[keen]

Hi all.

Deep end milling work with slender cutters in pre hardened P20 steel can really push the limits of milling....and expose issues that are not usually so apparent.

I have been cutting a mould cavity - finishing with a 1/8" end mill 21 mm deep and thought it might be useful to post what have learned - and welcome any input on this subject .

Some tricks I learned are:

• Undercut the cutter so only the last portion in in contact with the work.
• Lap the cutter razor sharp or use a new cutter
• Use conservative speeds and feeds
• Rough out with a cutter only slightly bigger than the finishing cutter so the finishing rad cut is small.
• Take only a tiny finishing cut - in this case 0.06mm and 0.20 mm deep cuts
• Tungsten carbide is better than HSS

Just spilled a drink on my keyboard and will have to quit early !

Cheers. Keen

[mountaindew]

Nice skills!
Surface grinding your tooling for custom or unique needs.
Looks like this takes time, nice surface finish on finished work!
Well done

md

[BAMCNC.COM]

I agree MD, sounds like a great excuse to buy a surface grinder, lol. Since I use Titanium, I never have needed one.

[keen]

Cheers - You can purchase hog nose undercut or relieved cutters for that kind of deep work, but in this case I just used dull cutters I had and diamond lapped the hog nose rad. I was not sure if I could go that deep in p20 steel so I just tried it with what I had on hand. 3.15mm dia x 20.1 mm deep and 21 mm projection is 6.5 x the diameter....I was not optimistic. I tried it first with a less than full relief ground, and the rubbing gave a poor finish and errors.

You can grind the undercut with a low cost D bit cutter grinder also if you don't have a cylindrical or surface grinder etc.

[Steve Seebold]

I don't think I would try to cut the corners out of your project by side cutting with a very small end mill. I think I would work out a program and cut it out with a larger cutter then with your small cutter, make your moves strait down to take the corner radius out to what you want.

[keen]

Hi Steve

Yeah I know that seems logical, But I have tried it in the past with less success. The side cutting process I used actually exceeded expectations and went well. I think the trick is very light cuts - a 4mm cutter 0.40 mm deep roughing and a 3.15 cutter 0.2 deep finishing.

I was going to try the straight down method again, but I phoned a colleague that does a lot of this work and they described the above method.

[ajg762]

Very nice work! the surface looks alot better than i thought it would have turned out. I tend to use EDM for cavitys and cores like that, but it is slow and requires polishing for good nice smooth finish. Cant wait for my Tormach to turn up so i can start trying it out on jobs like that and hopefully replace a lot of the EDM work.
Keep us posted on any tips and tricks you find

[keen]

Thanks ajg762. Good to hear I have been of assistance to someone else!

Yes I was going to EDM that cavity also - at the last minute I thought I would try the Tormach, thinking I could always finish it with EDM if I couldn't finish with the long slender cutter. I knew if I sparked it I would need to redress the electrode at least once, re spark the bottom - and so I was looking at a couple of days of full on work - and then there is the polishing.

Now I have done this I can move into this deep slender work with more confidence. My colleague (mentioned above) saw the work I did and said if I use a special type of Iscar cutter that they use, I must get the code and order a few, then I can go even deeper to diameter ratio. (they are a solid diameter 'stalk' (and so more stiff) with the cutter ground only on the end into the last few mm - the 'stalk' has a small clearance - slightly smaller than the cutter diameter)

Of course grinding the clearance and hand lapping your own means you can use an existing dull cutter - so I will still use the above method for the less extreme work.

.Cheers, Keen