[2rdesigns]

Hi everyone,

Updated design pics.

Still haven't decided on what kind of ACME thread size to use. I would like to get rapids of 250ipm or better, I was initially thinking 1/2-10 5 start with 425oz Steppers. Any suggestions?


Here is my design so far;







Some of my parts.

1"Dia Rail and 6" carriage


t-slot extrusion and 1"Dia rail and carriage blocks


6"x60" Aluminum Channel


Z axis rails

[cyberkeith]

Nice work on the drawings, I am new so little advice, but just starting my build also.
I am using SBR20's for all the rails, mine is 1000mm X 800mm
what size is your machine?
thanks for the pictures!
Keith

[ger21]

I was initially thinking 1/2-10 5 start with 425oz Steppers

425oz motors will limit your speed unless you use Gecko G203V or G201x drives, and run them at 72V.

381oz motors run from a G540 and 48V will most likely be faster, and cheaper.

While you 'll lose some travel, I'd space the bearings apart for your X and Y axis. At least 6" between them. It'll make everything more rigid.

[2rdesigns]

Nice work on the drawings, I am new so little advice, but just starting my build also.
I am using SBR20's for all the rails, mine is 1000mm X 800mm
what size is your machine?
thanks for the pictures!
Keith

Thanks cyberkieth, my table travel will be about 30"x48" (762mm x 1219mm). I noticed your build thread and I'm curious how things go for you. Looks similar to mine. Do you have drawings?

Rick

[2rdesigns]

425oz motors will limit your speed unless you use Gecko G203V or G201x drives, and run them at 72V.

381oz motors run from a G540 and 48V will most likely be faster, and cheaper.

While you 'll lose some travel, I'd space the bearings apart for your X and Y axis. At least 6" between them. It'll make everything more rigid.

I will look into 381oz motors. My current machine has a Zylotex 269oz kit, but I figured this machine needed a little more power. Any good sources for that setup?

Also, the bearings I'm using are 6" long and I'm using one per side. I only have 4 total.

[louieatienza]

I use the xylotex 425in-oz steppers with my G540, and achieve over 725ipm rapids on the x and y with 8 start (1tpi) leadscrews, with a relatively heavy gantry. I think you'd easily get 250 and possibly over 300ipm, though as Gerry says, probably not as efficient or cost-effective as the 381in-oz Kelings... Of course my decision was based on what I already had on hand...

[2rdesigns]

I use the xylotex 425in-oz steppers with my G540, and achieve over 725ipm rapids on the x and y with 8 start (1tpi) leadscrews, with a relatively heavy gantry. I think you'd easily get 250 and possibly over 300ipm, though as Gerry says, probably not as efficient or cost-effective as the 381in-oz Kelings... Of course my decision was based on what I already had on hand...

725ipm rapids would be great! I didn't think I could get that speed. I definitely want to use a G540. From what I've read using high tpi ACME threaded rod tends to be less accurate. I was hoping to have an accuracy around +/- .005" or better. With 1/2-10 5 start I figured I could get 250-500ipm. 500ipm using a G540. What Kind of accuracy are you getting?

Thanks,
Rick

[kevincnc]

Nice looking design. I think your biggest chance for increased rigidity would be by making that Y-axis extrusion taller (square.) The rails help some, but I think that extrusion will your weakest part and will want to flex (twist) during cutting. Maybe it's too late for that, just a thought.

[louieatienza]

725ipm rapids would be great! I didn't think I could get that speed. I definitely want to use a G540. From what I've read using high tpi ACME threaded rod tends to be less accurate. I was hoping to have an accuracy around +/- .005" or better. With 1/2-10 5 start I figured I could get 250-500ipm. 500ipm using a G540. What Kind of accuracy are you getting?

Thanks,
Rick

I would say I get at least .005" accuracy with my machine, and repeatability is excellent. I routinely cut parts for a speed shop, and get within .002-.004". That said, I think trying to get 500ipm with 5-start (2tpi) leadscrews will be difficult at best, despite some claims you may see on the forum. Aside from the faster speed that 8-start provides, it is probably 15-40% more efficient than the 5-start screws. So the finer the lead or the more threads per inch, usually the less efficient since your steppers will have to overcome more "friction." On the other hand there is more of a mechanical advantage with 5-start as opposed to 8-start, since it's harder to backdrive.

The other thing is, under load, at 725ipm, I have enough torque to move the machine around (and that gantry weighs over 100lbs without the router) but I don't have much power in reserve after that. I would say my max cutting speed would be about 400-500ipm. With most steppers in this size, 700-800ipm to me seems to be the upper limit of usable RPM, any higher and there's not a lot of usable torque. I will probably crank back the rapids on the X to about 650 just to give me a little headroom, in case I run into something while rapiding (dirt on the linear rails for example.)

My best guess, considering you have very smooth movement on your axes, would be about 300-375ipm max....

Video of my machine here:
AtienzaLouie's channel - YouTube

And the build thread here:
http://www.cnczone.com/forums/diy-cn...ml#post1146696

[ger21]

Aside from the faster speed that 8-start provides, it is probably 15-40% more efficient than the 5-start screws.

If you look in Nook's acme catalog, they both have the same efficiency - 75% when used with plastic nuts.

On the other hand there is more of a mechanical advantage with 5-start as opposed to 8-start, since it's harder to backdrive.

Again, according to Nook's catalog, they are both virtually the same.

8 start requires .107 in-lbs of torque to raise 1 lb.
5 start requires .106 in-lbs of torque to raise 1 lb.

