What will happen if the steppers run one of the axis to the end? Will there be any damages?
Will it be advisable to mount switches in order to prevent this?

Any experiences?

I can't speak for steppers, as I use servos. However, I did some major damage before I put some limits in. They can't hurt, but only help if you run out of space at a high rate of speed.
I don't know what kind of rapids you can achieve, but lets assume 100 IPM and a heavy axis. Hitting something SOLID will not be minimal! I would seriously consider using them.

Unlike an ordinary electric motor steppers don't really care whether the rotor is turning or not, the current hardly changes. Whether you damage the mounts really depends on how much spring is built in to the system.

You should never hit the end anyway because you will lose position. OTOH your machine will almost certainly survive unless it is either brittle or totaly flimsy :)

I got a Taig... was gonna put in limit switches but never got around doing so. I over run the axis average one a week (mainly on the Z going up and not paying attention and it hits the top). The Taig is such a small machine that it really does not hurt it... it's just like skipping steps... that's it. Keep in mind max rapids on a Taig is 25ipm... with mod maybe 45. And it is direct drive and most use 120oz steppers (I've got 180oz in mine) and most mod will not go over 280oz steppers.

I'm about to purchase a IH Mill and on that... I would install limit switches on for sure.

I have a taig and I also bought some limit switches to put on, but haven't gotten around to it. Steppers are kind of nice in that they just growl when they can't move. I do plan on installing the switches though, mostly to keep from going too far in the X direction because it will unscrew out of the brass backlash nut. If it does that, you need to carefully screw it back in by hand.

Al Z.

I haven't found the need in the 8 plus years I've had the Taig cnc. They sound useful, I just haven't needed them so bad that I've done it.

Generally you should try and avoid overtravel through dry runs with your hand near the e-stop (escape in mach) and careful planning. The only time I do it is when accidentally jogging to close to the limits of travel. It shouldn't damage the machine, but it can wear/damage the coupler pins if you do it too much.

Drop a mouse off a 100 story building and when it hits nothing breaks on the mouse, drop a horse off the same building and you will have a mess of guts.

A small mill like a Taig is unlikely to build up enough kinetic energy to do much damage. A 30,000 lb mill with 1000 IPM rapids is like the horse, when it hits the hard stops a lot of things are going to break. :)

If you're running Mach 3, you can use 'Soft Limits' in place of limit switches.
This video (http://www.hossmachine.com/Videos7.html#videos39&40) explains the principle.
Also watch the 'Coordinate Systems (http://www.machsupport.com/Videos/Mach3%20Video%20Selections/Mach3%20Video%20Selections.html)' tutorial from the master himself at Artsoft.

If you're running Mach 3, you can use 'Soft Limits' in place of limit switches.

Trouble is to use soft limits you really want home switches. Not essential but sort of.

I have an X3, bit bigger, hits the stops slightly harder than a taig, and I have limits but if starting again I wouldn't bother.

However I would bother with home switches. Got used to using them, like them.

Many operate small routers and mills without any switches quite happily.

Just because a big iron servo driven machine could not safely be used without limits does not mean that one size fits all. :)

Greg

I do not plan on installing any limit switches on mine. I run 200oz servos good for 40ipm in X/Y and 20ipm in Z, but I am cautious during rapids and also have the master power switch right beside my keyboard.

But then, I am a newbie as well. Getting ready to make my first part this weekend. Going to be using a 1/64" end mill through aluminum. I got a two flute and four flute. Should be fun.

1/64th will break from looking at it sideways!
Hope you have spares. From experience any chip loading will break the cutter, so keep depth of cut very shallow and clear those chips!

I am using a flood cooling system and the cuts are shallow. The bits are TiN coated carbide. Hopefully that helps. What rpm would you use to push that through aluminum 6061? 10,500?

I do know I need to leave as little of the bit protruding out from the collet as possible. That will not be an issue. All the tiny cuts are in the same Z plane.

And I have 10 of the 2 flute and 20 of the 4 flute sizes. I figure that should hold me for the 10 pieces I have to make. I hope.

What a first project.

Definitely run flat out at 10k rpm. 30 endmills should see you through, after you break the first 5 or 6 figuring out the right feedrate you'll probably do all those parts with one...I'd start slow and ramp up, maybe 2 ipm to start (I'm conservative) with very little depth of cut, maybe .003"-.005". Let us know how it works out.

Also after each part examine the endmill under a scope or loupe and make sure the flutes are clean and it's still sharp...

Ok, thanks for the information. I was going to be really conservative and start at 1ipm, maybe 1.5ipm. Good call on the depth. I was going to start at .007.

I figure the two flute bits should do well about not clogging. The run lengths are pretty short, so it will be easy enough to check for clogging. I would imagine they would clog easily. Hmmm. How would you clear the flutes on a bit that small?

I plan on showing pics of the work after it is done. It is my first mill piece so I am looking forward to it. Again, thanks for the tips.

All this talk of limit sensors started me wondering if what I really want is a switch to tell me if I am left or right of center.

Once I know where the slide is I don't need limit switches unless everything goes horribly wrong.

