hey folks, I've finally got my issues with the smoothstepper and mach in order and am now doing a big rough cut.  I'm running into an issue where the bit is starting to bite into the wood instead of smoothly cutting.  I little roughness is fine, since this is a rough cut, but it was really biting.  I caught it a bit too late as the bit broke;(



This is happening about 3/4 the way through the rough cut.  The beginning was fine.  The depth I'm doing is 9mm, so not too bad and 90mm/min feed, nothing crazy.  The bit is double fluted 6.35 mm, downward spiral.  My overlap is 5mm for the roughing.  The spindle is spinning, approx 14,000 rpm.  Is this an indication of the bit wearing out?  Or should my feed rate be slow, or should the spindle be spinning faster?  Maybe the depth is too large?  Is my overlap too large?  Should I use upward spiral instead?  I don't think the feed rate is too slow, as it's almost intolerably slow;)  I was thinking of increasing the feed rate till I saw this happening.  I'm new to this, so this like most issues is an all new problem to me.  So you people that are more used to issues, please let me know what you think.

Barry

Try 3000mm/min, or even faster at 14,000 rpm. An upcut might be better, but is more prone to tearout. YOU should be OK with 9mm depth, but you might want to try 5-6mm and see if it's better.

However, it appears that you have some serious flex in your machine. Or something is loose. I honestly can't see the cut being that rough without the whole spindle shaking that much.

Hi, I agree with Ger21, look like there's a lot of vibration along your cut, you could post some pics of your setup.

If the bit produce loud noise when cutting, reduce cutting depth , will help.

Jeff

The only flex I have in the machine is from the B/C drive itself.  The rest is really really sturdy.  I'll try using an upward spiral, and a shallower depth.  I think the 5mm, stepover might be a bit much too.  I'll make it the radius of the bit instead.  I did notice one thing after looking at the bit.  The plastic clamps I was using were cut into with the bit and I think it acted like glue to the bit.  I think that's one of the reasons the bit was biting.  Hopefully I'll have more to show very soon.

Barry

5mm stepover should be no problem at all. I've heard of people using 1/4" bits cutting 10mm deep, at 15,000mm/min.
Are you sure the part isn't moving? The only reason the bit would be grabbing is if there's play in the system somewhere. Either in the machine, or in the part.

As I stated before, that only play I see right now is from the B/C head itself.  I suppose that could cause the issues, but that's not something in my control to fix as it's 3rd party.  I have to investigate the other avenues first.

15000 mm/min, that's just crazy to me.  He must have a very high hp machine, mines only 2 hp on a gantry with the b/c head.  There's no way I could move mine that fast.

Barry

5mm step over with a 6mm tool is almost full cutter, prone to vibration, would try step over less than half the bit, like 3mm and you could increase feed.

Jeff

I've been routing wood with a $150K cnc for over 10 years. The stepover is not the problem here. You can cut wood all day with a 100% stepover with no problems.

My homebuilt mdf and plywood machine has a fair bit of visible flex, and the worst cut's I've seen from it are infinitely better than those.

No need to get testy.  I think by your own definition this is probably not flex since your plywood/mdf machine has a fair bit of visible flex.  This is a extruded aluminum and aluminum plate router.  The flex is nearly nonexistent.  I could probably stand on the gantry if I wanted it and it wouldn't flex visibly.  The only flex, I can discern is from the B/C head and even then it's so incredibly small.  I'd have to pull on it, with I bet about 70 lbs force.

I took the part and jig pieces off the table.  Remember I said the bit went through the plastic jig and basically melted it?  Well, I'm willing to be that's the reason the bit was biting.  Look at this:





I bet that melted plastic basically acted like glue and the bit never recovered from it.

And, btw, these jigs aren't really meant to secure a part to a table.  I need to make some that do.  They were the closest thing I could find at the hardware store;)

Still though, I'm going to try out everybody's suggestions.  For the next test, I'm going to use a 3mm stepover, 5mm depth, 160mm feed rate, upturn bit, and 14,000 rpm.  Wish me luck.

Barry

Hi Barry

Just an observation... the first pic shows several steps in the work piece with 2 board thicnesses above the bottom piece. However there are similar gouges in each layer (different z) and this seems to indicate the tool path was similar in each... Highly unliely that this was vibration as they were cut at different times if I'm seeing right. Can I make the suggestion to rerun the code at a much slower rate to air cut over what you have already done and see if it follows the same path.

You're not using some high speed machining paths are you? Whats the gcode look like? is it using circular interpolation of short vectors?

Might be way off but maybe food for thought.

Cheers