Grinding Sound in Y-Axis and Circles/Arcs Not Cutting Perfectly Smooth

[bwbramer]

Hello All,

I have a PRT Alpa 2004 that I purchased used in June of this year. Overall the machine has been great and I have very few complaints. However, most of the work that we do requires very smooth edges and this is where I am having my only problem. To clarify, straight cuts produce very smooth edges, but curves arcs and circles of various sizes, large and small produce a decent amount of chatter

To start, I will list everything I can think of regarding how I run the machine. Standard operation is either a 1/4" or 3/8" Compression Bit from Onsrud. We run at 12,000 RPM with our Colombo 5.5hp spindle at a feed rate of 350 in/min. We typically cut Baltic Birch and the compression helps us with reducing chipout on the top and bottom laminate layers. In an attempt to reduce our rough edges, we have moved the feed rate down to 300, 250 and 200 in/min. We have not altered the RPMs however. As we do quite a bit of production, we can't really afford to run slower than 200ipm, so I really hope running slower is not the solution!

Regarding maintenance, I have kept the machine is good shape in the 7 months I've had it. While doing maintenance recently though, I noticed that when I moved the Y carriage by hand, it runs smoothly for a few seconds and then makes an awful grinding sound. The X axis does not do this. The grinding goes in and out but its ultimately there and does not sound right. I am careful to push from a central point on the gantry and I do not use excessive force to move the gantry. When the machine is on and motors engaged, it runs without grinding, thankfully. That noise is just very suspicious to me and does not seem right. I have checked the Rack, the Pinions, the tension of the turnbuckles, have ran the motors, free of the track and nothing seems out of the ordinary. I'm truly at a loss for what is going on.

I've attached a picture of a rather large circle with a wavy edge. It's a little tough to see in the picture but it is certainty there and is very noticeable when running your hand over it. I have a video of the grinding but it will not let me upload it.

Any help or insight is greatly appreciated.
- Ben