Messages

1

General Mach Discussion / Re: Creeping Y position. Anyone know something else I can try?

« on: August 07, 2008, 05:46:44 PM »

Hi Chip,

The Gecko's only run when the "Step Low Active" is set to Green checkmark. Both tom Caulde (the manufacturer - very knowledgable), amd Dan Mausch (another very knowledgable CNC guru from  way back), both say that they need to have the Red "X". When I do that though, I get a low groaning from the motors, with very, very little movement. Put them back, and the run silky smooth. I have no idea why it doesn't work as it was designed.

The BOB is CandCNC's Mini-IO combo board. They're at: http://www.candcnc.com/   The website has changed to some new products, but the The BOB is under "Quick Pick and Buy". I also have their MTA Mass Termination Card, two EZPlug Gecko dual Stepper Cards, their Mini-IO Remote Relay, and Mini-IO_Port2. The  manuals for all of these can be read from the menu on the right of the website.

I tihnk the opto-isolators must be OK - the board runs fine. In fact everything does..., : motors are silky smooth, there is no excessive heat, X and Z axes do exactly what they're told, etc. The only problem is that the router tip increments on the +Y direction for every round of my test program. (traces a 4" X 4" square hole, in Absolute mode.

You might be right - it may be time to go directly from the BoB to the Geckos.

Thanks!

Dave

2

General Mach Discussion / Re: Creeping Y position. Anyone know something else I can try?

« on: August 07, 2008, 12:54:09 PM »

Hi,

Thanks for that - I am using Absolute Stop. It's slower, but I found it to be far more accurate on the corners.

Thnaks

Dave
Saltspring Island

3

General Mach Discussion / Re: Creeping Y position. Anyone know something else I can try?

« on: August 07, 2008, 11:45:08 AM »

Thanks Hood! That's going to help on a smaller CNC conversion I'm planning for my lathe. I appreciate that!

Thanks!

Dave
Saltspring Island

4

General Mach Discussion / Re: Creeping Y position. Anyone know something else I can try?

« on: August 07, 2008, 12:05:21 AM »

Chip: BTW, I'm using Gecko 303V's. I set the Pulse Width at each option from 1 to 5.

Thanks

Dave

5

General Mach Discussion / Re: Creeping Y position. Anyone know something else I can try?

« on: August 07, 2008, 12:02:40 AM »

Hi Chip,

I may be misunderstanding you, but all my ratios are small pulley to large pulley, so there wouldn't be any cancelling out. I have: 10 teeth to 36 teeth  (3.6 : 1), 10 teeth  to 24 teeth  (2.4 : 1), and 10 teeth to 24 teeth  (2.4 : 1), so I have 3.6* 2.4*2.4 = 20.736 : 1, correct? What would I change around?

The error is at the cutter tip. The DRO reads just as it should (X0.00 Y0.00).

I have the pins set exactly as you described in your previous post. Tom Caudle frmo Cand CNC.com says that the Step needs to be positive (Red "X"), in order to get proper accuracy, but if I do that, the motors jsut groan and dont move any discernible amount. Putting a Green checkmark on them makes the motors sing along very smoothly. Just with this extremely frustrating creeping on Y. (It starts at X0.00 Y0.00, goes out and does some movements, and when it come back, the DRO reads X0.00 Y0.00, but the cutter bit is offset by 0.016".) It's entirely repeatable - if I run the program 100 times, the offset is 0.016" X 100, everytime.

Let me know if I'm misunderstanding your post.

Thanks

Dave
Saltspring Island

6

General Mach Discussion / Re: Creeping Y position. Anyone know something else I can try?

« on: August 06, 2008, 07:56:07 PM »

Well, thank you for that kind word but around here it's known more as the "Rube Goldberg" approach than it is "brilliant". As in..., "if you can go expensive, go rustic!" :-) However, if you liked that one, here are a few more views.

I've already converted the Z Axis to aluminum, and it still uses an ACME screw. I think I'll leave that as it is..

The next picture is of the Y-Axis Reduce (short axis). It's the same as the X-Axis Reducer (long Axis), except that the final driver pulley is behind the reducer frame.

Next is the where the long drive belt mounts to the gantry. The reason that it is so far away from the table, is because I decided to widen the gantry when I make it out of aluminum, to give me 26 inches of cutting width. At that time, the belts will be attached directly to the gantry, without the outboard mount.

The table is stationary, because I wanted to be able to cwork on twelve foot boards. According to my plan (I've never done it), I should be able to make four feet of carvings, move the board along the X Axis,  re-register it, then carve the next section. Theoretically, there is no limit to the length of board I can carve, other than the length of the wood I can find.

As I said, it's pretty crude at this stage - I'd never seen a CNC machine before I built this one, so there are many things that I'll do differently on the next iteration.

Thanks again fro your help, Hood - I look forward to seeing what you come up with tomorrow.

Thanks to everyone else, as well.

Dave
Saltspring Island

7

General Mach Discussion / Re: Creeping Y position. Anyone know something else I can try?

« on: August 06, 2008, 06:49:05 PM »

Hi Hood,

Sorry - my explanation is lacking badly. I've attached a photo of the speed reducer. Please excuse how it all looks - I had no faith in the beginning that I could do this, so I built it out of MDF and ACME screws..., to prove out the concept. It worked, but showed up the weak points, so now I'm converting it to 1/4" aluminum and belts. I'm an ex-millwright, and metal makes a whole lot more sense to me.

Yes, there are three axles for each speed reducer, the final one being the shaft that drives the X axis belt on either side of the table. Each axle runs on sealed bearings, First one is tensioned by sliding the motor mount, second one is tension with the idler wheel, third one is tensioned by sliding the Reductioon assembly. The long drive belts are tensioned with sliders too (see lower left). The Y axis is reduced in exactly the same manner.

Hope this helps.

Thanks again for your time.

Dave
Saltspring Island.

8

General Mach Discussion / Re: Creeping Y position. Anyone know something else I can try?

« on: August 06, 2008, 05:56:43 PM »

Hi Arnie,

It's your second paragraph - it is very repeatable. If I run the test program 20 time, Y+ is out by 0.16 X 20. If I run the program 100 times, it's out 0.16 X 100. In each case, , the DRO is reporting Y0. I'm not saying that there is NO backlash, but it's not noticable.

Thanks

Dave
Saltspring

9

General Mach Discussion / Re: Creeping Y position. Anyone know something else I can try?

« on: August 06, 2008, 05:42:06 PM »

Correction on the reduction - I have three stages:

10 teeth to 24 teeth
10 teeth to 36 teeth
10 teeth to 24 teeth

Then the long belts that drive the gantry

Sorry about that.

Dave
Saltspring

10

General Mach Discussion / Re: Creeping Y position. Anyone know something else I can try?

« on: August 06, 2008, 05:37:35 PM »

Pitch is 0.375(L)

Thanks

Dave
Saltspring