# Thread: Hobbymat BFE65 Conversion - Gearing my Steppers?

1. ## Hobbymat BFE65 Conversion - Gearing my Steppers?

I'm busy converting a BFE65 head with an unknown XY table + stand. It's coming along well - but

I'm a little stuck with gearing the table/head...

I'm using 3Nm SY60 steppers with a microstepping PM542 driver. It's driving 5mm lead 16mm (RM1605) linearmotionbearing ballscrews. (600/300/300mm) Any idea what factors I should be using to calculate my pulley ratios?

Should I be basing it on what I want the jog speed to be, or max torque or pulses per inch?

Any advice would be most appreciated - thanks!

James

2. Deciding to gear down your steppers is a balance between rapid speeds and torque available while cutting. Most systems use steppers direct driving the spindle due to their limited rpm range and declining torque/speed curve.

For say an upper end of 1000 rpm on your motors, thats going to be a rapid speed of 5000 mm/min, or about 200 in/min. Thats pretty quick for a small table.

To figure force you can use the equation given by figure 11 at the Nook site here:

Ball Screws, Ball Screw Glossary

This equation will give you the linear force applied for the load you will have on the table. Run your numbers through this equation and see if you think you will have sufficient force direct.

If you decide to gear down your steppers, the torque multiplication effect will give you more cutting force at the expense of rapid speed.
HTH, Jeff

3. The seller of the stepper kit also suggests 1000rpm in bipolar parallel. What is a sensible rapid speed for a machine of this size - 5000mm/min seems too fast?

James

4. I'm not familiar with your machine there... does the column bolt to that XY table? What do you plan to cut with this setup? If you're primarily working with aluminums and mild steels, I would suggest that direct drive with your steppers may be appropriate.

Keep in mind that just because the system may be capable of that rapid speed doesn't mean you have to use it. Your g-code will specify what speeds to move at. But yes, 5000 mm/min or 200 ipm is a pretty quick rapid speed. You can scout around on youtube for some videos to get a feel for how quick this really is.

I think what you need to do is determine if you NEED more cutting force at the expense of this rapid speed. You may want to work through some cutting force calcs cases using the machinery handbook for the materials you will be cutting typically to determine if the direct drive torque will be acceptable or if you need to increase it.

Keep in mind too that at the limits, all sorts of other factors come into play here too, like rigidity of the machine (can you really push it that hard without chattering), spindle motor power, etc.
Jeff

5. Thanks Jeff,

To clarify 90% of it's workload will be aluminium with the occasional small mild steel job, the table is upside down in the picture and mounts to 400 odd kg of cast iron stand, the column is then mounted to that....

James