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Author Topic: Metal Nibbler 5  (Read 47682 times)
Bob La Londe
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« on: October 15, 2013, 17:10:09 pm »

Metal Nibble 5 doesn't exist yet.  I am looking at designing a "best compromise" for a high speed mold cutter.  

The Taig (Metal Nibbler 1) is not bad, but its antiquated design (sorry Jeff - I won't argue or compromise on that point so save it) doesn't hold up to level of work I want to do with it without constant tuning and adjusting.  Its got fair rigidty for such a small machine, fair accuracy and repeatability, and pretty slow working feed rates.  Currently it has a problem I can't find in Y where it binds and stalls if I set rapids and accel faster than 40 5 i/s/s.  I've already spent way more time trying to find it than its worth.  

The MaxNC (Metal Nibbler 2) did a fair job after I rebuilt it with Acme screws and antibacklash nuts.  In fact its faster and much more repeatable than the Taig using the same motors and controller.  Both are running wood routers as spindles so its all on the mechanics and rigidity for how fast they can work.  Neither can really run fast enough for the spindles they have, but I have cranked out some parts pretty darn quick on the MAxNC5.  Being an all aluminum machine its probably not very rigid, but its done amazingly accurate work in spite of that.  I have never had it stall unless it crashed or hit a stop.  It doesn't seem to need the same level of babying as the Taig, but its got its own problems.  The biggest being I can't really fit anything larger than a 1/4" acme lead screw in the machine.  Now way I could fit ball nuts in it even for 6mm screws.  Ok, maybe, but it would be tough.  The next is under heavy loads it will flex some.  The acetal plastic Dumpster nuts on the X & Y give it very good accuracy and repeatability, but they wear at the mounting points from the strains of cutting aluminum all the time.  If I could use bigger screws and had room for bigger Dumpster nuts (with a backing plate to hold them from flexing) that might not be an issue.  It will FEED at 80ipm and accel at 25 i/s/s with no problem.  I was concerned about its anodized aluminum dovetail ways, and its aluminum gibbs with multi set screw adjustment, but they haven't really been a problem.  I just grease them once in a while with high pressure white lithium grease from the auto parts store and they work fine.  I use the same stuff on the acme screws on the machine.  My biggest problem was that generation of machine didn't have any captive bearing on the screws.  It was just direct coupled to the motor.  When the motors had seen some use they developed some internal end play which resulted in backlash.  Yuck!  I designed a reverse end captive bearing for it and its a lot better.  I am under .001 backlash and its all in my captive bearings.  I suspect a simple shim stock between the bearings will fix that.  Then the only backlash will be if I over power the springs in the Dumpster nuts.  

Metal Nibbler 3 (The Hurco KMB1) has its own issues.  Right now I have it set at 150ipm and 10 (Z) or 15 i/s/s (X/Y).  It will repeatably rip metal at high cutting loads with large DOC and WOC.  If I take heavy cuts followed by light cuts (depending on exact cut type) I get very accurate results.  Usually < +/- .001.  Some of that is me.  The quill can deflect some at full extension and I am to lazy to constantly crank the table up and down to keep the quill in its ideal 0-3" range. Still its not bad even extended.  Its got horsepower to spare.  It only faults if I plan a bad cut like to fast of a plunge without ramping with an end mill, or if I hit a clamp when speeds are set for aluminum.  Even then it often makes the cut, just badly.   Where it fails as a mold maker is in the spindle speed.  3600RPM max (I have it set at 3500).  I can rough out a cavity quick, but detail finish work with small cutters would take weeks on some molds.  I tried a speeder, but the combined flex of everything was more than I felt was good.  It was like using the MaxNC only slower. 

