Web Goblin cnc has begun

[Web Goblin]

Right I decided that I had to have a go at aluminium, just couldnt resist the urge!.
I made up a dxf through autocad for a box drilling jig for some welding test boxes that I make.
The material is 10mm thick alu and I used a 3/16 end mill, didnt have a 5mm one, I need to build up my cutting tool supplies.


Admittedly I did forget about the top face of the jig, at the moment I am still too used to programming for profile cutting. This would have looked better with a bit of a clean up.



The box lid to be drilled and it fits snugly inside the jig.
All in all I am quite pleased with my first alu job. For using an old cutter and for a first attempt I'm a happy chappy.
I have also done a bit of video for parts of the cut and hopefully after my little gilrs 5th birthday party this afternoon I might get it loaded up to youtube.


Regards

Ian

[Web Goblin]

Links to some video of the first alu job.

http://www.youtube.com/watch?v=ABNmolGdUJ0

and

http://www.youtube.com/watch?v=3agFg5x53JY

Regards

Ian

[Jonathan]

What depth of cut, speed, feed, stepover was that? Looks like you took it very gently. Seems a bit of a random place to choose to cut it within the aluminium sheet, but I guess you had your reasons.

I see you're very generous with the cutting fluid!

Finished part looks nice, are there any marks in the corners due to backlash. Were you using G64? I think so, but it's difficult to tell in the videos.

[Web Goblin]

Jonathan,
I did take it very easy with that cut. Depth of cut was only 0.5mm, step over was 20% which would be just under 1mm and feed speed was 10mm/sec for that cutter was 10mm/sec. The only cutter I was was not new so I did go slowly with it. The alu also has some hard sections in it so that was why the cutting fluid was generously applied. The starting point was a mistake, I for got to set my dxf to 0,0 in cad and I think cut2d picked that up.
I have had a look at the program file and cant see any G64 codes in it. Youll need to excuse my ignorance in G codes at the moment, I havent got round to learning them yet!!
Some photos are attched of the cut edge. Quality looks good for an old cutter.

[JAZZCNC]

Some photos are attched of the cut edge. Quality looks good for an old cutter.

Hi Ian,

Congrats on your first Hot Chip's. . . . . . . (Now the BUT.:lol:)
I think your single spindle mount is causing chatter/resonance looking at the edges I can see chatter lines.!
I know you say the cutter was old but that does look more like flex chatter..? Also when cutting it sounded ringy more like a resonate ring not a blunt cutter.

Too little DOC, too slow spend n feed or more importantly wrong chip load can be just as bad for cutter than too much, esp in sticky Ali. Don't be shy give the cutter some work to do as your going far too conservative. . . .Heat is the enemy so send it away with the chip.!!

[Jonathan]

I think your single spindle mount is causing chatter/resonance looking at the edges I can see chatter lines.!

Just what I was thinking - the vertical lines are a bit of a give-away.

Definately too low feed and stepover - with only 20% stepover you need to feed much faster to attain the same chipload, look up chip thinning. This explains some of it, though it is aimed at making you buy the program...

http://www.cnccookbook.com/GWCalcFeedsSpeeds.htm

The alu also has some hard sections in it so that was why the cutting fluid was generously applied.

I was joking when I said that was generous!

I have had a look at the program file and cant see any G64 codes in it.

Mach3 may have defaulted to it anyway, it depends.
G64 puts mach3 in constant velocity mode, so that within reason the feedrate remains constant. This means that external corners will become slightly rounded - more if the acceleration is very low.
G61 puts mach3 in exact stop mode, so it stops once it has got to the point specified by each line of code, then continues. This makes the motion very 'jerky', though depending on the situation it will make the final part more accurate.

Using constant velocity makes the motion a lot smoother, and a constant feedrate is clearly faster overall and kinder on the cutter. To try it just type G64 at the begining of the program. You'll notice the most difference when a program uses lots of small lines to approximate a curve.

[JAZZCNC]

G61 puts mach3 in exact stop mode, so it stops once it has got to the point specified by each line of code, then continues. This makes the motion very 'jerky', though depending on the situation it will make the final part more accurate.

Ye Try G61 with an high feed rate/accelleration and watch it turn into a "Darlick on Whiz" as it try's to break dance thru the workshop wall after it's destroyed all in it's path. . .:rofl:

[luke11cnc]

what would you look for or what would it look like . for backlash??

James

[Web Goblin]

James,
backlash would look like an uneven cut. The finish edge at the corners would be like a wavey line. This happens when there is play in the mechanics of the machine like a set of cogs not meshing together correctly so that when your turn one cog it moves slighlty before the other one moves. In a profiling machine that drives atart to wobble a bit at a change of direction until the machine sort of balances itself out.
t I have found that the best way the check for backlash is to run your machine at a 45 degree cut so that both x and y axis are travelling at the same time ie cut a square but rotate it to 45 degrees on the bed. The corners should be nice a smooth without any wobble in the cut surface. Cutting at 45 also tells if your speeds are the same in both axis at the same time. If they are not you would have an uneven cut surface all the way along the cut.

Ian

[Jonathan]

Whether or not you get a wavy line/arc depends on the direction of cut (climb/conventional), the cutting force and the friction of the slides. Either way you will get a 'blip' on the corners, or wherever any axis changes direction. Here's an example:




The corners should be smooth, but as you can see each corner has a line/offset portion where the axis changed direction. For that part it doesn't really matter - it's still shiny

That was on my milling machine which currently has more than it's fair share of backlash.

This part was made on my router which has very little backlash, so the corners are smooth with no 'blips':