Belt drive gear boxes

[richards]

I never had a lot of success cutting plastic. Using a cutter specifically designed for plastic at the manufacturer suggested feed and speed gave me the best results, but they were still far from ideal, i.e., lots and lots of handwork.

I got basically the same rough (chatter) marks on my PRT-Alpha with non-geared motors, my PRT-Alpha upgraded with a 3:1 belt-drive and my PRT-Alpha that had been upgraded to the 7.2:1 geared Alpha motors when cutting plastic.

There is also a lot of misunderstanding about stepper motors, particularly the PK299-F4.5 with belt-drive vs the Alpha 7.2 geared motor. The PK299 motor is larger and has more holding torque (880 oz*in when wired parallel). With a 3.6:1 belt-drive, that will give you 3,168 oz*in holding torque, or about 200 lb*in. The Oriental Alpha motor is limited to about 80 lb*in.

The PK299-F4.5 will easily spin at 1,000 RPM when powered by a 45 VDC power supply. Using a 30-tooth pinion gear, that means that the axis is traveling at 21 ips. (Oriental Motor recommends a maximum gearbox RPM that would give 20-IPS for the Alpha.) Running the motor at 1,000 RPM requires 33,333 pulses per second. I use Mach 3 on my test bench which allows me to run at 45,000 pulses per second without doing anything special. I BELIEVE that the Shopbot controller can handle 30,000 pulses per second, but I have not tried it.

Resolution for a PK299-F4.5 geared 3.6:1 is exactly the same as the Alpha geared 7.2:1. The Geckodrive G203v requires 2,000 pulses per revolution. The Alpha requires 1,000 pulses, so the Alpha moves an axis 2X farther per step, which also means that its 7.2:1 gearbox gives the same distance per step as a Gecko drive driven 3.6:1 gearbox.

You lose the Alpha MODE capability of the Alpha motors; however, with 2.5X more torque, you shouldn't need the Alpha mode if you use similar speeds and feeds.

The PRS-Standard is a fine machine and so is the PRS-Alpha. Both will give amazing results if you, the operator, do your part. If you have a Geckodrive equipped PRS-Standard, you can add belt-drive, new motors, and a 45VDC to 50VDC power supply to give you a machine that will give the PRS-Alpha a run for the money.

NOTE: At 50VDC, the PK299-F4.5 motors can run HOT, too hot to touch, so be careful. Those motors are rated at 80-Centigrade, so they can handle the heat, but your skin will blister if you touch a hot motor.

[bleeth]

Mike:

Every time you post I learn something!!
Theoretically the comparison between the added gearbox and the built in Alpha one should be valid but couldn't backlash come into play? Although the Tapered hob gears cut way down on backlash from straight gears over time they still will develop increased backlash. I spoke to Oriental Tech about this as I had always been under the impression that on the TH Gears they either self adjusted as the gears got worn or could be manually "tightened". They said no and when backlash becomes an issue then the fix is to replace the motors.

On another note the parts from Misumi shipped Friday. Although the 30 percent first order discount is given unless you open a credit account directly with them it comes in the form of a credit to use on another order and is usable for 1 year after issuance. Frankly I think I am way ahead anyway just by having the custom shafts done by them at way less then anyone could machine them for and I expect to be ordering more from them soon as their catolg has lots of linear actuator components as well and I'm starting to think about building a flatbed laser. Lots lighter frame and motors needed for that!!

[richards]

Dave,

Yes, mechanical gearboxes can have backlash, but so can belt-drives. It is impossible to have infinite tension on a belt-drive, so a belt that is too loose can also cause backlash. Most belt-drive designs have tensioning slots cut into the motor mount to allow you to adjust the belt's tension.

Also, the Oriental Motors with the TH gearbox are MUCH more compact than the PK299-F4.5 motors with a belt-drive transmission.

On my PRT-Alpha, the belt-drive extended below the Y-axis sufficiently to affect the height of material that I could cut; but, because the thickest material that I cut was less than 2" thick, that was not a problem.

Sometimes it's best to make a chart that lists the positives and negatives for each type of transmission. That way, there will be no surprises.

[roney c]

Hi all, it's been quite a while since I last posted anything on the SB forum. I used to use my Bot quite extensively for my custom work (I'll try later to post some pics). But in the last 2 yrs. , my vision took a turn for the worst and 7 eye surgeries later I'm left with aprox. 1/3 of my vision left *(not complaining mind you). Additionally i might add that this past Wed the ladder I was up about 10' on slipped out from under me, OUCH! The good news is that *this past Dec. I was able to sell *my 9000 sqft bldg, and auctioned off 25 yrs of tools BUT NOT MY BOT. And thank God, because, as it turns out I can see the computer screen from about 4" away w/my left eye and distance ok w/rt eye haha! So I've just relocated my Bot in a business incubator in NYC, (where I moved to recently from the PA countryside to live full time with my wife -even longer story). That reason plus the fact that NYC is an easier place for a vision impaired person to get around in. Anyway, in addition to doing CNC work for the young adults who call this place (3rdWard) their "craft business home" , I'll bring in outside CNC work, plus I'll be teaching basic, mid-level and advanced CNC routing classes! *
* * *All this having been said, I have spent many enjoyable hours with my iPhone 3-4" from my left eye reading these threads and this one in particular, with rapt interest. You fellow botters who post on here are all so brilliant and creative that I'm concerned my problem with my Bot will be overlooked as too simple, but it's not so simple to me. Here's my dilemma: '98-00 *PRT96, PC-3.25, (held into the alum C-channel w/2 large hose clamps) PK299-01AA 1:1 w/IMS drivers. - It runs very rough (vibrates the frame) and causes a lot of artifact in the product, (didn't always though).*
* * I wanted to upgrade to either the $1400 gecko board or the G4 board because I wanted better resolution and better cut/run speed, as the fastest I can jog is 4ips and cut @ 2-3 ips. However after a lengthy talk w/Frank @ SB, he basically told me that these upgrades won't be of much help. Being impaired as I am I'm just GLAD that I have a place to go to possibly make some bit of a living, but, I only have so much $$$ to spend to improve my Bots' performance. What does the Bot hive suggest?
* * If you've not fallen asleep reading this tome Bless you * *,-)

