Hi all,

Here are a few more things I have been cutting. [ATTACH]Attachment 13235[/ATTACH]

thanks al

time for a 4th axis
 

Hi all,

I guess it is time to add a 4axis to my machine. I have just purchased a PK296A2A SG36 to drive the indexer, yet to be built.

I am currently running a PMDX 122 and I am not current with the new BOBS.

Is it easier to leave the current BOB in place and just add an additional PMDX122 of is there a better way to get the additional driver output needed?

I am also running Geko G203v drivers if that helps.

Thanks

Al l

Al,
You should be able to drive it all with the 122. With the203v drivers you can use one output from the 122 to drive two 203 stepper inputs (for the x) that will free up the other A output for your indexer.

Heath,

When you say that I can run both my x motors from on one output say J1on the PMDX122since both motors should be in step but in different directions by calling one a slave in Mech 3?

That will make to easy. we need to complicate it

Al,
No you would only use the X output in mach3. The step and direction signals get wired to two 203s .
You will have to flip the output phases of one motor to get it to run in the right direction.
The A output in Mach is now free for the 4th axis. There have been a few people here who have done it this way.
Probably a good idea to drop your motors for the x axis when trying all this out to make sure you have them
rotating in the proper directions before hooking them up to the rack.

Note though that this approach is driver dependent. If the drivers you are using have too much input current draw, then the 122 output will not be able to drive them. This is not a problem with the 203V from what I have read from posts from Mariss.

...I'll hop in as the "guy that has done this".

Al,
On the PMDX
Use the outputs as follows

j1 - x left and x right
j2 - y
j3 - z
j4 - a axis

As Heath mentioned, you will need to share the step/direction signal from the PMDX to the G203V drives. Most likely, you will have to use ferrels or a really tight twist and solder to bond the wires together to fit in the headers on the J1 block. It's a small connection really only made for 1 wire. The manufacturer for both devices have verified that using a PMDX122 and G203V this current output and draw is permissible.

In Mach, you will NO longer slave the x1 to x. You will only have 4 active outputs on the configuration tree. x, y, z and a

Good luck - it's easy...it works.

Thanks

Not use to having things that easy

Will post pictures of the progress when I start construction

Al

Hi All,

Another question to do with 4th axis mounting of motor.

I see many couple the gearhead motor directly to the chuck with apairs to be with only one flang mounted bearing is that enough to support the working loag or should there be two spaced faitly close say 2" appart thus reliving any load directly on the motor/gearbox bearings?

An example of one bearing is shown in this thread.
http://mechmate.com/forums/showthrea...9&postcount=55

Thanks

Al

Al,
It all depends on how you want to go about it. Your resolution is the deciding factor. I have read a lot of posts and have seen reductions of 100:1 to 16:1. If this was on a mill you would most definitely want a 40:1 minimum and Zero backlash. With wood, a little backlash will not be as noticeable but should be limited. Spur gears have more backlash than the planetary that Oriental sells and don't soak the bank either. Planetary will have anywhere between 3 and 40 arc minutes but a spur gear will have more than that, probably around 90+. I chose to mount the motor as shown here on the side. If your 4th axis has harmonic drive, then a direct mount would would be preferred. You can mount on the side with a 1:1 belt ratio also and leave the option for change later. I would look at buying a zero backlash coupler if direct mount as it will limit any motion you will get from keyways. In the end, it is your design and your choice. There really is no wrong way as long as you assembly it carefully. Sean has one on his machine if I remember correctly.

Hi Pete,

That is what I was thinking of. Only closer together about 2" apart. I have a 36:1 Oriental now from my reading I believe I can adjust the backlash in Mech3. I will be turning wood and no larger than around 6-7" in dia. If there is to much slop I can easily change change it to a belt drive system.

Thanks

Al

Good morning,

I have read a lot on backlash and have no first hand experiance with it.

I was under the impression that I could program out the backlash with Mech 3. Is my thinking correct or not?

Or since I am in the just beging should I just pull the 36:1 gear box off the motor and go directly to timing belts in the same reduction range?

