Large plasma table gantry help

[Buckmaster1967]

Hello,
Couple of years a go I built a 11 ft x 6 ft plasma table with a 400 gallon water tank under the table to floord the cutting area. Use 6" steel box tubing for the gantry. Use 1600 oz Long motors with 3.2:1 belt drive reduction for NEMA 34 motors on X,Y & Z drives. Rack & Pinion drive on all. The table does great for signs and rough items. But tight tolerance circle and tight cuts, feels like the gantry is to heavy for quick and tight moves.If I run above 150 imp, feels like the table I start getting slop cuts, the ganty feels like it is just to jerky. I did not know what I was doing when I built the table. Believe the 1600 oz motors are over kill.

I think I would like to upgrade my gantry to a lighter alumium gantry and new smaller motors, not shure If I should keep the reduction gears. Using a 45 amp hypertherm cnc torch on screw Z Drive. I want to make the table as as tight of a tolerance as I possible can. Any on put whould be helpful.

[acourtjester]

Ok some food for thought, The X axis will be carrying the most weight. I have my table made of steel and use a 900 OZ nema 34 motor 3:1 gearing for the X with 60 volt power supply and a driver set for that voltage. For the Y and Z I use a 425 Oz nema 23, the Y is 3:1 gearing, and the Z is a 10 turn to 1 inch lead screw. Both powered with a 36 volt power supply and separate drives. I run about 220 IPM for 18 Ga steel and 48 IPM for 1/4" steel I am very happy with the cut quality. I have built and sold 4X8 tables set up like this, no problems. The size of the table has a small factor in the motor size, your 6 foot wide adds a small additional amount of weight. I use a cable boom for the Plasma cable which help with the cable load on the table. Now it out to the fox hole to wait for incoming.

[Buckmaster1967]

Yes, my thinking the extra weight of the 1600 oz motors are part of my issues. Once the mass is moving, harder to change directions.

[weldguy]

I would swap out the 6" steel beam for an aluminum one to start with. Should shed a pile of weight doing that and may be all that you need.

[Buckmaster1967]

Yes, researching now. Beleive I will invest in some smaller, maybe better quality motors too.

[adbuch]

I would be interested to see some photos of your table so I can better understand what you are dealing with.
David

[Buckmaster1967]

Been working long shifts with little time to play. Here is a picture I have On my pc. Not the ideal picture but...

[adbuch]

Thanks for the photo! When you get time, maybe post some of the business end of the table.
David

[Buckmaster1967]

Very dirty. Knowing I was changing the gantry made me lazy.

[adbuch]

Yes indeed! That might be a tad overkill on that gantry tube. If you could duplicate it in aluminum, or thinner wall tubing - I'm pretty sure that would help some.
David

[Buckmaster1967]

Yes indeed! That might be a tad overkill on that gantry tube. If you could duplicate it in aluminum, or thinner wall tubing - I'm pretty sure that would help some.
David

Yes, my thoughts

[weldguy]

The pics certainly show how heavy and clunky that gantry is. For sure i would build a lighter gantry and just stick with those motors for now and see how it works. Can always swap the motors later and I prefer to do 1 major modification at a time.

[SegoMan DeSigns]

While this machine is running I would do new skates and and gussets with spider webs or a similar design to shed the pounds. Like others have said down grade that tubing wall size and leave the same motors on it. Aluminum is not always lighter, I needed a H.D. beam for my Y axis on the 6'x12' as I plan to mount an air drill to it capable of 400 - 600 lbs of down force, I looked at the 80/20 profiles but with oversize / weigh charges it was going to be in the $800+ range for a 9' 3" section. I did a little research and found that 4x6x1/8 wall tubing weighs the same / foot and bought a 20' piece for $120.

Here is my gantry, I even added a buggy to it to help with acceleration.

[Buckmaster1967]

Very nice looking gantry. I believe I will do a complete rebuild on a new gantry. Leaving my table intact till I do a gantry swap. Swapping the for steel tubing to aluminum will lighten it the gantry by 39lbs.

[SegoMan DeSigns]

Keep us updated and post up some pics of your work. Another thought I had is perhaps some of yuor bearing are getting worn or dirty

[adbuch]

Keep us updated and post up some pics of your work. Another thought I had is perhaps some of yuor bearing are getting worn or dirty

[Rodw]

I don't know your gantry weights but your motors are surely too big. You are adding weight adn also the rotational inertia on a motor that size sucks a lot of energy
You are stuck with the Nema 34 footprint.
Talking higher quality drives

After a lot of engineering, on a 90 lb gantry
I use 2 x Moon ML34HD0L4700 538 oz/in NEMA34 motors on my gantry and it accelerates at 0.5 G and rapids at 1200 in/min
Across the gantry, I use a 2 amp NEMA24 Sanyo Denki that I tested to 0.8G and over 2400 in/min rapids
I think that would be a good motor for your torch lifter and across the gantry.
Because of your extra weight, Maybe 2 x Moon ML34HD1L4700 1019 Oz/in might be a better choice to move the whole gantry.
Your reduction ratios of 3.2:1 are fine. I use 3:1 and 5:1 (which was convenient but arguably limits performance a tad).
Z axis is direct coupled to a 1605 ball screw

I am using 90 volts at the motors (64 volts AC to the drives actually) and high quality Lam Technology drivers.
But your 60v power supply is not a performance limiting factor based on our spreadsheet which says I only need about 30 volts.

