[Numb Nut]

I'm a bit clueless about cnc but was pondering - can cnc mills typically find the edge of a work piece automatically or does the operator need to setup the workpiece manually?

In a production run is the 1st piece typically setup manually and the vice has some sort of locating stop so the cnc can reuse the position data for the 1st work piece?

Also when the cnc has a tool changer - is it assumed that the tool ends up in the same location as before or does the cnc somehow need to figure out it's new Z position - because the depth of seating can vary?

[GdeColigny]

I'm exactly at the same level of cluelessness. Would be happy to have the answer and more. Is their any amateur-beginner website for this, with tutorial on how to make/carve specific/difficult shapes ?

[mrcodewiz]

There are probably ways to find the edge automatically. If you had a jig to put your part on and it was a known distance from your limits/stops then you would always know where the work piece is. I dont have limit switches on my machine so I normally find the edge manually. If I am doing more than one piece, I will make a jig and find the edge for the first piece and then I don't have to do it again for the subsequent ones.

[philbur]

You set and locate the first part manually then you place all subsequent parts in the same position using what ever means is appropriate for the accuracy required.

For an ATC (or manual tool changes) the depth of seating in the taper is normally assumed to be the same (unless you need super accuracy). If you change the tool in the holder then you have to tell the system where the end of the newly installed tool is relative to the tool holder seat. This can either be done off the machine, by physical measurement, you then enter the dimension into a table. Alternatively you can determine the tool "offset" as it is called by using a switch that senses when the end of the tool touches it.

Phil

I'm a bit clueless about cnc but was pondering - can cnc mills typically find the edge of a work piece automatically or does the operator need to setup the workpiece manually?

In a production run is the 1st piece typically setup manually and the vice has some sort of locating stop so the cnc can reuse the position data for the 1st work piece?

Also when the cnc has a tool changer - is it assumed that the tool ends up in the same location as before or does the cnc somehow need to figure out it's new Z position - because the depth of seating can vary?

[JQ_Quint]

EdgeFinding..

If it is a corner then a simple method would be to use a touch trigger probe which would beep or light up (these are battyer operated). A cheaper method would be to jog upto edge with say a 6mm dia bar in the tool holder and put a slip (of a known size say 5mm) between the edge and the 6mm bar. Keep jogging until you get a light bite feel. At this point you are exactly 3mm (half of your bar) + 5mm (the slip) away from your edge so you could set your datum to +8mm. repeat for other axis.

Of course a method which i use for real rough ass setting is use a pin and blue tack on the end of a holder. Spin the spindle up "low revs" and touch the end of the pin until it looks central. Move the pin to your corner then set your axis zero points.

Even less accurate can be done with a small drill.

All methods will involve you saving the postions in your datum page (g54 g55 etc positions) and as long as you call these in your program then yes it will repeat on each part.

You shouldn't have to worry about Z repeating on toolchanges.

Hope this helps.
J.

[TOTALLYRC]

EdgeFinding..

If it is a corner then a simple method would be to use a touch trigger probe which would beep or light up (these are battyer operated). A cheaper method would be to jog upto edge with say a 6mm dia bar in the tool holder and put a slip (of a known size say 5mm) between the edge and the 6mm bar. Keep jogging until you get a light bite feel. At this point you are exactly 3mm (half of your bar) + 5mm (the slip) away from your edge so you could set your datum to +8mm. repeat for other axis.

Of course a method which i use for real rough ass setting is use a pin and blue tack on the end of a holder. Spin the spindle up "low revs" and touch the end of the pin until it looks central. Move the pin to your corner then set your axis zero points.

Even less accurate can be done with a small drill.

All methods will involve you saving the postions in your datum page (g54 g55 etc positions) and as long as you call these in your program then yes it will repeat on each part.

You shouldn't have to worry about Z repeating on toolchanges.

Hope this helps.
J.

Of course you could just by a mechanical edge finder for $30 or so and they are accurate within a couple of thou.

[bertmiller]

im not using any edgefinder yet. i work like this:
i make a centerpoint on the aluminium block, usualy exactly in the middle.
this is my zero point for x and y, the z is zero'd on the upper surface.
the zero point is for all the operations and programs i have on that block.
usualy each millbit has its program.
i have an absolute dro system connected to my milling program so i can do some manual work in between the cnc programs.
if i need to make several boxes, i bolt an extra fixture on the table to which i push the object while clamping it in the vice.
then i rough all boxes first, then finish it, and then drill all.

