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Ok now parts cutting questions
http://w-ww.luthiersforum.com/forum/viewtopic.php?f=10102&t=8208		 Page 1 of 1
Author:  Sprockett [ Tue Aug 29, 2006 5:45 am ]
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So far so good, the router is out there cutting out my parts holder, I triple checked everything and it looks really good. The Dust Collection is great, I'm cutting MDF and it's not dusty at all so that was a good investment, the CNC area will or should stay clean.

One thing I noticed was that the pockets it's cutting are not super precise (some have little ledges), that could be backlash but I'm not sure, should I profile my pockets after I cut them out?? It's not %100 finished with them just yet but they look pretty good so far. It's a noisy bugger so I think I'm going to have to build a cover for it to keep the noise down....

There's nothing like seeing your first part cut after all the work and help from the good people here

-Paul-
Author:  Jim Watts [ Tue Aug 29, 2006 7:40 am ]
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Paul,
I'd check the backlash, steps are what lead me into checking my backlash and now I'm having to rebuild part of my machine, which hasn't cut a part yet.
You might consider puting a hole into a spoil board at some location far away from home using both the x & Y axis and then running the machine around a bunch and seeing if the machine accurately comes back to the center of the hole afterwards.
I hope you don't have a backlash issue.
Author:  Sprockett [ Tue Aug 29, 2006 9:37 am ]
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Well from what I have read all machines have some backlash I don't think you can *totally* avoid it, but we are talking a very very small amount here. I'm going to do some playing tonight and see if I can dial it in, MachII has settings to allow you to overcome it. The machine seems very solid and has not given me any issues as of yet.

I also did some tinkering on the tool pathing in RhinoCam, I was able to get something sensible finally, it took almost 2 hours to make that whole board. A couple of reasons came into play:

1. The Feed Rate Was Really Slow.

2. It was busy jogging all over the place to and fro.

3. It was doing 'Finish' passes at the end.

I changed the feed rate a little (don't want to push too much), raised the drop in rate and removed the cleanup passes, this is MDF after all

The more I play with RhinoCam the more I like it, I was able to get a number of little things done today and pop out the toolpaths pretty quickly.

Cheers

-Paul-
Author:  Rand Kennedy [ Tue Aug 29, 2006 10:23 am ]
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If the little ledges are more like tooling marks at the bottom of each pass that's pretty normal. If you can measure them that's probably an issue to be solved. Making sure your Z-axis and router are dead perpendicular to the table is critical. I use a 1" dial guage on a stand sitting on my table measuring the side of my spindle as I go up & down to check/adjust. A 1/4" bit will bend a little depending on feed rate too. I don't know PC routers but I'd think 20-40ipm at .25 depth-of-cut would be a good starting point. Dust is too slow, chunks is too fast.

You make smooth sides by leaving 1/16ths or so in your rough pocketing using a depth of cut and then doing a finish pass at full depth to remove that all at once reversing the direction of cut.

Try a test box (pocket) of 2x2 or 4x4 at whatever depth and check the squareness and depth with calipers. It should be really really close.Rand Kennedy38958.8093171296
Author:  John Watkins [ Tue Aug 29, 2006 10:32 pm ]
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That's good advice. What was your feed rate, Paul?

You're stair step problem is one of three things; a) backlash, b) out of plumb router, c) loss of position.

Here's how to find out:

Cut a 4x4 square in multiple depth passes. Take note of which side the steps are on. Cut another square in the opposite cutting direction (switch your toolpath from 'climb', to 'conventional' or vice versa).

If the steps are in the exact opposite place, it's backlash.

If the steps are in the exact same place, it's an out of plumb router.

If the steps are now on a different axis or seem to come and go at random, you're losing position.

Author:  Sprockett [ Wed Aug 30, 2006 12:38 am ]
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Cut Feedrate was 45 or some odd number around there and I upped to 50.

I'm going to try the box thing today, we are talking very very small ledges here, I need to go get some batteries for the camera and I'll post some pics. We also bought a better router last night, one of the new PC's that a 2-1/4hp, there is NO play in the shaft at all. I was using my old hand held one and it had a little play, so I'm re-running everything this morning and I'll post results.

I did check backlash by setting a dial gauge in the X and Y positions, pressing the guage by setting a known position and then running the axis to it's limit and back, it was within .001 each time and I used the backlash option to pull it as tight as I could make it.

Cheers

-Paul-
Author:  npalen [ Wed Aug 30, 2006 2:24 am ]
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Another way of checking backlash is to bring a tool or test bar mounted in the spindle up against an indicator.
Jog it in slow and zero the indicator and DRO. Then, with jog in incremental mode, back the axis off a thousandth or so watching the DRO on the screen. See if the indicator changes the same amount as the DRO. Any difference in the readings would indicate backlash on that axis.
Author:  Sprockett [ Wed Aug 30, 2006 5:39 am ]
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Ooooohhh I like that idea Nelson... that would be fast and easy to check too...

Gotta try that today

-Paul-
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