What gearing should I use?

[1armsbandit]

Hi Guys,
I finished building my first cnc router (dremel) measures a 24" x48". The whole machine is made of Aspen wood. I'm using 425 oz stepper motors with 1/2 10 2 starts acme leadsrews. My x-axis is 48 inchs long and would like to put a timing pulley belt system on it for more efficiency. The gantry is 32 inches wide, there is some mass there. I've looked at timing belt pulleys, and not really certain what to use. Any suggestions would be appreciated.

[lunchtrayrider]

my first cnc's were out of mdf and used a dremel. i had motors that were approximately 75 oz/in and running 1 to 1 on a 3/8 12 single start acme would jam the dremel tool easily. based on that you could shoot for the sky for transit speed as very little power will actually be needed to push the dremel into material.

make sure that your also getting the resolution you still want when you make it faster too.

could you post a picture? it sounds like it would look pretty cool made of aspen.

[1armsbandit]

Ok I found a gear that were 16 teeth on the timing pulley, is that good one? I added some pics

[lunchtrayrider]

it is really kind of an equation. figure out how fast (rpm) that your motors turn. then decide how how fast you want the gantry to move. on an xl belt for instance there are 5 teeth per inch. if you were turning 100 rpm on your stepper motors with a 16 tooth pinion you would be pulling the belt at a rate of 1600 teeth per minute which would be 320 inches per minute. that is pretty fast. it would also mean that if you were half stepping you would have 400/16*5 would be 125 half steps an inch. that could be pretty low resolution, but if you have microstepping drives you might be alright.

just to verify you are talking about removing the drive screws and replacing them with belts correct?

[1armsbandit]

Hi
Thanks for the info, but no I don't want to replace the lead screw. I have 1/2 10 2 starts acme lead screws. My x-axis is 48 inches long and would like to put a timing pulley belt system on it for more efficiency. The gantry is 32 inches wide, there is some mass there. I've looked at timing belt pulleys, and not really certain what to use.I found a 16 tooth timing pulley, but you say it's to fast. I would move the motor and lead screw to one side of the table. Put another lead screw on the opposite side with a idler arm in the middle to add tension, that's the plan. The pulley's would be attach to the lead screws, then motored together thus moving the gantry. What would you use for pulley's? Any suggestions would be appreciated.

[ger21]

So you want to run two screws from a single motor.

What drives are you using, and what voltage are you running at?

[lunchtrayrider]

are you trying to just get two leadscrews on the x axis? or are you trying to make the gantry move faster?

[1armsbandit]

Yes, I'm trying to make the gantry move faster using two lead screws; also I read that it's more efficient.My velocity settings on Mach 3 are set at 30 which I know it can improve with a pulley set up.I'm using the xylotex 425 oz motors with an output of 1.6 volts.

[ger21]

I'm using the xylotex 425 oz motors with an output of 1.6 volts. Edit/Delete Message

Assuming a Xylotex drive, what voltage? Not 1.6V??

I think you may end up spending a bunch of time and money and not gain anything.

I think you can maybe triple your speed by getting a smaller motor, like the Keling KL23H276-28-4B, and maybe making a damper. I'd try that for $40 first.

[1armsbandit]

I'm amusing you meant the voltage output for the motor. The voltage for the driver board is set at 24v max is 27. I have seen a number of people with this set up using pulleys on the lead screws. My friend that has a homemade cnc has a pulley set up his, but he's out of town. My expense would be the timing pulley's and the lead screw and anti backlash nut, belt.

[ger21]

What is 1.6V? Where are you getting that number?

[lunchtrayrider]

okay im going to take a shot at what your numbers are. I'm going to assume that the velocity being 30 means that your running 30 inches per minute. yes that is pretty slow. if your running lead screws that give you 5 turns per inch then you are turning 150 rpm out of your motors. I'm not an expert on how many rpm's you should be getting but that seems low.

you need to decide what parts you want to use to make this go faster. if you go to two lead screws that can help with racking. this may help you keep from getting jams that may be keeping you from going faster. ger21 is right though, your running a low rpm stepper motor to begin with.

secondly, your going to need to decide on a ratio between the pulley on the motor and the pulley on the lead screw. 1:2 will double your speed, 1:3 will triple it, etc. your going to lose some serious resolution doing this so just remember that. if your running your xylotex in 1/8th step and you do a 1:4 ratio then the output will be roughly as if you were half stepping.

i kinda feel as if your speed problems might be related to something else perhaps? what is currently keeping you from just cranking up the speed in mach3?