Metal Nibbler 4 (Chinese Noname 3020 Router) is really fast.  At 300 IPM and 30 i/s/s it never stalls unless I do something wrong.  It might lose a few steps, but its only noticeable over very very large jobs, and then only in CV mode.   Its not really rigid enough at all for cutting aluminum.  I have never used it to cut a mold.  I use it for hardwoods with feeds upto 180ipm, and plastics mostly, but I do occasionally do 2D template style cutting out of aluminum sheet  (.090" to .125") with it.  If I plan light fast cuts and hand lube the plate it actually does very acceptable work.  Realisticly though it should be named "Wood Ripper 1."

I want to build a compromise machine.  Something like Metal Nibbler 4 for speeds and feeds with its ball screws, but atleast as rigid as the Taig.  I want as small a foot print as possible with a modestly large working envelope.  18-20(X) 10(Y) 2-5(Z).  Something that doesn't lose steps over the course of a 10 hour job.  

Buying cast iron plate seems to be out.  Its really expensive unless you get lucky and stumble across some.  Casting is definitely out.  I may setup a foundry someday for aluminum, but I doubt I'll want to do cast iron.  

METAL NIBBLER 5

Here is my plan so far.  Basically over build a gantry style router with a fixed rather than moving gantry.  Use all 1" x 4" and 1" x 6" MIC 6 or 7075.  Cut most of the parts on the Hurco for accuracy, and cut everything to bolt up square, but leave room to shim and clamp against the shims if it isn't.  I know at this point somebody is going to give me the knee jerk aversion to building a machine out of aluminum, but I think by over building I can reduce flex to an acceptable level.  Remember Metal Nibbler 2?  Its an all aluminum machine, and its biggest failing is that it can't handle large robust mechanical parts like bigger screws and nuts.  With a fixed Gantry there will be a lot less flex in that whole union, and I'll design for larger hardware.  I'll still have a modestly small foot print in X even though Y will be a compromise.  I think if I cut the back plate on the gantry out of one piece with angle braces at each end it will be really rigid.  Yes, I'll have less Z clearance at the X extremes, but I only need about 2 inches for 99.9% of molds, and those that might be thicker can be cut in the middle where I will have about 5" Z clearance.  I don't plan to ever have a vise mounted on this machine.  I'll use lever clamping like I do most of the time on Metal Nibbler 1 & 2 now.  

Use all supported linear bearings.  This means a little more planning upfront, more materials, and less quick and dirty machine to fit, but that will eliminate one of the sources of flex I see in Wood Ripper 1 under heavy loads.  I am not sure which linear bearings to use.  Supported obviously, but the round ones from guys like LinearBearings2008 or the flat ones like Arie used on his grinder mill.  Is there in inherent benefit to one over the other or is it a price:quality relationship only?  

The table.  I'll just steal a cast iron (cast steel?) table off a cheap XY table.  I already have one and there is really nothing to machine off the bottom.  I can just clamp it up face down on the Hurco and face mill and drill a couple precision surfaces for the linear bearings and ball nut mount.   Its going to be smaller than my envelope in Y, but I can live with that.  I already hang 6" wide plates off the 3.5" wide table on the Taig and can get acceptable results.  

This is intended to be a purpose built machine for high speed machining of aluminum for mold making.  It will sit on a steel frame open to the bottom with a cabinet around the frame and a catch bin between the legs.  It will have a cabinet built onto the machine base itself with a flip up front half for easy part loading and unloading.  I have not decided on mist or flood coolant, but the base catch bin will double as a sump with screen trays to filter chips incase I get recoverable amounts of coolant, and the coolant nozzles will be rigid tubes ball mounted directly on the spindle mount.    

I was thinking to build this as servo based machine, but I am tired of servo tuning after buyilding just one servo system.  LOL.  If I use easier tuning servo drivers like Larkins Viper 200, it adds substantially to the price.  As well.  I am tired of cumulative error and the mandatory mechanical perfection of stepper based machines as well.  (I have three of them after all).  I am thinking I'll go with a closed loop stepper system.  It cost more than throwing G540 and a some 320-380 steppers on it, but it will self correct, and it will fault if it can't.  Its still cheaper than a servo system even if I scrounge motors.  

