Z problems. I upgraded control on my pr to v4g

[JimMetully]

Hello all. I just upgraded my mid 90's pr shopbot to a 4vg control with gecko drives. I didn't mess with changing the gecko drive settings for more power, because I saw a post warning against doing this for pr machines.

usb connection to windows 7 instead of serial port is nice. In order to get the new control card to work, I needed to change out my electric motor on z axis to a pk 268m-03a. My old one was a pk 268-02a.

When I use the "default settings", my unit values for all axis need to be changed to a negative number to get them oriented properly. So default settings for a prt. My machine is a pr, but default settings not offered for a pr in instructions for 4vg upgrade.

Instructions for v4g say that the correct unit values for a prt with 3.6 motors and 25 tooth pinions are......

1833.465 on x and y
2291.831 on z And I change these to negative to get it to work

So -2291.831 in unit values makes it so the bit rises less than a half inch when I ask it to go up 2".

I messed with the unit values and made z -21,000 to get it to be close to going up 2" when I asked it to go up 2".

That seems way too high, and makes a funny noise, which tells me I must have another setting wrong.

Is there a setting other than unit values that I missed? I have a ball screw z axis.

Tom Hartnett has been helping me a lot with this. He says that Frank will be back on Wednesday, and can help with it then. I just figured I would throw it out there in case this sounds familiar to someone.

Thanks again
Jim

[bleeth]

The PRT unit values are for geared motors. pk268's are straight shaft.
You need to get the unit values for the correct gearing.
SB has a fill-in sheet for that. They also need to know what size pinions (teeth count)
you actually have to give you the right unit values.

[Brady Watson]

I believe your PR has a 5:1 screw. The PK268-03A is a 2.1 Amp motor (about the same current as a PRT PK296 according to OM) so you should not have to mess with the resistors. Oriental recommends wiring it in Bipolar Serial, not Bipolar Parallel. You should have already clipped the white & yellow wires from the 6-pin PR Wago and taped them up. Refer to Oriental's Connection Diagram (http://catalog.orientalmotor.com/item/stepping-motors--1068/pk-series-stepping-motors/pk268-03a?jumpMenu=%23#) for bipolar serial. Any wires shown with 3 in a row - the center are not connected.

So...We have to back track here so the math makes sense. The motor has 400 full steps @ 0.9 deg/step, (even though Oriental says it is 1.8 deg & 200). The Gecko multiples this 10X via microstepping. The screw multiplies that 5X (if that is the ratio)...So, 400 X 10 X 5 = 20000. Your unit value should be close to this. The only way to tell 100% is to use a dial indicator and measure the distance travelled, but you should be close.

As for the (-) sign in front of the VU, if you want it to be a positive number to feel better, just swap the green and black wires in the connector with each other. This will change the motor direction.

You will get killer resolution in the Z, but this will be at the expense of speed. Let's assume you have a wicked quick PC with excellent COM. I would estimate that it is good for around 50,000 pulses per second. If you have a UV of 20,000 on your Z, then the absolute max theoretical speed you can run is 2.5 inches per sec. Not that you want to run that fast anyway, but keep the Z @ 1 IPS and you should be fine.

-B

[JimMetully]

Thank you. I will measure teeth too. Am I measuring teeth per inch? Teeth per foot? Stated unit values are for 25 tooth pinions. There are approximately 25 teeth per 3 3/4" length on my pinions.

[JimMetully]

Brady, thank you also. Looks like I will be buying a dial indicator to improve my ability to measure.

[Brady Watson]

25T @ 3.6:1 gearbox = 1833.xxx UV probably no need to measure that. Cut something slowly...and measure that. If it measures right, you are good.

-B

[JimMetully]

Correct unit values for my pr machine being upgraded to a v4g card are.......I just figured I would leave a trail of bread crumbs for the next guy that still has a pr machine, as instructions are mostly geared for upgrading a prt machine.

So I first reversed black and green wires on all of my electric motors so that controls didn't move tool head in opposite direction of where I tried to make it go, and made it so I didn't have to have a - in front of the values.

2546 unit values on x and y axis (with oriental motors pk296a 1a-sg 3.6) was perfect.

20,000 unit value on z axis was perfect for my ball screw z(with oriental motor pk 268m 03a). I was originally having problems because I had the jog speed set too high on the z axis. 1 seems to give good results without a high pitched sound (3 was too high). I had to switch out my z axis electric motor as a part of this v4g upgrade (old one was a pk 268m 02a). I was able to keep my x and y motors that I already had.

version 3.6.46 was the best control software for my windows 7 computer.

You will be asked to pick what machine you have at some point. The one you need is in Older Shopbots, the size of your machine, and prt (there is not an option for a pr machine, but it will work with a pr machine). v4g(probably in prt standard under older shop bots).

If you have problems with getting your card to recognize the control box, it is likely that you need to go to Utilities, and then Install control box firmware.

Thanks to everyone that helped me get my machine running again. Shopbot tech support guys Tom and Frank were really great, Bleeth and Brady Watson were super helpful too.

[Brady Watson]

Correct unit values for my pr machine being upgraded to a v4g card are.......2546 unit values on x and y axis (with oriental motors pk296a 1a-sg 3.6) was perfect.

This is because you are running 18 tooth pinions. I would strongly suggest that you chuck them and get 25s for XY. With more teeth in the rack your pinions will last a lot longer and the tool will move more smoothly. The smaller you go on the pinion, the less teeth are engaged and the force of cutting and moving the gantry is completely transferred to only one or two teeth...and the smaller you go, the more prone you are to gear cogging as they wear.

Running 25T pinions, your unit values will be the same as a PRT 4G @ 1833.xxxx

In case nobody told you, pinions are consumable. They do not last forever, and even less if they are not greased. Normal maintenance for pinions is replacement every 1 to 2 years, depending on use. Cut quality is directly affected by pinion condition.

-B

[JimMetully]

Brady, this is the first I have heard of pinions being consumable, or the difference in 18 and 25 tooth pinions. That would definitely explain a light grinding sound that I hear every now and again. That's a really good piece of information to have. That part of the instructions were correct, I just didn't understand.

Thank you
Take good care
Jim