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David - Machinist in wood
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Discussion Starter · #1 · (Edited)
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! :grin: This Saturn frame is one stout and rigid CNC setup!

Circle Font Pattern Beige Floor


Text Eye Organism Font Circle


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
 

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David - Machinist in wood
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Discussion Starter · #4 ·
That had to be a little un-nerving as soon as it started moving!!
You have no idea!! LOL! In the video I can see me whipping around to look at Mach4 to see what the speed was and it showed 600, which is about what it looked like when it was making the circle.

Rapids are set at 600 ipm and I see that all the time but it's in a straight line and not cutting anything. 600 ipm cutting in a 16" circle is really fast!

David
 

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David - Machinist in wood
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Discussion Starter · #7 ·
Clean your glasses.
The cleanest glasses in the world won't do any good at all if you never look at what you type. :wink:

New SOP - type, review, type, review, type, review, ad nauseum :grin:

David
 

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A few years back I spent some time doing the math to calculate optimum feed speeds for certain bits with specific depth of cut and spindle speed. I kept getting numbers far faster than my Probotix hardware limits (200ipm). They implied I could cut through 3/4" hardwood in one pass with a 2-flute upcut bit and the chips produced would be carrying away the heat generated. Now the older Probotix CNCs would complain about such a cut, but our shop technician often does such cuts on the large Multicam industrial CNC we have. The routers we use would also complain if pushed too fast through hard wood even if the bit was keeping up with chip removal. The more face of a bit cutting wood the more drag there is against the router motor.

You've given me something to try this weekend. I often cut tenons on the end of hardwood boards. I'll make some test scraps, then cut 3 (or more) versions of the same toolpath, with pass depth the only thing I change between tenon cutting tests. I suspect my meteor can handle all variants ( 1/4" pass, 1/2" pass, 3/4" pass) despite me normally 1/8" per pass with a 1/4" upcut spiral. There may be some difference in the finished face of the cuts. I'll report back.

4D
 

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Rick
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I didn’t realize or couldn’t visualize how fast it was going till I broke it down into seconds .
So your cutting 10” per second?
Obviously not in one pass ,but in multiple passes at different depths .
I wonder if that’s hard on the machine itself?
 

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On our machine at work, we normally cut 3/4" plywood and particle board at about 800-850/min with a 3/8" or 1/2" 2 flute bit. With a 3 flute, I've at at about 1250ipm. At these speeds, holding your parts can be a real issue.


My normal speed with a 1/4" bit is 400-450ipm.

The two main limitations with hobby machines are spindle power, and machine rigidity. 1/4" bits don't take a lot of power, so it comes down to whether or not the machine flexes.
 

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Rick
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On our machine at work, we normally cut 3/4" plywood and particle board at about 800-850/min with a 3/8" or 1/2" 2 flute bit. With a 3 flute, I've at at about 1250ipm. At these speeds, holding your parts can be a real issue.


My normal speed with a 1/4" bit is 400-450ipm.

The two main limitations with hobby machines are spindle power, and machine rigidity. 1/4" bits don't take a lot of power, so it comes down to whether or not the machine flexes.
I never considered that the speed would put more pressure on the part your cutting .
Good to keep in mind
 

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Results are in with my quick tenon test. The Meteor didn't balk at any of the 2 toolpaths I've done. Wood was white oak, scraps from a pallet I took apart. End grain cuts.

First test: 1/4" deep passes, 1/8" stepover, 3/4 total depth. Climb cut perimeter profiles. The feed speed self limited as it went around the perimeter, slowing down on the curves, speeding up most on the long straight side. Despite being set at 200ipm the speed never got higher than 60ipm on the straights. Finished surface looks fine and tenon measures within .002" of what I'd programmed it to be.

Second test: 1/2" deep passes, 1/8" stepover. 1" total depth. Feed speed same as above. Finished surface looks/feels a little rougher than before. Tenon measures larger than programmed, implying the climb cut deflected somewhat as it went around the tenon. I suspect a followup conventional pass would clean up the surface and bring it down to the final dimension.

