Tormach 440 Chatter when cutting on Y

[LeeWay]

Then it is not chatter.
The next step it to look very closely at the model.
You would see different results on a loose machine running in differing directions of travel.

[coffeetek]

Then it is not chatter.
The next step it to look very closely at the model.

I agree, I do not think its chatter either, just don't know what to call it. Its not model I reproduce it with simple G01 Y-100 F800 command... Here is video I just made:

[IMT]

What process did you use to adjust the gibs? .01mm = .0004", seems too low. I use the lost motion process described in the manual (for 1100). i.e. loosen the gib and measure lost motion, this produces a baseline number with the minimum amount of friction, then tighten the gib a little and re-measure lost motion. Repeat until the lost motion increases.

[coffeetek]

What process did you use to adjust the gibs? .01mm = .0004", seems too low. I use the lost motion process described in the manual (for 1100). i.e. loosen the gib and measure lost motion, this produces a baseline number with the minimum amount of friction, then tighten the gib a little and re-measure lost motion. Repeat until the lost motion increases.

Procedure from manual.

[IMT]

What was the baseline value with the gibs loose?

[coffeetek]

What was the baseline value with the gibs loose?

Don't remember, sorry. The Y and Z axis backlash I measured was with gibs untouched by me. That's how machine came out of factory...

[LeeWay]

Don't remember, That's how machine came out of factory...

Or at least out of the crate.

[coffeetek]

Or at least out of the crate.

True. For all I know it came to me like this. I did not do any aluminum cutting until couple of months ago when I started immediately seeing this... Its one issue after another with 440...

[IMT]

Don't remember, sorry. The Y and Z axis backlash I measured was with gibs untouched by me. That's how machine came out of factory...

So you have not gone through the gib adjustment process for Y+Z? I recommend doing so. My 1100 had chatter issues when I first set it up too. Went away when I adjusted the gibs on X Y and Z.
I don't know what process the factory in China uses but I bet it isn't the lost motion one described in the manual.

[LeeWay]

have you tried roughing like you did and then doing a less DOC finish pass in the opposite direction?
It seems to me like doing this should still see the same pattern if it is in the machine. If you don't see it in the same locations, then I might suspect something else. Do the finish pass a little higher so you can see the original pattern.

[coffeetek]

Wohooo! Solved! So Tormach support suggested adjusting Y gib as you guys did here. So I went and adjusted it as described in manual and problem went away. Here is picture of finish while moving on Y axis. Adjusted Y gib on top, original problem on bottom. HUGE difference:

[LeeWay]

Excellent.

[C*H*U*D]

Glad you got it fixed!

But as a side note, that's really not a good way to clamp stock in the vise. Being on just one side of the vise screw is bad, but extending it even farther out like that compounds the issue of the movable jaw racking. If you absolutely have to cut like that, you should equalize the force with a piece of stock on the other side as well. Just a thought.

[coffeetek]

If you absolutely have to cut like that, you should equalize the force with a piece of stock on the other side as well. Just a thought.

Can you explain this, I can't picture what it means?

[LeeWay]

He means that you are forcing the jaws to lock on only one side while the other side is not fast against something. It wants to skew the jaws like that, but when you engage the full jaws, you have equal force on them and no one sided force on the screw.

[coffeetek]

I see. Makes sense.

[joshetect]

Put a piece about the same size on the opposite side of the vise jaw. The vise force is in the center line of the jaws, if you work is off center the vise jaws will clamp at an angle. So your work isnt held in as well is it could (should) be.

[IMT]

If you cut another piece of stock the same size and clamp it on the other side of the vise it balances the load and the movable jaw stays straight.
With an aggressive cut and the setup you had the part is likely to pull out of the vise because the front jaw is really only contacting the left corner of the workpiece.

[C*H*U*D]

Can you explain this, I can't picture what it means?

You would use two pieces of the same size stock. One that you are cutting, and the second on the other side of the vise jaws (which is on the other side of the vise screw). What happens when you use only one side of the jaws, the movable jaw can (actually it WILL) twist slightly as pressure is applied to the stock on just one side. Supporting both sides prevents that.

I don't have pictures, but here's a quick explanation video:



Looks like a bunch beat me to the explanation! Can't seem to delete, so I'll just leave this here. Good luck and again congratulations on fixing your 440.

[coffeetek]

Thank for pointing this out guys, but I do not make parts with setup like that, it was just done like that to test this light cut finish...

Back to this issue, I have machined the original part again today (part held in center of vise ;-) and wave pattern is back on side while cutting on Y axis. Its not as pronounced as before but its still there. So I will tighten Y gib again and see what happens. What is different from my test cut is that dept of cut is greater, test cut I posted picture of was on 3/4" stock, this part cut is on almost 1" thick stock, so more force.

But there are couple of things I have observed that I would like to get your comments on.

1. It seems like on my Tormach 440 its not possible to tighten gibs so much to stop movement completely. I would have thought that this should be possible, but it does not appear that I can do that on my machine which is very confusing.

2. I looked at the gibs from the side and it looks to me like they are made from plastic. Is that possible or do my eyes deceive me?