[roney c]

Edit: Bot is younger than I thought prob 2001-2002 as it has
an angled steel rail and precision V Wheels---

[jerry_stanek]

I would start with new bearings in the router. I don't have the PRT i do have an older PR that I upgraded to the 4g board and it did make a big difference. For I am not limited to the 2000 lines of code before you have the wait to load the next 2000 lines that alone speeds up the cut. Also my values went way up so my cuts look better.

[bleeth]

Beyond that I would also get a more robust clamp system set up for the router. Not sure why Frank doesn't think the 4g would help. Due to the frame construction you probably won't pick up much cutting speed but you will pick up Jog speed and resolution.
Triple check all your alignments for square and level and mechanical connections for tightness. If your computer is that old you will need one with more RAM if you change to the 4G as well as a USB hub and high speed convertor. This change will also allow you to update your control software and the newer version is smoother than the old.
And of course check those pinions!

[roney c]

Jerry, what do you mean by "bearings in the router" ? The PC 3.25 router is brand new.*
* * Dave, what about my frame (all steel tubing and heavy "C" channel const. with square corner angle rails) are you suggesting, is keeping my speed down? *My computer was "state of the art" 6 yrs *ago, I know I know six years is Moore's law X 4.*
* * My steppers are PK299-01AA
Would this be the best possible upgrade:
A - 3 new pk299-F4.5A (for X and Y)*
what about Z axis?*
B - G4 upgrade, plus High speed converter (what is that for and where do I buy one for $$?)
C - New 1/2" pinion (how many teeth)?
D - new 1/2" racks (are these sold in longer than 6' lengths)?
E - New or refurb Dell dual core USB 2/3
D - Vee Rollers maybe hardened Vee rails
* * What are the obvious and not so obvious flaws in my *current plan?
Thanks!

[bleeth]

Assuming that all is tight, square, and true, the part of your frame that keeps your speed down when cutting is the Y Gantry, not the main bed. It just has trouble handleing the torque put on it by the cutting bit. The PRT bolted together frame style gantry was redesigned to the PRS style for this reason. When I put the 4-G box on my PRT jog went way up but cutting speed didn't increase that much as the gantry just couldn't handle a lot more.
Odds are your racks are fine. I don't see much point in 1:1 new motors unless your's have an issue. Note that previously in this thread the whole package that included the F-4.5's was to be done with gearboxes. My purpose was to get the torque necessary to increase cutting speed on my new PRS style gantry beyond standard speeds as well as get smooth resolution over lower torque geared standard motors.
Here is a link to Orientals comparisons of what you have and the F4.5's:
http://catalog.orientalmotor.com/com...rd&pcat=mypage


Brady has posted quite a bit about playing with pinion gear tooth ratio's.

The high speed converter is to get from the serial port that limits com speed and is how the 4-g gets its info to USB and the hub seems to keep the signal clean as well. They are pretty cheap. As I recall I got one part from Tiger and another from Amazon. After install my com speed went way up and loss steps caused by this went away. It wasn't an issue until I upgraded SB software to a newer version that allowed much larger and faster transfers. Previous to that I used a high speed serial port for quite a while.
I also recommend for any new standard computer to follow the Black Viper route for cleaning out the garbage, particularly Dell's.

Bear in mind that my machine has a 5HP Columbo that has a lot more power and weight then the PC router.

You said "It runs very rough (vibrates the frame) and causes a lot of artifact in the product, (didn't always though)."
The question I have is when did that change?
If this is new after the move then I will stand for now on needing to verify squareness, tightness and levelness before committing to major changes on the existing gantry. I'd also take a close look at the pinions and make sure they are tight as well as not worn. They are cheap to replace and if it has run quite a while since the last change (machine time, not calender) you should pay attention to all the posts by people who were getting rough results and did fix it with replacing pinions they "thought" were fine.

[roney c]

Thanks Dave and Jerry,
I'm going in tomorrow and put her all back together as she was before thus move, and just do just what you guys advise. Square, square, square. Check and replace pinions if necessary (most likely). Locate and install a new PC router holder on her (any suggestions here)? I do notice through feeling that the Vee rails have some burrs through wear and am wondering if purchasing new 90 degree Vee rails and (4) matching 90 degree Vee rollers for my axis aprox $300 from http://www.imsrv.com/ and bolt them onto my current X rails.