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frbush
10-01-2003, 09:20 PM
Don't know what the sam hell is happening. The project requires a 4.500 piece of 360 brass with a stock size of .750 x .500. The .750 dimension is to be milled down to .250 for 4.000 leaving the last half inch untouched. L shaped sort of like a miniature putter. I thought I would save time by bandsawing away most of the unwanted material and just leave enough for a clean up cut to the finished dimensions. Put new blade in bandsaw and clamped excellent guides so all parts would be cut the same. As usual the brass cuts like a dream. The blade cuts a .045 kerf. Here is the problem. As the cut proceeds down the 4.000 dimension the previously cut ends start to spread and at the completion of the cut the starting ends have opened up to .170 and both sides have developed a curve. Are there internal stresses that cause this? Other than clamping in a vise and milling the excess material away what is the solution. Would the stresses still cause the warpage if I milled off the excess material. Never had crap like this happen before. Would annealing the brass solve the problem?

Alistair Hosie
10-01-2003, 09:38 PM
Are you positive the blade tension is correctly set.Could be that the saw blade is wandering slightly causing a drag effect. Which means the blade is cutting off the 90 degree set and cutting if you like sideways a little as you progress (twisting a touch if you like)with the cut.I would check the blade tension first.Hope this helps Alistair

brunneng
10-01-2003, 09:43 PM
Not being a pro machinist but I'll take a guess and see what follows from the others.

It sounds like what you would see if there was a lot of stress.

If you're not using coolant on the cut could the blade be heating the inside of the cut and expanding the inside surface causing the outward bend?
I wouldn't expect that much heat to be generated in that thin a stock but...

Take a little clamp set to just over .75 and slip it over the top edge as soon as the blade clears keeping it from spreading but being careful not to clamp the blade?

frbush
10-01-2003, 09:43 PM
Alistair,
First thing I checked. Everything with the saw seams great. Damned brass thinks its a tuning fork.
Fred

frbush
10-01-2003, 09:47 PM
I tried putting the parts in a milling vise to squeeze them closed but they spring right back when the pressure is released. I think I need a few beers.
Fred

JCHannum
10-01-2003, 09:48 PM
Cold rolled steel will do the same thing. It is internal stresses. Milling would have the same effect.
I do not know if annealing will help, it is worth a try, but you probably will have cut oversize and mill all dimensions to end up with a straight part. You may be able to anneal and straighten, and then true it up.

C. Tate
10-01-2003, 10:12 PM
I don't think you are getting stress relief. I am not sure what the cause is other than band sawing is not a precise machining technique. If it is stress relief you will not encounter any more after sawing. Just mill to size after band sawing. I would mill the whole thing anyway. I could mill to size in the same amount of time or less than all of that sawing. My opinion.

frbush
10-01-2003, 10:30 PM
First thing in the morning I am going to try milling the excess material away just to see what happens. If it still warps I'm taking a trip to McMurray Brass in Dallas to see if they have any ideas. Brass is the only metal they sell and it's where I purchased the material to start with. Thanks for all of the suggestions.

Rich Carlstedt
10-01-2003, 11:23 PM
Heat up the piece till it is dull red and let it cool , then try it.
If it does it again, it's your method of sawing

darryl
10-02-2003, 02:07 AM
It's stress in the material from forming it. Any material you remove from the piece will allow the remaining metal to curl and twist even more, except not to the same extent that, say, a saw cut down the middle would produce. If you don't stress relieve the piece before the first cut, it will drive you nuts with all subsequent operations. You may have to start with a piece that's much wider, say 1.5 inch, and remove the same width of material from each side, leaving the 'L' on one edge only. You'll be balancing the stress forces that way, and clean-up milling won't warp the piece nearly as much, maybe not at all. I seriously doubt if the saw, or the method of sawing is causing it. You'd be having a serious problem just getting the cut to proceed. As far as annealing the piece now that it's been warped, I think it will remain warped, but could then be milled without further problem, except that there won't be enough material left to maintain your dimensions.

[This message has been edited by darryl (edited 10-02-2003).]

SGW
10-02-2003, 09:22 AM
Almost certainly internal stresses. Anneal, as stated: heat dull red, let cool (or dunk in some water, with brass it doesn't make any difference how fast it cools). Then do your cuts.

Stepside
10-02-2003, 10:03 AM
Internal stress is your problem. It came from how the bar was manufactured. So anneal it like the others have said. As to band machining--If you have the right blade and the correct cutting speed and fixture/clamp the part correctly it is by far a more economical method to remove material, both in time and in tool cost. An additional benefit is the piece that is scrap for one part is usable for something else, with a mill it is "just swarf". If the part you are cutting is hot after sawing you have either an incorrect blade or the wrong cutting speed or maybe the blade is just plain dull/worn out.

frbush
10-02-2003, 12:06 PM
Went to McMurray Metal and took sample of the warped materials. As luck would have it, the representative of the brass manufacturer walked in for a sales call. Everyone was amazed at the amount of warpage. The rep thought I was trying to make tuning forks when he first looked at the piece. Told him just how I had machined and sawed the parts. He stated that I had done every thing OK and that I just got hold of a ****ty piece of brass that not been stress relieved. Since his company had supplied the material they replaced it for no charge. Of course you just can't go into a supply house without spending money so I just loaded up on more material while I was there Great people to do business with for all of those who reside in the Dallas, TX area. Back to the shop to do it all over again.