See page 23 in the catalog here. Acme and Lead Screw PDF Catalog Downloads - - Nook Industries, Inc. PowerAc Acme Screws and Nuts

[louieatienza]

If you look in Nook's acme catalog, they both have the same efficiency - 75% when used with plastic nuts.



Again, according to Nook's catalog, they are both virtually the same.

8 start requires .107 in-lbs of torque to raise 1 lb.
5 start requires .106 in-lbs of torque to raise 1 lb.

See page 23 in the catalog here. Acme and Lead Screw PDF Catalog Downloads - - Nook Industries, Inc. PowerAc Acme Screws and Nuts

The guys at Roton would probably beg to differ. The 1/2"-10, 5 start has a drive torque ratio of .121in-lbs/lbs, or to drive 75lbs would requre 9.075in-lbs torque. They don't have a 1/2"-8, 8 start, but their 7/16"-8, 8 start has a drive torque ratio of .221in-lbs/lbs, or requires 16.575in-lbs to mvve the same weight. The forward drive efficiency is close at 72% for the 8-start and 68% for the 5-start, but the 5-start still has to spin twice as fast to do the same work as the 8-start. Roton does not list the backdrive efficiency of the 1/2"-5 start, but the list 3/8"-5 start at 62%, and the 7/16"-8 start at 70%.

But in general, the higher the number of starts (or the lower the effective tpi)for the same diameter screw, the higher the lead angle and therefore the higher the efficiency. A 1/2"-8, 4 start may even be slightly more efficient than a 1/2"-10, 5 start just because it has a higher lead angle....

[2rdesigns]

Nice looking design. I think your biggest chance for increased rigidity would be by making that Y-axis extrusion taller (square.) The rails help some, but I think that extrusion will your weakest part and will want to flex (twist) during cutting. Maybe it's too late for that, just a thought.

I agree. My original design called for a square t-slot section of about 3" (76mm). I currently only have the 40mmx80mm t-slot but I'll be on the lookout for something larger.Thanks for your input.

Rick

[2rdesigns]

I like the idea of using 1/2-8 8 start ACME leadscrews. Assuming the efficiency is close to being the same or better then 1/2-10 5 start and I can get accuracy of around +/- 0.005, I'm happy.

ger21,
I will be using this machine to cut aluminum occasionally so I want to make sure I size the steppers right. Will the 381oz steppers you suggested still work well with 1/2-8 8 leadscrews?

louieatienza,
I watched the video of your machine cutting aluminum. Is this with the 425oz steppers and 1/2-8 8 start lead-screws ? If so what are the settings you cut at (cutter dia, spindle speed, feed rate, depth of cut and alloy) ?


Thanks everyone for your input.
Rick

[louieatienza]

I like the idea of using 1/2-8 8 start ACME leadscrews. Assuming the efficiency is close to being the same or better then 1/2-10 5 start and I can get accuracy of around +/- 0.005, I'm happy.

ger21,
I will be using this machine to cut aluminum occasionally so I want to make sure I size the steppers right. Will the 381oz steppers you suggested still work well with 1/2-8 8 leadscrews?

louieatienza,
I watched the video of your machine cutting aluminum. Is this with the 425oz steppers and 1/2-8 8 start lead-screws ? If so what are the settings you cut at (cutter dia, spindle speed, feed rate, depth of cut and alloy) ?


Thanks everyone for your input.
Rick

Rick, the steppers are 425in-oz connected to a G540. As Gerry points out, not ideal, but works just fine dor my needs. If I had to do it all over again I'd probably opt for a larger PSU and G203s. Since I used the original Y axis stepper on the X axis for the tandem drive, I used a spare 380in-oz stepper for the Y.

For cut parameters, check the descriptions on the videos. I've used different parameters for different tasks.

[2rdesigns]

So I did a little searching and found a kit from Automation technologies.

It includes;
G540 4-Axis kit (115V/230VAC):
(1) G540 4 axis Stepper driver with 4pcs DB9 connectors
(4) NEMA23 KL23H2100-35-4B (1/4” Dual shaft with a flat) 381 oz-in
(1) KL-600-48 48V/12.5A 115V /230VAC Power Supply

All for $589.95

A bit steep compared to the Xylotex 4 axis kit for $325.

Is it really worth $264+ dollars?

Rick

[ger21]

Is going twice as fast worth $264?

[2rdesigns]

Yes, it's worth it. But out of curiosity, why. Is the 380oz a better motor? I guess I'll be saving up.

[OCNC]

Yes, it's worth it. But out of curiosity, why. Is the 380oz a better motor? I guess I'll be saving up.

It's really the capability of the drive that makes the difference.

Chris

[2rdesigns]

Tried doing a little FEA. Seems my gantry is sufficiently rigid, In think. I used a 200lb load, which is probably too much.

I used both a twist and linear force for each simulation.

I don't see enough difference to upgrade. Am I missing something?

[louieatienza]

Yes, it's worth it. But out of curiosity, why. Is the 380oz a better motor? I guess I'll be saving up.

The 380in-oz is better matched to the 48v psu included with the kit. The G540 max voltage is 50V while the xylotex is 35v absolute max, and 30v recommended max. While you can definitely use a 425in-oz stepper with a G540, you wouldn't be able to get that rating since it needs more voltage than the 380in-oz to perform at its best. Also probably lower inductance with the 380in-oz so it should be more responsive than 425in-oz.

There are also other benefits with the G540, such as current reduction at idle, and electronic damping. The xylotex does not have the e-damping, and many xylotex users have added mechanical dampers to their steppers.

As to kits... I was able to purchase a G540 pre-wired box from deepgroove1 on eBay for about $450, including a 48v psu and nice aluminum enclosure. You could then shop for motors and cables, but it does make things faster.