Author Topic: After Much Internal Debate I Did Not Buy Another CNC Machine  (Read 405 times)

Offline Bob La Londe

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After Much Internal Debate I Did Not Buy Another CNC Machine
« on: March 10, 2021, 15:23:51 pm »
I need to be able to cut 20+ by 30+ inches for a particular industry standard production mold.  For a while I considered something like one of the Vectrax 10x54 CNC mills from MSC Industrial.  I could do them without changing the stock setup.  Just telescope the ram.  Still it was a huge compromise, and the price was nearly $40K.  I couldn't afford to pay for it out of pocket so I would have had to finance.  Still I thought about it for a long time. 

I also thought about making a bridge mill.  The thing is I wanted to do that as well as I could, and in my mind that meant cutting some of the critical surfaces in one setup.  My biggest machine in service was the Hurco KMB1 with a stock envelope of 24X by 14Y and a modified envelope of 26X+ as currently configured.  In good shape its advertised as +.003 repeatability, and mine is almost 40 years old.  It was actually better than that, but I couldn't quite do some things in one cut.  Its also developed some problems I don't really have time to fix right now.  The Y axis has nearly 8 thousandths backlash (according to dial indicator travel) and in the middle of a job early last year the X screw had a catastrophic ballscrew failure in the middle of a job.  Going from an acceptable .002 to 30+ thousandths mid job.  I mostly quit using the machine.  Took the heart right out of me.  I will fix it, but I intend to change a lot of its configuration when I do.  (I am not asking for help on this.  I have a plan.  I will ask for help if I need it)

Still I need to be able to make those single setup critical surface cuts to make the bigger envelope machine(s) I need to grow.  I finally settled on doing it with a new manual milling machine.  A knee mill. 

Yes Gary.  We know you don't like knee mills.  Its ok.  I won't make you use it.

I ordered a new South Bend 10x54 from Grizzly.  I swung back and forth between South Bend and Vectrax.  Ultimately it came down to time and features.  I could have called MSC Industrial and had them build a machine up with everything I wanted.  That requires a lot of back and forth and presumes the counter person (phone person) hears everything I say the way I said it, and that I remember to say everything... correctly.  The South Bend machine had everything I wanted except one minor thing I was undecided about.  It has an R8 spindle taper, and I was leaning more towards an NT40 spindle.  If I had bought the Vectrax I would have gone with the NT40.  Power draw bar preinstalled with buttons on the front. Coolant system built in.  5HP 3phase spindle with 7.5HP VFD configured to run on single phase.  Adjust on the fly variable speed.    Power feeds.  Power knee.  Fagor DRO  Etc Etc Etc

One of the things that decided me on a knee mill is the huge amount of flexibility.  I will still have uses for it even after my bridge mill(s) are finished.  For instance I need to gun drill those big production molds for coolant passages.  I was going to do it on the lathe with a tool in the spindle, and I still might, but I can also do it on the knee mill, by clamping it up off the side of the table and using the knee. 

Right now I am cleaning up and organizing in the shop in order to make a place for it and move it into position.  I moved my surface plate into the front office to make room for it next to the PM1440 manual lathe.  Its going to share the same circuit (manually switched for now).  I don't see myself using the manual lathe and the manual mill at the same time.   Not in my one man shop anyway. 

I have three folding tables (and some other stuff) full of machine parts for those bridge mill builds in the way path of travel right now.  Maybe I'll have it in place and wired up by this weekend.  Maybe not.  LOL.



« Last Edit: March 10, 2021, 15:33:53 pm by Bob La Londe »
Getting started on CNC?  In or passing through my area?
If I have the time I'll be glad to show you a little in my shop. 

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http://www.CNCMOLDS.com

Offline Bob La Londe

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Re: After Much Internal Debate I Did Not Buy Another CNC Machine
« Reply #1 on: March 10, 2021, 15:30:56 pm »
Which leads me to an idea for a CamBam Feature.  An instruction list output instead of g-code.  Generally you do 2.5D machining on a manual milling machine.  Sure with head tilt/swivel, rotabs, sine vises, and other things you can do a lot more, but most of the time you will be drilling bolt patterns and machining square(ish) features.  CB could likely generate instruction lists for manual machining those kinds of parts.  Especially if you have a DRO to follow them. 

Nah!  That's a crazy idea. 
Getting started on CNC?  In or passing through my area?
If I have the time I'll be glad to show you a little in my shop. 

