stalling problem

[cxixer]

Hi, A while back I built a 4x4' rack drive router with 4 425oz-in xylotex motors. I had troubles with the rack staying against the pinion which led to gross inaccuracies. After failing to remedy this with several different adjustable and non-adjustable spring loaded contraptions to press the pinion against the rack, I gave up, tore off the racks, and replaced them with 1/2"-10 ACME screws, same motors, 2 screws on the y axis. Since the switch, every cut is very accurate.

I'm pretty sure (measured to .002 with my digital caliper) I have the screws aligned. My problem is I do not think the lead nuts are squared up properly. When first installed, I stalled the motors out at 15ipm, after adjusting on them for a little bit, I could attain 30ipm before stalling.


So my question - how do you guys square up your lead nuts properly? I've read with this set up some people are getting 50-70ipm! I tell you 30ipm burns up bits very quickly!

I also need to stiffen up my z axis, so it stops flexing if the cut is too deep, but one problem at a time...

[TOTALLYRC]

Hi, A while back I built a 4x4' rack drive router with 4 425oz-in xylotex motors. I had troubles with the rack staying against the pinion which led to gross inaccuracies. After failing to remedy this with several different adjustable and non-adjustable spring loaded contraptions to press the pinion against the rack, I gave up, tore off the racks, and replaced them with 1/2"-10 ACME screws, same motors, 2 screws on the y axis. Since the switch, every cut is very accurate.

I'm pretty sure (measured to .002 with my digital caliper) I have the screws aligned. My problem is I do not think the lead nuts are squared up properly. When first installed, I stalled the motors out at 15ipm, after adjusting on them for a little bit, I could attain 30ipm before stalling.


So my question - how do you guys square up your lead nuts properly? I've read with this set up some people are getting 50-70ipm! I tell you 30ipm burns up bits very quickly!

I also need to stiffen up my z axis, so it stops flexing if the cut is too deep, but one problem at a time...

Depending on what you are using for a driver and power supply voltage, 30 ipm may be all that you can get. those 425 Xylotex motors are rated for a top voltage of around 60-70v. If you are using a Xylotex board at 24 -30v, 30 ipm is near the max speed.

Let us know more about your electronics and we will try to help.
Mike

[cxixer]

I replaced the xylotex board with prbotix boards with a 24v power supply. How can I go faster? Or... how do I make my bits last longer?


And not that I want to re-do anything again, but would I get better speeds with a belt drive? I assume these would be easier to set up, even with a tensioner. I have seen some belt driven routers move very rapidly. I'm not concerned with accuracy past about .010, so long as I can cut square and perfect circles.

[cxixer]

After more reading, I realize I skipped over what may be an easy fix to my speed problem. What if I used 2 or more start screws? Effectively a 2 start screw would turn the nut twice as much per rotation as a single start screw, correct? So if I get 30ipm with the single start 1/2"-10, shouldn't I get 60ipm with a 2 start screw?

This wouldn't cost that much for the conversion, just new screws and nuts. They're already direct driven, and the x axis screw got a smidge bent during the original installation and should be replaced anyway.

[TOTALLYRC]

I replaced the xylotex board with prbotix boards with a 24v power supply. How can I go faster? Or... how do I make my bits last longer?


And not that I want to re-do anything again, but would I get better speeds with a belt drive? I assume these would be easier to set up, even with a tensioner. I have seen some belt driven routers move very rapidly. I'm not concerned with accuracy past about .010, so long as I can cut square and perfect circles.

2 way sto go faster come to mind. Both are easier than replacing the mechanicals.
Replace the motors to something that is more compatable with 24v.

Remember that amps is torque. Voltage is torque at speed. The higher the voltage, the faster a stepper motor can go with out stalling, within the limits of the motor. Read the stepper motor primer on the gecko drive website.

The other way and the one I recommend is to upgrade to either a G540 and a 50v power supply which is a lot closer to the max voltage for the existing motors or go all out and get a G203v for each axis and a power supply at the max of the motors. Will cost a lot more.
Both of these options feature morphing from micro to full step at the higher speeds. This will give good low speed performance and resolution. It will also give great rapids. These drives also feature mid-band instability compensation, which the xylotex and other low end boards do not.

