An elusive chatter and I am out of ideas.

Attached is a pic of a test piece I cut out tonight on my DIY machine. 10mm 2F endmill at a full depth of 24mm, followed by a contour same depth with a 3F taking off 0.4mm finishing run. The little red area is where my machine will chatter. Feels like its the whole machine bumping around. Even when the cut is a light pass.

I have tried every way I can think of to find where this chatter is? Its kind of on the diagonal axis between X and Y in direction. Honestly, I have swung and twisted and pulled in every direction and when I find something that I think might be loose?? Nope. It is still there. I think even with a tiny 6mm endmill it is enough to hear the chatter but not so evident in the work. So I can actually climb cut with this machine quite well, except in that one direction - or almost the opposite. It sometimes sounds worse than it is on the workpiece.

I dunno, I wasnt going to write on here about it. Its a DIY machine. I guess if someone has an idea on something I can address that is new, well thats what it is all about huh?

I am about to build a new steel frame and sit a cast T slot table on it in the next 12 months. The frame will be pretty heavy as it needs to hold the 600kg cast table off the floor. I still think it might be no different.

Oh, yes I do know I can decrease my workload, but it would be nice to sort this - kind of a challenge.

Thoughts?

Quote:

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Originally Posted by boydage

Attached is a pic of a test piece I cut out tonight on my DIY machine. 10mm 2F endmill at a full depth of 24mm, followed by a contour same depth with a 3F taking off 0.4mm finishing run. The little red area is where my machine will chatter. Feels like its the whole machine bumping around. Even when the cut is a light pass.

I have tried every way I can think of to find where this chatter is? Its kind of on the diagonal axis between X and Y in direction. Honestly, I have swung and twisted and pulled in every direction and when I find something that I think might be loose?? Nope. It is still there. I think even with a tiny 6mm endmill it is enough to hear the chatter but not so evident in the work. So I can actually climb cut with this machine quite well, except in that one direction - or almost the opposite. It sometimes sounds worse than it is on the workpiece.

I dunno, I wasnt going to write on here about it. Its a DIY machine. I guess if someone has an idea on something I can address that is new, well thats what it is all about huh?

I am about to build a new steel frame and sit a cast T slot table on it in the next 12 months. The frame will be pretty heavy as it needs to hold the 600kg cast table off the floor. I still think it might be no different.

Oh, yes I do know I can decrease my workload, but it would be nice to sort this - kind of a challenge.

Thoughts?

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i would watch how the chips are ejected from around the work piece. if they hang up on that section they could be getting recut and messing with the load while finishing. might want to leave less on the finish pass too? the walls don't look bad at all in the part except for the area you pointed out but i have to wonder what is going on with the bottom surface? it looks pretty chewed up.

full depth of cut on the roughing pass offers little insight to how rigid the machine is to begin with without knowing how much step over you are able to get on the roughing operation.

longer tools will chatter more at the bottom and improve the closer the cut gets to the holder since it's supported better at the collet end but it looks about the same in your case. i would say the fame does have some flex since you can see it in the roughing but that's fine during roughing as long as it's not so bad the tool ends up walking up over the part :)

24 mm deep on a finish pass is pretty deep using the side of a cutter on a light duty machine. you might be better off using a ramping tool path to do your finishing.

Hi. Yeh thanks for that. Oh the bottom finish, I had been pushing a new endmill to see just how hard I could push it during the adaptive.

Mmmm my problem is most certainly something in my mechanics or structure. I think the sample pic was a poor representation. If I am roughing out or just running a contour it will run and sound great. You know.... that metallic "Vvvvvvppppp" followed by the rooster tail of chips being ejected. But the gantry will change direction (and not in the -Y necessarily) and it will all change to a "BbbbbarrrrPPP" and vibrate the whole machine. Until that direction changes, and we get the right again.

But what is weird is that even a small 6mm endmill will do it and even during a ramp down - you know - very little load.

I have worked out some good strategies to overcome this problem. I guess that I have seen what my machine is capable in 75% direction. And surely it wouldnt be too much work to get it 100%. I just cant see or find the cause.