If it changed over in exactly the same place regardless of which way the slide was travelling I could power down half way through a job and let it find itself when I came back, I could also check backlash before every job and compensate for it.

I've been looking at those cheap U shaped light beam breaker opto electronic gizmo's. If I fitted a bar to the slide which broke the beam only when I was left of center I could read it in the software as left/right. The light beams are usually about half a mm wide and you get a really good component for a quid.

The simple transistor output type seem to ramp up linearly as the obstruction moves through the slot. If I fitted a comparator to the output, I might get that very precise change over point regardles of direction.

I think I'll have to put one together and try it out, confidence being that feeling you get just before you understand the problem.

All this talk of limit sensors started me wondering if what I really want is a switch to tell me if I am left or right of center.


In my opinion a small machine can get by without limit switches. But for ease of use if nothing else it still needs home switches and soft limits. Which is what I think you are talking about.

if nothing else it still needs home switches and soft limits. Which is what I think you are talking about.

Absolutely, but for best effect the home switch wants to be in the middle, tell you left from right and have extremely low hysteresis. I was just thinking out loud wondering if someone might see the fatal flaw in my plan and save my time making something naff :)

Well, so far, so good. I have managed to only break 3 bits, so far. One was just a homing error on my part. One of the DOH! moments. It is slow going. Those 1/64" bits are flimsy!

I had to adjust the pressure of the flood coolant to keep it from flexing the bit. That is how I managed to break the first two. As the bit was lifting from a groove, the coolant flexed it just enough to catch the side of the work and started a rapid chatter.

I check the bit every 10 minutes for buildup. Not a problem yet. I am probably feeding it slower than I could, but it seems to be working just fine. Probably wear the bits out faster with the slow feed rates, but the cuts look good.

That '27' Machinery Handbook book has been very helpful in just getting a good understanding of exactly how and why milling works. I use it for my light reading while waiting for the mill to finish.

My Taig Mill started life with steppers. I was running a Zylotec board with bipolar Pacific Scientific steppers. I developed problems on one of the Axis in that it started missing steps, like it was underpowered. I did not have limit switches. Since there is no feedback, if the machine is running unattended and it looses steps, it could do damage. My solution was to switch to servos. The servos have shut down a couple of times in the almost two years since due to lost steps, but no damage has been done to my machine or equipment. I never did get around to adding limit switches. I mainly use my machine carving wood, like a tiny router, but do an occassional aluminum part or two. It is 3+ years old, and I love the thing. When making batches of the same piece, I just set it up, lube it, let it run, go do whatever, come back and set up the next part. The servos with feedback give me little worry about a carved up vise or table. Rich

Here is a story I wrote about the project I was working on at the time, and the trials and tribulations with the steppers.
http://www.fieldlines.com/story/2006/1/9/181658/3402

I have home switches on my taig but not Limit switches, I may add some soon as ive started to push the envelope a bit and am working very close to the limits size wise. Im using steppers but work at upto 75ipm, at that speed and being so close to the limit i won't have time to stop it, but 90% of the time im at slower speeds so no problem.

The thing that annoys me most is if working on 6" wide plate, the Y axis gets the way cover jammed up between the plate and the column, causing it to not have enough room and jams :(

DJH

Yes, that's an annoyance with the rubber way covers - the older mills used plastic bag material and were much thinner, but didn't hold up as well. You could try replacing the rear cover with some plastic sheeting, which will be ugly and wear out quick, but not jam up...

The thing that annoys me most is if working on 6" wide plate, the Y axis gets the way cover jammed up between the plate and the column, causing it to not have enough room and jams :(

DJH

Absolutely, but for best effect the home switch wants to be in the middle, tell you left from right and have extremely low hysteresis. I was just thinking out loud wondering if someone might see the fatal flaw in my plan and save my time making something naff :)

The only problem I see, is that you need to center your work piece before you start. There might be a time or two that it's annoying with a part that will just barely fit on your table.

With the idea of using home to avoid the use of limit switches. The moment you skip steps, you don't know where you are, and the table will run to the ends. I have servos, and instead of skipping steps when the flutes got full and would not cut, the servos kept pushing, and spun the gear on the shaft. Now, out of position, I ran into the limit. :(

The only problem I see, is that you need to center your work piece before you start.

I had some spare space on a circuit board today so I've laid out a couple of opto switches and comparators. Be interesting to see what kind of hysteresis I get on the switching position if nothing else.

Yes, that's an annoyance with the rubber way covers - the older mills used plastic bag material and were much thinner, but didn't hold up as well. You could try replacing the rear cover with some plastic sheeting, which will be ugly and wear out quick, but not jam up...


Yeh Ive had the rear way cover flop over on to the table and get cut up a bit by the end mill.

Ive been trying to think of an elegant solution for it

DJH

Yeh Ive had the rear way cover flop over on to the table and get cut up a bit by the end mill.

Ive been trying to think of an elegant solution for it

DJH

You might want to try bellows from a Sieg. He used them for the Z azis but I am sure they would work on the Y with a bit of thinking.

http://web.mac.com/tikka308/Herbie/HERBIES_BLOG/Entries/2007/12/2_Z-axis_Way_covers___bellows.html