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Ring Height for C-Beam Z axis

I continue to have challenges with depth precision.

The design I am attempting to cut has tab / slot assembly, and my tabs all “ramp in” and never quite reach the correct depth, leaving me with tabs too thick for the slots. I have checked my design, and the tab and slots are the same size. Perhaps I need to add some tolerance offsets, but the differences I am seeing are beyond the realm of tolerance.

Perhaps this is a sled balance issue? Or a weight issue?

No matter where I position the ring, I seem to tip up when starting a cut.

I see some of you getting what appear to be high precision cuts. Is anyone achieving this with a c-beam setup?

I don’t know exactly what the issue is, so I’m going to rapid-fire some possibilities and you can shoot them out as you like:

What is the angle of your frame? It almost sounds like it is too steep.
Is your sled ligher than it should be and doesn’t plunge?
what are you cutting? Is your bit dull or your feed rate too high?
Are your chains parallel to the work surface?
Is your sled tipping up (bottom lifting as the sled moves up)?
Is your sled pulling away (top lifting near the top of the frame) or as the sled moves down?

Most of these point to a balance / chain / weight issue except for the bit. if the frame is 15 degrees off vertical, it should be fine. If it is 10 degrees, it will lift and tilt easier. Put a 2x4 under the front frame legs and it should tilt back roughly 5 degrees if you have a standard frame. If the ring is too low and the motors are too far out from the board, put in another spoil board to move everything out, but this is less likely. If the ring is too high and the motors are too far in then it will tilt as well. Start with balancing the sled so when you hang it from the ring, it hangs at the “right” angle (get it, the one on the right?):
image
then check your chains are parallel and adjust the motors if necessary. Good luck. Please report back what works.

How far out does your top beam extend from the frame? Did you build a standard frame?

Standard frame with a 10’ unistrut top bar. The chains are about 6" from the frame:

Frame angle is 14 degrees.

Is your sled lighter than it should be and doesn’t plunge?
What should my weight be? (I see many answers on the forums)

what are you cutting? Is your bit dull or your feed rate too high?
1/2" plywood. What would you recommend for feed rate? You have made me go back and look…perhaps my lead-ins here are a bit too much?

Is the top beam angle back 14-degrees like the frame as well? It should be, but from the photos it appears to be closer to level. This can cause chain skipping if its not.

Is the height of the ring above the frame legs equal to 6-inches as well (can’t tell from photos)? Remember to take into account the spoilboard and sled thicknesses.

looks like your spoil board is 3/4", the material is 1/2" and the sled is 3/4" which is 2" total and the ring height is typically 3" so 5" would be a better off set than the 6" you have, but probabaly not a deal breaker.

maybe it is the angle of the photo, but it looks like the face of your motor gears are closer to perpendicular to the floor rather than parallel to your cutting surface and if your chain is 6" out from your frame, the ring should be about 4.5-5" out from the sled surface:

image

you want that chain to be the same distance from the work piece at the sled and at the motor if it were to extend that far up. I hope it is just an angle of the camera thing, but you may need to slide that top beam back to the right in the picture you posted.

Edit: looks like while I was typing a few others said the same thing…

Correct. The face of my motors is 4 degrees. This expalins much of my earlier chain slippage pain.

So I need to adjust my top bar angle. Do I have to recalibrate after?

Really hard to say, but it is a very, very minor change to the chain length and tend to think it will be insignificant. :man_shrugging: