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Author Topic: How To Know If You Are Stressing Your Machine  (Read 1898 times)

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How To Know If You Are Stressing Your Machine
« on: April 12, 2013, 04:45:02 PM »
Hello everyone.

I've only recently (few weeks back) switched a small mill I have to Mach3 and it is working wonderfully since then. I do have one question though.

The mill I have is a relatively old Haase mill, 1.6m x 0.6m in dimensions and while I'm not exactly sure what it's steppers are they're relatively small. On it I have a 900w (if anyone could explain to me what the advantage of wattage is I would appreciate it, what does it matter if you have 900w or 3kw if you have 26k RPM, bear with me, I'm new in this) milling motor with 26k RPM.

A project I currently have (it's pretty awesome and I'm sure more of the like will follow soon so this is important for me) requires me to cut 8mm thick acrylic. I had a custom two spiral carbide bit made for me specifically for this purpose, 8mm in diameter and it works perfectly.

The one problem I have with it is that I think that I'm forcing the machine. The first thing I do is mill a small channel into the acrylic, 8mm wide and 3mm deep I try to do this at 800mm/min and 26k RPM. This works almost perfectly the only problem is that the spindle/mill motor carriage starts shaking from time to time which is a bit alarming to me, holding it for a few seconds with my hand will usually stabilize it and that tends to be the end of it. Another thing I need to do on this project is cut through the acrylic, so for that I go 8.5mm deep into the acrylic and set the speed to 400mm/min and it works well enough for a while but soon afterwards it starts shaking again, the only thing that will prevent this, other than holding it with my hand, is setting the feed speed to 120mm/min which seems ridiculously slow to me.

What bothers me with this whole situation is that my guess is that the motors shouldn't have any resistance whatsoever while going through the material. That's at least how I always imagined it, I thought that the mill/spindle would take care of all the materials and that the motors would basically have the same resistance as when going through the air.


Another issue I have is when jogging at some points the mill seems to encounter some resistance and I hear a screaching noise and sometimes it even gets stuck during jogging (just pressing the jogging button in that direction will get it going again). My first thought was of course lack of lubrication so I got out and got myself an entire can of machine grease but that didn't really help as I still have the same problem after putting lots of grease on it. Grease actually made it worse as it got stuck at all the places where I put huge lumps. I set the job speed from 2000mm/min to 800 mm/min and I don't seem to be having problems anymore during jogging but the max of the X motor as far as I could determine is around 2500mm/min so running it at 800 is less than ideal.

I really hope that someone can help me with my issues, any replies are greatly appreciated.

Regards

Offline Hood

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Re: How To Know If You Are Stressing Your Machine
« Reply #1 on: April 13, 2013, 05:16:42 AM »
You will always have extra forces acting when cutting material, how much depends on the material, size of cutter chipload etc.
 It does sound like you are pushing your machine too hard as it sounds like it is not rigid enough to do what you are asking.
Regarding the screaching motors, that is them stalling because you are asking too much of them, this could be you have the acceleration set too high or the velocity set to high or simply the motors just do not have enough power/torque to do what you are asking.
Hood
Re: How To Know If You Are Stressing Your Machine
« Reply #2 on: April 13, 2013, 07:50:16 PM »
That's for the reply Hood.

Just to clarify one thing, it's not the motors themselves that are screaching they sound normal it's just that the carriage when it comes across a certain part of the axis it screaches, that's why I assumed it needs oiling/greasing but that didn't really help. Another thing I considered is that the axis on which the carriage moves might be slightly bent but that doesn't sound likely to me either.

I'll try to capture the problems on video tomorrow and post it, that's bound to give you more info.

Offline rcaffin

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Re: How To Know If You Are Stressing Your Machine
« Reply #3 on: April 14, 2013, 06:32:39 AM »
Quote
the spindle/mill motor carriage starts shaking from time to time which is a bit alarming to me, holding it for a few seconds with my hand will usually stabilize it and that tends to be the end of it.

Sounds as though the motor support structure is resonating.
To check: get a few house bricks (or large lumps of steel) and attach them onto the structure in different places with solid G-clamps. If the extra mass stops the shakes, you know where you are.

Mind you, I think you are taking rather large bites. Me, I would be a shade more conservative.

Cheers