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shorty
08-13-2003, 07:28 PM
I've been turning saw collars at our mill for the last couple of days.....Yes, those crazy bosses of mine even let lowly welders run the lathe...anyway. I was wondering if there is an easy way to true my stock after roughing my disk with the torch.I'm usaully within a 1/8"after torch cutting but it seems like I'm doing an awful lot of bit sharpening. For example today I went through one whole tool bit to cut three collars. That's six torched surfaces trued. Is this normal?? By the time I take my final rough cut on the lathe, leaving .020 to clean up, the bit is pretty chewed up. In fact I sharpen it to take my final cut and then start turning the next flame cut piece.

Evan
08-13-2003, 07:54 PM
I don't know how heavy these things are but if you give it a bit of cleanup on a grinder first it should help.

wierdscience
08-13-2003, 09:37 PM
If using carbide,quit,use hss and true up complete in one pass at low sfpm(80-100),then switch back to carbide and finish to size.

Cass
08-13-2003, 10:11 PM
If the lathe will pull it slow things down and take a much heavier cut to get under more of the crust. Getting a bigger lathe is probably not an option. A lot of so called "mild" steel these days is coming from recycled cars and it has enough chrome, nickel and other stuff in it to make it air harden to some extent. If you have the option of heating up the parts to a bright red or orange color and then letting them cool in still air they will be softer and that will probably help the machinability. Knocking the slag off with a grinder as suggested by others is a good idea if you have a rough torch cut. Of course getting as close as possible to a torch cut like a flame cutting machine gives is going to have less slag and variation. Taking all the material off in once pass would be nice.

Thrud
08-14-2003, 03:25 AM
shorty:
Try sawing the collars. The cutting torch is just exascerbating the problem Cass has mentioned with "bastard" steels. The heat hardens the hell out of it and your tools dull fast.

You could use T-15 bits to cut through the mess, but be warned they are a bitch to sharpen because of their high red-hardness (the reason they work so well in the first place).

I usually use a highly negative rake carbide insert for rough stuff like this (only because I have lots of them).

Dr. Rob
08-14-2003, 04:15 AM
Yeah, I was about to say...Thrud is onto something there. I'm not sure what your saw collars are, but I'd like to recommend putting the torch away and holesawing or bandsawing these discs of yours. Might take longer, but fussing around with ornery tool bits and unruly discs takes some time too, I can imagine.

Really, in my humble experience, hot work (welded/torched) + machine work = nothing but trouble.

But in agreement with the other guys, yes- grind it some.

Forrest Addy
08-14-2003, 02:08 PM
Can you heat them to 1200 degrees and bury them in dry sand till they cool? God a furnace or a pile of firebick and a propane torch?

The problem is partly scale and partly flame hardened edges. If you burn them out and imediately dunk them in water to cool you've made the edges harder.

I cut miles of raggedy burned edges in my day and a simple draw at temperature solves many problems. If you leave a little stock you can get under it and machine it off on one cut if your lathe has the power (5 HP?).

I always used C-5 carbide with negative rake and dressed a 0.005 to 0.008 edge radius.

shorty
08-15-2003, 01:41 AM
I tried grinding these one a bench grinder to knock off the slag and to true up any lumps the cutting left. Seems to have worked well. All they are are 6"-7" x 5/8" circles that have to be turned to 5.392 with a .125 shoulder left at the origonal size minus the cleanup. They're for sharpening and straightening saw blades at a saw mill.
I'm going to have to look up in my machinist "how to" book to see what you mean by negative rake and "high red hardness" Thrud.
Oh yeah, what"s a reasonable size cut to take off?? I'm usually taking from .015" - .030" dependiing on how backed up I am with welding jobs that need to be done. I'm new at this so I still think it's cool to watch the cuts...hence the .015 cuts. When I'm in a hurry I take .030". The lathe I'm using is an old Stanley with a 8' ways and 16" 4 jaw chuck so the only real limitations are the operator. I'm pretty proud that I can true stuff up lickity split now so that should give you an idea of my machining prowess. I can make up collars and bearing retainers and stuff but the more complicated stuff takes me a while. Fortunately I'm a welder so I can always build up and re-machine...keeps me humble http://bbs.homeshopmachinist.net//smile.gif

C. Tate
08-15-2003, 10:49 AM
I would use the carbide and put a 45 degree lead on the tool with a very generous radius on the two corners and take as much in one pass as possible. If you are flame cutting then these are probably to thick to make sawing and the like practical. I would stick to the torch and turn method. Use as big a piece of carbide as possible it will give stability to the whole setup. If you can use one tool for roughing and one for finishing. Let the roughing tool get chewed up who cares as long as it cuts. The finish tool will remain in good condition and you won't have to sharpern as often.

[This message has been edited by C. Tate (edited 08-15-2003).]

winchman
08-15-2003, 11:27 AM
I'm really curious about something here. You're using a torch to cut these discs from 5/8" plate. The outside is "as cut" with a little grinding to remove the slag, etc.

How do you hold them in the chuck? Do you grip a little of the OD, take some off and then turn them around? Do you hold them on the OD, bore the center out, and then grip the ID while you cut the OD?

I often bandsaw discs out of aluminum plate and was wondering what the best sequence is for finishing them.

Thanks,
Roger

Evan
08-15-2003, 12:23 PM
For an aluminum disk you can hold it by bringing the tailstock center up and pressing it against the chuck, using just friction and take light cuts. That's what I have done and it works. Stick a few bits of peel and stick fine paper to the front of the jaws. Better is if you can stand to have three holes in the work. Then you can bolt it to a chunk of round stock as a temp arbor that can be chucked.

shorty
08-16-2003, 12:11 AM
Roger,
There's actually a 5/8" hole in the center of the plate to put it on a spindle. This allows the blade that's getting sharpened to stay true. I've made up a jig with a 1" shaft about 6" long that has a 1/2" plate, about 3" round welded to it. Then I turned the 1/2" to be square to the 1" shaft and left a 1/2" stub sticking out of the 1/2" plate of the 1" shaft which I turned to .625". I drilled and tapped for a 3/8" bolt in the 5/8" stub. Now I can put the plates on the stub, bolt them down and face the one side. Then I turn them over and turn the other side for the shoulder I need and then true the last bit that's left on the outside edge of the .125" shoulder.
Lemme know if this makes sense. I'm sure there are easier ways but this seems to work for me.