I don't need a ton of horsepower on the spindle for this type of work so I am thinking .75-.8 kw 3 phase spindle.  This leaves me the option of using a 110-220 VFD or a 220V VFD.  I believe the Hitachi 1HP 110-220 VFD also has the ability to work in a closed loop configuration if I can figure out where to mount a tach pickup.  

Then I get to lead screws.  I want low maintenance modestly fast pitch accurate leads.  Chinese 1604 or 1605 ballscrews would be ok, but from what I read they have about .003 internal backlash.  I'm not sure I have the ability or desire to refill them with oversize balls so that leaves with going back to acme screws or buying more expensive ballscrews that have double nuts.  I can make my own acme nuts with good enough accuracy, and I am pretty sure I can make them antibacklash like the dumper style clamping collar or with in a spring loaded fit together double nut style.  I am just not sure about acetal nuts long term.  I want to really use this machine, and I don't want to have to tear it down and rebuild more than once a year at worst.  

I will definitely use some form of automatic oiler on it.  I have several ideas there, but I am thinking timed electric valves fed by an air tool oiler will be the easiest for me to build.   I could just run a pressure vessel with oil only too into the same bank of electric valves.  Most of the hydraulic oilers require air anyway.  The only advantage I see with them is they are easier to fill.  
« Last Edit: October 16, 2013, 01:00:02 am by Bob La Londe » Logged

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« Reply #1 on: October 15, 2013, 21:19:25 pm »

I've been thinking about it for quite a while.  Almost as long as I've been working on the conversion of Metal Nibbler 3.  I expect it to be a modestly long slow build, but once one is done and proven I'll probably build a couple more fairly quickly. 

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« Reply #2 on: October 15, 2013, 22:50:39 pm »

Bob,
How about something like this?  I used 3 THK GL20N slides with 20 mm ballscrews that I got off Ebay for 4 for $450 each.  So I have a spare.  My travels are 18" x 18" x 18".  While building it I put a 10ths indicator on the slide and pulled and pushed on it in all directions as hard as I could.  No detectable play in any direction!  Motors are 800 oz/in Nema 34 low inductance and driven by a 68 vdc unregulated 1500 watt power supply, using Leadshine drivers.  Everything is bolted down to a 205 lb hand scraped 24" x 24" surface plate, that I got at a junkyard for $98.

The  full machine picture shows a Sherline spindle mounted on it, which was way under powered.  The other picture shows my 2-1/4 HP Hitachi 8000-24000 rpm variable speed router on the new mounts I made.  I am almost done with a minimill R8 spindle from LittleMachineShop that I modified and is driven by a 1-3/4 HP Treadmill motor by timing belt giving me a 2800 RPM spindle with enough torque to tap holes.  Tooling is all Tormach and I picked up a couple of tapping heads etc.  Both the regular spindle and the router can be rotated 90 degrees and use as a horizontal mill.  I can then drill in the ends of long stock or cut deep pockets with good chip control.

I also have a mini lathe bed with a headstock, 4" chuck, large stepper motor, and tailstock that clamps down to the table.  Mounted behind the mill spindle is Tormach 0XA Aloris style tool post holder for the lathe tools.  Mounted along side that is a bracket for the 3D printing extruder, which I nearly have finished.

My design gives me the highest possible rigidity when working very close to the table and close to the X axis bolted to the table.  I still have a very large work cube, and the weight of a part and fixtures are of no consequence.  You can see the two 4" CNC vices and the 12" x 12" heated 3D printing plate behind them.

I built the machine to teach my 9 year old grandson about manufacturing so it has a full safety enclosure with door limit switches.


* DSC00704.JPG (144.01 KB, 640x480 - viewed 349 times.)