The nice feature of either of these options is that you can upgrade the drivers and keep the existing power supply. Then upgrade the power supply as time and money allow.

Search for the posts by sppedscustom to see how well the g540 works on his machine. And then seach for posts that mention g540. There were some initiall "problems" but it really was more of people getting the settings right.
For mach3 users they now include an .xml file to get you started.

Mike.

[cxixer]

Ack! Maybe I should have made my intentions clear. I'd like the machine to move faster, possibly downgrading accuracy in exchange, but be as inexpensive as possible. I'd like to keep what's left of my wallet in tact!


I realize I've got a machine that can cut products VERY accurately (compared to me routing them freehand anyway) for about 1/5 the cost of the cheapest commercial machine, but this router has yet to pay for itself, and most of the rediculous (wife's word) things I buy can do so within a month (ie: vinyl cutter). I keep throwing money at this thing and keep finding things wrong with it. What still needs to be upgraded: x axis needs to have precision rails, z axis needs new precision rails (both of these would dramatically increase rigidity compared to it's current situation). These things I don't have the money for right now, so... I definately don't have the money for a new driver... maybe in time, I'd love to get that gecko!

Depending on what you mean by 'easy', I can see for some a driver swap and/or motor swap would be easier to do, but that, to me requires spending $300 on the gecko drive, modifying my lovely polycarbonate driver case, installing (learning to wire yet another driver setup), and changing mach 3 settings...

I'd like to go the inexpensive route, and to me it's just as easy. A quick coupler disconnect, cut the acme screw to length, pop it in, and poof - I'm done.

I'm just questioning how well this will help my situation. If I'll end up with the same problem for some reason - if the nuts really aren't square enough, increasing friction causing stalling, or whatever, screws wont help. I still think this is at least partly the problem because if I loosen the nuts holding the leadnuts to the gantry, I can rapid at a faster rate.

I'd like to fix this issue if possible, then if not, I'll look at modifying!

[ger21]

Look at the thread with the stepper dampers. Sorry, don't have the link handy. There's a very good chance that resonance is limiting your speed. Most who've made the dampers have doubled their top speed.

Multi start screws will also help, but resonance may still be an issue. Switching to a 5 start screw and adding dampers should give you significantly more speed.

[TOTALLYRC]

Changing the lead crews is definitely an option. And on a plasma cutter, I would say go for it, because a plasma cutter has zero cutting force. On a router setup there is a cutting force of ?lbs.
If you go to a multi start screw, it will in theory go faster. What I am afraid of is you will get diminishing returns with respect to the amount of torque available from the motor. I don't know if it will work. Hopefully somebody will chime in and help out with this problem. I would hate to see you spend the money and time on new screws and find out that it doesn't work.

Mike

[ger21]

On a router setup there is a cutting force of ?lbs.
If you go to a multi start screw, it will in theory go faster. What I am afraid of is you will get diminishing returns with respect to the amount of torque available from the motor.

Typically, by spinning the stepper slower with the multi start screw, you gain a lot of torque that the stepper was losing at the higher rpm of the single start screw, so you end up with a similar amount of force, but with higher speeds.

[cxixer]

Totallyrc: I would hate that too! I'd really like to have faster rapids, even if I could only cut at 40ipm, even that little bit I think would help out the bit burning problem. I've actually switched to using cheaper (still carbide) bits than what I use with my hand router, I find they cut the same and last just as long due to the heat generated from moving so slow... and they're cheaper.

ger21: I've read that damper thread in the past, great thread. I may have to re-visit it. I actually purchased some hardwood to use for the dampers (no mill here), I just have been putting it off.

Can anyone tell me the theoretical gains I would get switching to a multi-start screw?

For example: 30ipm single start, translates to 60ipm 2 start? Or no?

[cxixer]

Typically, by spinning the stepper slower with the multi start screw, you gain a lot of torque that the stepper was losing at the higher rpm of the single start screw, so you end up with a similar amount of force, but with higher speeds.

Good stuff there!


Any source for multiple start screws less expensive than mcmaster ($100 per 1/2-10 2 start, 6').

[ger21]

www.roton.com