Al

You can use the backlash compensation built into Mach to remove it. What it does is rapidly move in the opposite direction the amount you tell it before moving the rest of the axes. It is a little nerve racking to watch and will add time to the program. It would be better in my opinion to shoot for zero backlash and move on from there. I have removed and modified the gearbox motors to work on a belt drive but this is not an easy task. I can be done by not easily. The motor shaft is ground with a spline to adapt to the gearbox. Stepper shafts are extremely hard. I had a choice of grinding the stepper shaft down to remove the spline or use the spline to cut or broach the aluminum pulley. I opted for the broach method and used Loctite 480 retaining compound. But to press the pulley on it has to be controlled and a special pressing block must be made to hold the stepper back side of the shaft from moving inside the motor so you do not damage it well applying the massive force it requires to seat the pulley.

If the motor is unopened and unused, you may be able to do an exchange. You could try it and see how back the backlash is and if you can live with it. Backlash is a funny thing, depending on what you are doing it my not affect you. Wood is forgiving that way as it moves greatly with small amounts of temperature and humidity.

Al,
Backlash sucks when it affects you, I can tell you that much.

Hi all it been almost 7 years since i finished building my machine and have had any problems with my machine till now.

The problem is my x drive motor it runs fine then it chatters and louses steps then it runs fine again. I have a new PK296A2A-SG7.2 motor and plan to replace it.

Many moons ago I read that if you are wired to half coil you are only using half of the motor and should there be a problem you can change to another winding. Am I correct and or was i dreaming. I have looked and can no longer find the thread i believed to have read.

Thanks Al

Also if i jog it slow it is fine If I fast jog it acts up Checked all wiring it's fine . I also ordered a new 203v

Found problem. One of the wires supplying the x drive in the wire e chain broke thru the insulation and was occasionally shorting to the outer shield of the cable. Replaced cable no problems in the first three hours of operation.

Humm...interesting, what brand cable is it ( was it ?!)
Later

This was used cable when i put it in. Now I changed all stepper wires with Southwire from Automation Direct Item code is MCTC-18-45-1

The first time that happened to me, on my other router. I spent a few hours scratching my head. It is not an uncommon problem. Especially, if you use your machine.

I gets used daily for almost 7 years now

Al what are you cutting mostly signs?, a spare wire would be a good diagnostic tool instead of searching for the break.I will be using mic cable until mine (not completed) earns its keep, and expecting to have issues with it.

i cut all kinds of stuff from full table pieced. A lot custom one off items to several hundreds of the same.

I just bought a whole reel of wire for spare parts.

-
 

Keyaki is the preferred wood for traditional Japanese tables, laquered to a shine that blinds. The wolod also is pretty expensive and getting scarcer every year. I have 5 or 6 slabs stashed away but havent found the time to work on them yet

Today my x axis stopped moving and the x is fine. I am using oriental motors and gecko drivers. The program Mech3 shows it is stepping on the screen.Should I try to change the gecko or the motor first . I have both. Or is there a better way to locate the problem.

Thanks Al

I had a very similar story on my plasma machine under Mach3. The machine is more than 8 years old today. Everything was working fine. Then it started to malfunction. Then the machine stopped working. I had to take everything apart.

Turned out to be a simple DB9-DB9 cable. One wire had fallen off in it! Only 1 !!! And the machine went down. Replacing the cable solved the problem.

I think you need to check the LPT cable, every wire. And everything around the LPT connectors.

Will look at that . Everything except the x axis it just keeps carving away only in a straight line.

I'm sure. You can do it!

I have had this single axis problem with my CNC before and what solved the issue for me is tightening the screw/wire connections at the Gecko. I have found that at the beginning of every cold season, I will occasionally have this intermittent problem and going through the box and tightening everything seems to solve the issue.

Unplugged parrell cable from computer and controller cleaned and reinstalled reinstalled . Only had time to run a small project everything ran good. Will run large rojec this week will keep my fingers crossed.

Thanks Al

I am considering selling my machine after 12 years of continuous operation.
Runs great nothing wrong except.... I am getting old.

To many spare parts to mention.

Located in Mystic Ct.

My computer is dying, old xp machine. I am thinking of upgrading to mach 4.
I am sure several have done this . any good suggestions ?
Thanks Al