Hi,
I'm working on the first part on my new SVM2, and I need some help with speed and feed settings. I've broken three cutters so far, one before it took a cut, I dropped it out of the spindle straight on to the vice jaw, the second I machined the vice jaw ( video at silentworkshop.com), and now the third by what I think is having the wrong feedrate. My vice now has rigidity problems, it's quivering wondering what I'm going to do to it next....
The attached picture shows the last cut, it's in mild steel, 4mm dia coated carbide ball nose mill, cut width 4mm, depth 2mm, spindle at 6000 rpm ( max spindle speed) feed at 150 mm/min, under flood coolant. It seemed to be cutting fine until it broke, the surface finish in the cut is good, looks much better than it shows up in the picture. I checked the cutter temp as soon as the machine stopped, it was cold, it's cutting edges are still perfect. It had broken off up at the collet. I think I know why, I calculated the feed rate from the cutter manufacturers data, but I missed that is was based on 0.25 D side cut. I also checked it with Bob Warfield's gwizard, and it gave very similar settings, except it showed the cutter deflection in red, which I also missed . So I think the feed rate was too aggressive. Looking at it now, I can also see that it wandered off at the start of the cut, I could not see that when it was cutting under the coolant.
The part itself is an exercise to set a style for all the brackets in a 1930 Ford Tudor hot rod I'm setting up to build, I'm trying to get something that is practically machinable but rather different to anything you can buy off the shelf. I still have a long way to go to work out how to best size it's features, the order of cutting operations, how to hold it, just about everything really. I now know a few things not to do.
I do have some cnc experience, but it was a long time ago, we were simulating the cutter paths on an Apple 2 E and a Roland plotter if I recall correctly.
Given that I have no experience in setting the speeds and feeds correctly, any advice on how to make this would be greatly appreciated.
regards,
John