acceleration let's assume its set to 1000 and 160 steps per in mach with dual RM2010 and 4Nm motors. How much kinetic energy is transferred to the motors when doing a direction change at say 1000rpm or 10m/min? You got to decelerate that 80kg in a very short space of time and I'd hate to think how big this number is going to be or if the motors can even handle that.

Right, so you have said let:
acceleration =1000mm/s^2=1m/s^2
velocity = 10m/min = 10/60= 0.167 m/s (not actually required for the initial calculation)
mass = 80kg

It's just newtons 2nd law, so F=ma=80*1=80 Newtons (equivalent to lifting about 8.2kg), so not far off my earlier estimate.

From the motor's point of view it's not 80N, since we have to consider the ballscrew in between. The ballscrew gives the motors a huge mechanical advantage. The relevant formula, which can be derived from considering the ballscrew as a ramp, is:

T=F*p/(2*pi*e)
Where T is the torque, F is the force applied to the nut, p is the ballscrew pitch (so 10mm=0.01m) and e is the efficiency (about 0.9). So chuck the numers in:
T=80*0.01/(2*pi*0.9)=0.14 Nm

So changing direction at 10m/min and 1m/s, as you describe, only translates to an extra 0.14Nm torque on the ballscrew, compared to going at a constant speed and 80N force on the ballnut.