* DSC00713.JPG (142.17 KB, 640x480 - viewed 348 times.)
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« Reply #3 on: October 15, 2013, 23:50:17 pm »

Kind of a radial arm CNC mill?  LOL.  I dunno.  Its a neat looking multi purpose machine, but to much for what I want to do with this build.   I actually plan to A-axis my mini lathe to use on the Hurco Bed (keyed of course), but Metal Nibbler 5 is going to be a very specific purpose built machine to do one thing.  Cut 3D cavities in flat aluminum plates at the maximum material rate possible with small cutters. 





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« Reply #4 on: October 16, 2013, 18:14:00 pm »

Bob,
If what you want is fast cutting of small cavities and you don't need the size of my machine then you could do this quite inexpensively by picking up one long THK GL20N slides with a ball screw and cutting it up to make 3 shorter slides. You should consider making it a horizontal too.  With your cavity on it's side chips will naturally just fall out. The slides I bought took a whole lot of work out of building an accurate machine.  The slides were already very accurately made, and I actually hand scraped them just a little for a perfect fit.  I picked up a 9" x 9" x 9" granite angle plate on Ebay that allows me to accurately check all three axis in one setup.  I have less than 0.001" deviation in all directions.  Yet it wasn't difficult to achieve.
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Bob La Londe
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« Reply #5 on: October 16, 2013, 18:46:18 pm »

I feel stupid.  The biggest problem with cavity and slot cutting aluminum is chip clearing.  Building a machine with a vertical bed and a horizontal spindle makes perfect sense.
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« Reply #6 on: October 17, 2013, 13:40:01 pm »

Bob,
I think chip handling is one of the major reasons horizontal machines are so popular in high production applications. I think the machine bed should still be horizontal though. If you look at the pictures of my machine I have two 4" CNC style vises sitting on the table. I chose them because they can be mounted lying on their side or standing on end for horizontal use. You can get angle plates fairly cheap if need just a bed. That makes it really easy to do angled cuts by just rotating the angle plate on the table.


Also my X axis is mounted to the table. So no matter how long it is it never gets flimsy from over hang. I have two vises because I need to machine some long parts and I felt this was cheaper than building dedicated long fixtures. Of course I can also mount two parts at a time, and my table will easily hold 4 of those 4" vises. The stiffness of my machine is the same for every vise location.

One other thing. I drilled my table with 144 5/16-18 tapped holes on a 40mm pattern. Those sizes match the 80/20 aluminum extrusions so I can use that for fixturing. The unused holes are all plugged with nylon set screws.
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Bob La Londe
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« Reply #7 on: October 17, 2013, 16:47:50 pm »

I see what you are saying about your design.  Its very versatile.  I think for my purpose the horizontal bed makes more sense though.  Chips can just fall into the screen below. 

By the way, I have 3-6" screwless vises on the bed on my Hurco mill so I can hold and support longer pieces.  There is a 2" gap for the hold down in between. This also allows for cutting both ends of smaller pieces easily. I still have issue with chip clearing.  Not from the part with flood, coolant, but from the table.  The T-slots get so plugged up that it doesn't drain well. Yes, I've considered a number of ideas for covering them, but that's for another conversation. 
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« Reply #8 on: October 17, 2013, 21:42:15 pm »

Bob,
At every shop I've worked at I purchased a heavy duty shop vac for chips. I just bought a Greenlee blower vac for $250 on Ebay.  Steel tank, good solid wheels, all aluminum blower with 11 feet of water lift.  Cost about $900 new!  Legacy vacuum, I'll pass it along to my grandson, unlike the typical shop vac. It sucks chips and coolant out of slots and threaded holes really well.
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Gary H. Lucas

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« Reply #9 on: October 18, 2013, 00:43:19 am »

I am using a Rigid brand shop vac and its not bad, but its not enough to clear the slots when they get full.  I usually have to stick a rod in there and move them around to get them going.  The surprising (or maybe not) thing is how packed in the chips get under the vises. 

