Stepped cutout????

[djarboe]

:confused:
I was carving/cutting end pieces for deck rail planters. So, for three planters, I needed six carved/cut end pieces. I used short boards, with long rails screwed to the sides, and masking tape across the ends of the rails to set the length.

The first five went great. The cutout for the sixth board had steps in it on one side, however. See attached photo. This "stepping" is on the side of the cut oriented toward the front of the machine. I set the maximum cut depth per pass at 1/8", and these steps correlate to each pass.

Thinking maybe I didn't have enough feather, I redid the design with a larger feather and ran a new piece. The exact thing happened.

Now it gets more interesting... on the cutoff waste piece, the cut is perfectly flat.

The plot thickens even more... on closer inspection, the side of the piece toward the front of the machine, just the opposite happened. The workpiece has a flat edge, and the cutoff piece has the steps.

So, on these two cuts which were more or less perpendicular to the belt movement, the side towards the front of the machine have steps, while the side to the back of the machine are flat. The other two cut edges that are parallel to the belt movement cut just fine.

Any suggestions as to what is causing this?? And, how do I prevent it.

[djarboe]

Sorry, the photo I tried to attach to my original message was too large. Here's the photo.

[Digitalwoodshop]

It's all about the Brass Roller..... If I got you right that it is error along the length of the piece.

If the board looses contact with the brass roller that is tracking the length of the board it keeps moving until the encoder reads the correct reading. That creates the step as the computer did not know the board moved the extra length as it's feedback, the encoder did not move while the board lost contact with the brass roller. When it again made contact with the roller it moved to the correct place but the board moved more than was required.

So in your case it lost contact the same amount each time.

Masking tape on the underside of the board where the brass roller bites the wood will give the roller something to bite into.

A Warped board will do this.

A head out of level will do this. To check head level use options and a bit and touch the board in a few places along the Y axis and look at the numbers.

Sawdust UNDER the board can cause this.

Dirty sand paper belts can cause this.

OAK is hard and the brass roller has a harder time to bite in AND the sand paper belts can slip but the brass roller would still track correctly.

Hope that helps.

Here is a clock I made that had a stepping problem. Tape fixed it...

With 55 posts you have seen the tips and tricks and you are doing a great job making up challenging projects for the machine. Good Job. More Pictures pleases.

AL

[djarboe]

I think you are dead on about the brass roller and part slippage. To add a bit more information, after this first happened I pondered on it for quite a while, and slippage was the only answer I could come up with that made sense for what I was seeing.

Since my belts looked good, and free of dust, I checked the clamping load. It was about 90 pounds. Ok there. I then looked at my rail and saw a small indentation running along the length of the rail made by the brass roller due to repeated use. In order to avoid tracking over knots in the rails (using pine), I wanted to use that rail and face again, so I put masking tape along the rail over the crushed groove - just as you recommended. I think the problem was that the groove was just too deep for the masking tape to fully compensate for the groove depth. I thought it would be, but I was apparently wrong. Also, since I only have time to "play" on weekends, way toooo much time had passed between carvings for me to remember my previous conclusion.

Thanks for your input - it realigned my thinking. Another lesson learned... the rail is just as critical as the workpiece, and don't use it if it has defects.

The good news is now that I have two pieces with the same configuration, I can use my table sander to make them identical. They will be a bit smaller than my design plan, but with my limited woodworking skills adaptability is critical (and routine).

Thanks again!!:)

[Digitalwoodshop]

Check your out feed tables, if the end of the board hits the roller sometimes it can cause that. Are you staying under 2 rollers all the time?

AL

[djarboe]

Check your out feed tables, if the end of the board hits the roller sometimes it can cause that. Are you staying under 2 rollers all the time?

AL

I actually did check that as well, on the very first part. They were lifting the board slightly, so I adjusted them. Also, I made sure the rails were long enough so they were always under the rollers. In fact, they were over a foot longer than the workpiece. I marked centers on the rails and workpiece, and aligned/assembled them so the workpiece was centered with the rails. Finally, while carving the first couple, I watched to make sure the rails were staying under the rollers, which they were.

Having ruled out everything else I could think of, I truly think your assessment of the brass roller slippage is the key.

I have another question. Perhaps you can save me from another problem. I'm carving some side pieces for the same planters that are from 3/8" stock. I would like to use 1/8" thicker rails, that is, 1/2" thick. Should I mount the pieces so they are flush with the top of the rails, or the bottom? And, if I use the bottom, how do I tell the machine to measure thickness off the thinner workpiece and not the rail? I've left plenty of room on the sides to avoid the carving bit hitting the rail. Or, is this just a bad idea?

P. S. I plan on cutting the finished carving out of the workpiece on the table saw after carving. No reason to make this more difficult than it has to be. The table saw is just a better tool for long straight cuts.

[cruzer40]

I had the same problem. It seems that the drive belts, the sand paper things that move the work piece and the gears that drive them might be the problem. I had to replace tha drive belts and a couple of gears. Problem fixed. Also, do not tighten the pressure rollers too much, it causes drag and the work piece doesn't track smoothly. Hope this helps.

[djarboe]

I had the same problem. It seems that the drive belts, the sand paper things that move the work piece and the gears that drive them might be the problem. I had to replace tha drive belts and a couple of gears. Problem fixed. Also, do not tighten the pressure rollers too much, it causes drag and the work piece doesn't track smoothly. Hope this helps.

I suppose if this persists, I'll have to consider that. I bought spare belts, just in case. What gears are you talking about? I haven't taken my system apart to look at it, figuring I'd never get it back together the same way.

[Digitalwoodshop]

Chris places thin pieces of stock on top of his Acrylic to keep the rollers from harming the top surface. So I would think placing the strips on top would be the best thing.

Al