Messages

1441

General Mach Discussion / Re: Z AXIS KNEE

« on: November 16, 2008, 11:59:54 AM »

The gears are from MSC, they are off the shelf Boston Gear units. I had to modify them of course. Does yours have straight cut or spiral cut gears? I don't think these gears are much quieter than the original ones but i don't get the cogging noise from the old acme screw. The gears sound better at 150ipm than they do at 100ipm.....figure that one out. Soon we'll see how they sound at 180ipm.

Mine are straight-cut.  What kind of drive are you using to get 150 IPM?

Regards,
Ray L.

1442

General Mach Discussion / Re: Z AXIS KNEE

« on: November 16, 2008, 11:09:56 AM »

I put spiral cut hardened bevel gears in it. I never use it manually so i don't know if it would drop down or not if the servo is unpowered. I wish i had gone belt drive but hey, it works pretty good and makes money.

Where did you get the gears?  I'm actually very pleased with how mine works, I just want to make it quieter, and more durable.  The gears, I think, are a significant source of noise.  Other than that, it works great as-is - less than 0.0001" backlash, and excellent repearability.

Regards,
Ray L.

1443

General Mach Discussion / Re: Z AXIS KNEE

« on: November 16, 2008, 10:47:25 AM »

I had some chunking and jerky movement of the knee on the down move with the acme screw. I just figured it was protesting this kind of movement. After the ballscrew upgrade, everything smoothed out. I couldn't be happier with it, well after this week i will be happier becasue it's getting a new encoder and then it will be moving 180ipm. It's also getting an automatic lube pump.

Do you still go through the bevel gears, or belt drive?  Any problems with back-driving when the motor is not powered?

Regards,
Ray L.

1444

General Mach Discussion / Re: Z AXIS KNEE

« on: November 15, 2008, 10:22:35 PM »

Ray,L can you post a photo of the gas springs you mounted on the knee? Id like to see exactly where you put them.

I have continued to work with my new AC servo on the knee. I have run it up and down very smoothly many times, but every once in a while it will hang and fault the motor going DOWN. I have also heard a bit of a growl, or chatter going down. I suspect I have a gib problem. I think it may be shifting slightly and acting as a wedge.

Eliminating the gears and driving the screw directly works very well. The crank shaft came out through the side in a bolt on casting, so I simply removed that and have a nice access hole into the knee. I was able to get the motor inside the knee casting. with a short belt to the screw. Mechanically it looks very neat, almost like it was designed that way.

Ron,

    Some bad cell-phone pictures below.  I placed the gas springs next to the dovetails.  I thought a lot about the merits of putting them there, or alongside the pedestal, and decided this was best, to avoid the problem you seem to be having.  I figured this was more likely to keep the dovetails moving smoothly. 
    Mine does make more noise coming down than going up.  Up is actually pretty quiet.  On the way down, I get a small amount of "clunking" that I believe is the knee lagging slightly, then dropping.  The noise, I believe, comes from the bevel gears as the small amount of backlash opens and closes.  I haven't had a chance yet to really get to the bottom of it, but I don't think it's anything to be too concerned about.  And it also happens only at high speed (above ~50 IPM).

Regards,
Ray L.

1445

General Mach Discussion / Re: Help getting set up

« on: November 15, 2008, 05:27:59 PM »

Ray that is the schematic from the CNC4PC site so if the connections are in a different place from yours its either been changed or its the wrong diagram on his site. As for the E-Stop yes thats true, was thinking of my BOB, it requires a jumper or a NC switch on pin 10 to gnd.
Hood

Hood,

    Once again, I'm an idiot.  Mine is a C11.  Sorry for the confusion.

Regards,
Ray L.

1446

General Mach Discussion / Re: Help getting set up

« on: November 15, 2008, 04:48:15 PM »

Ray I think that is a problem, so many revisions of the same BOB and major differences between them that you have to make sure you have the docs for the correct one, certainly makes things difficult from an advice of connecting things up.

Hood

Hood,

    But as far as functionality, and basic layout I don't think they've changed much.  I've had boards from v1 all the way to 7.2, and the connections have been identical on all.

Regards,
Ray L.

1447

General Mach Discussion / Re: Help getting set up

« on: November 15, 2008, 04:35:59 PM »

Heres where the enable goes

Hmmmmm.... That is completely unlike the enable inputs on my C10.  Mine is right next to the Pin 1 output terminals.  Also, no connection is required on Pin 10 unless you've configured Mach to use this as an E-Stop.  The C10 does not require it.

Regards,
Ray L.

1448

General Mach Discussion / Re: Help getting set up

« on: November 15, 2008, 04:33:32 PM »

I am using a cnc4pc breakout board... the c10. I did notice that plugging in the parallel port, the break out board led lit up. It is also powered by a 5 volt dc power source... does this make sence?

The C10 requires a connection to the PCs USB port to power the PC side of the opto-isolators.  The USB cable connects to the 2-pin connector block on one corner of the board near the incoming PP connector, on the side where all the input signal connections are.  It also requires a completely separate +5V power supply to power all the other logic on the board.  This one connects to the +5V/GND pins on the side of the board opposite the incoming PP connector.  Several LEDs will light up as soon as either power supply is turned on.

Regards,
Ray L.

1449

General Mach Discussion / Re: Bugs in Mach 3.42.015

« on: November 15, 2008, 11:17:09 AM »

Ray
 couple of things, first if your z is relatively out of the way such as on a manual  bridgeport you can use an optical without any coolant protection, I did that on my first conversion (manual bridgeport) What I did  was have the signal interupted by a piece of steel with two slots in it, one top other bottom. Now if you did that for a home switch then you could have it so that the slot is any desired location of the travel, in fact you could have it so that it is open from your desird position up the way (or down) and write a bit of VB to go in the Ref All button. It would look at the home input from the Z and see if its active or not, if its active then it would move off first so tht its inactive then reverse and start the homing procedure. That is the way my servo drives do their homing, its a great idea as it means you dont have to make sure you are at the correct side of the switch before you do the homing.

hood

Hood,

    That's a good idea!  BTW - On a (loosely) related topic - What precautions, if any, are normally taken to prevent machine damage in the case of a servo runaway.  I'm wondering if I should provide hard limit switches a bit inboard of the physical end of travel, to prevent the table from running full-speed into the end of travel.  (One of the places steppers have an edge - runaways can't happen....)

Regards,
Ray L.

1450

General Mach Discussion / Re: Can someone explain the current draw of these stepper motors, please.

« on: November 15, 2008, 10:13:54 AM »

That's what I did, Ray.

The Y axis is working OK now, but I think I am going to put jack screws on the bearing block and do a fine adjustment without the table on the machine to get the ball screw lined up properly. The machining on the front of the base is not perpendicular to the ways, so the accuracy in the bearing block is defeated.

I had read a lot about binding ball screws in my intial homework before diving into the retrofit. I never read where anyone had solved the issue though. Now that I've been down that road, I know what causes the problem (in my case anyway) and I think I have a solution other than having the base remachined accurately.

There won't be any servos on this X2. For my purposes, it is not worth the time to get an X2 up to the level I want it, because even if I make it into a 'good machine" it is still going to be too small and not rigid enough for upcoming projects.  I'm hoping the X3 is better quality.

Rather than jackscrews, I'd suggest going to McMaster-Carr, and getting some shim stock, and shim the bearing cover.  Jackscrews will likely dig into the soft cast iron base, or the bearing support, and change adjustment over time.

I think you'll find the X3 is a FAR better machine in all respects.

Regards,
Ray L.