Have considered a number of soltutions, but haven't decided on a best idea before committing material to it.  I'll probably use a piece of PETG lightly tacky glued to the table, but that still leaves me with the headache of blocking the slots under the vises where the chips can get down there through the vise. 




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« Reply #10 on: October 18, 2013, 00:49:45 am »

Bob,
I've always used a 1-7/8" suction hose and then get a piece of 1-1/2" chrome plated brass sink drain pipe.  I flatten the end in a vice so that it fits down in the slots.  It is better than the plastic ones because the wall is real thin so you get the biggest opening for chips.  I have also used them with a drain elbow with the nut on it and nozzle is a tailpiece with a flange.  That makes it easy to get the nozzle in under the spindle and it can be rotated 360 degrees as you work. I sucked up so many chips with one that the brass elbow wore through!
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Gary H. Lucas

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Bob La Londe
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« Reply #11 on: December 09, 2013, 21:24:22 pm »

I ordered some linear bearings yesterday.  I don't know any better so I went with 20mm supported round rod with open bearings.  I have the basic shape of the machine and the necessary bearing lengths figured out, but I'm still torn about the framework of the machine.  I know I talked about heavy aluminum, but I have steel tube that I could use and go with epoxycrete to fill it and add mass, and I have a piece of 3/4" steel plate that is about 18" by 70" I could cut up (if I had a good way to cut it besides my torch.) 

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Bob La Londe
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« Reply #12 on: December 09, 2013, 23:05:29 pm »

First Rendition:  Some things with scale are off.  I made the drawing 24" wide for some reason even though my target is 18" with 12-14" travel in X.  I actually drew this up as a regular vertical setup, and then I realized it would turn horizontal like we discussed with absolutely no mods. 


* Metal Nibbler 5.jpg (83.75 KB, 1440x714 - viewed 193 times.)
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Bob La Londe
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« Reply #13 on: December 14, 2013, 22:17:12 pm »

I decided to go with 1" 6061 for the first build of this machine due to price.  If it works I'll start looking for a reasonably price source for something stronger for subsequent builds.  I ordered all the aluminum to build this machine yesterday.  It will probably get here before the bearings and rods.  LOL.  Tentatively the plan is to build it around an 18" base for the 18.4 (apx) cast iron table I already have, and extend the X travel ways to 22" (apx) so I can use nearly the entire surface of the table if I choose  16" X envelope including room for limits should be possible.  I probably won't do it as a vertical table on this first build, but I may lay it over to see how it does work at some point.  I think reaching over the spindle motor to change cutters would be a bit awkward.  No matter how I rotate the machine it looks like it will either be awkward to load the work piece or awkward to change the cutters with a vertical table.   Protecting the ways from chips is an issue too.

I'm still studying the difficulty of single or double screw on Y.  I'ld like to eliminate any possibility of twist or racking.  I guess the thing to do is build it up to that point clamp one side of the table in place and see how much I can deflect the other side with thumb pressure using a dial indicator to read deflection.  Then if its more than a couple thousandths go dual screw. 


New:  Just in!!! 

I may bolt it to a stone base or through stone slabs to the stand.  I recently found a source for discarded stone counter top pieces.  Some of them are plenty large enough.  I would still have to do some cutting on them though.  I still want the bulk of chips to fall into a bin below.  And... Yes I did consider making the whole machine out of stone.  LOL.  Maybe for the next one. 

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« Reply #14 on: December 14, 2013, 22:24:47 pm »

I may bolt it to a stone base or through stone slabs to the stand.  I recently found a source for discarded stone counter top pieces. 
------------
Bob, if they're less than 4" thick, they're darned brittle, and subject to cracking under vibrations.  Just consider that.

As far as cutting... they cut just fine (if slowly) with a carbide throw-away blade for a circular saw, and plenty of water from a spray bottle.

Lloyd
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