Hi guys,
I was wondering if someone here would be interested in checking my ratio calculations before I purchase belts and pulleys.

My y and z axies will be using threaded rod 2mm pitch.
The servos (Electrocraft E543) have a maximum continuous rpm of 4000.
I suspect a 3:1 ratio will be suitable, so 1333.33rpm * 2mm = 2666.66mm per minute.
2666.66mm / 25.4 = 104.98 inches per minute (not taking frictional losses into consideration).

My x axis will be using a belt and pulley system.
The driving pulley has a pitch of 11.4mm and has 18 teeth = 205.2mm per revolution.
To get the x and y axies proportional 2666.66 / 205.2 = 12.995:1

I may not be able to achieve the perfect ratio match between x and y but Mach2/3 has a calibration adjustment for this situation. Dose anyone see anything wrong with my calculations?

Thanks
Splint

Splint, Unless I am missing something, your numbers are flawed for the X.
1/ If the x axis has the same motor and using the same pitch screw, (you did not indicate any different) the ratio will still be still be the same. A 11.4mm pitch and 18 teeth do not automatically come out at 205.2mm/rev, that is a circumference amount and not a linear amount.
If you have the same pitch screw, the feed rate at 4000 rpm would be 666mm/min.
What are you using on the Y & Z if not belt and pulley?
I could be proved wrong.
Al.

Thanks for the resonse Al,

OK, all the motors I will be using are the same for each axis (Electrocraft E543).
The drive mechanism for the y and z axies will simply be all thread, the only belts and pulleys used will be to reduce the maximum rpm from 4000 at the motor to 1333.33 at the leadscrew, so a 10 tooth pulley on the motor shaft and a 30 tooth pulley on the allthread leadscrew (2mm pitch) I think should equate to 104.98ipm.
The x axis will be running a fixed belt (no leadscrew)each side of the gantry running the full lenght of the machine with the 18 tooth pulley in mesh with the belt being turned to move the gantry. What I need to know is what ratio will reduce the 4000rpm at the x axis motor to acheive 104.98ipm (or close to) so I can get the x and y maximum speeds proportional to each other and be able to calibrate them in Mach2.

Thanks
Splint

Your calculations for the y and z axis are correct. I'm working on the ones for the x axis. Before I can come up with the right numbers, I need to know the 18 tooth's pitch or the type of belt you are using on it.

Duh-- I see that it is 11.4 mm. Is that the belts pitch or the pulleys pitch diameter.

That makes more sense now on the x, the problem with the long belt drive is the degree of reduction needed, you have a similar problem when Rack & pinion is used, I generally look at a surplus planetary gearbox with this setup otherwise at around 12:1 it makes for a large pulley, also you have to maintain a certain centre distance to engage the recommended number of teeth.
Al

Thanks guys,
thats the belts pitch, I laid the belt flat on its back and measured over 10 teeth and divided by ten (to be more accurite than measuring over 1 tooth) and the pitch worked out to be 11.4mm. The belts are second hand and appear to have no part numbers or brand on them.
A surplus planetry gearbox would be hard to find here in Australia (I've not been able to find a place anywhere in oz the deals in surplus motion control equipment), I think I will end up using a series of belts and pulleys (a bit like a belt driven drill press) rather than one small pulley and one huge pulley.
As far as keeping the teeth engauged, that shouldn't be an issue as I'll have idlers either side of the drive pulley which will keep half of the pulley in mesh with the belt.
It might be an idea to show the math to calculate the ratio for future reference.

Thanks
Splint

Hi Al and Splint,
Can I jump in on this thread.
I just bought 3 E543's from a guy in Kansas (Ebay 6 left)
Are these suitable for my mill drill conversion. Will they have enought torque to run it.
Alumininium and small steel parts is what will be cut/millied.
What's the best way to drive them ? Gecko ? etc
I'd appreciate your help
Thanks
George