Rookie again - bumps on circles

[coopcnc]

I am making a dust boot and all four of the circle cutouts have significant bumps at 12 o'clock. They are collocated with one of the tabs but they start at the first level of cutting so don't seem to be related to the tab.

The photo preview is rotating 90 degrees left, but the issue is at the top of the circle in case it makes a difference.

Thanks,
Marcus

[Rcnewcomb]

slow the feedrate down and use ramping to ease into the cuts. Check for something loose on the machine and double-check how the material is being held.

[Leo]

Looks like you may be trying to take that in one cut. That may be too much for your machine. Try 2-4 passes.

[coopcnc]

It's actually 4 passes, .2" per pass. The odd thing is the bump is there in the same place on each pass. Everything seems tight and the feed rate is working everywhere else. I'll give the ramping a try.

[Bonch]

.2 DOC is too much on the Shapeoko 3 XXL. Go down to .125 or even .1 and slow your feed rate down to less than 75. You will get much better results. Ramping in over an inch or more will help alot too.

I would also check your grub screws. They are known to not be tight or loosen up over time. Put in large head capscrews instead of the grubs and use blue loctite. Make sure one of the the screws is on the flat when you tighten them.

[coopcnc]

After much experimenting it seems like the feed rate was the biggest issue. I'm down to .125" DOC and 25 IN/Min on the feed rate and the circle is almost perfect. I had a shorter ramp so will try experimenting with that. The Shapeoko recommended numbers for plywood are .25" DOC and 100 feed rate, I'm surprised I had to back it off so much. I even redid the belt stretch calibration just in case, didn't make a difference.

Looks like the grub screws are M3, any error in that?

Thanks for all the help!
Marcus

[Bonch]

No that is the right size. Just get a caphead screw. It will be longer and the head will be outside of the actual pulley. You can tighten these down better and they hold much tighter. Just make sure you dont get them too long. You want them to be tight and just of the pulley edge. You can get them at Ace Hardware, Lowes and Home Depot. I am sure they can be gotten at many hardware stores but I have bought them at these three locations recently. I have replaced them in all my axis gearing.

[coopcnc]

Thanks, I'll get some tomorrow. I guess plywood is a lot tougher to machine than I expected.

This forum is spectacular, thanks for all of the inputs,
Marcus

[Leo]

Yes Plywood is actually pretty tough stuff. Because of all the glue, which is also not very good for the cutters.

Make sure all your drive components are tight. Drive rails, drive blocks(trucks), lead screws, lead screw axis nuts, pulleys on the lead screws, belts. Check that you spindle mounting bracket is tight and plumb. Make sure your work holddown is secure.

[AlbertaClipper]

I had a similar problem that I fixed by reducing the acceleration of my axis.

[coopcnc]

I had a similar problem that I fixed by reducing the acceleration of my axis.

That makes sense, how did you do that?

[martin54]

I had a similar problem that I fixed by reducing the acceleration of my axis.

That makes sense, how did you do that?

Depends what control software you are using. Somewhere within the set up for your control software you should be able to alter the acceleration/deceleration of each axis along with the axis velocity

[AlbertaClipper]

I had a similar problem that I fixed by reducing the acceleration of my axis.

That makes sense, how did you do that?

Depends what control software you are using. Somewhere within the set up for your control software you should be able to alter the acceleration/deceleration of each axis along with the axis velocity

Like Martin said it depends on your control software. I'm using Mach3 so it is pretty easy. Under machine tuning you can play with the graphs to get the desired speeds and accelerations. There is a formula you can use to get the optimum acceleration for an axis but I find it gives results that are too fast for my machine so I just play with the graph until I find a spot I'm happy with.

Mike