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wildcat
11-17-2006, 07:12 PM
Today was the first time that I ran an Al part on a newly converted IH mill. The part is a small flywheel drawn up in a CAD package and has a diameter of 3in. A four flute 1/4in end mill was used - if you look closely you can see see the tip of the endmill - hence first CNC fart. :) The chips got packed in the flutes and something had to give. I am really happy with the finish considering I have not even trammed or squared the head yet. Feed was only 3ipm at 1800rpm at .3in depth. This was a cheap end mill from Enco (from the pack of twenty box). The speed/feed equation would seem suggest that I should be able to go a lot faster than 3ipm. What do you think? What is the best way to avoid the packing and breaking of the end mill? Thanks!

http://www.cnczone.com/gallery/data/500/medium/CRW_3668.jpg

widgitmaster
11-17-2006, 07:51 PM
Nice!
I would suggest you use a 2-flute end mill in aluminum, NOT 4-flutes!
The 4-Flutes do not have enough chip clearance and build up between flutes!
Also, you did not mention the use of coolant, I hope you use a spray mister or flood coolant at that feedrate!

2-Flutes and feed much faster and deeper when flooded!

Eric

wildcat
11-17-2006, 09:29 PM
I don't have an automatic coolent system yet. I really don't want to go the flood coolent route unless absolutely necessary and instead was going to get a Trico Micro Drop system. Think this will be fine? For this part I brushed a little CoolTool on it but that's it. The part was 120 deg. F at the time the end mill snapped. Is 3ipm a fast feedrate? I checked a couple of books and it seems pretty slows compared to what is suggested by the feed equation. I should probably not have gone so deep at once and perhaps also made multiple passes on the outer diameter to provide additional clearance. Thanks

ViperTX
11-17-2006, 09:52 PM
It's not that the feed rate is too fast....it's that the chips are not clearing the mill.....don't you see chips wrapped around the mill??

drwc
11-17-2006, 10:04 PM
I think your spindle speed was too slow, should have been up in the 4000 range for a 1/4 in mill bit.
Coolant will definitely make a big difference, and hard to do without for long cnc runs.

I agree that that was a pretty aggressive depth of cut as well.I in my short experience find 1/3 diameter is max practical z feed on slotting style cut.

BobWarfield
11-18-2006, 02:15 PM
Wildcat, I'd even try a steady stream of air blowing in if you can't get flood. You have to clear those chips. Widgit is also of course correct in suggesting a 2 flute mill will have an easier time in aluminum.

I find when milling aluminum I can't go fast enough on the spindle so I crank the feed rate. It's a good argument to go to the bigger motor on the IH so you can get to 3200 rpm if you're going to do a lot of aluminum.

Here's another tip that works well if you can't get flood. WD-40 really seems to eliminate chips welding to the cutter with aluminum. Give the thing a healthy dose on the cutter and the workpiece before starting your cycle, and zap it a few more times along the way.

BTW, thanks for showing your part, even though incomplete. Show us some sequences once you got it working good so we can see how it comes out.

Best,

BW

Blaster33442
11-18-2006, 09:41 PM
Welcome to the world of cnc that most likely wont be the only endmill you break But it shure is fun lol

wildcat
11-20-2006, 12:40 AM
Thanks for the help everyone. I rigged up a mounted air stream to blow the chips out until I have a coolant system. Had no more 3/16 end mills so used a 1/4 which pretty much removed all the thin features, but it was a 2-flute variety. Also, instead of plunging to the target depth I redid the program to make several passes when pocketing. The total time did not increase much becase I could increase feed a little. The chips were like confetti instead of like hair before.

For the time being I have been mounting atop a piece of 2x8 until my limit switches arrive. The 2x8 has saved me big once already when an unexpected G28 sent the head striaght down to the table. Luckily the endmill was short and the table was not damaged. Anyway, looking foward to being able to use a vice again soon.

philbur
11-20-2006, 04:00 PM
Should make home on the Z up not down. Then an unexpected G28 doesn't do any damage. I've had a few when using CAD/CAM software.

Regards
Phil


Thanks for the help everyone. I rigged up a mounted air stream to blow the chips out until I have a coolant system. Had no more 3/16 end mills so used a 1/4 which pretty much removed all the thin features, but it was a 2-flute variety. Also, instead of plunging to the target depth I redid the program to make several passes when pocketing. The total time did not increase much becase I could increase feed a little. The chips were like confetti instead of like hair before.

