Can I cut at 600 ipm? Question answered!

[David Falkner]

David, try a .25" compression cutter, either full depth or two passes...I think you'll be surprised. The first pass must be just a little more than the height of the up-cut section at the tip of the bit. The Whiteside that I use would make that about .20" minimum depth. The advantage of the compression cutter is clean edges on both sides including where the spoilboard underneath might be slightly buggered from previous cutting. The up-cut section also helps at least a little with clearing chips where a full down-cut, well...you know...keeps stuff in the kerf.

I ordered one yesterday, Jim, and it should be here tomorrow (good ol' Prime!). I wish I had ordered earlier in the week because we got two orders yesterday and one today for chucks and I would love to have cut those with the new bit. Oh, well, assuming the Longworth chuck orders don't dry up I'll use it next week.

David

[Jim Becker]

I suspect you'll like that cutter, David. I can say for sure it did a bang-up job on the first tack trunk I cut on my machine and I've used it for a number of other things where I want the benefit of down-cut on the top edge with some actual chip-clearing on the other end of the bit.

[David Falkner]

I'll create a new toolpath using that bit and do a plunge 0.25" deep, I'll back off the feed rate from my normal 250 ipm to 175 ipm or 200 ipm. I don't want to break the bit on the first chuck! I still feel like the 1/2" shank is a stronger bit, less susceptible to vibration and chatter, so we'll see...

David

[Mick Simon]

That's interesting, Mick. I've always heard and read that a straight plunge isn't good for tooling or equipment. But I guess if Onsrud said it's ok then it's probably ok.

David

It wasn't the straight plunge itself, it was that when you plunge, whether straight or ramp, do it fast. They did not condone straight plunging, but there are times when you don't have the option.

[Jim Becker]

David, I think you'll be surprised at how you can move that cutter once you get it in your hands. Buy a piece of "cheap" plywood to burn and setup a bunch of straight, right angle and curved tool paths to test what you can do. Try some full thickness cuts, too, which is one of the real benefits of a compression cutter.

[David Falkner]

It wasn't the straight plunge itself, it was that when you plunge, whether straight or ramp, do it fast. They did not condone straight plunging, but there are times when you don't have the option.

Got it! Thanks, Mick.

David, I think you'll be surprised at how you can move that cutter once you get it in your hands. Buy a piece of "cheap" plywood to burn and setup a bunch of straight, right angle and curved tool paths to test what you can do. Try some full thickness cuts, too, which is one of the real benefits of a compression cutter.

At what feed rate do you recommend, Jim? Assuming I only cut 0.25" depth and assuming I cut the full 1/2" BB nominal in one pass...

David

[Jim Becker]

I looked at my tack trunk file.... .47" material, full depth, 200ips, but that was the first time and I was being conservative. I was also running the RPM lower than I probably should have at the time. Every job I refine things based on the success of the previous and I'm new to this.

[Richard Gonzalez]

Y

... 200ips, but that was the first time and I was being conservative.

If 200 inches per SECOND was conservative, love to see a video when you crank it up...

[David Falkner]

Y

If 200 inches per SECOND was conservative, love to see a video when you crank it up...

Oh, I don't know about that, Richard. That's less than half of the 25000 ipm I set mine at...

David

[Jim Becker]

Can you say..."fat finger"... "S" or "M"...they are at least both letters of the alphabet.

[Kevin L. Waldron]

I've read your remarks about cutting at 600 ipm but somewhat question if this is an acquire assessment. Granted your machine is probably running at maximum capacity given the duration and the distance but if you where to do the math on the amount of material and the distance cut in a timed process doubt that it would be 600 ipm.

I have a very large machine and it will run at 1200 ipm but from experience we know that in short distances the machine will not accelerate or decelerate anywhere close to these kind of speeds. Typically on small parts we will max out the ipm knowing that the machine will never obtain these kinds of speeds in the short distance and the up and down actions in the tool paths require ...but for our work it does very well.

[David Falkner]

I've read your remarks about cutting at 600 ipm but somewhat question if this is an acquire assessment. Granted your machine is probably running at maximum capacity given the duration and the distance but if you where to do the math on the amount of material and the distance cut in a timed process doubt that it would be 600 ipm.

Actually, Kevin, it did hit 600 ipm. Using my video editing software I can set a mark where the 600 ipm starts and completes one full circle and it shows 5.03 seconds. If I use that data then that calculates to 599.5 or just simply 600 ipm, which is the max setting for the steppers.

I understand what you're talking about, though, and it's not like it was accelerating from a dead stop. It was already going 200 ipm for the rough cut and stepping up to 600 ipm was, I guess, fairly quick based on my math.

David

[Mark Bolton]

This acceleration/deceleration hogwash is greatly overstated. Most any reasonably setup machine is going to reach its acceleration and deceleration limits in a matter of an inch or two. If one is going to carry on about accel/decel your talking about tiny parameters, 3D carvings, and so on. To think that David's machine never approached max speed is nuts. If he were running some tight tolerance 3D carving that didnt have a single move that exceeded a half inch in any direction sure.

The accel/decel argument seems to be an excuse for people who are cautious, new, want to run slow, all of which are perfectly fine. But any reasonable machine is going to hit programmed speed extremely fast.

[Kevin L. Waldron]

Mark,

Your opinion matters but..... our experience shows different.

We did a YouTube video of test cutting a ukulele neck in 2012 and machine was set at maximum and it never reached 1200 ipm... https://youtu.be/7zkj8vekG4o

[Gary Campbell]

There is a lot of truth on both sides of this argument. But as is usually the case, neither ever gets it 100% right. Just to make the math easy, lets use 1200 inches per minute and an average (between smaller low power stepper machines and larger servo machines) of a half second. This equates to 2400ipm/sec accel for those controllers that measure it that way. And lets assume there is no "lag" in positioning.

A mid range servo machine capable of that much acceleration will get to 1200ipm in 1/2 second, with an average velocity of 600 ipm for that half second, or 10" per second. In that half second it would have traveled 5 inches. The balance of the time would be traversed at 1200ipm or 20ips. Don't forget to add the 5" of decel on the other end. High end servo machines with 1kw+ servos may get there in half the time, some even less.

In many less expensive (read as stepper) machines accel is and has to be less. Less power, less rigid frame, less dollars. David explains his verification correctly. Done by video, to the 10th of a second.

One of my customers just did this test for me in the last 10 days. When he was ready to swap out his controller, he cut a file in MDF. After the controller swap he ran the same file, same speeds, same rapids. The only difference was that due to higher torque motors his accel was set at .6 second. Rapids were 12ips or 960ipm. A bit of a qualifier: the first controller must go a bit slower on curves as it has a data limit via USB. This is more obvious at 4X video speed than in real time.

Take a look, judge for yourself: https://youtu.be/ZXWOoKvPytc

I also did a similar Uke neck, but toolpathing it in the long axis reduces the number of starts/stops and will usually reduce the time: https://youtu.be/LHKHqkKT4aA