All that make sense? I think I will keep adding strength. And then some triangles. And then some more. Lol

It's hard to see the problem properly in the photo as it's too small and out of focus but, it kinda looks like the tool marks I get when I have tramming issues. Side cuts leave deep scores in the surface when the flutes engage at an angle.

Have you checked the spindle tramming and run-out recently?

Also, if you've been getting vibrations with certain movements then you should check that all the screws are tight.

After one particular mistake I managed to vibrate half the screws out of place on my machine. After re-tightening all the chatter issues went away. It was educational...

Also, are you using coolant when you cut? The surface finish with and without is night and day different.

Hi. Hey thanks. I do use coolant. To describe the chatter, it's quite a low frequency. I have checked everything. As much as I can anyway. Upgraded to 30mm linear rails from 20mm. Even my ballscrews that are 2000mm from 16 to 25mm. Added gussets and heaps of strength to the gantry. It's weird.

But, I have only just now built a tramming tool and am going to do that. I do know it's out for sure as I get lines when facing. I just didn't think tramming would be the cause. To be honest, hearing and seeing the results it really sounds like something is loose.

So I am going to tram the spindle and I have actually begin building a new base frame complete with a 600kg T Slot table I had made in China for cheap.

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did you try to increase/ reduce spindle rev ? Could be some case of resonance . . .
Did you evaluated the dynamic run-out of spindle?
What is static spindle run-out? ( it looks less than 2microns from the picture )
is the tool balanced ( together with toolholder )? what is balancing rpm ( or range ) ?

I found a whole bunch of ways my mistakes can cause a poor finish. I always seem to find new ones every time I think I know what I'm doing...

A machine not being properly square and trammed etc can cause all kinds of issues. Some look similar to (over) feeding errors.

A 1/8" x 1/8" cut with a 1/4" end mill at the start of a cut can turn into a 1/4" x 1/4" cut half way through the cut if the table is closer to the spindle at one end than the other. Suddenly a perfect feed n speed turns into a vibrating chattering or tool breaking mess...

A little nod in the spindle mounting means the end mill cuts deeper at one side than the other. This leaves an uneven finish with lines (you can feel) in the surface.

Feeding too slowly (for the spindle speed) or making cuts that are too shallow causes rubbing which creates a lot of excess heat.

As well as melting and re-cutting chips (which causes a poor finish on it's own), rubbing make the tool dull which leads to a poor finish, chatter etc.

Insufficient coolant pressure which fails to clear chips properly = poor finish.

Feeding too fast also leads to chatter, tool breakage and a poor finish.

Not holding thin metal properly when cutting makes it flex and vibrate when cutting. Poor work holding in general is an issue.

Using long thin tools is a recipe for chatter and a poor finish.

Poor quality end mills can cause issues in the finish.

Using end mills with the wrong coating for aluminum causes chips to weld to the tool and dull it's edge.

Using the wrong type of end mills for the spindle - i.e. Trying to use HSS end mills in a high speed router spindle. Or trying to cut hardened steel at 500rpm with thin sharp fluted end mills made for aluminum or plastic.

Runout in the tool, spindle and / or collet.

A poor fit of screw holes in mounting plates, or over (or under) tightening of screws.

Poorly installed linear rails and / or ballscrews. I.e, if they aren't properly straight, flat and parallel.

Grinding down and loosening the grip of the motor coupling from a feeding error can prevent the motor holding the axis still when cutting which leads to chatter-like marks (at least it did on mine).

If you've ever driven an axis into something and had the motors carry on turning the ballscrew when everything else stops, I'd check that all those couplings are still securely in place. And that the nut isn't damaged.

Using Gwizard made a huge difference for me though. 9 times out of 10, a poor finish is a feeds n speeds error for me.

My problem is that my machine will give me a perfect finish in one direction, same feeds/speeds, until it goes in the other direction (what's weird is its not exactly in a Y or X but a combination or diagonal) where it will "barrrp" low frequency and more violent chatter. Definitely mechanical. If I found a loose rail or linear block it would all make sense.

I did tram today (had to build a trimmer because I'm a tight arse) and it's almost perfect on Y and 0.6mm out on X. Lots.

I am going to build a new table/frame. Bolt it to the floor. Install a 650kg cast iron t table. Get the spindle tramming done. See what happens.

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