Timing pulley on ball screws

Hi,

This is my first post. I built my first CNC router a couple months ago and learned a couple things that I want to rectify on my second router.
I'm now in the process of building my second CNC router.

To my regret I bought ball screws from China. More specifically linearmotionbearings2008. What a lot of rubbish this guy sells and what a waste of money.

My first machine has steppers directly coupled to 5mm pitch ball screws (1605's). I get very low IPM's from this method. Firstly due to the ball screws being bent and if I push the router too fast the ball nut will jam causing the motor to stall.
Secondly, with 5mm pitch screws I need to push the motor hard to get high IPM's.

I've now purchased much better quality screws and know I can push the router faster with confidence (no more jamming).

I was thinking of increasing the speed by using a timing pulley ratio increment like 2:1 (40 teeth on the stepper and 20 teeth on the screw) but I'm not sure if I will really gain anything this way. I will get double the speed at high torque but due to the gear ratio I will need double the torque for that speed. If you get what I mean.

1.) Will I gain anything from using a ratio increment using timing pulleys?
2.) What could you recommend to get higher IPM's with my setup?

Here are two links to videos of my current machine. The one video demonstrates the homing speed and the other the cutting speed. I'm happy with the cutting speed but the homing speed is too slow. I'm not even sure if the cutting speed is fast enough even though it seems reasonable.

https://youtu.be/FAkWd3ND980
https://youtu.be/HCIEoBdYUT8

I will appreciate your feedback.

You can adjust the speed inside of your cnc program. You did not say if you are using Mach3, Mach4, LinuxCNC, KmotionCNC, or some other program. Need to know that first off. Second you need to keep in mind you are using a wood router for a spindle you will not be able to push that very much faster than your machine is going right now unless you swap it for a true Spindle, water cooled or air cooled at least 2.2Kw. A spindle has much more power than a wood router and is made to run for extended periods of time, where a wood router is meant to be used for short durations. The first thing that goes in wood routers if you push them hard and use the highest RPM is the bearings.

Next you need to think about what kind of material you plan on cutting. If you expected to cut red oak at 200 IPM you are kidding yourself unless you make a very small depth of cut and run at least a 1/4" bit or the bit will just snap.

You can add the timing pulleys and belts to increase your speed, but you really need to check the software first to make sure you are actually testing it at its full speed. Then if you really want more speed you can also go from stepper to servos which run at higher RPMs, usually up to 3000 RPM, so they spin much faster than a stepper.

Russ

The second video is private..

Quote:

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I was thinking of increasing the speed by using a timing pulley ratio increment like 2:1 (40 teeth on the stepper and 20 teeth on the screw) but I'm not sure if I will really gain anything this way.

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Yes, it will roughly double your speed. You should have purchased 1610 screws.

Quote:

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If you expected to cut red oak at 200 IPM you are kidding yourself unless you make a very small depth of cut and run at least a 1/4" bit or the bit will just snap.

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If the machine is rigid (none or minimal vibrations at the tool), 200ipm can be done easily. You can easily cut at 300ipm with an 1/8" bit.

Thanks for the replies.

@CNCMAN172:

I'm using Mach3 and did experiment with the motor velocity. This is the maximum speed I can run without the motors stalling. As you should know, the higher the RPM on the motor the lower the torque. The router is not my concern at this stage. I first want to get my structure working properly before investing in a proper spindle. I can always upgrade the router at a later stage.

@Gerry:

Sorry, the 2nd video is not private anymore. Yes, I would have liked to use 12mm pitch screws but it is much easier for me to get 5mm pitch good quality screws.


The question is about the pulleys. Introducing pulleys will double the speed but at the same time the motor will require double the torque and I will half my resolution.
If you look at the second video you will see the cutting speed looks reasonable? I'm asking? Its the homing speed that I would like to improve. I can always cut a lower speed even when the homing speed is fast.

So the question remains, would I gain anything form introducing a pulley ratio increment? What else can I do to get the machine faster other than using higher pitch screws?

I'd love to hear from someone who has done it before.

Thanks

Go to Config > Homing/Limits to change the homing speed.

Is it cutting fast enough? I would say no, but it depends on the spindle speed. With MDF, you can literally go as fast as your machine and spindle can handle.

Even with a 2:1 pulley reduction, you'll still have a resolution of about .001". Your machine will flex much more than this, and the MDF will shrink and grow more than that with changes in humidity.