I do a climb cut with a 1/4" spiral upcut bit as it leaves the shoulder of the tenon cleanly cut. A conventional profile pass typically splinters out the edge.

Chip were larger than when I do a 1/8" pass, and threw considerable farther (3x farther) from the router. Dewalt 2.5hp router set at 5 (of 6 max) speed.

I've concluded I can do similar tenons using a 3/8" pass depth, or 2 passes max on anything up to 3/4" depth. Face grain cuts using the whole width of a bit I'll keep at 1/8" or 3/16" pass depth, depending on the wood I'm cutting.

This points out that if one always only cuts 1/8" deep at a time, only the last 1/8" of a bit is being used and it will get dull 3x as fast as it has to do 6 passes while a 1/4" pass depth would only need to do 3 passes for a 3/4" deep cut. The job will finish in 1/2 the time. Aspire has a last pass offset option that can let you do the final face of a cut as if done in one pass with the bit.

4D
 

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David - Machinist in wood
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Discussion Starter · #13 ·
I didn’t realize or couldn’t visualize how fast it was going till I broke it down into seconds .
So your cutting 10” per second?
Obviously not in one pass ,but in multiple passes at different depths .
I wonder if that’s hard on the machine itself?
No idea, Rick. The Saturn didn't seem to mind at all but it sure gave me the heebie jeebies! :grin:

On our machine at work, we normally cut 3/4" plywood and particle board at about 800-850/min with a 3/8" or 1/2" 2 flute bit. With a 3 flute, I've at at about 1250ipm. At these speeds, holding your parts can be a real issue.

My normal speed with a 1/4" bit is 400-450ipm.

The two main limitations with hobby machines are spindle power, and machine rigidity. 1/4" bits don't take a lot of power, so it comes down to whether or not the machine flexes.
A friend owns a cabinet shop about 10 minutes from our house and he bought a new $100k CNC last year to replace his worn out machine. I watched it cutting 3/4" plywood like you mentioned. I don't recall the feed rate but it was far faster than my measly 600 ipm, seems like he said it was up around 1000 ipm but I don't know what bit he was using.

I think the Saturn is rigid enough and the spindle powerful enough to go much faster than the 250 ipm I have been cutting at but for what I normally cut, which is typically smaller items except for the larger Longworth chucks, 250 ipm just feels about right. Of course, when I first started on the CNC 125 ipm felt about right.

Do you have any video of your machine cutting at 400-450 ipm, Gerry? I'd love to see that.

David
 

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David - Machinist in wood
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Discussion Starter · #14 ·

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David - Machinist in wood
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Discussion Starter · #16 ·
It just doesn't look that fast on a big machine like that. 600 ipm on our little 2x4 machine seems very fast!

Is the gantry cantilevered on that machine? Seems like that would not be ideal, like it may have some flex out on the end of the gantry. I realize it's probably very strong, but still...

David
 

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Yes, it's cantilevered, and about 6 ft long. It's a roughly 16"X6" square tube, 1/4" steel. It probably has at least 1000lbs hanging on it too.

There's actually almost zero flex under most conditions. It has S-Curve acceleration, which makes it start and stop very smoothly, with no jerkiness. And it accleerates very fast. It'll get to 800ipm in about 2 inches.

Their new machines are not cantilevered, but it is really nice at times. Much easier to load 12ft sheets from the side, rather than the end.
 

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Don’t want to make you scared any more, but since you told it to feed 25000ipm, Mach4 obediently allowed X-axis and Y-axis to EACH go to their max of 600ipm and at all but 4 points (North, East, South and West) it was going faster than 600, up to 845 or so.
 

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Mike
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David maybe you standing right there when your CNC started the 600IPM makes it look faster than the other machine running at 800IPM. The "in your face moment" when something like this happens.

If mine did that it would the "on the floor moment" when the CNC came apart.
 
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