[JQ_Quint]

ha ha ha, yes you are right RC, i guess i have never bought good quality ones and always ended up slinging them. but yes they would be simpler....

[Regnar]

I use an edge finder probably like most here. But I have seen some that use lasers and I thought this was neat [ame="http://www.youtube.com/watch?v=JcHgKazSjyA"]YouTube - Zero Edge Finder[/ame] I think its just a matter of accurate you need it to be set up as

[Numb Nut]

Thanks everyone - found those replies interesting and educational.

[Geof]

If you want a really comprehensive course on CNC try this:

http://technology.calumet.purdue.edu/met/mfet/275/

A couple of links in on this page there is a list of pdf files you can download; these are very complete.

http://technology.calumet.purdue.edu...sematerial.htm

[GdeColigny]

I need this but for regular machining, not CNC. All the course I found are about how to setup a visse or how to put oil everywhere. Nothing about applied machining. How to mill a knob, or a custom rotary switch cover button with female insert having a woodruff key (like the one you insert on top of a potentiometer) would be fabulous...

[sansbury]

I need this but for regular machining, not CNC. All the course I found are about how to setup a visse or how to put oil everywhere. Nothing about applied machining. How to mill a knob, or a custom rotary switch cover button with female insert having a woodruff key (like the one you insert on top of a potentiometer) would be fabulous...

This is the best free online video series I've seen--linked from another thread here:

http://techtv.mit.edu/search?q=machining&x=0&y=0

Another resource is SmartFlix, which rents how-to DVDs for $10. There are a number of videos out there which demonstrate basic technqies like how to run a fly cutter or bore a hole.

You will have to piece things together yourself in terms of how to make the whole piece. That's part of the fun of the hobby

Generally, a knob is something most of us would think about as a lathe part, though you could make it on a mill with a rotary table.

The "official" way to make a key seat is using a broach cutter in an arbor press, but there are alternative ways to do this. If you look up threads/articles on home gear-making you will find other methods using homebrew tools that cost less than a broach.

[GdeColigny]

This is the best free online video series I've seen--linked from another thread here:

Thanks a lot. For smartflix, I don't think they are available in the country i'm actually dwelling... (Japan, but I'm french).

[Numb Nut]

Thanks alot for those links. Have viewed the MIT machining videos and am currently going through the CNC lecture notes. The lecture notes about speeds and feeds have pickled my brain though!

[Fixittt]

Im going to try and give the same answers but worded a little different.
An example, lets say you write a code to drill a hole, and tap it. Argument sake.
you will typically use 3 tools for this. a center drill, a drill bit and the tap. So now we have 3 tools all different lengths with tool changes. So we know that we need to find the edge of the material, and do a tool offset for the 3 tools which will zero from the top of the material. (Typically done when home switches or absolute coordinates are a known value)
it should also be noted that the zero points for X and Y should be a non-movable edge of the part. Lets say you mount a vise with the movable jaw to the front of the machine. Well we know that the back jaw will never move once bolted down. So I typically go with the back left corner for my zero points. Rough cut material will never be the exact same size, to the movable jaw of the vice will vary. I use a wobble type edge finder that is ground to a diameter of .200. To get the back left corner as my zero points mouth the edge finder in the spindle. Turn spindle on and set the edge finder to a off center spin. This it typical done by just touching the wobble end. Jog so the edge of the material untill the edge finder lines up, and keep jogging until it just throws off center. Zero axis here. jog z up untill you clear material. then move the axis in the same direction half the diameter of the edge finder which will be .100 zero again. you now have the center edge of that side. Repeat for next edge. Once you have done the 2 edges, you now have the corner. The center of your spindle will line up with the back left corner and every tool in the spindle will do the same. Now mount center drill. Jog the tip of the tool down untill to the top of the material. with a piece of paper between the tip of the tool and the top of the part jog down untill the paper has drag from the 2 surfaces. Tool offset measure the first tool. enter it into the table for tool 1. repeat the steps for the drill and the tap. The values will each be different but now the control software knows where to top of the part is for each tool by the tool offset table.
Hope I didnt confuse you even more.

[Numb Nut]

Fixittt - that seems to make sense to me - thanks for taking the time to post up the explanation.