Some Stuff I Make with CamBam
http://www.CNCMOLDS.com

Offline Bubba

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Re: After Much Internal Debate I Did Not Buy Another CNC Machine
« Reply #2 on: March 11, 2021, 01:21:32 am »
There is nothing wrong with knee type machines, I have run many for years, (Bridgeport) and see them used in both configurations as cnc and manual in production where I used to work and retired from, Gulfstream Aerospace. As always, all machines have its limit,s as long as you observe that you will be fine. Nice machine Bob, Congratulations.
My 2¢

Win10 (64 bit, CB(1.0)rc 1(64 bit) Mach3, ESS, G540, Endurance Laser.

Offline kvom

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Re: After Much Internal Debate I Did Not Buy Another CNC Machine
« Reply #3 on: March 11, 2021, 15:50:26 pm »
I'd have thought a 20x30 work envelope would suit a router best.  I recently had to square some al plate to 18x23 on my BP, and it was a pita.

Offline Garyhlucas

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Re: After Much Internal Debate I Did Not Buy Another CNC Machine
« Reply #4 on: March 11, 2021, 18:21:11 pm »
Bob,
You’ve got me wrong. I like knee mills, and had a Bridgeport for 20 years until it was truly worn out. My opposition is to CNC knee mills, where moving the table up and down to change tools and such is a huge hassle, and you only have quill Z motion.
Gary H. Lucas

Have you read my blog?
 http://a-little-business.blogspot.com/

Offline Bob La Londe

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Re: After Much Internal Debate I Did Not Buy Another CNC Machine
« Reply #5 on: March 11, 2021, 20:41:57 pm »
I'd have thought a 20x30 work envelope would suit a router best.  I recently had to square some al plate to 18x23 on my BP, and it was a pita.

In your case you can move the head or move the stock.  I think sometimes people forget the stock stays square to the ways if you move the head. 

A knee mill is a compromise for something like 20x30 but its relatively rigid compared to your average backyard CNC router.  The better alternative of course a big VMC bed mill.  The problem becomes price and in some cases spindle speed. 

A bridge mills is perhaps a more correct term for what folks call a CNC router.  I think the "rename" comes from the fact that so many are made using a wood router for a spindle and so many people learned the language of the trade and the trade at the same time.  "CNC Router" just made sense to them since it wasn't a bed mill or a knee mill and most folks had never seen a 100 ton bridge mill processing giant stock.  The thing is bridge mills don't have to be light weight single screw racking ridden flimsy extrusion machines.  I have some iron castings made for a totally different application that I will be squaring up, bolting together and fastening in some orientations with ground right angle blocks to create a structure I hope will be an order of magnitude stiffer than your average aluminum construction CNC "router" is.  It will not have a square circle wrapped all the way around the machine with cutting forces hitting it far away from the ways.  The ways will be on the top of the machine very close to the carriage.  It will have dual drives to prevent racking.  The z axis clearance will be small to reduce leverage disadvantage, but be relatively tall to give room for tool changes and longer tools.  I have been thinking about it for a very long time, and I may still not have it all figured out.  Still I think the bridge mill I make for mold cutting will be marginally atleast as good as a middle weight Chinese import mill like a Syil or a Tormach, and it won't require to be repaired out of the crate like a Syil.  It will be the second unit I build.  The first will be similar to bridge mills often called CNC routers. 

I have a use for both types of bridge mill.  One will be used mostly for wood.  One will get used exclusively for aluminum. 
Getting started on CNC?  In or passing through my area?
If I have the time I'll be glad to show you a little in my shop. 

Some Stuff I Make with CamBam
http://www.CNCMOLDS.com

Offline Garyhlucas

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Re: After Much Internal Debate I Did Not Buy Another CNC Machine
« Reply #6 on: March 12, 2021, 00:21:41 am »
The CNC router I am working on with the FIRST Robotics team. 24” x 48” x 6” with a full enclosure and a coolant pan under the entire table. Bridge design allows a full 48” x96” sheet to be fed through the front.  Will have a 4th axis/lathe mounted on the left end beyond the table. 700 lbs weight and on wheels and fits through 35” door opening.
Gary H. Lucas

Have you read my blog?
 http://a-little-business.blogspot.com/

Offline Bob La Londe

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Re: After Much Internal Debate I Did Not Buy Another CNC Machine
« Reply #7 on: March 13, 2021, 18:05:27 pm »
Bob,
You’ve got me wrong. I like knee mills.

I'm gonna save that and post it back at you every time you give me the old knee mill groan.  LOL. 
Getting started on CNC?  In or passing through my area?
If I have the time I'll be glad to show you a little in my shop. 

Some Stuff I Make with CamBam
http://www.CNCMOLDS.com