[rktman8888]

Just wanted to ask any of you that have a SMM2,... How's the surface finish?? The problem I'm having is every time the table changes direction it leaves a tool circle or a swirl on the face of the part. Different tools, programs, end mills do not mater. It's driving me crazy. I take pride in my work and the floor finishes look terrible. Machine is level, I checked the head tram and its good. Run out is .00005" The machine is only a couple months old. I can push on the head and measure a few tenths of play. I don't know if this is normal?. Im thinking when the table stops and starts its moving the head to some small degree and messing with my parts.

Thanks
J

[rktman8888]

And that's 6061 alum

[Geof]

You are stuck with it. The MiniMills both standard and Super are lightweight machines and they flex when the table accelerates; the head 'nods'. Slow the feed down and the 'swirls' are not as noticeable but they do not go away unless you go painfully slow. It is more noticeable on the Super MiniMills and I think that is because they have faster servos and higher acceleration.

I have contemplated a couple of experiments to try and reduce the 'nodding'. One is to fill the column of the machine with concrete, actually not filled directly, first I would insert a rubber bladder so there would be a resilient layer between the concrete and the casting. The problem with doing this experiment is that there are cables that would have to be rerouted and if it didn't help reduce the swirls, or if the weight of the concrete distorted the machine, it would be impossible to remove the concrete.

The other ideais to try a scaled down version of what is done on some tall buildings in high earthquake risk areas. Really heavy weights are fastened to the top of the structure on resilient mounts. The vibration frequency of these weights on their mounts is very different to the natural vibration frequency of the building and the two different frequencies interfere and reduce the sway of the building in an earthquake. Possibly some day I will try this, I have looked and I think I could figure out a way of fastening a few hundred pounds of something at the top of the column.

[rktman8888]

Geof,
Thanks for the reply. I sent my parameters over to Haas. They gave me a couple things to change. It did help a small amount. However I believe you are correct. If I put my hand on the very top of the casting. You can feel the shock wave when the machine makes a change in X or Y direction. The shock is proportional to the acceleration of the table. As a work around I may try and hone some corner rads on my finish tools. The concrete Idea would probably help. I was thinking of guide wires. A cable on each side of the machine anchored to the floor from the top of the casting. Tension them with a turn buckles. Sound crazy, but I bet a few hundred # of opposing force in the X direction would help stabilize the machine. Keeping the casting under tension should eliminate some movement. IT would be easy to try. I don't feel anything down on the base. I believe the machine has a high center of gravity and adding some amplitude to the problem. Tail waging the dog sort of thing. A larger, heavier base would probably fix allot of it. I will let you know if I try the guide wire thing. I think it could work?

J

[Geof]

Your wire stays may work and it would be an interesting experiment. But I thick the wires might even make it worse because they will have a resonant frequency and might make the column of the machine vibrate even more much like the the bridge on a guitar.

[Ydna]

The other ideais to try a scaled down version of what is done on some tall buildings in high earthquake risk areas. Really heavy weights are fastened to the top of the structure on resilient mounts. The vibration frequency of these weights on their mounts is very different to the natural vibration frequency of the building and the two different frequencies interfere and reduce the sway of the building in an earthquake. Possibly some day I will try this, I have looked and I think I could figure out a way of fastening a few hundred pounds of something at the top of the column.

you know, I was thinking about this a few weeks back while crawling up on top of our old VF1. it's a machine from 1993 and uses a big counterweight for the spindle head which hangs down into the middle of the column. (later this was replaced with the more common nitrogen piston to act as a counterbalance).
Anyway, later a guy was running a sinusoidal wave-like program with lots of tiny hesitation segments all over the place. the older machine ultimately couldn't handle it as good as a mill from even a few years later, but I couldn't get the image of the hanging counterweight out of my head. it's suspended by a pair of chains that wrap over a pulley, so it can only "swing" in the Y axis, but it's still an interesting thing to think about....

[Matt@RFR]

You bought a Haas, now you get to suffer with the rest of us.

If you have access to CAM with HSM toolpaths, you can apply that to finishing as well. I finish all of my pocket floors with HSM toolpaths with large stepovers. Reason being is with that style toolpath, there is never a sharp corner, thus no sharp direction changes.

[rktman8888]

I did try that using Volumill. Problem is it jumps around a lot. I will give it a try with larger step over and see if it helps.

Thanks

[keen]

Hi Geof. Thanks for your suggestion that I read this thread. Very interesting. (I have a Tormach 1100 and am considering a mini mill)

Yes I can see high feed rates etc you point out are probably the cause of the unwanted movements spoiling the surface finish. This is less noticeable on my slow stepper motor Tormach when I will often feed at less that F1000 mm.

I suppose a final pass at a slow feed rate would be a hassle to programme and take a lot more time. - And to slow the whole job down isn't economical. I would like to see some photos of this issue to see how bad it is - it may be minor compared with my Tormach finish issues.

What are you thoughts on a little Bridgeport GX480, or Sharp SV2424 , or HurcoVM5i ? They are about twice the weight - do you think the difference in surface finish or accuracy would be significant?

Cheers. Keen

[Geof]

The swirls that you see are not detectable by feel with fingertips or by a DTI. I suspect they are way down in the fifth or sixth decimal place (inch measure) but they are visible. Have a look at this picture which was done on a different machine but shows the type of swirl I am referring to: http://www.cnczone.com/forums/attach...yt-surface-jpg

If you do any subsequent finishing such as bead blasting or vibratory tumbling they are completely obscured very quickly. A bigger, heavier machine will produce a better finish but it all comes down to cost. Spend a modest sum and do a slow finishing pass or some subsequent finishing operation or spend more money for a bigger machine.

[mactec54]

I did try that using Volumill. Problem is it jumps around a lot. I will give it a try with larger step over and see if it helps.

Have you turned on the high speed look ahead, this helps a little,you have 200hrs to try it before you buy it, what you are seeing is a control & low count encoder problem, not a machine problem

[Geof]

The HSM option does not help much, we have it on some of our machines. And I do not think it is either a control or encoder count problem. I have run the same program on a SuperMiniMill and a VF2 and both created the swirl pattern. The difference was that on the VF2 it was not so pronounced and it faded away quicker.

[mactec54]

The HSM option does not help much, we have it on some of our machines. And I do not think it is either a control or encoder count problem. I have run the same program on a SuperMiniMill and a VF2 and both created the swirl pattern. The difference was that on the VF2 it was not so pronounced and it faded away quicker.

Why do you think Haas has increased the Encoder count, it is still not high enough,it is a definite problem with these machines even the newest one's, the machines have jerk instead of smooth transitions, the high speed look ahead help's to smooth out the jerk between directional change, using the right cutters speeds & feeds, you can eliminate the swirl, when you do your finishing cuts

[mactec54]

What are you thoughts on a little Bridgeport GX480, or Sharp SV2424 , or HurcoVM5i ? They are about twice the weight - do you think the difference in surface finish or accuracy would be significant?

There is only one in the list that you should consider, that being the GX480 Bridgeport, a very nice machine, so if you have the choice it should be the GX480 then the Haas, there is no comparison between the (2) machines