For the time being I have been mounting atop a piece of 2x8 until my limit switches arrive. The 2x8 has saved me big once already when an unexpected G28 sent the head striaght down to the table. Luckily the endmill was short and the table was not damaged. Anyway, looking foward to being able to use a vice again soon.

wildcat
11-20-2006, 04:35 PM
Phil - is "making home up" a function of Mach or something else? At the moment increasing values on Z-axis raise the head. This seemed more intuitive to me but I had to swap the motor and encoder wires on the Gecko to have this behavior.

Walt@SGS.Inc
11-20-2006, 06:28 PM
One way to remember Z
Axis directions is remember,
+ adds material
- removes materilal.
Minus should move Z axis down or
into the work.
See if that works for your machine.
Plus and minus can be wired either
way you want to wire them.
Rots o Ruck
Walt.

wildcat
11-20-2006, 06:53 PM
Walt - thanks for affirming the standard approach, that's how Z is wired now. Just seems more intuitive. Perhaps something was getting crossed in the breakout board? Works great now though.

Errol Groff
11-20-2006, 08:07 PM
I have god results using mineral spirits as a lubricant for milling aluminum. Much cheaper than WD 40. Can be brushed on or sprayed on with a recycled squirt bottle. Also, my usual attitude is what do I have more of, time or money and the answer is usually time. So I tend to take a lot of shallow cuts, ie .025 DOC instead of trying to plunge in and take a lot at one whack. Fewer broken mills that way although I have broken my share!

As always, this is what works for me, YMMV.

Errol Groff

BobWarfield
11-20-2006, 09:32 PM
Errol, I have also heard both Kerosene and Milk (?!??) recommended when cutting aluminum. I have tried the Kerosene (didn't want a sour milk smell in the shop!) with fairly good results on the lathe, but WD-40 works better for me on the mill.

Best,

BW

wildcat
11-26-2006, 03:43 PM
I gave this another try yesterday and had more success but another broke endmill for a different reason. The stock was being held in a vice and during the final contouring (actually turning the final corner no less) I think the forces of the vice started to be relieved and the endmill got squeezed. Perhaps I will have to start buying endmills by the box? :) Thanks for everyone's suggestions. I taped an airline to mill to blow across the part and that made a HUGE difference. I posted more notes in the Photo Gallery but here is the sequence.

http://www.cnczone.com/gallery/data/500/medium/CRW_3701.jpg
http://www.cnczone.com/gallery/data/500/medium/CRW_3704.jpg
http://www.cnczone.com/gallery/data/500/medium/CRW_3722.jpg
http://www.cnczone.com/gallery/data/500/medium/CRW_3725.jpg
http://www.cnczone.com/gallery/data/500/medium/CRW_3729.jpg
http://www.cnczone.com/gallery/data/500/medium/CRW_3731.jpg
http://www.cnczone.com/gallery/data/500/medium/CRW_3732.jpg

BobWarfield
11-26-2006, 03:55 PM
Nice, got a lot closer before breakage that time, eh?

Wildcat, did you write the g-code by hand or are you using a CAM program?

I can see where the vise may have squeezed the end mill. For a part like this, I think a lot of folks would have drilled the center hole and bolted the part to a tooling plate so you could go all the way around it without squeezing anything. Clamp the edges outside the cut path for additional rigidity and holding power.

You could also mill the spokes and hub in the vise and then do the bolting to mill the outside wheel cut.

Looks like you're having fun!

Best,

BW

zcases
11-26-2006, 04:12 PM
Is that an idler for a snowmobile......let me guess an Arctic Cat by your name. Nice job. Hope you could get going faster than 3ipm on that.....sometimes the faster feed will also help reduce heat because at a real slow feed theres a lot of "rubbing" of the flutes, rather than having them get a good bite and have the chip pull the heat out.

project5k
12-19-2006, 11:34 PM
thats a really pretty part.. i hope i can get to that stage sometime...

Randall
12-20-2006, 12:46 PM
I have seen this part before. How did you program it? Was it in bobcad?
Thanks
Randy

wildcat
12-20-2006, 03:05 PM
A similar one was on the cover of Digital Machinist. I drew up roughly the shape they had except they had an additional "twisted star" radiating from the center. I have no idea how to draw that. I hope they will consider making the G-Code available for the parts described in their magazine.

http://www.homeshopmachinist.net/?page=main.features.digitalmachinist