PRT 4896 upgrade?

[mikenicee]

Hello,
I am thinking of buying a used PRTalpha4896 for a good price.
Can someone tell me the main difference between the PRTalpha and the new PRS versions?

My main application is sign making.
I will be cutting mostly foamboards, cardboard, acrylic and some wood.

And this will be my first attempt at cnc routing, so if it works out well, I would consider upgrading the mechanics/drivers,motors if need be.

What would be the limitations of the PRT vs PRS?

thanks
Michael

[richards]

I have a PRT-Alpha 60X120 with the 7.2:1 geared motor upgrade. My good friend Jeff Bishop has a PRS-Alpha 48X96. Both machines have spindles. The cuts on either machine are virtually identical. I've cut parts on my machine using his files. When we compared the parts, my old eyes couldn't see the difference.

The original non-geared motors produced a lot of chatter. In fact, the cuts were extremely disappointing. (There are photos on the forum that show the chatter.) I added a 3:1 belt-drive transmission to the X and Y axes and the chatter mostly disappeared. When Shopbot offered the chance to upgrade to the 7.2:1 motors, I went that route. Parts cut with the belt-drive transmission are identical to the parts cut with the 7.2:1 motors.

[mikenicee]

Richard,
thanks for the response.

Do you know how much it cost to upgrade the gears?

Also do you know if mastercam software will output to the shopbot?

thanks

[richards]

You'll need to check with Shopbot on both items. I bought the upgrade quite awhile ago, when they offered a special price. That offer has ended, so I don't know what it would cost to replace the motors now. If you decide to build your own belt-drive transmission, it will cost about $150 to $200 per motor, depending on the materials that you use. Of course, if you do that, you'll be 100% for the design and implementation.

I've never used Mastercam. You could ask Shopbot or call Mastercam directly. Since it is licensed software, you'll probably have to give them your serial number.

[mikenicee]

Let me understand this, just so I am clear.

The three motors that drive the x,y,z are currently 1:1 drives, which makes it choppy. I can understand that. If I bought geared motors 7.2:1 and replaced it, do I need to build a belt drive system? or can they just be bolted on and wired as-is?

Are the motors operated start/stop by the controller per revolution of the motor? or is it all some sort of limit switches that control start and stop and location?

WHen you wrote about belt drive, I am envisioning a motor on the size with another gear and belt to give it a 3:1 or more ratio. Is that what you are talking about? and use existing motors?

Please explain. I appreciate your time. New at this.

[richards]

The Oriental Motor Alpha 7.2:1 motors do not need an additional belt drive. They come as a complete unit: motor with attached gearbox and stepper driver.

NOTE: The AS98AAE-T7.2 motors require a different stepper driver than the AS911 motors (non-geared), so you will need to replace both the motors and the drivers.

If I remember correctly, the upgrade kit was basically a plug-in / bolt on kit. It took about 1/2 hour to do the entire job.

The motors are completely controlled by the Shopbot controller. The controller sends the proper step/direction signals to the motors. The Alpha motors have built-in feedback that will send a fault signal to the controller if any axis stops unexpectedly. Most of us use proximity sensors as an additional safety feature. The sensors send a signal to the controller when they sense the "target". The controller stops the stepper motors before the motors drive the gantry into the stop blocks. The proximity sensors also make it very easy to XYZero the machine.

The belt drive unit that I built used the existing AS911 motors. It also used XL size belts and pulleys. I mounted a 20-tooth pulley onto the motor's shaft and a 60-tooth pulley on the drive shaft to get the 3:1 ratio. The final version of the belt-drive used two 1/2-inch pieces of Delrin separated by some spacers that were 1-1/2 inch deep. I posted some photos of the unit on the forum. Other 'botters posted photos of their designs. They're probably still there somewhere.

Depending on your budget, the Alpha 7.2:1 motors are the easiest upgrade, but they may be expensive. I have no idea what the cost would be through Shopbot, but buying directly from the Oriental Motor web site will cost you about $4,500 or more (for three motors). Adding a belt-drive transmission will cost closer to $600 (for three motors. I'm still running the original non-geared motor on the Z-axis), but it will require some time and effort to do that job yourself. My last version was v12. I didn't actually build all 12 models, but I built and installed at least four different versions before I was satisfied with the results. Most of the parts were reusable except for the two plates and the spacers so cost was minimal for the later versions.

(If you use the search function with the words "chatter photo" you'll find a photo that I posted, 10-5-2006 10:54 AM, that shows the chatter with the 1:1 motors compared to the lack of chatter when the same motors were used with 3:1 belt-drives.)

[mikenicee]

I really appreciate your time in answering these questions.

Another material I plan to use is Bamboo. Come sin 1/4"-3/4" thick plywood. Have you or anyone else you know cut and milled these type of sheets? If so, any problems I need to foresee?

thanks

[jimbo]

Richard,
thanks for the response.

Do you know how much it cost to upgrade the gears?

Also do you know if mastercam software will output to the shopbot?

thanks

They have a post(V7-V8) on shopbot site update it to what mastercam you are running im using V9 than i went too X3 works fine i made a few changes to mastercam post the way i want it to run but outputs good code
Thanks
Jim

[davidp]

Bamboo is awful. It is the greatest con perpetrate on mankind since ... I cnt think of when. Bamboo is a weed sure but to process it to a usable board consumes huge amounts of energy and water, and require the use of horrible chemicals.

The better quality sheets are very very expensive, the cheap sheets are just that cheap and nasty, full of voids and glue that would not stick the proverbial to a blanket.

To be frank it is used by wankers for wankers.