Y tracking problem

[cestout]

9 x 9 piece cut out in three passes - the top end (keyboard end) shrinks 1/8" on each pass but the bottom end stays dead on. The cutout is not shifting, it is shrinking. Y bearing asr new, belt tensioning pulley and screw are new so belt tension is ok, new bit. This is my C machine with only about 500 hrs. If I tried it in one pass, it would come up 1/8" short by the time It got back to the top. Has to be something dt do with drag, because I ran my test patten (I posted on the forum) and it was right on with shallow cuts. Any suggestions?

[DianMayfield]

Any chance the new bearings are a little too tight, binding up on the return? I guess if they were alternatively too loose the truck could be tipping as it returned home. If I remember correctly, getting that tension just right was a bear.

[Digitalwoodshop]

How does that Knot play into this? It sure looks like it is slipping in X... What is the board orientation and 7 inch rule? More info???

Looks like a brass roller slipping problem....

A screen shot of the artwork would be good.... Is the heart up side down on the screen with the knot going over the brass roller?

AL

[DocWheeler]

Definitely have both an "X" and a "Y" problem.
Interesting that the "Y" corrects itself at the back of the machine.
I have no idea how the "Y" would do that without the tension pulley moving.

Was that a two-trip or a three-trip cutout?

[bergerud]

I do not see a problem in the x direction at all. It looks to me like the y is "slipping" in both directions. I have seen this type of behavior before while I was carving cast acrylic. I could not find anything really wrong with the y system. There was no "y slipped" or "clean rails" or "y stall" messages, yet it seemed like somehow, the y reference was lost.

Could it be that when the bit climb mills and drags the truck ahead instead of dragging the truck behind, the computer does not notice? I can imagine that the firmware only notices when the truck drags behind and not when it is forced ahead.

That is all I can come up with to explain this seemly bizarre behavior.

[Digitalwoodshop]

The orientation confused me... so no X problem....

So if the Y is off and no fault that tells me the servo motor is skippping teeth on the big plastic gear. So likely the Y Gearbox Bearings and possible shaft....

I would do a test that repeats the cut except minimum bit load... do this by setting the cut depth very light and doing it in 3 passes with very shallow cuts like a .1 each... With a depth of .3... You want the machine to go throught the motions to check the other stuff....

AL

[lynnfrwd]

The orientation confused me... so no X problem....

So if the Y is off and no fault that tells me the servo motor is skippping teeth on the big plastic gear. So likely the Y Gearbox Bearings and possible shaft....

I would do a test that repeats the cut except minimum bit load... do this by setting the cut depth very light and doing it in 3 passes with very shallow cuts like a .1 each... With a depth of .3... You want the machine to go throught the motions to check the other stuff....

AL

Isn't this (shallow cut depth) putting a lot of stress on the tip of the bit? Could break it. Is it 1/8" or 3/16" cutting bit?

[DocWheeler]

I do not think that photo #3 can be explained with just a "Y problem.
More photos would be nice.

[lynnfrwd]

Clint...did you use a jig? I don't see 7 extra inches on the board. (I would like to see a straight on shot of this project to see if I can SEE where it got off track at in the cut out of the shape.)

I'm not saying it isn't the knot, however it would be a much bigger concern to me, if the knot was on the brass roller edge of the board (top edge in Designer view).

[cestout]

I had 3 1/2" pieces hot glued to each end and the X tracking is right on - see the point at the bottom of the heart. The point is toward the bit plate and the top of the heard is toward the key pad. There no art work as such, just cut out - middle part of a heart box posted here on the forum a while back. Cut is in 3 passes with the 1/8" cutting bit. Question for Al, where does the encoder ring ride. I had Y problems just before Christmas and checked the encoder for dust. I think the ring slipped up or down the shaft. Does it ride in the middle of the reader gap? Even with the end of the motor shaft it just clears the top of the gap. Could this positioning be the problem?
As I said, on a shllow cut on my test pattern there is no problem and there seems to be no problem with raster carving. I think I will roll the Y motor assemblies between the 2 machines.

Clint

[bergerud]

Maybe the vibration of a good cut makes the disc rotate a little on the shaft. Just how tight is it on the shaft? Sometimes the black plastic cracks is not as tight as it should be. Take a good close look. (I think the disc should be in the middle of the gap. I am not sure it makes a difference.)

[cestout]

I just did this MPC in pine on my C machine and it came out dead on. The heart ring was carved in alder - not particularly hard. The test carve has many and larger tabs. I already increased the number and size of the tabs for the heart ring and will try it in pine. But the tabs should have not effect on the first and second of the three passes?
Clint

[Digitalwoodshop]

Bit Feed Rate could be an issue here too... With a cut path, the bit speeds up on the long areas and if the bit was dull could actually push the board...

Masking tape on the under side of the board to prevent sliding.... Rubber belts both machines?

Just another WAG...

AL

[cestout]

The bit is quite new, I had masking tape, but X was not the problem - X was dead on (see the point on the bottom of the heart). I tried the mpc in pine. The inside heart was prefect, but the top of the outside cut was a little wide but no steps. The bottom at the point was 1/8".
Clint

[cestout]

I roller the Y assemblys between the B and C machines. There were only 35 hrs on the bearings in the suspect unit, but I replaced them anyway. The problem went with the roll. I am looking at replacing the Y assembly. the new one is $90 and the recon is $80. There is a $35 core refund - takes a while, but it happens eventually. Question is, should I go with the new or recon? Any opinions? Also think I need a $80 part for my old reliable truck - the Idle Air Control motor (sort of replaces the choke on throttle body)
Clint