[taxslave]

I need to square up some 4340 blocks. Unfortunately it sounds like I will have to order flamecut material because of the 14" X 12" X 9" size required. If anybody can give me an idea how hard the flamecut material will be to machine I would appreciate your input. I am also wondering how much excess material I should get between the flamecut and finished size, I more or less want to go until it machines like 4340 again. If you have used some good inserts doing this it would be nice to know what they are. Thanks!

[Geof]

Aarghh!!!! My first tip is to farm it out somebody who is too naive to know what they are getting into.

I hope you have a nice big machine that can drive a big negative rake insert face mill taking a good depth of cut at a feed of about 20 thou per tooth running at around 600 fpm. Last time I did anything like this was over thirty years ago on a big manual Cincinatti using Kennametal KC850 inserts that were the cat's meouw back then; these days I don't know what grade is equivalent.

You need to get the stock cut at least 1/4" oversize and whatever machine you are using your depth of cut has to be deep enough to get under the hardened skin from the cut and your cutter and machine combination has to be strong enough to have a feed that gives a good big strongly deformed fast moving chip so all the heat from the cutting gets carried away in the chip.

It is also a good idea to hand grind a good bevel along all the edges so that when the inserts first enter the cut they are not impacting directly on the flame cut surface but have a chance to get underneath it and attack it from the back. You will find, if everything is going fine, that the inserts start to break down right along the region that is hitting the skin, deeper in the material the insert has an easier job.

[Geof]

I tried to edit my other post but couldn't.

I should have said at least 1/2" oversize, I was thinking 1/4" per side to give adequate material for getting under the skin. Also you need to make sure your supplier can give a good smooth flame cut surface. Often times I have seen cuts that have gouges near the corners so the thickness under the gouge is much less than across the face. This causes two problems; one is that when the cutter reaches the gouge it hits a deeper section of hard material which can damage the cutter; the second is that the region beneath the gouge will have heat affected material going deeper into the bulk of the material and this can cause problems in the final machining.

Two more points I missed. Coolant is strictly forbidden for this machining, you want the chips coming off really hot. Coolant will kill the cutter in short order, a good strong airblast is a good idea. Use conventional milling not climb cutting so that the inserts are approaching the heat affected surface from underneath. I implied that in my other post and of course on the manual machine I mentioned it was conventional milling.

[jimmyjames1981]

after you get the block send it out and have it annealed and stress releaved. cut like butter. shouldnt cost but $50 to have that done if you dont have an oven.

[jimmyjames1981]

for the record flame cut 4340 is not even hard.... the max rc is gonna be like a 25-30rc, an indexible will plow right through that with no problem.