Take this with a grain of salt as I have not done a full design evaluation.

[Buckmaster1967]

I don't know your gantry weights but your motors are surely too big. You are adding weight adn also the rotational inertia on a motor that size sucks a lot of energy
You are stuck with the Nema 34 footprint.
Talking higher quality drives

After a lot of engineering, on a 90 lb gantry
I use 2 x Moon ML34HD0L4700 538 oz/in NEMA34 motors on my gantry and it accelerates at 0.5 G and rapids at 1200 in/min
Across the gantry, I use a 2 amp NEMA24 Sanyo Denki that I tested to 0.8G and over 2400 in/min rapids
I think that would be a good motor for your torch lifter and across the gantry.
Because of your extra weight, Maybe 2 x Moon ML34HD1L4700 1019 Oz/in might be a better choice to move the whole gantry.
Your reduction ratios of 3.2:1 are fine. I use 3:1 and 5:1 (which was convenient but arguably limits performance a tad).
Z axis is direct coupled to a 1605 ball screw

I am using 90 volts at the motors (64 volts AC to the drives actually) and high quality Lam Technology drivers.
But your 60v power supply is not a performance limiting factor based on our spreadsheet which says I only need about 30 volts.

Take this with a grain of salt as I have not done a full design evaluation.

Great infomation. Planning on a complete rebuild of the the carriage that carries the Z drive across the gantry. Changing from rolling on the box tubing,to using two Linear guides on the front of the bux tubing. In hopes of a smoother, sturdier movement. Similar to the photo.

[adbuch]

I don't know your gantry weights but your motors are surely too big. You are adding weight adn also the rotational inertia on a motor that size sucks a lot of energy
You are stuck with the Nema 34 footprint.
Talking higher quality drives

After a lot of engineering, on a 90 lb gantry
I use 2 x Moon ML34HD0L4700 538 oz/in NEMA34 motors on my gantry and it accelerates at 0.5 G and rapids at 1200 in/min
Across the gantry, I use a 2 amp NEMA24 Sanyo Denki that I tested to 0.8G and over 2400 in/min rapids
I think that would be a good motor for your torch lifter and across the gantry.
Because of your extra weight, Maybe 2 x Moon ML34HD1L4700 1019 Oz/in might be a better choice to move the whole gantry.
Your reduction ratios of 3.2:1 are fine. I use 3:1 and 5:1 (which was convenient but arguably limits performance a tad).
Z axis is direct coupled to a 1605 ball screw

I am using 90 volts at the motors (64 volts AC to the drives actually) and high quality Lam Technology drivers.
But your 60v power supply is not a performance limiting factor based on our spreadsheet which says I only need about 30 volts.

Take this with a grain of salt as I have not done a full design evaluation.

Great infomation. Planning on a complete rebuild of the the carriage that carries the Z drive across the gantry. Changing from rolling on the box tubing,to using two Linear guides on the front of the bux tubing. In hopes of a smoother, sturdier movement. Similar to the photo.

That looks like a great way to go! Keep us updated with your build.
Thanks,
David

[Rodw]

Great infomation. Planning on a complete rebuild of the the carriage that carries the Z drive across the gantry. Changing from rolling on the box tubing,to using two Linear guides on the front of the bux tubing. In hopes of a smoother, sturdier movement. Similar to the photo.

I think this will make a difference as it will reduce friction and power requirement.
For reference my gantry is 80mm x 40mm x 4mm Aluminiumn hollow rectangular section.
I used 2 x HGR15 rails with rack and pinion but when I look at the torque handling, I do sometimes think a single rail would have been enough and reduce some weight.

EDIT: I meant the Moon ML34HD0L4700 would be good on your gantry and Z axis

[Buckmaster1967]

Great infomation. Planning on a complete rebuild of the the carriage that carries the Z drive across the gantry. Changing from rolling on the box tubing,to using two Linear guides on the front of the bux tubing. In hopes of a smoother, sturdier movement. Similar to the photo.

I think this will make a difference as it will reduce friction and power requirement.
For reference my gantry is 80mm x 40mm x 4mm Aluminiumn hollow rectangular section.
I used 2 x HGR15 rails with rack and pinion but when I look at the torque handling, I do sometimes think a single rail would have been enough and reduce some weight.

EDIT: I meant the Moon ML34HD0L4700 would be good on your gantry and Z axis

Thanks, if I understant it right, yours is about half the size my tube.101.6 mm x 101.mm x 6.35mm . 1828.8mm across the table.

[Rodw]

Yes, if I could have got 5mm or 6mm wall I would have used it but I used what was readily available. 4mm wall is enough to hold a 6mm thread. I did not do any engineering but one did think it was a fair choice. I think he selected 6 x 2 x 0.25" but thats not in my market.