Can I cut at 600 ipm? Question answered!

[David Falkner]

Yes, definitely!! Did I mean to do that? Absolutely not!!

I have made several changes to the toolpath profile for cutting the Longworth chucks and all for the better. When I started cutting them 100 chucks and almost a year ago the feed was 125 ipm, 18k rpm, 0.125" depth of cut, with a 1/4" downcut spiral bit. These chucks are 1/2" Baltic Birch and I knew this was conservative but I tend to stay on that side. I have slowly crept the speed up to where I am now cutting chucks at 250 ipm and all the other specs are the same except depth of cut is now 0.2".

When I opened the file for the 16" chuck I realized it was still at 200 ipm for the outer profile, with tabs, so I changed it to 250 ipm. Or so I thought... What I actually did was replace the '2' with '250' and didn't delete the extra '00'. My new feed rate was now 25000 but since I thought I had overwritten the 200 all I did was hit Ok and went out to the shop.

Everything cut just fine until it got to the outer profile. The ramp was at 250 ipm but when the cut reached the 0.2" depth it jumped up to 600 ipm, which is the max setting I have on the X & Y steppers. I was in a mild state of shock for a second trying to figure out what had happened but it cut around that 16" circumference so quickly that all I basically did was watch it cut. And it cut perfectly! The 3kW (4HP) spindle didn't blink at what I had inadvertently thrown at it, the bit was cool when it finished, and the edge was just as clean as it could be.

I don't plan to move any future cuts to 600 ipm but I have to say, now that it's over and nothing broke, it was fascinating watching it cut that fast! This Saturn frame is one stout and rigid CNC setup!

052 - 16 inch Longworth chuck, perimeter cut at 600 ipm.jpg

053 - 16 inch Longworth chuck, feed at 25000 ipm.jpg

I have a camera in the shop but the output is proprietary and requires its own player. If I can figure out how to export that to something I can upload to YouTube I'll show y'all.

David

[Mark Bolton]

Great find. It's almost always the case that faster winds up to be better.

[Mick Simon]

I made a similar setup error recently and was (pleasantly) surprised to see it cut 3/4" BB at 350 ipm in one pass. Didn't balk at all.

[David Falkner]

Wow, Mick! That's aggressive, for sure. Mine was only 0.2" depth but it was aggressive enough for me. I guess that means I can cut faster than 250 ipm without too many issues.

David

[Jim Becker]

I think there are many times that we don't think we can go as fast as we actually can, assuming there's room to get up to speed. Many of us, like myself, who are new to CNC also tend to be more conservative than we likely should be with speeds/feeds. It's a learning process!

[Mark Bolton]

From my meager experience in the last 3+ years, and having never broken a bit other than to my own stupidity running it into the side of the machine having forgotten I had clicked off soft limits (something I never do any more without great caution).. I feel the answer is if you push your machines to the point that your about to have a nervous breakdown your about 1/2 way to where you should be. I think everyones machine in this string has a machine thats likely capable of running wide open by default. Jim continually carries on about acceleration and deceleration but thats an added safety net. If your job is small enough that it will never reach full speed then run it wide open. It will at least get as fast as it can in a given distance.

To use the horse analogy, I think these things (especially the tooling) are like thoroughbred horses. They need to run. They want to run. If you keep them trapped in a petting zoo, your investment is wasted, and your horse should probably bite you whenever you get close to it.

I have a few tools that I bough early on (a half inch solid carbide compression) that I have never put in the machine and never will because I cant run it fast enough. I'd guess Martin's machine would barely push a 1/2" solid carbide compression. You need to be closing in on 2000ipm to make use of that tool. That said, I run 3/8" tooling wide open, full depth on 3/4", and I dont doubt Jim's machine would do the same as would Davids.

For me there are some advantages of running wide open and not full depth and the main one is keeping the shop clean. I'd personally rather waste a little time and tool life to have the DC pick up nearly every spec of dust. If I had a machine with a house around it like Martin's I would single pass. But I run two pass quite often because there is zero cleanup after.

[Martin Wasner]

Skirt, other skirt, blowers and a way oversized dust collector helps too. It may be stuck to the parts, but there isn't much in the air at all.

I'm only onion skinning parts because they're too small and our undersized pumps won't hold. But the clean up is nice on those as there's almost nothing on the table.

[Jim Becker]

Jim continually carries on about acceleration and deceleration but thats an added safety net. If your job is small enough that it will never reach full speed then run it wide open. It will at least get as fast as it can in a given distance.

That's exactly what I do more and more of...

[David Falkner]

Here's the video of my little 'incident' at 600 ipm -



David

[Mark Bolton]

Looks like money in the bank. Run the whole thing at 500 now lol. ;-)

[Jim Becker]

Impressive for sure!

[Ted Reischl]

About five years ago I ran some tests on my machine. It is a homebuilt design based on CNC Routerparts and 8020. For all practical purposes it is a CNC Routerparts machine.

Sorry for the fuzzy video. In the beginning the machine is pocketing at 800 IPM, while profiling the letters it is at 550 IPM.

https://www.youtube.com/watch?v=Pt8n43_YRjI&t=68s

I never run the machine at this speed. My normal feedrates are usually in the 150 - 250 IPM range. I do a lot of one off stuff so running at a high speed leaves no time to react to the machine if things are going wrong. I suppose if I were doing production type work I would be bumping those feedrates up considerably.

Yup, a well built machine will run like a race horse.

[David Falkner]

Pretty cool, Ted. Why were you cutting that fast? Just curious...

David

[Ted Reischl]

Pretty cool, Ted. Why were you cutting that fast? Just curious...

David

I decided I wanted to see what the machine could actually do. If one does not push the envelope then there is a tendency to constantly underestimate what the machine and tools are capable of.

A sidenote. One of the reasons I like inexpensive chinese cutters is that I can then push up the feedrate. Recently I was doing some stuff that used a 1.5 mm cutter. (.059in). Since the cutters were less than a buck apiece I could afford to increase the feedrate without worrying about breaking an expensive bit. When that bit costs $4 or more, one does not fool around too much.

[David Falkner]

While we were at church tonight we got another order for a 12" Longworth chuck that I'll cut tomorrow morning and I think I will leave the slots at 250 ipm but bump the outer perimeter to 350 ipm to see how that does.

I also realize my depth of cut of 0.2" is conservative and I have a few of these 1/4" downcut spiral bits that are sharp enough to use but don't give as clean a cut as a brand new bit. The bit I'm using now is still pretty sharp but I'm thinking of using one of the older bits that has basically only cut 0.2" and setting a new depth of cut of 0.25" to introduce a sharp cutting edge for that last 0.050" and see how that does. Does that make sense and does it seem like a good thing to try out?

So, 1/4" downcut spiral bit running at 18k rpm - a depth of cut of 0.25" in Baltic Birch should be a walk in the park, right? I'm not under the gun to run these as fast as I possibly can so I'm not looking for world class levels of speed. Now if I had to cut 10 sets of these tomorrow or every day I might be looking for the fastest way possible but I only have one to cut tomorrow morning (unless more orders come in tonight )

I don't use an upcut bit because I want the top face to be very clean with as few chips and splinters as possible and a downcut bit gives me that. I don't yet have a compression bit or I would try full depth.

David