Cutter chatter

[Rob Gunn]

OK I have a question that only a newbie would ask but her it goes. We are starting to do more detail work on signs and mostly doing it in sign foam. Now that we are looking for more detail and crispness in the cuts we are wondering if what we are getting out of our ShopBot is normal and the best to expect, or is there more we can do to get the chatter of the edges? We are running a vintage 2000 PRT96 with original controller. Woulds a upgrade to the new controller take care of this issue (see attachment)? Also, yes I do try to reduce as may arcs and line segments a possible in the drawing and yes I have the guides on the ShopBot adjusted correctly and yes there is no issue with the bearings in the router head.
I love my Bot and getting better with it everyday but is this the best it can do on edge finish? Thanks for any advise you experts can give.

[jerry_stanek]

Have you watched the training video texturing on the vectric site. It is under either Aspire or Vcarve pro it shows how to clean up your lettering.

[kartracer63]

Jerry,

I don't think the clearance in the texturing is the issue here. Take a closer look at the V-carved scrolled element and the "R". They have the same "chattering" marks as in the textured areas.

[jerry_stanek]

Are you getting the chatter on you cedar signs. could you post the crv so we can take a look and see what we can come up with.

[srwtlc]

Rob,

You say it's a 2000 PRT with original control box, does it also have the original direct drive motors? If so, and if it's all tight mechanically, sorry to say, that's about as good as it gets. You can weld the carriages at the corners and apply a different type of holddown for the non motor side of the Y carriage or add a motor to it.

I had one too and had to deal with the same thing. I upgraded the motors to the 3.6:1 ones and SB gave me a different control board at the same time (had some other issues with the original one). That helped, but it was still evident. The next step was a Mach3 box and that made a big difference in edge quality. The 4G box wasn't out at the time I did that, but if you upgraded to that and the motors, you would get better edge quality. I also removed the Y car holddowns and added a v-rail and v-bearing spring loaded holddown to the side opposite the Y motor. Also made an aluminum plate for for the Y carriage to stiffen that up.

[Rob Gunn]

All good advice, thanks. Just to clarify I was not questioning the small amount of chatter in the texturing, that is no issue to me. I am trying to get better cuts in the v-carve, letters and scroll and side cuts that are shown in the photo. Sounds like the age of my ShopBot and the old controller are the limiting factors. I guess this old of machine just cant be expected to do the job of a new $20K setup?

[Brady Watson]

Rob,
Provided that your artwork vectors are clean, there are several things you can do to tighten up your machine. The first of which are the pinions. Make sure they are fresh, clean and lubricated. 2nd, Make sure that the machine is tight with the power on at a standstill, wiggle it in every direction. Feel for signs of slop & correct.

There is certainly nothing wrong with your machine, but the 1/4 stepping drivers used on your model have a lot of resonance to them at certain speeds. This resonance can translate into chatter. Regardless of whether you have gearbox motors or direct drive, a 4G upgrade would give you 2.5 times better/finer resolution and in turn, better edge quality. You'll also get smoother movement and some more speed to boot. It is well worth the upgrade price. Call SB.

I would also encourage you to tweak your VR settings when doing small or fine moves, as this can add some much needed 'cushion' in the corners and reduce reverberation of the machine when making abrupt moves. Also, inspect your X & Y rails for wear and jaggies at the bottom of the pyramid ^ because this is where little jaggies make the tool vibrate. Knock them down with a bastard file and smooth out with sandpaper. Don't be scared...just clean em up. Also, check the Z t-rail and make sure it is riding on the v-rollers correctly in ALL areas of it's travel.

The jump from my 2001 PRT (like yours) to an Alpha 7.2:1 setup was an incredible leap forward in cut quality - particularly on plastics. The 4G upgrade is pretty much on par with a 7.2:1 Alpha, albeit at a reduced level of torque and speed. It will be like the tool you always wished it could be, with the 4G upgrade alone.

-B

[myxpykalix]

Rob,
I would check the vectors in your sign. What i'm looking at is the curve on the design and in your lettering. To my eyes it looks too uniform to be random chatter as if the curves are made up of a series of straight lines rather then bezier curves. Try turning on node editing in whatever pgm you use and see how many nodes are in those curves.

[Rob Gunn]

The curves are made up of a series of bezier curves and simple arcs (not straight lines). I did use node editing in V-carve and reduced as many nodes as possible in those curves. As a test, I will make a simple circle and oval with the fewest nodes possible and see if the chatter is as bad. I guess that will tell me if it is due to vectors or if its in the mechanics of the ShopBot.

[paulkiecka]

or the track (pinion?) if they are worn couldn't this cause chatter? One way to check is to compare the chatter marks to the distance from tooth to tooth on the pinion. I have heard sometimes the gears and everything will look ok, but that they are still worn enough to have slop.

is there proper tension on the springs holding the gears to the tracks?

just another thought

[bobmoore]

what is your method of hold down? What are you using for a tool? Both of these issues can have big consequences with chatter.

[Rob Gunn]

The panel was screwed down to the table with no movement. The cutter was a new 90 degree carbide. The collect is in great shape. I am going to file my guides and adjust all rollers to work as they should. I think my issue is all in the old controller. Maybe someday will will be able to upgrade into a newer unit?

[kbraat]

Rob,

I have a machine similar to yours, but with the 4G upgrade. If you are interested, you could send me the file and I can see if the same chatter appears on my machine with the upgrade. Also, let me know what cutter type and settings you were using to best match the comparison.

I'm also only about 1 hour away, so you could see in person.

[Rick W]

Rob,

How about bearings in the router or spindle????

Just a thought.

Rik