[mc-motorsports]

So if you had a job that requires you to mill a .875" ID 3" deep in 304SS, how would you go about it? I was thinking 3/4" solid carbide, helix entry on a hole pocketing opp per CAD/CAM. Kinda wishing I could use insertable endmill but can't get atleast a 2 insert in 1/2", and single insert indexable endmills are about worthless in a application such as this.

What would you guys do?

BTW, I HATE 304!

[cam1]

Hi: One things for sure, I'd drill the hole to within 1/16 or so of finish diameter, and then do a boring routine like you outlined. Does the bottom of the hole need to be nice?
Coupe more questions:
What about the straightness of the bore?
How about surface finish?
Could you drill and bore with an offset boring head?
My concern about the long endmill approach is that I tnink yor L/D is reaaly large, and with the full 3 inches engaged on the wall it'll be a screaming chattering mess.

regards

[mc-motorsports]

Thanks for the reply.

It's basically a 3" long nut with a 1"/8 thread, .875 would be the minor diameter. I've had nothing but problems drilling 304 in the past, that's why I just wanted to bore it open with an endmill using a milling machine. Drills seem to work-harden the material too fast and larger drills are more difficult, refering to cobalt. It would be nice to get an indexable endmill and just use a helical pocketing operation, inserts are cheap, large cobalt and carbide drills are expensive. Need 500 pieces so tooling cost is a major factor, otherwise I would just drill and bore like you said....

Easy answer is lathe and drill, thinking outside the box... Or atleast trying!

[cam1]

Hi: Full points for thinking for an easier way.....
The benefit of doing it on the lathe would be that it's a 1 setup part.
Depending on the lathe you have (hope it's CNC), you should be able to rough drill, then bore & thread. I work with alot of different materials (some not so nice), and my experience with work hardening materials is that you have to commit (no peck drilling), with lots of coolant. We have a mofo waterjet cutter (8" on Z capacity) at work, so for me, I'd probably ask to have the hole "shot out" to .750, then chuck, bore & thread. The waterjet is nice because it doesn't work harden the material.

regards

[dertsap]

it might be worth looking at a kennametal insert drill if tool cost is the issue , they are pricey but the time it would take to drill and bore othewise will pay a large chunk on the purchase (time is money), they are a quick material removing tool and work great for drilling thread holes and such

[allchevy]

i have done similar hole on 303 on a older daewoo puma 8 cnc lathe i had too rough drill it pecking at .375 low spindle high feed if you stall the spindle just back the feed up you will no you got it when the ships start poping and they are nice and golden.. i sharpen the drill by hand never use a new drill with out looking at the point most new drills are way too thick from factory..and may have too split the point or thin the webbing

[mc-motorsports]

Looking into insertable drills, thought about waterjet, that did cross my mind, problem is that would more than likely be pretty expensive on 3" material, would be better finding a more cost effective solution per completed job price. The other problem is I don't do CNC turning, only cnc milling and conventional turning as far as machining. Plus there has to be a more efficient way of boring a 3" hole in 304 than drilling. Yes waterjet would be a quick solution, but the last waterjet quote I recieved for thick sections of SS was throught the roof! But I understand that the machine requires a lot of matenience and is in turn expensive to operate, plus you would have to slow the feedrates to limit "kerf" especially on a 3" thick section...

[neilw20]

Masonry drills do not cost too much. Roughing out is easy.
Resharpen to a reasonable edge, push it in hard at about 0.002-0.004/rev and use lots of compound.
Maybe 200-300 RPM on a 3/4" drill. Suck it and see.
Shouldn't squeal.

Best of luck. Don't let it work harden.
Carbide and SS like each other. HSS is useless for production.

Neil

[Baketech]

I've had good luck with insertable spade drills on 304. Fastest, and least expensive way to move material imho. You can get the inserts in 1/32" increments, so you would have very little to remove with the boring bar. (if you need to bore)

Good luck!

[cam1]

You will have arms like Popeye when you are done this lot of 500......

regards

[mc-motorsports]

You will have arms like Popeye when you are done this lot of 500......

regards

exactly! That's why I just wanted to do them on the mill, plus I don't have time to stand there and turn handles on a conventional machine, counter productive for my work-load.

Might just have to watch this job pass by, plus they want a short lead time, of course...

[cam1]

Yup: Sometimes it's best to take a pass on a job, or to sub it out to a shop that is more suited for that work.
If you take it on, pack a big lunch. You'll be hungry after all that drilling.

regards